THE PARATHYROID GLANDS

The parathyroids are endocrine glands, usually four in number, located at the front of the neck close to the tips of the thyroid lobes. They may actually be embedded in the thyroid tissue. Thus, during surgical extirpation of the thyroid gland, they may be accidentally removed. The parathyroid glands produce parathyroid hormone which regulates the levels of calcium, phosphorus, and magnesium, maintaining appropriate balance of these substances, and is essential for normal bone mineralization. Excessive amounts of parathyroid hormone result in increased blood calcium level by reabsorbing it from the bone. There is also an associated increased reabsorption of calcium in the kidneys and intestines.

The disorders of the parathyroid glands are characterized either by inadequate production of the parathyroid hormone, hypoparathyroidism, or by excessive production of it, hyperparathyroidism; the latter may be associated with tumor formation.

Hypoparathyroidism

Hypoparathyroidism is a disease characterized by low blood calcium levels due to diminished or absent parathyroid hormone production or to the absence of parathyroid glands (e.g., incidental surgical extirpation). When the calcium level drops a constellation of serious, even life threatening, symptoms develops. Hypoparathyroidism may be caused by a genetic disorder interfering with the ability of the gland to produce the hormone, a congenital absence of the parathyroid glands, an accidental removal or injury to the glands during surgery to remove the thyroid gland, or other neck surgery, massive radiation to the thyroid gland, or magnesium deficiency. The incidence of hypoparathyroidism is 4 out of 100,000 people.

Symptoms:

The most common symptoms are tingling around the lips and muscle cramps particularly in hands. Generalized muscle cramps may also occur leading to muscle spasms (tetany). The latter may cause laryngeal spasms with breathing difficulties. Brittle nails, dry hair and cataract formation are not uncommon.

Signs and test findings:

• low serum calcium level
• elevated serum phosphorus
• decreased serum parathyroid hormone level
• cardiac arrhythmias on ECG

Treatment:

Restoration of calcium and associated minerals balance in the body. This can be accomplished by life long therapy with calcium and appropriate vitamin D supplements.

Hyperparathyroidism

This abnormality is associated with an excessive production of parathyroid hormone by the parathyroid glands. Hyperparathyroidism can be caused by idiopathic enlargement of one or more of the glands, by parathyroid adenoma or in response to an abnormally low calcium level in the blood.

With overproduction of the parathyroid hormone, the calcium level in the blood becomes elevated by removing calcium from the bones and increasing calcium absorption from the gastrointestinal (GI) tract. The kidneys attempt to compensate for the increased blood calcium level by secreting excess calcium in the urine, which can result in the formation of kidney stones. The effects of increased parathyroid hormone levels are seen not only in the kidneys but also in the skeleton, stomach and intestines, the nervous system, and the muscles.

Symptoms:

fatigue, back pain, joint pain, fractures of long bones, decreased height, increased urine output, increased thirst, epigastric pain, loss of appetite, nausea, muscular weakness, depression, personality changes, stupor and possibly coma, itching of the skin, cataracts, clay colored stools, nail abnormalities, diarrhea, or bone pain and tenderness

Signs and test findings:

• Serum calcium is increased.
• Serum phosphorus is decreased.
• Serum alkaline phosphatase may be increased.
• A radioimmunoassay of parathyroid hormone shows elevated levels.
• Bone X-ray shows bone reabsorption or fractures.
• Kidneys or ureters may show calcification or obstruction.
• ECG may show abnormalities associated with hypercalcemia.
• A biopsy of the parathyroid gland may show a tumor or hyperplasia.

In primary hyperparathyroidism an increased secretion of parathyroid hormone occurs because of enlargement of one or more of the glands secondary to the presence of a tumor, a parathyroid adenoma, resulting in high plasma calcium levels.

In secondary hyperparathyroidism there is an increased activity of the parathyroid gland with excessive production of parathyroid hormone in response to an abnormality outside the parathyroid gland producing low plasma calcium levels. An increase in the cells of the parathyroid glands, called hyperplasia, occurs which is responsible for the elevation of parathyroid hormone levels. The causes of this disorder include rickets, vitamin D deficiency, or chronic renal failure. Secondary hyperparathyroidism is the most common cause of hyperparathyroidism in children.

The incidence of mild secondary hyperparathyroidism is 1 out of 1000 people. The incidence of severe hyperparathyroidism is 1 out of 10,000 people.

Prevention: Early detection of rickets or vitamin D deficiency may prevent secondary hyperparathyroidism.

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