Anatomy and Physiology
There are visually four parathyroid glands located just behind the thyroid gland in the neck. Each gland is normally less than ¼ inch long and weighs 25 – 35 mg. The glands produce parathyroid hormone (PTH) which regulates the calcium level in the body.
Primary hyperparathyroidism is generally caused (80%) by a benign tumor involving one of the four parathyroid glands of the neck. Occasionally, it is caused by a benign tumor of two glands or abnormal growth of all four glands. Parathyroid carcinoma is an extremely rare cause of hyperparathyroidism. The benign tumor produces too much parathyroid hormone (PTH), resulting in an elevated calcium level. The degree of the elevation can be mild to severe. These symptoms can include fatigue, muscle weakness, kidney stones, decreased memory, psychiatric problems, body aches, loss of bone strength and broken bones. Often these symptoms can be quite subtle.However, symptoms do not always correlate with the level of the calcium in the blood.
Normally PTH is responsible for raising calcium to normal levels in the blood. When calcium is normal, the PTH should decrease. In Primary Hyperparathyroidism, the gland continues to release PTH despite high or normal calcium levels.
Secondary and Tertiary Hyperparathyroidism
Secondary hyperparathyroidism occurs when external factors stimulate the parathyroid gland to secrete parathyroid hormone to the point where it develops hyperplastic overgrowth. This is most commonly seen in chronic renal failure. Tertiary hyperparathyroidism occurs after secondary hyperparathyroidism when the external factor is corrected but the parathyroid glands remain hyperplastic.
The only treatment of an overgrown parathyroid gland is surgical removal. The operation requires a small incision over the base of the neck, and may require an overnight stay in the hospital. Frequently, the parathyroid adenoma can be identified before surgery with either an ultrasound or a nuclear medicine scan (sestamibi-scan). This can aid the surgeons to focus their exploration for the abnormal gland. Recent advances in monitoring the PTH level during surgery allow these procedures to be done with local anesthesia and some mild sedation. This procedure is known as Minimally Invasive Parathyroid Surgery (MIP) with intraoperative PTH monitoring. These new techniques enable the surgeon to focus on the one abnormal gland, to avoid exploration of all the glands. Usually these patients can be discharged the afternoon of their operation.
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