Hyperparathyroidism is a syndrome of hypercalcemia resulting from excessive release of parathyroid hormone.

The parathyroid glands regulate calcium and phosphorus levels by releasing variable amounts of parathyroid hormone, which raises serum calcium levels while lowering serum phosphorus. Under usual conditions, the rate of secretion of parathyroid hormone (PTH) is inversely proportional to the serum calcium level. Secretion of PTH is mainly controlled through the interaction of calcium with specific calcium-sensing receptors on the membrane of parathyroid cells.

You have four tiny parathyroid glands, one located on each of the four corners of another gland — the thyroid, which is located at the base of your neck. But in spite of the similarity in name and location, the parathyroid glands and thyroid gland are separate glands with separate functions.

Your thyroid gland, for example, helps regulate nearly every aspect of your metabolism, from how quickly your heart beats to the rate at which you burn calories. The parathyroids, on the other hand, produce a hormone that helps maintain the proper balance of calcium and phosphorus in your body. When the glands sense that blood calcium levels are either too low or too high, they secrete just enough parathyroid hormone (PTH) to restore the levels to normal. Sometimes, however, the glands produce too much PTH — a condition known as hyperparathyroidism. This leads to consistently high levels of calcium in your blood (hypercalcemia).

Secondary hyperparathyroidism is less common. It occurs when another medical condition — particularly kidney failure — causes your parathyroid glands to secrete too much PTH.

Left untreated, hyperparathyroidism can cause additional health problems, such as kidney damage and a loss of calcium from your bones, leading to osteoporosis.

If you have mild hyperparathyroidism, you may not need any treatment, although your blood-calcium levels, kidney function and bone health will need to be regularly checked. When your kidneys or bones are affected, or you have bothersome symptoms, surgery may be the best option

Signs and symptoms

More than half the people with hyperparathyroidism have no symptoms. In those who do, the symptoms frequently come on slowly and are usually subtle, such as a feeling of weakness or fatigue, or vague aches and pains.

• Fatigue

But more severe signs and symptoms can develop over time, including:

• Increased thirst and urination due to increased excretion of calcium in the urine (hypercalciuria)

• Kidney stones

• Heartburn or Abdominal pain from Peptic ulcer  disease or pancreatitis

• Nausea, vomiting or loss of appetite

• Thinning bones, leading to an increased risk of fractures

• Confusion or poor memory

• Muscle weakness or Fatigue

Causes

Calcium is the most abundant mineral in your body. It's essential for the development and health of your teeth and bones. Calcium also helps your blood clot, aids in the transmission of signals in nerve cells and plays a role in muscle contraction. Another mineral, phosphorus, works in conjunction with calcium in these areas.

The parathyroid glands maintain proper levels of both calcium and phosphorus in your body by turning the secretion of parathyroid hormone (PTH) off or on, much as a thermostat controls a heating system to maintain a constant air temperature. Vitamin D also is involved in regulating the amount of calcium in your blood.

Normally, this balancing act works well. When calcium levels in your blood fall too low, your parathyroid glands secrete the right amount of PTH to restore the balance. PTH raises calcium levels by releasing calcium from your bones and increasing the amount of calcium absorbed from your small intestine. When blood-calcium levels are too high, the parathyroids produce less PTH. But sometimes one or more parathyroid glands produce too much hormone, leading to abnormally high levels of calcium and low levels of phosphorus in your blood.

In more than 80 percent of people with hyperparathyroidism, the cause is a benign growth (adenoma) on one of the parathyroid glands. Most other cases result from excess hormone that's produced when two or more parathyroids become enlarged — a condition known as hyperplasia.

Secondary hyperparathyroidism occurs when another medical condition, such as kidney failure, causes your parathyroid to produce too much PTH. Infants and children who have rickets — a disease caused by severe vitamin D deficiency — also may develop secondary hyperparathyroidism. In rare cases, hyperparathyroidism may be caused by cancer of one of the parathyroid glands.

Risk factors

Twice as many women as men develop primary hyperparathyroidism, and risk increases with age. Two out of every 1,000 women age 60 and older will develop the disease.

Infants or adults with vitamin D deficiency also are at greater risk of developing secondary hyperparathyroidism. Most children and adults get sufficient amounts of vitamin D from food — especially eggs, fish, green vegetables and fortified milk products — and from exposure to sunlight, which changes a chemical in the skin into an active form of vitamin D. But several factors have caused a resurgence of vitamin D deficiency among some infants and children.

Chief among these are breast-feeding and the use of sunscreen. Although breast milk is a baby's ideal food, it doesn't contain vitamin D. If your baby is breast-fed only, talk to your pediatrician about a vitamin D supplement. In addition, children who live in northern or cloudy climates or who consistently use sunscreen may not receive enough sunlight to manufacture vitamin D in their skin.

Also at increased risk are people with familial endocrine neoplasia type I — a rare inherited syndrome that affects the parathyroids as well as the pancreas and pituitary gland. Having familial hyperparathyroidism — hyperparathyroidism that runs in families — also puts you at risk.