Hypoparathyroidism
A deficiency in parathyroid hormone (PTH) secretion by the parathyroid glands or decreased action of peripheral PTH creates hypoparathyroidism. Because the parathyroid glands primarily regulate calcium balance, hypoparathyroidism causes hypocalcemia, which produces neuromuscular symptoms ranging from paresthesia to tetany.
PTH normally maintains serum calcium levels by increasing bone resorption and GI absorption of calcium. It also maintains the inverse relationship between serum calcium and phosphate levels by inhibiting phosphate reabsorption in the renal tubules. Abnormal PTH production in hypoparathyroidism disrupts this delicate balance.
Hypoparathyroidism may be acute or chronic and is classified as idiopathic, acquired, or reversible. The idiopathic and reversible forms are most common in children, and the clinical effects are usually correctable with replacement therapy. The acquired form, which is irreversible, is most common in older patients who have undergone thyroid gland surgery.
Causes
Idiopathic hypoparathyroidism may result from an autoimmune genetic disorder or the congenital absence of the parathyroid glands.
Acquired hypoparathyroidism typically results from accidental removal of or injury to one or more parathyroid glands during thyroidectomy or other neck surgery. It may also result from ischemic infarction of the parathyroid glands during surgery, hemochromatosis, sarcoidosis, amyloidosis, tuberculosis, neoplasms, trauma, or massive thyroid irradiation (rare).
Reversible hypoparathyroidism may result from hypomagnesemia–induced impairment of hormone synthesis, from suppression of normal gland function due to hypercalcemia, or from delayed maturation of parathyroid function.
Complications
In hypoparathyroidism, complications are related to long–standing hypocalcemia. Decreased calcium levels can cause reduced contractility and, eventually, heart failure. Lens calcification leads to cataract formation that persists despite calcium replacement therapy. Papillary edema from increased intracranial pressure, irreversible calcification of basal ganglion, and bone deformity also occur. Laryngospasm, respiratory stridor, anoxia, paralysis of the vocal cords, and death may occur in severe cases of tetany.
Pediatric pointerHypoparathyroidism that develops during childhood results in mental retardation, stunted growth, and malformed teeth.
Assessment
The patient’s history may reveal recent neck surgery or irradiation or long–term hypomagnesemia from GI malabsorption or alcoholism.
The patient may report symptoms that reflect altered neuromuscular irritability. (See Acute tetany.) The patient may also complain of personality changes, ranging
from irritability and anxiety to depression, delirium, and frank psychosis.
from irritability and anxiety to depression, delirium, and frank psychosis.
Life-threatening complications
