Decrease of serum calcium concentration and lost influence of calcium on parathyroid hormone release in a patient with primary hyperparathyroidism after treatment with diphosphonates.

Prolonged decrease of elevated serum calcium levels after treatment with diphosphonates in patients with primary hyperparathyroidism (pHPT) is very rare. A patient with water clear cell hyperplasia and five enlarged glands is presented who received diphosphonates (day 1 through day 8 dichloromethylene diphosphonate orally and a single dose of 60 mg pamidronate on day 8 intravenously) leading to a significant fall in serum calcium levels. Surprisingly, there was no reactive increase in intact parathyroid hormone (PTH) in the following 18 days. Patients with missing PTH regulation to hypocalcemia after diphosphonates who need a period of stabilization prior to parathyroid surgery might benefit most from this therapy.