Risk of Fracture in Patients with Myasthenia Gravis: A Nationwide Cohort Study in Korea

Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junctions, resulting in muscle weakness and fatigue. Muscle weakness, restricted mobility, and frequent use of corticosteroids in patients with MG may predispose them to a higher risk of fractures. However, studies on the impact of MG on bone health and the associated fracture risk are scarce. Utilizing claim database of the Korean National Health Insurance Service collected between 2002 and 2020, we compared the risk of major osteoporotic fracture between 23 118 patients with MG and 115 590 individuals as an age- and sex-matched control group using multivariable Cox proportional hazard models. Over a median follow-up duration of 5.58 years, the MG group (mean age 53.7 years; 55% women) had higher risk of major osteoporotic fracture compared to controls (incidence rate 13.59 versus 9.74 per 10 000 person-years), which remained independent of age, sex, comorbidities, drug use including anti-osteoporotic agents, and previous fracture history (adjusted hazard ratio [aHR] 1.19, p < 0.001; subdistributed HR 1.14, p < 0.001 adjusted for mortality as competing risk). Subgroup analyses showed a greater association between MG and major osteoporotic fracture risk in younger (age 50 or younger) than older individuals (aHR 1.34 vs. 1.17) and in men compared to women (aHR 1.32 vs. 1.15; p for interaction <0.05 for all). An imminent divergence of the fracture risk curve between MG and controls was observed for vertebral fracture while there was time delay for non-vertebral sites, showing site-specific association. Factors associated with higher fracture risk in patients with MG were older age, female gender, high dose glucocorticoid use (> 7.5 mg/day), immunosuppressant use, and previous history of fracture. In summary, patients with MG had higher risk of major osteoporotic fracture compared to controls, which calls further preventive actions in this patient group.