Carbimazole: Myositis: case report.

A man in his 30s developed myositis while being treated with carbimazole for Graves disease. Initially diagnosed with thyrotoxic periodic paralysis, he later experienced severe muscle cramps and myalgia, leading to a diagnosis of carbimazole-induced myositis. Treatment with carbimazole was stopped, and propylthiouracil was initiated, resulting in symptom improvement and normal levels of creatine kinase. After 6 months, occasional muscle cramps persisted, but myalgia progressively improved over 24 months on propylthiouracil. [Extracted from the article]