Thymectomy in patients with myasthenia gravis increases the risk of autoimmune rheumatic diseases: a nationwide cohort study.

Objectives. Previous studies have shown myasthenia gravis (MG) and autoimmune rheumatic diseases (ARDs) share common pathogenetic mechanisms. Therefore, the present study investigated the possible relationship between MG and ARDs. Methods. We analysed Taiwanese medical data from the Registry of Catastrophic Illness and identified patients with MG. From the entire general population data of the National Health Insurance Research Database, we randomly selected a comparison cohort that was frequency-matched by age (in 5-year increments), sex, and index date. We analysed the risk of ARDs by using a Cox proportional hazards regression model stratified by sex, age and treatment. Results. In the present study, we enrolled 6478 patients with MG (58.03% women; mean age, 50.55 years) and 25 912 age- and sex-matched controls. The risk of total ARDs was 6.25 times higher in the MG cohort than in the non-MG cohort after adjustment for age and sex. Furthermore, the MG cohort was associated with a significantly higher risk of primary SS (pSS), SLE and other ARD types (adjusted hazard ratios: 15.84 [95% CI: 8.39, 23.91]; 11.32 [95% CI : 5.04, 25.429]; and 4.07 [95% CI: 1.31, 12.62], respectively). The MG cohort who underwent thymectomy had an increased risk of RA, pSS and SLE (adjusted hazard ratios: 4.41; 15.06; and 23.68, respectively). Conclusion. The present nationwide cohort study revealed an association between MG and incident ARDs. The MG cohort who underwent thymectomy had an increased risk of RA, pSS and SLE. Future studies are needed to elucidate the underlying pathogenesis and to translate this into clinical therapeutic options.