Most people have four pea-sized glands, called parathyroid glands, on the thyroid gland in the neck. Though their names are similar, the thyroid and parathyroid glands are completely different. The parathyroid glands make parathyroid hormone (PTH), which helps your body keep the right balance of calcium and phosphorous.

If your parathyroid glands make too much or too little hormone, it disrupts this balance. If they secrete extra PTH, you have hyperparathyroidism, and your blood calcium rises. In many cases, a benign tumor on a parathyroid gland makes it overactive. Or, the extra hormones can come from enlarged parathyroid glands. Very rarely, the cause is cancer.

If you do not have enough PTH, you have hypoparathyroidism. Your blood will have too little calcium and too much phosphorous. Causes include injury to the glands, endocrine disorders, or genetic conditions. Treatment is aimed at restoring the balance of calcium and phosphorous.

Idiopathic infantile hypercalcemia is a condition characterized by high levels of calcium in the blood (hypercalcemia). Two types of idiopathic infantile hypercalcemia have been identified and are distinguished by their genetic causes: infantile hypercalcemia 1 and infantile hypercalcemia 2. In infants with either type, hypercalcemia can cause vomiting, increased urine production (polyuria), dehydration, constipation, poor feeding, weight loss, and an inability to grow and gain weight as expected (failure to thrive). As they age, affected babies usually have delayed development of mental and movement abilities (psychomotor delay). Individuals with infantile hypercalcemia 1 or 2 may also have high levels of calcium in their urine (hypercalciuria) and deposits of calcium in their kidneys (nephrocalcinosis).

With treatment, the outward symptoms of hypercalcemia, such as vomiting, dehydration, failure to thrive, and psychomotor delay, usually improve in childhood. However, affected children still tend to have higher-than-normal amounts of calcium in their blood and urine and calcium deposits in their kidneys. By adulthood, long-term hypercalcemia and hypercalciuria can lead to the formation of kidney stones (nephrolithiasis) and may damage the kidneys and impair their function. Affected adults may also develop calcium deposits in the joints or in the clear outer covering of the eye (the cornea), and some have low bone mineral density (osteoporosis).

In rare cases, affected individuals do not have symptoms of hypercalcemia in infancy, and the condition begins in later childhood or adulthood. These individuals usually develop hypercalciuria, nephrocalcinosis, and nephrolithiasis, although the features may not cause any obvious health problems.

Although most signs and symptoms are similar between the two known types of idiopathic infantile hypercalcemia, individuals with infantile hypercalcemia 2 have low levels of a mineral called phosphate in the blood (hypophosphatemia), while phosphate levels are typically normal in people with infantile hypercalcemia 1.

Primary hyperparathyroidism is a disorder of the parathyroid glands, four pea-sized glands located on or near the thyroid gland in the neck. “Primary” means this disorder begins in the parathyroid glands, rather than resulting from another health problem such as kidney failure. In primary hyperparathyroidism, one or more of the parathyroid glands is overactive. As a result, the gland makes too much parathyroid hormone (PTH).

Too much PTH causes calcium levels in your blood to rise too high, which can lead to health problems such as bone thinning and kidney stones. Doctors usually catch primary hyperparathyroidism early through routine blood tests, before serious problems occur.

In the United States, about 100,000 people develop primary hyperparathyroidism each year. Primary hyperparathyroidism is one of the most common hormonal disorders.

The parathyroid glands’ only purpose is to make PTH, which helps maintain the right balance of calcium in your body. PTH raises blood calcium levels by

• causing bone, where most of your body’s calcium is stored, to release calcium into the blood
• helping your intestines absorb calcium from food
• helping your kidneys hold on to calcium and return it to your blood instead of flushing it out in urine

When the level of calcium in your blood falls too low, the parathyroid glands release just enough PTH to bring your blood calcium levels back to normal.

You need calcium for good health. This mineral helps build bones and teeth and keep them strong. Calcium also helps your heart, muscles, and nerves work normally.

Although their names are similar, the parathyroid glands and the thyroid gland are not related.

