Introduction

Crohn's disease (CD) is an inflammatory condition that most commonly affects the small intestine. It may, however, affect any part of the GI tract from themouth to the anus. The colon (Crohn's colitis) or the perineum, with or without small-bowel involvement may be affected.

Incidence

Five new cases per 100 000 population per year in developed countries. The incidence is rising rapidly. Crohn's disease is most commonly diagnosed in 20–30 year olds, but shows a biphasic incidence, with a second peak in the sixth decade.

Aetiology

Unknown. Possible causes include infective (there are features that are similar to intestinal tuberculosis), immunological (there are suggestions of impaired cell-mediated immunity, and of autoantibody formation) and diet (possible causation of diet high in refined carbohydrates). In contrast to ulcerative colitis, smoking appears to be a risk factor.

Pathophysiology

Unlike ulcerative colitis, which is confined to the colon, CD can affect any part of the gastrointestinal tract. The disease is characteristically patchy in nature with normal segments of bowel between ‘skip lesions’ of disease. Macroscopically there is aphthous ulceration which progresses to deep fissuring ulcers. This leads to a cobblestone appearance and tight strictures or fistulae may develop. Microscopically there is chronic inflammation of all layers of the bowel wall, with ulceration, micro-abscesses and non-caseating granulomas.

Symptoms and signs

The presentation of CD can vary depending on the areas affected. The most common presenting features are diarrhoea, weight loss, abdominal pain and fever. There may be steatorrhoea if the small bowel is affected, or rectal bleeding in those with Crohn's colitis.