[The parathyroid function in patients with hyperthyroidism]

The parameters of calcium metabolism were determined in 22 patients with untreated hyperthyroidism (5 males and 17 females) and 5 control subjects. Hypercalcemia was found in the patients with hyperthyroidism in comparison with the control subjects (serum Ca: 10.0 +/- 0.56 vs. 9.0 +/- 0.18, p less than 0.001 and Ca++: 5.1 +/- 0.28 vs. 4.6 +/- 0.15 mg/dl, p less than 0.001, mean +/- SD). Although the urinary excretion of calcium was decreased in many patients, abnormalities of phosphate metabolism were not found in this study. The parameters of bone resorption, urinary hydroxyproline, serum alkaline phosphatase and acid phosphatase, were increased in all patients with hyperthyroidism. Serum immunoreactive PTH was decreased (0.23 +/- 0.05 vs. 0.29 +/- 0.05 ngEq/ml, p less than 0.05). In vitamin D metabolites, 25-OH-D did not differ from the control (16.9 +/- 7.76 vs. 17.9 +/- 5.52 ng/ml), 1,25-(OH)2D showed a tendency to decrease (32.6 +/- 19.53 vs. 37.2 +/- 13.75 pg/ml) and 24,25-(OH)2D was obviously increased (5.57 +/- 3.582 vs. 1.73 +/- 0.619 ng/ml, p less than 0.001) in the hyperthyroid patients. Thus, the parathyroid function was suppressed in the patients with hyperthyroidism, and hypercalcemia in hyperthyroidism was suggested to be due to the direct action of thyroid hormone upon the bone.