Hypoparathyroidism is is an endocrine disorder in which the parathyroid glands in the neck do not produce enough parathyroid hormone (PTH). Common signs and symptoms include abdominal pain, brittle nails, cataracts, dry hair and skin, muscle cramps, tetany, pain in the face, legs, and feet, seizures, tingling sensation, and weakened tooth enamel (in children). It may be caused by injury to the parathyroid glands (e.g., during surgery). Other causes, include low blood magnesium levels, a side effect of radioactive iodine treatment for hyperthyroidism, metabolic alkalosis, DiGeorge syndrome, and type I polyglandular autoimmune syndrome. The goal of treatment is to restore the calcium and mineral balance in the body.

KEY POINTS

• Parathyroid cancer is a rare disease in which malignant (cancer) cells form in the tissues of a parathyroid gland.
• Having certain inherited disorders can increase the risk of developing parathyroid cancer.
• Signs and symptoms of parathyroid cancer include weakness, feeling tired, and a lump in the neck.
• Tests that examine the neck and blood are used to detect (find) and diagnose parathyroid cancer.
• Certain factors affect prognosis (chance of recovery) and treatment options.

Parathyroid cancer is a rare disease in which malignant (cancer) cells form in the tissues of a parathyroid gland.

The parathyroid glands are four pea-sized organs found in the neck near the thyroid gland. The parathyroid glands make parathyroid hormone (PTH or parathormone). PTH helps the body use and store calcium to keep the calcium in the blood at normal levels.

Anatomy of the thyroid and parathyroid glands. The thyroid gland lies at the base of the throat near the trachea. It is shaped like a butterfly, with the right lobe and left lobe connected by a thin piece of tissue called the isthmus. The parathyroid glands are four pea-sized organs found in the neck near the thyroid. The thyroid and parathyroid glands make hormones.

A parathyroid gland may become overactive and make too much PTH, a condition called hyperparathyroidism. Hyperparathyroidism can occur when a benign tumor (noncancer), called an adenoma, forms on one of the parathyroid glands, and causes it to grow and become overactive. Sometimes hyperparathyroidism can be caused by parathyroid cancer, but this is very rare.

The extra PTH causes:

• The calcium stored in the bones to move into the blood.
• The intestines to absorb more calcium from the food we eat.

This condition is called hypercalcemia (too much calcium in the blood).

The hypercalcemia caused by hyperparathyroidism is more serious and life-threatening than parathyroid cancer itself and treating hypercalcemia is as important as treating the cancer.

Having certain inherited disorders can increase the risk of developing parathyroid cancer.

Anything that increases the chance of getting a disease is called a risk factor. Risk factors for parathyroid cancer include the following rare disorders that are inherited (passed down from parent to child):

• Familial isolated hyperparathyroidism (FIHP).
• Multiple endocrine neoplasia type 1 (MEN1) syndrome.

Treatment with radiation therapy may increase the risk of developing a parathyroid adenoma.

The parathyroid glands are tiny, round structures usually found embedded in the posterior surface of the thyroid gland (image). A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. The function of one type of parathyroid cells, the oxyphil cells, is not clear. The primary functional cells of the parathyroid glands are the chief cells. These epithelial cells produce and secrete the parathyroid hormone (PTH) , the major hormone involved in the regulation of blood calcium levels.

The parathyroid glands produce and secrete PTH, a peptide hormone, in response to low blood calcium levels (image). PTH secretion causes the release of calcium from the bones by stimulating osteoclasts, which secrete enzymes that degrade bone and release calcium into the interstitial fluid. PTH also inhibits osteoblasts, the cells involved in bone deposition, thereby sparing blood calcium. PTH causes increased reabsorption of calcium (and magnesium) in the kidney tubules from the urine filtrate. In addition, PTH initiates the production of the steroid hormone calcitriol (also known as 1,25-dihydroxyvitamin D), which is the active form of vitamin D₃, in the kidneys. Calcitriol then stimulates increased absorption of dietary calcium by the intestines. A negative feedback loop regulates the levels of PTH, with rising blood calcium levels inhibiting further release of PTH.

