Removal of, or trauma to, the parathyroid glands due to thyroid surgery, parathyroid surgery or other surgical interventions in the central part of the neck is a recognized cause. It is the most common cause of hypoparathyroidism. Although surgeons generally make attempts to spare normal parathyroid glands at surgery, inadvertent injury to the glands or their blood supply is still common. When this happens, the parathyroids may cease functioning. This is usually temporary but occasionally long term.
Kenny-Caffey Syndrome
Autoimmune invasion and destruction is the most common non-surgical cause. It can occur as part of autoimmune polyendocrine syndromes.
Hemochromatosis can lead to iron accumulation and consequent dysfunction of a number of endocrine organs, including the parathyroids.
A defect in the calcium receptor leads to a rare congenital form of the disease
Idiopathic, occasionally familial
Mechanism
The parathyroid glands are so named because they are usually located behind the thyroid gland in the neck. They arise during fetal development from structures known as the third and fourth pharyngeal pouch. The glands, usually four in number, contain the parathyroid chief cells that sense the level of calcium in the blood through the calcium-sensing receptor and secrete parathyroid hormone. Magnesium is required for PTH secretion. Under normal circumstances, the parathyroids secrete PTH to maintain a calcium level within normal limits, as calcium is required for adequate muscle and nerve function. PTH acts on several organs to increase calcium levels. It increases calcium absorption in the bowel, while in the kidney it prevents calcium excretion and increases phosphate release and in bone it increases calcium through bone resorption.
Diagnosis
Diagnosis is by measurement of calcium, serum albumin and PTH in blood. If necessary, measuring cAMP in the urine after an intravenous dose of PTH can help in the distinction between hypoparathyroidism and other causes. Differential diagnoses are:
Medication: steroids, diuretics, some antiepileptics.
Other tests include ECG for abnormal heart rhythms, and measurement of blood magnesium levels.
Treatment
Severe hypocalcaemia, a potentially life-threatening condition, is treated as soon as possible with intravenous calcium. Generally, a central venous catheter is recommended, as the calcium can irritate peripheral veins and cause phlebitis. In the event of a life-threatening attack of low calcium levels or tetany, calcium is administered by intravenous infusion. Precautions are taken to prevent seizures or larynx spasms. The heart is monitored for abnormal rhythms until the person is stable. When the life-threatening attack has been controlled, treatment continues with medicine taken by mouth as often as four times a day. Long-term treatment of hypoparathyroidism is with vitamin D analogs and calcium supplementation, but may be ineffective in some due to potential renal damage. The N-terminal fragment of parathyroid hormone has full biological activity. The use of pump delivery of synthetic PTH 1-34 provides the closest approach to physiologic PTH replacement therapy. Injections of recombinant human parathyroid hormone are available as treatment in those with low blood calcium levels.
