Irritable Bowel Syndrome (IBS, or spastic colon) is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. 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), a stressful life event, or onset of maturity without any other medical indicators.

Although there is no cure for IBS, there are treatments that 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 coeliac disease, fructose malabsorption, mild infections, parasitic infections like giardiasis, several inflammatory bowel diseases, bile acid malabsorption, functional chronic constipation, and chronic functional abdominal pain. In IBS, routine clinical tests yield no abnormalities, although 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 does not lead to more serious conditions in most patients. However, it is a source of chronic pain, fatigue, and other symptoms and contributes to work absenteeism. Researchers have reported that the high prevalence of IBS, in conjunction with increased costs, produces a disease with a high social cost. It is also regarded as a chronic illness and can dramatically affect the quality of a sufferer’s life.

Irritable bowel syndrome (IBS) Classification

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 characterized 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).

Irritable bowel syndrome (IBS) Symptoms

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 gastroesophageal 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 depression.

Irritable bowel syndrome (IBS) Causes

Active infections

The cause of IBS is unknown, but several hypotheses have been proposed. The risk of developing IBS increases sixfold 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. Studies have shown that the nonabsorbed antibiotic Rifaximin can provide sustained relief for some 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-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.

Irritable Bowel Syndrome (IBS) Diagnosis

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.

Differential diagnosis

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. 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, 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 mis-diagnosis 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.

Investigations

Investigations are performed to exclude other conditions:

• Stool microscopy and culture (to exclude infectious conditions)
• Blood tests: Full blood examination, Liver function tests, Erythrocyte sedimentation rate, 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, malignancies)
• Hydrogen breath testing (to exclude fructose and lactose malabsorption)

Misdiagnosis

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

Coeliac 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.

Bile acid malabsorption is also often missed in patients with diarrhea-predominant IBS. SeHCAT tests suggest that around 30% of D-IBS have this condition and most respond to bile acid sequestrants.

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.