In gastroenterology, irritable bowel syndrome (IBS) is a functional bowel disorder characterized by mild to severe abdominal pain, discomfort, bloating and alteration of bowel habits. In some cases, the symptoms are relieved by bowel movements. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). IBS may begin after an infection (post-infectious, IBS-PI) or a stressful life event. Other functional or pain disorders and certain psychological conditions are more common in those with IBS.
Although there is no cure for IBS, there are treatments which attempt to relieve symptoms, including dietary adjustments, medication and psychological interventions. Patient education and a good doctor-patient relationship are also important.
Several conditions may present as IBS including celiac disease, mild infections, parasitic infections like giardiasis, several inflammatory bowel diseases, functional chronic constipation and chronic functional abdominal pain. In IBS, routine clinical tests yield no abnormalities, though the bowels may be more sensitive to certain stimuli, such as balloon insufflation testing. The exact cause of IBS is unknown. The most common theory is that IBS is a disorder of the interaction between the brain and the gastrointestinal tract, although there may also be abnormalities in the gut flora or the immune system.
IBS can be classified as either diarrhea-predominant (IBS-D), constipation-predominant (IBS-C) or IBS with alternating stool pattern (IBS-A or pain-predominant). In some individuals, IBS may have an acute onset and develop after an infectious illness characterised by two or more of the following: fever, vomiting, diarrhea, or positive stool culture. This post-infective syndrome has consequently been termed "post-infectious IBS" (IBS-PI).
Because there are many causes of diarrhea and IBS-like symptoms, the American Gastroenterological Association has published a set of guidelines for tests to be performed to diagnose other conditions which may have symptoms similar to IBS. These include gastrointestinal infections, lactose intolerance and Coeliac disease. Research has suggested that these guidelines are not always followed. Once other causes have been excluded, the diagnosis of IBS is performed using a diagnostic algorithm. Well-known algorithms include the Manning Criteria, the Rome I Criteria, the Rome II Process, the Kruis Criteria, and studies have compared their reliability. The more recent Rome III Process was published in 2006. Physicians may choose to use one of these criteria, or may use other guidelines based on their own experience and the patient's history. The algorithm may include additional tests to guard against mis-diagnosis of other diseases as IBS. Such "red flag" symptoms may include weight loss, GI bleeding, anemia, or nocturnal symptoms. However, researchers have noted that red flag conditions may not always contribute to accuracy in diagnosis — for instance, as many as 31% of IBS patients have blood in their stool.
The diagnostic algorithm identifies a name which can be applied to the patient's condition based on the combination of the patient's symptoms of diarrhea, abdominal pain, and constipation. For example, the statement "50% of returning travelers had developed functional diarrhea while 25% had developed IBS" would mean that half the travelers had diarrhea while a quarter had diarrhea with abdominal pain. While some researchers believe this categorization system will help physicians understand IBS, others have questioned the value of the system and suggested that all IBS patients have the same underlying disease but with different symptoms.
Celiac disease in particular is often misdiagnosed as IBS:
Recognizing celiac disease can be difficult because some of its symptoms are similar to those of other diseases. In fact, sometimes celiac disease is confused with irritable bowel syndrome, iron-deficiency anemia caused by menstrual blood loss, Crohn's disease, diverticulitis, intestinal infections, and chronic fatigue syndrome. As a result, celiac disease is commonly underdiagnosed or misdiagnosed.
Other chronic disorders. Interstitial cystitis may be associated with other chronic pain syndromes, such as irritable bowel syndrome and fibromyalgia. The connection between these syndromes is unknown.
One of the first references to the concept of an "irritable bowel" appeared in the Rocky Mountain Medical Journal in 1950. The term was used to categorize patients who developed symptoms of diarrhea, abdominal pain, constipation, but where no well-recognized infective cause could be found. Early theories suggested that the Irritable Bowel was caused by a psychosomatic, or mental disorder. One paper from the 1980s investigated "learned illness behavior" in patients with IBS and peptic ulcers. Another study suggested that both IBS and stomach ulcer patients would benefit from 15 months of psychotherapy. Later, it would be found that most stomach ulcers were caused by a bacterial infection with Helicobacter pylori.
