An unusual cause of hypercalcemia.

We describe a case of pronounced symptomatic hypercalcemia as a consequence of thyrotoxicosis alone. Primary hyperparathyroidism and other secondary causes of hypercalcemia were excluded. Hypercalcemia completely abated after treatment of thyrotoxicosis. Notwithstanding that hypercalcemia is an unusual manifestation of hyperthyroidism, asymptomatic elevation of serum calcium concentration had been documented in up to one-fourth of patients with proved hyperthyroidism. The current case is unusual in that the patient demonstrated a significant degree of hypercalcemia secondary to hyperthyroidism alone, with a serum calcium level as high as 3.14 mmol/L. We further discuss the putative pathophysiology of this "thyroid bone disease," highlighting the repercussion on calcium and bone metabolism in hyperthyroidism.