Hyperparathyroidism

Hyperparathyroidism 

Definition

Parathyroid glands are four pea-sized glands located just behind the thyroid gland in the front of the neck. The function of parathyroid glands is to produce a hormone called parathyroid hormone (parathormone), which helps regulate calcium and phosphate in the body. Hyperparathyroidism is the overproduction of this hormone.

Description

Thyroid glands and parathyroid glands, despite their similar name and proximity, are entirely separate, and each produces hormones with different functions. Hyperparathyroidism may be primary or secondary. It most often occurs in those over age 30, and most commonly in patients 50 to 60 years old. It rarely occurs in children or the elderly. Women are affected by the disease up to three times more often than men. It is estimated that 28 of every 100,000 people in the United States will develop hyperparathyroidism each year.

Normally, parathyroid glands produce the parathormone as calcium levels drop and lower to meet the demands of a growing skeleton, pregnancy, or lactation. However, when one or more parathyroid glands malfunctions, it can lead to overproduction of the hormone and elevated calcium level in the blood. Therefore, a common result of hyperparathyroidism is hypercalcemia, or an abnormally high level of calcium in the blood. Primary hyperparathyroidism occurs as a malfunction of one of the glands, usually as a result of a benign tumor, called adenoma. Secondary hyperparathyroidism occurs as the result of a metabolic abnormality outside the parathyroid glands, which causes a resistance to the function of the parathyroid hormones. Primary hyperparathyroidism is one of the most common endocrine disorders, led only by diabetes and hyperthyroidism.

Causes and symptoms

Often, there are no obvious symptoms or suspicion of hyperparathyroidism, and it is first diagnosed when a patient is discovered to be hypercalcemic during a routine blood chemistry profile. Patients may believe they have felt fine, but realize improvements in sleep, irritability, and memory following treatment. When symptoms are present, they may include development of gastric ulcers or pancreatitis because high calcium levels can cause inflammation and pain in the linings of the stomach and pancreas.

Most of the symptoms of hyperparathyroidism are those present as a result of hypercalcemia, such as kidney stones, osteoporosis, or bone degradation resulting from the bones giving up calcium. Muscle weakness, central nervous system disturbances such as depression, psychomotor and personality disturbances, and rarely, even coma can occur. Patients may also experience heartburn, nausea, constipation, or abdominal pain. In secondary hyperparathyroidism, patients may show signs of calcium imbalance such as deformities of the long bones. Symptoms of the underlying disease may also be present.

Most commonly, hyperparathyroidism occurs as the result of a single adenoma, or benign tumor, in one of the parathyroid glands. About 90% of all cases of hyperparathyroidism are caused by an adenoma. The tumors are seldom cancerous. They will grow to a much larger size than the parathyroid glands, often to the size of a walnut. Genetic disorders or multiple endocrine tumors can also cause a parathyroid gland to enlarge and oversecrete hormone. In 10% or fewer of patients with primary hyperparathyroidism, there is enlargement of all four parathyroid glands. This condition is called parathyroid hyperplasia.

Diagnosis

Diagnosis of hyperparathyroidism is most often made when a blood test (radioimmunoassay) reveals high levels of parathyroid hormone and calcium. A blood test that specifically measures the amount of parathyroid hormone has made diagnosis simpler. X-ray examinations may be performed to look for areas of diffuse bone demineralization, bone cysts, outer bone absorption and erosion of the long bones of the fingers and toes. Hypercalcemia is mild or intermittent in some patients, but is an excellent indicator of primary hyperparathyroidism. Dual energy x-ray absorptiometry (DEXA or DXA), a tool used to diagnose and measure osteoporosis, is used to show reduction in bone mass for primary hyperparathryroidism patients. Once a diagnosis of hyperparathyroidism is reached, the physician will probably order further tests to evaluate complications. For example, abdominal radiographs might reveal kidney stones.

For secondary hyperparathyroidism, normal or slightly decreased calcium levels in the blood and variable phosphorous levels may be visible. Patient history of familial kidney disease or convulsive disorders may suggest a diagnosis of secondary hyperparathyroidism. Other tests may reveal a disease or disorder, which is causing the secondary hyperparathyroidism.

Treatment

Hyperparathyroidism cases will usually be referred to an endocrinologist, a physician specializing in hormonal problems, or a nephrologist, who specializes in kidney and mineral disorders.

Patients with mild cases of hyperparathyroidism may not need immediate treatment if they have only slight elevations in blood calcium level and normal kidneys and bones. These patients should be regularly checked, probably as often as every six months, by physical examination and measurement of kidney function and calcium levels. A bone densitometry measurement should be performed every one or two years. After several years with no worsened symptoms, the length of time between exams may be increased.

Patients with more advanced hyperparathyroidism will usually have all or half of the affected parathyroid gland or glands surgically removed. This surgery is relatively safe and effective. The primary risks are those associated with general anesthesia. There are some instances when the surgery can be performed with the patient under regional, or cervical block, anesthesia. Often studies such as ultrasonography prior to surgery help pinpoint the affected areas.

Alternative treatment

Forcing fluids and reducing intake of calcium-rich foods can help decrease calcium levels prior to surgery or if surgery is not necessary.

Prognosis

Removal of the enlarged parathyroid gland or glands cures the disease 95% of the time and relief of bone pain may occur in as few as three days. In up to 5% of patients undergoing surgery, chronically low calcium levels may result, and these patients will require calcium supplement or vitamin D treatment. Damage to the kidneys as a result of hyperparathyroidism is often irreversible. Prognosis is generally good, however complications of hyperparathyroidism such as osteoporosis, bone fractures, kidney stones, peptic ulcers, pancreatitis, and nervous system difficulties may worsen prognosis.

