Conditions: Hyperparathyroidism

Hyperparathyroidism explained

Parathyroid glands’ job is to detect a low blood calcium level and when this happens, produce parathyroid hormone. This parathyroid hormone is released into the blood and acts on the gut, kidneys, and bones to increase the blood calcium level. When the blood calcium has risen, the parathyroid glands slow or stop the production of parathyroid hormone. This feedback system is the normal mechanism for maintaining a normal calcium level. Unfortunately, parathyroid glands are somewhat prone to getting “stuck in the on position,” or “losing their brakes,” pumping out parathyroid hormone in excess, even when the blood calcium level is high. When this happens, both blood calcium and parathyroid hormone levels are high, a conditioned called primary hyperparathyroidism.

This aberrancy is most commonly due to a single parathyroid gland having lost it ability to decrease parathyroid hormone production, but may result from the defect occurring in two, three, or all glands. Genetically, a mutation in the “Menin” gene accounts for the loss of inhibitory function, and the affected gland(s) will grow in size and be called a parathyroid adenoma (a benign parathyroid tumor). In contrast, parathyroid cancer, is a rare condition that causes extremely high parathyroid hormone output and blood calcium levels.

Another form of hyperparathyroidism, called secondary hyperparathyroidism, is characterised by an elevated blood parathyroid hormone, but in contrast to primary hyperparathyroidism, the serum calcium is normal or low. Chronic renal failure and vitamin D deficiency are the most common causes of secondary hyperparathyroidism because both conditions lead to malabsorption of calcium and phosphate, and consequent decreased blood calcium levels that induce normal parathyroid glands to become overactive. In other words, the parathyroid glands are not malfunctioning in secondary hyperparathyroidism—they are responding appropriately to the condition created by kidney disease.

Tertiary hyperparathyroidism is a condition in which the overactive parathyroid glands of secondary hyperparathyroidism fail to revert back to normal parathyroid hormone output despite resolution of the cause of secondary hyperparathyroidism (such as a kidney transplant or correction of vitamin D deficiency).

sestamibi parathyroid scan

Since we typically have four parathyroid glands, and since their location may be different in different individuals, a scan to locate the one or more parathyroid glands that are working too much is commonly done prior to surgery so that the operation can be quicker and more anatomically focused. It is important to note that an imaging study is not useful in making a diagnosis of hyperparathyroidism, but rather, only trying to identify the site of one or more overactive glands (parathyroid adenomas) after the diagnosis has been made.

For finding enlarged parathyroid glands, the technique entails delivery of the gamma-emitting radioisotope technetium-99m into the patient, by injecting it into the bloodstream. The technetium-99m collects in certain types of tissues, including parathyroid glands, salivary glands, and the heart. The scanned image is often conclusive and accurate, but occasionally the study fails to reveal a clear-cut parathyroid adenoma, which may be due to the enlargement of multiple parathyroid glands or the failure of one or more parathyroid adenomas to take up the technetium-99m.