Acute Disseminated Encephalomyelitis (ADEM) is a brief but intense attack of inflammation (swelling) in the brain and spinal cord and occasionally the optic nerves that damages the brain’s myelin (the white coating of nerve fibers).
- First clinical attack of inflammatory or demyelinating disease in the CNS
- Acute or subacute onset
- Affects multifocal areas of the CNS
- Polysymptomatic presentation
- Must include encephalopathy:
Acute behavioral change such as confusion or irritability
Alteration in consciousness ranging from somnolence or coma
- Attack should be followed by improvement on clinical and/or neuroradiologic (MRI) measures
- Sequelae may include residual deficits
- No other etiologies can explain the event
- ADEM relapses (with new or fluctuating symptoms, signs or MRI findings) occurring within three months of the inciting ADEM episode are considered part of the same acute event. In addition, ADEM relapses that occur during a steroid taper or within four weeks of completing a steroid taper are considered part of the initial inciting ADEM episode.
Lesion Characteristics on MRI FLAIR and T2 weighted images
- Large (>1 to 2 cm in size) multifocal, hyperintense, bilateral, asymmetric lesions in the supratentorial or infratentorial white matter. Rarely, brain MRI shows a single large ([greater than or equal to]1 to 2 cm) lesion predominantly affecting white matter.
- Gray matter, especially basal ganglia and thalamus, may be involved
- Spinal cord MRI may show confluent intramedullary lesion(s) with variable enhancement, in addition to the abnormalities on brain MRI
- No radiologic evidence of previous destructive white matter changes
Encephalopathy is a required feature for the diagnosis of ADEM, but is not a typical feature of multiple sclerosis. In addition, a cerebrospinal fluid pleocytosis [greater than or equal to] 50 white blood cells/mm can be observed in ADEM, whereas this finding is highly atypical for multiple sclerosis.
CNS: central nervous system.
- Krupp LB, Banwell B, Tenembaum S; International Pediatric MS Study Group. Consensus definitions proposed for pediatric multiple sclerosis and related disorders. Neurology. 2007 Apr 17;68(16 Suppl 2):S7-12.[Medline]
Created: May 15, 2009