A deficiency of parathyroid hormone (PTH), hypoparathyroidism is caused by disease, injury, surgical removal, or congenital malfunction of the parathyroid glands. Because the parathyroid glands primarily regulate calcium balance, hypoparathyroidism causes hypocalcemia, producing neuromuscular symptoms ranging from paresthesia to tetany.
The clinical effects of hypoparathyroidism are usually correctable with replacement therapy. Some complications of long-term hypocalcemia, such as cataracts and basal ganglion calcifications, are irreversible.
Hypoparathyroidism may be acute or chronic and is classified as idiopathic or acquired:
Idiopathic hypoparathyroidism may result from an autoimmune genetic disorder or the congenital absence of the parathyroid glands.
Acquired hypoparathyroidism commonly results from accidental removal of or injury to the parathyroid glands during thyroidectomy or other neck surgery or, rarely, from massive neck irradiation. It may also result from ischemic infarction of the parathyroid glands during surgery or from hemochromatosis, sarcoidosis, amyloidosis, tuberculosis, neoplasms, or trauma.
Acquired, reversible hypoparathyroidism may result from hypomagnesemia-induced impairment of hormone synthesis and release, from suppression of normal gland function due to hypercalcemia, or from delayed maturation of parathyroid function.
PTH isn’t regulated by the pituitary or hypothalamus. It normally maintains blood calcium levels by increasing bone resorption and GI absorption of calcium. It also maintains an inverse relationship between serum calcium and phosphate levels by inhibiting phosphate reabsorption in the renal tubules. Abnormal PTH production disrupts this balance. Incidence of the idiopathic and reversible forms is highest in children; incidence of the irreversible acquired form is highest in older patients who have undergone surgery for hyperthyroidism or other head and neck conditions.
Signs and symptoms
Although mild hypoparathyroidism may be asymptomatic, it usually produces hypocalcemia and high serum phosphate levels that affect the central nervous system (CNS) as well as other body systems.
In the chronic form, hypoparathyroidism typically causes neuromuscular irritability, increased deep tendon reflexes, Chvostek’s sign (hyperirritability of the facial nerve, producing a characteristic spasm when it’s tapped), dysphagia, organic brain syndrome, psychosis, mental deficiency in children, and tetany.