Evaluation of Sarcopenia by Psoas Muscle Measurements in Bullous Pemphigoid: A Single-Institution Survey in Japan

Bullous pemphigoid (BP) is a rare autoimmune blistering disease that primarily affects elderly individuals. Based on the Bullous Pemphigoid Disease Area Index (BPDAI) severity assessment, immunosuppressive drugs are recommended for severe cases that fall within the more than moderate classes. Sarcopenia, which is characterized by decreased skeletal muscle mass and function in elderly patients, is a progressive and widespread skeletal muscle disease. We retrospectively surveyed patients who received treatment for BP at our hospital between 2012 and 2024 to evaluate the relevance of sarcopenia, as assessed using the psoas muscle mass index (PMI), and to investigate the benefit of relapse-free survival (RFS). A total of 59 patients with BP were included in this study. A total of 57.6% (34 of 59 patients) of the BP patients had sarcopenia, as measured by PMI. Kaplan-Meier analysis showed that the sarcopenia group (n = 34) had a median RFS of 394 days, which was not longer than that of the non-sarcopenia group (n = 25, 275 days) (p = 0.894). No significant difference in RFS was observed in the subgroup analysis based on the severity of BPDAI. Our real-world data confirmed the high prevalence of sarcopenia in the BP population and the efficacy of standard treatment centered on immunosuppressive therapy based on the severity of BPDAI. There is little basis for reducing oral corticosteroids below 0.5 mg/kg based solely on the patient's perceived frailty, regardless of the severity of the BPDAI. Limited evidence is available to assess the association between sarcopenia and autoimmune diseases in terms of their etiology. As populations continue to age globally, it is important for clinicians to prioritize addressing diseases while considering whether patients experience frailty in daily practice.