Overview

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.