Articles on Thyroid Disease
Hyperparathyroidism
Primary hyperparathyrodism is a disorder of the parathyroid glands. Most people with this disorder have one or more enlarged, overactive parathyroid glands that secrete too much parathyroid hormone. In secondary hyperparathyroidism, a problem such as kidney failure makes the body resistant to the action of parathyroid hormone. This article focuses on primary hyperparathyrodism.
WHAT ARE THE PARATHYROID GLANDS?
The parathyroid glands are four pea-sized glands located on the thyroid gland in the neck. Occasionally, a person is born with one or more of the parathyroid glands embedded in the thyroid, the thymus, or elsewhere in the chest. In most such cases, however, the glands function normally.
Though their names are similar, the thyroid and parathyroid glands are entirely separate glands, each producing distinct hormones with specific functions.
The parathyroid glands secrete parathyroid hormone (PTH), a substance that helps maintain the correct balance of calcium and phosphorus in the body.
PTH regulates release of the calcium from bone, absorption of calcium in the intestine, and excretion of calcium in the urine.
When the amount of calcium in the blood falls too low, the parathyroid glands secrete just enough PTH to restore the balance.
WHAT IS HYPERPARATHYROIDISM?
If the glands secrete too much hormone, as in hyperparathyroidism, the balance is disrupted: blood calcium rises. This condition of excessive calcium in the blood, called hypercalcemia, is what usually signals the doctor that something may be wrong with the parathyroid glands. In 85 percent of people with this disorder, a benign tumour (adenoma) has formed on one of the parathyroid glands, causing it to become overactive. In most other cases, the excess hormone comes from two or more enlarged parathyroid glands, a condition called hyperplasia. Very rarely, hyperparathyroidism is cased by cancer of a parathyroid gland.
This excess PTH triggers the release of too much calcium 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 acts to lower blood phosphorus levels by increasing excretion of phosphorus in the urine.
WHY ARE CALCIUM AND PHOSPHORUS SO IMPORTANT?
Calcium is essential for good health. It plays an important role in bone and tooth development and in maintaining bone strength. It is also important in nerve transmission and muscle contraction. Phosphorus is found in every body tissue. Combined with calcium, it gives strength and rigidity to your bones and teeth.
WHAT CAUSES HYPERPARATHYROIDISM?
In most cases doctors don’t know the cause. The vast majority of cases occur in people with no family history of the disorder. Only about 3 to 5 percent of cases can be linked to an inherited problem.
Familial endocrine neoplasia type I is one rare inherited syndrome that affects the parathyroids as well as the pancreas and the pituitary gland. Another rare genetic disorder, familial hypocalciuric hypercalcemia, is sometimes confused with typical hyperparathyroidism.
HOW COMMON IS HYPERPARATHYROIDISM?
In the U.S., about 100,000 people develop the disorder each year. Women outnumber men by 2 to 1, and risk incrases with age. In women, 60 years and older, 2 out of 1,000 will get hyperparathyroidism.
WHAT ARE THE SYMPTOMS OF HYPERPARATHYROIDISM?
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, though symptom free, have mild forms of the disorder.
When symptoms do appear, they are often mild and non-specific, such as a feeling of weakness and fatigue, depression or aches and pains.
With more severe disease, a person may have 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 phosphorus excretion in the urine may cause kidney stones. Patients with hyperparathyroidism may be more likely to develop peptic ulcers, high blood pressure, and pancreatitis.
HOW IS HYPERPARATHYROIDISM DIAGNOSED?
Hyperparathyroidism is diagnosed when tests show that blood levels of calcium as well as 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 diagnsosis 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 may be done to assess bone loss and the risk of fractures.
Abdominal radiographs may reveal the presence of kidney stones and a 24 hour urine collection may provide information on kidney damage and the risk of stone formation.
HOW IS HYPERPARATHYROIDISM TREATED?
Surgery to remove the enlarged gland (or glands) is the only treatment for this disorder and cures it in 95 percent of cases.
However, some patients who have mild disease may not need immediate treatment, according to a panel of experts convened by the National Institutes of Health in 1990. Patients who are symptom-free, whose blood calcium is only slightly elevated and whose kidneys and bones are normal, may wish to talk to their doctor about long-term monitoring.
In the panel’s recommendation, monitoring would consist of clinical evaluation of calcium levels and kidney function every 6 months, annual abdominal x-ray, and bone mass measurement after 1 to 2 yars. If the disease shows no signs of worsening after 1 to 3 years, the intervals between exams may be lengthened.
If the patient and doctor choose long-term follow-up, the patient should try to drink lots of water, get plenty of exercise, and avoid certain diuretics, such as thiazides. Immobilization and gastronintestinal illness with vomiting or diarrhea can cause calcium levels to rise, and if these conditions develop, patients with hyperparathyroidism should seek medical assistance.
ARE THERE ANY COMPLICATIONS ASSOCIATED WITH PARATHYROID SURGERY?
Surgery for hyperparathyroidism is highly successful with a low complication rate when performed by surgeons experienced with this condition. About 1 percent of patients undergoing surgery have damage to the nerves controlling the vocal cords which can affect speech.
One to five percent of patients develop chronic low calcium levels, which may require treatment with calcium and/or vitamin D. The complication rate is slightly higher for hyperplasia than it is for adenoma since more extensive surgery is needed.
ARE PARATHYROID IMAGING TESTS NEEDED BEFORE SURGERY?
The National Institutes of Health panel recommended against the use of expensive imaging tests to locate benign tumours before initial surgery.
Research shows that such tests do not improve the success rate of surgery, which is about 95 percent when performed by experienced surgeons. Localization tests are useful in patients having second operations for recurrent or persistent hyperparathyroidism.
WHICH DOCTORS SPECIALIZE IN TREATING HYPERPARATHYROIDISM?
Endocrinologists (doctors who specialize in hormonal problems), nephrologists (doctors who specialize in kidney and mineral disorders), and surgeons who are experienced in endocrine surgery.
Additional information may be obtained from:
Bone Health and Osteoporosis Foundation
Republished for the Web and Thyrobulletin with permission of the National Institutes of Diabetes, Digestion and Kidney, National Institutes of Health.
Reprinted from Thyrobulletin, Vol. 19, No. 4, 1999.
Reviewed 2000
