Acute disseminated encephalomyelitis (ADEM) a monophasic autoimmune demyelinating disease of the central nervous system that occurs after a febrile infection or vaccination. Typically, ADEM manifests as multifocal high T2WI/ FLAIR signal lesions mimicking multiple sclerosis (MS). However, clinical and radiological findings may help in the differential. Patients with ADEM typically have at least two of the three following  

1. They have symptoms not matching for MS: altered consciousness, hypersomnia, seizures, cognitive impairment, hemiplegia, quadriparesis, aphasia, or bilateral optic neuritis.
2. They have no oligoclonal bands in cerebrospinal fluid sample.
3. They involve the gray matter (basal ganglia or cortical lesions); corpus callosal involvement is less frequent in patients with ADEM than in those with MS.