Hypoparathyroidism means decreased production of a substance known as parathyroid hormone (PTH) by parathyroid cells.
Parathyroid glands are four small glands located within the thyroid gland. Parathyroid cells produce the PTH hormone that is very important for calcium and bone metabolism. The main objective of PTH is to maintain adequate level of calcium in the blood (calcemia). PTH can increase serum calcium by decalcification of bones and by releasing the calcium into the blood. In addition, PTH stimulates production of vitamin D, which also increases calcemia (mainly by supporting calcium absorption from the gut). Absence of parathyroid hormone is associated with a subsequent decrease of calcium blood concentration (hypocalcemia).
Parathyroid glands can be damaged by an autoimmune process, when the immune system of our body attacks our own tissues, in this case the parathyroid cells. However, more often damage is done by surgical interventions in the cervical region, typically during the operations of thyroid gland. The surgeons try to preserve the parathyroid glands as much as possible but their anatomical relationship with thyroid gland is often too tight to make this possible. In addition, parathyroid cells can be damaged by abnormal deposition of different compounds within the glands (iron in hemochromatosis, amyloid in amyloidosis, copper in Wilson's disease). Local malignant tumors (usually thyroid gland cancers) can also destroy parathyroid tissue resulting in lack of PTH. We should not forget a rare congenital absence of the parathyroid glands as a part of the so-called DiGeorge syndrome.
Note: There is a special clinical unit described as the pseudohypoparathyroidism. This is a very rare genetic congenital condition when the production of parathyroid hormone is normal (or even increased), but the tissues of the body are unable to respond to its effect.
The symptoms are caused mainly by decrease of serum calcium (hypocalcemia). It has a general effect on neuromuscular transmission manifesting with increased irritability (increased deep tendon reflexes, muscle cramps, convulsions). Relatively severe muscle spasms in the airways may even result in choking. Hypocalcemia can have very serious effect on the heart triggering arrhythmias and increasing risk of a sudden cardiac arrest. Digestive tract reacts to hypocalcemia with increased peristalsis resulting in diarrhea. Old people suffering from hypocalcemia may manifest with confusion and dementia.
First, it is necessary to treat hypocalcemia. The calcium may be supplemented orally or intravenously. In chronic hypoparathyroidism we administer the calcium regularly in forms of tablets together with vitamin D to improve its absorption. In near future, the patients shall probably benefit from regular administration of artificially made PTH.