Diseases

Since the cause of microscopic colitis is not known, no advice can be provided about preventing this disease.

The prevalence of microscopic colitis in the U.S. is not clearly known.Microscopic colitis most commonly occurs in the middle aged and elderly patients and is more common among women than men.

The diagnosis of microscopic colitis is made by performing biopsies from different regions of the colon during colonoscopy or sigmoidoscopy.The abnormalities of the colon's lining in microscopic colitis occur in a patchy distribution (areas of normal lining may coexist adjacent to areas of abnormal lining). For this reason, multiple biopsies should be taken from several different regions of the colon in order to accurately make a diagnosis.The patchy nature of microscopic colitis also is the reason why flexible sigmoidoscopy often is inadequate in diagnosing the condition because the abnormalities of microscopic colitis may be absent from the sigmoid colon (the colonic segment that is closest to the rectum and is within the reach of a sigmoidoscope) in some of the patients with microscopic colitis.Thus, biopsies of other regions of the colon accessible only with colonoscopy may be necessary for diagnosing microscopic colitis.

The primary symptom of microscopic colitis is chronic, watery diarrhea. Individuals with microscopic colitis can have diarrhea for months or years before the diagnosis is made. Typically, the symptoms begin very gradually and are intermittent in nature with periods when the person feels well, followed by bouts of chronic diarrhea. This chronic diarrhea of microscopic colitis is different from the acute diarrhea of infectious colitis, which typically lasts only days to weeks. Some individuals with microscopic colitis also may experience mild abdominal cramps and pain. Blood in the stool is unusual.

The cause(s) of microscopic colitis is unknown. Some experts suspect that microscopic colitis is an autoimmune disorder similar to the autoimmune disorders that cause chronic ulcerative colitis and Crohn's disease. One study has implicated long term (longer than 6 months) use of nonsteroidal anti-inflammatory drugs (NSAIDs) as a cause of microscopic colitis. Some individuals' diarrhea improves after stopping the NSAIDs. Several other drugs have also been incriminated as a cause of microscopic colitis. The most common are proton pump inhibitors (PPIs) such as lansoprazole (Prevacid, Prevacid SoluTab), omeprazole (Prilosec, Zegerid), and esomeprazole (Nexium); the Statin simvastatin (Zocor); H2 blocker ranitidine (Zantac); SSRI sertraline Zoloft); and P2Y12 inhibitor ticlopidine (Tilcid).

Individuals with irritable bowel syndrome (IBS) do not have colitis, even though this condition is sometimes referred to as having "spastic colitis." These individuals may have symptoms that mimic colitis such as diarrhea, abdominal pain, and mucus in stool. Nevertheless, there is no inflammation of the colon in patients with IBS. The cause of symptoms in IBS is not clearly known; it may be caused by either abnormal motility (abnormal contractions) of the intestinal muscles or abnormally sensitive nerves in the intestines (visceral hypersensitivity).

Colitis means inflammation of the colon. The colon, also known as the large intestine or large bowel, constitutes the last part of the digestive tract. The colon is a long, muscular tube that receives digested food from the small intestine. It removes water from the undigested food, stores the undigested food, and then eliminates it from the body through bowel movements. The rectum is the last part of the colon adjacent to the anus. The common symptoms of colitis include:

• abdominal pain,
• diarrhea, and
• sometimes, rectal bleeding.

There are many different types of colitis with different causes. Some examples of colitis include:

• infectious colitis caused by bacteria (such as shigella, Campylobacter, E. coli, and C. difficile)
• infectious colitis caused by a virus (such as cytomegalovirus [CMV])
• radiation colitis (such as following treatment with radiation for prostate cancer)
• ischemic colitis (such as blockage of an artery in the colon by a blood clot. If the blood clot interrupts the flow of blood to a segment of the colon, the result is inflammation of that segment and, sometimes, even death [gangrene] of the segment)
• Crohn's disease and ulcerative colitis (two related conditions that are caused by abnormalities of the body's immune system in which the body inappropriately makes antibodies and chemicals that attack the colon). Crohn's disease and ulcerative colitis are also referred to as inflammatory bowel disease (IBD).

Infectious, radiation, ischemic, ulcerative, and Crohn's colitis all have visible abnormalities of the inner lining of the colon. These abnormalities include edema (swelling of the lining), redness, bleeding from the lining with gentle rubbing (friability), and ulcers. These abnormalities can be seen during colonoscopy (examination of the entire colon using a long flexible viewing tube) or flexible sigmoidoscopy (examination of the rectum and the sigmoid colon - the segment of the colon closest to the rectum). Edema and inflammation of the colon's lining interferes with the absorption of water from the undigested food, and the unabsorbed water exits the rectum as diarrhea. Pus and fluid also are secreted into the colon and add to the diarrhea. The redness, bleeding from the lining with gentle rubbing (friability), and ulcerations in the lining of the colon contribute to the rectal bleeding.

Microscopic colitis refers to inflammation of the colon that is only visible when the colon's lining is examined under a microscope. The appearance of the inner colon lining in microscopic colitis is normal by visual inspection during colonoscopy or flexible sigmoidoscopy. The diagnosis of microscopic colitis is made when a doctor, while performing colonoscopy or flexible sigmoidoscopy, takes biopsies (small samples of tissue) of the normal-appearing lining, and then examines the biopsies under a microscope. There are two types of microscopic colitis: 1) lymphocytic colitis and 2) collagenous colitis.

1. In lymphocytic colitis, there is an accumulation of lymphocytes (a type of white blood cell) within the lining of the colon.
2. In collagenous colitis, there is an additional layer of collagen (scar tissue) just below the lining.

Some experts believe that lymphocytic colitis and collagenous colitis represent different stages of the same disease. The inflammation and the collagen probably interfere with absorption of water from the colon, resulting in the diarrhea.

The long term prognosis (course) of microscopic colitis is not clear. In approximately two-thirds of the patients with microscopic colitis, the diarrhea resolves spontaneously after several years. The remaining one-third of the patients with microscopic colitis experience persistent or intermittent diarrhea and/or abdominal pain for many years (possibly indefinitely) as there is no cure for the condition.

The treatment of microscopic colitis has not been standardized because there have not been adequate large scale, prospective, placebo controlled treatment trials. The following strategies are safe and may relieve diarrhea in some patients:

• Avoid nonsteroidal anti-inflammatory drugs (NSAIDs) and the other drugs mentioned under causes of microscopic colitis.
• Trial of lactose elimination (just to eliminate the possibility that intolerance to lactose in milk is aggravating the diarrhea)
• Antidiarrhea agents such as loperamide (Imodium) or diphenoxylate and atropine (Lomotil)
• Bismuth subsalicylate (Pepto-Bismol)
• budesonide (Entocort EC)
• 5-ASA (mesalamine) compounds such as Asacol, Pentasa, or Colazal

Controlled trials showed that budesonide (Entocort, a poorly absorbed steroid) is effective in controlling diarrhea in more than 75% of the patients with collagenous colitis, but the diarrhea tends to recur soon after stopping Entocort. Though data supporting their use is lacking, some doctors may use medications that potently suppress the immune system such as azathioprine (Imuran, Azasan) and 6-mercaptopurine in patients with severe microscopic colitis that is unresponsive to other treatments.

A person should seek medical care if the diarrhea lasts for more than 2 weeks or is accompanied with symptoms such as weight loss, fatigue, and abdominal pain.