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Plasmacytoma

Summary

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  • Plasmacytoma is a localised neoplastic proliferation of plasma cells, occurring as solitary plasmacytoma of bone (SPB) or extramedullary plasmacytoma (EMP)
  • Clinical presentation varies based on location, with bone pain common in SPB and mass effect in EMP
  • Imaging plays a crucial role in diagnosis, staging, and treatment planning

Pathophysiology

  • Monoclonal proliferation of plasma cells, producing a single immunoglobulin type
  • Arises from post-germinal centre B cells
  • May progress to multiple myeloma in some cases
  • Genetic abnormalities include:
    • Chromosomal translocations involving the immunoglobulin heavy chain locus
    • Cyclin D dysregulation
    • RAS mutations

Demographics

  • Rare, accounting for <5% of plasma cell neoplasms
  • Median age at diagnosis: 55-65 years
  • Male predominance (male-to-female ratio 2:1 to 3:1)
  • SPB more common than EMP (2:1 ratio)
  • Higher incidence in African Americans compared to Caucasians

Diagnosis

  • Clinical presentation:
    • SPB: Bone pain, pathological fractures
    • EMP: Mass effect, local symptoms based on location
  • Laboratory findings:
    • Serum and urine protein electrophoresis
    • Serum free light chain assay
    • Complete blood count, calcium, and creatinine levels
  • Biopsy:
    • Essential for definitive diagnosis
    • Immunohistochemistry to confirm monoclonal plasma cell proliferation
  • Exclusion of systemic involvement:
    • Bone marrow biopsy (<10% clonal plasma cells)
    • Skeletal survey or whole-body imaging

Imaging

  • Radiography:
    • SPB: Lytic lesion without sclerotic rim
    • EMP: Soft tissue mass, may show bony erosion
  • CT:
    • Higher sensitivity for detecting small lesions
    • Useful for assessing cortical destruction and soft tissue extension
  • MRI:
    • Superior soft tissue contrast
    • SPB: T1 hypointense, T2 hyperintense, enhancing lesion
    • EMP: Well-defined, homogeneous mass with variable signal intensity
  • PET/CT:
    • High sensitivity for detecting lesions
    • Useful for staging and treatment response assessment
    • FDG-avid lesions
  • Whole-body low-dose CT:
    • Emerging modality for initial evaluation and follow-up
    • Lower radiation dose compared to conventional skeletal survey

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  • 60-year-old male presented with tingling in lower limbs and sudden loss of power.
  • There is a lucent lesion within T6 that is hyperintense on T2 and STIR.
  • There is hyperintense myelopathic signal change within the cord.

Treatment

  • Radiation therapy:
    • Primary treatment modality for both SPB and EMP
    • Typical dose: 40-50 Gy in 20-25 fractions
  • Surgery:
    • Consider for unstable SPB or resectable EMP
    • May be combined with radiation therapy
  • Chemotherapy:
    • Role in plasmacytoma management is controversial
    • May be considered for large tumours or high-risk patients
  • Follow-up:
    • Regular monitoring for disease progression or transformation to multiple myeloma
    • Includes serum protein electrophoresis, imaging studies, and bone marrow examination
  • Prognosis:
    • 5-year overall survival: 50-80%
    • 10-year progression-free survival: 50-60%

Differential diagnosis

Differential Diagnosis Differentiating Feature
Multiple myeloma Multiple punched-out lytic lesions; diffuse osteopenia; no isolated large solitary mass
Metastatic carcinoma Multiple lesions; heterogeneous enhancement; associated soft tissue component; permeative bone destruction
Lymphoma Permeative pattern with homogeneous enhancement; soft tissue mass; crosses disc space; no classic lytic punch-out
Giant cell tumour Soap bubble appearance; epiphyseal location; adjacent to articular surface
Chordoma Midline sacrum or clivus; T2 hyperintense with lobulated morphology; "honeycomb" trabeculation on CT
Osteosarcoma Osteoid matrix on CT; aggressive periosteal reaction; cortical breakthrough; sunburst pattern
Ewing sarcoma Onion-skin periosteal reaction; permeative pattern; aggressive soft tissue mass
Aneurysmal bone cyst Fluid-fluid levels on MRI; expansile thin cortical shell; multiple internal septations
Fibrous dysplasia Ground-glass appearance on X-ray, often polyostotic
Brown tumour Associated with hyperparathyroidism, multiple lesions