Acute disseminated encephalomyelitis

An autoimmune disorder occurring in the latter phase of a viral or bacterial infection, or after a vaccination or drug ingestion.

The clinical course of focal neurological signs/symptoms of headache, vomiting, impairment of consciousness, seizures, behavioral changes, hemiparesis, ataxia, and cranial nerve abnormalities may have different courses:

1. Monophasic ADEM: Multifocal clinical findings without a prior demyelinating event that may evolve over a period of 3 months.
2. Recurrent ADEM: A second attack involving the same anatomic areas, more than 3 months after the initial event
3. Multiphasic ADEM: A second event in a different anatomic area

10-25% of patients with ADEM will progress onto developing multiple sclerosis.

On imaging patients may develop asymmetric multifocal T2 hyperintense, T1 hypointense lesions ivolving the cortex, white matter, and deep grey matter (50-80%). Posterior fossa structures are involved in 30-50% of patients. Spinal cord lesions are located in the central grey matter, affecting > 3 vertebral body segments.