Abstract
Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), Sjögren's syndrome (SjS), and sarcoidosis are systemic diseases targeting multiple organs. While a careful differential diagnosis of these diseases is often required, their co-occurrence in the same patient has been previously reported. We herein report a 58-year-old Japanese man diagnosed with the co-occurrence of three systemic diseases (AAV, SjS, and sarcoidosis) in addition to monoclonal gammopathy of undetermined significance (MGUS), which emphasizes the importance of considering the possible co-occurrence of these diseases as well as their differentiation.