You are leaving Medscape Education
Cancel Continue
Log in to save activities Your saved activities will show here so that you can easily access them whenever you're ready. Log in here CME & Education Log in to keep track of your credits.



IBS: Improving Diagnosis, Serotonin Signaling, and Implications for Treatment

  • Authors: Authors: Lucinda Harris, MD; Lin Chang, MD
Start Activity

Target Audience and Goal Statement

This activity is intended for the physician and other healthcare professionals specializing in the care of the patient with irritable bowel syndrome (IBS).

The goal of this activity is to familiarize the clinician with the clinical relevance of serotonergic signaling in the gut, mechanisms of visceral hypersensitivity, and the role of pathophysiology in understanding symptom presentation in IBS, all with a view toward implications for disease management.

Upon completion of this activity, participants will be able to:

  1. Review issues important to the appropriate diagnostic evaluation of the patient suspected of having IBS.
  2. Explore the relationship between the pathophysiology of IBS and mechanisms of serotonin signaling.
  3. Evaluate the utility/role of serotonergic interventions in the management of patients with IBS.


  • Lin Chang, MD

    Associate Professor of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California; Co-Director, Center for Neurovisceral Sciences & Women's Health at UCLA, Los Angeles, California


    Disclosure: Dr. Chang disclosed that she has received grants for clinical research from, has served as an advisor or consultant for, and is on the Speakers' Bureau for Novartis and Glaxo SmithKline. She has received grants for clinical research from and has served as an advisor or consultant for Forest Laboratories, Solvay, and AstraZeneca. Dr. Chang reported that she discusses the investigational products cilansetron, prucalopride, renzapride, paroxetine, fluoxetine, venlafaxine, and desipramine.

  • Lucinda A. Harris, MS, MD

    Associate Professor of Clinical Medicine, Weill Medical College of Cornell University; Associate Attending, The New York Presbyterian Hospital, New York, NY


    Disclosure: Dr. Harris disclosed that she is on the Speakers' Bureau for Novartis , Janssen, GlaxoSmithKline, TAP Pharmaceuticals, and Wyeth. She has received grants for clinical research from Solvay, Forest Laboratories, and Glaxo SmithKline. She has served as an advisor or consultant for Solvay, and GlaxoSmithKline. Dr. Harris reported that she discusses the investigational products cilansetron, prucalopride, renzapride, paroxetine, fluoxetine, venlafaxine, and desipramine.

Accreditation Statements

    For Physicians

  • Medscape, LLC is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

    Medscape designates this educational activity for a maximum of 1.5 category 1 credits toward the AMA Physician's Recognition Award. Each physician should claim only those credits that he/she actually spent in the activity.

    Contact This Provider

For questions regarding the content of this activity, contact the accredited provider for this CME/CE activity noted above. For technical assistance, contact [email protected]

Instructions for Participation and Credit

There are no fees for participating in or receiving credit for this online educational activity. For information on applicability and acceptance of continuing education credit for this activity, please consult your professional licensing board.

This activity is designed to be completed within the time designated on the title page; physicians should claim only those credits that reflect the time actually spent in the activity. To successfully earn credit, participants must complete the activity online during the valid credit period that is noted on the title page.

Follow these steps to earn CME/CE credit:

  1. Read the target audience, learning objectives, and author disclosures.
  2. Study the educational content online or printed out.
  3. Online, choose the best answer to each test question. To receive a certificate, you must receive a passing score as designated at the top of the test. Medscape encourages you to complete the Activity Evaluation to provide feedback for future programming.
You may now view or print the certificate from your CME/CE Tracker. You may print the certificate but you cannot alter it. Credits will be tallied in your CME/CE Tracker and archived for 5 years; at any point within this time period you can print out the tally as well as the certificates by accessing "Edit Your Profile" at the top of your Medscape homepage.

The credit that you receive is based on your user profile.


IBS: Improving Diagnosis, Serotonin Signaling, and Implications for Treatment


Diagnosis of IBS

Symptom-Based Diagnostic Criteria

Due to the lack of a diagnostic biologic marker for IBS, the diagnosis is made using symptom-based criteria. A number of symptom-based criteria have been used in the past; however, the currently accepted criteria are those that have been developed by the Rome II committee, a group comprised of experts specializing in functional gastrointestinal disorders.[2] IBS is most recently defined as abdominal pain or discomfort not explained by biochemical or structural abnormalities that is present for at least 12 weeks (not necessarily consecutive) over the past 12 months and associated with at least 2 of the following features: (1) relief with defecation; (2) a change in stool consistency (eg, watery/loose or hard/lumpy); and/or (3) a change in stool frequency.

The Rome II criteria are a simplification of the Rome I Criteria.[12] The Rome I criteria were similar to the above indicated features, but also stated that 2 or more of the following features must be present as least 25% of the time: (1) abnormal stool form; (2) passage of mucus; (3) bloating or distension; (4) abnormal stool passage (feeling of incomplete evacuation, straining, or urgency); and (5) altered stool frequency (> 3 bowel movements/day or < 3 bowel movements/week). These symptoms are presently used as supportive symptoms for the diagnosis of IBS.

