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

Magnetic resonance imaging (MRI) and 18 F-fluorodeoxyglucose positron emission tomography–computed tomography ( 18 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 18 F-FDG PET-CT and WB-DWI and evaluated the diagnostic performance of 18 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. 18 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 18 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 18 F-FDG PET-CT were 0.75, 0.79 and 0.77, respectively. Although WB-DWI detected more FLs than did 18 F-FDG PET-CT, there was no difference in the detection of bone disease on a per-patient basis. 18 F-FDG PET-CT showed high performance, including for evaluation of diffuse infiltration.