2.1 Crohn's disease is a chronic inflammatory condition affecting the gastrointestinal tract (gut). It can affect any part of the gut from the mouth to the anus. The lining of the affected area becomes inflamed and may be ulcerated, and the wall of the intestine thickens. The clinical features of Crohn's disease vary and are determined partly by the site of the disease. Symptoms include diarrhoea, abdominal pain, weight loss, malaise, lethargy, anorexia, nausea, vomiting and fever.
2.2 Crohn's disease can be complicated by the development of strictures (narrowing of the intestine), obstructions, fistulae and perianal disease. Fistulae – abnormal connections between areas of the intestine or adjacent organs – develop in 17–43% of people with Crohn's disease. Perianal disease includes fissures, fistulae and abscesses. Other complications of Crohn's disease include acute dilation, perforation and massive haemorrhage of the gut, and carcinoma of the small bowel or colon.
2.3 People with Crohn's disease have acute 'flares' of the disease in between periods of remission or less active disease. These flares can affect any part of the gut. They may be defined by location (terminal ileal, colonic, ileocolonic, upper gastrointestinal), or by the pattern of the disease (inflammatory, fistulising or stricturing).
2.4 The prevalence of Crohn's disease in the UK is estimated to be about 50–100 per 100,000 people. It affects approximately 60,000 people in the UK. The incidence of Crohn's disease is greatest in people aged between 15 and 30 years. However, it may affect people of any age: 15% of people with the disease are older than 60 years at diagnosis and 20–30% are younger than 20 years. Mortality among people with Crohn's disease is only slightly higher than in the general population.
2.5 Crohn's disease is not medically or surgically curable. Treatment aims to control manifestations of Crohn's disease to reduce symptoms, and to maintain or improve quality of life while minimising short- and long-term adverse effects.
2.6 Clinical management depends on disease activity, site, behaviour of disease (inflammatory, fistulising or stricturing), response to previous medications, side-effect profiles of medications and extra-intestinal manifestations. Because Crohn's disease is unpredictable, successful treatment focuses on inducing and maintaining clinical remission.
2.7 Current treatment includes aminosalicylates, corticosteroids, immunosuppressants, TNF inhibitors, antibiotics, nutritional supplementation and dietary measures. Crohn's disease is typically treated in the short term (4–8 weeks) with corticosteroids. In severe active disease, hospital admission and intravenous administration of corticosteroids may be required. There is evidence that Crohn's disease in some people, despite a good initial response, becomes resistant to corticosteroids. Other people may become dependent on corticosteroid treatment, relapsing once the dose is reduced or treatment is stopped. Azathioprine and 6-mercaptopurine are widely used in the management of active Crohn's disease.
2.8 Between 50 and 80% of people with Crohn's disease will require surgery at some stage. The main reasons for surgery are strictures causing obstructive symptoms, lack of response to medical therapy, and complications such as fistulae and perianal disease.
2.9 The CDAI is frequently used to assess disease severity. It is a composite of overall activity of Crohn's disease as assessed by clinicians, and has eight variables weighted according to their ability to predict disease activity. It gives a score ranging from 0 to over 600, based on a diary of symptoms kept by the patient for 1–7 days, and other measurements such as the patient's weight and haematocrit. A CDAI score of less than 150 is considered to be remission, a score greater than 220 is considered to define moderate to severe disease, and a score greater than 300 is considered to be severe disease. The paediatric CDAI (PCDAI) is an instrument similar to the CDAI but with less emphasis on subjectively reported symptoms and more emphasis on laboratory parameters of intestinal inflammation.
2.10 The Harvey-Bradshaw Index is another commonly used tool, which correlates well with CDAI. It is based on assessments of general wellbeing, abdominal pain, number of diarrhoeal stools per day, and the presence of abdominal mass and associated complications. Patients with a score of 8 to 9 or higher are considered to have severe disease.