Irritable Bowel Syndrome Analysis Research Paper

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Overview

Pain is a multidimensional percept consisting of sensory and affective components. A key function of pain is to signal the presence or potential of injury and generate an escape from the (potential) damaging stimulus. For example, cutaneous pain produced by a pin prick, is easily localized, and rapidly triggers a withdrawal response. On the other hand, deep or visceral pain produced by injury to subcutaneous tissues may not be easily escaped, thus prolonging pain sensation.

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Furthermore, this type of pain can be diffuse, difficult to localize, and may be associated with many detrimental effects. If the pain is both prolonged and recurring such as with chronic pain syndromes, the pain experience can evoke profound affect and emotions that can lead to psychological and psychosocial problems.

Irritable bowel syndrome (IBS) is one such disorder that undeniably exemplifies the unique qualities of a chronic pain in which patients suffer severe distress with negative impact on their quality of life. Aside from the fact that IBS is a debilitating disorder that affects a notable proportion of the population, there are abundant reasons for research aimed at characterizing all aspects of this disorder. First and foremost, the mechanisms underlying this disorder remain elusive. Secondly, a component of visceral motility dysfunction contributes to the unpleasantness that is already produced by the general hypersensitivity to visceral stimuli experienced in IBS patients. Lastly, the precipitating cause of physiological abnormalities and symptoms of IBS appear to be multi-factorial.

It is important to study how visceral stimuli are perceived in IBS because a principal feature of IBS is hypervigilance to visceral stimuli. Presumably, this occurs because patients with IBS perceive visceral stimuli to be extremely unpleasant. Furthermore, while rectal hypersensitivity has been considered by some to be a biological marker for IBS, the existence of peripheral viscero-motor abnormalities remains a contentious issue.

While the mechanisms underlying IBS are unclear, recent neuroimaging studies suggest that IBS symptoms may be due to abnormalities in the central nervous system (CNS). The standard approach used in previous neuroimaging studies is to evaluate brain response during rectal distension. However, rectal distension provokes many reactions, some of which are not perceived (i.e., presumably for reflexes and/or homeostasis) and others which are perceived. To date, neuroimaging studies have not distinguished between CNS responses evoked by rectal distension per se and the various sensations (e.g., urge to defecate, pain and unpleasantness) evoked by the distension.

Irritable Bowel Syndrome

Diagnosis and Patient Characteristics

Irritable bowel syndrome is a debilitating disorder with a significant healthcare burden (Sandier et al. 2002). In the western world, IBS affects approximately 10-15% of the general population, and predominantly afflicts females. The ratio of female to male IBS patients is 2:1 in the general population and can be as high as 4:1 in the clinical setting (Muller-Lissner et al. 2001a). This disorder is difficult to diagnose because symptoms occur in the absence of any discernable organic pathology (Thompson et al. 1999), and many of the central IBS symptoms such as pain, bloating, and dysmotility can also exist in organic bowel disease.

Thus diagnosis of IBS has historically been one of exclusion (i.e. after organic disease has been ruled out) The Rome criteria have used a symptom-based approach to place the diagnosis in a more positive perspective (Thompson et al. 1999).

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There were many early publications which marked the beginning of efforts of an international group of gastroenterology experts to define diagnostic criteria for all types of functional bowel disorders. A consensus group was gathered in 1989 to determine a systematic classification for 21 types of functional bowel disorders. The conclusions drawn from this meeting were collectively known as “Rome I” (1992) and marked the first inclusion of pain as the primary symptom in IBS diagnosis.

Recommendations from the most recent meeting of functional bowel disorders, “Rome II” (1999), changed IBS diagnostic criteria slightly by including more detail of the chronicity of this disorder (Thompson et al. 1999). The diagnostic criteria primarily requires episodes of less than12 weeks of abdominal pain and/or discomfort relieved with defecation in the last 12 months, with a change in stool frequency and/or appearance. In addition to this criterion, IBS patients should present with two or more of the following symptoms of difficult stool passage, appearance of mucous, or feeling of bloating.

