Multiple myeloma (MM) is a neoplastic plasma-cell disorder that is characterized by clonal proliferation of malignant plasma cells in the bone marrow microenvironment (Palumbo and Anderson 2011). Extramedullary multiple myeloma (EMM) is a less frequent manifestation, where myeloma cells become independent of bone marrow microenvironment, infiltrate other organs, and patients could present involvement of lymph nodes, skin, soft tissues, central nervous system, thoracoabdominal organs, effusions, or any other anatomic sites (Bhutani et al. 2020). EMM can be present either at the time of initial diagnosis (primary EMM) or at the time of relapse (secondary EMM) (Usmani et al. 2012). The reported incidence of EMM ranges from 7 to 18% and the soft-tissues involvement in MM can have two different origins: direct extension from skeletal tumors when they disrupt the cortical bone or hematogenous metastatic spread (Bladé et al. 2012). This results from the extramedullary spread in MM and consists of single or multiple large highly vascularized subcutaneous nodules (Bladé et al. 2011). Moreover, patients with soft tissue related extramedullary release had significantly poorer overall survival (Pour et al. 2014).
The role of imaging in the work-up of patients with MM is aimed at allowing the recognition of both the effects of myeloma cells on the skeletal system and the presence of extramedullary disease (Nanni and Zamagni 2019). Over the last several decades, F18-FDG-PET/CT and magnetic resonance imaging (MRI) have shown incremental value in the management of patients with MM (Shah and Oldan 2017).
F18-FDG PET/CT can help to identify areas of metabolic activity in whole body that represent clonal plasma cell proliferation while MRI is particularly well suited for the imaging of bone marrow (Ferraro et al. 2015). Few cases are reported about soft tissue involvement in multiple myeloma in F18-FDG PET/CT (Ak and Gülbas 2007; Lapa et al. 2014) and this could be considered as a valuable diagnosis tool in particular for the detection of paramedullary and extramedullary soft tissue masses or solid organ involvement (Cavo et al. 2017).