Medical Grand Rounds

Our knowledge of the pathogenesis of thrombotic microangiopathies has greatly advanced in the last decade, improving the diagnosis and treatment of these diseases.

Many conditions involve thrombotic microangiopathies (Table 1). This article reviews the most common ones, ie, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, atypical hemolytic uremic syndrome, and antiphospholipid syndrome—their clinical features (focusing on the kidney), course, and management. Of note, although the diseases are similar, their pathogeneses and treatments differ.

DIFFERENT PATHWAYS TO MULTIORGAN THROMBOSIS

The thrombotic microangiopathies are multisystem disorders that can affect children and adults and often present with prominent renal and neurologic involvement. Endothelial injury is likely the inciting factor leading to thrombosis in the kidney and in many other organs. The causes variously include:

• Toxins from bacteria or drugs
• Abnormal complement activation, genetic or autoantibody-induced
• Procoagulant factors, eg, antiphospholipid antibodies
• Loss of anticoagulants, eg, from a defect of ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13); ADAMTS13 is also known as von Willebrand factor-cleaving protease
• Severe hypertension.

The histopathologic features are similar in all the thrombotic microangiopathies. Laboratory findings include thrombocytopenia, microangiopathic hemolytic anemia (with schistocytes on the peripheral blood smear), and high serum lactate dehydrogenase (LDH) levels; these are also markers of treatment progress. Bilirubin may be elevated and haptoglobin absent. Renal biopsy reveals thrombi in the glomeruli and arterioles.

THROMBOTIC THROMBOCYTOPENIC PURPURA

A young woman with fever, bruising, and renal failure, then blindness

A 36-year-old black woman who had been previously healthy presents to her doctor with fever and bruising.

Her hematocrit is 28% (reference range 38%–46%), platelet count 15 x 10⁹/L (150–450), and prothrombin and partial thromboplastin times are normal. Her peripheral blood smear shows microangiopathic hemolytic anemia with schistocytes.

Over the next few days, her urine output declines and she develops sudden blindness followed by decreased mental acuity. Blood is drawn and sent for ADAMTS13 assay. Treatment is started at once with daily therapeutic plasma exchange. The assay results, when they arrive, show marked ADAMTS13 reduction (< 5%). Over the ensuing weeks, her mental acuity improves, her vision returns, and her renal function improves.

ADAMTS13 deficiency is definitive

Thrombotic thrombocytopenic purpura is characterized by:

• Neurologic abnormalities and acute renal failure
• Thrombocytopenia and microangiopathic hemolytic anemia
• Histologic evidence of thrombotic microangiopathy
• Deficiency of von Willebrand factor-cleaving protease (ADAMTS13 < 10%).

von Willebrand factor forms ultralarge multimers in the circulation that interact with platelets; these are normally cleaved by ADAMTS13. With ADAMTS13 deficiency (from either a genetic mutation or autoantibodies), the ultralarge multimers lead to coagulation as blood flows through small vessels.¹

In 2003, Tsai² evaluated 127 patients over age 10 who had thrombocytopenia and microangiopathic hemolysis with no plausible cause or features suggestive of hemolytic uremic syndrome. All were severely deficient in ADAMTS13. Subsequently, thrombotic thrombocytopenic purpura has been defined by a severe actual or effective deficiency of ADAMTS13.

Prompt plasma exchange is critical

Although the ADAMTS13 assay is important for diagnosing thrombotic thrombocytopenic purpura, in suspected cases daily plasma exchange should be started promptly, before test results return. Plasma exchange removes autoantibodies to ADAMTS13 from the blood, removes circulating ultralarge von Willebrand factor multimers, and replaces the missing ADAMTS13. Untreated, the disease is progressive, with irreversible renal failure, neurologic deterioration, and a 90% mortality rate. Plasma exchange reduces the mortality rate to less than 15%. If another diagnosis is confirmed, plasma exchange can be stopped.

Plasma exchange has been shown in clinical trials to be superior to plasma infusion in normalizing platelet counts and reducing mortality.^3,4 Mortality rates were comparable with different replacement fluids vs fresh-frozen plasma, including solvent or detergent-treated plasma, and cryo-poor (cryosupernatant) plasma.⁴ Antiplatelet therapy, platelet transfusions, and splenectomy are ineffective.

Glucocorticoids for early treatment

An appropriate strategy is to add a glucocorticoid to plasma-exchange therapy at once (oral prednisone 1 mg/kg per day or intravenous methylprednisolone 125 mg twice daily) and withdraw it after several days if it is determined that it is not needed. Steroids for suspected thrombotic thrombocytopenic purpura can be justified for several reasons:

• The results of the ADAMTS13 assay are usually delayed, so steroids provide coverage for other diagnoses.
• They are helpful if thrombotic thrombocytopenic purpura is idiopathic (which is true for most cases) and if the patient has a poor response to initial therapy with plasma exchange.
• They are indicated for patients whose platelet counts do not increase with several days of plasma exchange or whose thrombocytopenia recurs as plasma exchange is decreased.

Rituximab improves survival

Rituximab, a chimeric (half murine) monoclonal antibody against CD19 and CD20 B cells, suppresses antibody production by knocking out the precursors of antibody-producing cells.

Anecdotal reports and small studies involving a total of 42 patients have been published on the use of rituximab for thrombotic thrombocytopenic purpura. Courses of rituximab varied greatly, from 1 to 13 weekly doses at 375 mg/m², with 4 doses being the most common. Complete remission occurred in 90% of cases.^5,6 A typical study from 2014 involved 48 patients (30 of whom received rituximab) followed by severe ADAMTS13 deficiency during remission.⁷ Despite the small study size, the investigators found significantly improved relapse-free survival rates with rituximab treatment.

But rituximab can cost $25,000 for 2 doses of 1,000 mg, and this will most likely prohibit its routine use. The cost and insurance coverage vary with location and policies.

Based on such studies, a reasonable strategy is to treat thrombotic thrombocytopenic purpura with:

• Daily plasma exchange
• Steroids, at least until the diagnosis is certain
• Rituximab if warranted.

New targeted therapies

Caplacizumab, a humanized immunoglobulin that inhibits the interaction between ultralarge von Willebrand factor multimers and platelets, has the potential to change this strategy when it receives US Food and Drug Administration approval, which is expected soon.

Peyvandi et al⁸ randomized 75 patients with acquired thrombotic thrombocytopenic purpura to either subcutaneous caplacizumab 10 mg daily for 30 days or placebo. Both groups had daily plasma exchange. The treatment group had a 39% reduction in median time to normalization of platelets vs the placebo group, and 3 of 36 patients had exacerbations, compared with 11 of 39 patients in the placebo group. Although 8 patients relapsed within the first month after stopping caplacizumab, their cases were brought under control. There were also more bleeding episodes with caplacizumab (54% vs 38%), most being mild to moderate. Two patients in the placebo group died, but none in the treatment group.

The fact that platelet normalization occurred significantly faster with caplacizumab, even in some patients who had not yet had plasma exchange therapy initiated, has enormous clinical significance. The low platelet count in thrombotic thrombocytopenic purpura is a marker of susceptibility to rapid damage to the brain and kidneys, so correcting it quickly is critical.

Other strategies for new drug development include replacing the deficient ADAMTS13 with a recombinant molecule and blocking antibody production (the same mode of action as rituximab and glucocorticoids).⁹ Using all 3 strategies to treat thrombotic thrombocytopenic purpura may be the future standard of care.

HEMOLYTIC UREMIC SYNDROME

A child with sudden onset of bloody diarrhea and kidney failure

A 4-year-old girl plays with baby animals at a petting zoo and does not wash her hands immediately afterwards. Three days later, she develops fever, abdominal cramps, nausea, vomiting, and bloody diarrhea. Her pediatrician gives her antibiotics. On day 6, she develops ecchymoses on the extremities and lips, thrombocytopenia, low urine output, and seizures. Her stool tests positive for Escherichia coli O157:H7

Classic presentation: Young patient with bloody diarrhea

The classic presentation of hemolytic uremic syndrome is of a young patient with bloody diarrhea typically lasting 5 to 10 days. Kidney failure may follow, requiring dialysis in about 60% of patients for a mean of 10 days. About one-fourth of patients develop neurologic symptoms, and about the same fraction are left with long-term morbidity, eg, hypertension, proteinuria, and reduced glomerular filtration rate. The mortality rate is typically 4%^10,11 but varies with the outbreak.

Histologically, the kidneys look identical to those in thrombotic thrombocytopenic purpura, with thrombi in glomeruli and small vessels.

E coli is the most common culprit, but other bacteria, including Shigella dysenteriae, and viruses are sometimes the cause. Fewer than 10% of children infected with Shiga toxin-positive E coli, also known as enterohemorrhagic E coli (O157:H7, O104:H4), develop hemolytic uremic syndrome.

Lessons from outbreaks

Petting zoos are a common source of transmission of pathogenic bacteria. Disease can be extremely serious: in 15 cases linked to a Florida petting zoo, 3 children died.

Other outbreaks involving pathogenic E coli have been tied to fresh vegetables and to undercooked hamburger at fast-food chains.

In Germany in 2011, more than 3,000 people acquired Shiga toxin nonhemolytic uremic syndrome due to E coli, and 16 of them died. In addition, 845 acquired hemolytic uremic syndrome, and 36 died. This outbreak was associated with the more virulent and less common O104:H4 strain, which has acquired a Shiga toxin-encoding phage. Patients were treated with quinolone antibiotics, which actually increase toxin production in this strain.¹²

Unusual in the German epidemic was that more adults were affected (88%), especially women (68% of cases).¹³ The source of infection was eventually found to be alfalfa sprouts, the seeds of which had been contaminated by E coli. Women did not harbor any intrinsic factor making them more susceptible; rather, they were more likely to eat salads.¹³

Supportive management

Supportive care is most important. Transfusion with packed red blood cells is indicated for hemoglobin below 6 g/dL. Hypertension should be controlled and dialysis provided. For central nervous system involvement or severe disease, plasma exchange is sometimes used.

Eculizumab was tried for a time as therapy but did not prove to be of benefit. Shiga toxin-binding agents have been developed, but by the time they are given it is too late in the disease process to help.

Antibiotics may harm; it is possible that they kill beneficial bacteria, allowing the Shiga toxin-producing E coli to better proliferate. Antimotility agents also are contraindicated. Other agents not recommended include urokinase, heparin, dipyridamole, and vincristine. Splenectomy is not advised.

The most important way to control hemolytic uremic syndrome is to prevent it by thoroughly cooking meat, cleaning fresh produce, and having children wash their hands after petting animals.

ATYPICAL HEMOLYTIC UREMIC SYNDROME

A young man in renal failure

A 28-year-old man has a history of “thrombotic thrombocytopenic purpura-hemolytic uremic syndrome” at age 12. He slowly progresses to end-stage renal disease and receives a renal transplant from his mother at age 20 that fails after 3 months. The renal transplant biopsy report at the time reads “thrombotic microangiopathy.” The patient’s brother also requires dialysis.

The patient’s complement values are low, especially C3. His father is offering him a kidney at this time, and the patient wants to know whether to proceed.

Normal ADAMTS13, no diarrhea

Hemolytic uremic syndrome without diarrhea is now called atypical hemolytic uremic syndrome. Patients have normal levels of ADAMTS13, do not have diarrhea, and have no evidence of Shiga toxin-producing E coli.

Continuous complement pathway activation

The complement system is part of the innate immune system, which provides immediate defense against infection and does not evolve as does the adaptive immune system. The classic complement pathway is activated by the C1 antibody-antigen complex. The alternative complement pathway leads to the same pathway via C3.¹⁴ Both pathways lead to the formation of C5 through C9 membrane attack complexes, which form channels across the membranes of target cells, leading to cell lysis and death.

The alternate pathway does not require an antibody trigger so is always active at a low level. Inhibitory factors (factor H, factor I, membrane cofactor protein, factor H-related proteins) are naturally present and slow it down at various steps. People who are born with an abnormal factor or, more commonly, develop antibodies against one of the factors, have uninhibited complement activation. If this happens in the blood vessels, massive coagulation and atypical hemolytic uremic syndrome ensues. The endothelial damage and clotting in the brain, kidney, and other organs are identical to that of hemolytic uremic syndrome caused by Shiga toxin.

Treat with eculizumab

Historically, atypical hemolytic uremic syndrome was treated with plasma exchange, which replaces defective complement regulatory proteins and removes inhibitory antibodies.

Understanding the complement pathways is key to developing drugs that target atypical hemolytic uremic syndrome, and about 60 are in the pipeline. The only one currently approved in the United States for atypical hemolytic uremic syndrome is eculizumab, a humanized monoclonal antibody that binds with high affinity to C5, blocking the end of the complement cascade and preventing formation of the membrane attack complex.^15–18

The effects of eculizumab on atypical hemolytic uremic syndrome were studied in 2 prospective trials.¹⁹ Platelet counts rose rapidly within weeks of starting treatment, and kidney function improved. Benefits continued throughout the 64 weeks studied. There were no deaths among the 37 patients enrolled, and although these were single-arm trials, they provide evidence of dramatic benefit considering the high mortality risk of this disease.

Eculizumab is now considered the treatment of choice. It may be used empirically for patients with hemolytic uremic syndrome who test negative for Shiga toxin and antiphospholipid antibody, and who do not have a very low level of ADAMTS13. The big drawback of eculizumab is its high price,^20–22 which varies by amount used, location, and pharmacy negotiation, but can be in the hundreds of thousands of dollars.

For a patient with atypical hemolytic uremic syndrome on dialysis, treatment with eculizumab should continue for 4 to 6 months if there are no extrarenal manifestations. But many patients continue to have the defect in the complement system, so the problem may recur.

Case revisited

For our patient considering a kidney transplant, many experts feel that a transplant can be done as long as platelet counts are monitored and treatment with eculizumab is restarted if needed. One can also make the case for waiting a few years for new oral drugs to become available before offering transplant.

ANTIPHOSPHOLIPID SYNDROME

A young woman with a history of thrombosis and miscarriages

A 27-year-old woman presents with arthralgias, low-grade fever, and malaise. She has a history of 3 spontaneous abortions and Raynaud phenomenon. Two years ago, she had deep vein thrombosis of the right calf after a long automobile trip.

