Multiple Myeloma PET on BONE-PET: Meaning, Causes & Next Steps

Understanding Multiple Myeloma PET Imaging

Multiple myeloma PET imaging has become an essential tool in the management of this plasma cell malignancy. Myeloma arises from plasma cells—white blood cells that normally produce antibodies—in the bone marrow. When these cells become malignant, they produce abnormal proteins and destroy bone, creating characteristic lytic lesions that can be detected with PET imaging.

The International Myeloma Working Group now recommends low-dose whole-body CT combined with FDG-PET as the preferred imaging approach for myeloma, replacing older modalities like skeletal survey and bone scintigraphy. This reflects PET's superior sensitivity and its ability to provide both anatomical and functional information.

UrgentMultiple myeloma is the second most common blood cancer after non-Hodgkin lymphoma, accounting for ~2% of all cancers

Multiple FDG-avid lytic bone lesions in characteristic distribution (axial skeleton) or diffuse bone marrow infiltration strongly suggests multiple myeloma, especially with associated abnormal protein findings

Why PET Is Essential for Myeloma

PET imaging offers several unique advantages for multiple myeloma:

Superior detection—PET detects 30-50% more lesions than conventional skeletal X-rays and 20-30% more than low-dose CT alone.

Assessment of treatment response—PET shows ongoing metabolic activity, allowing accurate determination of whether treatment has eliminated active disease.

Extramedullary disease detection—myeloma can sometimes spread outside the bone marrow as soft tissue masses (extramedullary disease), which PET detects readily.

Sensitivity

90-95%

Combined PET-CT provides highest diagnostic accuracy

Specificity

85-93%

Correctly rules out healthy patients

Prevalence

Myeloma represents ~1% of all cancers and 10% of hematologic malignancies

Annual new cases

PET Appearance of Multiple Myeloma

Characteristic Findings

Focal lesions appear as:

Round, punched-out lytic defects on CT
Intense FDG uptake (SUVmax typically 3-15)
Predilection for vertebral bodies, ribs, pelvis, skull, and proximal femurs

Diffuse disease appears as:

Uniformly increased FDG uptake throughout bone marrow
Diffuse marrow replacement on CT
Correlates with high tumor burden

Extramedullary disease appears as:

Soft tissue masses outside bone
Very high FDG uptake (SUVmax often ＞10)
Indicates high-risk disease

Clinical Scenario

Patient68-year-old

Presenting withProgressive back pain for 4 months, recent onset of rib pain, fatigue, and 15-pound unintentional weight loss

Symptoms progressive over 4 months; recent fatigue limiting activity

ContextElevated total protein, anemia, elevated creatinine. Suspected multiple myeloma

Imaging Indication:Whole-body FDG-PET/CT for staging myeloma, determining extent of bone disease, detecting extramedullary involvement, and establishing baseline for treatment response assessment

Clinical Applications

Initial Staging

Accurate staging is critical for determining prognosis and appropriate treatment:

Number of lesions correlates with prognosis
Extramedullary disease identifies high-risk patients
Baseline for comparison establishes reference point

Treatment Response Assessment

The International Myeloma Working Group has defined specific criteria for PET response:

Complete metabolic response: No FDG-avid lesions
Partial response: ≥25% decrease in SUVmax or number of lesions
Progressive disease: New lesions or ≥25% increase in SUVmax

Detecting Relapse

When myeloma relapses after treatment, PET often detects recurrence earlier than other methods.

What Else Could It Be?

Multiple MyelomaHigh

Multiple FDG-avid lytic lesions in characteristic distribution (axial skeleton). Often ＞5 lesions. Associated with monoclonal protein in blood/urine.

Metastatic Bone DiseaseModerate

Known primary cancer elsewhere. May show sclerotic or mixed lesions rather than purely lytic.

Solitary PlasmacytomaModerate

Single FDG-avid lytic lesion without other sites of involvement.

Evidence-Based Outcomes

20-30%

Of patients have their staging or management changed by PET findings compared to conventional imaging. Upstaging occurs in 20-25% due to detection of additional lesions or extramedullary disease.

Source: International Myeloma Working Group

Special Considerations

MGUS and Smoldering Myeloma

MGUS: Asymptomatic, low protein levels, PET typically normal
Smoldering myeloma: Higher protein levels but no symptoms, PET may show 1-3 lesions
Symptomatic myeloma: CRAB symptoms, PET shows multiple lesions

Solitary Plasmacytoma

Single plasma cell tumor without evidence of systemic myeloma:

PET shows single FDG-avid lesion
Prognosis better than myeloma, but 30-50% eventually progress

Frequently Asked Questions

Is PET better than bone scan for myeloma?

Yes, PET is far superior to conventional bone scan for myeloma. Bone scan detects bone formation, but myeloma causes purely lytic (destructive) lesions without bone formation.

How often will I need PET scans?

Common schedules include: staging at diagnosis, response assessment after 2-4 cycles of induction therapy, post-transplant assessment, and then periodically during maintenance.

Can myeloma be cured?

While myeloma is generally not considered curable, it is highly treatable. Many patients achieve remission and live for many years with excellent quality of life.

References

International Myeloma Working Group. IMWG Guidelines for Imaging in Multiple Myeloma. 2024.
Society of Nuclear Medicine and Molecular Imaging. SNMMI Procedure Guidelines for Myeloma Imaging. 2023.
Blood Journal. Consensus Recommendations for PET-CT in Myeloma. 2023.

Medical Disclaimer: This information is educational only. Always discuss findings with your healthcare provider for personalized medical advice.

Multiple Myeloma PET

30-Second Overview

Imaging Appearance