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.

Cardiac enzyme changes in myxedema coma.

A 74-year-old man with myxedema and hypothermia had increased activities in plasma of creatine kinase (CK; EC 2.7.3.2), aspartate aminotransferase (AST; EC 2.6.1.1), and lactate dehydrogenase (LD; EC 1.1.1.27) and increased proportions of CK-MB (up to 20% of total CK) and LD1 isoenzymes, but no clinical or investigational evidence of associated myocardial infarction. This case illustrates that plasma enzyme activity and isoenzyme profiles in such clinical settings should be interpreted with caution, because increases in CK-MB and LD1 may relate to myxedema coma or hypothermia (or both) rather than to myocardial infarction.

Histopathological data on six cases of hypothyroidism accompanying muscular chronic disease.

This study was carried out on 6 patients with myxedema that showed major muscular alterations. Light and electron microscopic examinations of the striated muscle structure revealed myxedematous myopathy lesions. Considering the existence of several hypotheses regarding the pathogeny of muscular alterations, the authors discuss the likelihood of a myogenic syndrome induced by an immunity deficit in hypothyroidism.

A possible explanation of myxedema and hypercholesterolemia in hypothyroidism: control of lysosomal hyaluronidase and cholesterol esterase by thyroid hormones.

Thyroid hormones control the levels of the lysosomal enzymes, cholesterol esterase and hyaluronidase, in rat liver, skeletal muscle and skin. Activities of these enzymes decreased to approximately 40-50% of normal levels in liver cell fractions, skeletal muscle homogenates and skin homogenates from thyroidectomized rats. Treatment of hypophysectomized rats with L-triiodothyronine increased the activities of cholesterol esterase and hyaluronidase approximately 2-fold in liver cell fractions. The low levels of hyaluronidase and cholesterol esterase in thyroidectomized rats may account for the accumulation of mucopolysaccharides in skin and for the elevation of serum cholesterol levels in hypothyroid patients.

Scleromyxedema myopathy. Histochemical and electron microscopic observations.

A biopsy-proven case of scleromyxedema (papular mucinosis) with IgG lambda light chain paraproteinemia, eosinophilia and severe proximal myopathy is presented. Muscle biopsy revealed an atypical necrotizing vacuolar myopathy. Histochemical studies of cryostat sections revealed fiber necrosis, severe type II fiber atrophy, and fiber vacuolization with NADH tetrazolium reductase hyperactivity. Electron microscopy showed myocytolysis, reduplication of the basement membrane, and unit membrane-lined vacuoles negative for acid mucopolysaccharide.

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.

The origin of the elevated activities of creatine kinase and other enzymes in the sera of patients with myxoedema.

An attempt has been made to establish the origin of the elevated serum creatine kinase which occurs in most patients with myxoedema. Parallel determinations of a number of other serum enzymes were made but the incidence of elevated values was appreciably less than in the case of creatine kinase. Rather surprisingly, the serum amylase activity was found to be increased in more than 50% of the patients studied. Creatine kinase isoenzymes were separated by starch-gel electrophoresis of the sera of 26 patients with myxoedema. In 25 the MM isoenzyme only could be identified while the remaining serum also contained a trace of the MB fraction. Similar isoenzyme studies were made with the sera of normal and thyroidectomized rats, all of which are shown to contain all three isoenzymes. (MM, MB and BB) irrespective of thyroid functional status. No consistent difference was apparent between the patterns exhibited by the thyroidectomized and control groups, and it was concluded that thyroidectomized rats cannot be regarded as a suitable experimental model for the study of this aspect of human hypothyroidism. It is suggested that enzyme release in myxoedema is a non-specific effect, possibly die to diminution in the ATP content of tissues generally. The greater incidence of creatine kinase elevation is probably due to the relatively high concentrations of this enzyme in skeletal muscle, the mass of which is much greater than that of any other tissue.