Survival Outcomes of Medicare-Covered Elderly US Population With Myasthenia Gravis.

Introduction/aim: Survival outcomes have been inadequately studied among people with myasthenia gravis (MG) in the United States (US). We examined the impact of MG and comorbid conditions on longevity.

Methods: We performed a longitudinal study using Medicare claims data (2006-2019). Incident MG cohort was identified based on the following criteria: age ≥ 65 years; ≥ 1 month of fee-for-service Parts A and B coverage; no health maintenance organization coverage; initial and subsequent MG claims within 2010-2011 separated by ≥ 28 days. A non-MG cohort of five times the number of the MG group was selected, matching for age, sex, region, and Medicare coverage duration. Overall and cause-specific mortality were compared between cohorts in the subsequent 8-10 Years using Kaplan-Meier plots and Cox proportional hazard models, adjusted for the Charlson Comorbidity Index (CCI).

Results: Cohorts of 6024 incident MG and 30,083 control beneficiaries were Included. The mortality rate was higher in the MG cohort compared to controls (66.8 vs. 57.1 per 1000-person-year, p < 0.0001). After adjusting for time-varying CCI, no significant difference in survival was observed between two cohorts (adjusted hazard ratio 1.09 [0.87-1.36], p = 0.47). Sixteen percent of deaths in the MG cohort were attributed to MG. Compared to the non-MG cohort, mortality rates (per 1000-person-year) specific to infections were higher among the MG cohort (2.0 vs. 1.2) while malignancies and dementia-specific mortality rates were lower (10.3 vs. 12.5 and 4.7 vs. 7.2), all p < 0.01.

Discussion: Long-term mortality is increased in elderly MG patients compared to non-MG counterparts, driven by their higher comorbidity burden.