Hypoparathyroidism is a deficiency of parathyroid hormone (PTH) often caused by an autoimmune disorder, treatment-related damage to the parathyroid glands, or removal of the glands during surgery.
(See also Overview of Parathyroid Function.)
Symptoms of hypoparathyroidism are due to low calcium levels in the blood and include tingling in the hands or around the mouth and muscle cramps.
Blood tests to check the levels of parathyroid hormone and calcium are needed for diagnosis.
The parathyroid glands are located near the thyroid gland. Their exact location, and even the total number of glands, is quite variable. These glands secrete parathyroid hormone (PTH), which regulates calcium levels in the blood and tissues through its effects on bones, the kidneys, and the intestine.
Hypoparathyroidism results from deficient parathyroid hormone (PTH) secretion, which can occur as the result of
Removal of or damage to several parathyroid glands during surgery to remove them (parathyroidectomy) or the thyroid gland (thyroidectomy)
An inherited autoimmune disorder (a malfunction of the body's immune system that causes the body to attack its own tissues)
An inherited disorder in which the parathyroid glands are missing or shrunken
Hypoparathyroidism causes a low level of calcium in the blood (hypocalcemia) and a high blood level of phosphate (hyperphosphatemia). Long-term hypoparathyroidism can cause a high level of calcium to be excreted in urine (hypercalciuria), which increases risk of kidney stones, and decreased bone mineral density (osteopenia).
The Parathyroid Glands
Postoperative hypoparathyroidism
Postoperative hypoparathyroidism is a common and usually temporary condition that occurs after partial removal of the thyroid gland (subtotal thyroidectomy). Permanent hypoparathyroidism occurs after less than about 3% of subtotal thyroidectomies. People usually develop hypocalcemia (low calcium level in the blood) about 24 to 48 hours after surgery, but hypocalcemia may occur months or years later.
PTH deficiency is more common after complete removal of the thyroid gland (such as to treat thyroid cancer) or after surgery to remove overactive parathyroid glands. Even if all the parathyroid glands are not removed or a small piece of normal gland is reimplanted in a muscle (subtotal parathyroidectomy), severe hypocalcemia may occur. Risk factors for severe hypocalcemia after subtotal parathyroidectomy include
High level of calcium in the blood before surgery
Removal of a large parathyroid adenoma (noncancerous tumor)
Inherited hypoparathyroidism
Some people have an inherited condition in which their parathyroid glands are absent or underdeveloped. Other people inherit a tendency for their immune system to attack their parathyroid glands (and sometimes other glands).
Pseudohypoparathyroidism
Pseudohypoparathyroidism is an uncommon group of inherited disorders that resemble true hypoparathyroidism except that they are caused by the resistance of target organs to the effects of PTH rather than a deficiency of PTH. There are several types of pseudohypoparathyroidism, each of which has a different and complicated genetic cause.
Symptoms of Hypoparathyroidism
Symptoms of hypoparathyroidism are due to hypocalcemia and include tingling in the hands or around the mouth and muscle cramps. In severe cases, tetany occurs. Tetany is periodic painful muscle spasms.
Diagnosis of Hypoparathyroidism
Blood tests to measure parathyroid hormone (PTH) and calcium levels
People with hypoparathyroidism have hypocalcemia (low level of calcium in the blood) and hyperphosphatemia (high level of phosphate in the blood). Because hypocalcemia prompts increased PTH secretion, the level of PTH in the blood should go up in response to hypocalcemia. Thus, in people with hypocalcemia, doctors can make a diagnosis based on the following blood test results:
Low or even low-normal PTH levels are inappropriate and suggest hypoparathyroidism.
Undetectable PTH levels suggest idiopathic hypoparathyroidism.
High PTH levels suggest pseudohypoparathyroidism or an abnormality of vitamin D metabolism.
Treatment of Hypoparathyroidism
Sometimes intravenous calcium is needed.
parathyroid hormone may decrease the risk of complications of long-term hypoparathyroidism, such as hypercalciuria and decreased bone mineral density, and lower the doses of calcium and vitamin D needed. Doctors monitor the person's blood levels of calcium and phosphate and may need to increase or decrease the dose of recombinant parathyroid hormone.
