Updated Multiple Sclerosis Incidence in France, 2011-2021

Multiple sclerosis (MS) is a chronic neurologic disorder with significant implications for public health as being the first cause of nontraumatic neurologic disability in young adults. Although the global prevalence of MS has been increasing, recent temporal trends in incidence remain unclear. We aimed to evaluate current MS incidence trends in France over 11 years using the Système National des Données de Santé, a nationwide administrative database covering 99% of the French population.

We used a published algorithm that incorporates multiple data sources, including benefits from long-term diseases, specific disease-modifying treatment prescriptions, and hospital discharge, to identify incident MS cases from January 1, 2011, to December 31, 2021. Sex-standardized and age-standardized incidence and prevalence were estimated using a "specific" and a "sensitive" definition providing bounds on the evolution of recent incidence. We used multivariable Poisson regression models to estimate temporal trends in incidence rates, calculating incidence rate ratios (IRRs) along with corresponding 95% CIs. In a sensitivity analysis, the time lag between past visits to neurologists and the database recording of MS was analyzed to ensure that the diagnosis extraction date was reliable.

A total of 67,311 individuals with suspected MS were identified between 2011 and 2021, with 50,320 individuals classified as incident MS using the specific definition. The sensitive definition identified 56,918 individuals with incident cases. The median age at diagnosis was 40.6 years for the specific definition and 41.5 years for the sensitive definition. The study found stable incidence of MS over the 11-year period (adjusted IRR: 0.998 [95% CI 0.996-1.001] for the specific cohort). The female-to-male ratio of incident MS cases remained stable while sex-standardized and age-standardized prevalence of MS continued to rise. The median time lag between probable diagnosis and database recording was estimated to be less than 18 months, with variations depending on age and method of patient identification.

This study provides a comprehensive analysis of MS epidemiology in France, demonstrating stable incidence and sex ratio. The increase in prevalence suggests improved management and survival and highlights the ongoing need for health care systems to support the growing population of individuals with MS.