Relationship of Extraintestinal Involvements in Inflammatory Bowel Disease: New Insights into Autoimmune Pathogenesis

Extraintestinal manifestations in patients with inflammatory bowel disease (IBD) are quite common (about 25%) and careful clinical observation and statistical analysis during the last five decades have demonstrated that in colitis-associated extraintestinal complications, the organs most commonly involved are the biliary tract, joints, skin, and eyes. However, almost all organs can be involved in IBD. Some of the extraintestinal manifestations may precede IBD, although the majority accompany the underlying disease and are influenced by its activity. Prompt recognition of extracolonic organ involvement in IBD is important because of the relative refractoriness of the disease and a possible increase in morbidity and mortality. The identified pathogenetic autoimmune mechanisms include genetic susceptibility, cytokine imbalances, antigenic display of autoantigen, aberrant self-recognition, and immunopathogenetic autoantibodies against organ-specific cellular antigen(s) shared by colon and extracolonic organs. Microbes may play an important role, probably by molecular mimicry.