She now has swollen metacarpophalangeal and proximal interphalangeal joints, livedo reticularis (a mottled venous pattern of the skin best seen under fluorescent light) of the legs and arms, and ankle edema (2-cm indentation).

Her blood pressure is 152/92 mm Hg. Laboratory values:

• White blood cell count 3.6 × 10⁹/L (reference range 4.5–11.0)
• Hematocrit 24% (36%–47%)
• Platelet count 89 × 10⁹/L (150–450)
• Urinalysis: protein 4+, heme 3+, red blood cells 8–15 per high-power field (< 3), red blood cell casts present
• Blood urea nitrogen 43 mg/dL (10–20)
• Creatinine 2.6 mg/dL (0.5–1.1).
• Prothrombin time 14.6 s (10–14)
• Partial thromboplastin time 85 s (25–35)
• Antinuclear antibody positive at 1:160
• Anti-double-stranded DNA and serum complement normal
• Syphilis serologic screening (VDRL) positive.

The patient has leukopenia, anemia, thrombocytopenia, hematuria, proteinuria, high blood urea nitrogen, and markedly elevated partial thromboplastin time. Although she has a positive antinuclear antibody test and renal dysfunction, her anti-dsDNA and serum complement tests are normal, making the diagnosis of systemic lupus erythematosus unlikely.

Consider antiphospholipid syndrome

In any patient with multiple pregnancy losses, lupus, or a history of thrombosis, antiphospholipid syndrome should be considered.

In a series of patients with antiphospholipid antibody who underwent kidney biopsy, more than half were men, indicating that, unlike lupus, this is not primarily a disease of young women.

Diagnosis based on specific criteria

Clinical criteria require at least one of the following in the patient’s history²³:

• One or more episodes of arterial, venous, or small-vessel thrombosis
• Unexplained pregnancy morbidity (death of a fetus or neonate with normal morphology or 3 or more spontaneous abortions).

Serologic criteria for any of the following antiphospholipid antibodies require that at least one of the following tests be positive at least twice and at least 12 weeks apart:

• Anticardiolipin antibodies—high-titer immunoglobulin (Ig) G or IgM
• Autoantibodies for beta 2-glycoprotein
• Lupus anticoagulant—autoantibodies that increase clotting time in vitro and target beta 2-glycoprotein I and prothrombin (despite its name and actions in vitro, lupus anticoagulant functions as a coagulant).

As with the other thrombotic microangiopathies, patients with anticardiolipin syndrome have microthrombi in the glomeruli and blood vessels that are evident on kidney biopsy.

Suspect condition in likely groups

Antiphospholipid syndrome is surprisingly common.²⁴ In a case-control study, de Groot et al²⁵ found that 3.1% of patients under age 70 with a first episode of venous thrombosis and no known cancer were positive for lupus anticoagulant vs 0.9% of controls. In another case-control study, Urbanus et al²⁶ found that 17% of women under age 50 with a stroke tested positive for lupus anticoagulant compared with less than 1% of controls. Because of such studies, it has become routine to test for anticardiolipin and lupus anticoagulant in young patients presenting with a stroke.

About 1% of women trying to have children have recurrent miscarriages, and of these, 10% to 15% have antiphospholipid antibody present.^27–30

Pathogenesis

Patients with antiphospholipid syndrome have a much higher proportion of plasma beta 2-glycoprotein in the oxidized form than do healthy controls. The level is also higher than in patients with a different autoimmune disease whether or not they have antibodies against beta 2-glycoprotein 1. Although about 40% of patients with lupus have an anticardiolipin antibody, only a small percentage develop antiphospholipid syndrome with clotting.

It is thought that antiphospholipid syndrome involves initial injury to the endothelium, then potentiation of thrombus formation. Oxidized beta 2-glycoprotein complexes may bind to the endothelial cell surface, causing it to become the target of antibodies. The exact relationships between the factors are not yet understood.

The risk of a thrombotic event in an asymp­tomatic patient positive for all 3 factors—lupus anticoagulant, anticardiolipin antibody, and anti-beta 2-glycoprotein I antibody—is more than 5% per year.³¹

Manage thrombosis with anticoagulation

Khamashta et al,³² in a 1995 study, retrospectively studied patients with antiphospholipid antibodies and a history of thrombosis. Of 147 patients, 66 had idiopathic primary disease, 62 had systemic lupus, and 19 had “lupus-like” disease. Almost 70% (101 patients) had a recurrence of thrombosis, totaling 186 events. The mean time to recurrence was 12 months (range 2 weeks to 12 years). Recurrence rates were 0.01 events per patient per year with high-dose warfarin, 0.23 with low-dose warfarin, and 0.18 with aspirin. But the highest bleeding rates were in the 6 months after warfarin withdrawal; 29 patients had bleeding events, one-fourth of which were severe.

Standard therapy has become anticoagulation, starting with heparin or enoxaparin, then warfarin. There is inadequate evidence for the role of newer oral anticoagulant therapy.

A very high INR is not generally better than a moderately elevated level

For a time, it was thought that the international normalized ratio (INR) should be kept on the very high side to prevent thrombosis.

Crowther et al³³ conducted a randomized, double-blind trial comparing moderate warfarin therapy (INR 2.0–3.0) and high-intensity warfarin therapy (INR 3.1–4.0) in antiphospholipid syndrome. Thrombosis actually recurred more frequently in the high-intensity therapy group (10.7% vs 3.4%), with no significant difference in major bleeding events.

A reasonable strategy is to keep the INR between 2.5 and 3.0, keeping in mind that values fluctuate in any individual patient. A higher goal often leads to excessive anticoagulation and bleeding. If the goal is too low, recurrent thrombosis becomes more likely. There are fewer data on the newer oral anticoagulants, but their role is likely to increase as reversal agents are developed.

Recommendations published in 2003 for treating antiphospholipid syndrome include³⁴:

• Warfarin (INR 2.0–3.0) after the first thrombotic event
• Warfarin (INR 3.0–4.0) if a clot develops despite warfarin
• Warfarin (INR > 3.0) for an arterial event.

For the rare but catastrophic antiphospholipid syndrome in which thrombosis occurs in multiple organs, recommendations are for heparin plus steroids, with or without intravenous immunoglobulin and plasmapheresis. This approach has not always been successful, and the mortality rate is high.

Treatment of asymptomatic carriers is uncertain

Treatment of asymptomatic carriers of the antiphospholipid antibody is controversial. Evidence for management is scarce; some experts recommend aspirin therapy, but benefit has yet to be proven in clinical trials.

Canaud et al³⁵ documented the role of activation of the kinase mammalian target of rapamycin (mTOR) in the vascular changes characteristic of antiphospholipid nephropathy. Postkidney transplant surveillance biopsies of patients with antiphospholipid antibodies showed vascular damage occurring over time (despite patients being asymptomatic) compared with other renal transplant patients. Patients with antiphospholipid antibodies who were treated with the immunosuppressive drug sirolimus were protected from developing these changes. Twelve years after transplant, 70% of patients with antiphospholipid antibodies taking sirolimus still had a functioning graft compared with 11% of untreated patients.

Our knowledge of the pathogenesis of thrombotic microangiopathies has greatly advanced in the last decade, improving the diagnosis and treatment of these diseases.

Many conditions involve thrombotic microangiopathies (Table 1). This article reviews the most common ones, ie, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, atypical hemolytic uremic syndrome, and antiphospholipid syndrome—their clinical features (focusing on the kidney), course, and management. Of note, although the diseases are similar, their pathogeneses and treatments differ.

DIFFERENT PATHWAYS TO MULTIORGAN THROMBOSIS

The thrombotic microangiopathies are multisystem disorders that can affect children and adults and often present with prominent renal and neurologic involvement. Endothelial injury is likely the inciting factor leading to thrombosis in the kidney and in many other organs. The causes variously include:

• Toxins from bacteria or drugs
• Abnormal complement activation, genetic or autoantibody-induced
• Procoagulant factors, eg, antiphospholipid antibodies
• Loss of anticoagulants, eg, from a defect of ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13); ADAMTS13 is also known as von Willebrand factor-cleaving protease
• Severe hypertension.

The histopathologic features are similar in all the thrombotic microangiopathies. Laboratory findings include thrombocytopenia, microangiopathic hemolytic anemia (with schistocytes on the peripheral blood smear), and high serum lactate dehydrogenase (LDH) levels; these are also markers of treatment progress. Bilirubin may be elevated and haptoglobin absent. Renal biopsy reveals thrombi in the glomeruli and arterioles.

THROMBOTIC THROMBOCYTOPENIC PURPURA

A young woman with fever, bruising, and renal failure, then blindness

A 36-year-old black woman who had been previously healthy presents to her doctor with fever and bruising.

Her hematocrit is 28% (reference range 38%–46%), platelet count 15 x 10⁹/L (150–450), and prothrombin and partial thromboplastin times are normal. Her peripheral blood smear shows microangiopathic hemolytic anemia with schistocytes.

Over the next few days, her urine output declines and she develops sudden blindness followed by decreased mental acuity. Blood is drawn and sent for ADAMTS13 assay. Treatment is started at once with daily therapeutic plasma exchange. The assay results, when they arrive, show marked ADAMTS13 reduction (< 5%). Over the ensuing weeks, her mental acuity improves, her vision returns, and her renal function improves.

ADAMTS13 deficiency is definitive

Thrombotic thrombocytopenic purpura is characterized by:

• Neurologic abnormalities and acute renal failure
• Thrombocytopenia and microangiopathic hemolytic anemia
• Histologic evidence of thrombotic microangiopathy
• Deficiency of von Willebrand factor-cleaving protease (ADAMTS13 < 10%).

von Willebrand factor forms ultralarge multimers in the circulation that interact with platelets; these are normally cleaved by ADAMTS13. With ADAMTS13 deficiency (from either a genetic mutation or autoantibodies), the ultralarge multimers lead to coagulation as blood flows through small vessels.¹

In 2003, Tsai² evaluated 127 patients over age 10 who had thrombocytopenia and microangiopathic hemolysis with no plausible cause or features suggestive of hemolytic uremic syndrome. All were severely deficient in ADAMTS13. Subsequently, thrombotic thrombocytopenic purpura has been defined by a severe actual or effective deficiency of ADAMTS13.

Prompt plasma exchange is critical

Although the ADAMTS13 assay is important for diagnosing thrombotic thrombocytopenic purpura, in suspected cases daily plasma exchange should be started promptly, before test results return. Plasma exchange removes autoantibodies to ADAMTS13 from the blood, removes circulating ultralarge von Willebrand factor multimers, and replaces the missing ADAMTS13. Untreated, the disease is progressive, with irreversible renal failure, neurologic deterioration, and a 90% mortality rate. Plasma exchange reduces the mortality rate to less than 15%. If another diagnosis is confirmed, plasma exchange can be stopped.

Plasma exchange has been shown in clinical trials to be superior to plasma infusion in normalizing platelet counts and reducing mortality.^3,4 Mortality rates were comparable with different replacement fluids vs fresh-frozen plasma, including solvent or detergent-treated plasma, and cryo-poor (cryosupernatant) plasma.⁴ Antiplatelet therapy, platelet transfusions, and splenectomy are ineffective.

Glucocorticoids for early treatment

An appropriate strategy is to add a glucocorticoid to plasma-exchange therapy at once (oral prednisone 1 mg/kg per day or intravenous methylprednisolone 125 mg twice daily) and withdraw it after several days if it is determined that it is not needed. Steroids for suspected thrombotic thrombocytopenic purpura can be justified for several reasons:

• The results of the ADAMTS13 assay are usually delayed, so steroids provide coverage for other diagnoses.
• They are helpful if thrombotic thrombocytopenic purpura is idiopathic (which is true for most cases) and if the patient has a poor response to initial therapy with plasma exchange.
• They are indicated for patients whose platelet counts do not increase with several days of plasma exchange or whose thrombocytopenia recurs as plasma exchange is decreased.

Rituximab improves survival

Rituximab, a chimeric (half murine) monoclonal antibody against CD19 and CD20 B cells, suppresses antibody production by knocking out the precursors of antibody-producing cells.

Anecdotal reports and small studies involving a total of 42 patients have been published on the use of rituximab for thrombotic thrombocytopenic purpura. Courses of rituximab varied greatly, from 1 to 13 weekly doses at 375 mg/m², with 4 doses being the most common. Complete remission occurred in 90% of cases.^5,6 A typical study from 2014 involved 48 patients (30 of whom received rituximab) followed by severe ADAMTS13 deficiency during remission.⁷ Despite the small study size, the investigators found significantly improved relapse-free survival rates with rituximab treatment.

But rituximab can cost $25,000 for 2 doses of 1,000 mg, and this will most likely prohibit its routine use. The cost and insurance coverage vary with location and policies.

Based on such studies, a reasonable strategy is to treat thrombotic thrombocytopenic purpura with:

• Daily plasma exchange
• Steroids, at least until the diagnosis is certain
• Rituximab if warranted.

New targeted therapies

Caplacizumab, a humanized immunoglobulin that inhibits the interaction between ultralarge von Willebrand factor multimers and platelets, has the potential to change this strategy when it receives US Food and Drug Administration approval, which is expected soon.

Peyvandi et al⁸ randomized 75 patients with acquired thrombotic thrombocytopenic purpura to either subcutaneous caplacizumab 10 mg daily for 30 days or placebo. Both groups had daily plasma exchange. The treatment group had a 39% reduction in median time to normalization of platelets vs the placebo group, and 3 of 36 patients had exacerbations, compared with 11 of 39 patients in the placebo group. Although 8 patients relapsed within the first month after stopping caplacizumab, their cases were brought under control. There were also more bleeding episodes with caplacizumab (54% vs 38%), most being mild to moderate. Two patients in the placebo group died, but none in the treatment group.

The fact that platelet normalization occurred significantly faster with caplacizumab, even in some patients who had not yet had plasma exchange therapy initiated, has enormous clinical significance. The low platelet count in thrombotic thrombocytopenic purpura is a marker of susceptibility to rapid damage to the brain and kidneys, so correcting it quickly is critical.

Other strategies for new drug development include replacing the deficient ADAMTS13 with a recombinant molecule and blocking antibody production (the same mode of action as rituximab and glucocorticoids).⁹ Using all 3 strategies to treat thrombotic thrombocytopenic purpura may be the future standard of care.

