What is irritable bowel syndrome (IBS)?
Irritable bowel syndrome comprises a group of functional bowel disorders in which abdominal discomfort or pain is associated with defecation or a change in bowel habits, and with features of disordered defecation.
How does one diagnose IBS?
The diagnosis of IBS is based on identifying positive symptoms consistent with the disorder, as described in the Rome Criteria and with the exclusion of other conditions (either organic or functional) with similar clinical presentation.
ROME II DIAGNOSTIC CRITERIA FOR IRRITABLE BOWEL SYNDROME
>At least 12 weeks or more, which need not be consecutive, in the preceding 12 months of abdominal discomfort or pain that has two out of three features:
Relieved with defecation; and/or
Onset associated with change in frequency of stool; and/or
Onset associated with a change in form (appearance) of stool.
>Symptoms that cumulatively support the diagnosis of irritable bowel syndrome:
Abnormal stool frequency (> 3 bowel movements/day or < 3 bowel movements/week);
Abnormal stool form (lumpy/hard or loose/watery stool);
Abnormal stool passage (straining; urgency; feeling of incomplete evacuation)
Passage of mucus
Bloating or feeling of abdominal distension
What is the Rome Committee?
The Rome Committee consists of a group of multinational experts in functional bowel disorders. The working team first met in Rome in 1988 to develop criteria for the diagnosis of functional gastrointestinal disorders (Rome Criteria). In 1998 the working team proposed changes and modifications, which were published in 1999 and are known as Rome II Criteria. A further update, Rome III Criteria, is expected in 2006.
Is there any specific biologic and pathophysiologic marker to diagnose IBS?
No. There is no specific discriminatory finding or diagnostic test for IBS.
Describe the supporting symptoms of IBS.
- Fewer than three bowel movements a week
- More than three bowel movements a day
- Hard or lumpy stools
- Loose (mushy) or watery stools
- Straining during a bowel movement
- Urgency (having to rush to have a bowel movement)
- Feeling of incomplete evacuation
- Passing mucus (white material) during a bowel movement
- Abdominal fullness, bloating, or swelling
What is the importance of the supportive symptoms of IBS?
The supportive symptoms help in the classification of IBS as either diarrhea predominant or constipation predominant.
Define diarrhea-predominant and constipation-predominant IBS.
Based on supporting symptoms, these disorders are defined as follows:
- Diarrhea-predominant (>three bowel movements per day): One or more of supporting systems 2, 4, or 6 and none of 1, 3, or 5; or two or more of 2, 4, or 6 and one of 1 or 5 (3, hard lumpy stools do not qualify).
- Constipation-predominant ( Subclassification of IBS into constipation-predominant or diarrhea-predominant and mixed patterns has limited value in understanding the pathophysiology of IBS.
Discuss the epidemiology of irritable bowel syndrome.
Most estimates indicate that the prevalence is approximately 10%, and this estimate is consistent with multiple non-U.S. studies. Constipation-predominant IBS is more common in women. Functional dyspepsia and IBS appear to overlap in this population.
What is the economic impact of IBS in the United States?
IBS is a distressing condition that impairs the quality of life and therefore requires treatment. Most persons with IBS do not consult physicians. Fewer than one quarter of individuals with IBS symptoms present for the evaluation and treatment of their symptoms. Patients with IBS are more likely to undergo surgical procedures, including hysterectomy and appendectomy.
The cost to society in terms of direct medical expenses and indirect costs, such as absenteeism, is considerable. There are between 2.4 and 3.5 million physician visits annually for IBS in the United States, during which 2.2 million prescriptions are written. IBS is associated with more than $8 billion (U.S.) a year in direct healthcare costs.
Describe the pathophysiology of IBS.
