A 30-year-old man complains of bilateral leg weakness and clumsiness of fine movements of the right hand. Five years previously he had an episode of transient visual loss. On physical examination, there is hyperreflexia with Babinski sign and cerebellar dysmetria with poor finger-to-nose movement. When the patient is asked to look to the right, the left eye does not move normally past the midline. Nystagmus is noted in the abducting eye. A more detailed history suggests the patient has had several episodes of gait difficulty that have resolved spontaneously. He appears to be stable between these episodes. He has no systemic symptoms of fever or weight loss.
Which of the following is the most appropriate next test to order?
A. Lumbar punctureThis patient’s episode of transient blindness was likely a result of optic neuritis. This transient loss of vision in one eye occurs in 25% to 40% of multiple sclerosis patients (a similar presentation can occur in SLE, sarcoidosis, or syphilis). In addition, the patient gives a history of a relapsing-remitting process. There are abnormal signs of cerebellar and upper motor neuron disease. Signs and symptoms therefore suggest multiple lesions in space and time, making multiple sclerosis the most likely diagnosis. All patients with suspected multiple sclerosis should have MRI scanning of the brain. MRI is sensitive in defining demyelinating lesions in the brain and spinal cord. Disease-related changes are found in more than 95% of patients who have definite evidence for MS. Most patients do not need lumbar puncture or spinal fluid analysis for diagnosis, although 70% have elevated IgG levels, and myelin basic protein does appear in the CSF during exacerbations. When the diagnosis is in doubt, lumbar puncture is indicated. Pleocytosis of greater than 75 cells per microliter or finding polymorphonuclear leukocytes in the CSF makes the diagnosis of MS unlikely. In some cases, chronic infection such as with syphilis or HIV may be in the differential of MS. Quantitative IgG levels would not be specific enough for diagnosis. Oligoclonal banding of CSF IgG is determined by agarose gel electrophoresis, but this is not the first test chosen. Two or more bands are found in 70% to 90% of patients with MS. CT scans are much less sensitive than MRIs in detecting demyelinating lesions, especially in the posterior fossa and cervical cord.