Visceral Physiology Abnormalities

Some have suggested that rectal motor physiology is abnormal in IBS, although this is a contentious issue. This issue is unresolved because of several experimental factors such as the type of physiological measure being assessed, the existence of possible differences between sub-types of IBS patients, and the method of rectal stimulation. Most studies of IBS rectal physiology studies use a distension technique to study rectal compliance, tone, accommodation, and frequency of rectal contractions.

Rectal compliance is calculated as the change in rectal volume divided by the change in rectal pressure, and graphically displayed as the slope of the pressure-volume curve (Bharucha et al. 2001; Azpiroz et al. 2002). While this definition of compliance is properly known as dynamic rectal compliance, the term static compliance was created to describe the instantaneous rectal volume attained at a given pressure. Normal dynamic compliance was reported for mixed populations of IBS patients (i.e., constipation- and diarrhea-predominant) (Kwan, Davis, Mikula & Diamant, 2004). However, diarrhea-predominant IBS patients reported a significantly lower dynamic compliance (Steens et al. 2002).

There is also conflicting data for studies involving constipation-predominant IBS patients, where dynamic compliance was lower in some (Steens et al. 2002), but not in other studies (e.g. Penning et al. 2001). Both volumetric and isobaric rectal distension produce s-shaped pressure-volume curves (Sloots et al. 2000; Bharucha et al. 2001; Penning et al. 2001). The shape of these pressure-volume curves can be attributed to an initial resistance to distension due to resting tone (less compliant phase), followed by a decrease in tone due to receptive reflex-mediated relaxation (more compliant phase), and finally increased resistance to stretch as the lengthening is limited by less compliant passive elastic components (Bharucha et al. 2001).

Rectal tone is generally thought to reflect motor activity in rectal wall musculature, and is often studied at basal pressure (i.e. basal rectal tone) when respiratory fluctuations in rectal volume can be noted. However, measurements of basal rectal tone changes in IBS are also inconsistent. Steens and colleagues (2002) reported an increase in basal rectal tone in diarrhea-predominant IBS patients as a decrease in spontaneous receptive relaxation to distension at baseline (operating) pressure, and Blomhoff and colleagues (2000) showed an increased rectal tone in IBS patients as an overall decrease in the volume-pressure ratio (ml/mmHg) during a long distension at operating pressure. However, other studies show no difference in basal rectal tone between IBS patients and controls (e.g. Penning et al. 2001).

As the rectum is stretched during active distension, there is an accommodation that occurs due to relaxation of rectal wall musculature that results in a decrease in rectal tone. This rectal accommodation has been described in two ways. One method is the assessment of the initial phase of rectal resistance to stretch that measures the rate of rectal volume increase during the initial rapid phase of isobaric distension from a low baseline pressure to a high destination pressure (Kwang, Jin & Sung, 2006).

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The other method is the assessment of receptive relaxation that measures the rate of rectal volume increase during isobaric distension from the time destination pressure is achieved to its release. Rectal resistance to stretch has been reported as significantly lower in IBS patients compared to control subjects but receptive relaxation of the rectum was not abnormal in IBS patients (Kwan, Davis, Mikula & Diamant, 2004).

Clearly, inconsistent data hamper a definitive description of rectal motor physiology in IBS. The inconsistencies could be due to a number of factors, including different methods of measurement, different patient groups, and failure to consider the dynamic responses of the rectum to rectal distension. Previous studies used different techniques to distend the rectum, controlling either volume (isometric or isovolumetric) or pressure (isobaric or isotonic) during various distension paradigms (Steens et al. 2002).

Sensations have been typically assessed at a specific time during or at the end of each distension of varying durations. Although pain is a constant feature of IBS patients, bowel habits may differ. Finally, rectal distension induces physiological events such as receptive relaxation, and/or contraction that may confound the assessments. These dynamic changes can be abolished by first applying a series of conditioning distensions to stretch the rectum and therefore avoid the accommodation phase. However, this conditioning will remove potentially important physiological mechanisms.

