High elevations of creatine phosphokinase in hypothyroidism. An isoenzyme analysis

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Abstract
In hypothyroidism, slight elevations of serum creatine phosphokinase (CPK) levels are common. In contrast, 6 hypothyroid patients are described with extreme elevations (17- to 160-fold) of CPK levels. Enzyme analysis showed only MM isoenzyme in 4 cases and MM plus trace MB isoenzyme in 2 patients. Hypothyroidism should be considered when elevated CPK levels, even if 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 source of the CPK elevations is skeletal muscle.