Acute disseminated encephalomyelitis
Acute disseminated encephalomyelitis is a monophasic, often postinfectious, immune-mediated demyelinating illness that produces large, diffuse inflammatory lesions of the brain and spinal cord. Fever and encephalopathy with multifocal deficits separate it from multiple sclerosis; treatment is high-dose IV methylprednisolone, with plasma exchange for steroid-refractory disease, after infection is excluded.
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What this article covers
- Overview
Definition: acute disseminated encephalomyelitis (ADEM) is a monophasic, often postinfectious, immune-mediated syndrome that causes large, diffuse areas of inflammatory demyelination in the central…
- Epidemiology
Age: ADEM usually presents in children or young adults and is rare in adults.
- Risk factors
Recent viral infection: measles and varicella are the classic triggers; ADEM is listed among the postinfectious demyelinating disorders.
- Pathophysiology
Postinfectious autoimmunity: an immune response following infection is directed against CNS myelin, in the same way that a viral trigger can produce postinfectious autoimmune encephalitis.
- Clinical features
Encephalopathy with fever: altered mental status, from disorientation to somnolence, with fever; both are atypical for MS and are the hallmark of ADEM.
- Differential diagnosis
Herpes simplex virus encephalitis: temporal lobe features (olfactory hallucinations, personality change, psychosis), CSF red cells, temporal edema or hemorrhage on MRI, and a positive CSF HSV PCR.
- Diagnosis
Diagnosis is established clinically and radiologically: a first, acute, multifocal CNS demyelinating event with encephalopathy (usually with fever), plus MRI showing large, diffuse…
- Management
First, stabilize and protect the airway: a patient with a Glasgow Coma Scale score of 8 or less needs airway protection before imaging and lumbar puncture.
- Complications
Death: up to 20% in measles-associated ADEM.
- Prognosis
Mortality up to 20% after measles: the most serious outcome figure for postinfectious ADEM.
- Prevention
Measles vaccination: MMR vaccine at age 1 year and again at age 4 years protects about 95% of recipients; give an early dose at 6 to 11 months before travel to a region with low vaccination rates.
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