In viral encephalitis the CSF is often abnormal and a rise in specific viral antibody may occur. To distinguish ADEM from multiple sclerosis in the initial phases may be more difficult. Magnetic resonance imaging and CSF examination may help. The brain at post mortem may appear entirely normal or may show the signs of congestion. Histologically the basic lesions consist of infiltrations of mononuclear cells from the blood which occur around small veins in the white matter.
Demyelination occurs and is limited to the area of the perivenous cellular cuff.
These are different from the lesions found in multiple sclerosis. The association of the disease with an antecedent infection or immunisation suggests an immunological process and detailed laboratory studies involving measurement of anti-brain antibodies and of cellular immune responses to specific myelin antigens have shown that these patients have indeed mounted an allergic response against their own brain constituents. The ideal form of treatment is immunomodulation to be instituted without delay once the diagnosis is made. High doses of steroids can often lead to a very rapid resolution of symptoms with an excellent prognosis. Overall the prognosis is good where the diagnosis is made early and the appropriate therapy instituted without delay.