Diagnosis and classification of Crohn's disease

Crohn's disease (CrD) is a chronic relapsing inflammatory bowel disease (IBD) potentially affecting any portion of the gastrointestinal tract from the mouth to the anus. CrD usually manifests between 15 and 30 years of age and presents typically with abdominal pain, fever, bloody or non-bloody diarrhoea, and weight loss. Paediatric patients may show failure to thrive, growth impairment, and delayed puberty additionally. Extraintestinal manifestations like arthritis, uveitis, and erythema nodosum are diagnosed in almost half of the patients. CrD is characterized by a discontinuous and ulcerous transmural inflammation often involving the ileocaecal region and leading to a stricturing or even fistulising phenotype in up to 50% of patients finally. Incidence and prevalence of CrD have been rising worldwide over the past decades. Although many details of the pathophysiology of CrD have been elucidated, no common aetiopathogenic model exists for all forms of CrD, presenting more an umbrella term for a phenotypically and genotypically heterogeneous clinical condition. In CrD, we see an inappropriate response of the innate and/or adaptive immune system to the intestinal microbiota in genetically predisposed individuals. The diagnosis of CrD is based mainly on patient's history and clinical examination and supported by serologic, radiologic, endoscopic, and histologic findings. Antibodies to Saccharomyces cerevisiae and autoantigenic targets such as glycoprotein 2 may aid in differentiating CrD from UC. Their single use, however, is limited by low sensitivity requiring antibody profiling for an appropriate serologic diagnosis. This review focuses on diagnostic and classification criteria of CrD.