Repeated Venous Sampling for Determination of a Gradient of Fibroblast Growth Factor 23 for Localization of an Osteomalacis Causing Tumor

Abstract

Background: Oncogenic osteomalacia (OOM) is a rare syndrome caused by a tumor that produces a phosphaturic factor: fibroblast growth factor 23 (FGF23). These tumors can be extremely difficult to localize because they are small, slow growing and cause no local Symptoms. Patient and methods: Venous sampling for detection of a gradient of FGF23 has been used to limit the area of further imaging. We describe a case of OOM in a 73-year old woman, with two years of spontaneous fractures, severe musculoskeletal pain and phosphate wasting. Results: Her scrum FGF23 level was increased and whole-body intravenous sampling (11 sites) revealed a FGF23 gradient from the right leg. The second sampling indicated that the source of FGF23 was below the knee, but imaging studies, including magnetic resonance imaging and octreotide scintigraphy, were not conclusive. A third sampling demonstrated increasing FGF23 the more distal one came in the lower leg. Imaging of the forefoot finally identified a 10 mm tumor that was removed. Histopathological examination showed a phosphaturic mesenchymal tumor of mixed connective tissue type. The phosphate level and symptoms improved in days after surgery. Conclusion: Repeated determinations of a venous gradient of FGF23 may be used to localize tumors of OOM.