Crohn’s Disease
A lifelong inflammatory bowel condition affecting any part of the gut
Crohn’s disease is a type of inflammatory bowel disease (IBD) that causes chronic inflammation in the digestive tract, most commonly the end of the small intestine and the beginning of the large intestine. It can affect people of any age but is most frequently diagnosed between the ages of 15 and 35, and its exact cause remains unknown though it involves a combination of genetic, immune and environmental factors.
What is Crohn’s Disease?
Crohn’s disease causes patches of inflammation that can occur anywhere from the mouth to the anus, though the terminal ileum (the last section of the small bowel) and the colon are the most commonly affected areas. Unlike ulcerative colitis, which only affects the inner lining of the colon, Crohn’s inflammation is transmural — meaning it goes through the full thickness of the bowel wall. This deep inflammation is what causes the characteristic complications of Crohn’s: strictures (narrowings), fistulae (abnormal tunnels between the bowel and other structures), and abscesses.
Symptoms and How It Presents
The symptoms of Crohn’s disease vary depending on which part of the gut is affected. The most common presentation is chronic diarrhoea lasting more than four weeks, abdominal pain (often in the right lower abdomen), weight loss and fatigue. Unlike ulcerative colitis, diarrhoea in Crohn’s is often non-bloody. Many patients experience mouth ulcers and perianal problems including fissures, skin tags and fistulae. Crohn’s can also cause problems outside the gut — including painful skin nodules (erythema nodosum), eye inflammation (uveitis), and joint pain affecting large joints or the lower back.
Diagnosis and Investigations
Crohn’s disease is diagnosed primarily through ileocolonoscopy with biopsies, which typically shows characteristic skip lesions, cobblestone appearance of the mucosa, and non-caseating granulomas on histology. Faecal calprotectin is an extremely useful non-invasive marker — a level above 250 micrograms per gram strongly suggests IBD and helps distinguish it from irritable bowel syndrome. Blood tests usually show raised CRP and ESR during flares, iron deficiency anaemia, and sometimes low B12 or folate if the terminal ileum is affected. MRI of the small bowel is the preferred imaging technique to assess for strictures, fistulae and abscesses.
Treatment and Living with Crohn’s
Treatment focuses on two phases: inducing remission during flares and then maintaining remission long-term. Corticosteroids such as prednisolone or budesonide are used to bring active disease under control but must never be used for maintenance due to serious side effects. Immunomodulators — azathioprine, mercaptopurine or methotrexate — are the backbone of maintenance therapy and reduce the need for repeated steroid courses. For moderate-to-severe disease that does not respond to conventional treatment, biologic therapies including infliximab, adalimumab, vedolizumab and ustekinumab have transformed outcomes. Stopping smoking is the single most important lifestyle change a patient can make — smoking doubles the risk of relapse and increases the likelihood of needing surgery.