Aside from the presence of pain, a key feature of the IBS diagnosis is dysmotility of the gut that is manifested as either diarrhea or constipation. However, relatively few studies focus on abnormalities in active contractile function of the gut. Nonetheless, there is contradictory data regarding this measure as well. Distension-induced motor activity (i.e. active contraction of gut musculature) was reported to be more frequent in a recent study of IBS patients (Corsetti et al. 2004), but no difference was found in a much earlier study that compared both constipation- and diarrhea-predominant IBS patients versus controls.

IBS physiological abnormalities have also been shown in more upstream segments of the digestive system. The primary rationale for investigations of the small bowel in IBS is the association of possible pathophysiology with unpleasant symptoms of bloating and cramping in the abdomen that is a common complaint of IBS patients. When the small bowel is not in a state of active digestion of food in a healthy individual, the major motor phenomenon in the upper gut is the migrating motor complex that is composed of three phases.

In IBS however, it has been demonstrated that phase II and III of the migrating motor complex is disrupted. Such findings indicate that intestinal gas may become trapped (or retained) in segments of the small bowel. Data supporting this concept include a study using radio-opaque transit markers to show that small bowel motility is altered in both constipation- and diarrhea-predominant IBS patients (Horikawa et al. 1999), and a study that demonstrated that gas transit in the small bowel during the inter-digestive state was significantly delayed in a mixed population of IBS patients (Serra et al. 2001). With induction of the digestive state with a lipid meal, IBS patients display further increases in intestinal gas retention and jejunum dysmotility accompanied by abdominal symptoms (Serra et al. 2002).

Psychophvsical and Psychological Abnormalities

Rectal hypersensitivity can generally be demonstrated by distension studies of the rectum. A significantly greater proportion of IBS patients versus controls report discomfort or pain at a level of distension that is typically not painful in healthy subjects. As a result, psychophysical investigations of IBS have focused primarily on determination of various sensory thresholds to rectal distension. While most studies agree with regard to the presence of much lower rectal sensory thresholds in IBS, a few studies have shown that there is no difference in urge and/or pain thresholds between IBS patients and controls (Drewes et al. 2001; Steens et al. 2001).

One important factor that may contribute to the report of negative findings in these studies is their use of rapid distension rates. Studies that show a significant difference between IBS and controls are numerous and findings may differ depending upon the rectal distension method (i.e. isobaric versus volumetric, phasic versus ramp) and the type of IBS patient. Using volumetric distensions, the thresholds for gas, stool, urgency and discomfort were demonstrated to be significantly lower in diarrhea-predominant and constipation-predominant IBS patients. These findings were supported by a study that used isobaric distension to demonstrate lower discomfort thresholds in a mixed population of IBS patients (Schmulson et al. 2000).

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Assessment with supra-pain threshold distensions has also shown that IBS patients had significantly lower maximum tolerated distension volumes compared to controls. The most convincing data that validates the use of rectal distension testing, and strengthens the concept that rectal hypersensitivity is a biological marker of IBS, comes from a recent study of 86 IBS patients. This study showed a high predictive value of IBS diagnosis at a rectal distension level of 40 mmHg (Bouin et al. 2002).

Although most studies of rectal or colonic thresholds in IBS reported abnormalities while patients were in their fasted state, lowered colonic thresholds for first sensation, gas and discomfort have also been reported in IBS patients in the digestive state (induced by infusion of lipids in the small intestine) (Simren et al. 2001). Finally as noted above, visceral hypersensitivity might not be specific to the rectum as esophageal thresholds for initial perception, and discomfort were also reportedly lower in IBS. Nevertheless, since changes in bowel habit are usually associated with the abdominal pain, study of the rectum has become a standard focus for assessment of the sensory and motor abnormalities of IBS.

Psychophysical studies of rectal distension in IBS have also used visual analogue scale (VAS) scores to assess various percepts such as urge to defecate, pain/discomfort, and unpleasantness. In contrast to studies of rectal thresholds, there is considerably less agreement between studies that examine VAS scores of rectal perception. Furthermore, some studies that specifically assess VAS scores of rectal pain intensity report much higher ratings in IBS (Penning et al. 2001; Verne et al. 2001), but one other showed no difference in pain intensity VAS scores between controls and both constipation- and diarrhea-predominant IBS patients (Steens et al. 2002).

