Tumor(s) Induced Osteomalacia—A Curious Case of Double Trouble

Abstract

We report a case of tumor-induced osteomalacia with evidence of synchronous multifocal fibroblast growth factor 23 (FGF23) production. The aim is to present a case of tumor-induced osteomalacia and to highlight the fact that incomplete removal of multifocal FGF23-producing tumors, which are not entirely picked up by functional imaging, could be the cause of treatment failure. The patient was treated in the Department of Endocrinology of a tertiary care center in India. We report the case of a 42-year-old male with tumor-induced osteomalacia. We treated the tumor-induced osteomalacia with staged surgery of the two tumors. The 18F-fluorodeoxyglucose (FDG)-avid lesion (considered the sole culprit lesion after functional imaging) was resected first, followed by the non-FDG-avid lesion. The sequential removal of both tumors resulted in complete cure. The patient had hypophosphatemia and hyperphosphaturia. C-Terminal FGF23 level was elevated. Positron emission tomography-computed tomography showed two lesions-an FDG-avid lesion in the right leg, and a non-avid lesion in the left thigh. After removal of the FDG-avid lesion, the hypophosphatemia persisted, and the FGF23 level showed only modest reduction. The patient had complete clinical and biochemical resolution only after removal of the second non-FDG-avid tumor. We present the case of a tumor-induced osteomalacia whose biochemical parameters did not improve after removal of the FDG-avid tumor initially. The possibility of multifocal FGF23 production was considered, and the second, non-FDG-avid lesion was resected, which resulted in complete cure. Thorough clinical examination and meticulous follow-up with documentation of the biochemical resolution are necessary for management of all patients with this rare disorder.