High elevations of creatine phosphokinase in hypothyroidism. An isoenzyme analysis.

In hypothyroidism, slight elevations of serum creatine phosphokinase (CPK) levels are common. In contrast, we describe six hypothyroid patients with extreme elevations (17- to 160-fold) of CPK levels. Enzyme analysis showed only MM isoenzyme in four cases and MM plus trace MB isoenzyme in two patients. Hypothyroidism should, therefore, be considered when elevated CPK levels, even extreme, are found. Isoenzyme analysis in such a case will show primarily an MM pattern, although trace MB fraction can also be seen. This isoenzyme pattern suggests that the sources of the CPK elevations is skeletal muscle.