Healing of tumor-induced osteomalacia as assessed by high-resolution peripheral quantitative computed tomography is not similar across the skeleton in the first years following complete tumor excision

Tumor-induced osteomalacia is caused by excessive fibroblast growth factor 23 production mainly from phosphaturic mesenchymal tumors. Surgical excision or tumor ablation are the preferred treatment. Information on bone microarchitecture parameters assessed by high-resolution peripheral quantitative computed tomography is limited. We report a woman with hypophosphatemic osteomalacia with generalized pain, weakness and recurrent fractures, and a large thoracic vertebral mass extending to the posterior mediastinum. Detailed radiologic and histopathologic evaluation revealed a phosphaturic mesenchymal tumor. Two surgeries were necessary for complete removal of the mass. Clinical symptoms improved after attaining normophosphatemia. Four-year post-surgical HR-pQCT parameters, compared to baseline, showed in the left distal radius, stable trabecular and cortical volumetric bone mineral density although below reference range. There was stability of trabecular number and thickness. Both stiffness and failure load decreased. A shift in cortical parameters was noted in year 2. In the left distal tibia, trabecular volumetric bone mineral density decreased whereas cortical volumetric bone mineral density markedly increased, as did cortical area. There was stability in the trabecular number and thickness. Both stiffness and failure load improved. Findings from HR-pQCT measurements in this patient disclosed that the healing of osteomalacia is not similar across the peripheral skeletal sites in the first years following tumor removal. Results contrasted low but stable volumetric bone mineral density in the distal radius with increase in the distal tibia at the expense of cortical bone. Our report helps further delineate the pattern of bone healing after treatment of this rare bone disorder.