Medical mystery: What's causing stomach problems?

A 40-year-old woman came to see me with a one-week history of explosive diarrhea that would come on about an hour after eating any solid food. She also had painful gas after drinking liquids. The stools were bright neon green; her urine was orange. But she didn't have any fever, nausea, or vomiting. Her appetite was fine, though she had lost seven pounds. Imodium, an effective over-the-counter medication for diarrhea, wasn't helping. She didn't really feel all that sick, though.

There was no blood in her stools and her urinalysis was completely normal, as was her physical exam. The abrupt onset made it sound like there might be an infectious cause, so I asked her to collect stools at home to be cultured and checked for parasites.

When she hadn't brought the specimens in four days later, I called her. She was all better, so she hadn't bothered.

A year and a half later, she returned. Since I'd last seen her, she'd been having intermittent pain in her upper abdomen. It came on every month or two, lasting for hours and sometimes days. Occasionally she had diarrhea, though generally she was constipated. There was still no blood in her stools. She'd seen a colorectal surgeon about a month earlier for an episode of severe bloating and diarrhea. A CT of her abdomen was normal, but he hadn't done a colonoscopy. He told her to take Miralax, a powerful, over-the-counter laxative previously available only by prescription, which was working well for her.

Her exam was still normal.

I diagnosed irritable bowel syndrome (IBS), a condition that causes alternating diarrhea and constipation, along with occasional abdominal pain. There is no cure, but symptoms can usually be managed with diet and fiber supplements. I also gave her a prescription for an intestinal anti-spasmodic to use for the pain.

Six months went by, and she came in with a bad case of hives. Turns out she had become allergic to cats and had been exposed to one. An urgent care center had given her a steroid injection and a course of oral steroids. I told her to finish them and provided her with a prescription to have on hand if it happened again.

She was back again after three months, telling me her IBS symptoms had completely resolved while she'd been on the steroids. Only now was she again having abdominal pain, gas, and cramping.

This was not IBS.

My patient had celiac disease.

Celiac disease, also known as celiac sprue, is an inflammatory condition of the small intestine in which antibodies to gluten, a protein found in certain grains, cause damage to the lining of the intestine. The damaged mucosa is unable to absorb nutrients, causing pain, bloating, diarrhea, and malnutrition, among other symptoms.

Blood tests revealed the characteristic tissue transglutaminase antibodies (tTG); an abnormal small-intestinal biopsy provided confirmation. Other intestinal conditions that could have been relieved by steroids include ulcerative colitis and Crohn's disease, but they typically present with bloody stools.

Celiac disease is treated with a strict gluten-free diet. Not only do symptoms improve, but the damaged intestinal mucosa can heal completely, and the offending antibodies go away. This is why testing for celiac disease is not accurate when someone is already on a gluten-free diet.

Although celiac disease can cause many abdominal symptoms, some of them are typical of other conditions as well. Celiac disease, a genetic disorder, is present in about 1 percent of people with any Northern European lineage. Because the severity and age at onset are extremely variable, the exact prevalence of the autoimmune disease isn't known, although it appears to be increasing. That could be due to greater awareness and more widespread testing. In any case, it is not nearly high enough to justify "gluten-free" as the latest food fad. If you think you have celiac disease, talk to your doctor about testing before beginning a gluten-free diet.

For me, the take-home message was a reminder that IBS is a diagnosis of exclusion, meaning everything else should be ruled out first. Irritable bowel syndrome is fairly common in the United States (an estimated 10 to 15 percent of the population has it), so there's a strong temptation to diagnose it based on history alone, as I did.

Most of the time that's not a problem. Fiber, the mainstay of IBS treatment, is generally good for you. After this case, however, I've begun testing all my IBS patients for celiac disease.