HEMOLYTIC UREMIC SYNDROME

A child with sudden onset of bloody diarrhea and kidney failure

A 4-year-old girl plays with baby animals at a petting zoo and does not wash her hands immediately afterwards. Three days later, she develops fever, abdominal cramps, nausea, vomiting, and bloody diarrhea. Her pediatrician gives her antibiotics. On day 6, she develops ecchymoses on the extremities and lips, thrombocytopenia, low urine output, and seizures. Her stool tests positive for Escherichia coli O157:H7

Classic presentation: Young patient with bloody diarrhea

The classic presentation of hemolytic uremic syndrome is of a young patient with bloody diarrhea typically lasting 5 to 10 days. Kidney failure may follow, requiring dialysis in about 60% of patients for a mean of 10 days. About one-fourth of patients develop neurologic symptoms, and about the same fraction are left with long-term morbidity, eg, hypertension, proteinuria, and reduced glomerular filtration rate. The mortality rate is typically 4%^10,11 but varies with the outbreak.

Histologically, the kidneys look identical to those in thrombotic thrombocytopenic purpura, with thrombi in glomeruli and small vessels.

E coli is the most common culprit, but other bacteria, including Shigella dysenteriae, and viruses are sometimes the cause. Fewer than 10% of children infected with Shiga toxin-positive E coli, also known as enterohemorrhagic E coli (O157:H7, O104:H4), develop hemolytic uremic syndrome.

Lessons from outbreaks

Petting zoos are a common source of transmission of pathogenic bacteria. Disease can be extremely serious: in 15 cases linked to a Florida petting zoo, 3 children died.

Other outbreaks involving pathogenic E coli have been tied to fresh vegetables and to undercooked hamburger at fast-food chains.

In Germany in 2011, more than 3,000 people acquired Shiga toxin nonhemolytic uremic syndrome due to E coli, and 16 of them died. In addition, 845 acquired hemolytic uremic syndrome, and 36 died. This outbreak was associated with the more virulent and less common O104:H4 strain, which has acquired a Shiga toxin-encoding phage. Patients were treated with quinolone antibiotics, which actually increase toxin production in this strain.¹²

Unusual in the German epidemic was that more adults were affected (88%), especially women (68% of cases).¹³ The source of infection was eventually found to be alfalfa sprouts, the seeds of which had been contaminated by E coli. Women did not harbor any intrinsic factor making them more susceptible; rather, they were more likely to eat salads.¹³

Supportive management

Supportive care is most important. Transfusion with packed red blood cells is indicated for hemoglobin below 6 g/dL. Hypertension should be controlled and dialysis provided. For central nervous system involvement or severe disease, plasma exchange is sometimes used.

Eculizumab was tried for a time as therapy but did not prove to be of benefit. Shiga toxin-binding agents have been developed, but by the time they are given it is too late in the disease process to help.

Antibiotics may harm; it is possible that they kill beneficial bacteria, allowing the Shiga toxin-producing E coli to better proliferate. Antimotility agents also are contraindicated. Other agents not recommended include urokinase, heparin, dipyridamole, and vincristine. Splenectomy is not advised.

The most important way to control hemolytic uremic syndrome is to prevent it by thoroughly cooking meat, cleaning fresh produce, and having children wash their hands after petting animals.

ATYPICAL HEMOLYTIC UREMIC SYNDROME

A young man in renal failure

A 28-year-old man has a history of “thrombotic thrombocytopenic purpura-hemolytic uremic syndrome” at age 12. He slowly progresses to end-stage renal disease and receives a renal transplant from his mother at age 20 that fails after 3 months. The renal transplant biopsy report at the time reads “thrombotic microangiopathy.” The patient’s brother also requires dialysis.

The patient’s complement values are low, especially C3. His father is offering him a kidney at this time, and the patient wants to know whether to proceed.

Normal ADAMTS13, no diarrhea

Hemolytic uremic syndrome without diarrhea is now called atypical hemolytic uremic syndrome. Patients have normal levels of ADAMTS13, do not have diarrhea, and have no evidence of Shiga toxin-producing E coli.

Continuous complement pathway activation

The complement system is part of the innate immune system, which provides immediate defense against infection and does not evolve as does the adaptive immune system. The classic complement pathway is activated by the C1 antibody-antigen complex. The alternative complement pathway leads to the same pathway via C3.¹⁴ Both pathways lead to the formation of C5 through C9 membrane attack complexes, which form channels across the membranes of target cells, leading to cell lysis and death.

The alternate pathway does not require an antibody trigger so is always active at a low level. Inhibitory factors (factor H, factor I, membrane cofactor protein, factor H-related proteins) are naturally present and slow it down at various steps. People who are born with an abnormal factor or, more commonly, develop antibodies against one of the factors, have uninhibited complement activation. If this happens in the blood vessels, massive coagulation and atypical hemolytic uremic syndrome ensues. The endothelial damage and clotting in the brain, kidney, and other organs are identical to that of hemolytic uremic syndrome caused by Shiga toxin.

Treat with eculizumab

Historically, atypical hemolytic uremic syndrome was treated with plasma exchange, which replaces defective complement regulatory proteins and removes inhibitory antibodies.

Understanding the complement pathways is key to developing drugs that target atypical hemolytic uremic syndrome, and about 60 are in the pipeline. The only one currently approved in the United States for atypical hemolytic uremic syndrome is eculizumab, a humanized monoclonal antibody that binds with high affinity to C5, blocking the end of the complement cascade and preventing formation of the membrane attack complex.^15–18

The effects of eculizumab on atypical hemolytic uremic syndrome were studied in 2 prospective trials.¹⁹ Platelet counts rose rapidly within weeks of starting treatment, and kidney function improved. Benefits continued throughout the 64 weeks studied. There were no deaths among the 37 patients enrolled, and although these were single-arm trials, they provide evidence of dramatic benefit considering the high mortality risk of this disease.

Eculizumab is now considered the treatment of choice. It may be used empirically for patients with hemolytic uremic syndrome who test negative for Shiga toxin and antiphospholipid antibody, and who do not have a very low level of ADAMTS13. The big drawback of eculizumab is its high price,^20–22 which varies by amount used, location, and pharmacy negotiation, but can be in the hundreds of thousands of dollars.

For a patient with atypical hemolytic uremic syndrome on dialysis, treatment with eculizumab should continue for 4 to 6 months if there are no extrarenal manifestations. But many patients continue to have the defect in the complement system, so the problem may recur.

Case revisited

For our patient considering a kidney transplant, many experts feel that a transplant can be done as long as platelet counts are monitored and treatment with eculizumab is restarted if needed. One can also make the case for waiting a few years for new oral drugs to become available before offering transplant.

ANTIPHOSPHOLIPID SYNDROME

A young woman with a history of thrombosis and miscarriages

A 27-year-old woman presents with arthralgias, low-grade fever, and malaise. She has a history of 3 spontaneous abortions and Raynaud phenomenon. Two years ago, she had deep vein thrombosis of the right calf after a long automobile trip.

She now has swollen metacarpophalangeal and proximal interphalangeal joints, livedo reticularis (a mottled venous pattern of the skin best seen under fluorescent light) of the legs and arms, and ankle edema (2-cm indentation).

Her blood pressure is 152/92 mm Hg. Laboratory values:

• White blood cell count 3.6 × 10⁹/L (reference range 4.5–11.0)
• Hematocrit 24% (36%–47%)
• Platelet count 89 × 10⁹/L (150–450)
• Urinalysis: protein 4+, heme 3+, red blood cells 8–15 per high-power field (< 3), red blood cell casts present
• Blood urea nitrogen 43 mg/dL (10–20)
• Creatinine 2.6 mg/dL (0.5–1.1).
• Prothrombin time 14.6 s (10–14)
• Partial thromboplastin time 85 s (25–35)
• Antinuclear antibody positive at 1:160
• Anti-double-stranded DNA and serum complement normal
• Syphilis serologic screening (VDRL) positive.

The patient has leukopenia, anemia, thrombocytopenia, hematuria, proteinuria, high blood urea nitrogen, and markedly elevated partial thromboplastin time. Although she has a positive antinuclear antibody test and renal dysfunction, her anti-dsDNA and serum complement tests are normal, making the diagnosis of systemic lupus erythematosus unlikely.

Consider antiphospholipid syndrome

In any patient with multiple pregnancy losses, lupus, or a history of thrombosis, antiphospholipid syndrome should be considered.

In a series of patients with antiphospholipid antibody who underwent kidney biopsy, more than half were men, indicating that, unlike lupus, this is not primarily a disease of young women.

Diagnosis based on specific criteria

Clinical criteria require at least one of the following in the patient’s history²³:

• One or more episodes of arterial, venous, or small-vessel thrombosis
• Unexplained pregnancy morbidity (death of a fetus or neonate with normal morphology or 3 or more spontaneous abortions).

Serologic criteria for any of the following antiphospholipid antibodies require that at least one of the following tests be positive at least twice and at least 12 weeks apart:

• Anticardiolipin antibodies—high-titer immunoglobulin (Ig) G or IgM
• Autoantibodies for beta 2-glycoprotein
• Lupus anticoagulant—autoantibodies that increase clotting time in vitro and target beta 2-glycoprotein I and prothrombin (despite its name and actions in vitro, lupus anticoagulant functions as a coagulant).

As with the other thrombotic microangiopathies, patients with anticardiolipin syndrome have microthrombi in the glomeruli and blood vessels that are evident on kidney biopsy.

Suspect condition in likely groups

Antiphospholipid syndrome is surprisingly common.²⁴ In a case-control study, de Groot et al²⁵ found that 3.1% of patients under age 70 with a first episode of venous thrombosis and no known cancer were positive for lupus anticoagulant vs 0.9% of controls. In another case-control study, Urbanus et al²⁶ found that 17% of women under age 50 with a stroke tested positive for lupus anticoagulant compared with less than 1% of controls. Because of such studies, it has become routine to test for anticardiolipin and lupus anticoagulant in young patients presenting with a stroke.

About 1% of women trying to have children have recurrent miscarriages, and of these, 10% to 15% have antiphospholipid antibody present.^27–30

Pathogenesis

Patients with antiphospholipid syndrome have a much higher proportion of plasma beta 2-glycoprotein in the oxidized form than do healthy controls. The level is also higher than in patients with a different autoimmune disease whether or not they have antibodies against beta 2-glycoprotein 1. Although about 40% of patients with lupus have an anticardiolipin antibody, only a small percentage develop antiphospholipid syndrome with clotting.

It is thought that antiphospholipid syndrome involves initial injury to the endothelium, then potentiation of thrombus formation. Oxidized beta 2-glycoprotein complexes may bind to the endothelial cell surface, causing it to become the target of antibodies. The exact relationships between the factors are not yet understood.

The risk of a thrombotic event in an asymp­tomatic patient positive for all 3 factors—lupus anticoagulant, anticardiolipin antibody, and anti-beta 2-glycoprotein I antibody—is more than 5% per year.³¹

Manage thrombosis with anticoagulation

Khamashta et al,³² in a 1995 study, retrospectively studied patients with antiphospholipid antibodies and a history of thrombosis. Of 147 patients, 66 had idiopathic primary disease, 62 had systemic lupus, and 19 had “lupus-like” disease. Almost 70% (101 patients) had a recurrence of thrombosis, totaling 186 events. The mean time to recurrence was 12 months (range 2 weeks to 12 years). Recurrence rates were 0.01 events per patient per year with high-dose warfarin, 0.23 with low-dose warfarin, and 0.18 with aspirin. But the highest bleeding rates were in the 6 months after warfarin withdrawal; 29 patients had bleeding events, one-fourth of which were severe.

Standard therapy has become anticoagulation, starting with heparin or enoxaparin, then warfarin. There is inadequate evidence for the role of newer oral anticoagulant therapy.

A very high INR is not generally better than a moderately elevated level

For a time, it was thought that the international normalized ratio (INR) should be kept on the very high side to prevent thrombosis.

Crowther et al³³ conducted a randomized, double-blind trial comparing moderate warfarin therapy (INR 2.0–3.0) and high-intensity warfarin therapy (INR 3.1–4.0) in antiphospholipid syndrome. Thrombosis actually recurred more frequently in the high-intensity therapy group (10.7% vs 3.4%), with no significant difference in major bleeding events.

A reasonable strategy is to keep the INR between 2.5 and 3.0, keeping in mind that values fluctuate in any individual patient. A higher goal often leads to excessive anticoagulation and bleeding. If the goal is too low, recurrent thrombosis becomes more likely. There are fewer data on the newer oral anticoagulants, but their role is likely to increase as reversal agents are developed.

Recommendations published in 2003 for treating antiphospholipid syndrome include³⁴:

• Warfarin (INR 2.0–3.0) after the first thrombotic event
• Warfarin (INR 3.0–4.0) if a clot develops despite warfarin
• Warfarin (INR > 3.0) for an arterial event.

For the rare but catastrophic antiphospholipid syndrome in which thrombosis occurs in multiple organs, recommendations are for heparin plus steroids, with or without intravenous immunoglobulin and plasmapheresis. This approach has not always been successful, and the mortality rate is high.

Treatment of asymptomatic carriers is uncertain

Treatment of asymptomatic carriers of the antiphospholipid antibody is controversial. Evidence for management is scarce; some experts recommend aspirin therapy, but benefit has yet to be proven in clinical trials.

Canaud et al³⁵ documented the role of activation of the kinase mammalian target of rapamycin (mTOR) in the vascular changes characteristic of antiphospholipid nephropathy. Postkidney transplant surveillance biopsies of patients with antiphospholipid antibodies showed vascular damage occurring over time (despite patients being asymptomatic) compared with other renal transplant patients. Patients with antiphospholipid antibodies who were treated with the immunosuppressive drug sirolimus were protected from developing these changes. Twelve years after transplant, 70% of patients with antiphospholipid antibodies taking sirolimus still had a functioning graft compared with 11% of untreated patients.

Our knowledge of the pathogenesis of thrombotic microangiopathies has greatly advanced in the last decade, improving the diagnosis and treatment of these diseases.

Many conditions involve thrombotic microangiopathies (Table 1). This article reviews the most common ones, ie, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, atypical hemolytic uremic syndrome, and antiphospholipid syndrome—their clinical features (focusing on the kidney), course, and management. Of note, although the diseases are similar, their pathogeneses and treatments differ.