The only studies dealing with VAS scores of urge intensity showed that only constipation-predominant IBS patients had much lower urge ratings compared to either controls or diarrhea-predominant IBS patients (Penning et al. 2001; Steens et al. 2002). Studies of the affective dimension of pain also differ in that the VAS for pain unpleasantness was demonstrated to be significantly higher for IBS patients (Verne et al. 2001).

While rectal distension continues to be the most commonly used method in the study of IBS, electrical stimulation of gut mucosa has also been sparsely used. The threshold for pain perception was shown to be much lower in IBS as shown using trans-mucosal electrical stimulation of the rectum. However, similar electrical stimulation of jejunum mucosa failed to show any difference in first perception and discomfort threshold between IBS and controls (Drewes et al. 2001).

Since IBS is a functional disorder that is characterized by chronic pain, some researchers have proposed that IBS patients may have a generalized hypersensitivity that is not restricted to visceral stimuli. There is once again contradictory data regarding whether IBS patients have generalized hypersensitivity; however, discrepancies are more difficult to rationalize given that very similar stimuli have been used amongst studies.

Early studies of this question tended to show that IBS patients were not hypersensitive to different types of stimuli. For example, transcutaneous electrical nerve stimulation of IBS patients showed that initial detection and pain thresholds were in fact significantly higher than in controls and also IBS patients had withdrawal times on the cold pressor test that were not notably different from healthy subjects. Recent findings contradicts those of earlier studies in that cold pressor test results showed that pain and withdrawal thresholds were much lower in IBS (Bouin et al. 2001b), and IBS patients were demonstrated to display thermal (using 45 and 47°C heat) allodynia and hyperalgesia (Verne et al. 2001).

Similar to other types of chronic pain, psychological abnormalities also exist for IBS patients. A large battery of psychometric tests has been employed to examine the psychological disposition of IBS patients. These include the Minnesota Multiphasic Personality Inventory (MMPI), NEO Personality Inventory, Spielberger State-Trait Anxiety Inventory, Beck Depression Inventory BDI, and the Symptoms Checklist 90 (SCL-90).

Using the MMPI, Bergeron and Monto showed inadequate dependency, somatization of affect, reactive depression, and anger and denial in IBS patients. IBS patients were found to have high anxiety and depression scores, but normal neuroticism scores (Verne et al. 2001). Results using the SCL-90 were also consistent with previous findings in that high anxiety, depression, hostility, interpersonal sensitivity, obsessive compulsive behaviour, phobic behaviour, and somatization were demonstrated in IBS (Chun et al. 1999).

IBS patients have also been shown to display high somatic focus (Verne et al. 2001), hypervigilence to any visceral stimuli, and suffer from a distortion in reality perception. When IBS patients were examined based on predominant bowel patterns, no difference was found for psychometric measures of anxiety, interpersonal sensitivity, hostility, depression or somatization between diarrhea- and constipation-predominant IBS patients (Schmulson et al. 1999).

However, there was one study showing that diarrhea-predominant IBS patients have higher anxiety compared to both constipation-predominant patients and controls perhaps related to the fear of incontinence. While there are slight differences in psychometric data between studies, there is good overall agreement that IBS patients have a high degree of psychological abnormalities associated with their condition.

In addition to just the report of psychological abnormalities in IBS, studies have related psychometric data to IBS symptoms and natural history. For example, while IBS patients have a higher than normal degree of psychological disturbances such as anxiety and depression, these were not causally related with hypersensitivity. Such findings indicate that anxiety and depression may just be associated with IBS and not produced by the disorder.

However, higher overall severity of abdominal symptoms as well as high maladaptive coping strategies in IBS was predicted by greater depression and psychological distress (Drossman et al. 2000b). Not surprisingly, the severity of abdominal pain represented as distension thresholds or abdominal symptoms clustered well with health seeking behaviour (Guthrie et al. 2003). Also consistent with this concept is data comparing IBS patients that seek health care versus those who do not (IBS non-patients).

It was shown that IBS non-patients had psychological scores intermediate between clinical IBS patients and controls, they had significantly better psychological scores and coping capabilities than the clinical group (Drossman et al. 2000a).

