An overview of the natural history of inflammatory bowel diseases.

Inflammatory bowel disease includes two main conditions: Crohn's disease (CD) and ulcerative colitis (UC). Natural history studies of these two entities have shown relevant differences in several clinical outcomes, mainly a more chronic and persistent (although often subclinical) inflammatory activity and the development of complications related to long-term tissue damage in CD. This led in recent years to different long-term therapeutic strategies in each disease. In this article, we review the main phenotypic features of UC and CD at the time of disease diagnosis and their changes along the course of the disease, as well as their consequences regarding drug therapy and surgical requirements.