The role of smoking in Crohn's disease as defined by clinical variables.

The development of Crohn's disease (CD) is related to an interaction of genetic and environmental factors, with tobacco smoking being one of the most commonly studied environmental factors. In 1998, the Vienna classification was created to define CD by using three accepted clinical variables: age at diagnosis, disease behavior, and disease location. In this qualitative systematic review, articles examining the relationship between smoking and CD, using variables outlined in the Vienna classification, were identified utilizing multiple health databases. Current smoking was found to be associated with late-onset CD (> or =40 years old) and current smokers were more likely to progress to stricturing or penetrating type CD than were nonsmoking patients. Conflicting evidence exists regarding the relationship between smoking with respect to CD disease location. The Vienna classification is an important tool in permitting comparisons and predicting clinical course among CD cases, especially when smoking status is taken into account.