Macro-creatine kinase: a neglected cause of elevated creatine kinase.

Macro-creatine kinase (macro-CK) is a neglected cause of raised CK. Over a 10-year period, we observed five cases. Three patients had macro-CK type 1. One patient with fibromyalgia underwent several explorations to find a muscular pathology; another, who had elevated CK-MB (muscle-brain fraction) activity, was referred to a cardiologist, and statin therapy was erroneously discontinued in two patients. Two patients had macro-CK type 2: a man with a neuroendocrine carcinoma and a woman with rheumatoid arthritis. Diagnosis of type 1 obviates the need to carry out pointless and expensive investigations seeking a neuromuscular or cardiac pathology, and also, the unwarranted discontinuation of statin therapy. Type 2 must prompt investigations for a neoplasm.