DEAR DR. ROACH: I am a 64-year-old female who is in moderate health. After a monthslong bout of diarrhea, blood work, and a colonoscopy, I’ve been diagnosed with microscopic colitis. After a round of budesonide, my symptoms subsided, and I had a normal few months. Can you explain what microscopic colitis is, what causes it and how to avoid flares?

• K.G.

ANSWER: Microscopic colitis is a chronic inflammatory disease of the colon. It comes in two pathologic forms — collagenous colitis and lymphocytic colitis — but diarrhea is the main symptom of both. It is most common in women, and you are right at the most common age for diagnosis.

Symptoms can begin slowly or suddenly, and other symptoms include abdominal pain. The volume of diarrhea is sometimes so much that a person can get dangerously fluid-depleted.

The exact cause of the inflammation is unknown. The diagnosis is made by colonoscopy but not by looking at the lining of the colon (since it’s usually normal); it requires a biopsy. Symptoms resemble celiac disease, inflammatory bowel disease and irritable bowel syndrome, among other possibilities, so the biopsy and blood tests are necessary to exclude other causes.

Some medicines are associated with the risk of microscopic colitis, so they should be stopped if possible. Aspirin, ibuprofen and other anti-inflammatories are the most common (and can cause a flare). But acid suppressors like omeprazole (Prilosec) and some other medicines may also increase the risk. People who smoke should stop. You should review all your medications with your gastroenterologist as there are a few possibly triggering drugs.

Budesonide is a potent glucocorticoid, which is an anti-inflammatory steroid that only works in the gut as it is not absorbed. Unfortunately, it is quite expensive, but my experience with this drug has been very good. Studies show 80% to 90% effectiveness. Experienced gastroenterologists usually continue budesonide until the symptoms are under control, then taper the person off after a month or so.

Relapse, unfortunately, is common but can usually be treated with budesonide again. Some experts keep their patients on budesonide at the lowest effective dose, especially if they have relapsed more than once. Because budesonide is not absorbed, it does not have the many risks (such as osteoporosis) that come with the chronic use of steroids like prednisone.

Readers may email their questions to Dr. Roach at ToYourGoodHealth@med.

cornell.edu.