What are parathyroid diseases?
Hyperparathyroidism refers to the production of too much PTH by the parathyroid glands. It is classified as primary, secondary, or tertiary:
- Primary hyperparathyroidism is a condition in which there is a problem with the parathyroid glands themselves. A person with primary hyperparathyroidism has too much PTH and too much calcium in the blood. Since calcium is pulled from the bones, the bones weaken over time, increasing the risk of fractures.
About 85% of the time, primary hyperparathyroidism is due to an adenoma (benign tumor) in a single parathyroid gland. Less commonly, it is due to multiple adenomas or to hyperplasia, an increase in the size and activity of all of the parathyroid glands. Very rarely (about 1% of the time), it is due to parathyroid cancer, as tumors can produce excess PTH.
About 100,000 people in the United States develop primary hyperparathyroidism each year. It is seen most frequently in people over 50 years old and occurs more often in women than men. In rare cases, it is linked to an inherited endocrine syndrome (MEN 1 or MEN 2).
- Secondary hyperparathyroidism is usually due to insufficient amounts of calcium in blood, which may occur in the following conditions:
- Kidney failure; this can cause increased phosphate and lowered levels of the active form of vitamin D, which lead to increased PTH production.
- Vitamin D deficiency
- Calcium malabsorption caused by gastrointestinal disorders, for example
- Tertiary hyperparathyroidism occurs rarely when the underlying cause of secondary hyperparathyroidism is resolved, but the parathyroid glands continue to produce excess PTH.
Hypoparathyroidism refers to a deficiency of PTH and can be persistent or temporary. This condition does not occur as frequently as hyperparathyroidism. Regardless of the cause, those affected by hypoparathyroidism have decreased blood calcium that may range from mild to severe.
- The most common cause is the removal of the parathyroid glands during surgery. This might occur when a person is being treated for thyroid cancer or cancer of the throat and the thyroid gland is removed. Surgery is also done to treat hyperparathyroidism that is due to hyperplasia. Three or 3.5 of the glands are typically removed and the remaining gland or gland portion may be autotransplanted (moved) to the person's neck or forearm. If the remaining gland does not function adequately, hypoparathyroidism may result.
- Sometimes, it is due to damage to all of the glands by an autoimmune disorder.
- Rarely, it is due to a failure of the glands to develop properly.
- Temporary hypoparathyroidism may be seen after treatment for hyperparathyroidism. This occurs as "hungry bone syndrome" when PTH decreases suddenly and the bones take calcium from the blood. It also can be seen after birth in newborns whose mothers have hyperparathyroidism.