Introduction
Multiple myeloma (MM) is a plasma cell malignancy characterized by bone marrow infiltration, osteolytic lesions, and systemic complications (CRAB: hyperCalcemia, Renal dysfunction, Anemia, Bone lesions).
Radiology plays a central role in diagnosis, staging, treatment monitoring, and detecting complications.
Conventional Radiography (Skeletal Survey)
- Traditionally the first-line imaging in myeloma.
- Findings:
- Multiple “punched-out lytic lesions” without sclerotic rim.
- Common sites: skull (“raindrop skull”), spine, ribs, pelvis, proximal humerur & femur.
- Pathological fractures are frequent.
- Limitations:
- Needs ≥30–50% bone loss before changes appear.
- Underestimates disease burden.
CT (Computed Tomography)
- More sensitive than radiographs for cortical destruction.
- Useful for detecting:
- Small lytic lesions (<5 mm).
- Fracture risk evaluation.
- Guiding biopsy.
- Low-dose whole-body CT (WBCT) is now often preferred over skeletal survey in many centers.
MRI (Magnetic Resonance Imaging)
- Most sensitive modality for detecting marrow infiltration.
- Patterns of marrow involvement:
- Focal lesions.
- Diffuse infiltration.
- Variegated (“salt-and-pepper”).
- Normal (especially early disease).
- Advantages:
- Detects lesions before cortical bone destruction.
- Best for spinal cord compression and soft tissue plasmacytomas.
- Sequences: T1 (low signal in lesions), STIR (bright), DWI adds sensitivity.
PET-CT (FDG PET/CT)
- Detects metabolically active disease.
- Useful in:
- Staging.
- Treatment response assessment.
- Detecting extramedullary disease.
- Shows both bone lesions and systemic spread.
Imaging Guidelines (IMWG Recommendations)
- First-line: Whole-body low-dose CT or whole-body MRI.
- PET-CT for treatment response and follow-up.
- Plain X-rays are now less favored but may still be used in resource-limited settings.
Key Imaging Signs in Multiple Myeloma
- Raindrop skull (lytic punched-out lesions in the skull).
- Diffuse osteopenia with vertebral compression fractures.
- Plasmacytoma: solitary expansile lytic lesion with soft tissue mass.
📝 Teaching Points
- X-rays: detect classic lytic lesions but insensitive.
- CT: more sensitive for bone destruction.
- MRI: most sensitive for marrow disease and complications.
- PET-CT: best for metabolic activity and treatment monitoring.
- Shift in practice → from skeletal survey → whole-body CT/MRI as standard of care.
✅ Conclusion
Modern imaging has transformed myeloma care. While plain radiographs show the classic lytic lesions, whole-body MRI and PET-CT are now the gold standards for early detection, risk stratification, and response assessment. A multimodality approach ensures optimal patient management.