Additional publications suggesting the role of brain-gut "axis" appeared in the 1990s, such as a study entitled Brain-gut response to stress and cholinergic stimulation in IBS published in the Journal of Clinical Gastroenterology in 1993. A 1997 study published in Gut magazine suggested that IBS was associated with a "derailing of the brain-gut axis.
Specific forms of immune response that have been implicated in IBS symptoms include Coeliac disease and other Food allergy conditions. Coeliac disease (also spelled "celiac") is an immunoglobulin type A-(IgA) mediated allergic response to the Gliadin protein in gluten grains, which exhibits wide variety of symptoms and can present as IBS. "Some patients with diarrhea-predominant irritable bowel syndrome (IBS-D) may have undiagnosed celiac sprue (CS). Because the symptoms of CS respond to a gluten-free diet, testing for CS in IBS may prevent years of morbidity and attendant expense. "Coeliac disease is a common finding among patients labelled as irritable bowel syndrome. In this sub-group, a gluten free diet may lead to a significant improvement in symptoms. Routine testing for coeliac disease may be indicated in all patients being evaluated for irritable bowel syndrome. Food allergies, particularly those mediated by IgE and IgG-type antibodies have been implicated in IBS.
There is research to support IBS being caused by an as-yet undiscovered active infection. Most recently, a study has found that the antibiotic Rifaximin provides sustained relief for IBS patients. While some researchers see this as evidence that IBS is related to an undiscovered agent, others believe IBS patients suffer from overgrowth of intestinal flora and the antibiotics are effective in reducing the overgrowth (known as small intestinal bacterial overgrowth). Other researchers have focused on an unrecognized protozoal infection as a cause of IBS as certain protozoal infections occur more frequently in IBS patients. Two of the protozoa investigated have a high prevalence in industrialized countries and infect the bowel, but little is known about them as they are recently emerged pathogens.
Blastocystis is a single-celled organism which has been reported to produce symptoms of abdominal pain, constipation and diarrhea in patients, along with headaches and depression, though these reports are contested by some physicians. Studies from research hospitals in various countries have identified high Blastocystis infection rates in IBS patients, with 38% being reported from London School of Hygiene & Tropical Medicine, 47% reported from the Department of Gastroenterology at Aga Khan University in Pakistan and 18.1% reported from the Institute of Diseases and Public Health at University of Ancona in Italy. Reports from all three groups indicate a Blastocystis prevalence of approximately 7% in non-IBS patients. Researchers have noted that clinical diagnostics fail to identify infection, and Blastocystis may not respond to treatment with common antiprotozoals.
Dientamoeba fragilis is a single-celled organism which produces abdominal pain and diarrhea. Studies have reported a high incidence of infection in developed countries, and symptoms of patients resolve following antibiotic treatment. One study reported on a large group of patients with IBS-like symptoms who were found to be infected with Dientamoeba fragilis, and experienced resolution of symptoms following treatment. Researchers have noted that methods used clinically may fail to detect some Dientamoeba fragilis infections.
A questionnaire in 2006 designed to identify patients’ perceptions about IBS, their preferences on the type of information they need, as well as educational media and expectations from health care providers, revealed misperceptions about IBS developing into other conditions, including colitis, malnutrition, and cancer.
The survey found IBS patients were most interested in learning about foods to avoid (60%), causes of IBS (55%), medications (58%), coping strategies (56%), and psychological factors related to IBS (55%). The respondents indicated that they wanted their physicians to be available via phone or e-mail following a visit (80%), have the ability to listen (80%), and provide hope (73%) and support (63%).
