Extramedullary disease in multiple myeloma: what you might not expect on [18F]FDG PET/CT - a pictorial essay

Introduction Extramedullary disease (EMD) represents an aggressive manifestation of multiple myeloma (MM), characterized by autonomous cancer clone growth outside the bone marrow. Despite the International Myeloma Working Group's endorsement of 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography/CT ([F-18]FDG PET/CT) for assessing EMD patients, a consensus on the imaging workup in this distinctive clinical context is lacking. Methods In this pictorial essay, we collected clinical MM cases from eight high-volume Italian PET/CT clinical centers. Each center checked its database to identify the most representative and unusual EMD cases detected on [F-18]FDG PET/CT. Subsequently, the selected cases underwent consensus discussion among the authors, prioritizing those deemed clinically relevant. Results The selected cases demonstrate a diverse range of manifestations, including leptomeningeal involvement, two instances of pancreatic masses, two renal/para-renal localizations, one skin localization, one pleural involvement, one adnexal/fallopian involvement, and one suspected neck nodal localization later confirmed as lymphoma upon histological examination. Conclusions These cases underscore the highly variable presentations of EMD on [F-18]FDG PET/CT. EMD can manifest with widespread anatomical localization as either single or multiple lesions. Tracer uptake patterns also vary in terms of intensity and homogeneity. In patients with a history of MM, nuclear medicine physicians should be vigilant for possible EMD localizations, not only at the time of diagnosis but as well as recurrence setting, with or without concurrent bone involvement.