Hyperparathyroidism during lithium therapy. Two new cases.

We report two new cases of hyperparathyroidism during lithium therapy. The patients were a 50-year-old male and a 48-year-old female under lithium for bipolar disease. Both developed osteoporosis without fractures and laboratory test abnormalities consistent with moderate hyperparathyroidism. Although only 30 or so cases of lithium-associated hyperparathyroidism have been reported, as many as 10 to 15% of lithium-treated patients may have laboratory test evidence of hyperparathyroidism. Typically, urinary calcium excretion is normal, serum phosphate levels are moderately decreased and cyclic AMP levels are normal. An adenoma is the most common lesion. Surgery is usually required in patients whose clinical and laboratory test abnormalities persist despite discontinuation of the drug. Lithium-associated hyperparathyroidism may be due to dysregulation of the caliostat, a feedback loop that subordinates parathyroid hormone secretion to serum calcium levels. Little is known about lithium-induced osteoporosis. Trabecular bone was predominantly affected in one of our patients and cortical bone in another.