SUMMARY

We report the development of tertiary hyperparathyroidism 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 hyperparathyroidism. Caution is recommended when relatively large doses of phosphate are used to treat hypophosphataemic osteomalacia of diverse causes. KEY WORDS: Hypophosphataemic osteomalacia, Long-term phosphate therapy, Tertiary hyperparathyroidism. PARATHYROID function is generally described as normal in patients with hypophosphataemic osteomalacia before initiation of therapy with phosphate salts; however, hyperparathyroidism is an occasional complication of treatment. The sporadic adult-onset form of hypophos-phataemic osteomalacia responds to treatment with phosphate, calcium and vitamin D or calcitriol, and it is generally believed that this combination (especiall