Hyperparathyroidism refers to excessive production of parathyroid hormone. The parathyroid glands are located at the front and base of the neck at the 4 corners of the thyroid gland. The glands produce parathyroid hormone (PTH), which regulates calcium and phosphorus balance in the body.

Primary Hyperparathyroidism
In primary hyperparathyroidism, increased secretion of parathyroid hormone occurs because one or more of the glands have become enlarged. The effects of increased calcium are seen in several body systems including the skeletal, gastrointestinal, renal (kidney), muscular, and central nervous system. The disease is most common in people over 60, but can also be seen in younger adults. Women are more likely to be affected than men. Primary hyperparathyroidism (PHPT) is characterized by excessive parathyroid hormone secretion in respect to calcium homeostasis needs, due to parathyroid adenoma (80% of cases), hyperplasia (15-20%), or carcinoma (1-2%).
     Hyperparathyroidism symptoms and signs include hypercalcemia which may cause fatigue, anorexia, thirst, and polyuria. Vague neurological and psychiatric symptoms, such as weakness, anxiety, depression, paresthesias, and muscular cramps may ameliorate after parathyroidectomy. Recent reports indicate increased cardiovascular mortality in primary hyperparathyroidism patients.

Diagnosis of Hyperparathyroidism
Diagnosing hyperparathyroidism is based on the detection of hypercalcemia, together with inappropriately high serum parathyroid hormone levels. Preoperative localization of the diseased glands is mandatory in persistent or recurrent primary hyperparathyroidism, when minimally invasive surgery is planned. High resolution ultrasonography and SPECT double-phase 99m Tc-sestamibi scintigraphy are the most commonly employed techniques. Intraoperatory parathyroid hormone assay may confirm successful surgery when serum concentrations decrease more than 50%.

Hyperparathyroidism treatment
Surgical therapy is indicated in patients with renal or skeletal complications, such as in those with previous parathyrotoxic crisis. Many surgeons in recent years adopted minimally invasive parathyroidectomy. Medical treatment is an option for patients unwilling or unfitted for surgery because of severe concomitant diseases. Employed therapy includes estrogens, SERMs, bisphosphonates and calcimimetics.

Secondary Hyperparathyroidism
Secondary hyperparathyroidism is characterized by parathyroid gland hyperplasia resulting from end-organ resistance to parathyroid hormone. The excess secretion of PTH depresses calcium levels. The most important cause of secondary hyperparathyroidism is chronic renal insufficiency.
     Secondary hyperparathyroidism can be due to disorders of vitamin D metabolism, disorders of phosphate metabolism, and calcium deficiency (either lack of calcium in the diet or excessive calcium loss in the urine).