Does multiple myeloma (MM) bone disease show up on a Positron Emission Tomography (PET) scan?

Does Myeloma Bone Disease Show Up on PET Scan?

Yes, myeloma bone disease shows up on FDG PET/CT scan, and this imaging modality is now recommended as one of the primary diagnostic tools for detecting bone involvement in multiple myeloma. 1

Primary Imaging Recommendations

For initial diagnostic workup of suspected multiple myeloma, either whole-body low-dose CT or FDG PET/CT should be used. 1 The NCCN explicitly states that skeletal survey is only acceptable where advanced imaging is not available (e.g., in low-resource settings). 1

Why PET/CT Works for Myeloma Bone Disease

• FDG PET/CT identifies more bone lesions than plain X-rays and can detect lesions in patients with negative skeletal surveys. 1
• Active myeloma is positive on PET scan due to the increased metabolic activity of malignant plasma cells. 1
• PET/CT detects both medullary (bone marrow) and extramedullary disease with high sensitivity and specificity. 2
• The technique can identify early marrow involvement before significant bone destruction occurs. 3

Critical Technical Consideration

If PET/CT is chosen instead of whole-body low-dose CT, the CT component must have imaging quality equivalent to a whole-body low-dose CT—not just for attenuation correction. 1 This is essential because the low-dose CT used only for attenuation correction may not be sufficient to assess bone disease stability and spine integrity. 1

Comparative Performance

PET/CT vs. Other Modalities

• FDG PET/CT is superior to conventional bone scintigraphy for myeloma bone disease. 1 Unlike most other cancers, myeloma bone disease is often missed on radionuclide bone scans because the predominantly lytic lesions may not generate sufficient osteoblastic response. 1
• MRI has higher sensitivity (97%) compared to PET/CT (76%) for detecting bone marrow involvement. 4 However, PET/CT findings correlate more strongly with clinical management decisions. 4
• Whole-body low-dose CT detected positive findings in 25.5% of patients with negative skeletal surveys. 1

Prognostic Value

Baseline PET/CT parameters have independent prognostic value for both progression-free survival and overall survival. 2 Key prognostic factors include:

• Presence of extramedullary disease 2
• Number of focal bone lesions 2
• Maximum standardized uptake values (SUVmax) 2
• Persistence of focal lesions with SUVmax > 4.2 after treatment is associated with shorter time to progression. 1

Response Assessment

FDG PET/CT is the most robust modality for treatment response evaluation in multiple myeloma. 5 Key points include:

• PET/CT normalization can occur as early as day 7 post-induction therapy. 1
• Complete metabolic response on PET/CT is a strong prognostic indicator. 1
• The IMWG recommends baseline FDG PET/CT to enable comparison during response assessment. 1

Important Limitations and Caveats

When PET/CT May Be Negative

10-20% of patients with newly diagnosed multiple myeloma may have negative baseline FDG PET/CT scans. 1 In these cases:

• If baseline PET/CT is negative, whole-body low-dose CT should be performed at end of treatment for comparison during follow-up. 1
• Consider whole-body MRI without contrast if both whole-body low-dose CT and FDG PET/CT are negative, particularly to distinguish smoldering myeloma from active disease. 1

Specificity Concerns

• FDG PET/CT has relatively low specificity and can show uptake in inflammatory or infectious processes. 5
• PET/CT has lower sensitivity for diffuse bone marrow infiltration patterns compared to focal lesions. 5
• Slowly proliferating lesions can be missed on FDG PET. 1

Practical Algorithm for Bone Disease Detection

1. At diagnosis: Obtain either whole-body low-dose CT or FDG PET/CT 1
2. If PET/CT chosen, ensure diagnostic-quality CT component 1
3. If both are negative but clinical suspicion remains high, proceed to whole-body MRI 1
4. For therapy assessment: Use the same modality as baseline for consistency 1
5. If baseline PET was negative, use whole-body low-dose CT for follow-up 1

Emerging Considerations

Novel immunotherapeutic strategies (e.g., T-cell redirecting bispecific antibodies) may cause immune-related phenomena that create potential pitfalls in FDG PET scan interpretation. 1 This requires careful clinical correlation when interpreting post-treatment scans in patients receiving these newer therapies.