Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that is characterized by abdominal pain and changes in defecation patterns. Abdominal discomfort as seen in IBS is often relieved by defecation. IBS can be associated with changes in bowel function. This bowel dysfunction may present as an alteration in the frequency, form, or appearance of stool (1). Irritable bowel syndrome is considered a functional gastrointestinal (GI) disorder, and its diagnosis is traditionally one of exclusion and symptom-based. IBS may be subdivided into one of three classifications: diarrhea predominant, constipation predominant, or mixed constipation and diarrhea. Mixed (alternating diarrhea and constipation) accounts for approximately one-third to one-half of patients (2). A patient's predominant pattern may change over time (3).
In this article we will review IBS, covering the epidemiology, proposed pathophysiology, and diagnosis. Accepted treatment of IBS will be covered with an emphasis on the current state of knowledge regarding the effect of IBS and exercise.
EPIDEMIOLOGY OF IBS
IBS is increasingly being diagnosed by both primary care practitioners as well as gastroenterologists. Approximately 5%-11% of the population worldwide is affected, with a female predominance of 1.1-2.6. Diagnosis peaks in the third and fourth decades, and there is no race predominance (4).
Although patients typically fall into one of three categories, approximately one-third of patients will change subtype over time ("alternators") (4). There is no risk of progression to more serious gastrointestinal disease, but a change in symptoms may signify a new diagnosis rather than persistence of the IBS. Symptoms may last more than 10 yr, and duration may be associated with persistent stressors (4).
IBS is thought to be a "functional disorder," meaning that there is the presence of symptoms that are not associated with structural or biochemical factors. In essence, the syndrome is not considered organic in etiology (5). However, there is newer evidence that there may be genetic factors related to the following: serotonin transporter 5-HTT, alpha-adrenergic receptor, IL-10, and TNF-α genes (4).
Other theories related to the etiology of IBS include post-infectious IBS (more prevalent in the 6-12 months after gastrointestinal infection) and inflammatory IBS (which is associated with a small amount of inflammation seen on colonic biopsy) (5). There is also increasing investigation into abnormal gut serotonin regulation in IBS. Serotonin levels in patient's serum seem to be higher in those with diarrheal component and lower in those with constipation. People with IBS may have a visceral hypersensitivity response. Patients with IBS tend to have a more pronounced pain response to gut stimulation, for instance with endoscopy (4). The response may be related to a direct brain-gut connection.
The diagnosis of IBS is predominantly based upon patient history. While it is typically a diagnosis of exclusion, patients who have had symptoms that have come and gone for greater than 2 yrs or whose symptoms are worsened by stressors are more likely to suffer from IBS than other GI pathology. The differential diagnosis is listed in Table 1 (2).
Symptoms often experienced with IBS include abdominal pain or discomfort, bloating, gas, abnormal stool frequency or consistency, and abnormal defecation. Constipation predominant subtype is present when there is presence of hard stools more than 25% of the time and loose stools less than 25% of the time; diarrhea predominant subtype is present when the opposite is true; the mixed subtype is present when both hard and loose stools are present greater than 25% of the time (4).
There are multiple sets of diagnostic criteria that have been developed for use in clinical trials, some of which were further refined to also be helpful in the clinical setting. The Manning criteria, developed in 1978, were the first criteria developed based upon symptom constellation. The Rome criteria, a consensus-based guideline developed in 1989, further expanded upon the Manning criteria. In 1999 the Rome criteria were refined (Rome II) to improve clinical applicability, and finally in 2006 the Rome III criteria were released which further clarified the subtypes of IBS (2) (Tables 2 and 3).
Recommended evaluation includes a complete history and physical examination, plus fecal occult blood testing, obtainment of a complete blood count (CBC), and erythrocyte sedimentation rate (ESR). "Red flag" symptoms (Table 4) should be asked during the history to exclude other GI etiology. Approximately 85% of patients with IBS have these "red flag" symptoms (6). In young patients who meet Rome or Manning criteria and have no red flags, there is no need for further testing. In all patients, if the history, physical examination, and lab testing are normal, the likelihood of there being a significant alternate diagnosis is only 1%-3% (2). The positive predictive value of the Rome criteria has been found to be approximately 98%.
There is no diagnostic test specific for IBS, only tests to evaluate for other etiologies. Stool testing is warranted if there has been recent antibiotic use or if symptoms began after a suspected infection (enteritis). Endoscopy is appropriate if colon cancer or inflammatory bowel disease are suspected. Imaging studies are typically not helpful unless there is concern for a bowel obstruction or severe constipation (2).
