What is the rationale for using spine MRI (Magnetic Resonance Imaging) and pelvis MRI as part of the initial workup for a patient suspected of having multiple myeloma, and would a complete X-ray of the femur and tibia also be recommended?

Rationale for Spine and Pelvis MRI in Multiple Myeloma Workup

Spine and pelvis MRI is mandatory in the initial workup of suspected multiple myeloma because it detects occult bone marrow involvement that skeletal surveys miss, and the presence of more than one focal lesion ≥5mm on MRI now defines symptomatic disease requiring treatment, even without lytic bone destruction. 1, 2

Why Spine and Pelvis MRI is Essential

Detection of Occult Disease

• MRI identifies bone marrow infiltration before bone destruction occurs, making it far more sensitive than plain radiographs for early disease detection 2
• The spine and pelvis are the most common sites of myeloma involvement, and MRI is superior to skeletal surveys for detecting abnormalities specifically in these anatomical regions 3
• 25.5% of patients show positive findings on advanced imaging despite negative skeletal surveys, meaning one in four patients would be missed by X-rays alone 3

Diagnostic and Prognostic Impact

• The International Myeloma Working Group now requires spine and pelvis MRI (or whole-body MRI if available) in all patients with smoldering/asymptomatic myeloma because more than one focal lesion >5mm upgrades the diagnosis to symptomatic myeloma requiring immediate treatment 2
• MRI pattern (focal, diffuse, or variegated) provides critical prognostic information and predicts progression risk in asymptomatic patients 1
• MRI can detect unsuspected lesions that change staging and management, particularly in identifying patients at risk for rapid progression 1

Specific Clinical Scenarios

• MRI of spine and pelvis is absolutely mandatory in all patients with presumed solitary plasmacytoma to exclude additional occult lesions that would change the diagnosis to multiple myeloma 1, 4
• For patients with bone pain, MRI is the gold standard for evaluating painful lesions and distinguishing benign versus malignant vertebral fractures 2
• MRI detects spinal cord or nerve compression and soft tissue masses that require urgent intervention 2

Complete X-rays of Femur and Tibia: Yes, Include Them

Complete X-rays of the femur should be included in the skeletal survey, but tibia X-rays are not part of standard recommendations. 1

Rationale for Femur X-rays

• The standard skeletal survey explicitly includes anteroposterior and lateral views of the femora to detect long bone lesions at risk of impending pathologic fracture 1
• Plain radiographs remain important for assessing cortical bone destruction and fracture risk in weight-bearing long bones, which MRI may underestimate 3
• Detecting femoral lesions is critical because pathologic fractures in the femur cause significant morbidity and require prophylactic surgical fixation 1

Why Tibia X-rays Are Not Standard

• The standard skeletal survey does not include routine tibia imaging 1
• Tibial involvement is less common and typically not at high risk for pathologic fracture compared to the femur
• If there is specific clinical concern (localized pain, palpable mass), then targeted imaging of the tibia would be appropriate, but it is not part of routine screening

Optimal Imaging Algorithm for Multiple Myeloma Workup

First-Line Imaging Approach

1. Whole-body low-dose CT (WBLDCT) is now recommended as the primary imaging modality by the National Comprehensive Cancer Network, as it is superior to skeletal surveys for detecting lytic lesions throughout the skeleton 3
2. If WBLDCT is negative or unavailable, perform MRI of spine and pelvis (or whole-body MRI if available) to detect bone marrow involvement before bone destruction 3, 2
3. The skeletal survey (including femora) is acceptable only where advanced imaging is not available, but it should be considered inferior to WBLDCT or MRI 3

Combined Imaging Strategy

• Combining MRI of spine-pelvis with whole-body imaging (WBLDCT or PET-CT) detects active myeloma in 92% of patients, providing the most comprehensive assessment 5
• WBLDCT is particularly superior for spine, pelvis, skull, and ribs—the exact areas where skeletal surveys perform poorly 3
• MRI detects 30% of bone marrow abnormalities that PET-CT misses (particularly diffuse infiltration patterns), while PET-CT identifies extramedullary disease outside the MRI field of view 5

Critical Pitfalls to Avoid

Interpretation Cautions

• Never diagnose multiple myeloma based solely on MRI findings—you must confirm clonal plasma cells (≥10% on bone marrow biopsy) and monoclonal protein on serum/urine studies 4
• MRI can show nonspecific bone marrow lesions from metastases, osteomyelitis, lymphoma, or inflammatory conditions that mimic myeloma 4
• 30-50% of smoldering myeloma patients have bone marrow abnormalities on MRI, but only those with >1 focal lesion ≥5mm meet criteria for symptomatic disease requiring treatment 4

Follow-up Considerations

• If equivocal small lesions are seen on initial MRI, repeat imaging in 3-6 months—progression on MRI indicates symptomatic myeloma requiring treatment 2
• Use the same imaging modality for follow-up that was used at diagnosis to ensure consistency in response assessment 3
• MRI provides prognostic information after treatment (especially post-transplant), though this does not currently change treatment selection 2