Normocalcemic primary hyperparathyroidism.

Primary hyperparathyroidism is a common disorder of mineral metabolism characterized by incompletely regulated, excessive secretion of parathyroid hormone from one or more of the parathyroid glands. The historical view of this disease describes two distinct entities marked by two eras. When primary hyperparathyroidism was first discovered about 80 years ago, it was always symptomatic with kidney stones, bone disease and marked hypercalcemia. With the advent of the multichannel autoanalyzer about 40 years ago, the clinical phenotype changed to a disorder characterized by mild hypercalcemia and the absence of classical other features of the disease. We may now be entering a 3rd era in the history of this disease in which patients are being discovered with normal total and ionized serum calcium concentrations but with parathyroid hormone levels that are consistently elevated. In this article, we describe this new entity, normocalcemic primary hyperparathyroidism, a forme fruste of the disease.