Tumor-Induced Osteomalacia Caused by a Bone Tumor in the Ulna

Hypophosphatemic osteomalacia induced by overproduction of fibroblast growth factor 23 (FGF23) by a tumor is a relatively rare paraneoplastic syndrome that recently has been recognized. During the course of the disease, termed “tumor-induced osteomalacia” (TIO), the level of phosphorus in the blood becomes reduced as a result of accelerated diuresis due to excessive FGF23 production by the tumor, resulting in bone calcification dysfunction in the entire body, which leads to osteomalacia1-4. TIO most commonly develops in middle-aged adults, with no differences between men and women. Clinically, it is characterized by general bone pain, muscular weakness, and pathological fractures. A TIO-like syndrome can also be seen in association with other diseases such as prostate cancer, small-cell carcinoma (oat cell cancer), hematologic malignancies, neurofibromatosis, epidermal nevus syndrome, and polyostotic fibrous dysplasia of bone5-15. We describe a tumor resection and ulnar bone reconstruction in a patient with an ulnar tumor that caused TIO. The patient was informed that data concerning the case would be submitted for publication, and he provided consent. A forty-nine-year-old left-handed man presented to our department with pain in the left forearm. There was no appreciable family or previous medical history. He worked as a delivery person. Plain radiographic findings revealed a cystic lesion of the bone and a pathological fracture in the diaphysis of the left ulna. Moreover, a Looser zone, which is a lucent band adjacent to the periosteum representing an unhealed insufficiency-type stress fracture commonly associated with osteomalacia, was seen in the diaphysis of the left radius (Fig. 1). Systemic bone disease was suspected. The patient initially had noticed bone pain throughout the entire body about two years prior, but did not seek treatment. Fig. 1 Anteroposterior (top) and lateral (bottom) radiographs show a cystic lesion and pathological fracture in the …