A fulminant and often fatal demyelinating disease of the brain which primarily affects young adults and children. Clinical features include the rapid onset of weakness, seizures, and coma. It may follow a viral illness or mycoplasma pneumoniae infections but in most instances there is no precipitating event. Pathologic examination reveals marked perivascular demyelination and necrosis of white matter with microhemorrhages. (Adams et al., Principles of Neurology, 6th ed, pp924-5)