Pseudohypoparathyroidism Presenting with Rickets

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Abstract
Psuedohypoparathyroidism (PHP) is a condition characterized by hypocalcemia, hyperphosphatemia and an impaired phosphaturic response to exogenous parathormone (PTH). A minority of patients with PHP had associated bone disease and in some the radiological appearances have been suggestive of rickets. A patient with PHP who had epiphyseal enlargement and long bone bowing similar to that seen rickets is reported. Radiology showed generalized osteomalacia with epiphyseal calcification failure and several pseudofractures. Bone biopsy showed increased osteoid seams. The phalanges of both hands showed subperiosteal erosions consistent with hyperparathyroidism. Biochemically, he had persistent hypocalcemia, hyperphosphatemia and an elevated alkaline phosphatase. Plasma calcitonin, Mg and 25-hydroxycholecalciferol levels were normal. The 1,25-dihydroxycholecalciferol level was within the normal adult range but was probably inappropriately low for an adolescent. Plasma parathormone was elevated (1.3-1.7 .mu.g/l, normal, < 0.73). His diet was not deficient in vitamin D. Gastrointestinal function was normal. Renal function was normal, apart from an increase in the maximum tubular phosphate reabsorption (46-52.6 mg/l glomerular filtration rate; normal, 38 .+-. 5). PTH infusion (i.v.) tests were performed on the patient and a control subject before and 6 mo. after serum Ca levels had returned to normal. The maximum increases in cAMP excretion in the patient were 0.03 and 0.05 mmol/g creatinine before and after treatment, respectively (control, 0.53 and 0.24); the maximum increases in phosphate excretion in the patient were 0.14 and 0.04 mmol/g creatinine before and after treatment, respectively (control, 0.32 and 0.07). He responded to initial treatment with a high dose of calciferol and later to 1,25-dihydroxycholecalciferol in a dose of 1 .mu.g/day. Apparently, renal resistance to PTH is his primary abnormality, with the bone disease representing a secondary phenomenon.