Acute Disseminated Encephalomyelitis

Acute disseminated encephalomyelitis (ADEM) is a monophasic, immune-mediated demyelinating disorder of the CNS, typically occurring 1 to 4 weeks after a viral infection or, less commonly, vaccination, thought to reflect molecular mimicry triggering an autoimmune attack on CNS myelin.

Predominantly affects children, and, by definition, is monophasic, distinguishing it from multiple sclerosis, though a minority of cases later prove to be a first MS episode.

Rapid onset (over days) of multifocal neurological deficits: encephalopathy (a required diagnostic feature distinguishing ADEM from other demyelinating syndromes, ranging from confusion to coma), alongside any combination of pyramidal signs, ataxia, cranial neuropathies, and visual disturbance (optic neuritis).

Fever and meningism may accompany the preceding infectious trigger.

MRI brain and spinal cord shows multiple, large, poorly demarcated T2/FLAIR hyperintense lesions in white matter, often with deep gray matter (basal ganglia, thalamus) involvement, distinguishing the pattern from typical MS lesions.

CSF shows a lymphocytic pleocytosis with elevated protein; oligoclonal bands are typically absent or transient (unlike MS, where they are usually persistent), an important discriminating feature.

Infectious encephalitis (particularly HSV) must be excluded given overlapping presentation, with CSF PCR as detailed in that entry.

• High-dose IV corticosteroids (methylprednisolone 1 g IV od for 3 to 5 days), followed by an oral taper over 4 to 6 weeks, is first line
• IVIG or plasma exchange for steroid-refractory or severe cases
• Supportive care and rehabilitation for residual deficits
• Most children make a good recovery; a minority have residual deficits or, over subsequent follow-up, are reclassified as having had an initial MS attack if further demyelinating episodes occur, warranting long-term neurological follow-up

Referral: neurology for all cases, given diagnostic overlap with MS and the need for long-term follow-up.