Electronic Health Record-Based Estimates of Acute Disseminated Encephalomyelitis Epidemiology in a Large Healthcare Network, 2000-2025.

Background: Acute disseminated encephalomyelitis (ADEM) is a rare, rapidly progressive, immune-mediated demyelinating disorder with limited contemporary data describing its epidemiology in adults and real-world uptake of myelin oligodendrocyte glycoprotein (MOG) autoantibody testing.

Methods: We used the TriNetX global collaborative network (112 contributing healthcare organizations) to estimate ADEM prevalence and incidence rates from 2000 to 2025, both overall and stratified by age of onset, sex, race, and ethnicity. We also assessed uptake of MOG autoantibody testing among people with an ADEM diagnosis code.

Results: We identified 4911 ADEM cases among 153,342,461 individuals from 2000 to 2025. Overall period prevalence was 3.26 (95% CI [confidence interval] 3.17-3.35) per 100,000 persons and overall incidence rate was 0.63 per 100,000 person-years (95% CI: 0.61-0.65). ADEM diagnosis codes were most frequently recorded in those ≤14 years old. Estimated were similar between sexes, lower among Black compared to White individuals, but similar across other racial groups and ethnicities. Only 11% of ADEM-coded individuals had documented MOG autoantibody testing.

Conclusion: In a large, real-world, electronic health record network, ADEM diagnosis codes were most frequently recorded in children, though cases were observed across the adult age range. MOG autoantibody testing was uncommon.