Autoimmune blistering diseases treated with glucocorticoids: An international study of steroid‐induced myopathy

BACKGROUND: Patients with autoimmune blistering diseases (AIBDs) are often exposed to chronic glucocorticoid (GC) treatment with many side effects. Glucocorticoid-induced myopathy (GIM) is a well-established side effect, which particularly affects the proximal muscles. The Glucocorticoid Toxicity Index (GTI) is a validated global assessment tool which quantifies GC toxicity over time. OBJECTIVES: This study marks the first study which analyses GIM in patients with AIBDs. The objectives of this study were to utilize the GTI to investigate the nature and prevalence of GIM in AIBD patients and explore potential risk factors. METHODS: This international cohort study was conducted in blistering disease clinics across Australia, China, Greece, Iran, Japan, the Philippines, Turkey and the United States of America between February 2019 and July 2023. The GTI tool was completed by a medical practitioner at each patient visit. Data related to glucocorticoid toxicity were entered into the Steritas GTI 2.0 to generate an aggregate improvement and cumulative worsening score at each visit. RESULTS: The study included 139 patients. There were 132 episodes of myopathy, and 47.5% of patients developed muscle weakness at some point during the study period. Cumulative GC dose correlated positively with myopathy risk, while average dose and treatment duration were not significant. Older age, male gender and obesity more than doubled the likelihood of developing GIM. CONCLUSIONS: GIM is a common side effect experienced by AIBD patients on GC treatment. Muscle weakness is less likely to occur if cumulative GC dose is less than 0.75 mg/kg/day. Studies of exercise programs to mitigate myopathy and newer alternative treatments to reduce cumulative GC dose should be considered.