Myasthenia gravis following the initiation of statin therapy: A multinational self‐controlled case series study

BACKGROUND: Evidence regarding the risk of new-onset myasthenia gravis (MG) following statin therapy initiation is limited. OBJECTIVES: To investigate this potential adverse effect using multinational real-world population-based data. METHODS: A self-controlled case series (SCCS) study was conducted using electronic medical records and claims databases from Hong Kong, the United Kingdom (UK) and Japan. Individuals aged ≥18 years with first diagnosis of MG and initiated statins were included. Conditional Poisson regression compared the risk of MG in different risk periods (up to 2 years after initiation) with non-exposure period, adjusted for age. Pooled results based on meta-analysis across all study sites were reported. RESULTS: In total, 2267 MG cases were analysed. Combined across all study sites, a significantly increased risk of incident MG was observed during the first year after statin initiation compared to non-exposure period, with a higher risk from Days 0-179 (pooled incidence rate ratio [IRR] [95% CI]: 2.662 [1.276-5.553]) than Days 180-364 (1.407 [1.014-1.954]). No increased risk of MG was observed more than 1 year after statin initiation (1.011 [0.848-1.206]). Moreover, the magnitude of MG risk elevation within the first 180 days after statin initiation was more pronounced with higher intensity statin regimens. CONCLUSION: In this multinational SCCS study, statin initiation may be associated with increased risk of new-onset MG during the first 6-12 months, with greater magnitude of risk elevation for higher intensity statin therapy. Consideration of the possibility of new-onset MG may be advisable within first 6-12 months after initiating statins, especially for medium-to-high-intensity statin therapy.