Unusual case of phosphaturic mesenchymal tumor.

1 A 40‐year‐old patient was referred to the De‐ partment of Endocrinology, Medical Center for Postgraduate Education, Warsaw, Poland, due to prolonged and profound hypophospha‐ temia, causing pain, cramps, and weakness of the proximal muscles. The patient was treated with 1 μg calcitriol, 1 μg alphadiol, 1.0 g calcium, and 1500 mg/d phosphorus. The regimen had no effect on serum phosphorus concentrations and only a moderate effect on the clinical signs and symptoms. Calcium and parathormone levels were nor‐ mal, alkaline phosphatase slightly elevat‐ ed (137 U/l; normal range, 40–129 U/l), and serum phosphorus very low (0.41 mmol/l; range, 0.81–1.45 mmol/l). A 24‐hour urine collection showed high phosphorus excretion (66.5 mmol/24 h; range, 12.00–65.00 mmol/24 h). CLINICAL IMAGE