[Phosphorus metabolism in a case of tumoral calcinosis]

Hyperphosphataemia with levels of 65 mg/l was found in a black African aged 20 with a 10-year history of tumour calcinosis. Levels of blood calcium, plasma ionised calcium, serum alkaline phosphatase, 24-hour urinary calcium and phosphate were all normal, as was renal function. Tubular phosphate reabsorption (TmP) was greater than 90 mg per litre of glomerular filtrate (N = 22-42). Levels of circulating parathyroid hormone, nephrogenic cAMP and serum vitamin D metabolites [25 OH D3, 24,25 (OH)2 D3 and 1,25 (OH)2 D3] were normal. The TmP fell by 36% on exogenous PTH stimulation (N = 30.25 +/- 6.7), and by 7.9% 120 min. after injection of acetazolamide. Our results confirm the conclusions of recent studies: patients with tumour calcinosis have disordered renal phosphate excretion with normal PTH secretion, normal PTH action on the renal tubule and normal vitamin D metabolism. In fact in these hyperphosphataemic patients, circulating 1,25 (OH)2 D3 levels would be expected to be low, whereas they were normal in our patient. An attempt at treatment with acetazolamide and phosphate chelating agents gave no significant results.