What does a whole body low-dose Computed Tomography (CT) scan contain for multiple myeloma?

Whole Body Low-Dose CT for Multiple Myeloma

Whole body low-dose CT (WBLDCT) is superior to conventional skeletal surveys for detecting bone lesions in multiple myeloma and should be used as the primary imaging modality for initial diagnosis and follow-up. 1

Components and Features of WBLDCT in Multiple Myeloma

Imaging Protocol

• WBLDCT extends from skull vertex to knees without intravenous contrast, with radiation doses of 3.2-4.8 mSv 1
• CT contrast agents are not necessary for detection of myeloma bone disease and should generally be avoided in myeloma patients 1
• The scan is performed using low X-ray tube voltage/current settings while maintaining diagnostic image quality 2

Detection Capabilities

• WBLDCT detects osteolytic lesions that may be missed by conventional skeletal surveys, with 25.5% of patients showing positive findings on WBLDCT despite negative skeletal surveys 1
• WBLDCT is particularly superior for detecting abnormalities in:
  • Spine and pelvis 1
  • Skull and ribs (areas difficult to visualize with skeletal surveys) 1, 3
• WBLDCT can identify bone stability issues and fracture risk that may require intervention 2, 4

Clinical Value

• WBLDCT can detect up to 60% more relevant findings compared to conventional skeletal surveys, leading to treatment changes in up to 20% of patients 5
• In prospective studies, WBLDCT consistently identified more bone lesions per patient (8.2) compared to skeletal surveys (3.6) 6
• WBLDCT demonstrated progressive bone disease in 19 cases versus only 8 cases detected by skeletal surveys in follow-up studies 6

Comparison with Other Imaging Modalities

FDG PET/CT

• If PET/CT is chosen instead of WBLDCT, the CT component should have imaging quality equivalent to WBLDCT, not just for attenuation correction 1
• PET/CT offers additional value in detecting:
  • Extramedullary disease outside the spine 1
  • Metabolically active lesions that may not show structural changes 1
• Some studies suggest LDCT co-registered with PET has comparable performance to standalone WBLDCT, potentially allowing for a single multimodal examination 7

MRI

• MRI is particularly useful when WBLDCT or FDG PET/CT is negative, to help discern smoldering myeloma from active multiple myeloma 1
• MRI provides superior soft tissue contrast and can demonstrate bone marrow involvement before cortical bone destruction occurs 1
• MRI is especially valuable in patients with smoldering multiple myeloma, as 30-50% of such patients will have bone marrow abnormalities 5

NCCN Recommendations for Imaging in Multiple Myeloma

Initial Diagnostic Workup

• The NCCN Panel recommends either WBLDCT or FDG PET/CT for initial diagnostic workup of patients suspected of having multiple myeloma 1
• Skeletal survey including long bones is acceptable only where advanced imaging is not available (e.g., in low-resource settings) 1

Follow-up Imaging

• For follow-up after primary treatment, advanced imaging (WBLDCT, FDG PET/CT, or whole-body MRI without contrast) should be used as clinically indicated 1
• The same imaging modality used during initial workup should be used for follow-up assessments for consistency 1
• Minimum assessment frequency of every 3 months during active treatment is recommended 5

Clinical Considerations and Pitfalls

• WBLDCT is much faster and more convenient for patients compared to conventional skeletal surveys 3
• The effective radiation dose of WBLDCT (approximately 4.1 mSv) is higher than conventional skeletal surveys (2.4 mSv) but significantly lower than standard diagnostic CT protocols 2
• WBLDCT may also incidentally detect other clinically relevant findings such as pleuro-pulmonary lesions or other malignancies 4
• Image quality can be affected by diffuse skeletal infiltration or concurrent osteoporosis 2
• When using WBLDCT for follow-up, using CSS instead would underestimate progression rates 6