The parathyroid glands are four small, pea-sized glands that are located behind the larger, butterfly-shaped thyroid gland. The parathyroid glands are named for their location. There are two superior thyroid glands, which are found behind the top part of the thyroid lobes; one behind the right thyroid lobe and one behind the left thyroid lobe. There are also two inferior parathyroid glands which can vary in their location. They are usually found behind the lower part of the right and left thyroid lobes. In some people, the inferior parathyroid glands may be located below the level of the thyroid gland, or may be found near the inferior thyroid veins. The parathyroid glands are usually 6mm in length and 3-4mm wide.
The parathyroid glands are involved in the regulation of blood calcium levels. This is important to ensure normal function of other organs and tissues, including the heart, kidneys, bones and nerves. The parathyroid glands produce a hormone called parathyroid hormone, or PTH, which controls the levels of calcium in the body. When the level of calcium in the blood drops, the parathyroid glands release PTH which works in a number of ways to increase the level of calcium in the blood.
Parathyroid hormone functions
Parathyroid hormone – PTH
PTH acts on the bone to stimulate reabsorption of bone which results in the release of calcium stored in the bone
PTH acts on the kidney to increase the amount of calcium that is reabsorbed so that less calcium is lost through the urine
PTH also stimulates the activation of vitamin D in the kidney. Activated vitamin D is important because it helps the small intestine to reabsorb more calcium from the diet into the bloodstream
All of these actions work to increase the level of calcium. Once the calcium levels have returned to normal or become too high, the parathyroid glands become less active and do not secrete as much PTH.
Relationship between blood ionized calcium concentrations and plasma parathyroid hormone (PTH) levels in persons with normal renal and parathyroid gland function. American Journal of Physiology – Renal Physiology Published 6 May 2004 Vol. 286 no. 6.
What is hyperparathyroidism?
Hyperparathyroidism is a term used to describe increased activity in one or more of the parathyroid glands. There are three types of hyperparathyroidism:
Primary hyperparathyroidism, where the affected parathyroid gland produces too much PTH as a result of a problem within the parathyroid gland itself. The most common cause of primary hyperparathyroidism is a benign tumour within the gland called a parathyroid adenoma. Parathyroid adenomas are usually only found within one parathyroid gland, it is very uncommon to find a parathyroid adenoma in more than one gland. Less common causes of primary hyperparathyroidism include parathyroid hyperplasia, and very rarely, parathyroid carcinoma, a malignant parathyroid tumour.
Secondary hyperparathyroidism, where the underlying cause of the hyperparathyroidism is due to low levels of blood calcium, which is known as hypocalcaemia. Hypocalcaemia may be the result of poor calcium absorption in the intestines, or the result of severe dietary deficiency. Because vitamin D is necessary for calcium absorption, severe vitamin D deficiency can also cause hypocalcaemia and secondary hyperparathyroidism. People with chronic renal failure may also develop secondary hyperparathyroidism.
Tertiary hyperparathyroidism, which occurs after chronic secondary hyperparathyroidism. Once the underlying cause of the longstanding secondary hyperparathyroidism is addressed, the affected parathyroid gland or glands still continue to secrete too much PTH.
Parathyroid hormone testing
Parathyroid hormone levels are routinely measured by a blood test. Intact PTH (iPTH) is the biologically active form and is secreted when the calcium level is low. iPTH is the most frequently ordered parathyroid hormone test. iPTH is used to diagnose the cause of a high calcium level and to distinguish between parathyroid and non-parathyroid causes. A calcium test is almost always ordered along with an iPTH test. The key to diagnosis of a parathyroid gland disorder is the relationship between the calcium and iPTH and the response of the parathyroid glands to changing levels of calcium.
Symptoms of hyperparathyroidism can vary depending on whether the cause is primary, secondary or tertiary hyperparathyroidism. The symptoms of primary and tertiary hyperparathyroidism are similar, because both cause a high level of calcium in the bloodstream.
Symptoms of primary and tertiary hyperparathyroidism include:
Bone and joint pain due to the breakdown of bone to release calcium
Loss of appetite
The symptoms of secondary hyperparathyroidism are different to the symptoms of primary and tertiary hyperparathyroidism because elevated levels of blood calcium cause many of the symptoms in primary and tertiary hyperparathyroidism; but high levels of blood calcium are not an issue with secondary hyperparathyroidism. Increased fracture risk is common to all forms of hyperparathyroidism. Underlying renal problems are the cause of many of the symptoms of secondary hyperparathyroidism.
Symptoms of secondary hyperparathyroidism include:
Changes to urinary habits
Ankle and leg swelling
Surgery is the most common treatment for primary hyperparathyroidism and provides a cure in about 95 percent of all cases. Your surgeon will remove only those glands that are enlarged or have a tumour (adenoma).
If all four glands are affected, your surgeon will likely remove only three glands and perhaps a portion of the fourth. This approach will leave some functioning parathyroid tissue.
Parathyroid surgery can be done through a very small neck incision which leaves a minimal scar.
Complications from parathyroid surgery are uncommon. Risks include damage to nerves controlling the vocal cords and long-term low calcium levels requiring the use of calcium and vitamin D supplements.
For more information about the parathyroid glands click here.
If you have questions about the parathyroid glands, contact your local doctor who will arrange for you to see a thyroid surgeon.