Prospective comparison of 18-FDG PET/CT and whole-body diffusion-weighted MRI in the assessment of multiple myeloma.

Magnetic resonance imaging (MRI) and F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG 18F-FDG PET-CT) are standard procedures for staging multiple myeloma (MM). Diffusion-weighted sequences applied to whole-body MRI (WB-DWI) improve its sensitivity. We compared the number of MM bone focal lesions (FLs) detected by F-FDG PET-CT and WB-DWI and evaluated the diagnostic performance of F-FDG PET-CT for diffuse infiltration. Thirty newly diagnosed MM patients prospectively underwent 18F-FDG PET-CT and WB-DWI. The criteria for skeletal region positivity were ≥ 1 focal bone lesions (FLs) and/or diffuse disease. MRI with the MY-RADS criteria was used as a reference standard for the diagnosis of diffuse infiltration. F-FDG PET-CT and WB-DWI were both interpreted as positive in 28/30 patients with an agreement of 1.00 (95% CI 0.77-1.00) between the two methods. The mean numbers of FLs were 16.7 detected by F-FDG PET-CT and 23.9 detected by WB-DWI (P = 0.028). WB-DWI detected more FLs in the skull (P = 0.001) and spine (P = 0.006). Agreement assessed using the prevalence and bias-corrected kappa index was moderate (0.40-0.60) for the spine, sternum-ribs and upper limbs and substantial (0.60-0.80) for the pelvis and lower limbs. As regards the diagnosis of diffuse bone marrow infiltration, the sensitivity, specificity and accuracy of F-FDG PET-CT were 0.75, 0.79 and 0.77, respectively. Although WB-DWI detected more FLs than did F-FDG PET-CT, there was no difference in the detection of bone disease on a per-patient basis. F-FDG PET-CT showed high performance, including for evaluation of diffuse infiltration.