Definitive determination of dietary issues can be accomplished by testing for the physiological effects of specific foods. The ELISA food allergy panel can identify specific foods to which a patient has a reaction. Other testing can determine if there are nutritional deficiencies secondary to diet that may also play a role. Removal of foods causing IgG immune response as measured using the ELISA food panel has been shown to substantially decrease symptoms of IBS in several studies.
There is no evidence that digestion of food or absorption of nutrients is problematic for those with IBS at rates different from those without IBS. However, the very act of eating or drinking can provoke an overreaction of the gastrocolic response in some patients with IBS due to their heightened visceral sensitivity, and this can lead to abdominal pain, diarrhea, and/or constipation.
Several of the most common dietary triggers are well-established by clinical studies at this point; research has shown that IBS patients are hypersensitive to fats and fructose.
It also appears that some foods are more difficult for the gut as evidenced by elevated food-specific IgG4 antibodies being present, while others increase colonic contractions, which may be painful, due to increased visceral sensitivity in IBS sufferers.Fiber: In patients who do not have diarrhea predominant irritable bowel, soluble fiber at doses of 20 grams per day can reduce overall symptoms but will not reduce pain. The research supporting dietary fiber contains conflicting, small studies that are complicated by the heterogeneity of types of fiber and doses used. The one meta-analysis that controlled for solubility found that only soluble fiber improved global symptoms of irritable bowel and neither type of fiber reduced pain Positive studies have used 20-30 grams per day of psyllium seed. One study specifically examined the effect of dose and found that 20 grams of ispaghula husk was better than 10 grams and equivalent to 30 grams per dayAn uncontrolled study noted increased symptoms with insoluble fibers. It is unclear if these symptoms are truly increased compared to a control group. If the symptoms are increased, it is unclear if these patients were diarrhea predominant (which can be exacerbated by insoluble fiber), or if the increase is temporary before benefit occurs. There is a mistaken presumption that fiber therapy only works for those with constipation. In actuality soluble fiber can act as a counterbalance to both constipation, by retaining water in the bowel, and for diarrhea, by absorbing excess water.
For patients who do not adequately respond to dietary fiber, osmotic agents such as polyethylene glycol, sorbitol, and lactulose can help avoid 'cathartic colon' which has been associated with stimulant laxatives. Among the osmotic laxatives, 17 to 26 grams/day of polyethylene glycol (PEG) has been well studied.
The use of antispasmodic drugs (e.g. anticholinergics such as hyoscyamine or dicyclomine) may help patients, especially those with cramps or diarrhea. A meta-analysis by the Cochrane Collaboration concludes that if 6 patients are treated with antispasmodics, 1 patient will benefit (number needed to treat = 6). Antispasmodics can be divided in two groups: neurotropics and musculotropics. Neurotropics, such as atropine, act at the nerve fibre of the parasympathicus but also affect other nerves and have side effects. Musculotropics such as mebeverine act directly at the smooth muscle of the gastrointestinal tract, relieving spasm without affecting normal gut motility. Since this action is not mediated by the autonomic nervous system, the usual anticholinergic side effects are absent. Antispasmodic drugs are also available in combination with tranquilizers or barbiturates, such as chlordiazepoxide and Donnatal. The value of the combination therapies has not been established.
Recent studies have suggested that rifaximin can be used as an effective treatment for abdominal bloating and flatulence, giving more credibility to the potential role of bacterial overgrowth in some patients with IBS.
The multi-herbal extract Iberogast was found to be significantly superior to placebo via both an abdominal pain scale and an IBS symptom score after four weeks of treatment.
Enteric coated peppermint oil capsules has been advocated for IBS symptoms in adults and children; however, results from trials have been inconsistent.
For severe diarrhea-predominant IBS, more potent opioids may be used, such as codeine or propoxyphene; refractory cases may even be treated with paregoric, or, more rarely, deodorized tincture of opium or morphine sulfate. The use of opioids remains controversial due to the lack of evidence supporting their benefit and the potential risk of tolerance, physical dependence and addiction.
