Tumour-Induced Osteomalacia Due To An Intra-Abdominal Mesenchymal Tumour

A 50-year-man presented with debilitating lower-limb proximal muscle weakness and hip pain since 3 years. Investigations (serum calcium (8.9mg/dL), serum phosphorus (1.5mg/dL), serum albumin (40g/L), parathyroid hormone (116pg/mL (12.30pmol/L)), 25(OH)D3 (25.2ng/mL (63nmol/L)) 1,25(OH)(2) D3 (19pg/mL (45.60pmol/L)), tubular reabsorption of phosphate of 0.22 and elevated serum fibroblast growth factor 23 (FGF23) (387.7 RU/mL)) were consistent with tumour-induced osteomalacia (TIO). Localisation studies (Ga-68 DOTATATE positron emission tomography (PET)/CT and (18)FDG-PET/CT) did not reveal any lesion. Re-evaluation after 2 and 5 years with Ga-68-DOTANOC PET/CT showed 2x1.4cm progressively increasing rounded soft tissue enhancing mass close to splenic hilum (SUV max: 26.4). Tumour was resected by laparotomy. Both FGF23 (120 RU/mL on day 3) and serum phosphorus (2.5mg/dL on day 10) normalised with significant clinical improvement after surgery. Histopathology revealed phosphaturic mesenchymal tumour. Here, we report the first case of intra-abdominal mesenchymal tumour causing TIO diagnosed by serial functional imaging.