Microscopic colitis is an inflammation of the large intestine (colon) that causes persistent watery diarrhea. The disorder gets its name from the fact that it's necessary to examine colon tissue under a microscope to identify it, since the tissue may appear normal with a colonoscopy or flexible sigmoidoscopy.

There are different subtypes of microscopic colitis:

• Collagenous colitis, in which a thick layer of protein (collagen) develops in colon tissue
• Lymphocytic colitis, in which white blood cells (lymphocytes) increase in colon tissue
• Incomplete microscopic colitis, in which there are mixed features of collagenous and lymphocytic colitis.

Researchers believe collagenous (kuh-LAYJ-uh-nus) colitis and lymphocytic colitis may be different phases of the same condition. Symptoms, testing and treatment are the same for all subtypes.

Signs and symptoms of microscopic colitis include:

• Chronic watery diarrhea
• Abdominal pain, cramps or bloating
• Weight loss
• Nausea
• Fecal incontinence
• Dehydration

The symptoms of microscopic colitis can come and go frequently. Sometimes the symptoms resolve on their own.

When to see a doctor

If you have watery diarrhea that lasts more than a few days, contact your doctor so that your condition can be diagnosed and properly treated.

It's not clear what causes the inflammation of the colon found in microscopic colitis. Researchers believe that the causes may include:

• Medications that can irritate the lining of the colon.
• Bacteria that produce toxins that irritate the lining of the colon.
• Viruses that trigger inflammation.
• Autoimmune disease associated with microscopic colitis, such as rheumatoid arthritis, celiac disease or psoriasis. Autoimmune disease occurs when your body's immune system attacks healthy tissues.
• Bile acid not being properly absorbed and irritating the lining of the colon.

Risk factors for microscopic colitis include:

• Age. Microscopic colitis is most common in people ages 50 to 70.
• Sex. Women are more likely to have microscopic colitis than are men. Some studies suggest an association between post-menopausal hormone therapy and microscopic colitis.
• Autoimmune disease. People with microscopic colitis sometimes also have an autoimmune disorder, such as celiac disease, thyroid disease, rheumatoid arthritis, type 1 diabetes or psoriasis.
• Genetic link. Research suggests that there may be a connection between microscopic colitis and a family history of irritable bowel syndrome.
• Smoking. Recent research studies have shown an association between tobacco smoking and microscopic colitis, especially in people ages 16 to 44.

Some research studies indicate that using certain medications may increase your risk of microscopic colitis. But not all studies agree.

Medications that may be linked to the condition include:

• Pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve)
• Proton pump inhibitors including lansoprazole (Prevacid), esomeprazole (Nexium), pantoprazole (Protonix), rabeprazole (Aciphex), omeprazole (Prilosec) and dexlansoprazole (Dexilant)
• Selective serotonin reuptake inhibitors (SSRIs) such as sertraline (Zoloft)
• Acarbose (Precose)
• Flutamide
• Ranitidine
• Carbamazepine (Carbatrol, Tegretol)
• Clozapine (Clozaril, Fazaclo)
• Entacapone (Comtan)
• Paroxetine (Paxil, Pexeva)
• Simvastatin (Zocor)
• Topiramate

Most people are successfully treated for microscopic colitis. The condition does not increase your risk of colon cancer.

A complete medical history and physical examination can help determine whether other conditions, such as celiac disease, may be contributing to your diarrhea.

Your doctor will also ask about any medications you are taking — particularly aspirin, ibuprofen (Advil, Motrin IB, others), naproxen sodium (Aleve), proton pump inhibitors, and selective serotonin reuptake inhibitors (SSRIs) — which may increase your risk of microscopic colitis.

Tests

To help confirm a diagnosis of microscopic colitis, you may have one or more of the following tests and procedures:

• Colonoscopy. This exam allows your doctor to view your entire colon using a thin, flexible, lighted tube (colonoscope) with an attached camera. The camera sends images of your rectum and entire colon to an external monitor, allowing your doctor to examine the intestinal lining. The doctor can also insert instruments through the tube to take a tissue sample (biopsy).

• Flexible sigmoidoscopy. This procedure is similar to a colonoscopy, but rather than viewing the entire colon, a flexible sigmoidoscopy allows your doctor to view the inside of the rectum and most of the sigmoid colon — about the last 2 feet (61 centimeters) of the large intestine.

  The doctor uses a slender, flexible, lighted tube (sigmoidoscope) to examine the intestinal lining. A tissue sample can be taken through the scope during the exam.

Because intestinal issues often appear normal in microscopic colitis, a definite diagnosis of microscopic colitis requires a colon tissue sample (biopsy) obtained during a colonoscopy or flexible sigmoidoscopy. In both subtypes of microscopic colitis, cells in colon tissue have a distinct appearance under the microscope, so the diagnosis is definite.

Additional testing

In addition to a colonoscopy or flexible sigmoidoscopy, you may have one or more of these tests to rule out other causes for your symptoms.

