Irritable Bowel Syndromes (IBS)
Inflammatory Bowel Disease (IBD)

The primary symptoms of IBS are abdominal pain or discomfort in association with frequent diarrhea or constipation, a change in bowel habits. There may also be urgency for bowel movements, a feeling of incomplete evacuation (tenesmus), bloating or abdominal distention. People with IBS, more commonly than others, have gastro-esophageal reflux, symptoms relating to the genitourinary system, chronic fatigue syndrome, fibromyalgia, headache, backache and psychiatric symptoms such as depression and anxiety. Some studies indicate that up to 60% of persons with IBS also have a psychological disorder, typically anxiety or depressions.

The cause of IBS is unknown, but several hypotheses have been proposed. The risk of developing IBS increases six-fold after acute gastrointestinal infection. Post-infection, further risk factors are young age, prolonged fever, anxiety, and depression. 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.” Psychological factors may be important in the etiology of IBS.

There is research to support IBS being caused by an as-yet undiscovered active infection. 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-cell organism that has been reported to produce symptoms of abdominal pain, constipation and diarrhea in patients 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-cell organism that 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. It is also found in people without IBS.

There is no specific laboratory or imaging test that can be performed to diagnose irritable bowel syndrome. Diagnosis of IBS 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 it is recommended that they undergo a screening colonoscopy.

Published research has demonstrated that some poor patient outcomes are due to treatable causes of diarrhea being misdiagnosed as IBS. Common examples include infectious diseases, celiac disease, Helicobacter pylori, and parasites.

Celiac disease in particular is often misdiagnosed as IBS. The American College of Gastroenterology recommends that all patients with symptoms of IBS be tested for celiac disease. Chronic use of certain sedative-hypnotic drugs especially the benzodiazepines may cause irritable bowel like symptoms that can lead to a misdiagnosis of irritable bowel syndrome.

Researchers have identified several medical conditions, or comorbidities, which appear with greater frequency in patients diagnosed with IBS.

Headache, Fibromyalgia, Chronic fatigue syndrome and Depression: A study of 97,593 individuals with IBS identified co-morbidities as headache, fibromyalgia, and depression. A systematic review found that IBS occurs in 51% of chronic fatigue syndrome patients and 49% of fibromyalgia patients, and psychiatric disorders were found to occur in 94% of IBS patients.

Inflammatory bowel disease (IBD): Some researchers have suggested that IBS is a type of low-grade inflammatory bowel disease. Researchers have suggested that IBS and IBD are interrelated diseases, noting that patients with IBD experience IBS-like symptoms when their IBD is in remission. A 3-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 (see Causes).

Abdominal surgery: A recent (2008) study found that IBS patients are at increased risk of having unnecessary cholecystectomy (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. A 2005 study reported that IBS patients are 87% more likely to undergo abdominal and pelvic surgery, and three times more likely to undergo gallbladder surgery. A study published in Gastroenterology came to similar conclusions, and also noted 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.

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, such a common presentation and testing for these conditions would yield such low numbers of positive results that it is considered difficult to justify the expense. Because there are many causes of diarrhea that 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 that these guidelines are not always followed. Physicians may choose to use one of these guidelines, or may simply choose to rely on their own anecdotal experience with past patients. The guidelines 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, 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 many possibly from hemorrhoidal bleeding.

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 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. On this line is a recent study, which showed that constipation and/or diarrhea seems to be different manifestations of the same underlying condition, that is a build-up of fecal retention reservoirs in the colon. Abdominal X-rays were analyzed for colon transit time and fecal distribution, which correlated significantly with bloating and abdominal pain. Thus a group of patients were identified with an increased fecal loading compared to controls, but having a colon transit time equal or less to the controls. This suggests that defecation patterns do not reflect the amount of feces in the colon and is called hidden constipation. This phenomenon may be linked to bacterial overgrowth.

Some people with IBS are likely to have food intolerances. In 2007 the evidence base was not strong enough to recommend restrictive diets.

Many different dietary modifications have been attempted to improve the symptoms of IBS. Some are effective in certain sub-populations. As lactose intolerance and IBS have such similar symptoms a trial of a lactose free diet is often recommended. A diet restricting fructose and fructan intake has been shown to successfully treat the symptoms in a dose-dependant manner in patients with fructose mal-absorption and IBS.

While many IBS patients believe they have some form of dietary intolerance, tests attempting to predict food sensitivity in IBS have been disappointing. One study reported that an IgG antibody test was 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.

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 may lead to abdominal pain, diarrhea, and/or constipation.

Gibson and Shepherd state 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.

A randomized controlled trial on IBS patients found relaxing an IgG-mediated food intolerance diet led to a 24% greater deterioration in symptoms compared to those on the elimination diet and concluded food elimination based on IgG antibodies may be effective in reducing IBS symptoms and is worthy of further biomedical research.

Further information: NIH funding of IBS Research

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