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Causes
By Mayo Clinic staff
Hyperparathyroidism is caused by factors that increase the production of parathyroid hormone. The parathyroid glands maintain proper levels of both calcium and phosphorus in your body by turning the secretion of parathyroid hormone (PTH) off or on, much as a thermostat controls a heating system to maintain a constant air temperature. Vitamin D also is involved in regulating the amount of calcium in your blood.
Normally, this balancing act works well. When calcium levels in your blood fall too low, your parathyroid glands secrete enough PTH to restore the balance. PTH raises calcium levels by releasing calcium from your bones and increasing the amount of calcium absorbed from your small intestine. When blood calcium levels are too high, the parathyroid glands produce less PTH. But sometimes one or more of these glands produce too much hormone, leading to abnormally high levels of calcium (hypercalcemia) and low levels of phosphorus in your blood.
The mineral calcium is best known for its role in keeping your teeth and bones healthy. But calcium has other functions. It aids in the transmission of signals in nerve cells, and it's involved in muscle contraction. Phosphorus, another mineral, works in conjunction with calcium in these areas.
The disorder can generally be divided into two types based on the cause. Hyperparathyroidism may occur because of a problem with the parathyroid glands themselves (primary hyperparathyroidism) or because of another disease that affects the glands' function (secondary hyperparathyroidism).
Primary hyperparathyroidism
Primary hyperparathyroidism occurs because of some problem with one or more of the four parathyroid glands:
- A noncancerous growth (adenoma) on a gland is the most common cause.
- Enlargement (hyperplasia) of two or more parathyroid glands accounts for most other cases.
- A cancerous (malignant) tumor is a rare cause of primary hyperparathyroidism.
Primary hyperparathyroidism usually occurs randomly, but some people inherit a gene that causes the disorder.
Secondary hyperparathyroidism
Secondary hyperparathyroidism is the result of another condition that lowers calcium levels. Therefore, your parathyroid glands overwork to compensate for the loss of calcium. Factors that may contribute to secondary hyperparathyroidism include:
- Severe calcium deficiency. Your body may not get enough calcium from your diet, often because your digestive system doesn't absorb the calcium you consume.
- Severe vitamin D deficiency. Vitamin D helps maintain appropriate levels of calcium in the blood, and it helps your digestive system absorb calcium from your food. Your body produces vitamin D when your skin is exposed to sunlight, and you consume some vitamin D in food. If you don't get enough vitamin D, then calcium levels may drop.
- Chronic kidney failure. Your kidneys convert vitamin D into a form that your body can use. If your kidneys function poorly, useable vitamin D may decline and calcium levels drop. Chronic kidney failure is the most common cause of secondary hyperparathyroidism.
- Rodgers SE, et al. Primary hyperparathyroidism. Current Opinion in Oncology 2008;20:52.
- The American Association of Clinical Endocrinologists and the American Association of Endocrine Surgeons position statement on the diagnosis and management of primary hyperparathyroidism. Endocrine Practice. 2005;11:49.
- Hyperparathyroidism. National Institute of Diabetes and Digestive and Kidney Diseases. http://www.endocrine.niddk.nih.gov/pubs/hyper/hyper.htm. Accessed March 23, 2009.
- El-Hajj Fuleihan G. Clinical manifestations of primary hyperparathyroidism. http://www.uptodate.com/home/index.html. Accessed March 23, 2009.
- Taniegra ED. Hyperparathyroidism. American Family Physician. 2004;69:333.
- Bringhurst FR. Hormones and disorders of mineral metabolism. In: Kronenberg, HM, et al., eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa.: Saunders Elsevier; 2008. http://www.mdconsult.com/das/book/body/127508547-4/0/1555/168.html#4-u1.0-B978-1-4160-2911-3..50029-7--p1224. Accessed March 23, 2009.
- Dietary supplement fact sheet: Vitamin D. National Institutes of Health Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/VitaminD_pf.asp. Accessed March 24, 2009.
- Dietary supplement fact sheet: Calcium. National Institutes of Health Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/Calcium_pf.asp. Accessed March 24, 2009.
- Phosphorus. Foods Standards Agency (UK). Accessed March 25, 2009.
- Wuthrich RP, et al. The role of calcimimetics in the treatment of hyperparathyroidism. European Journal of Clinical Investigation. 2007;37:915.
- Silverberg SJ, et al. Management of asymptomatic primary hyperparathyroidism. http://www.uptodate.com/home/index.html. Accessed March 23, 2009.
