Backwash Ileitis—From Pathogenesis to Clinical Significance: Literature Review

Backwash ileitis (BWI) refers to inflammation in the distal ileum in patients with extensive ulcerative colitis (UC) that is thought to be caused by a “reflux” or “backwash” of colonic contents. In the absence of well-defined diagnostic criteria for BWI, more recently, the term UC-associated ileitis was proposed in favor of the backwash theory, which questions the existence of backwash ileitis as a distinct disease-specific subset of patients. Moreover, distinguishing UC-associated BWI from terminal ileitis of Crohn’s disease or other conditions could be a diagnostic challenge and significantly affect treatment management. Therefore, clinical, endoscopic, histologic, and imagistic diagnostic features may aid in making this distinction. This literature review related to BWI outlines the hypothesis that the ileum may also become involved in UC as a primary manifestation of UC based on recent findings. This study also highlights the possibility that associated ileitis in UC patients may represent a potential risk factor for neoplasia, a positive association with primary sclerosing cholangitis, and a higher risk for the subsequent development of pouchitis after restorative proctocolectomy. It synthesizes recent key findings and highlights areas for further research.