Bilateral femoral neck fractures and 11 rib fractures unmask tumour-induced osteomalacia caused by a phosphaturic mesenchymal tumour

Phosphaturic mesenchymal tumours (PMTs) are rare benign tumours that secrete fibroblast growth factor 23 (FGF23), leading to phosphate wasting, disordered vitamin D metabolism and impaired bone mineralisation, clinically known as tumour-induced osteomalacia. PMTs are frequently misdiagnosed due to rarity and non-specific presentation. We report a case of a male in his 60s who presented to the hospital with 7 years of progressive muscle weakness and diffuse pain, resulting in inability to walk. His work-up was significant for hypophosphataemia with imaging showing chronic bilateral femoral neck fractures and 11 posterior rib fractures. Copper-64 DOTA-Phe 1 -Tyr 3 -Thr 8 -octreotate positron emission tomography/CT demonstrated increased uptake within the left femur. Venous sampling revealed elevated FGF23. He underwent resection of the femoral tumour with histology consistent with PMT. Within 1 year of resection, the patient showed significant improvement. This case highlights the diagnostic challenge of PMTs and the dramatic improvement that can occur following resection.