Which factors affect the incidence of acute disseminated encephalomyelitis (ADEM)?

Updated: Nov 08, 2018
  • Author: J Nicholas Brenton, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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ADEM is somewhat more common in the colder months of the year, during which these various viral illnesses are more prevalent. Prior to widespread immunization programs, measles was the most common associated illness. Now, most cases occur in the wake of respiratory or gastrointestinal illnesses that are presumed to be of viral etiology; specific viral agents are seldom identified.

The hiatus between onset of viral symptoms and onset of ADEM may range from 2-21 days. The two phases of illness are typically separated by a phase of recovery from fever and other constitutional manifestations of the initial infectious phase of illness. ADEM may possibly arise after intervals as long as 30 or more days after an infectious prodrome. The longer the interval between the presumed prodrome and ADEM, the less certain one can be of the etiologic association. A minority of cases lack a prodromal phase. Establishing the etiologic role of immunizations has proven controversial.

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