Irritable Bowel Syndrome"DIAGNOSIS OF IBSThe diagnosis of IBS is based on identifying characteristicsymptoms and excluding organic disease. An earlyconfident diagnosis permits tests to be minimized andreassures the patient that there is no lethal disease. Thereare no physical findings or diagnostic tests that confirm thediagnosis of IBS. Therefore, diagnosis of IBS involvesidentifying certain symptoms consistent with the disorderand excluding other medical conditions which may have asimilar clinical presentation. The symptom-based Rome IIdiagnostic criteria for IBS (Table 1) emphasize a �positivediagnosis� rather than exhaustive tests to exclude otherdiseases. A validation study of the Rome criteria afterexcluding patients with symptoms suggestive of othermedical conditions other than IBS (�alarm signs� e.g.bloody stools, weight loss, family history of colon cancer,refractory and severe diarrhea) showed that 100% ofindividuals who met the diagnosis of IBS based on theRome criteria truly had IBS rather than an alternativediagnosis. At 2 years follow-up, none of the IBS patientsrequired a change in diagnosis.Other medical conditions which may present withsymptoms similar to those seen in IBS includeinflammatory bowel disease, GI infections, lactoseintolerance, thyroid disease, microscopic or collagenouscolitis and malabsorption syndromes such as celiac sprue(Table 2). A medical history and physical examination,laboratory and GI tests can help to exclude these otherdiagnoses. These tests include routine blood tests, stoolstudies for infection, and endoscopic procedures such asupper endoscopy, sigmoidoscopy and colonoscopy. Inpatients 50 years of age who meet diagnostic criteria forIBS and have no �alarm signs� suggestive of diseases otherthan IBS, initial screening tests such as a complete bloodcount to check for anemia and a chemistry panel can beobtained. Other screening tests to consider are a thyroidtest (TSH) and a blood test for celiac sprue. However,further tests and procedures such as a colonoscopy are notgenerally recommended. Patients 50 years of age with IBS symptoms should undergo a screening colonexamination with either a colonoscopy or flexiblesigmoidoscopy and barium enema if these tests have notbeen done previously, regardless if they have alarm signs(see Figure 1).In some centers, the presence of bacterial overgrowth isoften determined because this condition may causesymptoms similar to those of IBS. It is most commonlydiagnosed by a lactulose hydrogen breath test. Two studiesfrom the same research group found that 78% to 84% ofpatients with IBS had bacterial overgrowth. In patientswith evidence of bacterial overgrowth, those treated withan antibiotic such as neomycin had a greater reduction intheir GI symptoms compared with placebo. Although thesedata are intriguing, there are some methodologiclimitations in these studies and, therefore, the use ofwidespread hydrogen breath testing for bacterialovergrowth is still not generally advocated. PATHOPHYSIOLOGIC MECHANISMS OF IBS Although psychological and physiological abnormalitieshave been described, the overall pathophysiology of IBS isnot well understood. Similar to other chronic medicalconditions, a multi-component conceptual model of IBS,which involves genetic, physiologic, emotional, cognitive,and behavioral factors, has been formulated (Figure 2).Although all factors are closely interconnected, theimportance of individual factors in the generation of IBSsymptoms may vary greatly between individuals.Previously, IBS was considered primarily a disorder ofaltered gut motility. Currently, increased bowel sensitivity(visceral hypersensitivity) and altered brain-gutinteractions are felt to play a principal role in thepathophysiology of IBS. Recently, it has been found thatgenetic and environmental factors are important in IBS butfurther studies are needed to understand the importance ofthese factors in the prevalence, symptoms, physiologicresponses and response to treatment in IBS.Altered intestinal motor function.Altered intestinalmotility has been found in IBS, particularly exaggeratedcontractions (motor response) in the lower (sigmoid) colonto psychological stress and food intake. These alterationsmay explain why many IBS patients experience typicalIBS symptoms following meals and develop exacerbationsduring stressful life events. These changes in bowelmotility are likely due to alterations in the autonomicnervous system outflow to the intestine. Increased gut sensitivity.There has been compellingevidence that IBS patients have enhanced perception ofbowel (visceral) stimuli such as food or distensions of thegut wall. The initial clinical observations that led to thehypothesis that patients with IBS have visceralhypersensitivity included the presence of recurringabdominal pain as a principal symptom, the presence oftenderness during palpation of the sigmoid colon (leftlower abdominal area) during physical examination inmany patients, and excessive pain