Diagnosis: Spinal Cord MRI in Multiple Sclerosis

From time to time, lesions that appear to be typical for MS turn up unexpectedly on MRI scans of persons with no clinical symptoms suggestive of MS, no history of them, and no findings on examination. The MRI has usually been obtained for reasons unrelated to MS, such as headaches or head trauma. Several groups have followed such persons with this so-called radiologically isolated syndrome (RIS) for a decade or more. Many RIS cases have gone on to develop radiologic progression with new, enlarging, or GD-enhancing, but still asymptomatic, lesions. A smaller proportion have converted to clinically apparent MS. MS usually has a preclinical phase with asymptomatic lesions acquired in the past detected on MRI scans obtained at the time of a first clinical event. It is also agreed that treatment of a first MS attack is more effective than when treatment is delayed. As a counterbalance, it is well known that a forme fruste of MS exists. There are numerous reports of MS being found at autopsies of elderly persons with no known neurologic deficit during life.

Thus the conundrum: should one treat based on new asymptomatic lesions seen on an MRI scan? Can probability to develop overt MS be predicted? It has been proposed that presence of cervical spinal cord lesions shifts the odds for early appearance of clinically definite MS dramatically upward. If so, the absence of a cervical spinal cord lesion shifts the odds downward. The issue of when to treat remains open.

TUMEFACTIVE MS

One unusual radiologic imaging feature of MS is the presence of a large tumefactive lesion. Clinical features vary with the specific anatomic location of the lesion and may be atypical for MS. There may be cognitive abnormalities, mental confusion, aphasia, agnosia, seizures, ataxia, hemiplegia, and visual field defects. Median age at onset is about 37 years (8-69), and there is a slight female preponderance. Tumefactive lesions may be found in patients with an established diagnosis of MS, but when they present as a single, ominous-appearing, space-occupying lesion in patients experiencing a first neurologic event, there may be considerable diagnostic difficulty. Tumefactive lesions are larger than 2 cm in diameter, with an open-ring–enhancing edge, an edematous surround, and frequently, depending on their size, a mass effect. These imaging features may mimic a brain tumor, an abscess, other inflammatory disorders, vasculitis, or granulomatous disease and may lead to brain biopsy. Histologic examination reveals hypercellularity, confluent demyelination, foamy macrophages full of myelin debris intermingled with reactive large-bodied astrocytes, relative axonal preservation, and variable perivascular and parenchymal lymphocytic infiltration.

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