Phosphaturic mesenchymal tumor of spinal nerve in a patient with osteomalacia and multiple fractures

Abstract

Osteomalacia associated with a neoplasm (oncogenic osteomalacia, OO) is a rare and unusual paraneoplastic syndrome that subsides after complete tumor resection. It results from hypophosphatemia due to renal phosphate loss [6]. OO was originally reported by McCance in 1947 in a patient with a femoral tumor, while Prader et al. described its direct correlation with giant cell reparative granuloma of the rib [3]. The term phosphaturic mesenchymal tumor (PMT) was proposed by Weidner and Santa Cruz [7] in 1987 and the largest series was reported by Folpe et al. [3] in 2004. OO depends on tumor secretion of phosphatonins. Fibroblast growth factor-23 (FGF23), which is expressed in almost 90% of PMTs, plays a significant role in the pathogenesis of OO [3]. We report a 56-year-old female with osteomalacia and multiple fractures associated with PMT developing within the Th5 nerve. Laboratory examination disclosed hypophosphatemia (1.9 mg/dl), elevated serum alkaline phosphatase activity (217 U/l), and normal serum calcium level (9.07 mg/dl). Parathyroid and thyroid gland dysfunction and multiple myeloma were excluded as a potential cause of the osteolysis. CT and MRI scans revealed an extradural spindle lesion measuring 30 9 22 mm within the confines of the Th5 nerve. It compressed the meninges and the spinal cord (Fig. 1). The tumor was resected with the surgical diagnosis of neurofibroma. After surgery, blood concentrations of calcium and phosphate gradually returned to normal levels. In the following 6 months the bone lesions receded. Morphologically, the tumor was delivered in pieces measuring up to 1 cm in the largest diameter. Microscopically, cellular areas of the tumor were intermingled with hypocellular ones (Fig. 2a). The tumor cells were monomorphous with bland nuclei (Fig. 2b). Small spindle cells were arranged in a storiform pattern. Small conglomerates of tumor cells were surrounded by a network of capillaries, but larger angulated vessels were also present. The hypocellular areas were rich in eosinophilic matrix with