Irritable bowel syndrome
|Irritable bowel syndrome|
|Classification and external resources|
Irritable bowel syndrome (IBS) or spastic colon is a symptom-based diagnosis. It is characterized by chronic mast cell activation has a central pathophysiological role in the disorder. IBS is a disorder of the gut–brain axis. Onset of IBS is more likely to occur after infections (postinfectious IBS-PI), or a stressful life event, but varies little with age. For at least some individuals, abnormalities in the gut flora occur, and it has been theorised that these abnormalities result in inflammation and altered bowel function. A diagnosis of IBS may be made on the basis of symptoms, in the absence of worrisome features such as age of onset greater than 50 years, weight loss, bloody stool, signs of infection or colitis, or family history of inflammatory bowel disease. Routine testing yields no abnormalities, although the bowels may be more sensitive to certain stimuli, such as balloon insufflation testing. Several conditions may present similarly, including coeliac disease, fructose malabsorption, mast cell activation disorders, parasitic infections, inflammatory bowel disease, bile acid malabsorption, functional chronic constipation, small intestinal bacterial overgrowth, and chronic functional abdominal pain. Although no cure for IBS is known, treatments to relieve symptoms exist. This including dietary adjustments, medication, and psychological interventions. Patient education and good doctor–patient relationships are also important. Dietary measures that have been found to be effective include increasing soluble fiber intake. IBS has no direct effect on life expectancy. It is, however, a source of chronic pain, fatigue, and other symptoms, and contributes to work absenteeism. It is common and its effects on quality of life make it a disease with a high social cost. Psychiatric disorders such as anxiety and major depression are common in IBS.
- Classification 1
- Signs and symptoms 2
Risk factors 3.1
- Post-infectious 3.1.1
- Stress 3.1.2
- Small intestinal bacterial overgrowth 3.1.3
- Dysbiosis 3.1.4
- Active infections 3.1.5
- Risk factors 3.1
- Mechanism 4
- Differential diagnosis 5.1
- Investigations 5.2
- Misdiagnosis 5.3
- Comorbidities 5.4
- FODMAPs diet 6.1.1
- Fiber 6.1.2
- Laxatives 6.2.1
- Antispasmodics 6.2.2
- Discontinuation of proton pump inhibitors 6.2.3
- Tricyclic antidepressants 6.2.4
- Serotonin agonists 6.2.5
- Serotonin antagonists 6.2.6
- Other agents 6.2.7
- SIBO therapy 6.2.8
- Psychological therapies 6.3
Stress relief 6.4
- Probiotics 6.4.1
- Herbal remedies 6.4.2
- Yoga 6.4.3
- Acupuncture 6.4.4
- Diet 6.1
- Gender 7.1
- History 8
- In the US 9.1
- Research 10
- See also 11
- References 12
- External links 13
IBS can be classified as either diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), or with alternating stool pattern (IBS-A) or pain-predominant. In some individuals, IBS may have an acute onset and develop after an infectious illness characterized by two or more of: fever, vomiting, diarrhea, or positive stool culture. This postinfective syndrome has consequently been termed "postinfectious IBS" (IBS-PI).
Signs and symptoms
The primary symptoms of IBS are abdominal pain or discomfort in association with frequent diarrhea or constipation and a change in bowel habits. There may also be urgency for bowel movements, a feeling of incomplete evacuation (tenesmus), bloating, or abdominal distension. In some cases, the symptoms are relieved by bowel movements. People with IBS, more commonly than others, have gastroesophageal reflux, symptoms relating to the genitourinary system, chronic fatigue syndrome, fibromyalgia, headache, backache, and psychiatric symptoms such as depression and anxiety. About a third of men and women who have IBS also report sexual dysfunction typically in the form of a reduction in libido. Some studies indicate up to 60% of people with IBS also have a psychological disorder, typically anxiety or depression.
While the cause of IBS is unknown, a disruption of the brain-gut "axis" and small intestinal bacterial overgrowth are thought to be important factors. The risk of developing IBS increases six-fold after acute gastrointestinal infection. Postinfection, further risk factors are young age, prolonged fever, anxiety, and depression. Antibiotic use also appears to increase the risk of developing IBS.
