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Irritable bowel syndrome (IBS)


Irritable bowel syndrome (IBS) is a common disorder of the gastrointestinal (GI) tract that gives rise to recurrent upper and lower GI symptoms. Most commonly, patients suffer abdominal pain associated with altered bowel habits such as constipation, diarrhoea or both.

The cause of IBS is unknown and is termed a 'functional disorder' because there is no sign of disease when the bowel is examined and yet the function has clearly changed from its previous functional quality. IBS can cause a great deal of discomfort and distress but will not result in permanent harm to the bowel and does not increase the risk of developing cancer. Women are 2 to 3 times more likely to be diagnosed with IBS than men.  Some people not many with IBS are able to control the symptoms through diet and medication use.  Many do not seek medical help or turn to alternative therapies .


IBS usually appears for the first time in the second or third decades of life. Intermittent attacks can occur or symptoms can be continous. The precise cause of IBS remains unknown. A similar condition in children, of abdominal pain of unknown origin, may be a precursor of adult IBS. While emotional conflict or stress may worsen IBS symptoms, research has shown that it does not cause the disease and indeed may not coincide with onset or severity of symptoms. It is no longer acceptable to suggest that the cause of IBS in someone has been caused by anxiety, stress, or by a psychological abnormality or by diet. Such concepts are now completely out of date.

Findings now suggest that patients with IBS not only  have overly sensitive bowels compared to healthy controls but most likely this is due to bacterial overgrowth of the normal flora in the small and large bowel. Ordinary events such as eating and gas production in the large intestine can cause the colon to overreact in patients with IBS. Certain medications and foods may trigger symptoms. Chocolate, fatty foods, dairy and grain-containing, as well as alcohol are frequent offenders. Caffeine can have a laxative effect in many people but it is more likely to affect those with IBS. Notwithstanding foods etc initiating or aggravating IBS, these again are not causes of IBS but triggers. Food molecules may be reacting with other molecules being manufactured within the bowel, so causing the IBS symptoms. Researchers also have found that women with IBS may have more symptoms during their menstrual periods, suggesting that reproductive hormones can influence the course of IBS.

There is much growing and accumulated data on the development of IBS after acute gastroenteritis. This is called 'post-infective IBS'. The resulting IBS may be either diarrhoea-predominant or constipation-predominant IBS, which suggests that both chronic diarrhoea and chronic constipation may be bacterially derived. Because metronidazole and vancomycin markedly reduce diarrhoea and constipation-predominant IBS respectively during treatment and so it appears that these forms of IBS may be mediated by an ongoing, bowel flora infection rather than a persisting damage of gut nerves. After all, such antibiotics would scarcely affect dead or dying nerves. Hence, currently, the most likely cause of IBS would appear to be a chronic infection of the luminal bacteria which live within the bowel. Nonetheless, progressively nerve damage can develop with such an infection, and this can be seen in some patients with severe constipation. Indeed constipation is not caused by lack of fibre, water or exercise but is most likely caused by a bacterial infection of the normal human bowel flora with a Clostridium like-agent and produces substances that affect the enteric nervous system. Such patients can respond well to treatment with anti-clostridial agents such as Rifamycins, Vancomycin and Metronidazole.


There is no rigid reference for 'normality' of bowel behaviour and community norms cannot be used to determine 'normality' since a small or large proportion of the community may have abnormal function to start with. According to some normality of bowel movements may range from as many as three stools a day to as few as three a week. This presupposes absence of 'symptoms'. A healthy bowel movement is one that is formed but not hard, contains no blood and is passed without cramps or pain. Patients with IBS may have abdominal pain, constipation and/or diarrhoea and bloating. Many have a sensation of incomplete evacuation after defecation. Stool may be accompanied by passage of variable amounts of mucus. Symptoms generally occur during the hours when the patient is awake. Between 25% and 50% of patients with IBS also complain of heartburn, nausea, and vomiting. Bleeding, fever, weight loss, and persistent severe pain are not symptoms of IBS and require further investigations.


IBS should be diagnosed only after the presence of any other disease is excluded. In particular, the presence of secondary bowel flora infections such as Dientamoeba fragilis, some Blastocystis hominis strains, and Clostridium difficile need to be excluded. Common illnesses that may be confused with IBS include lactose intolerance, diverticular disease, cancer, drug-induced diarrhoea, laxative abuse, parasitic diseases, bacterial gastroenteritis and inflammatory bowel disease such as Crohn's disease and ulcerative colitis and bowel cancer The doctor must therefore take a complete medical history which includes careful description of symptoms. A thorough physical examination and laboratory testing will need to be performed to exclude other causes for symptoms. A stool sample should be tested for evidence of common bacteria, parasites and bleeding. The doctor also may perform procedures such as x-ray or colonoscopy (viewing the colon through a flexible tube inserted through the anus) to rule out other diseases such as cancer of the bowel.

Official diagnostic criteria for IBS (after other diseases have been excluded) include abdominal pain relieved by defecation or accompanied by change in stool consistency and/or frequency. These symptoms must be present for more than 3 months.


There is currently no cure for IBS. Therapy is tailored to each individual patient. For many people, eating a healthy diet and avoiding trigger foods and factors e.g. grains or lactose containing foods is enough to relieve the symptoms of IBS. Registered dieticians can help make appropriate dietary changes and supplementation of necessary nutrients. Regular physical activity helps relieve triggers such as stress and assists in bowel function, particularly in patients with constipation. Increasing dietary fibre - which works in a similar capacity as a drug - can also help many patients with constipation-predominant IBS, given there is no evidence that lack of fibre has anything to do with the development of IBS. Medications that target specific symptoms may be effective in IBS eg. anti-diarrhoeal or anti-spasmodic agents. Medications which target psychiatric syndromes also have an effect on the bowel 'cytokines' and bacteria and can help IBS symptoms even though there is no psychiatric nor 'psychologic' cause for IBS.

In patients with diarrhoea-predominant IBS treatment with safe, long term anti-microbial agents such as 5-ASA compounds can arrest the diarrhoea and reduce dramatically urgency and cramping. Salazopyrin, Salofalk, Asacol, Mesasal and others can be used. In those with constipation-predominant IBS olsalazine with or without colchicine has been useful. In those with severe constipation and bloating Vancomycin, Metronidazole and Rifamycins can result in dramatic improvement. (Ref – The effect of oral Vancomycin on chronic idiopathic constipation. A. F. Celik et al Alimentary Pharmacol Ther 1995;9:63-68).


There is some evidence to suggest that an imbalance between the amount of 'good' and 'bad' bacteria in the bowel may be responsible for IBS symptoms. Some studies have indicated that it is possible to restore the healthy balance of bacteria in patients with IBS by introducing new living organisms, known as probiotics, into the gut. Commercially available probiotics can be found in certain yoghurts and other products containing Lactobacillus acidophilus and Bifidobacterium bifidum. Other species of bacteria that have shown success in the treatment of IBS include Lactobacillus plantarum and caseii, Enterococcus fecalis and Clostridium butyricum. Because it has proven difficult to determine the precise organisms that may be lacking in IBS, international researchers, including those here at the Centre for Digestive Diseases, are investigating the potential use of the entire natural bacteria contained in human faeces for the treatment of IBS. This treatment has been successfully used in patients with severe diarrhoea caused by Clostridium difficile and in a small number of cases of severe inflammatory bowel disease and may yet offer the most effective treatment alternative for patients suffering IBS. (see