Psychometric scores also vary with regard to the duration of IBS symptoms as test scores can distinguish between long-term and recent-onset IBS patients. Furthermore, another study showed that recent-onset IBS patients had lower severity of abdominal symptoms, less complaint of constant symptoms, and a better quality of life compared to long-term IBS patients. Since IBS patients have numerous physiological and psychological disturbances, it is not surprising that using questionnaires assessing quality of life have demonstrated a much lower quality of life in IBS (Drossman et al. 2000a; Gralnek et al. 2000).

Postulated Mechanisms and Etiology

Sensitization of gut neuraxis has been a popular basis for investigations into the proposed mechanism and etiology of IBS. Recent evidence shows that similar to central sensitization of somatic afferent pathways, visceral hypersensitivity after sensitization of gut afferent pathways may involve N-methyl-D-aspartate (NMDA) mechanisms (Willert et al. 2004). Various stimuli have been used as a means to sensitize the gut. Intracolonic injection of glycerol, which is a mucosal irritant, produces symptoms of IBS such as colonic contractions and abdominal pain. Mechanical stimulation in the form of a conditioning stimulus applied to the sigmoid colon (i.e. sensitization of an adjacent segment of the gut) would lead to a much lower pain threshold to rectal distension and greater referral of sensations (Schmulson et al. 2000).

A recent animal (rat) model for rectal hyperalgesia achieves sensitization of the gut via both mechanical and chemical stimulation of the colon early in neonatal life (Al Chaer et al. 2000). Studies of the neonatally sensitized rats reveal a lower pain threshold for colonic distension in adulthood (Al Chaer et al. 2000), and that the visceral hyperalgesia may be due to amplification of ascending visceral input through sensitization of primary afferents (Lin & Al Chaer 2003) and/or a dysfunction of thalamic modulation (Saab et al. 2004). While the above models of IBS have good face validity, construct validity remains to be supported with reports of IBS patients that have experienced such stimuli prior to developing IBS.

Microbiological studies of IBS have also provided strong evidence for the involvement of bacterial infections of the gut as a precipitating cause of IBS. Some patients that have recovered from bacterial enteritis have been shown to exhibit IBS symptoms, and previous bacterial infection has been demonstrated to be a risk factor for development of IBS (Quigley, 2005). However, factors such as psychological disposition and inflammatory response of gut mucosa may also determine susceptibility to the development of post-infectious IBS.

Post-infectious IBS patients have been demonstrated to have abnormal psychometric scores (i.e. high anxiety, depression, somatization and neuroticism) at the time of their gastroenteritis episode. Furthermore, high psychometric scores in post-infectious IBS patients remain elevated from three to six months after diagnosis (Spiller, 2007). In addition to psychological abnormalities, biopsies of rectal mucosa of post-infectious IBS patients display an abnormally high inflammatory response even months after eradication of the infection. Specifically, post-infectious IBS patients have significantly higher counts of serotonin-containing enterochromaffin cells, mast cells, and lamina propria T-lymphocytes compared to gastroenteritis patients that did not develop post-infectious IBS and non-post-infectious IBS patients (Dunlop et al. 2003b).

While high psychometric scores and an inflammatory response of gut mucosa after gastroenteritis are important predictors of the development of post-infectious IBS, it is unknown if these two factors may be causally related.

Additional evidence linking gastroenteritis and the development of IBS come from animal models of post-infectious IBS and detailed microbiological study of the gut mucosa. For example, the cardinal symptoms of visceral hypersensitivity and dysmotility have been demonstrated in recently developed animal models of post-infectious IBS (La et al. 2003; Bercik et al. 2004). Other evidence implicating a microbiological link in IBS was shown in a study demonstrating overgrowth of small intestine bacteria in a high proportion of IBS patients (Pimentel et al. 2000). This study also showed that in IBS patients where the overgrowth was successfully eradicated with antibiotics, there was a significant decrease in symptoms of diarrhea and abdominal pain.

