Nejm 2008;359:391; 2000;343:1863

Cause:

• Postthyroidectomy
• Acquired: renal failure, hypomagnesemia, alcoholism (by hypomagnesemia or direct suppression of PTH—Nejm 1991;324:721)
• Familial types from genetic hormone defects
• AUTOIMMUNE POLYENDOCRINOPATHY CANDIDIASIS/ECTODERMAL DYSTROPHY(Nejm 1990;322:1829); 80% are hypoparathyroid, 70% are hypoadrenal, 60% of women with it are hypogonadal while 15% of men with it are; by age 20 yr, 100% have had significant candidial infections

Pathophys:

PTH necessary for osteoclastic response to low calcium, renal tubular calcium resorption and PO₄ excretion, and vit D activation

Alkalosis due to blocked PTH stimulation of organic acid production in bones (Ann IM 1972;76:825); monilia infections due to suppressor T-cell defects (Nejm 1979;300:164)

Associated with Addison's, PA, Hashimoto's, DiGeorge syndrome (3rd and 4th pharyngeal pouches)

Sx:of hypocalcemia: circumoral paresthesias, carpal-pedal spasms, stridor, seizures (brief, mild), bronchospasm, gi cramps, anxiety, cataracts

Si:of hypocalcemia: tetany (carpal-pedal spasm, Chvostek's si and Trousseau's si); cataracts, vascular corneal opacities (band keratopathy), psychiatric changes, dystonias, and dyskinesias (Nejm 1972;286:762)

Pustular psoriasis and dermatitis herpetiformis (Ann IM 1984;100:677)

r/o: PSEUDOHYPOPARATHYROIDISM,which is genetic, sex-linked vs dominant; associated with hypopituitarism, esp types with low TSH and gi lactase deficiency; end-organ (bone and kidney) defect in cyclic AMP protein receptor for PTH as well as other hormones, eg, TSH (Ann IM 1986;105:197); si of hypercalcemia and mental retardation, short stature and phalanges; hypoplastic carious teeth; dx w Ellsworth-Howard test: iv PTH causes no increase in phosphate excretion (<25 mg/h) and/or no increase in cAMP excretion (Ann IM 1988;109:800)

FAMILIAL HYPERCALCIURIC HYPOCALCEMIA from defective calcium-sensing receptor (Nejm 1996;335:1115)

Lab:

Chem:Hypocalcemia, r/o hypoalbuminemia (Calcium Levels, Corrected in Serum for correction formulas), lung cancer or its rx, leukemia, rickets/osteomalacia, thyrocalcitonin-producing medullary carcinoma of the thyroid?, pancreatitis

Serum PO₄ elevated; metabolic alkalosis

Urine:Hypocalciuria

Xray:Skull films may show basal ganglia calcification (Nejm 1971;285:72)