Approximately 10 percent of IBS cases are triggered by an acute gastroenteritis infection. Genetic defects relating to the innate immune system and epithelial barrier as well as high stress and anxiety levels appear from evidence to increase the risk of developing post-infectious IBS. Post-infectious IBS usually manifests itself as the diarrhea predominant subtype. Evidence has demonstrated that the release of high levels of proinflammatory cytokines during acute enteric infection causes increased gut permeability leading to translocation of the commensal bacteria across the epithelial barrier resulting in significant damage to local tissues which is likely to result in chronic gut abnormalities in sensitive individuals. However, increased gut permeability is strongly associated with IBS regardless of whether IBS was initiated by an infection or not.
Publications suggesting the role of brain-gut "axis" appeared in the 1990s and childhood physical and psychological abuse is often associated with the development of IBS.
Given the high levels of anxiety seen in IBS patients and the overlap with conditions such as fibromyalgia and chronic fatigue syndrome, a potential model of IBS involves a disruption of the stress system. The stress response in the body involves the HPA axis and the sympathetic nervous system, both of which have been shown to operate abnormally in IBS patients. Psychiatric illness or anxiety precedes IBS symptoms in two-thirds of patients, and psychological traits predispose previously healthy people to developing IBS after gastroenteritis.
Small intestinal bacterial overgrowth
Small intestinal bacterial overgrowth occurs with greater frequency in patients who have been diagnosed with IBS compared to healthy controls. SIBO is most common in diarrhea predominate IBS but also occurs in constipation predominant IBS more frequently than healthy controls. Symptoms of SIBO include bloating, abdominal pain, diarrhea or constipation among others. IBS may be the result of the immune system interacting abnormally with gut microbiota resulting in an abnormal cytokine signalling profile.
There is growing evidence that alterations of gut microbiota (dysbiosis) is associated with the intestinal manifestations of IBS, but also with the psychiatric morbidity that coexists in up to 80% of patients with IBS. The role of the gut mycobiota, and especially of the abnormal proliferation of the yeast Candida albicans in some patients with IBS, is under investigation.
Other researchers have focused on a possible unrecognized
- UNC Center for Functional GI & Motility Disorders
- Irritable bowel syndrome at DMOZ
- The IBS Network - UK charity supporting people living with IBS
Wouters MM, Vicario M, Santos J (2015). "The role of mast cells in functional GI disorders". Gut. PMID 26194403. doi:10.1136/gutjnl-2015-309151.
Functional gastrointestinal disorders (FGIDs) are characterized by chronic complaints arising from disorganized brain-gut interactions leading to dysmotility and hypersensitivity. The two most prevalent FGIDs, affecting up to 16–26% of worldwide population, are functional dyspepsia and irritable bowel syndrome. ... It is well established that mast cell activation can generate epithelial and neuro-muscular dysfunction and promote visceral hypersensitivity and altered motility patterns in FGIDs, postoperative ileus, food allergy and inflammatory bowel disease.
▸ Mast cells play a central pathophysiological role in IBS and possibly in functional dyspepsia, although not well defined.
▸ Increased mast cell activation is a common finding in the mucosa of patients with functional GI disorders. ...
▸ Treatment with mast cell stabilisers offers a reasonably safe and promising option for the management of those patients with IBS non-responding to conventional approaches, though future studies are warranted to evaluate efficacy and indications.
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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 about 56 grants related to IBS, totalling around $18.7 million.
A questionnaire in 2006 designed to identify patients’ perceptions about IBS, their preferences on the type of information they need, and 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 they wanted their physicians to be available by phone or e-mail following a visit (80%), have the ability to listen (80%), and provide hope (73%) and support (63%).
Differences in visceral sensitivity and intestinal physiology have been noted in IBS. Mucosal barrier reinforcement in response to oral 5-HTP was absent in IBS compared to controls. IBS/IBD individuals are less often HLA DQ2/8 positive than in upper functional gastrointestinal disease and healthy populations.
An IgG-mediated food intolerance diet led to a 24% greater deterioration in symptoms compared to those on the elimination diet and food elimination based on IgG antibodies may be effective in reducing IBS symptoms and is worthy of further biomedical research. The main problem with this study was that the differences in symptoms were only observed in exclusion diets is limited, treatment based on “abnormally” high IgG antibodies cannot be recommended.
There is increasing evidence for the effectiveness of mesalazine an aminosalicylate drug in the treatment of IBS. Mesalazine is a drug with anti-inflammatory properties that has been reported to significantly reduce immune mediated inflammation in the gut of IBS affected individuals with mesalazine therapy resulting in improved IBS symptoms as well as feelings of general wellness in IBS affected people. It has also been observed that mesalazine therapy helps to normalise the gut flora which is often abnormal in people who have IBS. The therapeutic benefits of mesalazine may be the result of improvements to the epithelial barrier function.