Immunological abnormalities have been proposed to be involved in IBS pathobiological mechanisms. An immunologically abnormal gut mucosal environment has been demonstrated in IBS patients (Chadwick et al. 2002). Specifically, this study showed that while histological examination of colonic mucosa was normal in symptomatic IBS patients, immunohistology revealed changes such as increases in lymphocytes and mast cells. Furthermore, there is compelling evidence linking the severity of abdominal discomfort in IBS patients with the proximity of colonic nerve fibers to colonic mucosal areas and increased occupation of mast cells (Barbara et al. 2004).

While precise role of stress as a factor in IBS etiology is unclear, it has been shown to exacerbate IBS symptoms and result in alterations of physiological functions in IBS patients. Studies have demonstrated stress in IBS patients is correlated with abnormal autonomic responses such as high heart rate and reduced rectal mucosal blood flow (Murray et al. 2004). In addition, application of both experimentally-induced physical and psychological stress in IBS patients results in further lowered rectal perception and pain thresholds (Murray et al. 2004). A significantly higher stress response in the brain-gut axis (measured as levels of corticotropin releasing hormone and adrenocorticotropic hormone) was found in IBS patients compared to controls during application of mental stress (Posserud et al. 2004).

Interruption of this increased stress response by application of an inhibitor of corticotropin releasing hormone showed a significant reduction of abdominal pain and anxiety evoked by electrical stimulation of rectal mucosa (Sagami et al. 2004). Most importantly, the level of associated life stress has a profound effect on the clinical outcome of IBS patients. Since stress plays a central role in the exacerbation of IBS symptoms, some have suggested that it is involved in chronically activating an already hyperactive brain-gut circuit (Naliboff et al. 2000).

IBS treatments

Historically, it has been very difficult to treat IBS because symptoms are multi­dimensional and there is an absence of organic disease. The treatment of patients with IBS usually involves alleviation of the cardinal symptoms of altered bowel habit and abdominal pain, along with managing psychological conditions such as depression and anxiety (for review, see (Camilleri et al. 1999; Read 1999). Calcium channel blockers such as octylinium bromide and mebeverine hydrobromide are effective as anti-spasmodic agents to relax the smooth muscle of the gut through interference with calcium mobilization or blockage of L-type calcium channels (Martin et al. 2004; Strege et al. 2004).

In IBS patients, these anti-spasmodic agents have been shown to both effectively enhance small bowel motility and reduce colonic motor activity (Lu et al. 2000; Bouchoucha et al. 2000). More importantly, anti-spasmodic agents reduced overall abdominal pain and bloating (Gilbody et al. 2000), and rectal distension studies of IBS patients demonstrated reduced pain pressure threshold and maximum tolerable pressure and volume (Czimmer et al. 2001).

Anti-depressants such as desipramine and fluoxetine have also been used to treat IBS patients (for review, see Crowell et al. 2004). The efficacy of anti-depressant treatment is likely due to its alteration of mood in IBS patients (Halpert et al. 2005; Kuiken et al. 2003; Guthrie et al. 2004). Furthermore, anti-depressant treatment efficacy is not equal in all IBS patients in that desipramine treatment was shown to be more effective in patients displaying moderate versus severe bowel disorder scores and in diarrhea-predominant IBS patients (Drossman et al. 2003b). The actions of anti-depressants are thought to be mediated by the CNS.

Recent functional brain imaging data support this concept as amitriptyline treatment appears to act on the CNS to reduce pain perception associated with stress in IBS patients (Morgan et al. 2005). These drugs have also demonstrated efficacy in reducing visceral motor activity in diarrhea-predominant IBS patients. The reduction of abdominal pain in IBS patients by anti-depressant treatment is reflected as an increase tolerance to rectal distension that is associated with an overall improvement of psychological scores (Halpert et al. 2005; Kuiken et al. 2003; Guthrie et al. 2004). However, evidence showing that anti-depressants reduce rectal distension threshold is controversial (Poitras et al. 2002; Kuiken et al. 2003; Guthrie et al. 2004).

