Osteosarcomatous Transformation in Paget’s Disease of Bone: Detection on Bone Scintigraphy with SPECT/CT

Paget’s disease of bone (PDB) is a chronic metabolic disorder of bone remodelling characterised by excessive osteoclastic resorption followed by disorganised osteoblastic bone formation. Although generally benign, malignant transformation to osteosarcoma is a rare but serious complication associated with poor prognosis. We report a 47-year-old female with known PDB who presented with a progressively enlarging scalp swelling. Technetium-99m methylene diphosphonate (Tc-99m MDP) whole-body bone scintigraphy demonstrated intense tracer uptake in the left skull region with diffuse increased calvarial uptake. Single-photon emission computed tomography/computed tomography (SPECT/CT) revealed a scintigraphically active expansile lesion involving the left temporal and parietal bones with extracalvarial soft-tissue and intracranial extension, raising suspicion for sarcomatous transformation. Histopathological examination confirmed osteosarcoma, with immunohistochemical positivity for SATB2 and CD99. This case underscores the role of bone scintigraphy with SPECT/CT in raising early suspicion of malignant transformation in PDB.