Incidence of pediatric neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein antibody-associated disease in Denmark 2008‒2018: A nationwide, population-based cohort study

•Pediatric NMOSD and MOG antibody-associated disease are rare.•One-third of anti-MOG-positive children relapsed.•In pediatric ADEM, only anti-MOG-positive children relapsed.•The overall risk of relapse after pediatric ADEM was low. The incidence of pediatric neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease have not been reported previously. Our aim was to estimate the incidence of pediatric NMOSD and the occurrence of anti-MOG antibody-associated disease in Denmark during 2008–18, and to evaluate the diagnostic usefulness of antibodies against MOG and aquaporin-4 (AQP4) in children