DIFFERENT PATHWAYS TO MULTIORGAN THROMBOSIS

The thrombotic microangiopathies are multisystem disorders that can affect children and adults and often present with prominent renal and neurologic involvement. Endothelial injury is likely the inciting factor leading to thrombosis in the kidney and in many other organs. The causes variously include:

• Toxins from bacteria or drugs
• Abnormal complement activation, genetic or autoantibody-induced
• Procoagulant factors, eg, antiphospholipid antibodies
• Loss of anticoagulants, eg, from a defect of ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13); ADAMTS13 is also known as von Willebrand factor-cleaving protease
• Severe hypertension.

The histopathologic features are similar in all the thrombotic microangiopathies. Laboratory findings include thrombocytopenia, microangiopathic hemolytic anemia (with schistocytes on the peripheral blood smear), and high serum lactate dehydrogenase (LDH) levels; these are also markers of treatment progress. Bilirubin may be elevated and haptoglobin absent. Renal biopsy reveals thrombi in the glomeruli and arterioles.

THROMBOTIC THROMBOCYTOPENIC PURPURA

A young woman with fever, bruising, and renal failure, then blindness

A 36-year-old black woman who had been previously healthy presents to her doctor with fever and bruising.

Her hematocrit is 28% (reference range 38%–46%), platelet count 15 x 10⁹/L (150–450), and prothrombin and partial thromboplastin times are normal. Her peripheral blood smear shows microangiopathic hemolytic anemia with schistocytes.

Over the next few days, her urine output declines and she develops sudden blindness followed by decreased mental acuity. Blood is drawn and sent for ADAMTS13 assay. Treatment is started at once with daily therapeutic plasma exchange. The assay results, when they arrive, show marked ADAMTS13 reduction (< 5%). Over the ensuing weeks, her mental acuity improves, her vision returns, and her renal function improves.

ADAMTS13 deficiency is definitive

Thrombotic thrombocytopenic purpura is characterized by:

• Neurologic abnormalities and acute renal failure
• Thrombocytopenia and microangiopathic hemolytic anemia
• Histologic evidence of thrombotic microangiopathy
• Deficiency of von Willebrand factor-cleaving protease (ADAMTS13 < 10%).

von Willebrand factor forms ultralarge multimers in the circulation that interact with platelets; these are normally cleaved by ADAMTS13. With ADAMTS13 deficiency (from either a genetic mutation or autoantibodies), the ultralarge multimers lead to coagulation as blood flows through small vessels.¹

In 2003, Tsai² evaluated 127 patients over age 10 who had thrombocytopenia and microangiopathic hemolysis with no plausible cause or features suggestive of hemolytic uremic syndrome. All were severely deficient in ADAMTS13. Subsequently, thrombotic thrombocytopenic purpura has been defined by a severe actual or effective deficiency of ADAMTS13.

Prompt plasma exchange is critical

Although the ADAMTS13 assay is important for diagnosing thrombotic thrombocytopenic purpura, in suspected cases daily plasma exchange should be started promptly, before test results return. Plasma exchange removes autoantibodies to ADAMTS13 from the blood, removes circulating ultralarge von Willebrand factor multimers, and replaces the missing ADAMTS13. Untreated, the disease is progressive, with irreversible renal failure, neurologic deterioration, and a 90% mortality rate. Plasma exchange reduces the mortality rate to less than 15%. If another diagnosis is confirmed, plasma exchange can be stopped.

Plasma exchange has been shown in clinical trials to be superior to plasma infusion in normalizing platelet counts and reducing mortality.^3,4 Mortality rates were comparable with different replacement fluids vs fresh-frozen plasma, including solvent or detergent-treated plasma, and cryo-poor (cryosupernatant) plasma.⁴ Antiplatelet therapy, platelet transfusions, and splenectomy are ineffective.

Glucocorticoids for early treatment

An appropriate strategy is to add a glucocorticoid to plasma-exchange therapy at once (oral prednisone 1 mg/kg per day or intravenous methylprednisolone 125 mg twice daily) and withdraw it after several days if it is determined that it is not needed. Steroids for suspected thrombotic thrombocytopenic purpura can be justified for several reasons:

• The results of the ADAMTS13 assay are usually delayed, so steroids provide coverage for other diagnoses.
• They are helpful if thrombotic thrombocytopenic purpura is idiopathic (which is true for most cases) and if the patient has a poor response to initial therapy with plasma exchange.
• They are indicated for patients whose platelet counts do not increase with several days of plasma exchange or whose thrombocytopenia recurs as plasma exchange is decreased.

Rituximab improves survival

Rituximab, a chimeric (half murine) monoclonal antibody against CD19 and CD20 B cells, suppresses antibody production by knocking out the precursors of antibody-producing cells.

Anecdotal reports and small studies involving a total of 42 patients have been published on the use of rituximab for thrombotic thrombocytopenic purpura. Courses of rituximab varied greatly, from 1 to 13 weekly doses at 375 mg/m², with 4 doses being the most common. Complete remission occurred in 90% of cases.^5,6 A typical study from 2014 involved 48 patients (30 of whom received rituximab) followed by severe ADAMTS13 deficiency during remission.⁷ Despite the small study size, the investigators found significantly improved relapse-free survival rates with rituximab treatment.

But rituximab can cost $25,000 for 2 doses of 1,000 mg, and this will most likely prohibit its routine use. The cost and insurance coverage vary with location and policies.

Based on such studies, a reasonable strategy is to treat thrombotic thrombocytopenic purpura with:

• Daily plasma exchange
• Steroids, at least until the diagnosis is certain
• Rituximab if warranted.

New targeted therapies

Caplacizumab, a humanized immunoglobulin that inhibits the interaction between ultralarge von Willebrand factor multimers and platelets, has the potential to change this strategy when it receives US Food and Drug Administration approval, which is expected soon.

Peyvandi et al⁸ randomized 75 patients with acquired thrombotic thrombocytopenic purpura to either subcutaneous caplacizumab 10 mg daily for 30 days or placebo. Both groups had daily plasma exchange. The treatment group had a 39% reduction in median time to normalization of platelets vs the placebo group, and 3 of 36 patients had exacerbations, compared with 11 of 39 patients in the placebo group. Although 8 patients relapsed within the first month after stopping caplacizumab, their cases were brought under control. There were also more bleeding episodes with caplacizumab (54% vs 38%), most being mild to moderate. Two patients in the placebo group died, but none in the treatment group.

The fact that platelet normalization occurred significantly faster with caplacizumab, even in some patients who had not yet had plasma exchange therapy initiated, has enormous clinical significance. The low platelet count in thrombotic thrombocytopenic purpura is a marker of susceptibility to rapid damage to the brain and kidneys, so correcting it quickly is critical.

Other strategies for new drug development include replacing the deficient ADAMTS13 with a recombinant molecule and blocking antibody production (the same mode of action as rituximab and glucocorticoids).⁹ Using all 3 strategies to treat thrombotic thrombocytopenic purpura may be the future standard of care.

HEMOLYTIC UREMIC SYNDROME

A child with sudden onset of bloody diarrhea and kidney failure

A 4-year-old girl plays with baby animals at a petting zoo and does not wash her hands immediately afterwards. Three days later, she develops fever, abdominal cramps, nausea, vomiting, and bloody diarrhea. Her pediatrician gives her antibiotics. On day 6, she develops ecchymoses on the extremities and lips, thrombocytopenia, low urine output, and seizures. Her stool tests positive for Escherichia coli O157:H7

Classic presentation: Young patient with bloody diarrhea

The classic presentation of hemolytic uremic syndrome is of a young patient with bloody diarrhea typically lasting 5 to 10 days. Kidney failure may follow, requiring dialysis in about 60% of patients for a mean of 10 days. About one-fourth of patients develop neurologic symptoms, and about the same fraction are left with long-term morbidity, eg, hypertension, proteinuria, and reduced glomerular filtration rate. The mortality rate is typically 4%^10,11 but varies with the outbreak.

Histologically, the kidneys look identical to those in thrombotic thrombocytopenic purpura, with thrombi in glomeruli and small vessels.

E coli is the most common culprit, but other bacteria, including Shigella dysenteriae, and viruses are sometimes the cause. Fewer than 10% of children infected with Shiga toxin-positive E coli, also known as enterohemorrhagic E coli (O157:H7, O104:H4), develop hemolytic uremic syndrome.

Lessons from outbreaks

Petting zoos are a common source of transmission of pathogenic bacteria. Disease can be extremely serious: in 15 cases linked to a Florida petting zoo, 3 children died.

Other outbreaks involving pathogenic E coli have been tied to fresh vegetables and to undercooked hamburger at fast-food chains.

In Germany in 2011, more than 3,000 people acquired Shiga toxin nonhemolytic uremic syndrome due to E coli, and 16 of them died. In addition, 845 acquired hemolytic uremic syndrome, and 36 died. This outbreak was associated with the more virulent and less common O104:H4 strain, which has acquired a Shiga toxin-encoding phage. Patients were treated with quinolone antibiotics, which actually increase toxin production in this strain.¹²

Unusual in the German epidemic was that more adults were affected (88%), especially women (68% of cases).¹³ The source of infection was eventually found to be alfalfa sprouts, the seeds of which had been contaminated by E coli. Women did not harbor any intrinsic factor making them more susceptible; rather, they were more likely to eat salads.¹³

Supportive management

Supportive care is most important. Transfusion with packed red blood cells is indicated for hemoglobin below 6 g/dL. Hypertension should be controlled and dialysis provided. For central nervous system involvement or severe disease, plasma exchange is sometimes used.

Eculizumab was tried for a time as therapy but did not prove to be of benefit. Shiga toxin-binding agents have been developed, but by the time they are given it is too late in the disease process to help.

Antibiotics may harm; it is possible that they kill beneficial bacteria, allowing the Shiga toxin-producing E coli to better proliferate. Antimotility agents also are contraindicated. Other agents not recommended include urokinase, heparin, dipyridamole, and vincristine. Splenectomy is not advised.

The most important way to control hemolytic uremic syndrome is to prevent it by thoroughly cooking meat, cleaning fresh produce, and having children wash their hands after petting animals.

ATYPICAL HEMOLYTIC UREMIC SYNDROME

A young man in renal failure

A 28-year-old man has a history of “thrombotic thrombocytopenic purpura-hemolytic uremic syndrome” at age 12. He slowly progresses to end-stage renal disease and receives a renal transplant from his mother at age 20 that fails after 3 months. The renal transplant biopsy report at the time reads “thrombotic microangiopathy.” The patient’s brother also requires dialysis.

The patient’s complement values are low, especially C3. His father is offering him a kidney at this time, and the patient wants to know whether to proceed.

Normal ADAMTS13, no diarrhea

Hemolytic uremic syndrome without diarrhea is now called atypical hemolytic uremic syndrome. Patients have normal levels of ADAMTS13, do not have diarrhea, and have no evidence of Shiga toxin-producing E coli.

Continuous complement pathway activation

The complement system is part of the innate immune system, which provides immediate defense against infection and does not evolve as does the adaptive immune system. The classic complement pathway is activated by the C1 antibody-antigen complex. The alternative complement pathway leads to the same pathway via C3.¹⁴ Both pathways lead to the formation of C5 through C9 membrane attack complexes, which form channels across the membranes of target cells, leading to cell lysis and death.

The alternate pathway does not require an antibody trigger so is always active at a low level. Inhibitory factors (factor H, factor I, membrane cofactor protein, factor H-related proteins) are naturally present and slow it down at various steps. People who are born with an abnormal factor or, more commonly, develop antibodies against one of the factors, have uninhibited complement activation. If this happens in the blood vessels, massive coagulation and atypical hemolytic uremic syndrome ensues. The endothelial damage and clotting in the brain, kidney, and other organs are identical to that of hemolytic uremic syndrome caused by Shiga toxin.

Treat with eculizumab

Historically, atypical hemolytic uremic syndrome was treated with plasma exchange, which replaces defective complement regulatory proteins and removes inhibitory antibodies.

Understanding the complement pathways is key to developing drugs that target atypical hemolytic uremic syndrome, and about 60 are in the pipeline. The only one currently approved in the United States for atypical hemolytic uremic syndrome is eculizumab, a humanized monoclonal antibody that binds with high affinity to C5, blocking the end of the complement cascade and preventing formation of the membrane attack complex.^15–18

The effects of eculizumab on atypical hemolytic uremic syndrome were studied in 2 prospective trials.¹⁹ Platelet counts rose rapidly within weeks of starting treatment, and kidney function improved. Benefits continued throughout the 64 weeks studied. There were no deaths among the 37 patients enrolled, and although these were single-arm trials, they provide evidence of dramatic benefit considering the high mortality risk of this disease.

Eculizumab is now considered the treatment of choice. It may be used empirically for patients with hemolytic uremic syndrome who test negative for Shiga toxin and antiphospholipid antibody, and who do not have a very low level of ADAMTS13. The big drawback of eculizumab is its high price,^20–22 which varies by amount used, location, and pharmacy negotiation, but can be in the hundreds of thousands of dollars.

For a patient with atypical hemolytic uremic syndrome on dialysis, treatment with eculizumab should continue for 4 to 6 months if there are no extrarenal manifestations. But many patients continue to have the defect in the complement system, so the problem may recur.

Case revisited

For our patient considering a kidney transplant, many experts feel that a transplant can be done as long as platelet counts are monitored and treatment with eculizumab is restarted if needed. One can also make the case for waiting a few years for new oral drugs to become available before offering transplant.

ANTIPHOSPHOLIPID SYNDROME

A young woman with a history of thrombosis and miscarriages

A 27-year-old woman presents with arthralgias, low-grade fever, and malaise. She has a history of 3 spontaneous abortions and Raynaud phenomenon. Two years ago, she had deep vein thrombosis of the right calf after a long automobile trip.

She now has swollen metacarpophalangeal and proximal interphalangeal joints, livedo reticularis (a mottled venous pattern of the skin best seen under fluorescent light) of the legs and arms, and ankle edema (2-cm indentation).