Historical elements that should be explored when a constipation predominant picture is suspected include thorough evaluation of medications, supplements, or herbal remedies that the patient is using to exclude medication side effects as an etiology. Also evaluating for hypothyroidism, neurologic disease, and slow colonic transit is warranted if symptoms suggest these diagnoses (2).
If a diarrhea-predominant diagnosis is possible, ensuring that there is no infection present is important, as well as excluding medications that increase gut motility or transit time. Malabsorption and inflammatory bowel disease also are possible, but positive Rome or Manning criteria and absence of red flags makes IBS more likely. Endoscopy should be considered if the patient is older or if symptoms are refractory to common IBS treatments or are severe (2).
Many patients with IBS also have other somatic symptoms such as fatigue, musculoskeletal pain, headache, or dyspareunia. Many patients with IBS have depression or anxiety (50%), and many patients with IBS (20%-50%) also have concomitant fibromyalgia or other chronic pain syndromes, including chronic fatigue (2).
TREATMENT OF IBS
As IBS is largely a symptom-driven diagnosis, its treatment likewise is predominantly symptom-driven. For all the different sub-types of IBS, patient education and reassurance about the disease, dietary advice, and exploration and treatment of comorbid psychosocial factors is important and helpful. Regardless of the treatment type, there is a large placebo effect seen in patients with IBS (7). Patients should be informed that the disease is not life-threatening, and stress should be placed on self management as a means to reduce symptoms. Self management may include trigger avoidance, stress reduction, and proper use of medications for symptom control (8).
Dietary therapy for IBS overall has not been shown to reduce symptoms (9). The possible exception is the role of fiber in constipation relief. Since some patients find relief of diarrheal symptoms with evaluating for foods that may result in diarrhea, such as lactose-containing products, reduction of excessive intake of cruciferous vegetables, and with evaluation for any supplements which may have laxative properties, evaluation of an individual's diet and a trial of adjustment may be warranted.
Patients in whom constipation predominates can benefit from the addition of fiber, as fiber has been found helpful in the treatment of constipation. They are unlikely, however, to have a reduction in their pain from fiber supplementation (10). If fiber fails to adequately address constipation in these patients, laxatives, particularly the osmotic type laxatives such as polyethylene glycol, are indicated.
Pharmacologic therapies in IBS are likewise targeted to the predominant symptoms. In patients in whom IBS pain is severe, anti-spasmodics such as hyoscyamine and dicyclomine are indicated for as needed use. These drugs are anti-cholinergics and thus, exhibit anti-cholinergic side effects such as dry mouth, urinary retention, and constipation, which are dose-dependent. For patients with diarrhea-predominant IBS, loperamide, a non-absorbable synthetic opioid that slows gastrointestinal transit, allowing for increased water absorption, is considered a first-line agent (11). Alosetron is a 5-HT3 receptor antagonist that may be used in diarrhea-predominant IBS. Its use has been restricted, due to an increased risk of the development of ischemic colitis (12). Direct effects on exercise are unknown, but common side-effects include headache, constipation, dizziness, and tiredness. All of these symptoms can affect exercise performance.
Tegaserod is a 5-HT4 receptor agonist that is indicated for the relief of constipation, bloating, and abdominal discomfort in females with IBS. Like alosetron, the use of tegaserod is restricted to specific populations because of the potential for serious adverse effects. No studies have specifically looked at the effect of tegaserod on exercise, but its most common side effect is diarrhea. Other pharmacological therapies for IBS currently being studied include antibiotic therapy to decrease bacterial overgrowth in the intestine and the use of probiotics to replenish the intestinal flora.
Depression and anxiety are often associated with IBS. Given this close association, the use of antidepressants in the treatment of IBS has been shown to be effective (13). Considering that tricyclic antidepressants have anticholinergic side effects, they are best suited towards diarrhea-predominant patients. Selective serotonin reuptake inhibitors may be beneficial for patients with constipation-predominant IBS.
