Hypoparathyroidism

In medicine (endocrinology), hypoparathyroidism is decreased function of the parathyroid glands, leading to decreased levels of parathyroid hormone (PTH). The consequence, hypocalcaemia, is a serious medical condition.

Signs and symptoms

• Tingling lips, fingers, and toes
• Muscle cramps
• Pain in the face, legs, and feet
• Abdominal pain
• Dry hair
• Brittle nails
• Dry, scaly skin
• Cataracts
• Weakened tooth enamel (in children)
• Muscle spasms called tetany (can lead to spasms of the larynx, causing breathing difficulties)
• Convulsions (seizures)
• Tetanic contractions

Additional symptoms that may be associated with this disease include:

• Painful menstruation
• Hand or foot spasms
• Decreased consciousness
• Delayed or absent tooth formation

In contrast to hyperparathyroidism (hyperfunction of the parathyroids), hypoparathyroidism does not have consequences for bone.

Diagnosis

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:

• Pseudohypoparathyroidism (normal PTH levels but tissue insensitivity to the hormone, associated with mental retardation and skeletal deformities) and pseudopseudohypoparathyroidism (sic).
• Vitamin D deficiency or hereditary insensitivity to this vitamin (X-linked dominant).
• Malabsorption
• Kidney disease
• Medication: steroids, diuretics, some antiepileptics.

Other tests include ECG for abnormal heart rhythms, and measurement of blood magnesium levels.

Causes

Hypoparathyroidism can have a number of divergent causes:

• Removal of or trauma to the parathyroid glands in thyroid surgery (thyroidectomy) or other neck surgeries is a recognised cause. It is now uncommon, as surgeons generally can spare them during procedures after identifying them. In a small percentage of cases, however, they can become traumatized during surgery and/or their blood supply can be compromised. When this happens the parathyroids may cease functioning for a while or stop altogether.
• 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.
• Absence or dysfunction of the parathyroid glands is one of the components of chromosome 22q11 microdeletion syndrome (other names: DiGeorge syndrome, Schprintzen syndrome, velocardiofacial syndrome).
• Magnesium deficiency
• DiGeorge syndrome, a disease in which hypoparathyroidism can occur due to a total absence of the parathyroid glands at birth. Familial hypoparathyroidism occurs with other endocrine diseases, such as adrenal insufficiency, in a syndrome called type I polyglandular autoimmune syndrome (PGA I).
• Some very rare diseases
• Idiopathic (of unknown cause), occasionally familial

Treatment

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.

Long-term treatment of hypoparathyroidism is with calcium and Vitamin D3 supplementation (D1 is ineffective in the absence of renal conversion). Teriparatide, a synthetic form of PTH (presently registered for osteoporosis) might become the treatment of choice for PTH supplementation, although further studies are awaited.

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.

Possible Complications

• Tetany can lead to a blocked airway, requiring a tracheostomy.
• Stunted growth, malformed teeth, and slow mental development can occur if hypoparathyroidism develops in childhood.
• Overtreatment with vitamin D and calcium can cause hypercalcemia (high blood calcium) and sometimes interfere with kidney function.
• There is an increased risk of pernicious anemia, Addison's disease, cataract development, and Parkinson's disease.

References

• Hurd, Robert (2006-10-25). "Hypoparathyroidism". Medical Encyclopedia. Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/000385.htm. Retrieved 2007-11-02. 

See also

• Hyperparathyroidism
• Pseudopseudohypoparathyroidism