Her blood pressure is 152/92 mm Hg. Laboratory values:

• White blood cell count 3.6 × 10⁹/L (reference range 4.5–11.0)
• Hematocrit 24% (36%–47%)
• Platelet count 89 × 10⁹/L (150–450)
• Urinalysis: protein 4+, heme 3+, red blood cells 8–15 per high-power field (< 3), red blood cell casts present
• Blood urea nitrogen 43 mg/dL (10–20)
• Creatinine 2.6 mg/dL (0.5–1.1).
• Prothrombin time 14.6 s (10–14)
• Partial thromboplastin time 85 s (25–35)
• Antinuclear antibody positive at 1:160
• Anti-double-stranded DNA and serum complement normal
• Syphilis serologic screening (VDRL) positive.

The patient has leukopenia, anemia, thrombocytopenia, hematuria, proteinuria, high blood urea nitrogen, and markedly elevated partial thromboplastin time. Although she has a positive antinuclear antibody test and renal dysfunction, her anti-dsDNA and serum complement tests are normal, making the diagnosis of systemic lupus erythematosus unlikely.

Consider antiphospholipid syndrome

In any patient with multiple pregnancy losses, lupus, or a history of thrombosis, antiphospholipid syndrome should be considered.

In a series of patients with antiphospholipid antibody who underwent kidney biopsy, more than half were men, indicating that, unlike lupus, this is not primarily a disease of young women.

Diagnosis based on specific criteria

Clinical criteria require at least one of the following in the patient’s history²³:

• One or more episodes of arterial, venous, or small-vessel thrombosis
• Unexplained pregnancy morbidity (death of a fetus or neonate with normal morphology or 3 or more spontaneous abortions).

Serologic criteria for any of the following antiphospholipid antibodies require that at least one of the following tests be positive at least twice and at least 12 weeks apart:

• Anticardiolipin antibodies—high-titer immunoglobulin (Ig) G or IgM
• Autoantibodies for beta 2-glycoprotein
• Lupus anticoagulant—autoantibodies that increase clotting time in vitro and target beta 2-glycoprotein I and prothrombin (despite its name and actions in vitro, lupus anticoagulant functions as a coagulant).

As with the other thrombotic microangiopathies, patients with anticardiolipin syndrome have microthrombi in the glomeruli and blood vessels that are evident on kidney biopsy.

Suspect condition in likely groups

Antiphospholipid syndrome is surprisingly common.²⁴ In a case-control study, de Groot et al²⁵ found that 3.1% of patients under age 70 with a first episode of venous thrombosis and no known cancer were positive for lupus anticoagulant vs 0.9% of controls. In another case-control study, Urbanus et al²⁶ found that 17% of women under age 50 with a stroke tested positive for lupus anticoagulant compared with less than 1% of controls. Because of such studies, it has become routine to test for anticardiolipin and lupus anticoagulant in young patients presenting with a stroke.

About 1% of women trying to have children have recurrent miscarriages, and of these, 10% to 15% have antiphospholipid antibody present.^27–30

Pathogenesis

Patients with antiphospholipid syndrome have a much higher proportion of plasma beta 2-glycoprotein in the oxidized form than do healthy controls. The level is also higher than in patients with a different autoimmune disease whether or not they have antibodies against beta 2-glycoprotein 1. Although about 40% of patients with lupus have an anticardiolipin antibody, only a small percentage develop antiphospholipid syndrome with clotting.

It is thought that antiphospholipid syndrome involves initial injury to the endothelium, then potentiation of thrombus formation. Oxidized beta 2-glycoprotein complexes may bind to the endothelial cell surface, causing it to become the target of antibodies. The exact relationships between the factors are not yet understood.

The risk of a thrombotic event in an asymp­tomatic patient positive for all 3 factors—lupus anticoagulant, anticardiolipin antibody, and anti-beta 2-glycoprotein I antibody—is more than 5% per year.³¹

Manage thrombosis with anticoagulation

Khamashta et al,³² in a 1995 study, retrospectively studied patients with antiphospholipid antibodies and a history of thrombosis. Of 147 patients, 66 had idiopathic primary disease, 62 had systemic lupus, and 19 had “lupus-like” disease. Almost 70% (101 patients) had a recurrence of thrombosis, totaling 186 events. The mean time to recurrence was 12 months (range 2 weeks to 12 years). Recurrence rates were 0.01 events per patient per year with high-dose warfarin, 0.23 with low-dose warfarin, and 0.18 with aspirin. But the highest bleeding rates were in the 6 months after warfarin withdrawal; 29 patients had bleeding events, one-fourth of which were severe.

Standard therapy has become anticoagulation, starting with heparin or enoxaparin, then warfarin. There is inadequate evidence for the role of newer oral anticoagulant therapy.

A very high INR is not generally better than a moderately elevated level

For a time, it was thought that the international normalized ratio (INR) should be kept on the very high side to prevent thrombosis.

Crowther et al³³ conducted a randomized, double-blind trial comparing moderate warfarin therapy (INR 2.0–3.0) and high-intensity warfarin therapy (INR 3.1–4.0) in antiphospholipid syndrome. Thrombosis actually recurred more frequently in the high-intensity therapy group (10.7% vs 3.4%), with no significant difference in major bleeding events.

A reasonable strategy is to keep the INR between 2.5 and 3.0, keeping in mind that values fluctuate in any individual patient. A higher goal often leads to excessive anticoagulation and bleeding. If the goal is too low, recurrent thrombosis becomes more likely. There are fewer data on the newer oral anticoagulants, but their role is likely to increase as reversal agents are developed.

Recommendations published in 2003 for treating antiphospholipid syndrome include³⁴:

• Warfarin (INR 2.0–3.0) after the first thrombotic event
• Warfarin (INR 3.0–4.0) if a clot develops despite warfarin
• Warfarin (INR > 3.0) for an arterial event.

For the rare but catastrophic antiphospholipid syndrome in which thrombosis occurs in multiple organs, recommendations are for heparin plus steroids, with or without intravenous immunoglobulin and plasmapheresis. This approach has not always been successful, and the mortality rate is high.

Treatment of asymptomatic carriers is uncertain

Treatment of asymptomatic carriers of the antiphospholipid antibody is controversial. Evidence for management is scarce; some experts recommend aspirin therapy, but benefit has yet to be proven in clinical trials.

Canaud et al³⁵ documented the role of activation of the kinase mammalian target of rapamycin (mTOR) in the vascular changes characteristic of antiphospholipid nephropathy. Postkidney transplant surveillance biopsies of patients with antiphospholipid antibodies showed vascular damage occurring over time (despite patients being asymptomatic) compared with other renal transplant patients. Patients with antiphospholipid antibodies who were treated with the immunosuppressive drug sirolimus were protected from developing these changes. Twelve years after transplant, 70% of patients with antiphospholipid antibodies taking sirolimus still had a functioning graft compared with 11% of untreated patients.

The advent of targeted therapies has dramatically changed the management of chronic leukemia. Chemotherapy—highly toxic, nonspecific drugs that can be dangerous to patients and providers and result in only modest success—is gradually being replaced by biologic targeting of malignancy. Scientists are rapidly identifying extracellular and intracellular targets on tumor cells and are developing and testing promising new therapies aimed at these targets. Survival of cancer patients has become so common that clinicians outside the specialties of hematology and oncology are now caring for them.

This article describes new biologic therapies for chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL), along with the diagnosis of these diseases and management of survivors in the primary care setting.

CHRONIC MYELOGENOUS LEUKEMIA

A seemingly healthy person needs laboratory blood work, perhaps for an insurance physical examination or for a preoperative workup. Or a patient comes to the emergency department with a sore throat and routine blood tests are ordered. Their laboratory values:

• White blood cell count 250 × 10⁹/L (reference range 3–11)
• Neutrophils 70% (40%–70%)
• Blasts 1% (0)
• Metacytes and myelocytes 5% (0)
• Bands 5% (0)
• Lymphocytes 10% (22%–40%)
• Monocytes 5% (0–7%)
• Basophils 3% (0–1%)
• Eosinophils 1% (0–4%)
• Hemoglobin 12.1 g/dL (11.5–15.5 in women, 13.0–17.0 in men)
• Platelet count 525 × 10⁹/L (150–400).

Leukocytosis and a ‘left shift’

Although this scenario often raises concern for acute leukemia, a careful look shows evidence of a chronic myeloproliferative disorder instead. Specifically, this patient’s laboratory values show a “left shift”—an increase in immature neutrophils, ie, blasts, myelocytes, and bands.

This picture is characteristic of CML, an uncommon leukemia with about 4,500 new cases annually in the United States. Patients can present at any age, but the disease occurs more often in older people, with a median age of 66.¹

The presentation is usually subtle: about half of cases are detected by routine laboratory testing, which typically reveals a left-shifted leukocytosis with basophilia and a few blasts. Mild anemia is common. The platelet count is elevated in 30% to 50% of patients at diagnosis. Bone marrow aspirate shows significant myeloid hyperplasia without dysplasia, and sometimes shows mild fibrosis.

Philadelphia chromosome is diagnostic

A definitive diagnosis is made by demonstration of an abnormally short chromosome 22. Described in 1960 by Peter Nowell of the University of Pennsylvania and David Hugerford of the Institute for Cancer Research,² this abnormality, called the Philadelphia chromosome, was the first specific genetic abnormality associated with a human cancer. Later, researchers used banding techniques to find that the Philadelphia chromosome results from a reciprocal translocation of genetic material between the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9, t(9:22).^3,4 The resulting  chimeric gene, called BCR-ABL, codes for an oncogenic protein, a tyrosine kinase with constitutive activity.

The Philadelphia chromosome is present in 95% of patients with CML and can be found in all myeloid cell lineages, including erythrocytes, granulocytes, monocytes, and megakaryocytes as well as some cells of lymphocytic lineage, indicating that malignant transformation to CML takes place at the stem cell level.

The mutation causes several problems: the abnormal tyrosine kinase increases cell proliferation, inhibits apoptosis, and alters adhesion molecules in the stroma of the bone marrow, allowing immature cells to leak into the bloodstream. Most important, the mutation increases genomic instability so that additional mutations are likelier to occur over time, making it inevitable that, without treatment, the disease will progress to a fatal blast crisis within an average of 5 years of diagnosis.

CML has three clinical phases

Untreated, CML progresses through three distinct phases: chronic, accelerated, and blast crisis, defined by abnormalities in the blood smear and bone marrow (Table 1).^5,6 Most patients (85%) are diagnosed during the chronic phase. The accelerated and blastic phases resemble acute leukemia.

Chronic phase management

Therapies over the years have included arsenic (Fowler solution), splenic radiotherapy, busulfan, hydroxyurea, cytarabine, and interferon. All had some palliative success, but usually did not suppress leukemic progression.⁷

In contrast, patients undergoing allogeneic bone marrow transplant had a 5-year survival rate of 60% to 80% during the chronic phase of CML, 40% to 60% during the accelerated phase, and 10% to 20% during a blast crisis.⁸ Long-term survival confirmed the ability of transplant to cure CML, and bone marrow transplant with matched donors was the standard of care for younger patients until the end of the 20th century.

Tyrosine kinase inhibition

A new paradigm in treatment began with the development of imatinib, a tyrosine kinase inhibitor that directly interferes with the product of the chimeric BCR-ABL gene.⁹

Patients treated with imatinib during the chronic phase of CML have survival rates similar to those of people without the disease, and they usually do not progress to the accelerated and blast phases. As a result of this success, the number of transplants for CML has fallen precipitously.

Other tyrosine kinase inhibitors (dasatinib, nilotinib) that have since been developed have shown even better results in achieving remission and preventing progression. Improved survival is more difficult to demonstrate because the control groups in studies receive imatinib and have 10-year survival rates of about 90%.^10–12

With the tyrosine kinase inhibitors, CML can be regarded as functionally cured.¹³ Patients take these drugs for life and usually experience a relapse if they stop. Patients with CML are now more likely to die of a comorbidity than of CML.

Choose therapy by tolerability

Which tyrosine kinase inhibitor to use depends more on the side-effect profile of the drug than on its efficacy. Nilotinib should be avoided in patients with vascular disease, and dasatinib avoided in patients with pulmonary disease. Each drug may be associated with some degree of nausea, diarrhea, cramps, rash, and edema.^10–12

CML is not an immunosuppressive disease, nor are the drugs used to treat it. Patients with CML have an intact immune system. Therefore, precautions taken for patients with acute leukemia or lymphoid malignancy are not required for patients with CML.

Managing survivors

Since imatinib was introduced in 2000, the US Food and Drug Administration (FDA) has approved approximately 20 tyrosine kinase inhibitors for various cancers. These drugs are improving survival rates so well that patients with cancer are increasingly being seen by their primary care doctors for their medical problems.

About half of CML cases are detected by routine laboratory testing

Some problems have emerged that are consequences of this successful therapy. Angiogenesis inhibitors such as bevacizumab affect vascular endothelial growth factors, which injure endothelial cells. These effects may result in high blood pressure and arterial occlusive disease. Algorithms have been proposed for managing cardiovascular complications for patients taking tyrosine kinase inhibitors.¹⁴ Further, cardiovascular risk factors such as hyperlipidemia, diabetes, and obesity must be aggressively managed in patients taking tyrosine kinase inhibitors.

Vascular effects, rashes, and drug interactions may best be managed by primary care physicians, cardiologists, and nephrologists, who deal with such problems regularly.

CHRONIC LYMPHOCYTIC LEUKEMIA

A patient undergoes routine laboratory blood work in the emergency department or clinic, with these results:

• White blood cell count 250 × 10⁹/L
• Neutrophils 1%
• Lymphocytes 99%
• Hemoglobin 12.1 g/dL
• Platelet count 160 × 10⁹/L.

Like patients with CML, those with CLL usually present with no symptoms. The complete blood cell count reveals numerous white blood cells and lymphocytosis. Patients may have painless lymphadenopathy, anemia, and thrombocytopenia, but they do not typically have fever, sweats, or weight loss.

The disease is characterized by clonal proliferation and accumulation of mature-appearing neoplastic B lymphocytes in the blood, bone marrow, lymph nodes, and spleen. The peripheral blood smear shows “smudge cells,” indicating fragile lymphocytes.

The median age at diagnosis is about 70, with fewer than 15% of newly diagnosed patients under age 50.

CLL is the most common leukemia in the Western world, accounting for about 30% of cases of leukemia in adults. It is rare in Asians, probably because of genetic differences.

