The pathophysiology, diagnosis, and treatment of IBS

Laboratory testing The history and physical examination allow the practitioner to glean information useful in determining the need for further studies. The AGA recommends a routine CBC and fecal occult blood testing. If alarm symptoms are present, a full workup and referral to a gastroenterologist are warranted.¹⁴ If there are no alarm symptoms and the Rome criteria are met, the patient may be evaluated based on age. Those older than 50 years should be referred to a gastroenterologist for a colonoscopy; those younger than 50 years may be evaluated based on their predominant symptom. Further tests may include a chemistry panel, ESR, thyroid-stimulating hormone level, stool analysis for ova and parasites, and tests for antiendomysial and antigliadin antibodies.²⁰ Additional testing may be indicated but is more often performed after referral to a gastroenterologist.

Treatment

Once the diagnosis of IBS has been made, the treatment plan is based on the nature and severity of the symptoms, the degree of functional impairment, and the presence of psychosocial factors. A therapeutic relationship is essential for effective management and decreases the number of follow-up visits.²¹ The provider must be nonjudgmental, give a thorough explanation of the disorder and its chronicity, provide reassurance that
IBS is not dangerous or life threatening, and involve the patient in the treatment plan.²² Despite the benign nature of IBS, studies show that it significantly affects quality of life; therefore, providers must actively listen and communicate understanding and compassion to these patients.

Diet While patients are more likely to have generalized postprandial symptoms than reactions to specific types of food, symptom diaries can sometimes identify social and dietary triggers. Problematic dietary substances often include coffee, alcohol, carbonated drinks, disaccharides, beans, and leafy vegetables.²⁰

Increased fiber intake has long been recommended for treatment of IBS, but studies are not conclusive as to its benefit. Fiber is thought to increase stool bulk, to bind to agents such as bile, to enhance the stool's water-holding properties, and to promote gel formation to provide lubrication. ²³ Safety and low cost make a trial of fiber, 20 to 25 g daily, either dietary or in supplements, reasonable in all patients.24 The dosage may require titration over several weeks to reduce abdominal pain and bloating.

For patients with mild symptoms, reassurance and education may be sufficient, but those with moderate to severe symptoms may require pharmacologic therapy (see Table 4). This decision is based on the predominant symptom and presence of comorbid psychiatric conditions.

Medication Antispasmodic agents relax smooth muscle in the gut and reduce propulsive contractions, decreasing postprandial abdominal pain, gas, bloating, and fecal urgency.^21,23,25 Dicyclomine, hyoscyamine, and clidinium bromide/chlordiazepoxide work through anticholinergic or antimuscarinic properties and may be used in an as-needed or in an anticipatory fashion.^25,26 Higher dosages are more effective, but anticholinergic side effects may be a limiting factor.

At low dosages, tricyclic antidepressants (TCAs) and, potentially, selective serotonin reuptake inhibitors (SSRIs) have analgesic properties independent of their effect on mood.^26,27 The proposed mechanism is a facilitation of endogenous endorphin release and blockade of norepinephrine reuptake, which leads to an enhancement of descending inhibitory pain pathways and blockade of the pain neuromodulator serotonin.²⁸ Additionally, the anticholinergic properties of TCAs may slow intestinal transit time, making them effective in the treatment of diarrhea. Studies have shown improvement in global symptoms, abdominal pain, and diarrhea in patients taking low-dose TCAs. One in three patients treated with TCAs experiences an improvement in symptoms.²⁹ TCAs such as amitriptyline, nortriptyline, imipramine, and desipramine should be started at lower dosages than those used for treatment of depression, and then they should be slowly titrated until pain control or tolerance is achieved. Allow 3 to 4 weeks before reassessment.²⁶ TCAs should be used with caution in the elderly and in patients with constipation, conduction abnormalities, and impaired ventricular function. SSRIs such as paroxetine, fluoxetine, and sertraline may also be beneficial, but supporting studies are limited and these agents are currently recommended only for patients with concomitant depression or anxiety.^30,31 Because of the high rate of coexisting anxiety and its role in IBS exacerbations, benzodiazepines are sometimes prescribed. Their use should be limited, however, because of the risks of drug interactions, habituation, and rebound withdrawal.^26,30 A systematic review found that loperamide improved diarrhea symptoms in patients with IBS; in some small studies, it was found to improve global symptoms.^26,30 This agent is an opioid that does not cross the bloodbrain barrier and works to slow intestinal transit and increase both intestinal water absorption and resting sphincter tone.²⁴

Alosetron is a 5-HT3 receptor antagonist that has been shown to alleviate abdominal pain and improve quality of life in women with diarrhea-predominant IBS.³² Due to risks of ischemic colitis and serious complications related to constipation, the FDA removed it from the market in 2000. Currently, its use is restricted to those in whom traditional treatments have failed and whose providers are enrolled in the prescribing program for alosetron.^24,26,30

Tegaserod, a partial 5-HT4 receptor agonist, is approved by the FDA for those with constipation-predominant IBS. It stimulates the release of neurotrans mitters, increases colonic motility, and inhibits visceral sensitivity to rectal distention. A dosage of 6 mg twice daily has been shown to improve global symptoms and constipation. Tegaserod is approved for short-term use and is contraindicated in those with severe renal impairment, moderate or severe hepatic impairment, or a history of bowel obstruction, symptomatic gallbladder disease, suspected sphincter of Oddi dysfunction, or abdominal adhesions.^30,33,34

Antibiotics have been reported to be helpful in those with refractory diarrhea but should be used only when a bacterial source is suspected.^30,35 Other agents, such as peppermint oil, ginger, Chinese herbals, aloe vera, fennel, and probiotics, may have some role in the treatment of IBS, but more studies of these agents are needed before strong recommendations can be made.^30,35

Psychological and behavioral therapies Significant methodologic limitations accompany the study of these modalities; however, cognitive behavior therapy, dynamic (interpersonal) therapy, and stress management or relaxation techniques including hypnosis, biofeedback training, meditation, and yoga may be useful tools. Patients with an associated psychological diagnosis, maladaptive coping styles, intermittent bowel symptoms of short duration, and exacerbations occurring at times of stress are most likely to benefit from psychological treatment.²²

Conclusion

While the pathophysiology of IBS remains something of a mystery, this condition is one of the most common seen in primary care and has a significant effect on quality of life. A thorough history and physical examination accompanied by appropriate testing help to rule out other conditions and establish trust and rapport. Treatments are intended to control symptoms and should be chosen based on their severity and character. When diagnostic and therapeutic tools are used appropriately, IBS can be less challenging and frustrating to both patient and provider. JAAPA

The author practices at the Swedish Family Medicine Center, Littleton, Colo. She has indicated no relationships to disclose relating to the content of this article.

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