Epidemiology

According to a study published in 2008, the estimated incidence in California is 0.4 per 100,000 population per year, and there are approximately 3 to 6 ADEM cases seen each year at regional medical centers in the US, UK, and Australia.¹ ADEM is more common in children and adolescents than it is in adults, and there does not seem to be a higher incidence of ADEM among males or females, nor does there seem to be a higher frequency among any particular ethnic group.

Post-infectious:  In approximately 50-75 percent of ADEM cases, the inflammatory attack is preceded by a viral or bacterial infection. There have been a large number of viruses associated with these infections, including but not limited to measles, mumps, rubella, varicella zoster, Epstein-Barr, cytomegalovirus, herpes simplex, hepatitis A, influenza, and enterovirus infections.  A seasonal distribution has been observed showing that most ADEM cases occur in the winter and spring. The inflammatory attack and neurological symptoms often begin within a couple of weeks after the viral or bacterial illness.

Post-immunization:   Less than 5 percent of ADEM cases follow immunization.¹ The association between an inflammatory attack following an immunization has only been temporal and the direct connection between a vaccination and an immune attack has not been established.  Post-vaccinial ADEM has been associated with immunization for rabies, hepatitis B, influenza, Japanese B encephalitis, diphtheria/pertussis/tetanus, measles, mumps, rubella, pneumococcus, polio, smallpox, and varicella. Currently, the measles, mumps, and rubella vaccinations are most commonly associated with post-vaccinial ADEM. No infectious agent is isolated in most cases.  The incidence of ADEM associated with the live measles vaccination is 1 to 2 per million. Neurologic symptoms typically appear 4 to 13 days after a vaccination.

1. Lotze TE, Chadwick DJ. Acute disseminated encephalomyelitis in children: Pathogenesis, clinical features, and diagnosis. UpToDate. 2009.