Monoclonal B-cell lymphocytosis precedes CLL

Monoclonal B-cell lymphocytosis is related to CLL and always precedes it. It is a common condition, detectable in up to 5% of older adults. The differential count shows a less severe lymphocytosis than in CLL.

Because monoclonal B-cell lymphocytosis does not always convert to leukemia, it is important for insurance coverage purposes not to diagnose it as a leukemia. Treatment-free survival of patients diagnosed with monoclonal B-cell lymphocytosis is 87% at 5 years.^15,16

Diagnosing CLL

Lymphocytosis can indicate other low-grade lymphoproliferative diseases and malignancies, so further evaluation is critical. To diagnose CLL, the B-cell count by flow cytometry (not the absolute lymphocyte count from the complete blood cell count) must be at least 5 × 10⁹/L. Below that threshold, monoclonal B-cell lymphocytosis is diagnosed unless lymphadenopathy is present, indicating small lymphocytic lymphoma. Unlike in benign lymphoproliferations, CLL lymphocytes coexpress the B-cell marker CD19 and the T-cell marker CD5.¹⁷ Bone marrow examination is rarely needed for the diagnosis of CLL.

Two types of CLL can be defined, depending on whether the B cells carry V genes that are mutated or unmutated. B cells expressing ZAP-70 and CD38 tend to carry the unmutated gene, which is associated with a worse prognosis.¹⁸ Regardless of which type a patient has, treatments and the indications for treatment are the same.

Increasing immune dysfunction

CLL is staged according to effects on lymph tissue and hematopoiesis. The Rai system for clinical staging of CLL has been used since 1975 with little alteration (Table 2).¹⁹

CLL is often an indolent lymphoproliferative malignancy and does not always progress to a fatal end stage. Therefore, treatment may be deferred, with a watch-and-wait approach until symptoms develop or the disease progresses. Approximately half of patients never require treatment.²⁰ Progression involves increasing bone marrow impairment with greater susceptibility to infection (due to intrinsic features of CLL and its therapy) and hypogammaglobulinemia in advanced disease.^21,22 Systemic infection is the cause of death for most patients.

Because CLL is a disease of the immune system, the development of autoantibodies is a cardinal feature. Autoimmune complications are almost exclusively limited to blood and can include hemolytic anemia, pure red cell aplasia, immune-mediated thrombocytopenia, and granulocytopenia. Other autoimmune diseases, such as rheumatoid arthritis, thyroiditis, and Addison disease, are uncommon.^23,24

Other complications may occur in patients who have been treated with chemotherapy, and these are usually fatal. The Richter transformation (to an aggressive lymphoma) occurs in about 15%. Other less common complications include prolymphocytoid transformation and secondary malignancies, particularly carcinomas of the lung and gastrointestinal tract and acute (myeloid) leukemia.²⁵

Survival rates in CLL have improved substantially over the past decades,^26–28 with significant gains following the introduction of antibiotics and, to a lesser extent, transfusions. Median survival is generally between 6 and 9 years, but many patients live for years without requiring therapy.

Chemotherapy: The mainstay of treatment

When to begin therapy remains one of the most challenging issues of patient management. Unlike in CML, there is no advantage to starting at diagnosis when most patients are asymptomatic.²⁹

In 1996, the National Cancer Institute issued guidelines for starting treatment, which were updated in 2008 with very little change (Table 3).³⁰ In general, the onset of symptoms and evidence of impaired marrow function, including an abnormal hemoglobin level and platelet count, are indications. The white blood cell count continuously increases during the disease course but is not usually an important factor for initiating treatment.

The therapeutic goal for most patients who require treatment has historically been palliation of symptoms. Therapy must be individualized to a patient’s age and clinical status, with a heavier reliance on chemotherapeutic agents for patients who can tolerate it and on immunotherapy for others. General strategies are as follows:

• “Go-Go” patients—young, fit, with few comorbidities, good renal function—are the minority. Recommendation: combination chemotherapy with fludarabine, cyclophosphamide, and rituximab (FCR).
• “Slo-Go” patients are reasonably fit and can tolerate chemotherapy but not FCR. Recommendation: combination therapy with either bendamustine and rituximab or chlorambucil and rituximab (for less fit patients). Recent evidence indicates ibrutinib may be useful for such patients.³¹
• “No-Go” patients are frail with short life expectancy. Recommendation: rituximab or observation (see below)

All CLL treatments are potentially toxic. Chemotherapy damages DNA and often causes blood cell counts to fall. Immunosuppression worsens with almost any treatment, involving a substantial risk of secondary malignancy. Although survival improves with therapy, relapse is universal.

Targeting CLL pathways

The new paradigm for cancer therapy is to identify a cellular pathway that drives oncogenesis or proliferation and interfere with it. The B-cell receptor pathway is enormously complex with numerous complex factors, making it difficult to discern the critical mutation that drives the proliferation of lymphocytes.

Bruton tyrosine kinase (Btk) is one factor that is critical for CLL proliferation. Patients with congenitally mutated or dysfunctional Btk have lymphopenia and agammaglobulinemia, making it a promising target for patients with B-cell disorders. Other experimental therapies are based on other such identified factors.

In 2014, the FDA approved two drugs for CLL—ibrutinib, a Btk inhibitor, and idelalisib, an inhibitor of phosphoinositide 3-kinase—after they were shown in clinical trials to dramatically improve outcomes in patients with relapsed CLL.^32,33 Trials with these drugs are ongoing. These drugs also inhibit tyrosine kinase and so have vascular side effects in addition to their own idiosyncratic effects.

Ibrutinib has anticoagulant effects and should be stopped before surgery. It also can cause or exacerbate atrial fibrillation, making management of CLL difficult. It is associated with hypogammaglobulinemia, often requiring ongoing immunoglobulin replacement.

Idelalisib tends to cause systemic autoimmune phenomena such as pneumonitis and colitis.

Using T cells as therapy

It has long been observed that patients who undergo bone marrow transplant for leukemia have lower relapse rates if the transplant is allogeneic rather than from a twin. Further, if T cells are removed from the donor graft, graft-vs-host disease may be prevented but the risk of relapses increases. Finally, the presence of graft-vs-host disease tends to reduce the risk of relapse.³⁴ Therefore, T cells clearly are key ingredients for success in the setting of bone marrow transplant. In fact, merely providing T cells for a relapse after allogeneic transplant can induce remission. However, because donor T cells are not targeted, acute and chronic graft-vs-host disease often can ensue.

‘Designer’ monoclonal antibodies

The B lymphocyte has multiple potential targets for new therapies for CLL as well as other cancers involving B cells. CD20 was identified on the surface of B cells in 1988 and is the target protein of the monoclonal antibody drug rituximab. Monoclonal antibodies can be modified to target other surface antigens, to link radioisotopes to deliver radiation therapy, and to deliver drugs that would otherwise be too toxic to be given systemically.³⁵ Monoclonal antibodies can also be modified to enhance function.

Antibodies alone, however, must often rely on the host T cells for cytotoxicity and they are often compromised by either the underlying disease or treatment. Adapting the targeting function of antibodies to enhance or genetically alter T cells to recognize cancer-specific antigens is now being explored for leukemias.³⁶

In 2014, the FDA approved blinatumomab for the treatment of relapsed or refractory acute lymphoblastic leukemia. This biopharmaceutical agent recruits T cells with one antibody-like moiety and targets the CD19 receptor of B cells with another. Given as a single intravenous treatment without chemotherapy, it has an almost 50% response rate, and those who respond tend to stay in remission. Other similar drugs are being developed, and using them earlier in treatment and for other B-cell leukemias is being explored.

New B-cell targeted therapy with CAR-Ts

Newer treatments are being developed based on chimeric antigen receptor T (CAR-T) cells. These engineered T cells express an anti-CD19 moiety that targets B cells, but also activate upon binding to them.³⁷ CAR-T technology is being refined and shows great promise for cancer treatment.

Multiple clinical trials are currently under way in which the investigators collect autologous T cells by leukopheresis from a patient with a relapsed or refractory B-cell malignancy, transduce the T cells with retroviral vectors into anti-CD19 CAR-T cells, and then reinfuse them into the patient following modest chemotherapy.³⁸

Study results from a small number of patients with relapsing or refractory CLL showed that some patients achieved long-term, progression-free survival.³⁹ The most success with this therapy, however, has been in acute lymphoblastic leukemia.⁴⁰ Possibly, this treatment could be applied to other lymphoid malignancies that also express CD19.

More advances

CAR-T cell therapy has drawbacks. The cells attack only the target antigen, which currently limits their use mostly to hematologic malignancies. In addition, autologous T cells are not robust. Also, the use of allogeneic T cells is restricted by their major histocompatibility complex, and the cells will be rejected by the recipient if not matched.

An attempt to overcome some of these drawbacks is to develop T cells redirected for universal cytokine killing. CAR-T cells are modified with a gene that causes them to excrete interleukin 12, which attracts macrophages and natural killer cells to the environment to better fight the tumor.⁴¹

Other modifications include editing out certain genes including the major histocompatibility complex, which avoids the problem of rejection. Another modification is to insert a “suicide gene” that allows the engineered T cells to be killed with an antidote if they do not work as planned.

Such gene-editing techniques hold great promise for curing cancers without chemotherapy in the not so distant future.

The advent of targeted therapies has dramatically changed the management of chronic leukemia. Chemotherapy—highly toxic, nonspecific drugs that can be dangerous to patients and providers and result in only modest success—is gradually being replaced by biologic targeting of malignancy. Scientists are rapidly identifying extracellular and intracellular targets on tumor cells and are developing and testing promising new therapies aimed at these targets. Survival of cancer patients has become so common that clinicians outside the specialties of hematology and oncology are now caring for them.

This article describes new biologic therapies for chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL), along with the diagnosis of these diseases and management of survivors in the primary care setting.

CHRONIC MYELOGENOUS LEUKEMIA

A seemingly healthy person needs laboratory blood work, perhaps for an insurance physical examination or for a preoperative workup. Or a patient comes to the emergency department with a sore throat and routine blood tests are ordered. Their laboratory values:

• White blood cell count 250 × 10⁹/L (reference range 3–11)
• Neutrophils 70% (40%–70%)
• Blasts 1% (0)
• Metacytes and myelocytes 5% (0)
• Bands 5% (0)
• Lymphocytes 10% (22%–40%)
• Monocytes 5% (0–7%)
• Basophils 3% (0–1%)
• Eosinophils 1% (0–4%)
• Hemoglobin 12.1 g/dL (11.5–15.5 in women, 13.0–17.0 in men)
• Platelet count 525 × 10⁹/L (150–400).

Leukocytosis and a ‘left shift’

Although this scenario often raises concern for acute leukemia, a careful look shows evidence of a chronic myeloproliferative disorder instead. Specifically, this patient’s laboratory values show a “left shift”—an increase in immature neutrophils, ie, blasts, myelocytes, and bands.

This picture is characteristic of CML, an uncommon leukemia with about 4,500 new cases annually in the United States. Patients can present at any age, but the disease occurs more often in older people, with a median age of 66.¹

The presentation is usually subtle: about half of cases are detected by routine laboratory testing, which typically reveals a left-shifted leukocytosis with basophilia and a few blasts. Mild anemia is common. The platelet count is elevated in 30% to 50% of patients at diagnosis. Bone marrow aspirate shows significant myeloid hyperplasia without dysplasia, and sometimes shows mild fibrosis.

Philadelphia chromosome is diagnostic

A definitive diagnosis is made by demonstration of an abnormally short chromosome 22. Described in 1960 by Peter Nowell of the University of Pennsylvania and David Hugerford of the Institute for Cancer Research,² this abnormality, called the Philadelphia chromosome, was the first specific genetic abnormality associated with a human cancer. Later, researchers used banding techniques to find that the Philadelphia chromosome results from a reciprocal translocation of genetic material between the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9, t(9:22).^3,4 The resulting  chimeric gene, called BCR-ABL, codes for an oncogenic protein, a tyrosine kinase with constitutive activity.

The Philadelphia chromosome is present in 95% of patients with CML and can be found in all myeloid cell lineages, including erythrocytes, granulocytes, monocytes, and megakaryocytes as well as some cells of lymphocytic lineage, indicating that malignant transformation to CML takes place at the stem cell level.

The mutation causes several problems: the abnormal tyrosine kinase increases cell proliferation, inhibits apoptosis, and alters adhesion molecules in the stroma of the bone marrow, allowing immature cells to leak into the bloodstream. Most important, the mutation increases genomic instability so that additional mutations are likelier to occur over time, making it inevitable that, without treatment, the disease will progress to a fatal blast crisis within an average of 5 years of diagnosis.

CML has three clinical phases

Untreated, CML progresses through three distinct phases: chronic, accelerated, and blast crisis, defined by abnormalities in the blood smear and bone marrow (Table 1).^5,6 Most patients (85%) are diagnosed during the chronic phase. The accelerated and blastic phases resemble acute leukemia.

Chronic phase management

Therapies over the years have included arsenic (Fowler solution), splenic radiotherapy, busulfan, hydroxyurea, cytarabine, and interferon. All had some palliative success, but usually did not suppress leukemic progression.⁷

In contrast, patients undergoing allogeneic bone marrow transplant had a 5-year survival rate of 60% to 80% during the chronic phase of CML, 40% to 60% during the accelerated phase, and 10% to 20% during a blast crisis.⁸ Long-term survival confirmed the ability of transplant to cure CML, and bone marrow transplant with matched donors was the standard of care for younger patients until the end of the 20th century.

Tyrosine kinase inhibition

A new paradigm in treatment began with the development of imatinib, a tyrosine kinase inhibitor that directly interferes with the product of the chimeric BCR-ABL gene.⁹

Patients treated with imatinib during the chronic phase of CML have survival rates similar to those of people without the disease, and they usually do not progress to the accelerated and blast phases. As a result of this success, the number of transplants for CML has fallen precipitously.

Other tyrosine kinase inhibitors (dasatinib, nilotinib) that have since been developed have shown even better results in achieving remission and preventing progression. Improved survival is more difficult to demonstrate because the control groups in studies receive imatinib and have 10-year survival rates of about 90%.^10–12

With the tyrosine kinase inhibitors, CML can be regarded as functionally cured.¹³ Patients take these drugs for life and usually experience a relapse if they stop. Patients with CML are now more likely to die of a comorbidity than of CML.