Individuals with IBS have been found to have decreased diversity and numbers of bacteroidetes microbiota. Preliminary research into the effectiveness of fecal microbiota transplant in the treatment of IBS has been very favourable with a 'cure' rate of between 36 percent and 60 percent with remission of core IBS symptoms persisting at 9 and 19 months follow up.
The aggregate cost of irritable bowel syndrome in the United States has been estimated at $1.7–10 billion in direct medical costs, with an additional $20 billion in indirect costs, for a total of $21.7–30 billion. A study by a managed care company comparing medical costs of IBS patients to non-IBS controls identified a 49% annual increase in medical costs associated with a diagnosis of IBS. IBS patients incurred average annual direct costs of $5,049 and $406 in out-of-pocket expenses in 2007. A study of workers with IBS found that they reported a 34.6% loss in productivity, corresponding to 13.8 hours lost per 40 hour week. A study of employer-related health costs from a Fortune 100 company conducted with data from the 1990s found IBS patients incurred US $4527 in claims costs vs. $3276 for controls. A study on Medicaid costs conducted in 2003 by the University of Georgia's College of Pharmacy and Novartis found IBS was associated in an increase of $962 in Medicaid costs in California, and $2191 in North Carolina. IBS patients had higher costs for physician visits, outpatients visits, and prescription drugs. The study suggested the costs associated with IBS were comparable to those found in asthma patients.
In the US
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, and constipation, but where no well-recognized infective cause could be found. Early theories suggested the irritable bowel was caused by a psychosomatic or mental disorder.
Women are around two to three times more likely to be diagnosed with IBS and four to five times more likely to seek specialty care for it than men. These differences likely reflect a combination of both biological (sex) and social (gender) factors. Studies of female patients with IBS show symptom severity often fluctuates with the menstrual cycle, suggesting hormonal differences may play a role. Endorsement of gender-related traits has been associated with quality of life and psychological adjustment in IBS. Gender differences in healthcare-seeking may also play a role. Gender differences in trait anxiety may contribute to lower pain thresholds in women, putting them at greater risk for a number of chronic pain disorders. Finally, sexual trauma is a major risk factor for IBS, with as many as 33% of all patients reporting such abuse. Because women are at higher risk of sexual abuse than men, gender-related risk of abuse may contribute to the higher prevalence of IBS in women.
|Percentage of population reporting symptoms of IBS in various studies from various geographic areas|
|Japan||10%||Quigley, 2006||Study measured prevalence of GI abdominal pain/cramping|
|Prevalence increased substantially 1970–2004|
|United States||14.1%||Hungin, 2005||Most undiagnosed|
|United States||15%||Boivin, 2001||Estimate|
|Pakistan||14%||Jafri, 2007||Much more common in 16–30 age range. Of IBS patients, 56% male, 44% female|
|Pakistan||34%||Jafri, 2005||College students|
|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|
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:
A meta-analysis found no benefits of acupuncture relative to placebo for IBS symptom severity or IBS-related quality of life. Acupuncture might be beneficial for some patients with IBS, but current evidence does not support its use.
Yoga may be effective for some IBS patients, especially poses which exercise the lower abdomen.
Only limited evidence exists for the effectiveness of other herbal remedies for IBS. As with all herbs, it is wise to be aware of possible drug interactions and adverse effects.
Peppermint oil appears useful. Safety during pregnancy has not been established, however, and caution is required not to chew or break the enteric coating; otherwise, gastroesophageal reflux may occur as a result of lower esophageal sphincter relaxation. Occasionally, nausea and perianal burning occur as side effects. Iberogast, a multi-herbal extract, was found to be superior in efficacy to placebo. Commiphora mukul and Plantago ovata
Probiotics may exert their beneficial effects on IBS symptoms via preserving the gut microbiota, normalisation of cytokine blood levels, improving the intestinal transit time, decreasing small intestine permeability, and by treating small intestinal bacterial overgrowth of fermenting bacteria.