EXERCISE EFFECTS UPON IBS
Exercise has long been prescribed to patients with IBS as a way to decrease their symptoms, and study results support this recommendation (14). Recent studies have helped elucidate the beneficial effects of exercise on IBS symptoms by showing that physical activity facilitates intestinal gas transit (15). In patients with IBS, mild to moderate physical activity has been shown to increase intestinal gas clearance and reduce symptoms (16). Exercise can cause abdominal bloating in patients with constipation features of IBS if the disease is not under control. The patient with diarrheal symptoms could develop increased diarrhea with prolonged endurance activity. These setbacks can be counteracted with continual exercise and proper treatment of the disease. Exercise is more effective in the treatment of IBS than pharmacologic treatments (17).
IBS TREATMENT AND EXERCISE
IBS treatment is targeted at IBS symptoms; for athletes, the lowest possible doses should be used to prevent side effects. Fiber and laxatives do not appear to have a direct effect upon exercise. Anticholinergic drugs (hyoscyamine and dicyclomine) can cause dehydration and predispose athletes to heat illness. Although these medications are not contraindicated, caution should be used with exercise in the heat and during high-intensity workouts. The effects of the 5-HT receptor agonists and exercise are not well known at this time. 5-HT is implicated in central-mediated exercise fatigue; therefore, 5-HT agonists may accentuate fatigue like 5-HT-1 receptor agonists.
IBS is a common disorder that predominately affects women. Currently, its diagnosis and treatment is based on the predominant symptoms that are present, whether constipation, diarrhea, or a mixed presentation. Comorbid psychosocial problems such as depression or anxiety are commonly seen in those with IBS. Exercise has been shown to be a safe and effective form of treatment and should be recommended to all patients with IBS to not only help alleviate the symptoms associated with IBS but to also help address the comorbid conditions.
1. Drossman, D.A. The functional gastrointestinal disorders and the Rome III process. Gastroenterology.
2. Wilson, J.F. In the clinic. Irritable bowel syndrome. Ann. Intern. Med.
3. Guilera, M., A. Balboa, and F. Mearin. Bowel habit subtypes and temporal patterns in irritable bowel syndrome: Systematic review. Am. J. Gastroenterol.
4. Spiller, R., Q. Aziz, F. Creed, et al
. Guidelines on the irritable bowel syndrome: mechanisms and practical management. Gut.
5. Talley, N.J. Irritable bowel syndrome. Intern. Med. J.
6. Whitehead, W.E., O.S. Palsson, A.D. Feld, et al
. Utility of red flag symptom exclusions in the diagnosis of irritable bowel syndrome. Aliment Pharmacol. Ther.
7. Patel, S.M., W.B. Stason, A. Legedza, et al. The placebo effect in irritable bowel syndrome trials: A meta-analysis. Neurogastroenterol. Motil.
8. Colwell, L.J., C.M. Prather, S.F. Phillips, and A.R. Zinsmeister. Effects of an irritable bowel syndrome educational class on health-promoting behaviors and symptoms. Am. J. Gastroenterol.
9. Quartero A.O., V. Meineche-Schmidt, J. Muris, G. Rubin, and N. de Wit. Bulking agents, antispasmodic and antidepressant medication for the treatment of irritable bowel syndrome. Cochrane Database Syst. Rev.
10. Brandt, L.J., D. Bjorkman, M.B. Fennerty, et al. Systematic review on the management of irritable bowel syndrome in North America. Am. J. Gastroenterol.
11. Schoenfeld, P. Efficacy of current drug therapies in irritable bowel syndrome: What works and does not work. Gastroenterol. Clin. N. Am.
12. Watson, M.E., L. Lacey, S. Kong, et al. Alosetron improves quality of life in women with diarrhea-predominant irritable bowel syndrome. Am. J. Gastroenterol.
13. Jackson, J.L., P.G. O'Malley, G. Tomkins, et al. Treatment of functional gastrointestinal disorders with antidepressant medications: A meta-analysis. Am. J. Med.
14. Lustyk, M.K., M.E. Jarrett, J.C. Bennett, and M.M. Heitkemper. Does a physically active lifestyle improve symptoms in women with irritable bowel syndrome? Gastroenterol. Nurs.
15. Dainese, R., J.Serra, F. Azpiroz, and J.R. Malagelada. Effects of physical activity on intestinal gas transit and evacuation in healthy subjects. Am. J. Med.
16. Villoria, A., J. Serra, F. Azpiroz, and J.R. Malagelada. Physical activity and intestinal gas clearance in patients with bloating. Am. J. Gastroenterol.
17. Henningsen, P., S. Zipfel, and W. Herzog. Management of functional somatic syndromes. Lancet.