Choose therapy by tolerability

Which tyrosine kinase inhibitor to use depends more on the side-effect profile of the drug than on its efficacy. Nilotinib should be avoided in patients with vascular disease, and dasatinib avoided in patients with pulmonary disease. Each drug may be associated with some degree of nausea, diarrhea, cramps, rash, and edema.^10–12

CML is not an immunosuppressive disease, nor are the drugs used to treat it. Patients with CML have an intact immune system. Therefore, precautions taken for patients with acute leukemia or lymphoid malignancy are not required for patients with CML.

Managing survivors

Since imatinib was introduced in 2000, the US Food and Drug Administration (FDA) has approved approximately 20 tyrosine kinase inhibitors for various cancers. These drugs are improving survival rates so well that patients with cancer are increasingly being seen by their primary care doctors for their medical problems.

About half of CML cases are detected by routine laboratory testing

Some problems have emerged that are consequences of this successful therapy. Angiogenesis inhibitors such as bevacizumab affect vascular endothelial growth factors, which injure endothelial cells. These effects may result in high blood pressure and arterial occlusive disease. Algorithms have been proposed for managing cardiovascular complications for patients taking tyrosine kinase inhibitors.¹⁴ Further, cardiovascular risk factors such as hyperlipidemia, diabetes, and obesity must be aggressively managed in patients taking tyrosine kinase inhibitors.

Vascular effects, rashes, and drug interactions may best be managed by primary care physicians, cardiologists, and nephrologists, who deal with such problems regularly.

CHRONIC LYMPHOCYTIC LEUKEMIA

A patient undergoes routine laboratory blood work in the emergency department or clinic, with these results:

• White blood cell count 250 × 10⁹/L
• Neutrophils 1%
• Lymphocytes 99%
• Hemoglobin 12.1 g/dL
• Platelet count 160 × 10⁹/L.

Like patients with CML, those with CLL usually present with no symptoms. The complete blood cell count reveals numerous white blood cells and lymphocytosis. Patients may have painless lymphadenopathy, anemia, and thrombocytopenia, but they do not typically have fever, sweats, or weight loss.

The disease is characterized by clonal proliferation and accumulation of mature-appearing neoplastic B lymphocytes in the blood, bone marrow, lymph nodes, and spleen. The peripheral blood smear shows “smudge cells,” indicating fragile lymphocytes.

The median age at diagnosis is about 70, with fewer than 15% of newly diagnosed patients under age 50.

CLL is the most common leukemia in the Western world, accounting for about 30% of cases of leukemia in adults. It is rare in Asians, probably because of genetic differences.

Monoclonal B-cell lymphocytosis precedes CLL

Monoclonal B-cell lymphocytosis is related to CLL and always precedes it. It is a common condition, detectable in up to 5% of older adults. The differential count shows a less severe lymphocytosis than in CLL.

Because monoclonal B-cell lymphocytosis does not always convert to leukemia, it is important for insurance coverage purposes not to diagnose it as a leukemia. Treatment-free survival of patients diagnosed with monoclonal B-cell lymphocytosis is 87% at 5 years.^15,16

Diagnosing CLL

Lymphocytosis can indicate other low-grade lymphoproliferative diseases and malignancies, so further evaluation is critical. To diagnose CLL, the B-cell count by flow cytometry (not the absolute lymphocyte count from the complete blood cell count) must be at least 5 × 10⁹/L. Below that threshold, monoclonal B-cell lymphocytosis is diagnosed unless lymphadenopathy is present, indicating small lymphocytic lymphoma. Unlike in benign lymphoproliferations, CLL lymphocytes coexpress the B-cell marker CD19 and the T-cell marker CD5.¹⁷ Bone marrow examination is rarely needed for the diagnosis of CLL.

Two types of CLL can be defined, depending on whether the B cells carry V genes that are mutated or unmutated. B cells expressing ZAP-70 and CD38 tend to carry the unmutated gene, which is associated with a worse prognosis.¹⁸ Regardless of which type a patient has, treatments and the indications for treatment are the same.

Increasing immune dysfunction

CLL is staged according to effects on lymph tissue and hematopoiesis. The Rai system for clinical staging of CLL has been used since 1975 with little alteration (Table 2).¹⁹

CLL is often an indolent lymphoproliferative malignancy and does not always progress to a fatal end stage. Therefore, treatment may be deferred, with a watch-and-wait approach until symptoms develop or the disease progresses. Approximately half of patients never require treatment.²⁰ Progression involves increasing bone marrow impairment with greater susceptibility to infection (due to intrinsic features of CLL and its therapy) and hypogammaglobulinemia in advanced disease.^21,22 Systemic infection is the cause of death for most patients.

Because CLL is a disease of the immune system, the development of autoantibodies is a cardinal feature. Autoimmune complications are almost exclusively limited to blood and can include hemolytic anemia, pure red cell aplasia, immune-mediated thrombocytopenia, and granulocytopenia. Other autoimmune diseases, such as rheumatoid arthritis, thyroiditis, and Addison disease, are uncommon.^23,24

Other complications may occur in patients who have been treated with chemotherapy, and these are usually fatal. The Richter transformation (to an aggressive lymphoma) occurs in about 15%. Other less common complications include prolymphocytoid transformation and secondary malignancies, particularly carcinomas of the lung and gastrointestinal tract and acute (myeloid) leukemia.²⁵

Survival rates in CLL have improved substantially over the past decades,^26–28 with significant gains following the introduction of antibiotics and, to a lesser extent, transfusions. Median survival is generally between 6 and 9 years, but many patients live for years without requiring therapy.

Chemotherapy: The mainstay of treatment

When to begin therapy remains one of the most challenging issues of patient management. Unlike in CML, there is no advantage to starting at diagnosis when most patients are asymptomatic.²⁹

In 1996, the National Cancer Institute issued guidelines for starting treatment, which were updated in 2008 with very little change (Table 3).³⁰ In general, the onset of symptoms and evidence of impaired marrow function, including an abnormal hemoglobin level and platelet count, are indications. The white blood cell count continuously increases during the disease course but is not usually an important factor for initiating treatment.

The therapeutic goal for most patients who require treatment has historically been palliation of symptoms. Therapy must be individualized to a patient’s age and clinical status, with a heavier reliance on chemotherapeutic agents for patients who can tolerate it and on immunotherapy for others. General strategies are as follows:

• “Go-Go” patients—young, fit, with few comorbidities, good renal function—are the minority. Recommendation: combination chemotherapy with fludarabine, cyclophosphamide, and rituximab (FCR).
• “Slo-Go” patients are reasonably fit and can tolerate chemotherapy but not FCR. Recommendation: combination therapy with either bendamustine and rituximab or chlorambucil and rituximab (for less fit patients). Recent evidence indicates ibrutinib may be useful for such patients.³¹
• “No-Go” patients are frail with short life expectancy. Recommendation: rituximab or observation (see below)

All CLL treatments are potentially toxic. Chemotherapy damages DNA and often causes blood cell counts to fall. Immunosuppression worsens with almost any treatment, involving a substantial risk of secondary malignancy. Although survival improves with therapy, relapse is universal.

Targeting CLL pathways

The new paradigm for cancer therapy is to identify a cellular pathway that drives oncogenesis or proliferation and interfere with it. The B-cell receptor pathway is enormously complex with numerous complex factors, making it difficult to discern the critical mutation that drives the proliferation of lymphocytes.

Bruton tyrosine kinase (Btk) is one factor that is critical for CLL proliferation. Patients with congenitally mutated or dysfunctional Btk have lymphopenia and agammaglobulinemia, making it a promising target for patients with B-cell disorders. Other experimental therapies are based on other such identified factors.

In 2014, the FDA approved two drugs for CLL—ibrutinib, a Btk inhibitor, and idelalisib, an inhibitor of phosphoinositide 3-kinase—after they were shown in clinical trials to dramatically improve outcomes in patients with relapsed CLL.^32,33 Trials with these drugs are ongoing. These drugs also inhibit tyrosine kinase and so have vascular side effects in addition to their own idiosyncratic effects.

Ibrutinib has anticoagulant effects and should be stopped before surgery. It also can cause or exacerbate atrial fibrillation, making management of CLL difficult. It is associated with hypogammaglobulinemia, often requiring ongoing immunoglobulin replacement.

Idelalisib tends to cause systemic autoimmune phenomena such as pneumonitis and colitis.

Using T cells as therapy

It has long been observed that patients who undergo bone marrow transplant for leukemia have lower relapse rates if the transplant is allogeneic rather than from a twin. Further, if T cells are removed from the donor graft, graft-vs-host disease may be prevented but the risk of relapses increases. Finally, the presence of graft-vs-host disease tends to reduce the risk of relapse.³⁴ Therefore, T cells clearly are key ingredients for success in the setting of bone marrow transplant. In fact, merely providing T cells for a relapse after allogeneic transplant can induce remission. However, because donor T cells are not targeted, acute and chronic graft-vs-host disease often can ensue.

‘Designer’ monoclonal antibodies

The B lymphocyte has multiple potential targets for new therapies for CLL as well as other cancers involving B cells. CD20 was identified on the surface of B cells in 1988 and is the target protein of the monoclonal antibody drug rituximab. Monoclonal antibodies can be modified to target other surface antigens, to link radioisotopes to deliver radiation therapy, and to deliver drugs that would otherwise be too toxic to be given systemically.³⁵ Monoclonal antibodies can also be modified to enhance function.

Antibodies alone, however, must often rely on the host T cells for cytotoxicity and they are often compromised by either the underlying disease or treatment. Adapting the targeting function of antibodies to enhance or genetically alter T cells to recognize cancer-specific antigens is now being explored for leukemias.³⁶

In 2014, the FDA approved blinatumomab for the treatment of relapsed or refractory acute lymphoblastic leukemia. This biopharmaceutical agent recruits T cells with one antibody-like moiety and targets the CD19 receptor of B cells with another. Given as a single intravenous treatment without chemotherapy, it has an almost 50% response rate, and those who respond tend to stay in remission. Other similar drugs are being developed, and using them earlier in treatment and for other B-cell leukemias is being explored.

New B-cell targeted therapy with CAR-Ts

Newer treatments are being developed based on chimeric antigen receptor T (CAR-T) cells. These engineered T cells express an anti-CD19 moiety that targets B cells, but also activate upon binding to them.³⁷ CAR-T technology is being refined and shows great promise for cancer treatment.

Multiple clinical trials are currently under way in which the investigators collect autologous T cells by leukopheresis from a patient with a relapsed or refractory B-cell malignancy, transduce the T cells with retroviral vectors into anti-CD19 CAR-T cells, and then reinfuse them into the patient following modest chemotherapy.³⁸

Study results from a small number of patients with relapsing or refractory CLL showed that some patients achieved long-term, progression-free survival.³⁹ The most success with this therapy, however, has been in acute lymphoblastic leukemia.⁴⁰ Possibly, this treatment could be applied to other lymphoid malignancies that also express CD19.

More advances

CAR-T cell therapy has drawbacks. The cells attack only the target antigen, which currently limits their use mostly to hematologic malignancies. In addition, autologous T cells are not robust. Also, the use of allogeneic T cells is restricted by their major histocompatibility complex, and the cells will be rejected by the recipient if not matched.

An attempt to overcome some of these drawbacks is to develop T cells redirected for universal cytokine killing. CAR-T cells are modified with a gene that causes them to excrete interleukin 12, which attracts macrophages and natural killer cells to the environment to better fight the tumor.⁴¹

Other modifications include editing out certain genes including the major histocompatibility complex, which avoids the problem of rejection. Another modification is to insert a “suicide gene” that allows the engineered T cells to be killed with an antidote if they do not work as planned.

Such gene-editing techniques hold great promise for curing cancers without chemotherapy in the not so distant future.

The advent of targeted therapies has dramatically changed the management of chronic leukemia. Chemotherapy—highly toxic, nonspecific drugs that can be dangerous to patients and providers and result in only modest success—is gradually being replaced by biologic targeting of malignancy. Scientists are rapidly identifying extracellular and intracellular targets on tumor cells and are developing and testing promising new therapies aimed at these targets. Survival of cancer patients has become so common that clinicians outside the specialties of hematology and oncology are now caring for them.

This article describes new biologic therapies for chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL), along with the diagnosis of these diseases and management of survivors in the primary care setting.

CHRONIC MYELOGENOUS LEUKEMIA

A seemingly healthy person needs laboratory blood work, perhaps for an insurance physical examination or for a preoperative workup. Or a patient comes to the emergency department with a sore throat and routine blood tests are ordered. Their laboratory values:

• White blood cell count 250 × 10⁹/L (reference range 3–11)
• Neutrophils 70% (40%–70%)
• Blasts 1% (0)
• Metacytes and myelocytes 5% (0)
• Bands 5% (0)
• Lymphocytes 10% (22%–40%)
• Monocytes 5% (0–7%)
• Basophils 3% (0–1%)
• Eosinophils 1% (0–4%)
• Hemoglobin 12.1 g/dL (11.5–15.5 in women, 13.0–17.0 in men)
• Platelet count 525 × 10⁹/L (150–400).

Leukocytosis and a ‘left shift’

Although this scenario often raises concern for acute leukemia, a careful look shows evidence of a chronic myeloproliferative disorder instead. Specifically, this patient’s laboratory values show a “left shift”—an increase in immature neutrophils, ie, blasts, myelocytes, and bands.

This picture is characteristic of CML, an uncommon leukemia with about 4,500 new cases annually in the United States. Patients can present at any age, but the disease occurs more often in older people, with a median age of 66.¹

The presentation is usually subtle: about half of cases are detected by routine laboratory testing, which typically reveals a left-shifted leukocytosis with basophilia and a few blasts. Mild anemia is common. The platelet count is elevated in 30% to 50% of patients at diagnosis. Bone marrow aspirate shows significant myeloid hyperplasia without dysplasia, and sometimes shows mild fibrosis.

Philadelphia chromosome is diagnostic

A definitive diagnosis is made by demonstration of an abnormally short chromosome 22. Described in 1960 by Peter Nowell of the University of Pennsylvania and David Hugerford of the Institute for Cancer Research,² this abnormality, called the Philadelphia chromosome, was the first specific genetic abnormality associated with a human cancer. Later, researchers used banding techniques to find that the Philadelphia chromosome results from a reciprocal translocation of genetic material between the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9, t(9:22).^3,4 The resulting  chimeric gene, called BCR-ABL, codes for an oncogenic protein, a tyrosine kinase with constitutive activity.

