| Hypoparathyroidism | |
|---|---|
| Classification and external resources | |
| ICD-10 | E20, E89.2, P71.4 |
| ICD-9 | 252.1 |
| OMIM | 146200 |
| DiseasesDB | 6490 |
| MedlinePlus | 000385 |
| eMedicine | med/1131 emerg/276 ped/1125 |
| MeSH | D007011 |
Hypoparathyroidism is decreased function of the parathyroid glands with under production of parathyroid hormone. This can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involunary muscle contraction), and several other symptoms. The condition can be inherited, but it is also encountered after thyroid or parathyroid gland surgery, and it can be caused by immune system-related damage as well as a number of rarer causes. The diagnosis is made with blood tests, and other investigations such as genetic testing depending on the results. The treatment of hypoparathyroidism is limited by the fact that there is no artificial form of the hormone that can be administered as replacement; calcium replacement or vitamin D can ameliorate the symptoms but can increase the risk of kidney stones and chronic kidney disease.[1]
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The main symptoms of hypoparathyroidism are the result of the low blood calcium level, which interferes with normal muscle contraction and nerve conduction. As a result, people with hypoparathyroidism can experience paresthesia, an unpleasant tingling sensation around the mouth and in the hands and feet, as well as muscle cramps and severe spasms known as "tetany" that affect the hands and feet.[2] Many also report a number of subjective symptoms such as fatigue, headaches, bone pain and insomnia.[1] Crampy abdominal pain may occur.[3] Physical examination of someone with hypocalcemia may show tetany, but it is also possible to provoke tetany of the facial muscles by tapping on the facial nerve (a phenomenon known as Chvostek's sign) or by using the cuff of a sphygmomanometer to temporarily obstruct the blood flow to the arm (a phenomenon known as Trousseau's sign).[3]
A number of medical emergencies can arise in people with low calcium levels. These are seizures, severe irregularities in the normal heart beat, as well as spasm of the upper part of the airways or the smaller airways known as the bronchi (both potentially causing respiratory failure).[1]
In hypoparathyroidism, urinary calcium excretion is increased. This can lead to kidney stones that can cause painful attacks when released into the ureters, but also to ongoing kidney damage and chronic kidney disease, the symptoms of which are non-specific but include fatigue, nausea.[1]
Hypoparathyroidism can have a number of causes:
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 (including the autonomic nervous system). 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 is by measurement of calcium, serum albumin (for correction) and PTH in blood. PTH degrades rapidly at ambient temperatures and the blood sample therefore has to be transported to the laboratory on ice.
If necessary, measuring cAMP (cyclic AMP) in the urine after an intravenous dose of PTH can help in the distinction between hypoparathyroidism and other causes.
Differential diagnoses are:
Other tests include ECG for abnormal heart rhythms, and measurement of blood magnesium levels.
Severe hypocalcemia, a potentially life-threatening condition, is treated as soon as possible with intravenous calcium (e.g. as calcium gluconate). 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 (prolonged muscle contractions), calcium is administered by intravenous (IV) 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 may be ineffective in some due to potential renal damage. [4] The N-terminal fragment of parathyroid hormone (PTH 1-34) has full biological activity. The use of pump delivery of synthetic PTH 1-34 provides the closest approach to physiologic PTH replacement therapy.[5] Teriparatide, a recombinant form of PTH (presently registered for osteoporosis) might become the treatment of choice for PTH supplementation.[6] Currently, hypoparathyroidism is the only hormonal insufficiency state that does not have a hormone-replacement-therapy approved,[1] but research is being conducted to establish recombinant human parathyroid hormone (1-84) (rhPTH[1-84]) as just such a replacement.
A number of complications can occur in hypoparathyroidism:
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