often reported bypatients during endoscopic examination of the sigmoidcolon. Published studies measuring visceral sensitivitysuggest that a variety of abnormal sensations orperceptions in relation to bowel stimuli may be morefrequent in IBS patients. At least two perceptualalterations can be distinguished, a hypervigilance(increased attention or vigilance) towards expectedaversive events arising from the bowel, and hyperalgesia(lowered threshold to pain) which is inducible by sustainedpainful visceral stimulation. These findings are paralleledby similar findings of target system hypersensitivity inother disorders such as fibromyalgia and myofascial paindisorder. In contrast to their enhanced perception ofvisceral pain, most IBS patients have normal or evendecreased pain sensitivity and tolerance for painful coldand mechanical stimulation of somatic (skin and muscle).However, there is a recent study that has demonstratedincreased somatic sensitivity to thermal heat in IBSpatients. Patients with IBS who also have co-existing fibromyalgia have increased somatic sensitivitycomparable to patients with fibromyalgia alone.Increased stress mediators in IBS.There is increasingevidence to support the prominent role of stress in thepathophysiology and in the clinical presentation of IBSsymptoms. There are few published reports on alterationsin stress mediators, such as catecholamines and cortisol tostress or visceral stimulation in IBS. Several studies havereported increased in catecholamines (norepinephrine andepinephrine) and cortisol levels in IBS patients. However,it remains to be determined whether these neuroendocrinealterations play a direct role in gut function and symptomgeneration. Altered brain-gut communication in IBS.A unifyinghypothesis to explain the functional bowel disorders is thatthey result from a dysregulation of the brain-gut axis. Anevolving theory is that normal gastrointestinal functionresults from an integration of intestinal motor, sensory,autonomic and CNS activity and GI symptoms may relateto dysregulation of these systems. Brain imaging studiessuch as functional magnetic resonance imaging (fMRI) andpositron emission tomography (PET) have been performedin IBS patients to measure brain activation patterns tovisceral stimuli. These studies suggest that brainactivation responses to visceral stimuli are distinctlydifferent in IBS patients compared to healthy individuals.IBS patients may have different emotional and cognitiveprocessing of sensory information from the gut comparedto healthy individuals. Post-infectious IBS.Symptoms suggestive of IBS occurin approximately 7-30% of patients following acute GIinfections, often persisting for years following completeresolution of the infection. A large cohort study identifieda self-reported history of acute gastroenteritis as a majorrisk factor for the development of IBS. Reported riskfactors for the development of post-infectious IBS includefemale sex, the duration of the acute diarrheal illness andthe presence of sustained psychosocial stressors around thetime of infection. Post-infectious IBS is not restricted to aparticular organism and has been documented with avariety of bacterial infections (Salmonella, Campylobacterand E. coli) as well as parasitic infection. However, therole of acute viral gastroenteritis in this condition isunknown.In post-infectious IBS, low grade GI inflammation orimmune activation may be a basis for altered motility,and/or nerve and mucosal (lining of bowel) function of thegut in IBS. Recent studies have also shown that in a subsetof unselected IBS patients (no documented history of apreceding gut infection), there is evidence of increasedinflammatory cells in the colon mucosa. It remains to bedetermined if altered gut immune function is a generalcharacteristic of IBS patients. The implication of stressfullife events in the development of post-infectious IBSsuggests a convergence of central (brain) and peripheral (gut) mechanisms in the clinical presentation of thissyndrome.Gender differences.In addition to IBS, many functionalGI disorders and other chronic visceral pain disorders (e.g.interstitial cystitis and chronic pelvic pain) and somaticpain disorders (e.g. fibromyalgia, myofascial paindisorder) are more common in women than in men.Increasing evidence suggests that gender differences existin the symptoms, pathophysiologic responses and responseto certain treatments in IBS. Female IBS patients are morelikely to be constipated, complain of abdominal distensionand certain extra-intestinal symptoms. Studies have alsosupported an influential role of ovarian hormones (e.g.estrogen and progesterone) on bowel function and painsensitivity which can in part explain the gender differencesin IBS. Several investigators have reported a variation inGI symptoms during different phases of the menstrualcycle, particularly increased abdominal pain and loosestools at the perimenstrual (just prior to and at time ofmenses) phase. TREATMENTTreatment