Worldwide epidemiology of paediatric multiple sclerosis: data from the Multiple Sclerosis International Federation Atlas of MS, third edition.

Background: Limited data are available on the global rates of paediatric multiple sclerosis. Here, we report on the estimated worldwide prevalence of paediatric MS.

Methods: We included paediatric prevalence data in 2020-2022 (Multiple Sclerosis International Federation Atlas of MS) and the prevalence of child neurologists (International Child Neurology Association). Data were split into prevalence bands per 100 000. Countries were classified by the WHO Region and World Bank Income. Descriptive analyses were performed. An estimated worldwide prevalence rate was calculated from the 2020-2022 paediatric prevalence data, which was adjusted to reduce outliers' impact and to reflect worldwide income distribution. The Atlas of MS data was obtained via survey of coordinators from the countries who use different tracking methods including national registries vs crude estimates.

Results: Paediatric data were available in 24% (53/219) countries (38 higher and 15 lower income) with 31 420 total paediatric MS cases. In 2022, 67% (10/15) of lower income countries reported prevalence bands of '<1.0' compared with 34% (13/38) of higher income countries. Only 7% (1/15) of lower income countries reported prevalence bands '≥3.1'compared with 34% (13/38) of higher income countries. The rates of child neurologists positively correlated with the prevalence band. In 2020-2022, the estimated global prevalence (crude) was 2.53/100 000 (95% CI 2.51 to 2.56), with an adjusted prevalence rate of 1.48/100 000 (95% CI 1.45 to 1.51).

Conclusions: Access to epidemiology data from resource-limited countries is challenging including surveillance for case ascertainment. Increased resources and standard methodologies will facilitate the understanding of rare disease epidemiology.