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

Signs, symptoms and diagnosis

Hypocalcemia is the only real result of parathyroid dysfunction and low PTH levels. This presents with tremor, tetany and, eventually, convulsions.

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

Diagnosis is by measurement of calcium, 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:

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

Causes

Hypoparathyroidism can have a number of divergent causes:

• Removal of the parathyroid glands in thyroid surgery (thyroidectomy) is a recognised cause. It is now uncommon, as surgeons generally spare them during the procedure after identifying them.
• Autoimmune invasion and destruction is the most common non-surgical cause. It can occur as part of autoimmune polyendocrine syndromes (see there).
• 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
• Some very rare diseases
• Idiopathic (of unknown cause), occasionally familial

The physiologic function of PTH is the maintenance of sufficient calcium levels. This is achieved by bone resorption, renal reabsorption of calcium (in the distal tubule) and Vitamin D3 (1,25-OH-D3) synthesis (also in the kidney) from Vitamin D1 (25-OH-D3).

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.

See also

• Hyperparathyroidism