Hypothermic myxedema coma erroneously diagnosed as myocardial infarction because of increased creatine kinase MB.

As is well recognized, activities of creatine kinase (CK, EC 2.7.3.2) and lactate dehydrogenase (EC 1.1.1.27) in plasma may be substantially increased in hypothyroidism. We emphasize here that an increase and decrease in CK-MB isoenzyme, characteristic of acute myocardial infarction, can occur in hypothermic myxedema coma without myocardial infarction.