[Pseudo-idiopathic hypoparathyroidism]

Hypoparathyroidism can exist due to one or more of the following pathogenic mechanisms: 1) Parathyroid Hormone (PTH) deficit, b) biologically inactive PTH, c) PTH antagonists and d) target tissues defects. Biologically inactive PTH secretion, also named pseudo-idiopathic hypoparathyroidism, is an exceptional cause of hypoparathyroidism. We report a case of a patient with this illness. A 71-year-old male with a past history of cataracts since he was 48 was admitted to our hospital. Laboratory data showed a total calcium of 4.82 mg/dl, ionized calcium of 2.72 mg/dl, serum phosphate 5.30 mg/dl, intact PTH 83 pg/ml (N 15-60), osteocalcin 2,4 ng/ml (N 9-30), tubular resorption of phosphate 96% and 1.25 di-hydroxycholecalciferol 7 pg/ml (N 18-78); creatinine and magnesium values were between normal limits. The Ellsworth-Howard test showed a normal response of both urinary c-AMP excretion and phosphaturia to PTH. We review the diagnostic clues of hypoparathyroidism and the value of the Ellsworth-Howard test in order to enable distinction between the several variants of the syndrome.