Overview and Risk Factors
Irritable bowel syndrome (IBS) is characterized by chronic abdominal pain and altered bowel habits without an identifiable organic cause. It affects 10% to 15% of the U.S. population and represents up to 50% of all referrals to gastroenterologists.
The pathophysiology is unclear. To date, no physiologic or psychological etiology has been identified. Investigation has centered on abnormal gastrointestinal motility, hypersensitivity of gastrointestinal nerves, microscopic inflammation, infection, carbohydrate or bile acid malabsorption, and emotional stress, but clinical studies thus far are inconclusive.
Abdominal pain is the predominant symptom. Altered bowel habits are also often present and may occur as diarrhea, constipation, or alternating diarrhea and constipation. Other symptoms include bloating, incomplete evacuation, nausea, dyspepsia, dysphagia, reflux, and heartburn. The condition may also be accompanied by dysmenorrhea, urinary frequency and urgency, sexual dysfunction, or fibromyalgia.
About half of cases present in patients less than 35 years of age. Women are affected twice as often as men.
A careful history and physical examination are essential to avoid unnecessary and costly diagnostic testing. The examining physician should attempt to identify foods, nutrients or additives (eg, lactose, sorbitol, saccharin, sucralose), and medications (eg, antacids, calcium channel blockers, anticholinergics) that are related to symptoms. It is also important to look for factors that suggest organic disease and require further diagnostic testing to rule it out. Examples include hematochezia, weight loss greater than 10 pounds, family history of colon cancer, recurring fever, anemia, and severe diarrhea.
The Rome II criteria have been designed to create a standardized system for diagnosis, but the utility of these criteria has not been fully established. The criteria include:
- At least 12 weeks of continuous recurrent abdominal pain that is relieved by defecation, and/or a change in the consistency, frequency, or form of stool.
- Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation).
- Passage of mucus.
- Bloating or abdominal distention.
In appropriate patients, laboratory studies may include complete blood count (CBC), chemistry panel, thyroid function tests, 24-hour stool collection, and stool testing for ova and parasites.
Colonoscopy may be useful to rule out inflammatory bowel disease and colon cancer, especially in patients over 50. In younger patients with symptoms of irritable bowel syndrome, colonoscopy is not usually necessary.
There is no specific curative treatment. The therapeutic regimen should focus on relief of symptoms and reassuring the patient that a serious illness is not present. The following nutritional interventions and several medications have been used with varying success:
- Avoid possible food triggers, including lactose and artificial sweeteners (eg, sorbitol, saccharin, sucralose).
- Diarrheal symptoms can be treated with loperamide, cholestyramine, or other antidiarrheal medications.
- Constipation can be treated with fiber supplementation, osmotic laxatives, or prokinetic agents such as tegaserod.
- Abdominal pain may respond to antispasmodic agents (eg, mebeverine, dicyclomine, hyoscyamine) or tricyclic antidepressants (eg, amitriptyline).
- Recent studies suggest that antibiotic therapy (eg, rifaximin) can be useful in certain cases, especially in patients with bacterial overgrowth and diarrhea.
Psychological interventions should also be considered and are often necessary. Individuals with irritable bowel syndrome may have enhanced autonomic, neuroendocrine, attentional, and pain-modulatory responses to stimuli.1 Brain imaging studies have demonstrated increased activation of the anterior mid-cingulate cortex that is linked to fear and psychological distress, and repression of descending opiate-mediated inhibitory pathways originating in the anterior cingulated gyrus of the limbic system.2 Sympathetic activity is increased at rest.3
Affected individuals also have higher prevalence of psychological distress, major depression, anxiety, panic disorder and agoraphobia, somatization, and hypochondriasis, compared with other patients.4,5 A recent review of randomized, controlled trials of psychological treatments found that 8 out of 12 treatments showed positive responses, mainly reductions in pain and diarrhea, with no effect on constipation.6 Treatment guidelines published by the American Gastroenterology Association suggest that cognitive-behavioral treatment, dynamic (interpersonal) psychotherapy, hypnosis, and stress management/relaxation are effective in reducing abdominal pain and diarrhea.7 Hypnotherapy has also been critically evaluated and found to be effective.8,9
Irritable bowel syndrome appears to have both nutrition- and stress-related etiologies. As with some other intestinal diseases, it may be more common in individuals consuming Western diets than in persons consuming the high-fiber, low-fat diets that are traditional in developing societies.10 Both diet and psychological interventions have resulted in symptomatic improvements, and it is likely that patients will benefit most from a combination of medical, nutritional, and behavioral approaches. The following measures may be helpful:
Increased insoluble fiber. The rationale for treatment with increased fiber is the assumption that symptoms are caused by an increase in intraluminal pressure,11 which is relieved by a bulking agent such as wheat bran. Several studies have revealed that adding bran fiber decreases bloating, constipation, and diarrhea in patients with irritable bowel syndrome. However, a placebo effect appears to account for some of these benefits, and a subpopulation of patients experience an exacerbation of symptoms (eg, bloating) with bran treatment.12
Other investigations have indicated that fiber types other than wheat bran (eg, partially hydrolyzed guar gum) are more effective for this purpose than wheat bran.11 Additional controlled clinical trials are needed in which different types of fiber are compared for their effectiveness.
