Hyperparathyroidism is when your parathyroid glands create too much parathyroid hormone in the bloodstream. These glands, located behind the thyroid at the bottom of your neck, are about the size of a grain of rice.
The parathyroid glands produce parathyroid hormone. This hormone helps maintain an appropriate balance of calcium in the bloodstream and in tissues that depend on calcium for proper functioning.
Two types of hyperparathyroidism exist. In primary hyperparathyroidism, an enlargement of one or more of the parathyroid glands causes overproduction of the hormone. This causes high calcium levels in the blood, which can cause a variety of health problems. Surgery is the most common treatment for primary hyperparathyroidism.
Secondary hyperparathyroidism occurs due to another disease that first causes low calcium levels in the body. Over time, increased parathyroid hormone levels occur.
Symptoms
Hyperparathyroidism is often diagnosed before signs or symptoms of the disorder are apparent. When symptoms do occur, they're the result of damage or dysfunction in other organs or tissues due to high calcium levels in the blood and urine or too little calcium in bones.
Symptoms may be so mild and nonspecific that they don't seem related to parathyroid function, or they may be severe. The range of signs and symptoms include:
• Osteoporosis
• Kidney stones
• Excessive urination
• Abdominal pain
• Tiring easily or weakness
• Depression or forgetfulness
• Bone and joint pain
• Frequent complaints of illness with no apparent cause
• Nausea, vomiting or loss of appetite
Causes
• Hyperparathyroidism is caused by factors that increase the production of parathyroid hormone.
• 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 like 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 enough 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 parathyroid glands produce less PTH. But sometimes one or more of these glands produce too much hormone. This leads to abnormally high calcium levels and low phosphorus levels in your blood.
• Calcium is best known for its role in keeping your teeth and bones healthy. But calcium also aids in the transmission of signals in nerve cells, and it's involved in muscle contraction. Phosphorus, another mineral, works along with calcium in these areas.
• Hyperparathyroidism may occur because of a problem with the parathyroid glands (primary hyperparathyroidism) or because of another disease that affects the glands' function (secondary hyperparathyroidism).

Primary hyperparathyroidism
Primary hyperparathyroidism occurs because of some problem with one or more of the four parathyroid glands:
• A noncancerous growth (adenoma) on a gland is the most common cause.
• Enlargement (hyperplasia) of two or more parathyroid glands accounts for most other cases.
• A cancerous tumor is a very rare cause of primary hyperparathyroidism.
Primary hyperparathyroidism usually occurs randomly, but some people inherit a gene that causes the disorder.
Secondary hyperparathyroidism
Secondary hyperparathyroidism is the result of another condition that lowers calcium levels. This causes your parathyroid glands to overwork to compensate for the calcium loss. Factors that may contribute to secondary hyperparathyroidism include:
• Severe calcium deficiency. Your body may not get enough calcium from your diet, often because your digestive system doesn't absorb the calcium from it.
• Severe vitamin D deficiency. Vitamin D helps maintain appropriate calcium levels in the blood. It also helps your digestive system absorb calcium from your food.
Your body produces vitamin D when your skin is exposed to sunlight. You also consume some vitamin D in food. If you don't get enough vitamin D, then calcium levels may drop.
• Chronic kidney failure. Your kidneys convert vitamin D into a form that your body can use. If your kidneys work poorly, usable vitamin D may decline and calcium levels drop, causing parathyroid hormone levels to go up. Chronic kidney failure is the most common cause of secondary hyperparathyroidism. Some medical treatments, such as vitamin D, bisphosphonates and cinacalcet, will lower PTH levels.
In some people with long-term end-stage kidney disease, the parathyroid glands enlarge and begin to release PTH on their own, and PTH doesn't go down with medical treatment. This is called tertiary hyperparathyroidism, and people with this condition may require surgery to remove parathyroid tissue.