> Table of Contents > Irritable Bowel Syndrome
Irritable Bowel Syndrome
Mark B. Stephens, MD, MS, FAAFP, CAPT, MC, USN
image BASICS
  • A functional gastrointestinal disorder characterized by
    • Chronic abdominal pain associated with
      • Alteration in bowel habits
      • Absence of organic pathology
  • May be characterized as diarrhea-predominant or constipation-predominant or may alternate between the two
  • Synonym(s): spastic colon; irritable colon
Irritable bowel syndrome (IBS) accounts for up to 50% of visits to gastroenterologists:
  • Second only to upper respiratory infection as cause of lost workdays
Pooled estimate of 11% IBS prevalence internationally; ranges from South Asia (7%) to South America (21%) (1)
  • Predominant age: 20 to 39 years
  • If age >50 years, consider other diagnoses.
  • Predominant sex: in the United States, female > male (2:1)
  • More common in low socioeconomic communities
  • The etiology is unknown, associated with intestinal motility abnormalities and enhanced sensitivity to visceral stimuli.
  • The trigger may be luminal or environmental.
  • Evidence for the role of small intestine bacterial overgrowth (SIBO) in IBS and association with antibiotic therapy is conflicting; older age and female gender are predictors of SIBO in IBS patients.
Unknown, but more common in families of IBS patients
  • Other family members with similar GI disorder
  • History of childhood sexual abuse
  • Sexual/domestic abuse (primarily in women)
  • Depression
  • Gastrointestinal infection
Pregnancy Considerations
No risk to mother or fetus
See “Diet.”
  • Chronic migraine
  • Urinary frequency and urgency
  • Fibromyalgia
  • Chronic fatigue syndrome
  • Sleep disorders
  • Dyspareunia
  • Depression
  • Posttraumatic stress disorder
  • Generally normal
  • Perform to exclude other causes.
  • Vital signs typically are normal.
  • Generally, there is an absence of jaundice and organomegaly but may have tenderness to palpation.
  • Inflammatory bowel disease
  • Lactose intolerance; fructose malabsorption
  • Infections (Giardia lamblia, Entamoeba histolytica, Salmonella, Campylobacter, Yersinia, Clostridium difficile)
  • Celiac sprue
  • Microscopic colitis
  • Laxative abuse
  • Magnesium-containing antacids
  • Hypo-/hyperthyroidism
  • Pancreatic insufficiency
  • Depression
  • Small bowel bacterial overgrowth
  • Somatization
  • Villous adenoma
  • Endocrine tumors
  • Diabetes mellitus
  • Radiation damage to colon or small bowel
  • With a typical history and no danger signs (anemia or weight loss, obtain baseline labs to rule out other causes and begin treatment.
  • In patients who do not respond to treatment, further evaluation with imaging and/or endoscopy is warranted to exclude organic pathology.
Initial Tests (lab, imaging)
Rule out pathology specific to the patient's symptoms:
  • Diarrhea-predominant: ESR, CBC, tissue transglutaminase, thyroid-stimulating hormone (TSH), and stool for ova and parasites (2)
  • Constipation-predominant: CBC, TSH, electrolytes, calcium (2)
  • Abdominal pain: LFTs and amylase
  • Abdominal CT scan or abdominal ultrasound to evaluate pain is generally normal.
  • Consider small bowel series or video capsule endoscopy to rule out Crohn disease (will be normal).
  • Sitz Marker study may be used to evaluate colonic transit in patients with constipation.
Follow-Up Tests & Special Considerations
Consider lactulose breath test to assess for small bowel bacterial overgrowth associated with IBS (2)[C].
Diagnostic Procedures/Other
Sigmoidoscopy/colonoscopy may be used to rule out inflammatory bowel disease or microscopic colitis.
Test Interpretation
  • Goals: Relieve symptoms and improve quality of life (3).
    • Determine if diarrhea predominant, constipation predominant, or mixed type
  • Lifestyle modification
    • Exercise 3 to 5 times per week decreases severity (3).
    • Food diary to determine triggers (3)
  • Medications
    • Fiber supplementation (psyllium) increases stool bulk; does not typically relieve abdominal pain; may be used for all types (3,4)[B]
  • Medications that improve abdominal pain, global symptoms, and symptom severity in all types:
    • Antispasmodics such as hyoscyamine 0.125 to 0.25 mg PO/SL q4h PRN and dicyclomine 20 to 40 mg PO BID can be used for all types but have adverse effects such as dry mouth, dizziness, and blurred vision (3).
    • Probiotics such as Lactobacillus, Bifidobacterium, and Streptococcus (5)[C]
    • Serotonin antagonists 5-HT3 and 5-4T agonists (alosetron, cilansetron) have been shown to improve IBS symptoms (versus placebo) (6).
  • P.573

  • Diarrhea predominant
    • Antidiarrheal such as loperamide 4 to 8 mg/day orally divided into once a day to 3 times a day as needed to decrease stool frequency and increase stool consistency; does not help with abdominal pain; may also use diphenoxylate/atropine (3)
    • Antibiotics such as 2-week course of rifaximin improve bloating, pain, and stool consistency (7).
    • Alosetron (Lotronex 0.5 mg orally twice a day), used for women with severe symptoms but associated with ischemic colitis, constipation, and death in a small number of patients (8)
  • Constipation-predominant
    • Laxatives such as polyethylene glycol (MiraLAX) may improve stool frequency but not pain.
