Serum enzyme alterations in polymyositis. Possible pitfalls in diagnosis.

We report serum enzyme patterns in three patients with polymyositis or dermatomyositis whose cases posed potential problems in distinguishing malignancy, hepatocellular damage, and myocardial infarction from myositis. The alanine aminotransferase showed five- to 16-fold elevations. The creatine kinase MB isoenzyme and a predominance of lactate dehydrogenase isoenzymes 2 and 3 were present in each of the three patients. However, none of the patients showed any evidence of hepatocellular damage, myocardial infarction, or malignancy. We suggest that, although the individual occurrences are indicative of other processes, the concurrence of elevated alanine aminotransferase, creatine kinase MB, and elevated lactate dehydrogenase isoenzymes 2 and 3 is consistent with the diagnosis of polymyositis.