Extensive Extramedullary Disease Involving the Colon in Multiple Myeloma: A Case Report and Review of Literature

Introduction Organ involvement in multiple myeloma (MM) is characterized by infiltrative disease or by a myelomatous mass known as a plasmacytoma. We present a patient with MM who had extensive extramedullary involvement of the colon and a review of the literature on colon plasmacytomas. Case report A 57-year-old male with MM presented with disease relapse in 2007, workup showing biopsy confirmed left perinephric extra-medullary disease involving the adjacent colon. Positron emission-tomography (PET) exhibited intense pan-colonic fluoro-deoxyglucose (FDG) uptake and computed-tomography confirmed extensive infiltrating soft tissue thickening in the ascending, transverse, and descending colon representing plasmacytomas. The patient underwent an autologous hematopoietic stem cell transplantation after conditioning with high-dose melphalan. Restaging PET-scan showed complete resolution of colonic extra-medullary plasmacytomas. Extramedullary plasmacytomas (EMP) are rare and constitute 4% of all plasma cell tumors. Discussion and Conclusion Colonic plasmacytoma is an extremely rare site, with fewer than 25 cases reported in the literature. Colonic plasmacytomas have different presentations depending on the size and location. Treatment options for primary EMPs include surgical resection, radiotherapy, and chemotherapy. The primary treatment option for secondary EMP is systemic chemotherapy. This rare pan-colonic plasmacytoma, as a part of extramedullary myeloma, showed an impressive response to chemotherapy.