Pagetic Osteosarcoma — SCE Rheumatology MCQ

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ModerateMetabolic Bone DiseasePagetic OsteosarcomaSCE Rheumatology

A 70-year-old man with longstanding Paget disease affecting the right tibia develops a 6-week history of rapidly worsening localised pain and swelling. A radiograph, compared with previous imaging, shows a new destructive lytic lesion breaching the cortex with an associated soft-tissue mass within the Pagetic bone. What is the most likely diagnosis?

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Correct answer: E — Pagetic osteosarcoma

The diagnosis is **Pagetic osteosarcoma**, a rare but serious malignant transformation arising within Pagetic bone, particularly in older patients with longstanding disease. Rapidly progressive focal pain and swelling, cortical destruction and an extraosseous soft-tissue mass are red flags for sarcomatous transformation. A skeletal metastasis can be destructive but is less specifically associated with transformation at a previously Pagetic site. Osteomyelitis may cause lysis and cortical destruction, but the absence of an infective context and the soft-tissue tumour mass favour sarcoma. A Pagetic insufficiency fracture should show a fracture line rather than an aggressive destructive mass. A gouty tophus does not explain this pattern of cortical breakthrough and malignant-appearing soft-tissue extension.

Reference: Hansen MF, Seton M, Merchant A. Osteosarcoma in Paget's disease of bone. Journal of Bone and Mineral Research. 2006;21(Suppl 2):P58-P63. https://pubmed.ncbi.nlm.nih.gov/2028867/