Serum myoglobin in thyroid disease.

Serum myoglobin levels were measured longitudinally in patients undergoing therapy because of various thyroid disorders. Elevated myoglobin values - 72.6 (58.7-89.7) micrograms/l (mean +/- SEM) were found in group of hypothyroid subjects. The degree of myoglobin increase seemed related to the severity of hypothyroidism. When rendered euthyroid the myoglobin levels of these patients were normalized - 41.0 (37.3-45.1) micrograms/l. In patients with hyperthyroidism, due to Graves' disease or subacute thyroiditis (de Quervain), only minor changes of myoglobin values within the reference range of health subjects, were measured. This suggests that mechanisms not affecting myoglobin release are responsible for the muscular weakness of thyrotoxic patients.