Pseudohypoparathyroidism presenting with rickets.

Pseudohypoparathyroidism (PHP) is a condition characterized by hypocalcemia, hyperphosphatemia, and an impaired phosphaturic response to exogenous parathormone (PTH). A minority of patients with PHP have associated bone disease, and in some the radiological appearances have been suggestive of rickets. We report a patient with PHP who had epiphyseal enlargement and bowing of the long bones similar to that seen in rickets. Radiology showed generalized osteomalacia with failure of epiphyseal calcification 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, magnesium, 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 microgram/liter; 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 reabsorption of phosphate (46--52.6 mg/liter glomerular filtration rate; normal, 38 +/- 5). Intravenous PTH infusion tests were performed on the patient and a control subject before and 6 months after serum calcium 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 microgram/day. It is considered that renal resistance to PTH is his primary abnormality, with the bone disease representing a secondary phenomenon.