Multiple Myeloma: Morphofunctional Treatment Response Evaluation with Whole-Body Diffusion-weighted MRI and FDG PET/CT.

Whole-body (WB) diffusion-weighted (DW) (WB-DW) MRI and fluorine 18-fluorodeoxyglucose (FDG) PET/CT have increasing roles in the evaluation of treatment response in the setting of multiple myeloma (MM), complementing molecular and clinical criteria. The authors clarify the use of WB-DW MRI and FDG PET/CT in the follow-up of MM, emphasize the advantages and limitations of these examinations, and outline the use of the response criteria for each modality. The Myeloma Response Assessment and Diagnosis System is a consensus guideline that provides recommendations for the acquisition and interpretation of WB-DW MR images of MM for diagnosis and follow-up. It is used to categorize treatment responses into five response assessment categories (RACs): RAC 1 (highly likely to be responding), RAC 2 (likely to be responding), RAC 3 (no change), RAC 4 (likely to be progressing), and RAC 5 (highly likely to be progressing). Conversely, the Italian Myeloma Criteria for PET Use is used to standardize FDG PET/CT image interpretation. The five-point Deauville score (DS) scale is used to grade FDG uptake visually according to metabolic response: Complete response is defined as uptake lower than that in the liver (DS 1-3); partial response, as persistent lesions, with a decreased number of lesions or reduced uptake (DS 4-5 ); stable disease, as no change; and progressive disease, as new lesions or increased uptake. WB-DW MRI and FDG PET/CT provide valuable information for posttreatment MM assessment. FDG PET/CT is the reference standard for detecting extramedullary disease, while WB-DW MRI is more sensitive, particularly for diffuse disease. For comprehensive evaluation, the morphologic changes in MM lesions should be correlated with DW imaging and apparent diffusion coefficient values at MRI and with uptake values at FDG PET/CT. ©RSNA, 2026 Supplemental material is available for this article.