Clin Osteol 2016; 21(4): 136-141

Tumor-induced hypophosphatemia with osteomalacia - a case reportCase reports

E. Lokočová, N. Cibiček, P. Horák, P. Flodrová, J. Zadražil

Hypophosphatemia is a frequently overlooked laboratory finding as the signs are mostly non-specific. However, it causes considerable morbidity and may contribute to increased mortality of the affected patients. There are three main causes of hypophosphatemia: in­ creased renal secretion, decreased intestinal absorption or transfer of phosphates from the extra- to the intracellular space. Presented is a rare case of acquired hypophosphatemic osteomalacia in a 68-year-old female presenting with pains in the spine, ribcage, long bones and pelvis. Biochemistry tests showed marked hypophosphatemia (0.49 mmol/L) and an elevated level of the bone isoenzyme of alkaline phosphatase (97 ug/L) with a considerably decreased renal phosphate threshold (0.58 mmol/L) and a markedly increased FGF-23 level (90.76 ng/L). A PET/CT scan showed viable tumor tissue in the posterior part of the sacrum. The tumor was neurosur­ gically removed. Histological examination showed a giant cell tumor requiring subsequent cancer therapy. The clinical condition im­ proved considerably after treatment with potassium dihydrogen phosphate, calcium replacement and vitamin D3; the laboratory fin­ dings were less favorable. This is a typical example of tumor-induced osteomalacia. This relatively rare acquired osteomalacia usually accompanies benign mesenchymal tumors. It is caused by tumors producing phosphatonins, in particular FGF-23, inhibiting reab­ sorption of phosphorus in the proximal renal tubule and decrease calcitriol synthesis. Also discussed is the differential diagnosis of hy­ pophosphatemia.

Keywords: hypophosphatemia, tumor-induced osteomalacia, giant cell tumor, FGF-23

Published: December 11, 2016  Show citation