Clinical Pearls & Morning Reports
The irritable bowel syndrome (IBS) is a chronic and sometimes disabling functional bowel disorder. Traditionally, this functional diagnostic label has been applied when no obvious structural or biochemical abnormalities are found, but emerging evidence suggests that distinct pathophysiological disturbances may account for the symptoms and that IBS is unlikely to be one disease or merely a psychiatric (somatosensory) disorder. Read the latest Review Article on this topic.
Q. What is the prevalence of IBS in the United States?
A. The prevalence of IBS in the United States is between 7% and 16%, and the condition is most common in women and young people.
Q. How is IBS diagnosed and classified?
A. The Rome IV criteria, derived from a consensus process by a multinational group of experts in functional gastrointestinal disorders, constitute the current standard for diagnosing IBS. According to these criteria, IBS is diagnosed on the basis of recurrent abdominal pain related to defecation or in association with a change in stool frequency or form. On the basis of the Rome IV criteria, IBS is classified into four subtypes (IBS with diarrhea, IBS with constipation, IBS with mixed symptoms of constipation and diarrhea, or unsubtyped IBS) according to patients’ reports of the proportion of time they have hard or lumpy stools versus loose or watery stools.
Table 1. Rome IV Criteria for the Irritable Bowel Syndrome.
A: There has been a recent resurgence of interest in diet as a treatment for IBS. The recognition that fermentable oligosaccharides, disaccharides, and monosaccharides and polyols (FODMAPs), which are present in stone fruits, legumes, lactose-containing foods, and artificial sweeteners, exacerbate symptoms in some patients because of their fermentation and osmotic effects has led to the use of a low-FODMAP diet as a therapeutic maneuver. In a crossover randomized trial comparing a low-FODMAP diet with a normal local diet, global IBS symptom scores and bloating and pain were significantly reduced with the low-FODMAP diet. Two randomized trials comparing a low-FODMAP diet with conventional dietary recommendations (e.g., eating small, regular meals and avoiding insoluble fiber, fatty foods, and caffeine) showed no significant difference between the two approaches in the overall response to therapy. However, in one of these trials, significantly greater improvements in abdominal pain, bloating, stool frequency and consistency, and urgency were noted with the low-FODMAP diet.
A: Lubiprostone and linaclotide are novel drugs that act on intestinal enterocytes to increase fluid secretion into the gastrointestinal tract, through chloride and bicarbonate secretion, accelerating gastrointestinal transit. Both drugs are approved by the FDA for use in patients who have IBS with constipation. Abnormal 5-hydroxytryptamine (5-HT) expression is implicated in the pathophysiology of IBS. Drugs acting on 5-HT type 3 receptors slow colonic transit. In a meta-analysis, alosetron was more effective than placebo in patients who had IBS with diarrhea, for both reduction of global symptoms in four randomized trials, with a total of 1732 patients, and reduction of abdominal pain or discomfort in six trials, with a total of 2830 patients. Eluxadoline is a novel drug that acts on δ-, κ-, and μ-opioid receptors. In two phase 3 randomized trials, involving a total of 2427 patients, the drug was more effective than placebo for the treatment of IBS with diarrhea, with response rates of 27% in a pooled analysis, versus 17% with placebo (P<0.001). However, no benefit with respect to abdominal pain was noted. A meta-analysis showed that tricyclic antidepressants were more effective than placebo in 11 randomized trials involving a total of 744 patients. Tricyclic antidepressants have anticholinergic properties and slow intestinal transit. These drugs were also more effective than placebo for abdominal pain.
Table 2. Interventions for Patients with the Irritable Bowel Syndrome, According to Efficacy, Level of Evidence, Side Effects, and Cost.