What is Hypoparathyroidism?
A deficiency in parathyroid hormone (PTH) secretion by the parathyroid glands or the decreased action of PTH in the periphery causes 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 by stimulating renal conversion of vitamin D to its active form, which enhances GI absorption of calcium. PTH 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 of Hypoparathyroidism
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 secretion, from suppression of normal gland function due to hypercalcemia, or from delayed maturation of parathyroid function.
Signs & Symptoms of Hypoparathyroidism
It is often accompanied by the following Signs and symptoms:
The following Signs and symptoms often appear in children with hypoparathyroidism:
Radioimmunoassay for PTH shows diminished serum PTH concentration. Blood and urine tests reveal decreased serum and urine calcium levels, increased serum phosphate levels (more than 5.4 mg/dl), and reduced urine creatinine levels. X-rays indicate greater bone density and malformation. Electrocardiogram (ECG) changes disclose increased QT and ST intervals due to hypocalcemia.
Because calcium absorption from the small intestine depends on the presence of activated vitamin D, treatment initially includes vitamin D, with or without supplemental calcium. Such therapy is usually lifelong, except in patients with reversible hypoparathyroidism. If the patient can't tolerate vitamin D because of hepatic or renal problems, calcitriol may be used.
Acute, life-threatening tetany calls for immediate I.V. administration of 10% calcium gluconate, 10% calcium gluceptate, or 10% calcium chloride to raise ionized serum calcium levels. Sedatives and anticonvulsants may control muscle spasms until calcium levels rise. Chronic tetany calls for maintenance of serum calcium levels with oral calcium supplements.
If you thyroid or neck surgery, watch for early Signs of hypoparathyroidism so that treatment with calcium and vitamin D supplements can be started promptly.
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