Background and objectives: Epidemiologic studies suggest increasing incidence and prevalence of myasthenia gravis (MG) among the elderly population outside the United States. We aimed to provide an estimation of MG incidence and prevalence and their trend among the Medicare Fee-For-Service (FFS)-covered elderly US population.
Methods: We performed a retrospective longitudinal study using Medicare claims data (2006-2019). Study-eligible beneficiaries were aged 65 years and older, had at least 1 month of FFS Part A/B coverage, and were without any health maintenance organization insurance coverage. Study-eligible beneficiaries were aggregated into 2-year periods from 2006-2007 through 2018-2019. MG cases were ascertained using a validated algorithm of 2 MG claims within each 2-year period, from 2 outpatient office visits or a combination of 1 inpatient admission and 1 outpatient office visit, separated by ≥ 28 days. Period prevalence was calculated from MG-ascertained cases divided by FFS Part A/B beneficiaries and reported as cases per 100,000 population. Incident cases were determined among MG prevalent cases if the initial MG claim occurred in that period after a full calendar year since coverage initiation. Incidence was calculated as case counts per 100,000 at-risk beneficiary person-years (PYs) in each period excluding 2006-2007. Trends of prevalence and incidence over time were examined with Poisson regression. All-cause mortality of each 2-year period was calculated.
Results: The period prevalence of MG increased from 81 to 119 per 100,000 FFS A/B population from 2006-2007 to 2018-2019 (p < 0.001). Increasing trends of prevalence were observed in all sex (male/female), age (65-69/70-74/75-79/80+), race/ethnic (African American/Asian/Hispanics of any race/non-Hispanic White/other), and census region (Northeast/Midwest/South/West) subgroups. MG incidence increased from 12.2 to 13.3 per 100,000 PYs from 2008-2009 to 2018-2019 (p < 0.05). Increasing incidence trends were significant in the following subgroups: men and women; all age groups except 75-79 years; White non-Hispanic race; Northeast, Midwest, and South census regions. All-cause mortality among MG beneficiaries was stable from 6.26 deaths per 100 PYs in 2006-2007 to 5.67 in 2018-2019 (p = 0.18).
Discussion: Increasing trends in MG prevalence and incidence in the elderly US population, with variation in rates of certain subgroups, are confirmed in this 14-year period.