Elimination diets for patients with adverse food reactions. Salicylates, amines, and glutamates in foods are suspected of causing symptoms of irritable bowel syndrome. Among the foods that contain these compounds are milk, eggs, and wheat, the 3 foods that most frequently cause IBS exacerbations.13,14 Elimination diets help roughly half of patients.15 An intervention in which beef, wheat, and dairy products were eliminated significantly reduced total symptom scores, an effect attributed to a dramatic decrease in gas (hydrogen and methane) production.16
Probiotic therapy. A number of studies have indicated differences in intestinal microbial populations between irritable bowel sufferers and controls, suggesting that antibiotic treatments may play a causative role.15 Repopulating the intestinal tract with "friendly" bacteria may be of benefit. Most studies have suggested a benefit from probiotic treatment with Lactobacillus plantarum, Bifidobacterium breve, Streptococcus faecium, and combinations of these with other organisms.12,15
Peppermint oil. Enteric-coated peppermint oil capsules have been evaluated in controlled clinical trials and found helpful in reducing the symptoms of irritable bowel syndrome in more than half of patients overall, and in 75% of children.17,18 Proposed mechanisms for its effects include calcium channel blocking on a local level, causing smooth muscle relaxation, and a direct antimicrobial effect against symptom-inducing bacterial overgrowth in the small intestine.19
What to Tell the Family
Irritable bowel syndrome is a complex illness that is frequently exacerbated by stress and, possibly, by poor diet. Patients may benefit from taking medications, making diet changes that increase insoluble fiber (bran cereal, whole grain breads), and eliminating suspected offending foods. Stress reduction techniques and hypnotherapy may also be helpful.
3. Adeyemi EO, Desai KD, Towsey M, Ghista D. Characterization of autonomic dysfunction in patients with irritable bowel syndrome by means of heart rate
variability studies. Am J Gastroenterol. 1999;94:816-823.
4. Kumano H, Kaiya H, Yoshiuchi K, Yamanaka G, Sasaki T, Kuboki T. Comorbidity of irritable bowel syndrome, panic disorder, and agoraphobia in a Japanese representative sample. Am J Gastroenterol. 2004;99:370-376.
5. Locke GR III, Weaver AL, Melton LJ III, Talley NJ. Psychosocial factors are linked to functional gastrointestinal disorders: a population based nested case-control study. Am J Gastroenterol. 2004;99:350-357.
6. Mertz H. Psychotherapeutics and serotonin agonists and antagonists. J Clin Gastroenterol. 2005;39(suppl 3):S247-S250.
10. Walker AR, Segal I. Epidemiology of noninfective intestinal diseases in various ethnic groups in South Africa. Isr J Med Sci. 1979;15:309-313.
11. Parisi GC, Zilli M, Miani MP, et al. High-fiber diet supplementation in patients with irritable bowel syndrome (IBS): a multicenter, randomized, open trial comparison between wheat bran diet and partially hydrolyzed guar gum (PHGG). Dig Dis Sci. 2002;47:1697-1704.
12. Floch MH. Use of diet and probiotic therapy in the irritable bowel syndrome: analysis of the literature. J Clin Gastroenterol. 2005;39(suppl):S243-S246.
15. Madden JA, Hunter JO. A review of the role of the gut microflora in irritable bowel syndrome and the effects of probiotics. Br J Nutr. 2002;88(suppl 1):S67-S72.