Certain probiotics have different effects on certain symptoms of IBS. For example, Bifidobacterium breve, B. longum, and Lactobacillus acidophilus have been found to alleviate abdominal pain. B. breve, B. infantis, L. casei, or L. plantarum species alleviated distension symptoms. B. breve, B. infantis, L. casei, L. plantarum, B. longum, L. acidophilus, L. bulgaricus, and Streptococcus salivarius ssp. thermophilus have all been found to affect flatulence levels. Most clinical studies show probiotics do not improve straining, sense of incomplete evacuation, stool consistency, fecal urgency, or stool frequency, although a few clinical studies did find some benefit of probiotic therapy. The evidence is conflicting for whether probiotics improve overall quality of life scores.
A number of probiotics have been found to be effective, including Lactobacillus plantarum, and Bifidobacteria infantis; but one review found only Bifidobacteria infantis showed efficacy. B. infantis may have effects beyond the gut via it causing a reduction of proinflammatory cytokine activity and elevation of blood tryptophan levels, which may cause an improvement in symptoms of depression. Some yogurt is made using probiotics that may help ease symptoms of IBS. A probiotic yeast called Saccharomyces boulardii has some evidence of effectiveness in the treatment of irritable bowel syndrome.
Probiotics can be beneficial in the treatment of IBS; taking 10 billion to 100 billion beneficial bacteria per day is recommended for beneficial results. However, further research is needed on individual strains of beneficial bacteria for more refined recommendations. Probiotics have positive effects such as enhancing the intestinal mucosal barrier, providing a physical barrier, bacteriocin production (resulting in reduced numbers of pathogenic and gas-producing bacteria), reducing intestinal permeability and bacterial translocation, and regulating the immune system both locally and systemically among other beneficial effects. Probiotics may also have positive effects on the gut-brain axis by their positive effects countering the effects of stress on gut immunity and gut function.
- Relaxation techniques such as meditation
- Physical activities such as yoga or tai chi
- Regular exercise such as swimming, walking, or running
Reducing stress may reduce the frequency and severity of IBS symptoms. Techniques that may be helpful include:
The mind-body or brain-gut interactions has been proposed for IBS, and is gaining increasing research attention. Hypnosis can improve mental well-being, and cognitive behavioural therapy can provide psychological coping strategies for dealing with distressing symptoms, as well as help suppress thoughts and behaviours that increase the symptoms of IBS, although the evidence base for effectiveness of psychotherapy and hypnosis is weak and such therapies are in general not recommended. However, in treatment resistant cases where pharmacological therapies over a period of at least 12 months have failed to give relief, NICE clinical guidelines recommend that consideration should be given to psychological treatment strategies such as cognitive behavioural therapy [CBT], hypnotherapy and/or psychological therapy.
Statistically significant reduction in IBS symptoms occurs following antibiotic therapy for small intestinal bacterial overgrowth. However, recent research has shown that the lactulose hydrogen breath test does not actually measure SIBO, and that SIBO is unlikely to be the cause of IBS.
The use of opioids is controversial due to the potential risk of tolerance, physical dependence, and addiction, but can be the only relief for some diarrhea-predominant cases when other treatment has been ineffective.
Domperidone, a dopamine receptor blocker and a parasympathomimetic, has been shown to reduce bloating and abdominal pain as a result of an accelerated colon transit time and reduced faecal load, that is, a relief from 'hidden constipation'; defecation was similarly improved.
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.
Evidence is conflicting about the benefit of antidepressants in IBS. Some meta-analyses have found a benefit, while others have not. A meta-analysis of randomized controlled trials of mainly TCAs found three patients have to be treated with TCAs for one patient to improve. A separate randomized controlled trial found TCAs are best for patients with IBS-D.
Alosetron, a selective 5-HT3 antagonist for IBS-D and cilansetron (also a selective 5-HT3 antagonist) were trialed for IBS. Due to severe adverse effects, namely ischemic colitis and severe constipation, they are not available or recommended.
- Tegaserod (Zelnorm), a selective 5-HT4 agonist for IBS-C, is available for relieving IBS constipation in women and chronic idiopathic constipation in men and women. On March 30, 2007, the FDA requested Novartis Pharmaceuticals to voluntarily discontinue marketing of tegaserod based on the recently identified finding of an increased risk of serious cardiovascular adverse events (heart problems) associated with use of the drug. Novartis agreed to voluntarily suspend marketing of the drug in the United States and in many other countries. On July 27, 2007, the FDA approved a limited-treatment IND program for tegaserod in the US to allow restricted access to the medication for patients in need if no comparable alternative drug or therapy is available to treat the disease. The FDA had issued two previous warnings about the serious consequences of tegaserod. In 2005, it was rejected as an IBS medication by the European Union. Tegaserod, marketed as Zelnorm in the United States, was the only agent approved to treat the multiple symptoms of IBS (in women only), including constipation, abdominal pain, and bloating.
