Spontaneous return of normocalcemia. Association with long-term hypoparathyroidism.

A 58-year-old man was admitted to the hospital with the superior vena cava (SVC) syndrome. The patient had a 13-year history of hypocalcemia resulting from surgically induced hypoparathyroidism, which he controlled with calcium lactate. Nine months before admission, he discontinued his daily therapy and still remained in a normocalcemic state. After he had the SVC syndrome, a small-cell tumor of the lung was found. His serum calcium level decreased after radiation of the tumor mass, suggesting that the tumor may have been secreting a substance producing the normocalcemia. A substance was extracted from the tumor that reacted immunologically like parathyroid hormone.