WB DW-MRI and MY-RADS:
Diffusion-weighted imaging (DWI) has added advantages in the MR imaging of MM (figure 10):
- Direct evaluation of bone marrow.
- High Sensitivity (Gold Standard for diffuse disease).
- Prognostic Value → The number and size of focal lesions correlate with global survival (Hillengass et al. 2010).
- Analysis of cellularity and viability → crucial in evaluating early response to treatment before changes in lesions’ size are depicted.
The Myeloma Response Assessment and Diagnosis System (MY-RADS) characterizes the myeloma state, both at diagnosis and during therapy and follow-up (figure 10): It is aimed to standardize reports and minimize variations. 5 Response Assessment Categories (RAC) have been described and morphological changes consistent with treatment response (decrease in number and size of bone lesions, intra or peritumoral fat...):
- RAC 1 (High likely to be responding): the previously evident lesion shows an increase in ADC values from ≤ 1400 to >1400 μm2/sec or ≥ 40% increase in ADC from baseline (figures 11, 12, 13, and 14).
- RAC 2 (Likely to be responding): an increase in ADC from ≤ 1000 to <1400 μm2/sec, or >25% but <40% increase in ADC from baseline (figure 13).
- RAC 3: No morphologic observable change (figure 15).
- RAC 4 (Likely to be progressing): there is no change in size but increasing signal intensity with ADC values <1400 μm2/sec (figures 16 and 17).
- RAC 5 (highly likely to be progressing): new regions of high signal intensity with ADC values between 600–1000 μm2/sec (figures 16, 18, and 19).
18F-FDG PET/CT and IMPetUs:
Standardized recommendations for the use of 18 F-FDG PET/CT in patients with multiple myeloma (MM) have been established (figures 20, 21, and 22).
18F-FDG PET/CT may be considered a valuable tool in the workup of patients with newly diagnosed and relapsed/refractory MM, particularly for detecting paramedullary and extramedullary soft-tissue lesions.
The major strength of this technique is the ability to distinguish between metabolically active and inactive sites of the disease, making it the technique of choice by the International Myeloma Working Group (IMWG) for follow-up MM patients.
The Italian myeloma criteria for PET use (IMPetUs) have standardized PET interpretation in MM and have proved to be highly reproducible. Visual interpretation of images for quantifying FDG uptake is graded by the five-point scale of Deauville score (DS):
- Deauville 1: no up-take is observed.
- Deauville 2: uptake ≤ mediastinum.
- Deauville 3: uptake > mediastinum but ≤ liver.
- Deauville 4: uptake moderately increased compared to the liver.
- Deauville 5: uptake markedly increased compared to the liver.
Bone marrow non-focal uptake, focal bone lesions (size, number, and uptake), paramedullary and extramedullary lesions are also studied.
Imaging response is stringently defined as the disappearance of every area of increased tracer uptake (standardized uptake value - SUV) found at baseline, or a preceding PET/CT; or the reduction of focal lesion and bone marrow uptake lower than the liver uptake (DS score of <4).
IMPetUS are analogous to what has been used in lymphoma, in which a complete metabolic response has been defined as a score of 1, 2, or 3 on the five-point scale (DS) (figures 23, 24, and 25):
- Complete response (CR): DS of 1, 2, or 3 together with the absence of FDG-avid bone marrow lesion(s), irrespective of a persistent mass on CT.
- Partial response (PR): a DS of 4 or 5, provided: uptake is decreased compared with baseline or absence of structural progression development on CT.
- Stable disease (SD), also called no metabolic response: DS of 4 or 5 without significant change in FDG uptake from baseline.
- Progressive disease (PD): DS of 4 to 5 with increasing intensity compared to baseline or any interim scan and/or any new FDG-avid focus consistent with malignant disease.
Teaching cases of metabolic response are shown in figures 26, 27, and 28, whereas cases of metabolic progression are shown in figures 29 and 30.
