Tertiary hyperparathyroidism in X-linked hypophosphatemic rickets

We report a case of tertiary hyperparathyroidism in an X-linked familial hy pophosphatemic rickets (XLH) patient under regular calcitriol and self-adju sted large doses of oral phosphate salt (2.4-3.6 g/day in 4-5 divided doses ) according to his serum phosphate level. Tertiary hyperparathyroidism is a n unusual complication of XLH patients during treatment. As there is growin g evidence that a high phosphate diet may induce hyperplasia of the parathy roid glands, it is important to avoid the stimulation of the parathyroid gl ands by high doses of phosphate administration in XLH patients. Serum calci um, phosphate, alkaline phosphatase, and also parathyroid hormone should be measured regularly in order to facilitate an early diagnosis of secondary hyperparathyroidism during the treatment of XLH patients, since this stage is reversible with calcitriol and reduced doses of phosphate salt.