Treatment response assessment using whole body diffusion weighted-magnetic resonance imaging in myeloma: a retrospective cohort study

This bi-institutional retrospective cohort study evaluated whole-body diffusion-weighted MRI (WB DW-MRI) for myeloma response assessment and its concordance with bone marrow minimal residual disease (MRD) testing. Among 53 patients, 49.1% achieved imaging complete response (imaging-CR; defined as no active focal lesions or diffuse infiltration) on post-treatment WB DW-MRI, while 33.96% showed multiple active focal lesions, 7.5% had a single active lesion, and 5.7% demonstrated persistent diffuse infiltration. Patients achieving imaging-CR demonstrated superior progression-free survival compared to non-CR patients (median not reached vs 43.3 months respectively; p = 0.025). Notably, only slight concordance was observed between bone marrow MRD (at 10⁻⁵ sensitivity) and imaging (Cohen's kappa coefficient = 0.197). Importantly, 38.5% of MRD-negative patients with persistent imaging abnormalities progressed during follow-up, whereas PET/CT-based CR showed no prognostic impact. This study establishes WB DW-MRI as a feasible response assessment tool in myeloma with significant prognostic value in the context of modern therapies.