Seasonal variation in myasthenia gravis incidence.

Introduction: Environmental factors may contribute to myasthenia gravis (MG) development, sometimes with seasonal patterns of exposure. However, whether seasonality has an impact on MG incidence remains unclear. We aimed to investigate the association between seasonality and MG onset.

Methods: We reviewed data of MG patients with acetylcholine receptor (AChR)-IgG and disease onset between January 2010-December 2019, from two Italian cohorts: 1) an hospital-based cohort and 2) a population-based cohort. MG cases were assigned to four season-trimesters based on month of onset to determine seasonal association with MG incidence.

Results: We enrolled 316 patients:214 in the hospital-based and 102 in the population-based cohort. Median age at onset was 66 years (range, 8-92); Female accounted for 41.1 %. The median number of new MG cases per season-trimester was significantly higher in summer than other trimesters (p = 0.009), and associated with higher environmental temperatures.

Discussion: Our findings suggest that MG onset may be more common in summer and at higher environmental temperatures. Identifying the determinants of this association may improve our understanding of disease pathophysiology.