Objective:

To assess differences in mortality among Medicare beneficiaries with generalized myasthenia gravis (gMG) and without MG.

Background:

gMG is a rare autoimmune disorder characterized by loss of neuromuscular function that may progress to life-threatening exacerbation or crisis. While the overall burden of gMG is well documented, real-world mortality data among older adults remain limited.

Design/Methods:

A prevalent cohort design was used based on the 100% Medicare Fee-for-Service Database (10/01/2019–12/31/2023). The gMG cohort included patients with evidence of active disease (≥1 MG-related admission or ≥2 MG-related visits ≥30 days apart) and  ≥1 MG diagnosis confirmed by a neurologist; random MG diagnosis defined index date. The non-MG cohort had no MG diagnoses and was matched 10:1 to the gMG cohort on age and index year. Cohorts were further balanced using overlap weighting on sex, race, region, and mortality-related comorbidities. Mortality was evaluated using Kaplan-Meier and Cox proportional hazards models, censoring at the end of eligibility or data. 

Results:

37,321 and 373,210 patients were included in the gMG and non-MG cohorts, respectively. Post-weighting, the gMG and non-MG cohorts had similar demographics (mean age: 74.2-74.4 years; 47.1-47.2% males). Hypertension (gMG: 81.2%; non-MG: 76.9%) and dyslipidemia (75.8%; 74.6%) were most common comorbidities. Mean follow-up duration was 18.9 and 18.1 months in the gMG and non-MG cohorts, respectively. At 12, 24, and 36 months, survival rates between the gMG and non-MG cohorts were 85.3% vs 86.2%, 78.0% vs 79.3%, and 72.5% vs 73.9%, respectively. Across all time points, gMG patients were at 7-8% higher risk of mortality compared to non-MG patients (all p<0.001).

Conclusions:

Medicare beneficiaries with gMG had consistently higher mortality than those without MG. These findings highlight the need to better identify and understand drivers of excess mortality, which may provide targeted management strategies for this vulnerable population.