Because patients may present with diarrhea and/or constipation, patients are often subgrouped by predominant bowel habit. However, GI symptoms may fluctuate over time and, therefore, a special task force of the American College of Gastroenterology has suggested that patients with IBS be identified using the following designations: IBS associated with abdominal pain, fecal urgency, and diarrhea; IBS associated with abdominal discomfort, bloating, and constipation; and IBS associated with alternating diarrhea and constipation.[11]

Diagnostic Considerations

Once a dominant symptom complex is identified in the patient, it is also useful to exclude possible "red flags" that might be indicative of an organic disorder. Table 1 outlines the potential "alarm" symptoms that need to be considered when evaluating a patient with IBS.

Table 1. Alarm Symptoms Suggestive of Organic Disease

  1. Weight loss > 10 lbs
  2. Nocturnal symptoms
  3. Initial onset at age > 50 years
  4. Significant travel history
  5. Severe diarrhea or constipation
  6. Rectal bleeding
  7. Arthritis/rashes
Family History
  1. Colon cancer
  2. Inflammatory bowel disease
  3. Celiac disease
Physical Findings
  1. Fever
  2. Oral ulcers
  3. Palpable abdominal mass
  4. Guaiac-positive stool
  5. Other physical finding (eg, abdominal mass, distension)
  6. Rectal bleeding or obstruction
Laboratory Evaluation
  1. Increased white blood cell count
  2. Anemia
  3. Abnormal chemistry
  4. Increased thyroid-stimulating hormone
  5. Elevated erythrocyte sedimentation rate or C-reactive protein

Once a thorough medical history and physical examination are performed, a variety of laboratory tests that have been advocated in the literature may be considered.[1,13] These diagnostic tests include: (1) complete blood count (CBC); (2) thyroid-stimulating hormone (TSH) level; (3) erythrocyte sedimentation rate (ESR); (4) complete metabolic profile; (5) stool for ova and parasites (O&P); (6) stool culture and examination; (7) fecal occult blood testing; and (8) celiac sprue panel. Other diagnostic tests include flexible sigmoidoscopy, colonoscopy, or barium enema, and hydrogen breath tests, which should be considered on an individual basis. It is generally recommended that clinicians take an evidence-based medicine approach in their medical evaluation and consider the pretest probability of a test for diagnosing another medical condition (eg, colon cancer, inflammatory bowel disease, celiac sprue) before ordering it. The presence of alarm symptoms would suggest a higher pretest probability of an organic disorder that needs to be ruled out. The differential diagnosis of IBS often depends on the predominant symptom (eg, diarrhea or constipation), as outlined in Table 2.

Table 2. Differential Diagnosis of IBS*

Malabsorption Dietary Factors
Intestinal disorders Lactose intolerance
Pancreatic insufficiency Alcohol/caffeine
Postgastrectomy Sorbitol/high fructose corn syrup
  Gas-producing foods
Infection High-fat foods
Bacteria Wheat (celiac disease)
HIV and associated infections  
  Psychological Disorders
Inflammatory Bowel Disease Panic disorder
Crohn's disease Somatization
Ulcerative colitis Depression
Microscopic/collagenous colitis  
Gynecologic Disorders  
Endometriosis Malignancies
Dysmenorrhea Endocrine tumors
Ovarian cancer Colon cancer
Neurologic Disorders  
Parkinson's disease Medications
Multiple sclerosis Antibiotics
Spinal cord lesions Nonsteroidal anti-inflammatory drugs
Endocrine/Metabolic Disorders Opiates
Diabetes Calcium-channel blockers
Hypo/hyperthyroidism Antidepressants

*Consider dominant bowel symptom
†Not an all-inclusive list

Studies of reasonably good quality have suggested that the diagnostic yield associated with performing most of these tests is not very high -- for many, in fact, less than 2%.[14,15] However, there are a few exceptions. One exception is lactose intolerance, which is present in approximately 25% of the population. However, lactose intolerance is often coexistent with IBS and, when treated, the patient still has symptoms of IBS. The other exception is celiac sprue. The pretest probability in the patient with IBS is significantly higher than that found in the general population (4.67% vs 0.25% to 0.50%).[16,17] Therefore, screening with endomysial antibody, among other such screening tests, may be indicated, particularly if the patient has failed to respond to treatment. Seven percent of patients with celiac disease are IgA deficient and, therefore, the clinician may want to measure the IgA level as well when celiac disease is a diagnostic consideration.

Although the pretest probability of finding an etiology for symptoms by colonoscopy is not high, most gastroenterologists would agree that patients ≥ 50 years of age should undergo this examination (or, alternatively, a flexible sigmoidoscopy and barium enema) if a previous screening examination has not been done. This age threshold should be lowered to 40 years if there is a significant family history of colon cancer.

Another condition to consider excluding from the differential diagnosis when managing a patient with symptoms of IBS is bacterial overgrowth. Two studies from the same research group found that 78% to 84% of patients with IBS had bacterial overgrowth.[18,19] In patients with evidence of bacterial overgrowth, those treated with neomycin had a ≥ 35% reduction in clinical response (ie, improvement) compared with an 11% reduction in patients on placebo.[19] Although these data are extremely intriguing, there are some methodologic limitations in these studies and, therefore, the use of widespread hydrogen breath testing for bacterial overgrowth is still not generally advocated.

The diagnosis of IBS is primarily symptom-based, and the literature suggests that once made, the clinician can be confident of his/her diagnosis. Retrospective views of patients have suggested that the diagnosis is an enduring one, with 92% to 97% of the individuals maintaining the same diagnosis over 2-13 years.[20,21]