• Stool sample analysis to help rule out infection as the cause of persistent diarrhea.
• Blood test to look for signs of anemia or infection.
• Upper endoscopy with biopsy to rule out celiac disease. Doctors use a long, thin tube with a camera on the end to examine the upper part of your digestive tract. They may remove a tissue sample (biopsy) for analysis in the laboratory.

Microscopic colitis may get better on its own. But when symptoms persist or are severe, you may need treatment to relieve them. Doctors usually try a stepwise approach, starting with the simplest, most easily tolerated treatments.

Diet and discontinuation of medication

Treatment usually begins with changes to your diet and medications that may help relieve persistent diarrhea. Your doctor may recommend that you:

• Eat a low-fat, low-fiber diet. Foods that contain less fat and are low in fiber may help relieve diarrhea.
• Discontinue dairy products, gluten or both. These foods may make your symptoms worse.
• Avoid caffeine and sugar.
• Discontinue any medication that might be a cause of your symptoms. Your doctor may recommend a different medication to treat an underlying condition.

Medications

If signs and symptoms persist, your doctor may recommend:

• Anti-diarrheal medications such as loperamide (Imodium) or bismuth subsalicylate (Pepto-Bismol)
• Steroids such as budesonide (Entocort EC)
• Medications that block bile acids (which can contribute to diarrhea) such as cholestyramine/aspartame or cholestyramine (Prevalite), or colestipol (Colestid)
• Anti-inflammatory medications such as mesalamine (Delzicol, Apriso, others) to help control colon inflammation
• Medications that suppress the immune system to help reduce inflammation in the colon, such as mercaptopurine (Purinethol) and azathioprine (Azasan, Imuran)
• TNF inhibitors, such as infliximab (Remicade) and adalimumab (Humira), which can reduce inflammation by neutralizing an immune system protein known as tumor necrosis factor (TNF)

Surgery

When the symptoms of microscopic colitis are severe, and medications aren't effective, your doctor may recommend surgery to remove all or part of your colon. Surgery is rarely needed to treat microscopic colitis.

Changes to your diet may help relieve diarrhea that you experience with microscopic colitis. Try to:

• Drink plenty of fluids. Water is best, but fluids with added sodium and potassium (electrolytes) may help as well. Try drinking broth or watered-down fruit juice. Avoid beverages that are high in sugar or sorbitol or contain alcohol or caffeine, such as coffee, tea and colas, which may aggravate your symptoms.
• Choose soft, easy-to-digest foods. These include applesauce, bananas, melons and rice. Avoid high-fiber foods such as beans and nuts, and eat only well-cooked vegetables. If you feel as though your symptoms are improving, slowly add high-fiber foods back to your diet.
• Eat several small meals rather than a few large meals. Spacing meals throughout the day may ease diarrhea.
• Avoid irritating foods. Stay away from spicy, fatty or fried foods and any other foods that make your symptoms worse.

Here's some information to help you get ready for your appointment and know what to expect from your doctor.

What you can do

• Be aware of any pre-appointment restrictions, such as not eating solid food on the day before your appointment.
• Write down your symptoms, including when they started and how they may have changed or worsened over time.
• Make a list of all your medications, vitamins or supplements.
• Write down your key medical information, including other diagnosed conditions. Also mention if you have been hospitalized in the last few months.
• Write down key personal information, including any recent changes or stressors in your life, as well as a detailed description of your typical daily diet, including whether you usually use caffeine and alcohol.
• Write down questions to ask your doctor.

Questions to ask your doctor

Some basic questions to ask your doctor include:

• What is the most likely cause of my condition?
• Do you think my condition is temporary or chronic?
• What kinds of tests do I need?
• What treatments can help?
• Are there any other medical problems I might have that are associated with microscopic colitis?
• If I need surgery, what will my recovery be like?
• Are there any dietary restrictions that I need to follow? Would changing my diet help?

Don't hesitate to ask questions anytime you don't understand something.

What to expect from your doctor

Be ready to answer questions your doctor is likely to ask you:

• When did you begin experiencing symptoms?
• Have your symptoms been continuous or occasional?
• How many loose bowel movements are you having each day?
• How severe are your other symptoms, such as abdominal cramping and nausea?
• Has there been blood in your stools?
• Have you lost any weight?
• Have you traveled recently?
• Is anyone else sick at home with diarrhea?
• Have you been hospitalized or taken antibiotics in the last few months?
• Does anything make your diarrhea worse, such as particular foods?
• What medications are you currently taking, and did you start taking any in the weeks before your diarrhea began?
• What do you eat in a typical day?
• Do you use caffeine or alcohol? How much?
• Do you have celiac disease? If so, are you following a gluten-free diet?
• Do you have diabetes or thyroid disease?
• What, if anything, seems to improve your symptoms?
• What, if anything, seems to worsen your symptoms?

What you can do in the meantime

You may find some relief from persistent diarrhea by making changes to your diet:

• Eat bland, low-fat foods.
• Avoid dairy products, spicy foods, caffeine and alcohol.