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IBS is highly prevalent in the Western world, but despite the advancement of many theories, no clear cause has yet been established. IBS may be a conglomeration of disorders with similar symptoms but multiple different etiologies (root causes). In studies of twins, some but not all studies, a genetic role is found. In the two positive studies, IBS concordance in monozygotic twins is 17% - 22% compared to dizygotic twins having IBS concordance of 8% to 9%. In one of the studies further support for genetic inflences being a minority contributor, a dizygotic twin with IBS has 15.2% IBS in mothers, compared to 6.7% in their co-twin. As with many other medical conditions, there is a lot of speculation about causes, including in the field of alternative medicine. Increasing prevalence in developing countries suggests some possible links to diet and cultural factors.
Visceral hyperalgesia
Evidence of visceral hyperalgesia (increased sensitivity to noxious stimuli in the gut) includes perception of pain from distention of a rectal balloon at smaller volumes than in normal patients. However, somatic sensitivity testing, such as in controlled pressure on the nails of the hand show that IBS patients have greater pain tolerance than normal patients.
Post-infectious or post-antibiotic
Onset of IBS after an episodes of enteritis or antibiotics have been described. A meta-analysis found the prevalence of IBS to 9.8% after enteritis as compared to 1.2% in controls. In these cases, a prolonged immune reaction may be the cause. Patients with IBS after a viral illness may have a self limited course of only 3 to 6 months duration.
Food allergies and sensitivities
Argument continues on the definition of cause as regards IBS and food allergies, but studies demonstrate that IBS symptoms are sometimes caused by immune response to foods and exclusion of those foods to which the immune system is responding results in reduction or elimination of IBS symptoms, a cause and effect link.
Bacterial overgrowth
The intestine is colonised with bacteria (also termed the gut flora). Two studies from the same research group found that 78% to 84% of patients with IBS had bacterial overgrowth. In patients with evidence of bacterial overgrowth, those treated with neomycin had a ? 35% reduction in clinical response (ie, improvement) compared with an 11% reduction in patients on placebo. Subsequent studies have also identified significant bacterial overgrowth and demonstrated substantial reduction in symptoms following treatments, especially with antibiotics specific to the strains that are in excess. See section below on treatment with rifaximin.
Stress
Stress—feeling mentally or emotionally tense, troubled, angry, or overwhelmed—may trigger symptoms in people with IBS. One study found that women with IBS are more likely to report prior physical or sexual abuse; almost half of the patients reported prior abuse.
There are various ways that stress may interact with IBS. First, the colon has a vast supply of nerves, called the enteric nervous system, that connect it to the brain. These nerves control the normal rhythmic contractions of the colon and cause abdominal discomfort at stressful times. People often experience cramps or "butterflies" when they are nervous or upset. But with IBS, the colon can be overly responsive to even slight conflict or stress. Second, some evidence suggests that IBS is affected by the immune system, which fights infection in the body. The immune system is also affected by stress. Third, the link between stress and IBS may be due to socially stressful situations making the mind more tuned to the sensations that arise in the colon and makes the stressed person perceive these sensations as unpleasant.
There appears to be an overlap of IBS with stress, chronic pelvic pain, fibromyalgia, chronic fatigue syndrome, the American folk medicine use of term hypoglycaemia, and various mental disorders (in a small minority). While no single explanation for this phenomenon exists, it does strengthen the view that there is a neurological and psychological component to IBS. Recent studies indicate that presynaptic neural effects secondary to the release of histamine (part of immune response) is likely related to these problems.
It should be noted that the gut has its own nervous system - the enteric nervous system which has reciprocal connections to the main brain. The discovery of this system has led to the development of the field of neurogastroenterology.
For all these reasons, stress management is an important part of treatment for IBS.
Hormones
The role of hormones in IBS is not yet fully understood. Menstruation frequently triggers or exacerbates IBS symptoms, while pregnancy and menopause can either worsen or improve symptoms. Hormone replacement therapy is associated with an increased risk of developing IBS.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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