Monoclonal gammopathy of undetermined significance (MGUS) is associated with several autoimmune conditions, including central nervous system (CNS) vasculitis. Epstein-Barr virus (EBV) is a pathogen capable of triggering a systemic immune response and is involved in the occurrence of a wide range of B-cell lymphoproliferative disorders. In systemic autoimmune diseases, EBV infection is suspected to play a central role in pathogenesis. Here, we present a case that was thought to be a systemic autoimmune disease and CNS vasculitis that developed after EBV infection, demonstrating that rituximab is effective for the treatment.