Irritable bowel syndrome likely represents the clinical expression of multiple potential pathophysiologic factors, including a genetic predisposition to the disease, disturbed CNS pain processing, visceral hypersensitivity, mucosal inflammation, abnormal colonic motility, and emotional stress.
Anxiety disorders, somatoform disorders, and history of physical or sexual abuse have been identified in 42% to 61% of patients with IBS referred to gastroenterologists.
Irritable bowel syndrome (IBS) is one of the most common conditions encountered in family practices, with a prevalence ranging from 1% to 20% worldwide and approximately 7% in the United States. IBS is characterized by abdominal pain, bloating, and disturbed defecation in the absence of known structural or biochemical abnormality. It typically appears in the late 20s, although it may present in teenagers and in patients as old as age 45; patients over 45 with suspected IBS should be evaluated for organic disease. IBS is responsible for over $20 billion in direct and indirect expenditures annually in the United States, and patients with IBS consume 50% more health care resources than matched controls without IBS (ACG, 2009).
Irritable bowel syndrome likely represents the clinical expression of multiple potential pathophysiologic factors, including a genetic predisposition to the disease, disturbed central nervous system (CNS) pain processing, visceral hypersensitivity, mucosal inflammation, abnormal colonic motility, and emotional stress. Given the degree of variation of IBS symptoms in affected patients, it is likely that the etiology of IBS is a heterogeneous combination of these factors, as well as other undetermined mechanisms. Psychosocial stressors likely exacerbate symptoms in patients with functional GI disorders. Anxiety disorders, somatoform disorders, and a history of physical and/or sexual abuse have been identified in 42 to 61% of patients with IBS who have been referred to gastroenterologists (Miller et al., 2001).
The physical examination in patients with IBS is often non-specific, and may demonstrate a normal abdomen examination, a diffusely tender abdomen, or a focally tender abdomen. Multiple diagnostic screening tests have been recommended including a CBC, erythrocyte sedimentation rate (ESR), serum chemistries, thyroid function tests, stool cultures including ova and parasites, fecal occult blood test, colonoscopy, and hydrogen breath testing, specifically to rule out other causes of disease (ACG, 2009). Despite these
Box 38-8 Diagnosis of Irritable Bowel Syndrome: Rome III Criteria
Symptoms of recurrent abdominal pain or discomfort and a marked change in bowel habit for at least 6 months, with symptoms experienced on at least 3 days of at least 3 months. Two or more of the following must apply: Pain is relieved by a bowel movement. Onset of pain is related to a change in frequency of stool. Onset of pain is related to a change in the appearance of stool.
Modified from Longstreth GF, Thompson WG, Chey WD, et.al. Functional bowel disorders. Gastroenterology 2006;130:1480-1491.
recommendations, diagnostic testing should depend on the pretest probability of organic disease.
The differential diagnosis of IBS includes IBD, lactose intolerance, acute gastroenteritis, celiac disease, small intestinal bacterial overgrowth, colorectal cancer, and motility-altering metabolic disturbances (e.g., from hypo/hyperthyroidism. Currently, the Rome III criteria are the most widely accepted symptomatic classification of IBS (Box 38-8) (Longstreth et al., 2006).
There is no single evidence-based, consistently successful therapeutic approach for patients with IBS. Because it is largely a chronic condition, the goals of therapy should focus on patient reassurance, education about the natural course of the syndrome, and global symptomatic improvement, rather than on disease cure. This is best achieved through a well-developed physician-patient relationship with a clear delineation of realistic goals and expectations.
Newer treatments of IBS include tegaserod (ZelnormJ, a 5-HT4 receptor agonist, shown to be more effective than placebo in relieving global symptoms in women with constipation-predominant IBS. Alosetron (Lotronex), a 5-HT3
antagonist, is indicated for women with diarrhea-predominant IBS and also is more effective than placebo in RCTs. Reports of ischemic colitis have limited the use of alosetron to physicians participating in the manufacturer's risk management program. Treatment of diarrhea-predominant IBS can be achieved with loperamide, although no effect over placebo for global IBS symptoms has been reported (Brandt et al., 2002).
To date, all other classes of medications used in the management of IBS have more limited impact on the global symptoms of IBS. The tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs) have been shown to reduce abdominal pain, although global symptom reduction and HRQOL did not significantly improve compared with placebo. Treatment of constipation-predominant IBS can be achieved with fiber-bulking agents, but has not improved global IBS symptoms over placebo. Cognitive-behavioral therapy (CBT), interpersonal psychotherapy, group therapy, biofeedback, and hypnosis have been shown to improve individual aspects of diarrhea-predominant IBS, but these have also not been shown to improve global IBS symptoms (see Key Treatment). Complementary and alternative medicine (CAM) techniques include acupuncture, enteric-coated peppermint oil, probiotic therapy, and Chinese herbal medicine. CAM therapies are becoming increasingly popular in the treatment of GI disorders and have shown some limited symptomatic improvement in select patients with IBS (ACG, 2009).
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