A Case of Polymyositis with Normal Creatine Kinase

Proximal muscle weakness can be induced by many diseases, such as muscular dystrophies, inflammatory muscle diseases, and polymyalgia rheumatica.Differential diagnosis of these diseases is important.The patient had proximal muscle weakness with a normal creatine kinase (CK) level.Our initial diagnosis was polymyalgia rheumatica because the CK level was normal.The patient was treated with low-dose corticosteroid.However, the muscle weakness did not improve.The diagnosis of polymyositis was confirmed by a muscle biopsy.We suggest that if the patient has typical symptoms with normal CK, then evaluations for inflammatory muscle diseases are essential.(Korean