Clinical Risk Factors: Lessons from Epidemiology

Current therapeutic goals of inflammatory bowel diseases (IBD) have evolved from symptomatic remission to a complex remission defined by clinical, biochemical, and endoscopic remission, with ultimate outcomes involving prevention of disease progression, surgery, or hospitalization. Thus, risk assessment and prediction of expected disease course by clinical, biochemical, and endoscopic markers has become important in patient stratification, management, and therapy optimization and prediction of the aforementioned outcomes. This chapter highlights the importance of epidemiological studies. The role of clinical factors in the prediction of disease course has been studied in both population-based and referral cohorts. In the majority of papers, negative disease outcomes were defined as progression of disease behavior from inflammatory to complicated (penetrating/stricturing) phenotype and surgical intervention in CD, compared with proximal disease extension, hospitalization, and colectomy in UC. Age at onset, disease phenotype characteristics (early disease course, behavior and localization/disease extension), smoking status, and accelerated treatment algorithms in early disease were reported to be important in the prediction of the disease course in both CD and UC. An important challenge of the future is the harmonization of definitions of disease progression and disabling disease. In addition, the predictive potential of some factors needs to be addressed since most studies report associations rather than focusing on prediction. These require further elucidation with prospective studies. Despite all these limitations and heterogeneity of the definitions, the importance of clinical factors in predicting disease outcomes is unequivocal.