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.