Initial observations suggest that abnormal motility underlies IBS symptoms. Accelerated small bowel and colon transit has been demonstrated in patients with diarrhea predominant IBS. More than 50% of IBS patients report exacerbation of symptoms after eating, suggesting a prominent gastrocolonic response. Furthermore, high amplitude-propagated contractions in the postprandial period are seen in diarrhea-predominant IBS and a lack of these contractions are seen in severe constipation.
Later observations showed that visceral hypersensitivity is important in explaining the clinical manifestations of IBS. IBS patients have lower visceral pain thresholds than healthy patients. As knowledge increased about the interrelatedness of the brain and gut, it was recognized that the abnormal motility and visceral hypersensitivity in IBS are determined by reciprocal interactions between brain and gut. 5-HT is a neurotransmitter in both the central and enteric nervous systems and is a key mediator of visceral hypersensitivity and heightened bowel motility in patients with IBS.
What is postinfectious irritable bowel syndrome?
Patients who report an acute onset of IBS symptoms after a bout of gastroenteritis are defined as postinfectious IBS (PI-IBS). These patients have previously normal bowel habits. Up to 30% of IBS patients describe an acute onset of bowel disturbances following an acute infective enteritis. PI-IBS is associated with a modest increase in mucosal T-lymphocytes and serotonin containing enteroendocrine cells. Patients with PI-IBS have the same prognosis as noninfective IBS, with fewer than half recovering after 6 years.
What symptoms are not typical of IBS and should prompt an evaluation for organic disease?
- Acute onset of symptoms
- Rectal bleeding or anemia
- Weight loss
- Persistent diarrhea
- Severe constipation
- Nocturnal symptoms
- New onset of symptoms in patients >age 50.
- Abnormal colonoscopy/sigmoidoscopy
- Family history of GI cancer, inflammatory bowel disease (IBD), or celiac disease
What diagnostic tests are appropriate in a patient suspected of IBS?
To rule out anatomic disorders, the following screening tests are normally recommended: complete blood count, sedimentation rate, serum chemistries, thyroid stimulating hormone (TSH), stool, occult blood, stool for ova and parasites, and flexible sigmoidoscopy or colonoscopy (with mucosal biopsy), depending upon age and other associated symptoms (e.g., diarrhea). Serologic testing for celiac disease (tissue transglutaminase) should be performed on all patients suspected to have IBS-diarrhea predominant.
Additional studies should be based on presenting symptoms (diarrhea, constipation, or abdominal pain). The use of diagnostic studies to exclude organic disease should be prudent and cost-effective and made in the context of the entire clinical history, including psychological issues
What is the role of stress and psychological factors in IBS?
Stress is widely believed to play a major role in the pathophysiology and clinical presentation of IBS. The effect of stress on gut function is universal, and patients with IBS appear to have greater reactivity to stress compared with healthy individuals.
Psychological factors include anxiety disorders, depression, somatization, a history of sexual or physical abuse, stressful lifetime events, chronic social stress, or maladaptive coping styles. Psychological symptoms are more prevalent in patients who have severe symptoms and who are seen in tertiary care centers. Furthermore, stress is associated with symptom onset, exacerbations, and severity.
What are essential elements in the management of a patient with IBS?
Treatment of IBS patients is indicated when the patient and physician believe that the IBS symptoms diminish the quality of life of the patient. The algorithm for management of IBS based on symptom predominance.
It is important to emphasize to the patient the negative results of tests to exclude organic disease and to reassure the patient. Patients should be asked about psychological factors, stress, and history of physical and sexual abuse because these factors may require specific treatment.
There is evidence to suggest that the outcomes in IBS patients can be improved when physicians: (1) actively listen to patient concerns; (2) provide an adequate explanation of disorder; (3) set realistic goals; (4) establish a long-term relationship; (5) respond to patient concerns and expectations; and (6) identify behavior stressors that exacerbate symptoms.
What is the role of fiber in management of IBS?
As a group, patients with IBS do not consume less fiber than control subjects. Fiber has a role in treating constipation; its value for IBS, pain, and diarrhea is controversial.
