Crohn's disease has a worldwide distribution with an incidence or 0.5-5/100 000, which is rising. The disease usually appears in adolescents or young adults (there is also a peak in the older population) and is more common in people of European origin, especially people of Jewish heritage. Up to 40% will have a family history of some form of idiopathic inflammatory bowel disease (IIBD).
The pathogenesis of Crohn's disease is unknown.
The two main features that differentiate Crohn's disease from ulcerative colitis (UC) and other inflammatory gastrointestinal system disorders are that in Crohn's disease, the inflammation affects all layers of the bowel wall (i.e., it is transmural) and it is discontinuous, with segments of inflamed tissue separated by areas of uninflamed tissue (so-called skip lesions). Crohn's disease affects predominantly the ileum and cecum together in 40% of cases, the colon alone in 30% and the small bowel alone in 30%. Occasionally, patients will have esophageal and gastroduodenal involvement. Affected segments of bowel show marked wall thickening (because the disease is transmural), with fibrosis, mucosal ulcerations and a cobblestoned mucosal appearance. Inflammatory polyps and fistulae may occur, and bowel loops may become matted together. Histologically, the hallmarks are transmural inflammation, fissuring ulcers and epithelioid granulomas.
Major complications include obstruction, perforation, hemorrhage, and fistulization.
The course is typically characterized by intermittent attacks with remissions and exacerbations. The most frequent symptoms are abdominal pain and diarrhea with or without fever and bleeding. Intestinal obstruction and fistula formation are the the most common complications. Patients with long-standing Crohn's disease have an increased incidence of intestinal cancer.
Extraintestinal manifestations include inflammatory lesions of the eyes, arthritis, skin lesions and liver disease with bile duct inflammation. Crohn's disease cannot be cured with medications or surgery, but symptoms can be controlled with a variety of anti-inflammatory medications (e.g., corticosteroids and sulfasalazine). Surgery is reserved to control complications such as obstructive or fistulizing lesions.