What is the most common disease in overlap syndromes, and with which other diseases is it associated?
SS is the most common disease in overlap syndrome and is seen with RA, SLE, SSc, PM, MCTD, primary biliary cholangitis (PBC), necrotizing vasculitis, autoimmune thyroiditis, chronic active hepatitis, mixed cryoglobulinemia, and hypergammaglobulinemic purpura.