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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.
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- El-Hajj Fuleihan G. Diagnosis and differential diagnosis of primary hyperparathyroidism. http://www.uptodate.com/home/index.html. Accessed March 1, 2011.
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- El-Hajj Fuleihan G. Pathogenesis and etiology of primary hyperthyroidism. http://www.uptodate.com/home/index.html. Accessed March 1, 2011.
- Fitzgerald PA. Hyperparathyroidism. In: McPhee SJ, et al. Current Medical Diagnosis and Treatment. 50th ed. New York, N.Y.: The McGraw-Hill Companies; 2011. http://www.accessmedicine.com/content.aspx?aID=14894&searchStr=hyperparathyroidism. Accessed March 1, 2011.
- Silverstein SJ. Management of primary hyperthyroidism. http://www.uptodate.com/home/index.html. Accessed March 1, 2011.
- Estrogen and progestin combination (Ovarian hormone therapy) (Oral route). Micromedex Healthcare Series. http://www.micromedex.com. Accessed March 3, 2011.
- Bisphosphonates. Micromedex Healthcare Series. http://www.micromedex.com. Accessed March 3, 2011.
- Dietary supplement fact sheet: Vitamin D. Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/VitaminD-QuickFacts. Accessed March 3, 2011.
- Dietary supplement fact sheet: Calcium. Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/Calcium-QuickFacts. Accessed March 3, 2011.
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