Serum myoglobin and creatine kinase concentrations in patients with polymyositis or dermatomyositis.

SIR, Measurement of serum creatine kinase is an accepted procedure in the follow up of patients with polymyositis or dermatomyositis. This parameter is nearly always raised at some point in the illness, and serves as a useful guide in making decisions regarding therapy. There are preliminary reports on the importance of determination of serum myoglobin levels in such patients, however, suggesting that changes of myoglobin levels may precede alterations of creatine kinase and clinical features.' Since the assay for measuring myoglobin is time consuming and expensive and requires the use of radioactive isotopes, it was of interest to perform a prospective study dealing with the possible differences of myoglobin and creatine kinase levels in patients with polymyositis or dermatomyositis and their relevance to the clinical situation. Eight patients (one male, seven female) entered this study and were followed up for a mean period of 80 weeks (range 23-121 weeks). Five of them had definite polymyositis group I, the others definite dermatomyositis group II, according to the classification of Bohan and Peter.2 In all patients the diagnosis was confirmed by