Crohn's disease vs ulcerative colitis

Two conditions from the same family, each with its own features

• Where it affects
• Depth of inflammation
• Treatment plan

One family, called inflammatory bowel disease

What do they have in common?

Both are long-term (chronic) inflammation that goes through active periods and calm periods, and both need long-term treatment and follow-up. But where they affect the bowel, and how, are different.

Sometimes it is hard to tell them apart at first; this is called 'IBD unclassified' (unclassified colitis).

Where does the inflammation happen?

Where it affects

Crohn's disease:

• Location: any part from the mouth to the back passage (anus); the end of the small bowel is affected most often
• Pattern: patchy; affected sections separated by healthy sections

Ulcerative colitis:

• Location: the colon (large bowel) and rectum only
• Pattern: continuous; it starts in the rectum and extends up the colon

How deep is the inflammation in the bowel wall?

Depth of inflammation

• Crohn's disease — can affect all layers of the wall, so it can cause narrowings (strictures), fistulas or abscesses
• Ulcerative colitis — affects the inner lining of the colon, causing ulcers and bleeding

This is why the possible complications and the way follow-up is done differ between the two conditions.

What does the patient feel?

Symptoms

Crohn's disease:

• Common symptoms: tummy (abdominal) pain, diarrhoea, weight loss, tiredness
• Around the back passage: fistulas and abscesses are more common
• Nutrition: may cause poor absorption and low iron and vitamin B12
• Complications: narrowing of the bowel, fistulas, abscesses

Ulcerative colitis:

• Common symptoms: diarrhoea with blood or mucus, and an urgent need to open the bowels
• Around the back passage: fistulas are unusual; piles (haemorrhoids) or tears (fissures) may occur
• Nutrition: low iron due to bleeding is more common
• Complications: severe bleeding, or sudden severe widening of the colon (rare)

Both conditions can affect organs outside the bowel, such as the joints, skin, eyes and liver.

How does the doctor tell them apart?

Diagnosis

• Medical history and examination — including examining the area around the back passage
• Tests — blood tests, and measuring calprotectin in the stool
• Endoscopy (camera test) with biopsies — to see the shape and spread of the inflammation and examine the samples under the microscope
• Scans — bowel ultrasound or MRI to assess the small bowel

The diagnosis is based on putting all these results together, not on a single test.

Is the treatment different?

Treatment

• Mesalazine — a main treatment in mild to moderate ulcerative colitis; it has a limited role in Crohn's disease
• Biologic and advanced therapies — used in both conditions, with some options differing by disease type
• Surgery — in ulcerative colitis, removing the colon removes the diseased area; in Crohn's disease, surgery treats complications and the inflammation may come back afterwards
• Smoking — clearly makes Crohn's disease worse; stopping smoking helps all patients

The goal in both conditions is the same: calm the inflammation, maintain quality of life, and prevent complications.

The difference between the two: the summary

Key messages

• Both are long-term inflammatory conditions that need ongoing follow-up
• Crohn's disease can affect any part of the digestive tract, in a patchy way
• Ulcerative colitis affects the colon and rectum in a continuous way
• Knowing your type of disease and where it is helps choose the right treatment
• Do not compare your plan with another patient's; every patient has their own plan

Contact the clinic if you have:

• More frequent bowel movements or blood appearing
• Pain or discharge around the back passage
• A high temperature
• Ongoing or worsening tummy pain
• Unexplained weight loss
• Joint pain or a red eye

If you have heavy bleeding, severe pain or a very high temperature, go straight to the nearest emergency department.