Key terms

Demineralization — A loss or decrease of minerals in the bones.

Endocrine — Glands and hormone secretions in the body circulation.

Phosphate — An organic compound necessary for mineralization of bone and other key cellular processes.

Prevention

Secondary hyperparathyroidism may be prevented by early treatment of the disease causing it. Early recognition and treatment of hyperparathyroidism may prevent hypercalcemia. Since the cause of primary hyperparathyroidism, or the adenoma which causes parathyroid enlargement, is largely unknown, there are not prescribed prevention methods.

Resources

Organizations

Osteoporosis and Related Bone Diseases—National Resource Center. 1150 17th S. NW, Ste. 500, Washington, DC 20036. (800) 624-2663.

Paget Foundation. 200 Varick St., Ste. 1004. New York, NY 10014-4810. (800) 23-PAGET.

Other

"Endocrine Disorder and Endocrine Surgery." Endocrine Web Page. http://www.endocrineweb.com.

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hyperparathyroidism /hy·per·para·thy·roid·ism/ (-par?ah-thi´roid-izm) excessive activity of the parathyroid glands. Primary h. is associated with neoplasia or hyperplasia; the excess of parathyroid hormone leads to alteration in function of bone cells, renal tubules, and gastrointestinal mucosa. Secondary h. occurs when the serum calcium tends to fall below normal, as in chronic renal disease, etc. Tertiary h. refers to that due to a parathyroid adenoma arising from secondary hyperplasia caused by chronic renal failure.

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hy·per·par·a·thy·roid·ism (hpr-pr-throi-dzm)

n.

An increase in the secretory activity of the parathyroid glands, causing generalized osteitis fibrosa cystica, elevated serum calcium, decreased serum phosphorus, and increased excretion of both calcium and phosphorus.

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hyperparathyroidism (hī´pur-per´ethī´roidizm),

n (generalized osteitis fibrosa cystica, von Recklinghausen's disease of bone), 1. an increased parathyroid function resulting from primary hyperplasia, a functioning neoplasm of the parathyroid glands, or secondary hyperplasia related most often to chronic renal insufficiency. Manifestations are related to abnormalities of the bones, kidneys, and blood vessels. Skeletal changes are referred to as
generalized osteitis fibrosa cystica or von Recklinghausen's disease. Brown tumors, which are essentially giant cell tumors, may develop generally, as well as in the jaws. Kidney changes include renal stones and nephrocalcinosis. Calcification of muscles in arteries occurs. Renal rickets is associated with secondary hyperparathyroidism in children with chronic renal disease. Laboratory findings include a high serum calcium level, low phosphorus level, and a normal or high alkaline phosphatase level. Renal impairment, such as occurs in secondary hyperparathyroidism, tends to nullify hypercalcemia because of an increased loss of calcium in the urine.
n 2. an abnormal increase in activity of the parathyroid glands, causing loss of calcium from the bones and resulting in tenderness in bones, spontaneous fractures, muscular weakness, and osteitis fibrosa.
3. excessive production of parathormone by the parathyroid gland (as in parathyroid hyperplasia and/or adenoma), resulting in increased renal excretion of phosphorus by lowering of the renal threshold for this substance. The pathologic changes produced are osteoporotic or osteodystrophic in nature as a consequence of withdrawal of calcium and phosphorus from osseous tissues.

hyperparathyroidism, brown node of,

n See node, brown, of hyperparathyroidism.

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hyperparathyroidism

abnormally increased activity of the parathyroid gland. Primary hyperparathyroidism is associated with either neoplasia (chiefly adenomas) or hyperplasia.

An excess of parathyroid hormone leads to resorption of bone, increased resorption of calcium and increased excretion of phosphorus by the renal tubules, and increased absorption of calcium by the gastrointestinal mucosa. It may result in kidney stones and calcium deposits in the renal tubules; in generalized decalcification of bone (osteoporosis), resulting in pain and tenderness of bones and spontaneous fractures; and in hypercalcemia, leading to muscular weakness and gastrointestinal signs.

Secondary hyperparathyroidism develops as a compensatory mechanism when the serum calcium level is persistently below normal or serum phosphorus is elevated, as in chronic renal disease, insufficient calcium or excessive phosphorus in the diet, vitamin D deficiency, low-level soluble oxalate intoxication in horses, and intestinal malabsorption syndromes causing insufficient absorption of calcium and vitamin D.

See also pseudohyperparathyroidism.

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nutritional secondary hyperparathyroidism

a disease of horses, pigs, goats, dogs, cats, and rarely cattle. It is most commonly caused by an excessive dietary intake of phosphorus in the absence of adequate calcium, which in horses is likely to be the result of a diet mainly of grain and in dogs and cats one predominantly of meat, but it may also result from other dietary causes of secondary hyperparathyroidism. In most species there is swelling of the maxillae and mandibles which is most marked in horses, loosening of teeth, shifting lameness, and particularly in dogs and cats, weight-bearing skeletal deformities (angel wings) and folding or compression fractures. Called also miller's disease, bran disease, bighead, Siamese cat disease, paper-bone disease.

renal secondary hyperparathyroidism

caused by chronic renal dysfunction, mostly in dogs, sometimes in cats, in which there is a secondary hyperparathyroidism, caused by the retention of phosphates. There is demineralization of bones, particularly the maxillae and mandibles, with loosening of teeth and facial swelling. Clinical signs are often overshadowed by the effects of the renal failure. Called also rubber jaw, renal rickets, renal osteitis fibrosa.