Microscopic Colitis

Microscopic colitis (MC) is one of the lesser-known types of inflammatory bowel disease (IBD). These are chronic conditions of inflammation inside your bowels (intestines). “Colitis” means inflammation of your colon (large intestine) — specifically, the inner lining. Many things can cause temporary colitis, but MC causes it on an ongoing basis. It’s called “microscopic” because it can only be seen under a microscope.

If you have microscopic colitis, the cells in your intestinal lining are irritated. The result is most commonly frequent, watery diarrhea. As with all chronic conditions, microscopic colitis may come and go. It may flare up in reaction to certain triggers, then subside on its own, and then return. While it’s a lifelong condition, it’s usually manageable with medical treatments.

Who does microscopic colitis affect?

Anyone can get it, but it’s more common in older people and people who were assigned female at birth. It’s also more common in people who smoke, and in people who have certain autoimmune diseases, especially celiac disease. Microscopic colitis has traditionally been thought to be less common than other inflammatory bowel diseases. But because it requires a tissue sample to diagnose, it’s likely underestimated.

How serious is microscopic colitis?

It’s not as severe as other types of IBD, and not considered a life-threatening disease. Severe, unrelenting diarrhea could lead to dehydration, weight loss or even malnutrition, but microscopic colitis usually doesn’t manifest this way. It tends to come and go, and it can be managed with medication. It can affect your quality of life, however, with uncomfortable symptoms haunting your every meal.

What are the different types of microscopic colitis?

Healthcare providers can only diagnose microscopic colitis by looking at a sample of your intestinal mucosa under a microscope. When they do, they will recognize certain distinct features in the cells. Different features suggest different subtypes of the disease. There are at least two recognized subtypes, and several others have been suggested. The two recognized types are:

• Collagenous colitis. Collagen and elastin make up the connective tissue of your intestinal lining (lamina propria). With this type of MC, collagen bands in the lining of your colon are abnormally thickened. This thickened connective tissue is similar to other connective tissue diseases in which collagen and elastin become inflamed, such as rheumatoid arthritis. These autoimmune conditions are often seen in people with microscopic colitis.
• Lymphocytic colitis. In this version, the surface layer of your intestinal mucosa (the epithelium) has an abnormally high density of lymphocytes. Lymphocytes are a type of white blood cell. White blood cells function as part of your immune system to protect against infection. A high white blood cell count often accompanies inflammation when the immune system is involved.

These two variations of microscopic colitis come with the same symptoms, and they’re treated in the same way. Their differences only appear under the microscope. Some scientists believe they are actually just two different stages of the same condition. Occasionally, features of both types are seen together in one person. This has been called “incomplete microscopic colitis.”

In addition, some believe that mastocytic enterocolitis should be included as a type of microscopic colitis. It shares many similarities, although “enterocolitis” means that it affects the small intestine as well as the colon. “Mastocytic” means that it features an abnormally high density of mast cells in the intestinal mucosa. Mast cells are another kind of immune cell.