Acute Disseminated Encephalomyelitis

Synonyms: Postinfectious Encephalomyelitis, Immune-Mediated Encephalomyelitis

What is Acute Disseminated Encephalomyelitis?

Acute disseminated encephalomyelitis (ADEM) is characterised by a brief but intense attack of inflammation in the brain and spinal cord that damages myelin – the protective covering of nerve fibers.  It often follows viral infection, or less often, vaccination for measles, mumps, or rubella.  The symptoms of ADEM come on quickly, beginning with encephalitis-like symptoms such as fever, fatigue, headache, nausea and vomiting, and in severe cases, seizures and coma.  It may also damage white matter (brain tissue that takes its name from the white colour of myelin), leading to neurological symptoms such as visual loss (due to inflammation of the optic nerve) in one or both eyes, weakness even to the point of paralysis, and difficulty coordinating voluntary muscle movements (such as those used in walking).  ADEM is sometimes misdiagnosed as a severe first attack of multiple sclerosis (MS), since some of the symptoms of the two disorders, particularly those caused by white matter injury, may be similar.  However, ADEM usually has symptoms of encephalitis (such as fever or coma), as well as symptoms of myelin damage (visual loss, paralysis), as opposed to MS, which doesn’t have encephalitis symptoms.  In addition, ADEM usually consists of a single episode or attack, while MS features many attacks over the course of time. Doctors will often use imaging techniques, such as MRI (magnetic resonance imaging), to search for old and new lesions (areas of damage) on the brain.  Old “inactive” brain lesions on MRI suggest that the condition may be MS rather than ADEM, since MS often causes brain lesions before symptoms become obvious.  In rare situations, brain biopsy may show findings that allow differentiation between ADEM and severe, acute forms of MS. Children are more likely than adults to have ADEM. 

Is there any treatment?

Treatment for ADEM is targeted at suppressing inflammation in the brain using anti-inflammatory drugs. Most individuals respond to intravenous corticosteroids such as methylprednisolone.  When corticosteroids fail to work, plasmapheresis or intravenous immunoglobulin therapy has been shown to produce improvement.  Additional treatment is symptomatic and supportive. 

What is the prognosis?

Corticosteroid therapy can shorten the duration of neurological symptoms and halt further progression of the disease in the short term, but the long term prognosis for individuals with ADEM varies.  For most, recovery begins within days, and half will recover completely.  Others may have mild to moderate lifelong impairment.  Severe cases of ADEM can be fatal.   Some individuals who initially diagnosed as having ADEM will later be reclassified as MS, but there is currently no method to determine whom those individuals will be.