Primary Hyperparathyroidism.

The 4 parathyroid glands derive from the third and fourth pharyngeal pouches and descend caudally to the anterior neck. Through the secretion of parathyroid hormone (PTH), the parathyroid glands are primarily responsible for maintaining extracellular calcium and phosphorus concentrations. Hypercalcemia may be distinguished in parathyroid-hypercalcemia and nonparathyroid hypercalcemia. The most common disorders include primary hyperparathyroidism (PHPT), malignancy, granulomatous diseases, and medications. PHPT is a disease characterized by excessive secretion of PTH. PHPT is most commonly due to a single benign parathyroid adenoma (80%) and with multiglandular disease seen in approximately 15-20% of patients. PHPT is due to multiglandular involvement consisting of either multiple adenomas or hyperplasia of all 4 glands (5-10%), and very rarely parathyroid carcinoma (<1%). In most patients the disease is sporadic, without a personal or family history of PHPT. The genetic syndromes associated with PHPT include multiple endocrine neoplasia type 1 (MEN1), MEN2A, and MEN4, hyperparathyroidism-jaw tumor syndrome, familial isolated PHPT, familial hypocalciuric hypercalcemia, and neonatal severe hyperparathyroidism. The asymptomatic clinical presentation is most common in countries where biochemical screening is routine. Conversely, target organ involvement at presentation dominates the clinical landscape of PHPT in other countries, such as China and India, where biochemical screening is not routine practice.