A Rare Case of Phosphaturic Tumor/Oncogenic Osteomalacia - Diagnostic Challenges and Management Algorithm

INTRODUCTION: Oncogenic osteomalacia is a rare paraneoplastic syndrome of acquired hypophosphatemic osteomalacia, resulting from a deficit in renal tubular phosphate reabsorption, in which fibroblast growth factor 23 seems to be implicated. CASE REPORT: A 42-year-old male presented with complaints of low back pain for the past 4 years and inability to walk for the past 3 years. Blood investigations showed hypophosphatemia and elevated serum alkaline phosphatase. Radiographs and magnetic resonance imaging revealed features of osteomalacia. DOTONAC PET-computed tomography (CT) showed a lesion in the greater trochanter suggestive of a phosphaturic mesenchymal tumor. CT-guided biopsy of the lesion was done which confirmed the diagnosis. The tumor was resected by intralesional methods (burring and cementation) with correction of hypophosphatemia by oral phosphorus supplementation. Patient clinically improved and was able to walk with support at the time of discharge. CONCLUSION: Phosphaturic tumor was localized to be in the posterior aspect of the right greater trochanter. To find the tumor was a major diagnostic challenge involving various diagnostic modalities. The occurrence of such a condition is rare and it may take even years to correctly diagnose the disease.