Crohn’s disease is a chronic inflammatory condition of the gastrointestinal (GI) tract. It most commonly affects the last segment of the small intestine (ileum) and the first part of the large intestine (caecum), although it can occur in any part of the GI tract from the mouth to the anus and, very occasionally, in areas outside the intestine.

It is not uncommon for people with Crohn’s disease to have patches of normal tissue in between areas of inflammation. This has implications for how Crohn’s disease is treated, especially by surgery. Also, unlike ulcerative colitis, where the inflammation is limited to the innermost lining of the intestinal wall, Crohn’s disease can affect all layers of the GI tract. This can lead to the development of complications that are quite specific to the condition.

What is IBD?

An inflammatory bowel disease (IBD) is a chronic inflammatory condition that affects parts of the digestive tract, but most commonly involves the small and large intestines. The most common diseases are ulcerative colitis and Crohn’s disease.

Ulcerative colitis affects the large intestine (colon), while Crohn’s disease can affect any part of the gastrointestinal (GI) tract, from the mouth to the anus.

How does Crohn’s disease affect the intestines?

Crohn’s disease affects the GI tract, and the intestinal wall becomes inflamed (red and swollen). The inflammation can penetrate through all layers of the GI tract and may occur at one or more locations in the GI tract, from the mouth right through to the anus, with areas of normal tissue between areas of diseased tissue.

Depending on the main areas of the intestine involved in Crohn’s disease, the condition can be referred to as:

  • Ileocolitis: involves the ileum and colon
  • Ileitis: involves the ileum only
  • Crohn’s (granulomatous): involves the colon only
  • Crohn’s colitis: inflammation of the colon due to Crohn’s disease.
  • Gastroduodenal Crohn’s disease: involves the stomach and duodenum
  • Jejunoileitis: involves the jejunum

What are the signs and symptoms?

Typical symptoms include:

  • Frequent, watery diarrhoea
  • Sense of urgency to have a bowel movement
  • Crampy abdominal pain
  • A feeling of ‘blockage’
  • Fever during active stages of disease
  • Rectal bleeding (if the colon is involved)
  • Loss of appetite
  • Tiredness and fatigue
  • Weight loss

The signs and symptoms of Crohn’s disease can vary considerably among those who have the condition, depending on the location and severity of the inflammation within the GI tract. For example, if a narrowing (stricture) occurs in the intestinal wall at the site of the inflammation – especially in the upper parts of the GI tract – there could be nausea, vomiting, bloating, and constipation. Crohn’s disease in the colon can mimic the effects of ulcerative colitis, often making it difficult to differentiate between the two conditions.