Maarten Cozijnsen

11 Chapter 1 General introduction Crohn’s disease (CD) characteristics and pediatric CD Crohn’s disease (CD) is an inflammatory bowel disease (IBD) of unknown origin. It is a chronic, relapsing-remitting disease characterized by gastrointestinal symptoms (e.g. abdominal pain, watery and/or bloody stools), fatigue, weight loss and impaired longitudinal growth. The inflammation can result in increased concentrations of C-reactive protein (CRP) and an increased erythrocyte sedimentation rate (ESR) in patients’ blood and increased calprotectin concentrations in patients’ stool. The inflammation is mostly located in the terminal ileum, colon or both, but can be located throughout the gastrointestinal tract ( Figure 1 ). Although less common, the inflammation can even present outside the gastrointestinal tract, commonly referred to as extraintestinal manifestations. Additionally, CD inflammation can give rise to the formation of penetrating fistulas or intestinal strictures. Ulcerative colitis (UC) – the other mayor IBD subtype – in comparison is limited to the colon and does not lead to fistulas or strictures. The prevalence of IBD is around 0.3% in western countries, of which approximately 40% is CD. 1 Where the prevalence of CD in adults seems to be stable in Western countries, the incidence of CD in children and adolescents seems to be rising. 12 The incidence of childhood-onset CD is approximately 4 per 100,000 patient years. 3 When CD manifests during childhood or in adolescents, its course usually is more extensive and progressive than adult-onset CD. As a result more intensive treatment is required. 4,5 In the Netherlands, according to publicly available data at DIS opendata, pediatricians treat approximately 3,000 IBD patients annually, and physicians that treat adult IBD patients – mostly gastroenterologists and some internists – treat approximately 92,000 IBD patients, of which half are diagnosed with CD. Patients suspected of IBD undergo ileocolonoscopy, which allows for visual inspection of the gut mucosa and taking of biopsies. Besides disease location, the presence of aphthous ulcers, cobblestoning, and so called “skip” lesions helps distinguish CD from UC. Histologic signs of CD include epithelial damage, architectural changes, infiltration of mononuclear and polymorphonuclear cells in the lamina propria and / or epithelium, the presence of erosions, ulcers or granulomas. 6