Tertiary hyperparathyroidism after long-term phosphate supplementation in adult-onset hypophosphataemic osteomalacia.

We report the development of tertiary hyperparathyrodism in a patient with a sporadic form of adult-onset hypophosphataemic osteomalacia who had been treated with vitamin D or calcitriol and large doses of phosphate. This observation suggests that even with concomitant vitamin D or calcitriol therapy, long-term oral phosphate supplementation may lead to the development of hypercalcaemic hyperparathyrodism. Caution is recommended when relatively large doses of phosphate are used to treat hypophosphataemic osteomalacia of diverse causes.