The Philadelphia chromosome is present in 95% of patients with CML and can be found in all myeloid cell lineages, including erythrocytes, granulocytes, monocytes, and megakaryocytes as well as some cells of lymphocytic lineage, indicating that malignant transformation to CML takes place at the stem cell level.

The mutation causes several problems: the abnormal tyrosine kinase increases cell proliferation, inhibits apoptosis, and alters adhesion molecules in the stroma of the bone marrow, allowing immature cells to leak into the bloodstream. Most important, the mutation increases genomic instability so that additional mutations are likelier to occur over time, making it inevitable that, without treatment, the disease will progress to a fatal blast crisis within an average of 5 years of diagnosis.

CML has three clinical phases

Untreated, CML progresses through three distinct phases: chronic, accelerated, and blast crisis, defined by abnormalities in the blood smear and bone marrow (Table 1).^5,6 Most patients (85%) are diagnosed during the chronic phase. The accelerated and blastic phases resemble acute leukemia.

Chronic phase management

Therapies over the years have included arsenic (Fowler solution), splenic radiotherapy, busulfan, hydroxyurea, cytarabine, and interferon. All had some palliative success, but usually did not suppress leukemic progression.⁷

In contrast, patients undergoing allogeneic bone marrow transplant had a 5-year survival rate of 60% to 80% during the chronic phase of CML, 40% to 60% during the accelerated phase, and 10% to 20% during a blast crisis.⁸ Long-term survival confirmed the ability of transplant to cure CML, and bone marrow transplant with matched donors was the standard of care for younger patients until the end of the 20th century.

Tyrosine kinase inhibition

A new paradigm in treatment began with the development of imatinib, a tyrosine kinase inhibitor that directly interferes with the product of the chimeric BCR-ABL gene.⁹

Patients treated with imatinib during the chronic phase of CML have survival rates similar to those of people without the disease, and they usually do not progress to the accelerated and blast phases. As a result of this success, the number of transplants for CML has fallen precipitously.

Other tyrosine kinase inhibitors (dasatinib, nilotinib) that have since been developed have shown even better results in achieving remission and preventing progression. Improved survival is more difficult to demonstrate because the control groups in studies receive imatinib and have 10-year survival rates of about 90%.^10–12

With the tyrosine kinase inhibitors, CML can be regarded as functionally cured.¹³ Patients take these drugs for life and usually experience a relapse if they stop. Patients with CML are now more likely to die of a comorbidity than of CML.

Choose therapy by tolerability

Which tyrosine kinase inhibitor to use depends more on the side-effect profile of the drug than on its efficacy. Nilotinib should be avoided in patients with vascular disease, and dasatinib avoided in patients with pulmonary disease. Each drug may be associated with some degree of nausea, diarrhea, cramps, rash, and edema.^10–12

CML is not an immunosuppressive disease, nor are the drugs used to treat it. Patients with CML have an intact immune system. Therefore, precautions taken for patients with acute leukemia or lymphoid malignancy are not required for patients with CML.

Managing survivors

Since imatinib was introduced in 2000, the US Food and Drug Administration (FDA) has approved approximately 20 tyrosine kinase inhibitors for various cancers. These drugs are improving survival rates so well that patients with cancer are increasingly being seen by their primary care doctors for their medical problems.

About half of CML cases are detected by routine laboratory testing

Some problems have emerged that are consequences of this successful therapy. Angiogenesis inhibitors such as bevacizumab affect vascular endothelial growth factors, which injure endothelial cells. These effects may result in high blood pressure and arterial occlusive disease. Algorithms have been proposed for managing cardiovascular complications for patients taking tyrosine kinase inhibitors.¹⁴ Further, cardiovascular risk factors such as hyperlipidemia, diabetes, and obesity must be aggressively managed in patients taking tyrosine kinase inhibitors.

Vascular effects, rashes, and drug interactions may best be managed by primary care physicians, cardiologists, and nephrologists, who deal with such problems regularly.

CHRONIC LYMPHOCYTIC LEUKEMIA

A patient undergoes routine laboratory blood work in the emergency department or clinic, with these results:

• White blood cell count 250 × 10⁹/L
• Neutrophils 1%
• Lymphocytes 99%
• Hemoglobin 12.1 g/dL
• Platelet count 160 × 10⁹/L.

Like patients with CML, those with CLL usually present with no symptoms. The complete blood cell count reveals numerous white blood cells and lymphocytosis. Patients may have painless lymphadenopathy, anemia, and thrombocytopenia, but they do not typically have fever, sweats, or weight loss.

The disease is characterized by clonal proliferation and accumulation of mature-appearing neoplastic B lymphocytes in the blood, bone marrow, lymph nodes, and spleen. The peripheral blood smear shows “smudge cells,” indicating fragile lymphocytes.

The median age at diagnosis is about 70, with fewer than 15% of newly diagnosed patients under age 50.

CLL is the most common leukemia in the Western world, accounting for about 30% of cases of leukemia in adults. It is rare in Asians, probably because of genetic differences.

Monoclonal B-cell lymphocytosis precedes CLL

Monoclonal B-cell lymphocytosis is related to CLL and always precedes it. It is a common condition, detectable in up to 5% of older adults. The differential count shows a less severe lymphocytosis than in CLL.

Because monoclonal B-cell lymphocytosis does not always convert to leukemia, it is important for insurance coverage purposes not to diagnose it as a leukemia. Treatment-free survival of patients diagnosed with monoclonal B-cell lymphocytosis is 87% at 5 years.^15,16

Diagnosing CLL

Lymphocytosis can indicate other low-grade lymphoproliferative diseases and malignancies, so further evaluation is critical. To diagnose CLL, the B-cell count by flow cytometry (not the absolute lymphocyte count from the complete blood cell count) must be at least 5 × 10⁹/L. Below that threshold, monoclonal B-cell lymphocytosis is diagnosed unless lymphadenopathy is present, indicating small lymphocytic lymphoma. Unlike in benign lymphoproliferations, CLL lymphocytes coexpress the B-cell marker CD19 and the T-cell marker CD5.¹⁷ Bone marrow examination is rarely needed for the diagnosis of CLL.

Two types of CLL can be defined, depending on whether the B cells carry V genes that are mutated or unmutated. B cells expressing ZAP-70 and CD38 tend to carry the unmutated gene, which is associated with a worse prognosis.¹⁸ Regardless of which type a patient has, treatments and the indications for treatment are the same.

Increasing immune dysfunction

CLL is staged according to effects on lymph tissue and hematopoiesis. The Rai system for clinical staging of CLL has been used since 1975 with little alteration (Table 2).¹⁹

CLL is often an indolent lymphoproliferative malignancy and does not always progress to a fatal end stage. Therefore, treatment may be deferred, with a watch-and-wait approach until symptoms develop or the disease progresses. Approximately half of patients never require treatment.²⁰ Progression involves increasing bone marrow impairment with greater susceptibility to infection (due to intrinsic features of CLL and its therapy) and hypogammaglobulinemia in advanced disease.^21,22 Systemic infection is the cause of death for most patients.

Because CLL is a disease of the immune system, the development of autoantibodies is a cardinal feature. Autoimmune complications are almost exclusively limited to blood and can include hemolytic anemia, pure red cell aplasia, immune-mediated thrombocytopenia, and granulocytopenia. Other autoimmune diseases, such as rheumatoid arthritis, thyroiditis, and Addison disease, are uncommon.^23,24

Other complications may occur in patients who have been treated with chemotherapy, and these are usually fatal. The Richter transformation (to an aggressive lymphoma) occurs in about 15%. Other less common complications include prolymphocytoid transformation and secondary malignancies, particularly carcinomas of the lung and gastrointestinal tract and acute (myeloid) leukemia.²⁵

Survival rates in CLL have improved substantially over the past decades,^26–28 with significant gains following the introduction of antibiotics and, to a lesser extent, transfusions. Median survival is generally between 6 and 9 years, but many patients live for years without requiring therapy.

Chemotherapy: The mainstay of treatment

When to begin therapy remains one of the most challenging issues of patient management. Unlike in CML, there is no advantage to starting at diagnosis when most patients are asymptomatic.²⁹

In 1996, the National Cancer Institute issued guidelines for starting treatment, which were updated in 2008 with very little change (Table 3).³⁰ In general, the onset of symptoms and evidence of impaired marrow function, including an abnormal hemoglobin level and platelet count, are indications. The white blood cell count continuously increases during the disease course but is not usually an important factor for initiating treatment.

The therapeutic goal for most patients who require treatment has historically been palliation of symptoms. Therapy must be individualized to a patient’s age and clinical status, with a heavier reliance on chemotherapeutic agents for patients who can tolerate it and on immunotherapy for others. General strategies are as follows:

• “Go-Go” patients—young, fit, with few comorbidities, good renal function—are the minority. Recommendation: combination chemotherapy with fludarabine, cyclophosphamide, and rituximab (FCR).
• “Slo-Go” patients are reasonably fit and can tolerate chemotherapy but not FCR. Recommendation: combination therapy with either bendamustine and rituximab or chlorambucil and rituximab (for less fit patients). Recent evidence indicates ibrutinib may be useful for such patients.³¹
• “No-Go” patients are frail with short life expectancy. Recommendation: rituximab or observation (see below)

All CLL treatments are potentially toxic. Chemotherapy damages DNA and often causes blood cell counts to fall. Immunosuppression worsens with almost any treatment, involving a substantial risk of secondary malignancy. Although survival improves with therapy, relapse is universal.

Targeting CLL pathways

The new paradigm for cancer therapy is to identify a cellular pathway that drives oncogenesis or proliferation and interfere with it. The B-cell receptor pathway is enormously complex with numerous complex factors, making it difficult to discern the critical mutation that drives the proliferation of lymphocytes.

Bruton tyrosine kinase (Btk) is one factor that is critical for CLL proliferation. Patients with congenitally mutated or dysfunctional Btk have lymphopenia and agammaglobulinemia, making it a promising target for patients with B-cell disorders. Other experimental therapies are based on other such identified factors.

In 2014, the FDA approved two drugs for CLL—ibrutinib, a Btk inhibitor, and idelalisib, an inhibitor of phosphoinositide 3-kinase—after they were shown in clinical trials to dramatically improve outcomes in patients with relapsed CLL.^32,33 Trials with these drugs are ongoing. These drugs also inhibit tyrosine kinase and so have vascular side effects in addition to their own idiosyncratic effects.

Ibrutinib has anticoagulant effects and should be stopped before surgery. It also can cause or exacerbate atrial fibrillation, making management of CLL difficult. It is associated with hypogammaglobulinemia, often requiring ongoing immunoglobulin replacement.

Idelalisib tends to cause systemic autoimmune phenomena such as pneumonitis and colitis.

Using T cells as therapy

It has long been observed that patients who undergo bone marrow transplant for leukemia have lower relapse rates if the transplant is allogeneic rather than from a twin. Further, if T cells are removed from the donor graft, graft-vs-host disease may be prevented but the risk of relapses increases. Finally, the presence of graft-vs-host disease tends to reduce the risk of relapse.³⁴ Therefore, T cells clearly are key ingredients for success in the setting of bone marrow transplant. In fact, merely providing T cells for a relapse after allogeneic transplant can induce remission. However, because donor T cells are not targeted, acute and chronic graft-vs-host disease often can ensue.

‘Designer’ monoclonal antibodies

The B lymphocyte has multiple potential targets for new therapies for CLL as well as other cancers involving B cells. CD20 was identified on the surface of B cells in 1988 and is the target protein of the monoclonal antibody drug rituximab. Monoclonal antibodies can be modified to target other surface antigens, to link radioisotopes to deliver radiation therapy, and to deliver drugs that would otherwise be too toxic to be given systemically.³⁵ Monoclonal antibodies can also be modified to enhance function.

Antibodies alone, however, must often rely on the host T cells for cytotoxicity and they are often compromised by either the underlying disease or treatment. Adapting the targeting function of antibodies to enhance or genetically alter T cells to recognize cancer-specific antigens is now being explored for leukemias.³⁶

In 2014, the FDA approved blinatumomab for the treatment of relapsed or refractory acute lymphoblastic leukemia. This biopharmaceutical agent recruits T cells with one antibody-like moiety and targets the CD19 receptor of B cells with another. Given as a single intravenous treatment without chemotherapy, it has an almost 50% response rate, and those who respond tend to stay in remission. Other similar drugs are being developed, and using them earlier in treatment and for other B-cell leukemias is being explored.

New B-cell targeted therapy with CAR-Ts

Newer treatments are being developed based on chimeric antigen receptor T (CAR-T) cells. These engineered T cells express an anti-CD19 moiety that targets B cells, but also activate upon binding to them.³⁷ CAR-T technology is being refined and shows great promise for cancer treatment.

Multiple clinical trials are currently under way in which the investigators collect autologous T cells by leukopheresis from a patient with a relapsed or refractory B-cell malignancy, transduce the T cells with retroviral vectors into anti-CD19 CAR-T cells, and then reinfuse them into the patient following modest chemotherapy.³⁸

Study results from a small number of patients with relapsing or refractory CLL showed that some patients achieved long-term, progression-free survival.³⁹ The most success with this therapy, however, has been in acute lymphoblastic leukemia.⁴⁰ Possibly, this treatment could be applied to other lymphoid malignancies that also express CD19.

More advances

CAR-T cell therapy has drawbacks. The cells attack only the target antigen, which currently limits their use mostly to hematologic malignancies. In addition, autologous T cells are not robust. Also, the use of allogeneic T cells is restricted by their major histocompatibility complex, and the cells will be rejected by the recipient if not matched.

An attempt to overcome some of these drawbacks is to develop T cells redirected for universal cytokine killing. CAR-T cells are modified with a gene that causes them to excrete interleukin 12, which attracts macrophages and natural killer cells to the environment to better fight the tumor.⁴¹

Other modifications include editing out certain genes including the major histocompatibility complex, which avoids the problem of rejection. Another modification is to insert a “suicide gene” that allows the engineered T cells to be killed with an antidote if they do not work as planned.

Such gene-editing techniques hold great promise for curing cancers without chemotherapy in the not so distant future.