Ulcerative colitis (UC) and Crohn’s disease are both types of inflammatory bowel disease (IBD), but they have key differences in terms of location, depth of inflammation, symptoms, and treatment approaches. Here’s a breakdown of how they differ:

1. Location of Inflammation

Ulcerative Colitis:

Affects only the colon (large intestine) and rectum.

Inflammation is limited to the innermost lining (mucosa) of the colon.

It starts in the rectum and can spread continuously upwards in the colon but does not affect other parts of the gastrointestinal tract.

Crohn’s Disease:

Can affect any part of the digestive tract, from the mouth to the anus.

Inflammation often occurs in patches, with healthy tissue between inflamed areas (known as “skip lesions”).

Crohn’s affects all layers of the bowel wall, leading to deeper inflammation.

2. Symptoms

Ulcerative Colitis:

Symptoms are usually limited to the colon and include:

Bloody diarrhoea.

Abdominal pain (often in the lower left abdomen).

Urgency to defecate.

Rectal bleeding and tenesmus (feeling of incomplete evacuation).

Severe cases can lead to toxic megacolon, a life-threatening complication where the colon dilates and loses its ability to function.

Crohn’s Disease:

Symptoms can affect the entire gastrointestinal tract, including:

Chronic diarrhoea (which may or may not be bloody).

Abdominal pain (often in the lower right abdomen).

Weight loss and malnutrition (due to poor absorption of nutrients).

Fatigue.

Fistulas (abnormal connections between different parts of the bowel or between the bowel and other organs).

Mouth ulcers and perianal disease (skin tags, abscesses, or fistulas around the anus).

3. Depth of Inflammation

Ulcerative Colitis:

Inflammation is superficial, affecting only the mucosal (inner) layer of the colon. It doesn’t extend deeper into the wall of the colon.

Crohn’s Disease:

Inflammation can be transmural, meaning it affects all layers of the bowel wall. This deep inflammation can lead to complications such as:

Strictures (narrowing of the intestines due to scar tissue).

Fistulas (abnormal connections between the bowel and other tissues).

Abscesses.

4. Complications

Ulcerative Colitis:

Increased risk of developing colon cancer, especially if UC has been present for many years or if large areas of the colon are affected.

Toxic megacolon and severe bleeding are rare but serious complications.

Crohn’s Disease:

Complications often involve:

Strictures leading to bowel obstruction.

Fistulas that connect the bowel to other organs or the skin.

Abscesses (pockets of pus).

Nutritional deficiencies due to malabsorption.

Risk of small bowel cancer is higher, though less common than colorectal cancer in UC.

5. Extra-Intestinal Manifestations

Both conditions can cause symptoms outside the digestive tract, known as extra-intestinal manifestations, including:

Joint pain and arthritis.

Eye inflammation (uveitis).

Skin conditions (erythema nodosum, pyoderma gangrenosum).

Liver disorders (primary sclerosing cholangitis, more common in UC).

Management of Ulcerative Colitis and Crohn’s Disease

Treatment goals for both conditions are to reduce inflammation, control symptoms, and induce and maintain remission. The approach may vary slightly depending on the condition and severity.

1. Medications

Amino salicylates (5-ASA):

Ulcerative Colitis: First-line treatment for mild to moderate UC, such as Mesalazine. These drugs are used to reduce inflammation directly in the colon.

Crohn’s Disease: Less effective for Crohn’s, particularly in cases where the small bowel is involved.

Corticosteroids:

Used for short-term control of moderate to severe flares in both conditions (e.g., prednisolone). They reduce inflammation but are not suitable for long-term use due to side effects.

Immunomodulators:

Drugs like azathioprine and 6-mercaptopurine help suppress the immune system and are used to maintain remission in both UC and Crohn’s.

Biologics:

Anti-TNF drugs (e.g., infliximab, adalimumab) target inflammation-causing proteins. They are used in moderate to severe cases of both diseases when other treatments fail.

Other Biologics: Include drugs like vedolizumab and Ustekinumab, which target different inflammatory pathways. These are often used in Crohn’s.

Antibiotics:

Often used in Crohn’s disease for infections related to abscesses or fistulas. They are less commonly used in UC.

2. Surgery

Ulcerative Colitis:

Surgery can be curative in UC since the disease is limited to the colon. In severe cases or when there is a high risk of cancer, a colectomy (removal of the colon) may be performed, often followed by the creation of an ileal pouch (pouch made from the small intestine to act as a reservoir for stool).

Crohn’s Disease:

Surgery is not curative in Crohn’s as the disease can recur in other parts of the digestive tract. However, surgery may be necessary to treat complications such as strictures, fistulas, or abscesses.

3. Lifestyle Modifications

Diet: Tailored to the individual, as some patients may have food intolerances. In Crohn’s, low-residue diets may help reduce symptoms by limiting fibre during flares.

Smoking: Smoking is strongly associated with worsening Crohn’s disease. In contrast, smoking cessation may trigger flares in ulcerative colitis, but quitting is still recommended due to overall health benefits.

4. Monitoring and Follow-Up

Both conditions require regular follow-up to monitor disease activity and adjust treatment. Colonoscopy is often performed to assess the extent of inflammation and screen for cancer in long-standing UC or Crohn’s.

Reliable References for Further Reading

NHS - Ulcerative Colitis

NHS UC Overview

NHS - Crohn’s Disease

NHS Crohn's Disease Overview

Crohn’s & Colitis UK

Crohn's and Colitis UK

National Institute for Health and Care Excellence (NICE)

NICE - Ulcerative Colitis

NICE - Crohn’s Disease

Dr Geranmayeh