Successful Resection of FGF-23-Producing Tumor Resolves Severe Tumour-Induced Osteomalacia in a 40s Male

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting, often caused by Phosphaturic Mesenchymal Tumours (PMTs). These tumors overproduce fibroblast growth factor-23 (FGF-23), a hormone that inhibits renal phosphate reabsorption and vitamin D activation, leading to severe hypophosphatemia and bone demineralization. Diagnosing PMTs is a significant challenge due to their rarity, non-specific symptoms, and varied histological appearance, often resulting in prolonged morbidity and delayed treatment for affected patients.

This case report details a male patient in his late forties presenting with generalised body ache, weakness, and difficulty in walking for 3 years. Initial biochemical investigations revealed increased renal phosphate wasting. Functional imaging, specifically a somatostatin receptor-expressing lesion scan, identified a suspicious lesion in the distal epiphysis of the left tibia. A subsequent CT scan was performed to precisely localize the PMT, which was then resected en bloc. Postoperatively, the patient received oral phosphate and vitamin D supplementation.

Biochemical analysis confirmed significant renal phosphate wasting, consistent with tumour-induced osteomalacia. Functional imaging successfully pinpointed a somatostatin receptor-expressing lesion in the left tibia, which was subsequently confirmed as a Phosphaturic Mesenchymal Tumour (PMT) via CT scan and histological examination post-resection. The surgical removal of the tumor was critical for patient recovery. Post-operative management included oral phosphate and vitamin D supplementation. > The patient achieved complete recovery from symptoms and normalization of biochemical parameters at 1-year follow-up, demonstrating the curative potential of complete tumor resection. This outcome underscores the importance of accurate diagnosis and timely intervention in such cases.