What are the parathyroid glands?
Most of us have four parathyroid glands- each no larger than a grain of rice. They are located in the neck behind the thyroid gland, and sometimes in the thyroid itself. The parathyroid glands are part of the endocrine system and are responsible for the production and secretion of parathyroid hormone.
What is parathyroid hormone (PTH)?
All cells and organs require calcium to function properly and the body’s calcium levels are tightly controlled.
Parathyroid hormone increases the amount of calcium available by several actions that include:
- Increasing bone breakdown.
- Increasing calcium reabsorption from the kidney.
- Increased Vitamin D production, to enhance calcium absorption from the intestines.
- Directly acting on the intestines to increase calcium
- Increasing the excretion of phosphate (which attaches itself to calcium and decreases how much is available to the body)
How is parathyroid hormone regulated?
The cells of the parathyroid gland constantly monitor blood calcium levels.
When these levels become too low, the parathyroid gland increases the secretion of parathyroid hormone which increases blood calcium levels by the actions mentioned above. Once calcium levels return to the normal range the secretion of parathyroid hormone is reduced.
What is hyperparathyroidism?
Hyperparathyroidism is a condition where hyperactive parathyroid glands secrete too much PTH, hence blood calcium levels are elevated by:
- increased mobilisation of calcium from the bones, leading to osteoporosis and weakening of bones
- Increased reabsorption of calcium from the kidneys.
- Increased absorption of calcium from the intestines.
Since the blood is filtered by the kidneys, the kidneys become repeatedly exposed to high levels of calcium which can eventually lead to the formation of kidney stones and kidney damage.
In more than 95% of patients, primary hyperparathyroidism is caused by a single adenoma (hyperactive gland). Rarely, 2 or 3 parathyroid glands may be diseased and they are known as double or triple adenoma. All 4 parathyroid glands can also be affected and these patients have what is known as “Four gland hyperplasia”, and this is most common in patients with chronic kidney failure.
Primary hyperparathyroidism affects females twice as commonly as males. Incidence also increases with age above 45 years. Primary hyperparathyroidism is by far the most common cause of hypercalcaemia- elevated blood calcium levels.
What are the signs and symptoms of primary hyperparathyroidism?
The symptoms of hyperparathyroidism are a result of persistently elevated calcium levels.
Hyperparathyroidism typically affects your bones, digestive system and kidneys.
Painful bones occur as a result of increased removal of calcium from bones making them weak, osteoporotic and more prone to fractures.
Due to the ongoing exposure of the kidneys to high levels of calcium, kidneys stones are common and can be extremely painful, cause blood in the urine (haematuria) and damage the kidneys. Ultimately, this can lead to long-term kidney failure.
The high calcium load also results in an increased volume of urine (polyuria) or the need to wake up and pass urine at night (nocturia). Hyperparathyroidism can also cause abdominal pain, nausea and vomiting due to increased calcium levels.
Other symptoms of hyperparathyroidism include fatigue, depression, irritability and poor memory.
How is hyperparathyroidism diagnosed?
If you have any of the above symptoms you should consult your GP to identify a cause. Your doctor will then carry out a series of tests. Hyperparathyroidism can be usually tested by several tests. They are:
- Plasma parathyroid hormone and calcium levels
Parathyroid hormone is responsible for the strict control of plasma calcium. When calcium levels are low, more PTH is secreted and when calcium levels are high, less PTH is secreted. In hyperparathyroidism, both the plasma calcium and PTH levels are elevated.
- Plasma Phosphate level
This test will measure the phosphate levels in your blood. In primary hyperparathyroidism blood phosphate levels are reduced because high PTH levels increases the excretion of phosphate from the body.
- Plasma Vitamin D level
- Urine calcium level
This test will measure the amount of calcium excreted through your urine over a 24 hour period.
- DEXA scan
This test measures bone density. Since primary hyperparathyroidism increases your risk of osteoporosis, it is important to get a DEXA scan done so that treatment for osteoporosis can be started if necessary.