Hyperparathyroidism refers to a serum Parathyroid Hormone (PTH) level above the normal range. PTH secretion is regulated by the action of serum ionized calcium on the Calcium Sensing Receptor (CASR) in parathyroid chief cells. Physiologically, calcium level is maintained within normal limits mainly due to this calcium sensing mechanism. Hyperparathyroidism may be classified into three major subtypes based on pathophysiology; primary, secondary and tertiary hyperparathyroidism.
Normal parathyroid glands as seen during a thyroidectomy. The large arrow points to the superior parathyroid. The thinner arrow points to the inferior parathyroid. The forceps points toward the recurrent laryngeal nerve. The patient’s head is toward the right.