Immune Checkpoint Inhibitor-associated Myositis in a Patient with Metastatic Cholangiocarcinoma

An 83-year-old man with cholangiocarcinoma developed immune checkpoint inhibitor-associated myositis after two cycles of durvalumab, presenting with muscle weakness and myalgia. His serum creatine kinase (CK) level peaked at 26,329 U/L. Needle electromyography confirmed a myogenic process, and MRI revealed extensive muscle edema. Muscle biopsy indicated multifocal necrotic fibers. Following steroid treatment, his CK levels normalized and muscle strength returned. This case represents the first reported instance of durvalumab-associated myositis in Korea.