Fact-sheet: Acute disseminated encephalomyelitis - ADEM
Updated on 09/07/2021 at 11:59 AM
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Definition
Acute disseminated encephalomyelitis (ADEM) is a multifocal inflammatory demyelinating disease of the central nervous system.
It results from an autoimmune mechanism following vaccination (particularly in children) or an infectious episode, most often viral.
Overall prognosis is good.
Clinical features
Clinical presentation is highly variable and nonspecific, ranging from asymptomatic lesions to severe neurologic impairment.
CT
Hypodense lesions most often involving the white matter, which may also affect the gray matter, particularly the basal ganglia.
MRI
Lesions show T2 FLAIR hyperintensity, T1 hypo- or isointensity, with enhancement after gadolinium injection.
White matter involvement is most common, but gray matter, particularly the basal ganglia, may also be affected.
Management
Treatment of the underlying cause.
Monitoring in cases of post-vaccination ADEM.
Classification
3 clinical forms:
Monophasic ADEM: first clinical episode presenting as encephalopathy variably associated with multifocal neurologic signs related to demyelinating white matter lesions, with acute or subacute onset. - No prior white matter lesion or similar prior clinical episode. - If a relapse occurs within three months of the initial episode or within four weeks of discontinuing corticosteroid therapy, it is considered part of the initial episode.
Recurrent ADEM: defined by a new event meeting ADEM criteria, occurring at least three months after the initial episode and at least four weeks after discontinuation of corticosteroid therapy, with identical clinical presentation and involving the same territories on MRI as the initial episode. Multiphasic ADEM: defined by one or more recurrences with encephalopathy and multifocal deficits, involving new CNS regions, both clinically and on MRI.