Fifteen year of use of functional imaging in multiple myeloma: where we started from and where are we going.

Bone disease represents a hallmark feature of multiple myeloma (MM), affecting nearly all patients during the disease course. Morphological imaging techniques play a crucial role in detecting bone disease, whereas functional ones are in addition fundamental for differentiation of active from inactive disease and prognostic stratification. The International Myeloma Working Group (IMWG) currently recommends whole-body low-dose computed tomography (WBLDCT) as the first-choice imaging technique for the diagnosis of bone disease, whereas magnetic resonance imaging (MRI) is recommended in cases without further myeloma-defining events. However, 18F-fluorodeoxyglucose-positron emission tomography/CT (18F-FDG-PET/CT) currently represents a standard imaging technique, as it combines both morphological and functional data. Indeed, it allows detection of bone lesions (alternatively to WBLDCT), prognostic stratification and monitoring of treatment response, being recommended by IMWG for the assessment of imaging minimal residual disease. IMPeTUs criteria have proposed a visual descriptive assessment of 18F-FDG-PET/CT, with standardized definitions of metabolic responses. However, use of further functional imaging techniques is being investigated, with diffusion-weighted (DW)-MRI being related to very promising results regarding both staging and response assessment, so much so that MY-RADS guidelines have recently proposed a standardization of acquisition, interpretation and reporting of this technique in MM and the British guidelines consider DW-MRI an alternative to 18F-FDG-PET/CT. This review summarizes current knowledge on the use of functional imaging techniques in MM and their incorporation in recommendations/guidelines and discusses potential future developments in this setting.