Heterogeneity of inflammatory bowel disease: Clinical subgroups of patients

Demographic data, clinical characteristics at diagnosis, disease behaviour and disease course form the basis for a division of inflammatory bowel disease (IBD) into different clinical subgroups. Clinical features of IBD are uniform, but particular ethnic groups may be associated with more severe disease. Several studies argue that age at onset (diagnosis) may provide a valid form of stratification in Crohn's disease (CD). The gender-specific influence points toward a female predominance and some studies have indicated that treatment response may also be sex dependent. Familial CD is characterised by an early age at onset and more extensive disease with high concordance within families. Finally, there is increasingly good evidence that smokers form a group with a worse prognosis. There is a general agreement that disease location at onset is a critical prognostic factor both in CD and ulcerative colitis (UC). The classification of CD into primary perforating, inflammatory or fibrostenotic disease has yet to be validated in a prospective fashion. Longitudinal studies of large cohorts of patients support the concept of two forms of CD, one aggressive, the other indolent, and a similar dichotomy is well documented in the postoperative period. In UC, the major factors predicting the need for surgery are the extent and severity of disease at diagnosis and proximal extension of involvement. Conflicting evidence between centres trying to define clinical subgroups underlines the need for collaboration and a clear, reproducible classification system, which takes into account the complexity of IBD.