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 colonoscopy or flexible sigmoidoscopy.

There are two 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

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 both subtypes.

The symptoms of microscopic colitis can come and go frequently. Sometimes the symptoms resolve on their own. If not, your doctor can suggest a number of effective medications.

Microscopic colitis care at Mayo Clinic