- Selective serotonin reuptake inhibitor antidepressants (SSRIs), because of their serotonergic effect, would seem to help IBS, especially patients who are constipation predominant. Initial crossover studies and randomized controlled trials support this role.
Strong evidence indicates low doses of tricyclic antidepressants can be effective for IBS. However, the evidence is less robust as to the effectiveness of other antidepressant classes such as SSRIs.
Proton pump inhibitors (PPIs) used to suppress stomach acid production may cause bacterial overgrowth leading to IBS symptoms. Discontinuation of PPIs in selected individuals has been recommended as it may lead to an improvement or resolution of IBS symptoms.
Discontinuation of proton pump inhibitors
- Neurotropics — for example, phenobarbitals such as Donnatal or atropine — act at the nerve fibre of the parasympathicus, but also affect other nerves, causing side effects in many patients.
- 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.
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 if seven patients are treated with antispasmodics, one patient will benefit. Antispasmodics can be divided in two groups: neurotropics and musculotropics.
For patients who do not adequately respond to dietary fiber, osmotic laxatives such as polyethylene glycol, sorbitol, and lactulose can help avoid "cathartic colon" which has been associated with stimulant laxatives. Among the osmotic laxatives, doses of 17–26 g/d of polyethylene glycol have been well studied. Lubiprostone (Amitiza) is a gastrointestinal agent used for the treatment of idiopathic chronic constipation and constipation-predominant IBS. It is well tolerated in adults, including elderly patients. As of July 20, 2006, lubiprostone had not been studied in pediatric patients. Lubiprostone is a bicyclic fatty acid (prostaglandin E1 derivative) that acts by specifically activating ClC-2 chloride channels on the apical aspect of gastrointestinal epithelial cells, producing a chloride-rich fluid secretion. These secretions soften the stool, increase motility, and promote spontaneous bowel movements. Unlike many laxative products, lubiprostone does not show signs of tolerance, dependency, or altered serum electrolyte concentration.
Mast cells and the compound that they secrete are central to the pathophysiology and implicated in the treatment of IBS; some of the secreted mast cell mediators (and associated receptors) which have been implicated in symptoms of IBS or specific subtypes include: histamine (HRH1, HRH2, HRH3), tryptase and chymase (PAR2), serotonin (5-HT3), PGD2 (DP1). Histamine also causes epithelial secretion of chloride ions and water (associated with secretory diarrhea) by signaling through a receptor or ligand-gated ion channel that has not been identified as of 2015. A 2015 review noted that both H1-antihistamines and mast cell stabilizers have shown efficacy in reducing pain associated with visceral hypersensitivity in IBS; other lower quality studies have also suggested the benefit of these agents for IBS. In a related review on idiopathic mast cell activation syndromes (including IBS), a combined treatment approach using antileukotrienes, H1/H2-antihistamines, and a mast cell stabilizer are suggested.
Drugs affecting serotonin (5-HT) in the intestines can help reduce symptoms. On the other hand, many IBS-D patients report that SSRI type medications exacerbate spasms and diarrhea. This is thought to be due to the large number of serotonin receptors in the gut. 5HT3 antagonists such as ondansetron are effective in postinfectious IBS and diarrhoea-dominant IBS due to their blockade of serotonin on 5HT3 receptors in the gut; the reason for their benefit is believed to be that excessive serotonin in the gut is thought to play a role in the pathogenesis of some subtypes of IBS. Certain atypical antipsychotic medications, such as clozapine and olanzapine, may also provide relief due to serotonergic properties these agents possess, acting on the same receptors as other medications in this specific category. Benefits may include reduced diarrhoea, reduced abdominal cramps, and improved general well-being. Any nausea present may also respond to 5HT3 antagonists owing to their antiemetic properties. Serotonin stimulates the gut motility and so agonists can help constipation-predominate irritable bowel, while antagonists can help diarrhea-predominant irritable bowel. Selective serotonin reuptake inhibitors, SSRIs, frequently prescribed for panic and/or anxiety disorder and depression, affect serotonin in the gut, as well as the brain. The bowels are highly dependent on serotonin for neural communication. "Selective serotonin reuptake inhibitor antidepressants seem to promote global well-being in some patients with irritable bowel syndrome and, possibly, some improvement in abdominal pain and bowel symptoms, but this effect appears to be independent of improved depression. Further research is required."
