Acute disseminated encephalomyelitis (ADEM) is a brief but intense attack of inflammation in the brain, spinal cord and occasionally optic nerve that causes damage to myelin. Symptoms of ADEM come on quickly, typically beginning with encephalopathy including behavioral changes such as confusion or excessive irritability, and an alteration in consciousness (e.g., lethargy, coma). The damage to myelin may also cause neurological symptoms similar to those seen in MS such as visual loss in one or both eyes caused by optic neuritis, weakness and loss of coordination. ADEM may occur in association with a viral or bacterial infection, as a complication of inoculation or vaccination, or without a preceding cause. Children are more likely than adults to have ADEM.
ADEM is sometimes misdiagnosed as a severe first attack of MS since some of the symptoms of the two disorders may be similar. However, ADEM usually consists of a single episode or attack lasting weeks or months, while MS features many attacks over the course of time. Doctors will often use MRI to search for old and new lesions on the brain and spinal cord; old areas of damage suggest that the condition is ongoing and may be MS rather than ADEM. In the absence of old lesions, it is difficult to discriminate severe first attacks of what will eventually be diagnosed as MS from ADEM. For this reason, the physician carefully monitors the person with ADEM to see if a recurrence or progression suggests MS. Differentiating ADEM from MS is important because the treatment recommendations differ significantly; people with MS will usually require some form of continuing immune treatments while those with ADEM will not.
For more information about acute disseminated encephalomyelitis, consult the National Institute of Neurological Disorders and Stroke (National Institutes of Health) or The Transverse Myelitis Association.