of IBS includes both non-pharmacologic andpharmacologic therapies. An important component of non-pharmacologic treatment for IBS is a successful physician-patient relationship. The physician should strive toestablish effective bi-directional communication with thepatient, gain the patient�s confidence with a concise,appropriate medical evaluation and offer reassurance andeducation that IBS is a real medical condition with apotential impact on health related quality of life butwithout significant long/term health risk. Some IBSpatients, especially those presenting with new onset ofsymptoms, express relief that their symptoms are notcaused by a serious condition such as malignancy. Othercomponents of non-pharmacologic treatment of IBSinclude diet recommendations, lifestyle modifications, andpsychosocial intervention if needed. Patients with mild IBS symptoms comprise the mostprevalent group, and are usually treated by primary carepractitioners, rather than specialists. These patients haveless significant functional impairment or psychologicaldisturbance. These patients do not see a clinician veryoften, and usually maintain normal daily activities.Treatment is directed toward education, reassurance, andachievement of a healthier lifestyle and occasionalmedication. Dietary advice may include avoidingoffending foods which can trigger symptoms (e.g. lactoseor fructose products, fatty foods, caffeine, gas-producingfoods). Fiber supplementation has been shown to beeffective for symptoms of constipation. ""CONCLUSIONSIBS is a common, chronic disorder characterized byexacerbations and remissions, which presents withsymptoms of abdominal pain and/or discomfort and alteredbowel habits. It has a chronic relapsing course and canoverlap with other functional GI (dyspepsia) and non-GI(fibromyalgia) disorders. The clinical diagnosis of IBS is based on identifyingsymptom criteria with a �positive diagnosis� and excludingorganic disease with minimal diagnostic evaluation.Clinicians should feel secure with the diagnosis of IBS, ifmade properly, because it is rarely associated with otherexplanations for symptoms. Although there are manyexpensive and sophisticated tests available for theevaluation of IBS symptoms, these are generally notneeded for patients with typical symptoms and no featuressuggestive of organic diseases. ""An integrated diagnostic and treatment approach firstrequires an effective physician-patient relationship. Acareful history will also identify the need for diagnosticstudies and treatments as determined by the nature andseverity of the predominant symptoms, and the degree andextent of influencing psychosocial and other factors. The fact that definite structural or biochemicalabnormalities for these disorders cannot be detected withconventional diagnostic techniques does not rule out thepossibility that neurobiological alterations will eventuallybe identified to explain fully the symptoms of mostfunctional disorders. Examples of such a shift inperspective from symptom-based disorders withoutdetectable abnormalities to medically treatable diseasesbased on specific neurobiological alterations includeaffective disorders (depression, anxiety) and migraineheadaches. Similar to other chronic illnesses, amulticomponent model that involves physiologic,affective, cognitive, and behavioral factors can beformulated for IBS. Although all factors are closelyinterconnected, the importance of individual factors in thegeneration of IBS symptoms may greatly vary betweenindividuals. Physiologic factors implicated in thegeneration of IBS symptoms include hypersensitivity ofthe GI tract to normal events, autonomic dysfunctionincluding altered intestinal motility response to stress andfood intake, alterations in fluid and electrolyte handling bythe bowel, and alterations in sleep. Many of the traditional therapies have been used to treatspecific IBS symptoms because they have not been shownto significantly relieve global symptoms, which wouldimprove an overall sense of well-being. However, thediscovery of novel serotonergic agents such as tegaserodand alosetron have been shown to be effective in treatingglobal symptoms in patients with IBS compared withplacebo. More recently published studies evaluating theefficacy of antidepressants, such as tricyclics and SSRIs,suggest that these medications may help improve generalwell-being in addition to treating psychological co-morbidity in affected individuals but further studies areneeded. Psychological and behavioral therapies have alsobeen showed to be effective for IBS however it potentiallycan be limited by the availability of experienced therapists.Instituting a multidisciplinary approach using non-pharmacologic and pharmacologic therapeutic modalitiesmay result in the most effective outcome. Future studieswill further enhance our understanding of this conditionand lead to newer, more effective treatments."
http://216.109.117.135/search/cache?p=bloa...149D7A767&c=482 &yc=15315&icp=1[/URL]