Creatine Kinase MB Isoenzyme in Dermatomyositis: A Noncardiac Source

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Abstract
Three patients with polymyositis had elevated serum levels of creatine kinase MB isoenzyme. The presence of this isoenzyme is used extensively to diagnose myocardial infarction, but the isoenzyme is also found in sera of patients with primary muscular and neuromuscular disorders. Cardiac function was studied in 2 of the patients with ECG, Tc stannous pyrophosphate scanning, and Tc 99m-labeled erythrocyte gated blood pool imaging and, in the 3rd patient, by postmortem examination. There was no evidence of myocardial involvement to account for the high serum levels of isoenzyme. Creatine kinase MB in the sera of patients with polymyositis does not necessarily indicate myocardial necrosis.