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.