Medications may consist of stool softeners and laxatives in IBS-C and antidiarrheals (e.g., opiate, opioid, or opioid analogs such as loperamide, codeine, diphenoxylate) in IBS-D for mild symptoms and stronger opiates such as morphine and oxycodone for severe cases.
One meta-analysis found only soluble fiber improved global symptoms of irritable bowel, but neither type of fiber reduced pain. An updated meta-analysis by the same authors also found soluble fiber reduced symptoms, while insoluble fiber worsened symptoms in some cases. Positive studies have used 10–30 grams per day of psyllium. One study specifically examined the effect of dose, and found 20 g of ispaghula husk were better than 10 g and equivalent to 30 g per day.
Fiber might be beneficial in those who have a predominance of constipation. In people who have IBS-C, soluble fiber can reduce overall symptoms, but will not reduce pain. The research supporting dietary fiber contains conflicting, small studies complicated by the heterogeneity of types of fiber and doses used.
However, insoluble fiber (e.g., bran) has not been found to be effective for IBS. In some people, insoluble fiber supplementation may aggravate symptoms.
Some evidence suggests soluble fiber supplementation (e.g., psyllium/ispagula husk) is effective. It acts as a bulking agent, and for many IBS-D patients, allows for a more consistent stool. For IBS-C patients, it seems to allow for a softer, moister, more easily passable stool.
A diet restricted in fermentable oligo- di- and monosaccharides and polyols (FODMAPs) now has an evidence base sufficiently strong to recommend its widespread application in conditions such as IBS and IBD. They also state the restriction of FODMAPs globally, rather than individually, controls the symptoms of functional gut disorders (e.g., IBS), and the majority of IBD patients respond just as well. It is more successful than restricting only fructose and fructans, which are also FODMAPs, as is recommended for those with fructose malabsorption. Longer-term compliance with the diet was high.
No evidence indicates 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 owing to their heightened visceral sensitivity, and this may lead to abdominal pain, diarrhea, and/or constipation.
Some IBS patients believe they have some form of dietary intolerance; however, tests attempting to predict food sensitivity in IBS have proven disappointing. A small study reported that an IgG antibody test was somewhat effective in determining food sensitivity in IBS patients, with patients on the elimination diet experiencing 10% greater symptom-reduction than those on a sham diet. However, more research is necessary before IgG testing can be recommended.
Studies have shown that up to 70% of IBS patients benefited from eating a low FODMAP diet. Symptoms most likely to improve from such a diet include urgency, flatulence, bloating, abdominal pain, and altered stool output. One national guideline advises a low FODMAP diet for managing IBS when other dietary and lifestyle measures have been unsuccessful. This diet restricts various carbohydrates which are poorly absorbed in the small intestine, as well as fructose and lactose, which are similarly poorly absorbed in those with intolerances to them. Reduction of fructose and fructan has been shown to reduce IBS symptoms in a dose-dependent manner in patients with fructose malabsorption and IBS. Many individuals with IBS are lactose intolerant and a trial of a lactose-free diet is often recommended. Alternatively, an over-the-counter remedy containing lactase enzyme can be taken before consuming milk products. Allergy to milk products also causes diarrhea and other symptoms, and this will not be improved by a lactase enzyme supplement. Many who benefit from a low-FODMAP diet need not restrict fructose or lactose.
- Neurological/Psychiatric: A study of 97,593 individuals with IBS identified comorbidities such as headache, fibromyalgia, and depression. IBS occurs in 51% of chronic fatigue syndrome patients and 49% of fibromyalgia patients, and psychiatric disorders occur in 94% of IBS patients.
- Inflammatory bowel disease: IBS may be a type of low-grade inflammatory bowel disease. Researchers have suggested IBS and IBD are interrelated diseases, noting that patients with IBD experience IBS-like symptoms when their IBD is in remission. A three-year study found that patients diagnosed with IBS were 16.3 times more likely to be diagnosed with IBD during the study period. Serum markers associated with inflammation have also been found in patients with IBS.
