There are four parathyroid glands, situated just behind the thyroid gland, and they are normally about the size of a grain of rice each. In health, the main action of parathyroid hormone is to restore blood calcium levels back into the normal range by acting to increase calcium levels if they are too low. It does this by regulating the amount of calcium passed out in the urine, activating vitamin D, and increasing calcium release from bones.
If parathyroid hormone levels (PTH) are abnormally high (called hyperparathyroidism), blood calcium will rise above the normal range (hypercalcaemia). In recent years, a normocalcaemic form of primary hyperparathyroidism has been described, where the parathyroid hormone is high, but the calcium has yet to exceed the normal range.
It is the third most common endocrine disorder in men and women.
The most common cause of primary hyperparathyroidism (75–85% of cases) is a single benign growth or nodule (adenoma) in one of the four parathyroid glands. In 2–12% of cases, there are growths in two glands, in 1–2% there are growths in three glands, and in 1–15% of cases there are growths in all four glands. There are some rare genetic causes of primary hyperparathyroidism which cause generalised overgrowth of all four glands (see inherited causes below). The growths are usually too small to be seen or felt. It is very rare to find cancer in the parathyroid glands, and this accounts for less than 1% of all cases of primary hyperparathyroidism.
In this condition, calcium levels in the bloodstream are raised above normal levels (hypercalcaemia). In mild cases it is often discovered when a routine blood sample is taken for another reason and the test finds high calcium levels. Often these people have no other signs or symptoms of high calcium.
Where signs and symptoms related to hyperparathyroidism become overt, they are usually a result of long-term significant hypercalcaemia.
The constantly high levels of calcium in the blood mean that more calcium passes through the kidneys, so calcium levels in urine are increased (hypercalciuria). Some people with high calcium levels can develop calcium deposits in the kidney (called nephrocalcinosis) or kidney stones. Kidney stones occur in about 15–20% of patients with primary hyperparathyroidism.
Because parathyroid hormone increases calcium release from bones, primary hyperparathyroidism can lead to low bone mineral density or osteoporosis and an increased risk of bone fractures.
High calcium levels can also cause thirst and frequent urination, abdominal pain, constipation and nausea, as well as more general symptoms such as tiredness, aches, poor concentration, low mood, and confusion.
Primary hyperparathyroidism is more common with older age, and more common in women than in men. It is difficult to estimate how many people have primary hyperparathyroidism because cases often go undetected, but probably about 2% of older adults in the UK.
For most patients, primary hyperparathyroidism is not an inherited condition. However, there are rare forms of hyperparathyroidism that can be inherited. These include multiple endocrine neoplasia types 1 and 2a, familial isolated primary hyperparathyroidism and the hyperparathyroidism-jaw tumour syndrome. Inherited causes of primary hyperparathyroidism account for less than 10% of all cases of primary hyperparathyroidism, but it may be especially important to consider these in people who have primary hyperparathyroidism at younger age or who have a family history of relevant conditions.
The diagnosis of hyperparathyroidism is made by measuring calcium and parathyroid hormone levels in the blood, and calcium levels in the urine. These tests are done in an outpatient clinic. There is a rare genetic condition called ‘familial hypocalciuric hypercalcaemia’ (FHH) which also causes high parathyroid hormone and calcium levels, but low urine calcium levels. It is important to differentiate this from primary hyperparathyroidism because it does not need surgical treatment.
In many people with primary hyperparathyroidism, the calcium level is only mildly raised, and they don’t have any symptoms. A bone density scan (DXA) and kidney scan are recommended to check that there are no signs of osteoporosis or kidney stones. In mild cases, treatment is usually not needed. When patients with mild disease are monitored over ten years, only one-third of people will develop higher blood calcium or other problems and need to have treatment. People with mild disease who do not need treatment should be monitored with a check-up and blood test every year, and a bone density scan every few years. They should also take a vitamin D supplement to maintain normal levels and to keep their bones healthy.
If a person has significantly raised blood calcium levels, abnormal kidney function, osteoporosis, or symptoms due to the high calcium, then treatment is usually advised.
The only cure for hyperparathyroidism is surgical removal of the affected parathyroid gland or glands.
The operation is usually done under a general anaesthetic. The surgeon will do a neck exploration to find all four glands and remove any which look enlarged. In some patients, scans (including ultrasound, CT and Sestamibi) can be used to identify which of the four parathyroid glands are abnormal. If the scans can clearly identify which gland is abnormal, the surgeon may be able to do a smaller operation just to remove the abnormal gland. During the operation, blood tests can be done to check that the parathyroid hormone levels have decreased and the abnormal gland has been successfully removed, before the operation is closed.
Often it is recommended that people take calcium and vitamin D supplements for some months after surgery to help restore calcium levels in their bones.
For patients who are unable to have an operation, medication can be used to control the symptoms. A tablet called Cinacalcet reduces blood calcium levels, but it doesn’t prevent osteoporosis or kidney stones. Many people with primary hyperparathyroidism need to take a vitamin D supplement to protect their bones. Standard treatments for osteoporosis (bisphosphonates) work well to improve bone mineral density in osteoporosis due to primary hyperparathyroidism.
In people with normocalcaemic hyperparathyroidism, we do not yet know what the best treatment is. Research studies are being done to try to understand this disorder better and what treatment is best.
Surgery for hyperparathyroidism is usually highly successful. As with any operation, there are risks associated with an anaesthetic, bleeding and infection, but problems are rare. About 1% of patients experience damage to the nerves controlling the vocal cords, which can result in a hoarse voice. Some patients will have temporary low calcium levels after the operation, and a few patients who need to have all four glands removed will have permanently low calcium levels and need to take calcium and vitamin D life-long.
After successful surgery, calcium levels return to normal, and bone mineral density improves. General symptoms such as fatigue often improve too, but because symptoms like fatigue can have a lot of causes, it’s difficult to be sure how much these symptoms will improve in any individual patient.
In people with mild disease who don’t have surgery, two-thirds of people will not develop any problems or need any treatment. In one-third of people, blood calcium levels will rise (slowly over several years), or there will be signs that they are at risk of osteoporosis or kidney problems, so they will go on to have treatment.
Parathyroid UK may be able to provide advice and support to patients and their families dealing with hyperparathyroidism.
Last reviewed: Nov 2021