Hypoparathyroidism

Transient hypoparathyroidism is common after thyroidectomy, but permanent hypoparathyroidism occurs after < 3% of such thyroidectomies done by experienced surgeons. Manifestations of hypocalcemia usually begin about 24 to 48 hours postoperatively but may occur after months or years. PTH deficiency is more common after radical thyroidectomy for cancer or as the result of surgery on the parathyroid glands (subtotal or total parathyroidectomy). Risk factors for severe hypocalcemia after subtotal parathyroidectomy include

Idiopathic hypoparathyroidism is uncommon. It can be due to sporadic or inherited conditions in which the parathyroid glands are absent or atrophied. It manifests in childhood. The parathyroid glands are occasionally absent, and thymic aplasia and abnormalities of the tissue arising from the branchial arches (DiGeorge syndrome DiGeorge Syndrome DiGeorge syndrome is thymic and parathyroid hypoplasia or aplasia leading to T-cell immunodeficiency and hypoparathyroidism. Infants with DiGeorge syndrome have low-set ears, midline facial... read more ) are present.

Other causes include polyglandular autoimmune failure syndrome Polyglandular Deficiency Syndromes Polyglandular deficiency syndromes are characterized by sequential or concurrent deficiencies in the function of several endocrine glands that have a common cause. Etiology is most often autoimmune... read more , autoimmune hypoparathyroidism associated with mucocutaneous candidiasis Candidiasis (Mucocutaneous) Candidiasis is skin and mucous membrane infection with Candida species, most commonly Candida albicans. Infections can occur anywhere and are most common in skinfolds, digital... read more , and X-linked recessive idiopathic hypoparathyroidism.

Pseudohypoparathyroidism is an uncommon group of disorders characterized by target organ resistance to PTH, not by hormone deficiency. Genetic transmission of these disorders occurs through different modes of inheritance (ie, autosomal recessive, dominant, and x-linked forms) and different genes (and genes that control these genes) that all play a role in a complex pathway.

Type Ia pseudohypoparathyroidism (Albright hereditary osteodystrophy) is caused by a mutation in the stimulatory Gs-alpha1 protein of the adenylyl cyclase complex (GNAS1). The result is failure of normal renal phosphaturic response or increase in urinary cAMP (cyclic adenosine monophosphate) to PTH.

Patients are usually hypocalcemic and hyperphosphatemic. Secondary hyperparathyroidism and hyperparathyroid bone disease can occur. Associated abnormalities include short stature, round facies, intellectual disability with calcification of the basal ganglia, shortened metacarpal and metatarsal bones, mild hypothyroidism, and other subtle endocrine abnormalities.

Because only the maternal allele for GNAS1 is expressed in the kidneys, patients whose abnormal gene is paternal do not have hypocalcemia, hyperphosphatemia, or secondary hyperparathyroidism; this condition is sometimes described as pseudopseudohypoparathyroidism, although patients have many of the somatic features of the disease.

Type Ib pseudohypoparathyroidism is less well known. Affected patients have hypocalcemia, hyperphosphatemia, and secondary hyperparathyroidism but do not have the other associated abnormalities.

Type II pseudohypoparathyroidism is even less common than type I. In affected patients, exogenous PTH raises the urinary cAMP normally but does not raise serum calcium or urinary phosphate. An intracellular resistance to cAMP has been proposed.