- Abdominal surgery: IBS patients were at increased risk of having unnecessary gall bladder removal surgery not due to an increased risk of gallstones, but rather to abdominal pain, awareness of having gallstones, and inappropriate surgical indications. These patients also are 87% more likely to undergo abdominal and pelvic surgery and three times more likely to undergo gallbladder surgery. Also, IBS patients were twice as likely to undergo hysterectomy.
- Endometriosis: One study reported a statistically significant link between migraine headaches, IBS, and endometriosis.
- 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.
Several medical conditions, or comorbidities, appear with greater frequency in patients diagnosed with IBS.
Bile acid malabsorption is also sometimes missed in patients with diarrhea-predominant IBS. SeHCAT tests suggest around 30% of D-IBS patients have this condition, and most respond to bile acid sequestrants.
Coeliac disease in particular is often misdiagnosed as IBS. The American College of Gastroenterology recommends all patients with symptoms of IBS be tested for coeliac disease.
- Stool microscopy and culture (to exclude infectious conditions)
- Blood tests: Full blood examination, liver function tests, erythrocyte sedimentation rate, and serological testing for coeliac disease
- Abdominal ultrasound (to exclude gallstones and other biliary tract diseases)
- Endoscopy and biopsies (to exclude peptic ulcer disease, coeliac disease, inflammatory bowel disease, and malignancies)
- Hydrogen breath testing (to exclude fructose and lactose malabsorption)
Investigations are performed to exclude other conditions:
The diagnostic algorithm identifies a name that 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 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 all IBS patients have the same underlying disease but with different symptoms.
Colon cancer, inflammatory bowel disease, thyroid disorders, and giardiasis can all feature abnormal defecation and abdominal pain. Less common causes of this symptom profile are carcinoid syndrome, microscopic colitis, bacterial overgrowth, and eosinophilic gastroenteritis; IBS is, however, a common presentation, and testing for these conditions would yield low numbers of positive results, so it is considered difficult to justify the expense. Because many causes of diarrhea give IBS-like symptoms, the American Gastroenterological Association published a set of guidelines for tests to be performed to rule out other causes for these symptoms. These include gastrointestinal infections, lactose intolerance, and coeliac disease. Research has suggested 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 obsolete Rome I and II criteria, and 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 guidelines or may simply choose to rely on their own anecdotal experience with past patients. The algorithm may include additional tests to guard against misdiagnosis of other diseases as IBS. Such "red flag" symptoms may include weight loss, gastrointestinal bleeding, anemia, or nocturnal symptoms. However, 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, many possibly from hemorrhoidal bleeding.
No specific laboratory or imaging test can be performed to diagnose irritable bowel syndrome. Diagnosis involves excluding conditions that produce IBS-like symptoms, and then following a procedure to categorize the patient's symptoms. Ruling out parasitic infections, lactose intolerance, small intestinal bacterial overgrowth, and celiac disease is recommended for all patients before a diagnosis of irritable bowel syndrome is made. In patients over 50 years old, they are recommended to undergo a screening colonoscopy. IBS sufferers are at increased risk of being given inappropriate surgeries such as appendectomy, cholecystectomy, and hysterectomy due to their IBS symptoms being misdiagnosed as other medical conditions.
There is evidence that abnormalities occur in the gut flora of individuals who suffer from IBS such a loss of diversity with a decrease in Bacteroidetes. The changes in gut flora are most profound in individuals who have diarrhoea predominant IBS. Antibodies against common components (namely flagellin) of the commensal gut flora are a common occurrence in IBS affected individuals. Chronic low-grade inflammation commonly occurs in IBS affected individuals with abnormalities found including increased enterochromaffin cells, intraepithelial lymphocytes, and mast cells resulting in chronic immune mediated inflammation of the gut mucosa. Genetic, environmental, and psychological factors seem to be important in the development of IBS. Studies have shown that IBS has a genetic component even though there is a predominant influence of environmental factors. IBS has been reported in greater quantities in multigenerational families with IBS than in the regular population. This suggests a heritability factor. This factor does not follow classic Mendelian but is of the complex/multifactorial variety. 286 genes have been identified that are variably expressed in IBS-D patients. Some research suggests the consumption of spicy foods is directly associated with IBS, especially in women. Changes in serotonin metabolisms are thought to play a role in IBS development. One study found increased levels of serotonin transporter in the ileum of patients suffering from IBS. Another study suggested that an increased expression of apoptotic genes in IBS can lead to an increase in mast cells in the intestine. This may lead to internalization of cellular adhesion proteins such as ZO-1 and occludin.