Classification of inflammatory bowel disease: the old and the new

Purpose of review Inflammatory bowel diseases (IBDs) are disorders of multifactorial cause that present as a multitude of phenotypes, clinical behaviours and severity. Crohn's disease and ulcerative colitis are considered as the two extremes of what is believed to be a spectrum of chronic gut inflammation and this separation is still the first classification used when confronted with an IBD patient. An accurate classification within IBD has several benefits, with respect to patient counselling, assessing risk for disease progression, and particularly with respect to choosing the most appropriate therapy for an individual patient. Basic scientists on the other hand prefer classifications that would allow to better understand the pathophysiology of the different manifestations of Crohn's disease and ulcerative colitis. Recent findings Attempts to reclassify IBD based on recent genetic, serologic or immunologic findings have been made. Most, however, have not been translated to daily practice and need confirmation first. Summary Clinicians should apply a systematic approach to their patients by using existing phenotypic classifications such as Montreal or Paris. They should further recognize clinical and endoscopic features of bad outcome such as perianal disease, deep ulcers on colonoscopy and extensive small bowel involvement.