CROHN'S DISEASE

Crohn’s Disease is an Inflammatory Bowel Disease; a chronic, autoimmune-driven inflammatory condition where the immune system mistakenly attacks the gastrointestinal tract, from the mouth to the anus, causing ongoing inflammation. In contrast to Ulcerative Colitis, another inflammatory Bowel Disease which only affects the colon and rectum.

This immune attack leads to chronic inflammation, tissue injury, and a wide range of gastrointestinal symptoms.

A key feature of Crohn’s disease is transmural inflammation. This means the inflammation extends through all layers of the gut wall, from the innermost lining to the outermost layers. Because of this deep inflammation:

The inflammation is patchy (with healthy areas between diseased ones — called “skip lesions”).

It can cause strictures (narrowing of the bowel), fistulas (abnormal tunnels between organs), abscesses, and deep ulcers.

It can affect any part of the GI tract, but it most commonly impacts the end of the small intestine (the terminal ileum) and parts of the colon.

• Genetic predisposition (seen in twin studies)
• Western diet (low fibre and high sugar)
• Mental stress
• Nicotine and smoking

• Abdominal pain/cramping – in the right lower quadrant pain.
• Chronic watery diarrhoea (non-bloody or mildly bloody).
• Weight loss and fatigue
• Urgency to defecate
• Fever (low-grade)
• Perianal disease (fistulas, abscesses)
• Mouth ulcers, joint pain, anaemia

The exact cause of Crohn’s isn’t fully understood, but it’s known to involve three main factors:

1. Genetic Susceptibility: People with a family history of Crohn’s have a higher risk. Specific genes involved in immune regulation and have been linked to increased susceptibility.

2. Environmental Triggers: Exposure to infections, certain medications (like NSAIDs), smoking, and possibly dietary factors can trigger Crohn’s in genetically predisposed individuals.

3. Immune Dysfunction: In Crohn’s, there is a breakdown in immune regulation involving TH17 cells and the Interleukin-23 (IL-23) pathway. Instead of responding appropriately to gut bacteria and environmental antigens, the immune system becomes overactive, producing inflammation that damages the gut lining.

Because Crohn’s disease causes deep, full-thickness (transmural) inflammation of the digestive tract, it can lead to several serious complications over time. These complications are often more severe and complex than those seen in ulcerative colitis.

• Strictures (Narrowing of the Bowel) caused by chronic inflammation and healing causing scar tissue to form, leading to narrowing of sections of the bowel. This can block food passage, causing cramps, pain, bloating, nausea, and vomiting and sometimes requires surgery (strictureplasty or bowel resection).
• Fistulas (Abnormal Connections) caused when inflammation erodes through the intestinal wall, creating tunnels (fistulas) that connect the bowel to other organs (e.g., bladder, skin, other sections of bowel). This can cause infection, pain, stool leakage, abscesses, or severe nutritional problems and often requires medical treatment and sometimes surgery.
• Abscesses (pockets of pus) that form when bacteria from the gut spill into surrounding tissues through ulcers or fistulas. This causes severe pain, swelling, fever, and can become life-threatening if untreated. Treatment often requires antibiotics and drainage procedures.
• Increased Cancer Risk, with the risk rising after 8–10 years of active disease, especially if the colon is involved. Prevention requires regular colonoscopy screening to detect precancerous changes early.

1. Colonoscopy with Biopsy is the gold standard test that involves direct visualisation to identify skip lesions, deep ulcers and confirm transmural inflammation.