What is Microscopic Colitis?

Ulcerative colitis and Crohn’s disease involving the colon are two well-known types of inflammatory bowel disease; however there are additional types of colitis—microscopic colitis and ischemic colitis—each with its own symptoms and treatment requirements.

About microscopic colitis | Diagnosis | Who is affected? | Symptoms and treatment

Microscopic colitis, which includes collagenous colitis and lymphocytic colitis, is characterized by chronic watery diarrhea caused by inflammation in the colon. It is not related to ulcerative colitis or to Crohn's disease, and there is no evidence to suggest that microscopic colitis carries the same increased risk for colon cancer as ulcerative colitis.

This condition is known as "microscopic" colitis because physicians usually can't see the inflammation without a microscope. When looked at through an endoscope—a camera mounted at the end of a long, flexible tube that's inserted in the rectum—either during a colonoscopy or sigmoidoscopy, the colon appears entirely normal.

How is microscopic colitis diagnosed?

During a colonoscopy, a biopsy will be taken and examined. Even if the lining of the colon looks normal, it is important to remove tissue samples for a microscopic analysis. Without these diagnostic steps, it could take weeks, months, or even years to discover the reason for the chronic diarrhea.

Once the biopsy samples are examined under a microscope, various features may reveal the source of the inflammation and pinpoint the diagnosis even further. There results of the biopsy may show the following:

• In patients with collagenous colitis, a biopsy of the colon shows inflammation and thickened tissue made from a protein called collagen. The appearance of this tissue may vary, so it is important to look at several different samples.
• In those with lymphocytic colitis, a biopsy of the colon shows an increased number of special white blood cells (lymphocytes). A thickened band of collagen band can be seen on the biopsy, as patients can often exhibit features of both collagenous and lymphocytic colitis.

What causes microscopic colitis, and who is affected?

As with ulcerative colitis and Crohn's disease, the exact cause of microscopic colitis has yet to be identified. But bacteria, bacterial toxins, and viruses are leading candidates in research.

Some experts have suggested that use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen, might be the actual culprits. It is also possible that these medications might simply aggravate symptoms in individuals who are already prone to the illness. Another theory is that collagenous colitis and lymphocytic colitis are caused by an autoimmune response, which means that the body launches an attack upon itself —mistaking various cells in the colon for foreign invaders. The final answer may well turn out to be some combination of these theories.

There does seem to be a link between microscopic colitis and the autoimmune disease celiac sprue, also known as celiac disease. Caused by an immunologic reaction of the intestine to wheat, barley, rye, and oats, celiac sprue is a digestive disease that damages the small intestine and interferes with absorption of nutrients. Its hallmarks are chronic diarrhea and weight loss.

Symptoms and treatment

Although collagenous colitis and lymphocytic colitis display different characteristics under magnification, the symptoms of the two forms of microscopic colitis are virtually identical.

Common symptoms of microscopic colitis

• Chronic diarrhea, which can be severe. Up to 22% of patients with microscopic colitis can have more than 10 bowel movements per day, making prompt recognition and diagnosis important.
• Abdominal pain

Microscopic colitis treatment and therapy 

Treatment for collagenous colitis and lymphocytic colitis varies. Because the symptoms tend to wax and wane, the therapeutic approach depends a lot on the severity of the diarrhea.

Treatment generally starts with bulk-forming agents such as psyllium (Metamucil®), or various antidiarrheals that act as antimotility agents to slow the contractions that move bowel contents forward. These include loperamide (Imodium®) and diphenoxylate (Lomotil®). There is data indicating that bismuth subsalicylate (Pepto Bismol®) can be of benefit, too. Bile acid binders, such as cholestyramine (ex. Prevalite®, Questran Light®, Cholestyramine Light), have also been used to treat excessive bile acid in the colon, which can lead to diarrhea in some cases.

The most common therapy for use in microscopic colitis is budesonide (Entocort®), which works inside the intestines to reduce inflammation and symptoms of the disease. While budesonide is a corticosteroid, budesonide does not get absorbed until it is close to the colon, which minimizes the side effects commonly seen in other steroids such as prednisone.