Case
A 60-year-old man with stage IV hormoneindependent prostate cancer, with widely metastatic disease to the bone, presents to the ED with increased weakness and new onset of numbness in the lower extremities, which he states began earlier that day. After failing several lines of chemotherapy, he is currently being treated with hormonal therapy alone. Patient first noted weakness in the left lower extremity 5 days before presentation, which progressed to bilateral involvement, making ambulation difficult and requiring the use of a walker. He denies back pain or urinary or fecal incontinence. Regarding pain management, he had been recently treated at one of the pain clinics in the hospital and has continued on opioid medication at another institution. Until the past week, he states he had back pain without neurological deficits.
His vital signs are stable at presentation. Patient is obese but in no acute distress. His cardiopulmonary examination is unremarkable; abdominal examination is benign; and back examination is normal. On neurological examination, iliopsoas flexion is 4/5 bilaterally; the rest of the motor examination is normal, with toes downgoing bilaterally upon plantar stimulation. Diminished sensation to light touch is noted at the T4-T6 sensory level and below; patient also has diminished proprioception in his lower extremities.
Patient had undergone a whole body scan one month prior to presentation, which revealed increased tracer uptake of Technetium-99m in multiple areas in the thoracic and lumbar spine. The radiologist also reported bilateral involvement in the wrists, femurs, tibias, and humeri—all in concordance with multifocal bone disease noted in previous computed tomography scans.
How should you approach this case?
Overview of Metastatic Spinal Cord Compression
Malignant or metastatic spinal cord compression (MSCC) of the thecal sac is an ominous complication of advanced cancer and an oncologic emergency presenting clinically in approximately 3% to 10% of cancer-related deaths.1,2 Cancer patients have a median survival of 3 to 6 months from diagnosis of MSCC.1,3,4 This disease causes significant disability due to paralysis, sensory loss, protracted pain, and sphincter dysfunction.5 If left untreated, MSCC has the potential to cause paraplegia in almost all affected patients; therefore, prompt recognition and treatment are essential to maintain mobility and neurological function. Generally speaking, any cancer patient who presents with new or worsening back pain—even in the absence of neurological deficits—merits evaluation for spinal cord compression.6 Nevertheless, individual risk assessment is warranted.7
Epidemiology
In the United States, more than 20,000 cases of MSCC are reported each year.8 According to postmortem studies, this condition affects 5% to 36% of cancer patients.9,10 In a US nationwide study of 15,367 cases of MSCC,2 the mean age at hospitalization was 62 years, with 37% of cases occurring in women. In approximately 20% of cases, MSCC was the initial presentation of cancer4; this has been reflected in our experience at MD Anderson Cancer Center.
Cancers of the breast, lung, prostate, and multiple myeloma are the most frequent underlying conditions in MSCC.2,8 Its prevalence varies depending on tumor type, occurring in 0.2% of pancreatic cancers; however, MSCC may affect up to 7.9% to 15% of myelomas1,2 and 13% of lymphomas.2 Interestingly, 5.5% of patients with prostate cancer develop MSCC.2 According to a study by Lu et al,11 historical risk factors include known nonvertebral bony metastases and stage IV disease at the time of diagnosis.
The most common location of MSCC is the thoracic spine (69% of cases); 29% of cases occur at the lumbosacral level and 10% at the cervical area.12 Most likely this pattern follows the lymphatic drainage, as metastases from breast and lung cancers tend to be found in the thoracic spine. Pelvic and intra-abdominal malignancies most commonly migrate to the lumbar spine. Multiple spinal epidural metastases were noted in 31% of those who underwent complete imaging of the spine.12
Pathophysiology
Most cases of MSCC are epidural in origin, arising from the vertebral column in 85% of patients.8 Epidural spread is caused mainly by hematogenous mechanism through the Batson venous plexus,13 debilitating the bone and eventually causing vertebral collapse with compression of the spinal canal. Epidural spread is less likely caused by direct tumor extension (ie, erosion through the bone) or by direct deposition of tumor cells into the epidural space.14 Ultimate neuronal injury is thought to involve vasogenic edema,15 leading to ischemia13 through venous infarction, but there has been debate regarding this last phenomenon.16 In cases of paralysis, demyelination is striking.16
Clinical Presentation
Even though cancer accounts for less than 1% of episodes of low back pain, it is the most common systemic disease affecting the spine.17 An important clinical inquiry is to determine whether back pain in an established cancer patient can be ruled out without extensive imaging. Unfortunately, clinical examination alone cannot exclude MSCC. Because of the high specificity (0.98), any cancer patient with new back pain should be considered to have metastasis until proven otherwise.17