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Crohn's Disease

What is Crohn's disease?

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Crohn's disease is a chronic inflammatory bowel disease (IBD) that causes inflammation of the digestive tract. This leads to severe abdominal pain, diarrhoea, fatigue, weight loss, and malnutrition. It is non-contagious but can significantly affect a person's quality of life.

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Crohn's arises when the immune system mistakenly attacks the digestive tract, triggering chronic inflammation. The exact cause is unknown, but genetics play a significant role — having a close relative with IBD increases your risk. Environmental factors such as stress, certain medications, and diet can trigger or worsen symptoms.

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Although it can develop at any age, Crohn's most often first appears between 15 and 35 years. It affects around 1 in 100 people in Western countries, occurs equally in men and women, and appears to be increasing globally.

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Common locations where symptoms appear include the small intestine, colon, rectum, mouth, oesophagus, and areas around the anus.

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Common symptoms include:

• Persistent diarrhoea
• Abdominal cramping and pain
• Blood in stool
• Urgency to have a bowel movement
• Fatigue and low energy
• Unintended weight loss
• Loss of appetite
• Fever during flare-ups
• Nausea or vomiting
• Mouth sores
• Perianal pain or drainage

How Crohn's disease develops

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Crohn's disease develops when the immune system responds abnormally to bacteria, food, or other substances in the digestive tract. Instead of protecting the body, the immune system launches an attack on the lining of the gut, causing chronic inflammation. Over time, this inflammation can penetrate deep into the layers of the bowel wall, leading to thickening, scarring, and in some cases the formation of ulcers, fistulas, or strictures that narrow the intestine.

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The exact trigger is not fully understood, but researchers believe it results from a combination of factors:

• Genetics — over 200 gene variants have been linked to Crohn's, and people with a first-degree relative with IBD are up to four times more likely to develop it.
• Immune dysfunction — an overactive immune response fails to "switch off," keeping the gut in a persistent state of inflammation.
• Gut microbiome imbalance — an altered balance of bacteria in the digestive tract appears to play a role in triggering or sustaining inflammation.
• Environmental factors — diet, smoking, antibiotic use, and urban living have all been associated with higher rates of Crohn's.

Unlike a flare caused by infection, the inflammation in Crohn's is ongoing and self-perpetuating, which is why the condition requires long-term management rather than a single course of treatment.

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Types of Crohn's disease

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Crohn's is classified by the location of inflammation in the digestive tract. Knowing which type you have helps guide treatment decisions and explains why two people with Crohn's can have very different experiences of the condition.

• Ileocolitis is the most common form, affecting the lower small intestine (ileum) and part of the large intestine (colon). It typically causes cramping and pain in the lower right abdomen, along with diarrhoea and weight loss.
• Ileitis affects only the ileum. Symptoms are similar to ileocolitis and may also include fistulas or inflammatory masses in the lower right abdomen.
• Gastroduodenal Crohn's disease involves the stomach and the first part of the small intestine (duodenum). It can cause nausea, vomiting, and loss of appetite, and is less common than other forms.
• Jejunoileitis produces patchy areas of inflammation in the upper small intestine (jejunum). It often causes intense abdominal pain and cramps after eating, and can lead to fistula formation in more severe cases.
• Crohn's (granulomatous) colitis affects only the colon. It tends to cause diarrhoea, rectal bleeding, and skin, joint, or eye complications more frequently than other types. It can be difficult to distinguish from ulcerative colitis, another form of IBD.

It's worth noting that Crohn's can affect any part of the digestive tract from the mouth to the anus, and some people have inflammation in more than one area at the same time.

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