Acute disseminated encephalomyelitis (ADEM) is an immune mediated disease of brain. It usually occurs following a viral infection or vaccination, but it may also appear spontaneously.

There are multiple inflammatory cell deposits in the brain, particularly in the section called white matter. Although it occurs in all ages, most reported cases are in children and young adults.

It has an abrupt onset and a monophasic course. Symptoms usually begins 1-3 weeks after infection or vaccination. Major symptoms are fever, headache, drowsiness, seizures and coma. Although initially the symptoms are usually mild, later in the course of the disease patients may even die, if they are not treated properly. Some patients recover completely, while others have permanent neurological impairments.

The first treatment is usually steroids and intensive care is often required.