Abnormally high activity of the parathyroid gland can cause hyperparathyroidism , a disorder caused by an overproduction of PTH that results in excessive calcium reabsorption from bone. Hyperparathyroidism can significantly decrease bone density, leading to spontaneous fractures or deformities. As blood calcium levels rise, cell membrane permeability to sodium is decreased, and the responsiveness of the nervous system is reduced. At the same time, calcium deposits may collect in the body’s tissues and organs, impairing their functioning.

In contrast, abnormally low blood calcium levels may be caused by parathyroid hormone deficiency, called hypoparathyroidism , which may develop following injury or surgery involving the thyroid gland. Low blood calcium increases membrane permeability to sodium, resulting in muscle twitching, cramping, spasms, or convulsions. Severe deficits can paralyze muscles, including those involved in breathing, and can be fatal.

When blood calcium levels are high, calcitonin is produced and secreted by the parafollicular cells of the thyroid gland. As discussed earlier, calcitonin inhibits the activity of osteoclasts, reduces the absorption of dietary calcium in the intestine, and signals the kidneys to reabsorb less calcium, resulting in larger amounts of calcium excreted in the urine.

Overview

Calcium is required for a variety of important physiologic processes, including neuromuscular functioning; thus, blood calcium levels are closely regulated. The parathyroid glands are small structures located on the posterior thyroid gland that produce parathyroid hormone (PTH), which regulates blood calcium levels. Low blood calcium levels cause the production and secretion of PTH. In contrast, elevated blood calcium levels inhibit secretion of PTH and trigger secretion of the thyroid hormone calcitonin. Underproduction of PTH can result in hypoparathyroidism. In contrast, overproduction of PTH can result in hyperparathyroidism.

Parathyroid cancer is a rare cancer that usually affects people in their forties or fifties and occurs in one of the four parathyroid glands. The parathyroid glands are located in the neck and secrete parathyroid hormone, which enhances the release of calcium into the blood.

In about 90 percent of cases, the early signs of parathyroid cancer are high levels of parathyroid hormone (hyperparathyroidism) and calcium (hypercalcemia) in the blood. In these cases, the cancer is described as hormonally functional because the parathyroid glands are producing excess hormone.

Many individuals with hormonally functional parathyroid cancer develop hypercalcemic crisis, in which calcium levels in the blood are very high. Neurological problems can develop, including changes in mood and depression. About 30 percent of individuals with hypercalcemia due to parathyroid cancer develop kidney and skeletal problems. These problems include increased urine production (polyuria), deposits of calcium in the kidneys (nephrocalcinosis) leading to the formation of kidney stones (nephrolithiasis), bone pain, bone loss, and increased bone fractures. Abdominal pain, inflammation of the pancreas (pancreatitis), sores (ulcers) in the lining of the digestive tract, nausea, vomiting, weight loss, and fatigue are also common.

About 10 percent of cases of parathyroid cancer are described as hormonally nonfunctional. In these cases, levels of parathyroid hormone and calcium are normal. The signs and symptoms of hormonally nonfunctional parathyroid cancer are related to the tumor obstructing nearby structures in the neck. These problems include difficulty swallowing (dysphagia) and speaking (dysarthria), a hoarse voice, shortness of breath (dyspnea), or vocal cord paralysis.

Up to 85 percent of individuals with parathyroid survive at least 5 years after they are diagnosed. The disease recurs in approximately half of individuals. If cancer does recur, it will commonly be within 3 years of the original diagnosis and up to 78 percent of people with recurrent cancer survive at least 5 years. Hormonally nonfunctional parathyroid cancer has a lower survival rate because it is often found at a later stage, as it does not have early signs such as increased calcium and parathyroid hormone levels.

In hormonally functional parathyroid cancer, death is usually caused by organ failure (usually kidney failure) due to prolonged hypercalcemia and not directly due to the tumor. In hormonally nonfunctional parathyroid cancer, the cause of death is typically related to the tumor itself, such as its impact on the function of nearby structures or its spread to other tissues (metastasis).