    • Antibiotics such as neomycin and selective chloride channel activators such as lubiprostone (Amitiza) 8 mg twice a day can improve global symptoms and severity (3,9)[B].
    • Linaclotide (guanylate cyclase-C agonist) has been shown to improve bowel function and reduces abdominal pain and overall severity in adults only (10).
  • Mixed
    • Use medications above based on symptoms (3).
  • Treat underlying behavioral issues:
    • Use of SSRIs such as Prozac, sertraline, Paxil, and tricyclic antidepressants such as imipramine can improve abdominal pain and symptom score (4).
    • Tricyclic antidepressants can help control IBS symptoms in moderate to severe cases (11)[B].
    • Behavioral therapy helps reduce symptoms (7).
  • Behavioral health referral may help with management of affective or personality disorders.
  • Gastroenterology referral for difficult to control cases
Probiotics use may result in reducing IBS symptoms and decreasing pain and flatulence. There is no difference among Lactobacillus, Streptococcus, Bifidobacterium, and combinations of probiotics.
Patient Monitoring
The IBS Severity Score is a validated measure to assess the severity of IBS symptoms and can help monitor response to treatment.
IBS Severity Score:
  • How severe has your abdominal pain been over the last 10 days?
  • On how many of the last 10 days did you get pain?
  • How severe has your abdominal distension (bloating, swollen, or tight) been over the last 10 days?
  • How satisfied have you been with your bowel habit (frequency, ease, etc.) over the last 10 days?
  • How much has your IBS been affecting/interfering with your life in general over the last 10 days?
Low FODMAPs diet: This diet contains fermentable oligosaccharides, disaccharides, monosaccharides, and polyols that are carbohydrates (sugars) found in foods. FODMAPs are osmotic, so they may not be digested or absorbed well and could be fermented upon by bacteria in the intestinal tract when eaten in excess.
A low FODMAP diet may help reduce symptoms, which will limit foods high in fructose, lactose, fructans, galactans, and polyols.
  • Increase fiber slowly to avoid excess intestinal gas production.
  • During initial evaluation, may wish to try 2 weeks of lactose-free diet to rule out lactose intolerance.
  • Avoid large meals, fatty foods, and caffeine, which can exacerbate symptoms.
  • A gluten-free diet resolves symptoms for some patients (especially diarrhea predominant IBS) despite negative testing for celiac disease.
IBS is not a psychiatric illness.
  • IBS is a functional disorder that reduces quality of life. Many patients have behavioral health issues. IBS does not increase mortality (1).
  • Expect recurrences, especially when under stress.
  • Evidence suggests that “symptom shifting” occurs in some patients, whereby resolution of functional bowel symptoms is followed by the development of functional symptoms in another system (1).
1. Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clin Epidemiol. 2014;6:71-80.
2. Reddymasu SC, Sostarich S, McCallum RW. Small intestinal bacterial overgrowth in irritable bowel syndrome: are there any predictors? BMC Gastroenterol. 2010;10:23.
3. Wilkins T, Pepitone C, Alex B, et al. Diagnosis and management of IBS in adults. Am Fam Physician. 2012;86(5):419-426.
4. Ruepert L, Quartero AO, de Wit NJ, et al. Bulking agents, antispasmodics and antidepressants for the treatment of irritable bowel syndrome. Cochrane Database Syst Rev. 2011;(8):CD003460.
5. Ciorba MA. A gastroenterologist's guide to probiotics. Clin Gastroenterol Hepatol. 2012;10(9):960-968.
6. Ford AC, Brandt LJ, Young C, et al. Efficacy of 5-HT3 antagonists and 5-HT4 agonists in irritable bowel syndrome: systematic review and meta-analysis. Am J Gastroenterol. 2009;104(7):1831-1843.
7. Schey R, Rao SS. The role of rifaximin therapy in patients with irritable bowel syndrome without constipation. Expert Rev Gastroenterol Hepatol. 2011;5(4):461-464.
8. Rahimi R, Nikfar S, Abdollahi M. Efficacy and tolerability of alosetron for the treatment of irritable bowel syndrome in women and men: a metaanalysis of eight randomized, placebo-controlled, 12-week trials. Clin Ther. 2008;30(5):884-901.
9. Drossman DA, Chey WD, Johanson JF, et al. Clinical trial: lubiprostone in patients with constipation-associated irritable bowel syndrome—results of two randomized, placebo-controlled studies. Aliment Pharmacol Ther. 2009;29(3):329-341.
10. Videlock EJ, Cheng V, Cremonini F. Effects of linaclotide in patients with irritable bowel syndrome with constipation or chronic constipation: a meta-analysis. Clin Gastroenterol Hepatol. 2013;11(9):1084.e3-1092.e3.
11. Rahimi R, Nikfar S, Rezaie A, et al. Efficacy of tricyclic antidepressants in irritable bowel syndrome: a meta-analysis. World J Gastroenterol. 2009;15(13):1548-1553.
See Also
Algorithm: Diarrhea, Chronic
  • K58.9 Irritable bowel syndrome without diarrhea
  • K58.0 Irritable bowel syndrome with diarrhea
Clinical Pearls
  • Use Rome III criteria for diagnosis.
  • Goals of treatment are to relieve symptoms and improve quality of life.
  • If patient does not respond to initial treatment, consider further evaluation to exclude organic pathology.