A patient with hypercalcemia was found to have thyrotoxicosis and no other underlying cause for the elevated serum calcium level. Radioiodine therapy relieved hyperthyroidism and hypercalcemia. We discuss the incidence of hypercalcemia in patients with thyrotoxicosis and mechanisms for hypercalcemia in hyperthyroidism.
Hyperthyroidism is an uncommon cause of hypercalcemia.
Nevertheless, patients with hyperthyroidism frequently exhibit mild elevations of serum calcium levels. Initial workup of hypercalcemia involves investigation for more common causes such as primary and secondary hyperparathyroidism. Since hypercalcemia is frequently idiopathic, mere exclusion of obvious causes of hypercalcemia in a patient with hyperthyroidism does not establish a definite relationship until hypercalcemia is abated with relief of thyrotoxicosis. In the case presented here, hypercalcemia was proved to be caused by hyperthyroidism. Therapy with radioiodine relieved both hyperthyroidism and hypercalcemia.