Tumour-induced osteomalacia due to a rare intrathoracic phosphaturic mesenchymal tumour

Phosphaturic mesenchymal tumours (PMTs) are rare neoplasms that secrete fibroblast growth factor 23 (FGF23), a hormone that disrupts phosphate homeostasis and induces tumour-induced osteomalacia (TIO). This condition causes hypophosphataemia, bone pain, fractures and musculoskeletal weakness. Due to the non-specific nature of these symptoms, TIO is often misdiagnosed with treatment delays. Surgical resection of PMTs is curative with rapid normalisation of serum phosphorus and full symptom resolution. PMTs are often located in the extremities and axial skeleton but can also occur in less common areas such as the intrathoracic region. We report a case of an intrathoracic PMT in a young woman who suffered for over 2 years without a diagnosis. The PMT was identified on CT, MRI and fluorodeoxyglucose-positron emission tomography and confirmed by histopathology. The tumour was excised via combined video-assisted thoracoscopic surgery and posterior thoracic resection. Within 6 months, the patient experienced complete symptom resolution and normalised serum levels.