Tumor-Induced Osteomalacia Caused by Primary Fibroblast Growth Factor 23 Secreting Neoplasm in Axial Skeleton: A Case Report

Abstract

We report the case of a 66-year-old woman with tumor-induced osteomalacia (TIO) caused by fibroblast growth factor 23 (FGF-23) secreting mesenchymal tumor localized in a lumbar vertebra and review other cases localized to the axial skeleton. She presented with nontraumatic low back pain and spontaneous bilateral femur fractures. Laboratory testing was remarkable for low serum phosphorus, phosphaturia, and significantly elevated serum FGF-23 level. Magnetic resonance imaging (MRI) of the lumbar spine showed a focal lesion in the L-4 vertebra which was hypermetabolic on positron emission tomography (PET) scan. A computed tomography (CT) guided needle biopsy showed a low grade spindle cell neoplasm with positive FGF-23 mRNA expression by reverse transcriptase polymerase chain reaction (RT-PCR), confirming the diagnosis of a phosphaturic mesenchymal tumor mixed connective tissue variant (PMTMCT). The patient elected to have surgery involving anterior resection of L-4 vertebra with subsequent normalization of serum phosphorus. Including the present case, we identified 12 cases of neoplasms localized to spine causing TIO. To our knowledge, this paper represents the first documented case of lumbar vertebra PMT causing TIO. TIO is a rare metabolic bone disorder that carries a favorable prognosis. When a lesion is identifiable, surgical intervention is typically curative.

Surgical Treatments of Tumor-Induced Osteomalacia Lesions in Long Bones

“…To our knowledge, most publications about surgical excision of phosphaturic mesenchymal tumors have been case reports [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] , and very few were case series 2,33,34 . Phosphaturic mesenchymal tumors seem to be commonly located in long bones, but we are not aware of any studies comparing the results of curettage and segmental resection with a minimum one-year follow-up.…”

“…In our series, the serum P of all patients with complete resection returned to normal within fourteen days (mean, 6.5 days) after surgery, similar to the time previously described 1,2 , although we had four patients who developed recurrence even after normalization of serum P. In general, examination and management should be considered if serum P is still low at day 14 after surgery. However, FGF-23 appears to be the clinically relevant phosphatonin produced by phosphaturic mesenchymal tumors 27 , and serum FGF-23 levels usually return to normal within twenty-four hours; abnormal postoperative FGF-23 suggests a residual tumor. The increase of serum P follows more slowly after FGF-23 normalizes 2 , so changes of serum FGF-23 may be more sensitive than serum P to detect recurrence.…”

Comparison of 18F-FDG and 68Ga DOTATATE PET/CT in Localization of Tumor Causing Oncogenic Osteomalacia

“…18 F-FDG PET/CT Imaging 18 F-FDG PET/CT was performed in 4 of 6 patients to localize any tumor. All 6 patients had hypophosphatemic osteomalacia.…”

“…1,2 Patients with TIO usually present with clinical findings of osteomalacia, including bone and muscle pain, severe proximal muscle weakness, and occasionally pathological fractures. 18 F-FDG PET/CT has shown good sensitivity for localizing TIO tumors in several case reports. The localization of these tumors has always remained a challenge because they are small, slow growing, and located in peculiar or atypical sites.…”

Tumor-induced hypophosphatemia

“…These include computed tomography (CT), MRI, PET-CT, octreotide and sestamibi scans, and even bone scintigraphy. [8]…”