Hypercalcemia in Myxedema

Abstract

Recently an adult patient with myxedema and hypercalcemia was observed to become normocalcemic when rendered euthyroid. This experience prompted a study of the effect of oral administration of calcium to hypothyroid patients and animals. Eleven patients with hypothyroidism, all of whom were normocalcemic, were given 30 ml of 40 % calcium chloride in fractional doses during 1 day. Hypercalcemia ensued in 8 of the patients to a degree that was more marked than in any control subject. Administration of calcium orally (20 mg of calcium and 20 uC of calcium⁴⁵ per 100 g of body weight) to hypothyroid rats resulted in more marked hypercalcemia than occurred in normal rats. Furthermore, the relative specific activities of sera from hypothyroid rats was greater than in controls. Despite the latter finding, the relative specific activities of bones from hypothyroid and euthyroid animals were nearly identical, indicating a reduced calcium exchange and/or uptake by bone in the hypothyroid rats. These observations show that thyroid insufficiency may be accompanied by the propensity toward the development of hypercalcemia upon ingestion of large amounts of calcium. This phenomenon is best explained by an impaired rate of disposition of absorbed calcium, with the possibility of an increased absorption of this ion from the gut as a contributory factor.