abnormal increase in the secretion of parathyroid hormone by one or more parathyroid glands (see parathyroid gland). The oversecretion is usually caused by a tumour or enlargement of parathyroid tissue and results in high blood and urine calcium and low blood and high urine phosphorus. The excess calcium is withdrawn from the bones, resulting in ( osteoporosis) and an increased susceptibility to fracture. Other effects are kidney stones (kidney stone) and decreased nervous and muscular excitability. Treatment is usually surgical removal of the tumour or excess parathyroid tissue.