Hypoparathyroidism is a rare disorder in which the body produces too little or no parathyroid hormone. This hormone, together with vitamin D and another hormone called calcitonin, regulates the amount of calcium in the blood. Hypoparathyroidism can result in an abnormally low level of calcium in the blood, called hypocalcemia.
Parathyroid hormone is produced by the parathyroid glands, four small glands located behind the thyroid gland in the neck.
Doctors classify hypoparathyroidism as either hereditary or acquired. In hereditary hypoparathyroidism, the parathyroid glands are either absent at birth or fail to function properly for some unknown reason. Hereditary hypoparathyroidism sometimes occurs with other developmental defects, or as part of a syndrome that affects the thyroid gland and adrenal cortex. It generally causes symptoms before age 10, although occasionally symptoms will appear later.
Acquired hypoparathyroidism most commonly occurs when the parathyroid glands are removed or damaged during surgery. This can occur during surgery on the thyroid gland to treat hyperthyroidism or a thyroid tumor or during surgery on the parathyroid glands themselves to treat an overproduction of parathyroid hormone (hyperparathyroidism). The acquired hypoparathyroidism is most often temporary. Acquired hypoparathyroidism is less common than it once was because surgeons have recognized the importance of preserving the parathyroid glands during surgery and because nonsurgical treatments for hyperthyroidism have become more common.