What Is Ulcerative Colitis?

Ulcerative colitis is an inflammatory bowel disease. People with ulcerative colitis have chronic (long-term) inflammation and ulcers (sores) in the colon (also known as the large bowel), which is part of the large intestine and removes water and some nutrients from partially digested food before the remaining waste is passed out of the body. Inflammation is the process by which your body responds to an injury or a perceived threat, such as a bacterial infection. Although the exact causes of ulcerative colitis aren’t yet fully understood, it may be an autoimmune condition, which means that the body’s immune system wrongly attacks normal, healthy tissue. The intestines contain hundreds of different species of bacteria, which are part of the “gut microbiome” (the term given to all of the microorganisms and their genetic material that live in the intestines). Although some of these species can cause illness, many are essential to our health and wellbeing, playing key roles in digestion, metabolism (the chemical reactions in the body that produce energy from food), regulation of the immune system, and mood. Several diseases are now thought to be influenced by changes to the gut microbiome, including cancer. Some researchers believe that in ulcerative colitis, the immune system may mistake harmless bacteria inside the colon as a threat and start to attack them, causing the colon to become inflamed.

What Is Mucosal Healing?

There is currently no cure for ulcerative colitis, with treatment focusing on relieving symptoms during a flare up and trying to stop them coming back, and the importance of choosing treatment strategies based on a specific therapeutic target (known as a “treat-to-target” approach) has become popular as a way to improve the long-term outcomes of patients. One of the ways that the efficacy of treatment is monitored is by assessing the level of “mucosal healing” in the colon. The mucosa is the innermost layer of the colon, and it is this layer that comes into direct contact with partially digested food and that becomes ulcered in ulcerative colitis. Mucosal healing is usually defined as an absence of friability (when the mucosa is inflamed and bleeds easily when touched), blood, erosions, and ulcers, or as a total absence of inflammation and ulcers. It is now considered a target of ulcerative colitis treatment because there is evidence that it is associated with better clinical outcomes (such as lower risks of surgery and relapse, and improved quality of life) and reduced risk of developing colorectal cancer in the future.

How Is Mucosal Healing Assessed?

Assessment of mucosal healing usually involves endoscopy, which uses a long, thin tube with a small camera inside to look inside the body, and histology, which involves the examination of samples of tissue taken from the colon by biopsy during an endoscopy procedure. Although useful, the samples that are examined by histology only reflect what is happening in the part of the colon from which they were taken, and may not represent the situation in the colon as a whole. Traditional endoscopy, which uses white light (i.e. apparently colorless light such as “normal” daylight, which is a mixture of different wavelengths of light in the visible spectrum), can also have limitations. These include the subjective nature of assessment because the results depend on the opinion of the person reviewing the results, variations in opinions between different reviewers, and difficulties seeing microscopic inflammation, which may be hard to see without some sort of enhancement.

What Is Image-Enhanced Endoscopy?

Image-enhanced endoscopy techniques produce high-contrast images using optical or electronic methods. These high-contrast images make it easier to see the detail and differences in the mucosal surface, patterns of blood vessels, and color tones of the mucosa. As a result, image-enhanced endoscopy has the potential to enable more objective (i.e., less dependent on the personal opinions of the person reviewing the results) assessment of mucosal healing and detect minute differences in mucosal healing that cannot be detected by endoscopy with white light. There are a number of different image-enhanced endoscopy approaches.

• Narrow-band imaging uses narrow-band light created with two filters that filter light at specific wavelengths, one for blue light and one for green. It is better than white light for viewing microscopic blood vessel structures. It may be useful for detecting minor inflammation and predicting relapse by revealing incomplete renewal of blood vessels in patients with ulcerative colitis.
• Another technique called linked-color imaging uses narrow-band imaging to pre-process images and then color separation to post-process them, so that blue, green, and red can be used to amplify differences in color, making it easier for slight differences in the color of the mucosa to be recognized. It therefore improves the visualization of changes in the mucosa caused by inflammation or a decrease in the mucosa (known as “atrophy”).
• In contrast, a method called i-Scan uses three different algorithms to enhance images: surface, contrast, and tone enhancement. It is able to emphasize minute mucosal structures and subtle color changes, and there is evidence that it can be used to clinically stratify patients according to histologic activity, without them needing to undergo a biopsy procedure to obtain tissue samples.
• Autofluorescence imaging involves the detection of the autofluorescence (the fluorescence of naturally occurring substances) that is produced by naturally occurring substances in the intestinal tissues (mainly type-I collagen, which is found in many structures in the body including skin, bones, tendons, cartilage, and connective tissue). Because the intensity of the autofluorescence is induced by various conditions in the body, autofluorescence imaging is expected to become useful for assessing the severity of tissue inflammation and differentiating between those changes that are due to damage and those that are due to uncontrolled, abnormal growth of cells or tissue (which may result in the development of a tumor).
• Finally, dual-red imaging uses three wavelengths of light, of which two improve the ability to see blood vessels in submucosal tissues and bleeding points. Unusually, the pattern of blood vessels in the surface of the colon’s mucosa is partly or completely absent in the active phase of ulcerative colitis, making it difficult to assess it with traditional endoscopy that uses white light. Dual-red imaging enhances the pattern of blood vessels and makes it easier to visualize blood vessels in deeper tissues, so may be most useful in evaluating inflammation of the colon and predicting the prognosis of patients with mild to moderately active ulcerative colitis.

The approaches described above may contribute to the improved assessment of factors in ulcerative colitis that are difficult to assess by white-light endoscopy. It is hoped that this will, in turn, improve the use of treat-to-target approaches and the quality of life of people with ulcerative colitis.