Microscopic (Lymphocytic) Colitis

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:

1. Lymphocytic colitis. In lymphocytic colitis, there is an accumulation of lymphocytes (a type of white blood cell) within the lining of the colon.
2. Collagenous colitis. 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.

Picture of the colon.

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.

• The colon has the following functions:
  • Removes water from the undigested food
  • Stores the undigested food
  • Eliminates it from the body through bowel movements
• The common symptoms of colitis include:
  • Abdominal pain
  • Diarrhea
  • Sometimes, rectal bleeding

There are many different types of colitis with different causes, which include the following:

• Bacterial infectious colitis caused by bacteria (such as Shigella, Campylobacter, E. coli, and C. difficile)
• Viral 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 are 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.
• Inflammatory bowel disease (IBD). Crohn's disease and ulcerative colitis are also referred to as inflammatory bowel disease (IBD). 
• Visible abnormalities of the inner lining of the colon.

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), for example, ibuprofen (Advil, Motrin), 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 drugs that can cause microscopic colitis include:

• proton pump inhibitors (PPIs)
• lansoprazole (Prevacid, Prevacid SoluTab)
• omeprazole (Prilosec, Zegerid)
• esomeprazole (Nexium)
• the Statin simvastatin (Zocor)
• SSRI sertraline (Zoloft)
• P2Y12 inhibitor ticlopidine (Tilcid)
• H2 blocker ranitidine (removed from the market on April 1, 2020, due to the risk of cancer)

The primary symptom of microscopic colitis is chronic, watery diarrhea.

• People with microscopic colitis can have diarrhea for months or years before the diagnosis is made.
• Typically, the symptoms begin very gradually and are intermittent 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 for microscopic colitis.

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.

Individuals with irritable bowel syndrome (IBS) do not have colitis, even though this condition is sometimes referred to as "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 known; it may be caused by either abnormal motility (abnormal contractions) of the intestinal muscles or abnormally sensitive nerves in the intestines (visceral hypersensitivity).

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 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 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 the causes of microscopic colitis.
• Trial of lactose elimination (just to eliminate the possibility that intolerance to lactose in milk is aggravating 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 patients with collagenous colitis, but 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.

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). 

There is no cure for the microscopic colitis.

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