Recently, the pharmacological treatment of IBS patients has focused on alteration of serotonergic neuroenteric transmission in the gut. It is logical for researchers to focus their attention on serotonin (also known as 5-hydroxytryptamine (5-HT) because 5-HT is a major neuro transmitter in the gut, and 95% of the body’s 5-HT resides in the gut (for review, see Gershon 1999). Presently, one 5-HT3 antagonist and one 5-HT4 partial agonist have been found to be effective in relieving IBS symptoms.

Specifically the 5-HT3 antagonist, alosetron has been demonstrated to be effective in reducing abdominal pain and normalizing stool frequency in diarrhea-predominant IBS patients (Camilleri et al. 1999; Jones et al. 1999). The 5-HT4 partial agonist, tegaserod, has been shown to be effective primarily in constipation-predominant IBS patients in that symptoms of abdominal pain, bloating and constipation were all reduced (Muller-Lissner et al. 2001b). The mechanism of action is better understood for tegaserod in that application reduces the activity of rectal afferents to noxious distension in the cat (Schikowski et al. 2002), and decreases the sensitivity to rectal distension in healthy human subjects (Coffin et al. 2003).

One other pharmacological therapy that has recently shown promise is the non-selective CRH receptor antagonist, a-helical CRH (Sagami et al. 2004). Application of this drug significantly reduced anxiety, motility increase, and abdominal pain evoked by electrical stimulation of rectal mucosa. Finally, a small psychophysical study has shown the efficacy of rectally applied lidocaine jelly in reducing the rectal hyperalgesia (Verne et al. 2003b). However, this study did not report any effect of this treatment on visceral dysmotility.

Non-pharmacological treatments for IBS include stress reduction, hypnotherapy, and cognitive-behavioural therapy. Studies of these treatments usually had small sample sizes and clinical outcome was not positive in all IBS patients. Relaxation techniques aimed primarily at reducing stress via muscle relaxation or meditation significantly reduced abdominal pain and gastrointestinal symptoms (Harmon, 2007).

Hypnotherapy of IBS patients was mainly centered on improving overall relaxation with positive focus on the gut produced by warming of the abdomen. This type of therapy also significantly reduced overall abdominal pain, and rectal pain thresholds as assessed by distension, but did not affect rectal physiological parameters of tone or compliance (Lea et al. 2003; Gonsalkorale et al. 2003). However, one study has demonstrated that while hypnotherapy does improve overall IBS symptoms and decreases distress, somatization and depression, the therapy did not change rectal pain distension threshold, rectal tone or compliance (Palsson et al. 2002).

The findings of this particular study highlighting a reduction of psychological abnormalities appear to suggest that the efficacy of hypnotherapy in IBS is the result of an improvement of the psychological disposition of IBS patients. Cognitive-behavioural therapy can include group-mediated sessions aimed at educating IBS patients on the biosocial aspects of their disorder to facilitate self-recovery (Poitras et al. 2002) or individual sessions tailored to aid the patient to manage anxiety using realistic symptom appraisal, enhanced coping strategies, relaxation skills, and restructuring cognition (Boyce et al. 2003).

Cognitive-behavioural therapy has been shown to significantly improve both gastrointestinal symptoms and psychometric scores for depression and anxiety (Boyce et al. 2003; Drossman et al. 2003b).

However, one study has demonstrated that improvement of IBS symptoms is not accompanied by a decrease in rectal pain threshold (Poitras et al. 2002). While the effects of individual non-pharmacological IBS therapies have been tested, studies have also demonstrated that the use of multicomponent behavioural therapy and combining behavioural therapy with standard medical care (Heymann-Monnikes et al. 2000) are effective in improving psychological well-being. Although many studies with relatively small sample sizes have shown the benefit of non-pharmacological therapies for IBS, one larger randomized trial demonstrated that cognitive behaviour therapy and relaxation training was no better than standard medical care (Boyce et al. 2003).

However, another large clinical trial comparing the effects of anti-depressant treatment with placebo or cognitive behavioural therapy with education showed that cognitive behavioural therapy was more effective than anti-depressant treatment in improving bowel symptoms, quality of life and well-being in non-depressed IBS patients that were classified as having severe to moderate bowel symptoms (Drossman et al., 2003b).

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