The typical abnormalities on NM most commonly are located in the supratentorial white matter, especially in the periventricular region. They may appear as multiple descrete lesions, or they may coalesce to form more homogeneous borders surrounding the ventricles. These abnormalities have a location similar to that of the demyelinating lesions observed at autopsy. Less commonly, lesions can be detected in the cerebellum and in the brainstem. While CT is not as sensitive as NM in the detection of abnormalities in MS, it nevertheless may demonstrate a wide variety of findings.
Cerebral atrophy is the most common and least specific abnormality.
Hypodense lesions before administration of contrast agent may be present in periventriucular and deep white matter and, uncommonly, in the posterior fossa. Enhancement seems to correlate with acute disruption of the blood-brain barrier, and the areas of abnormal enhancement can be abolished by treatment with corticosteroids. Conditions to be ruled out include coflagenvascular disorders, sarcoidosis, acute disseminated encephalomyelitis, Behcet's disease, cerebrovascular occlusive disease, meningovascular syphilis, paraneoplastic disorders. Psychiatric disorders almost always enter in the differential diagnosis early in the course of the disease. The clinical therapeutic trials are all aimed at altering the patients' immune system, inasmuch as the demyelination in MS is thought to be immune mediated.