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Pagetic Osteosarcoma — SCE Rheumatology MCQ

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HardMetabolic Bone DiseasePagetic OsteosarcomaSCE Rheumatology

A 74-year-old man with polyostotic Paget disease of bone develops 6 weeks of progressive pain at rest and at night in his previously affected femur, with an enlarging thigh swelling. Serum total alkaline phosphatase has risen substantially, with normal bilirubin and gamma-glutamyl transferase. He is afebrile and his C-reactive protein is normal. Radiographs show new permeative osteolysis, cortical breach and an extraosseous soft-tissue mass containing irregular cloud-like mineralisation. Which diagnosis best accounts for these findings?

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Correct answer: C — Osteosarcoma arising in pagetic bone

The diagnosis is Paget-associated osteosarcoma. The key features are a new pattern of progressive rest and night pain, swelling, destructive permeative osteolysis, cortical breach and an extraosseous mass producing irregular osteoid-like mineralisation within pagetic bone. Paget-associated sarcomas are rare and aggressive; most are osteosarcomas and typically occur in older adults. A pathological fracture may complicate either Paget disease or sarcoma but does not itself explain an osteoid-producing soft-tissue mass. Osteomyelitis can cause cortical destruction, although the normal inflammatory profile and mineralised tumour matrix make it less likely. Giant-cell tumour is a recognised but less common pagetic neoplasm and is generally expansile and lytic rather than osteoid-producing. Bone lymphoma also does not characteristically produce a mineralised osteoid matrix. The ALP rise supports increased bone turnover but is not independently diagnostic or discriminatory.

Reference: Tilden W, Saifuddin A. An update on imaging of Paget's sarcoma. Skeletal Radiology. 2021;50:1275-1290. https://pubmed.ncbi.nlm.nih.gov/33386903/