Epidemiology of the transition from early to late Crohn's disease.

Phenotypically, the transition from early to late Crohn's disease is characterized by the occurrence of complications including strictures, intra-abdominal fistulas and perianal fistulas, all of them leading to various types of surgeries and currently non-reversible tissue damage. It must, however, be kept in mind that this transition is not at all a uniform and linear process. According to these simple phenotypic criteria, Crohn's disease can already be a late disease at diagnosis while in other patients, it can still be an early disease after 20 years of evolution. This simply highlights the relativity of time in this field, actually reflecting the nature, location and severity of the inflammatory process. The risk over time of the development of these complications has been described, first in cohort studies and then in population-based studies. Globally, at diagnosis, between 19 and 38% only of Crohn's disease patients have complicated Crohn's disease. After 10 years, between 56 and 65% of patients have developed either stricturing or penetrating complications. After 20 years, these numbers are between 61 and 88%. In parallel to these structural changes, changes in the immunobiology of the disease also seem to occur; the latter seem to happen quicker with major modification already within 2 years of the diagnosis. Beside these general figures, important questions remain pending. First, the real timing of these changes is still unclear. Second, the precise role of genetics and environment in the development of these changes remains to be clarified. Third, the correlation between changes in immunobiology and intestinal structural damages has not been specifically studied.