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Primary hyperparathyroidism is a disorder of the parathyroid glands, also called parathyroids. "Primary" means this disorder originates in the parathyroids: One or more enlarged, overactive parathyroid glands secretes too much parathyroid hormone (PTH). In secondary hyperparathyroidism, a problem such as kidney failure causes the parathyroids to be overactive. This publication focuses on primary hyperparathyroidism.
PTH is the most important regulator of calcium level in the blood. It also regulates the release of calcium from bone, absorption of calcium in the intestine, and excretion of calcium in the urine. When the blood calcium level falls too low, the parathyroid glands secrete just enough PTH to restore the blood calcium level. If the parathyroid glands secrete too much PTH, excess calcium will be released into the bloodstream. The bones may lose calcium, and too much calcium may be absorbed from food. The levels of calcium may increase in the urine, causing kidney stones. PTH also lowers blood phosphorous levels by increasing excretion of phosphorus in the urine.
In the United States, about 100,000 people develop the disorder each year. Women outnumber men two to one, and risk increases with age. In women 60 years and older, two out of 1,000 will develop hyperparathyroidism each year.
A person with hyperparathyroidism may have severe symptoms, subtle ones, or none at all. Increasingly, routine blood tests that screen for a wide range of conditions, including high calcium levels, are alerting doctors to people who have mild forms of the disorder even though they are symptom-free.
When symptoms do appear, they are often mild and nonspecific, such as a feeling of weakness and fatigue, depression, or aches and pains. With more severe disease, a person may have a loss of appetite, nausea, vomiting, constipation, confusion or impaired thinking and memory, and increased thirst and urination. Patients may have thinning of the bones without symptoms, but with risk of fractures. Increased calcium and phosphorous excretion in the urine may cause kidney stones.
Hyperparathyroidism is diagnosed when tests show that blood levels of calcium and parathyroid hormone are too high. Other diseases can cause high blood calcium levels, but only in hyperparathyroidism is the elevated calcium the result of too much parathyroid hormone. A blood test that accurately measures the amount of parathyroid hormone has simplified the diagnosis of hyperparathyroidism.
Once the diagnosis is established, other tests may be done to assess complications. Because high PTH levels can cause bones to weaken from calcium loss, a measurement of bone density can help assess bone loss and the risk of fractures. Abdominal images may reveal the presence of kidney stones and a 24-hour urine collection may provide information on kidney damage, the risk of stone formation, and the risk of familial hypocalciuric hypercalcaemia.
In 85 percent of people with primary hyperparathyroidism, a benign tumor called an adenoma has formed on one of the parathyroid glands, causing it to become overactive. Benign tumors are noncancerous. In most other cases, the excess hormone comes from two or more enlarged parathyroid glands, a condition called hyperplasia. Very rarely, hyperparathyroidism is caused by cancer of a parathyroid gland.
The vast majority of cases occur in people with no family history of the disorder. Only about 5 percent of cases can be linked to an inherited problem. Familial multiple endocrine neoplasia type 1 is a rare, inherited syndrome that affects the parathyroids as well as the pancreas and the pituitary gland. Another rare genetic disorder, familial hypocalciuric hypercalcaemia, is sometimes confused with typical hyperparathyroidism. Each accounts for about 2 percent of primary hyperparathyroidism cases.