Aggressive Extramedullary Multiple Myeloma Presenting as Small Bowel Obstruction

De novo extramedullary multiple myeloma (EMM) is a rare subset of multiple myeloma (MM) defined by the presence of clonal plasma cells (PC) outside of the bone marrow. It is associated with refractory disease and adverse outcomes. Even in EMM, plasmacytomas within the duodenum, jejunum, and ileum are uncommon, with fewer than 70 cases reported in the literature. Here, we present a particularly aggressive case of EMM resulting in a small bowel obstruction secondary to an intraluminal plasmacytoma while on myeloma-directed therapy. The patient underwent surgical resection with anastomosis and was transitioned to more definitive cytotoxic chemotherapy followed by autologous stem cell rescue. This case highlights challenges in the management of EMM over standard MM and argues that dedicated clinical trials for patients with aggressive EMM are warranted to further understand the unique pathophysiology and improve overall survival.