The Right Leg that Troubled the Left Leg.

Introduction: Oncogenic osteomalacia or tumor induced osteomalacia (TIO) is a rare acquired paraneoplastic syndrome characterized by defective bone mineralization secondary to release of Fibroblast Growth Factor-23 (FGF-23), a phosphaturic protein - released from small, slow-growing mesenchymal tumors. Here, we report such a case and how it was investigated.

Materials: A 31 year old female presented with history of left leg pain and difficulty in walking since 1 year. General and systemic examination were found to be within normal limits and initial diagnostic workup revealed elevated alkaline phosphatase. X-ray bilateral hip and legs showed pseudo fractures of femur and tibia. Hence a probable diagnosis of metabolic bone disease was considered and further workup showed isolated hypophosphatemia. Patient was worked up for hypophosphatemic osteomalacia and further investigations showed low Tmp-GFR with a high FGF23 level. Hence a diagnosis of oncogenic osteomalacia was considered and a whole body PET scan was done which showed evidence of mesenchymal tumor in the right lower limb. Removal of the tumor resulted in resolution of symptoms and hence the diagnosis of oncogenic osteomalacia was confirmed.

Result: Hypophosphatemia Normal S. Calcium and S. Vitamin D3 levels Conclusion: Oncogenic osteomalcia is a rare paraneoplastic form of renal phosphate wasting that results in severe hypophosphatemia and has excellent prognosis as surgical removal of the causative tumor results in dramatic improvement. High index of suspicion combined with prompt investigations can result in early diagnosis of the causative tumor and proper surgical treatment which will improve outcomes. Reference Chong WH, Molinolo AA, Chen CC, et al. Tumor-induced osteomalacia. Endocr Relat Cancer 2011;18(3):R53-R77.