Association between obesity and subsequent risk of myasthenia gravis: a nationwide population-based cohort study

Abstract Background Obesity causes a pro-inflammatory environment and is an established risk factor for a variety of autoimmune diseases. However, the association with the subsequent risk of myasthenia gravis (MG) was unclear. Methods This nationwide cohort study evaluated 3,937,214 adults over 20 years old, using data from the Korean National Health Insurance Service. Participants were categorized by body mass index (BMI) into underweight (BMI < 18.5), normal (18.5 ≤ BMI < 23.0), preobese (23.0 ≤ BMI < 25.0), obese class I (25.0 ≤ BMI < 30.0), and obese class II groups (≥ 30.0). The primary outcome was newly diagnosed MG during the follow-up period, identified through the International Classification of Diseases-10th revision, diagnostic codes and enrollment in the Rare Intractable Diseases program of South Korea. Cox proportional hazards models were used to calculate adjusted hazard ratios (aHRs) for MG risk by BMI. Results During about 10-year follow-up, 799 individuals developed MG (mean age 47.3 years old SD, 14.02 years, male 54.6%, and BMI ≥ 25 kg/m 2 32.6%). The incidence rate was highest in the obese class II group (3.39/100,000 person-years). Obese class I (aHR 1.20, 95% CI 1.00–1.43) and class II (aHR 1.88, 95% CI 1.37–2.56) groups demonstrated significantly elevated MG risks compared to the normal BMI group. In subgroup analyses, underweight males had a notably increased risk (aHR 2.16, 95% CI 1.24–3.78). Conclusion Obesity has an association with an increased risk of subsequent MG, suggesting a potential risk factor of MG. Further studies are needed to elucidate the association between obesity and MG.