Tumor-induced osteomalacia caused by phosphaturic mesenchymal tumor in the thoracic spine: an uncommon site.

INTRODUCTION

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome primarily associated with phosphaturic mesenchymal tumors (PMTs). It is characterized by severe hypophosphatemia, muscle weakness, defective bone mineralization, and fractures. TIO often presents with nonspecific symptoms, and the tumors responsible are typically small and difficult to detect with imaging, making both diagnosis and localization challenging. The standard treatment for TIO is complete surgical resection of the tumor.

CASE PRESENTATION

A 54-year-old postmenopausal woman presented with generalized bone pain and proximal lower limb muscle weakness that began about 10 years ago. Despite various treatments, her musculoskeletal condition progressively worsened and was further complicated by a fracture at the base of the left femoral neck two years ago. She underwent multiple orthopedic surgeries, which were ultimately unsuccessful, leaving her wheelchair-dependent. Laboratory tests revealed persistent hypophosphatemia, elevated alkaline phosphatase, and increased urinary phosphate excretion. Suspecting renal phosphate wasting related to TIO, a [Ga]Ga-DOTATATE positron emission tomography/computed tomography (PET/CT) scan was performed, which identified a somatostatin receptor-positive lesion at the T12 vertebra. Magnetic resonance imaging (MRI) confirmed the presence of a T12 posterior vertebral body mass with extradural extension, causing compression of the thecal sac. The mass was surgically resected, and histopathology confirmed a PMT. Following surgery, the patient experienced significant biochemical and clinical improvement.

DISCUSSION

Delays in diagnosis and frequent misdiagnoses continue to pose major challenges in managing TIO. This case of a thoracic spinal PMT causing TIO underscores the rarity and diagnostic complexity associated with these tumors.