Background and ObjectivesAcute disseminated encephalomyelitis (ADEM) is the most common phenotype in pediatric myelin oligodendrocyte glycoprotein (MOG) antibody–associated disease. A previous study demonstrated impaired brain growth in ADEM. However, the effect of MOG antibodies on brain growth remains unknown. Here, we performed brain volume analyses in MOG-positive and MOG-negative ADEM at onset and over time.MethodsIn this observational cohort study, we included a total of 62 MRI scans from 24 patients with ADEM (54.2% female; median age 5 years), of which 16 (66.7%) were MOG positive. Patients were compared with healthy controls from the NIH pediatric MRI data repository and a matched local cohort. Mixed-effect models were applied to assess group differences and other relevant factors, including relapses.ResultsAt baseline and before any steroid treatment, patients with ADEM, irrespective of MOG antibody status, showed reduced brain volume compared with matched controls (median [interquartile range] 1,741.9 cm3 [1,645.1–1,805.2] vs 1,810.4 cm3[1,786.5–1,836.2]). Longitudinal analysis revealed reduced brain growth for both MOG-positive and MOG-negative patients with ADEM. However, MOG-negative patients showed a stronger reduction (−138.3 cm3[95% CI −193.6 to −82.9]) than MOG-positive patients (−50.0 cm3[−126.5 to −5.2]), independent of age, sex, and treatment. Relapsing patients (all MOG positive) showed additional brain volume loss (−15.8 cm3[−68.9 to 37.3]).DiscussionPatients with ADEM exhibit brain volume loss and failure of age-expected brain growth. Importantly, MOG-negative status was associated with a more pronounced brain volume loss compared with MOG-positive patients.