Acute disseminated encephalomyelitis (ADEM) is an immune mediated disease of the brain.It usually occurs following a viral infection but may appear following vaccination, bacterial or parasitic infection, or even appear spontaneously. As it involves autoimmune demyelination, it is similar to multiple sclerosis.Although it occurs in all ages, most reported cases are in children and adolescents, with the average age around 5 to 8 years old.The mortality rate may be as high as 5%, full recovery is seen in 50 to 75% of cases, while up to 70 to 90% recover with some minor residual disability.
ADEM produces multiple inflammatory lesions in the brain and spinal cord, particularly in the white matter. Usually these are found in the subcortical and central white matter and cortical gray-white junction of both cerebral hemispheres, cerebellum, brainstem, and spinal cord,but periventricular white matter and gray matter of the cortex, thalami and basal ganglia may also be involved.
ADEM has an abrupt onset and a monophasic course. Symptoms usually begin 1–3 weeks after infection or vaccination. Major symptoms include fever, headache, drowsiness, seizures and coma. Although initially the symptoms are usually mild, they worsen rapidly over the course of hours to days, with the average time to maximum severity being about four and a half days.Additional symptoms include hemiparesis, paraparesis, and cranial nerve palsies.
The widely accepted first-line treatment is high doses of intravenous corticosteroids,such as methylprednisolone or dexamethasone, followed by 3–6 weeks of gradually lower oral doses of prednisolone.Other antiinflamatory and immunosuppressive therapies have been reported to show beneficial effect, such as plasmapheresis, high doses of intravenous immunoglobulin (IVIg) and cyclophosphamide.

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