Many patients with IBS complain of bloating with higher doses of natural fiber. Short chain fatty acids are produced by bacterial fermentation of dietary fiber, resulting in gas formation. Short chain fatty acids can also stimulate rectal contractions and produce pain.
Are anticholinergic and antispasmodic agents useful in IBS?
The evidence-based position statement on the management of IBS produced by the American College of Gastroenterology states that there is insufficient evidence to make any recommendation about the effectiveness of antispasmodic agents available in the United States. Antispasmodic and anticholinergic agents are sometimes used on an as-needed basis for acute attacks of pain, distention, and bloating.
Discuss the role of psychotropic agents in treating patients with IBS.
Antidepressants have utility in IBS because many patients present with associated psychological symptoms. Antidepressants have neuromodulatory and analgesic properties, and there is also potential benefit even in the absence of psychiatric comorbidity. Neuromodulatory effects may occur sooner and with lower doses in IBS patients than the dose used in the treatment of depression (e.g., 10-25 mg amitriptyline or 50 mg desipramine). Recent studies suggest that selective serotonin reuptake inhibitors (SSRIs) may offer benefit in some patients with IBS. Tricyclic antidepressants (TCAs), offer benefit for abdominal pain and diarrhea; SSRIs cause diarrhea and may be helpful in patients with constipation-predominant IBS.
IRRITABLE BOWEL SYNDROME TREATMENT STRATEGIES
- Educate and reassure the patient.
- In diarrhea-predominant IBS, tricyclic antidepressants relieve diarrhea and associated pain.
- Opioids are useful in relief of diarrhea but may precipitate constipation.
- Smooth muscle relaxants are indicated in patients with predominant pain/bloating. Their effectiveness is controversial.
- 5-HT4-agonists are effective in treating constipation-predominant IBS.
Describe various types of psychological treatments used in patients with IBS.
- Cognitive behavioral therapy: this attempts to change the way patients perceive and react to their symptoms; uses diaries and exercises to reframe maladaptive thoughts and increase control over symptoms.
- Interpersonal psychotherapy: identifies and addresses difficulties in relationships. Several studies suggest benefit compared with standard medical therapy.
- Hypnosis: suggestions are used to reduce gut sensation. This is the best-evaluated psychological treatment. Improvements noted 1 year later.
- Relaxation training: uses imagery and relaxation techniques to reduce autonomic arousal and stimulate muscular relaxation; improves gut motility.
What is the association between serotonin (5-HT) and IBS?
A fundamental observation in IBS is the presence of enhanced visceral perception. Serotonin has a role in mediating visceral hypersensitivity and the peristaltic reflex. Ninety-five percent of serotonin is found in the gut, with 90% localized within enterochromaffin cells and 10% in the enteric neurons. Of the various types of serotonin, 5-HT3 and 5-HT4 are involved in sensory and motor functions of the gut and are targets for pharmacotherapy in IBS.
What are the roles for 5-HT3 antagonist and 5-HT4 agonist in management of IBS?
The indications, mechanism of actions, and major side effects of common 5-HT4 agonist and 5-HT3-receptor antagonist. Alosetron is effective in inducing adequate relief of abdominal pain and discomfort, improvement in bowel frequency, consistency, and urgency in women with diarrhea-predominant IBS. A significant adverse effect is acute ischemic colitis. Because of adverse effects, alosetron was withdrawn from the market in November 2000. As a consequence of vigorous public outcry following withdrawal, the Food and Drug Administration (FDA) approved the restricted use of alosetron in June 2002. Another medication in this class, cilansetron, is undergoing phase III studies for treatment of diarrhea-predominant IBS.
Tegaserod is partial 5-HT4 agonist, which is indicated in women with constipation-predominant IBS. It is the only FDA-approved agent for the short-term treatment of IBS patients with constipation. It improves global assessment and individual symptoms of IBS, including abdominal pain, stool frequency, and bloating.
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