Cannabis has theoretical support for its role, but has not been subject of clinical studies. Although illegal in many countries, it has been prescribed to patients in nations such as Canada and The Netherlands. Some of the argued benefits of cannabis are the reduction of pain and nausea, appetite stimulation, and assisting in falling asleep.
Gut-directed or gut-specific hypnotherapy or self-hypnosis is one of the most promising areas of IBS treatment. An uncontrolled study shows that symptom reduction/elimination from IBS hypnotherapy can last at least five years.
Relaxation therapy in four 90-minute group sessions was found to help in a randomized controlled trial.
A prospective placebo-controlled study found patients with diarrhea predominant IBS taking Saccharomyces boulardii, a probiotic yeast, had a significant reduction on the number and improvement in consistency of bowel movements. Acupuncture: Many sufferers of IBS seek relief using Acupuncture, a component of Traditional Chinese Medicine. The meta-analysis by the Cochrane Collaboration concluded 'Most of the trials included in this review were of poor quality and were heterogeneous in terms of interventions, controls, and outcomes measured. With the exception of one outcome in common between two trials, data were not combined. Therefore, it is still inconclusive whether acupuncture is more effective than sham acupuncture or other interventions for treating IBS'. One practitioner of Traditional Chinese Medicine asserts that IBS has become a bit of a "garbage diagnosis" for some medical practitioners. Traditional Chinese Medicine does not recognize the Western diagnosis of IBS per se, as the named condition has no definitive single test for diagnosis, clear cause, or cure. Traditional Chinese Medicine approaches IBS on an individual symptom-by-symptom basis, rather than recognizing a standard "IBS" diagnosis, which then warrants a blanket "IBS" treatment. According to the National Institutes of Health, "Preclinical studies have documented acupuncture's effects, but they have not been able to fully explain how acupuncture works within the framework of the Western system of medicine that is commonly practiced in the United States."
By Country: Studies have reported that the prevalence of IBS varies by country and by age range examined. The bar graph at right shows the percentage of the population reporting symptoms of IBS in studies from various geographic regions (see table below for references).
The following table contains a list of studies performed in different countries that measured the prevalence of IBS and IBS-like symptoms:
|Percentage of Population Reporting Symptoms of IBS in Various Studies from Various Geographic Areas ** Check the Rome criteria studies (eg, at PubMed) and see how the reported prevalence rates drop! Also, one should be wary of trusting many of these study results - ref. 'Havidol'.|
|Japan||10%||Quigley,2006||Study measured prevalence of GI abdominal pain/cramping|
|United Kingdom||8.2% 10.5%||Ehlin,2003 Wilson,2004||Prevalence increased substantially 1970-2004|
|United States||14.1%||Hungin, 2005||Most undiagnosed|
|Pakistan||14%||Jafri, 2007||Much more common in 16-30 age range. Of IBS patients, 56% male, 44% female|
|Mexico City||35%||Schmulson, 2006||n=324. Also measured functional diarrhea and functional vomiting. High rates attributed to "stress of living in a populated city."|
|Brazil||43%||Quigley,2006||Study measured prevalence of GI abdominal pain/cramping|
|Mexico||46%||Quigley,2006||Study measured prevalence of GI abdominal pain/cramping|
Returning Travelers: A study of United States residents returning from international travel found a high rate of IBS and persistent diarrhea which developed during travel and persisted upon return. The study examined 83 subjects in Utah, most of whom were returning missionaries. Of the 68 who completed the gastrointestinal questionnaire, 27 reported persistent diarrhea that developed while traveling, and 10 reported persistent IBS that developed while traveling.
The National Institutes of Health provides a searchable database for grant awards since 1974 on its CRISP database, and provides dollar amounts for recent awards on its Intramural Grant Award Page In 2006, the NIH awarded approximately 56 grants related to IBS, totalling approximately $18,787,710.