Original articleJuvenile myasthenia gravis in Norway: A nationwide epidemiological study

•First nationwide epidemiological study of juvenile myasthenia gravis in Norway.•Incidence of juvenile myasthenia gravis (JMG) in Norway is 1.6 per million per year.•The incidence of JMG in Norway has been stable over the last 25 years.•We find that JMG is more frequent among females, also in the prepubertal group.

BackgroundThe aim of this study was to assess the incidence rate and prevalence of autoimmune myasthenia gravis (MG) among children in Norway.MethodsThis retrospective population-based study was performed in Norway from January 2012 to December 2013. Cases of juvenile MG (JMG) with onset < 18 years were identified through searches in coding systems of electronic patient records at the 15 main hospitals in Norway from 1989 to 2013. In addition, the acetylcholine receptor antibody database at Haukeland University Hospital and the clinical nationwide MG database at Oslo University Hospital were searched for cases of JMG. Diagnosis and age at onset were verified through medical records. Incidence and prevalence rates were calculated using the Norwegian population as reference.ResultsIn total 63 unique JMG cases were identified. This corresponds to an average annual incidence rate of 1.6 per million. Incidence rate was stable over the study period. Prevalence of JMG was 3.6-13.8 per million. Females constituted the majority of JMG cases (55 vs 8 males). The risk of JMG was higher among females both in the postpubertal and prepubertal group (p < 0.001 and p = 0.02, respectively).ConclusionThis study confirms the rarity of JMG in Norway, especially among males, and shows a stable incidence rate over the last 25 years.