Plasmacytoma

Part of plasma cell proliferative disordersPathology/Plasma cell proliferative disorders

Definition

A localized collection of neoplastic monoclonal plasma cells without systemic features of multiple myeloma (e.g., no CRAB symptoms, marrow involvement, or myeloma-defining biomarkers).

Subtypes

1. Solitary Bone Plasmacytoma (SBP)

• Most commonly affects axial skeleton (vertebrae, ribs, skull, pelvis).
• Often presents with bone pain or pathological fracture.

Imaging: lytic lesion without sclerotic margin; MRI shows T1 hypointense, T2 hyperintense lesion with soft tissue component.

2. Extramedullary Plasmacytoma (EMP)

• Arises in soft tissue, especially head and neck mucosa (e.g., nasal cavity, oropharynx).

Imaging: well-defined enhancing soft tissue mass without bone destruction (unless secondarily invaded).

Rare Variant

Multiple Plasmacytomas Without Myeloma

• Very uncommon
• Can present as multiple bone or soft tissue lesions
• Not considered MM unless any of the following are met:
  • Bone marrow plasma cells <10%
  • No CRAB features
  • No myeloma-defining biomarkers (e.g., BM clonal cells ≥60%, >1 MRI focal lesion, FLC ratio >100)
• Often termed multiple solitary plasmacytomas (MSP)
• High risk of progression → requires close follow-up

Diagnosis

• Clonal plasma cells confirmed by biopsy
• Bone marrow: <10% clonal plasma cells
• Absence of CRAB or MM-defining event
• Whole-body MRI or PET/CT for staging (to exclude systemic disease)

Management

• Radiotherapy is mainstay (high radiosensitivity)
• Surgery only for diagnostic biopsy or mechanical stabilization
• Systemic therapy only if progression to MM

Prognosis

• ~50–60% progress to MM within 10 years
  • Risk higher in SBP than EMP
• Lifelong follow-up: SPEP, FLC, and imaging

Key Imaging Clues

Related

• Multiple myeloma
• MGUS
• Smoldering myeloma