You are making rounds in the hospital one Saturday morning when you receive a call from the emergency department saying a 68-year-old man is having chest pain, weakness, and “positive cardiac enzymes.” His electrocardiogram (ECG) reading is reported as unremarkable. Because it is the weekend and no cardiology consultation is available at your hospital, the family medicine resident wants to know if you would like to admit the patient to your service or transfer him to a larger hospital. You decide that you can best make this decision by going to the emergency department and personally evaluating the patient.
History of present illness
- Approximately 4 weeks of generalized extremity pain and weakness; left-sided, nonexertional chest pain, which is much less severe than his extremity pains
- Symptoms are most prominent in the proximal upper extremities, especially with movement; the right side is more effected than the left
- Dyspnea on exertion
- Seen twice in local urgent care facilities in the past 10 days; diagnosed with congestive heart failure; treated with furosemide, digoxin, and an unknown antibiotic without relief
- 20- to 30-pound weight loss over the past year
Other medical history
- No chronic medical problems or medications
- Until this past month, last seen by a physician about 3 or 4 years prior
Review of systems
- Up to the day of admission has been ambulatory and able to care for himself despite his weakness
- No fever, chills, or rash; but has night sweats
- Smokes; does not drink alcohol
- Retired; lives with his wife
Physical examination
- Alert, appears mildly uncomfortable
- Temperature 101°F, respirations 32, blood pressure 164/72, pulse 80
- 3/5 strength in proximal upper and lower extremities (can barely lift arms and legs off the bed; movement also limited by pain)
- Normal distal strength (hand grips and dorsi/plantar flexion of foot)
- Normal sensation, reflexes, cranial nerves, and mental status; no neck weakness
- No abnormal joint findings; has pink discoloration over extensor surface of MCP joint, which patient dismisses as scars from previous abrasions that have been present “for a long time”
- Heart, lungs unremarkable; no peripheral edema
Laboratory studies completed in the emergency department
- ECG: normal
- Chest x-ray: bibasilar peribronchial infiltrates
- Hemoglobin/hematocrit: normal
- White blood count: 27,000 with 92% neutrophils
- Erythrocyte sedimentation rate: normal
- Urinalysis: negative for blood
- Brain natriuretic peptide: normal
- Creatine kinase (CK): 2205 IU/L (normal range 35–232)
- Troponin-I: 0.6 ng/mL.
[Reference range:
<0.05=Negative
0.05–0.09=Equivocal
0.10–0.49=Suspicious
0.50=Consistent with myocardial injury]
Q: What is your presumptive diagnosis? What is your management plan?
A: ____________________________________________________________ ______________________________________________________________
Is this acute non-ST elevation myocardial infarction (NSTEMI)?
The American College of Cardiology and the American Heart Association define myocardial infarction primarily as elevated cardiac-specific enzymes troponin-I and troponin-T in the appropriate clinical setting.1,2 Elevated cardiac troponins have a sensitivity approaching 100% for myocardial damage. Specificity is much lower for acute ischemic cardiac disease, however, particularly for patients with a low pretest probability (45% false-positive rate in one series of 1000 consecutive patients presenting to a large urban emergency department with symptoms of acute coronary ischemia).3
Mechanisms other than atherosclerotic coronary artery disease that can elevate cardiac troponins:
- Increased cardiac demand (eg, sepsis, hypovolemia)
- Nonatherosclerotic ischemia (eg, cocaine or other sympathomimetic agents, coronary vasospasm)
- Direct myocardial injury (eg, cardiac contusion, myocarditis)
- Myocardial strain (eg, congestive heart failure, pulmonary embolus)
- Chronic renal insufficiency (mechanism unclear).4
In light of this patient’s history and physical exam findings, you doubt he’s having an acute cardiac event. The most remarkable features are his weakness, muscle pain, and markedly elevated CK.
Though you have ruled out anemia and several other possibilities, the differential diagnosis of weakness is still broad. You decide to explore the differential diagnosis of elevated CK, a more specific finding in this case.
Pursuing the differential
You consult UpToDate, searching under “creatine kinase,” and find an article entitled “Muscle enzymes in the evaluation of neuromuscular disease.”5 You conclude that the most likely cause of your patient’s problems is an idiopathic inflammatory myopathy: polymyositis, dermatomyositis, or inclusion-body myositis.6
Other possibilities include post-viral myositis and myositis associated with connective tissue disease, hypothyroidism, or drug reactions.
D-penicillamine, zidovudine (AZT), and viral or bacterial infection may produce inflammatory myopathy similar to polymyositis.7 A history of exposure to myotoxic drugs (such as statins) and toxins has been excluded.
The absence of a family history for neuromuscular disease and the relatively recent onset of symptoms rule out an inherited muscular dystrophy or congenital muscle enzyme deficiency.
Myasthenia gravis presents with extraocular muscle involvement. Guillain-Barré syndrome is characterized by ascending muscle weakness. Lyme disease may cause weakness secondary to peripheral neuropathy but it does not produce evidence of muscle inflammation such as elevation of the CK. West Nile virus encephalitis may present with muscle weakness and flaccid paralysis.8 Trichinellosis may also cause muscle inflammation with weakness and elevation of CK, but it is rare in the United States.