Resolution of abnormal muscle enzyme studies in hypothyroidism.

Serum levels of muscle enzymes including creatine phosphokinase (CPK) have been reported to be abnormal in hypothyroidism. Seven patients with increased thyroid stimulating hormone (TSH) and elevated CPK levels were followed during replacement by oral l-thyroxine or l-thyroxine plus triiodothyronine. Data in three patients demonstrate a fairly constant rate of fall in CPK with a half-time for disappearance of approximately ten to 12 days. The normalization of muscle enzymes often precedes the correction of elevations in TSH.