Irritable bowel syndrome (IBS) is a highly prevalent disorder characterized by nonspecific symptoms that can mimic other common medical conditions. A careful history and physical examination may reveal clues that suggest a coexisting or alternative diagnosis, such as small intestinal bacterial overgrowth or celiac disease (CD). Testing for bacterial overgrowth has limitations, but emerging data suggest that antibiotics may be of some benefit in patients with IBS with diarrhea and bloating. CD seems to have a higher prevalence in patients with IBS. Some patients with IBS may have symptomatic improvement on gluten-restricted diets, without histologic or serologic evidence of CD.
A 33-year-old woman presents for a second opinion after recently being diagnosed with irritable bowel syndrome (IBS) by her primary care physician. She never had gastrointestinal problems until going on a vacation to South America 2 years ago. During the trip, both she and her husband had an episode of food poisoning from which he recovered uneventfully within several days. However, since that time she has had persistent abdominal cramping, bloating, and intermittent episodes of diarrhea. After reading about IBS on the Internet, she altered her diet to include more fresh fruits and vegetables and began taking fiber supplements. Despite these dietary modifications, she has had little symptomatic improvement. Her medical history is notable for 2 miscarriages and anemia. In your office her physical examination is normal, and the results of a recently ordered complete blood cell count and comprehensive metabolic panel are normal except for a mildly elevated mean corpuscular volume. Does this patient have IBS, or are there clues in her presentation to suggest an alternative or coexisting diagnosis, such as small intestinal bacterial overgrowth (SIBO) or Celiac disease (CD)? How do we best approach this case?
Irritable bowel syndrome
Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) tract disorder of unknown origin characterized by abdominal pain and altered bowel habits in the absence of detectable biochemical or structural abnormalities. IBS is one of the most common functional GI disorders with an estimated prevalence of 10% to 15% in Western adult populations. Although only a minority of patients with IBS seek medical care, they account for a large percentage of referrals to gastroenterologists and use a substantial portion of health care resources. Direct and indirect costs of IBS are staggering, reaching up to $30 billion per annum in the United States alone.
IBS occurs in both genders; however, women are affected roughly in the ratio of 2:1 and tend to seek medical care more often than men. The onset of symptoms occurs most frequently before the age of 50 years; however, all ages are affected and symptoms can persist well into advancing years. IBS is commonly subdivided into different phenotypes depending on the most prevalent bowel habit: diarrhea-predominant IBS (IBS-D), constipation predominant (IBS-C), and mixed features (IBS-M). The prevalence of each subtype has been shown to vary in different studies, but overall, IBS-D or IBS-M may be slightly more common. Comorbid symptoms and disorders are common with IBS, particularly in patients with severe symptoms and those seen in referral practices. Psychiatric comorbidities are estimated to occur in about 60% of patients with IBS presenting to gastroenterology clinics and in up to 70% of those seen in tertiary referral centers. Health-related quality-of-life scores are lower in patients with IBS than healthy controls and are similar to other chronic medical disorders, such as asthma, gastroesophageal reflux, and end-stage renal disease.
The pathophysiology of IBS is incompletely understood, although it is considered to be a multifactorial disorder arising from dysregulation in the brain-gut axis as well as interactions between genetics, motor and sensory dysfunction, dysregulated intestinal immunity, and psychosocial abnormalities. Recent data suggest that patients with IBS may have increased hydrogen gas production in their small bowel. This observation has led some clinicians to hypothesize a role for small intestinal bacterial overgrowth (SIBO) in the pathogenesis of IBS and propose treating patients with antibiotics, especially those with symptoms of bloating and diarrhea. Although still controversial, this approach is gaining popularity and at present is the subject of much research and debate. Postinfectious IBS (PI-IBS) is a well-described subtype of IBS that can present de novo following a bacterial or viral gastroenteritis. It tends to occur more often in women and with time, usually develops into an IBS-D phenotype. Although a recent study concluded that PI-IBS likely accounts for only a small subset of IBS cases, its existence argues for a strong association between environmental triggers and intestinal inflammation in the development of symptoms in certain at-risk individuals.
On further questioning, it was found that our patient’s bloating and diarrhea is generally worse following meals and seems to be particularly bad after consuming dairy products. She is always fatigued and has gained 20 pounds (9 kg) since the onset of her symptoms. She denies any rectal bleeding and has no family history of colorectal cancer. At this point, do we have enough information to diagnose her with IBS? What additional studies, if any, should be performed?
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