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Irritable Bowel Syndrome (IBS): Examining New Findings and Treatments

  • Authors: Authors: Marvin M. Schuster, MD; Michael D. Crowell, PhD; Nicholas J. Talley, MD, PhD
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Target Audience and Goal Statement

This activity is intended for gastroenterologists, primary care practitioners, and internists.

The goal of this activity is to examine the most up-to-date information available on: (1) the practical diagnosis of IBS; (2) the role of serotonin (5-HT) in enteric motility, visceral hypersensitivity, and secretion; and (3) 5-HT treatment options for IBS.

On completion of this CME offering, participants will be able to:

  1. List distinctive diagnostic markers for the identification and classification of patients with IBS

  2. Understand the role of 5-HT in the pathophysiology of IBS and its clinical manifestations

  3. Cite current and emerging 5-HT treatment options for patients with IBS


  • Michael D. Crowell, PhD

    Co-director of the Marvin M Schuster Center for Digestive and Motility Disorders at John Hopkins Bayview Medical Center, Baltimore MD


    Disclosure: Michael D. Crowell, PhD, has no significant financial interests to disclose.

  • Marvin M. Schuster, MD

    Director of the Marvin M Schuster Center for Digestive and Motility Disorders at John Hopkins Bayview Medical Center, Baltimore MD


    Disclosure: Marvin M. Schuster, MD has disclosed that he has been a consultant to and received research grants from Novartis, Glaxo and Janssen.

  • Nicholas J. Talley, MD, PhD

    Professor of Medicine, Mayo Medical School; Co-Director, Center of Enteric Neuroscience and Translational Epidemiological Research, Mayo Clinic, Rochester, Minnesota


    Disclosure: Nicholas J. Talley, MD, PhD has disclosed that he has been a consultant to Glaxo, Novartis and SmithKline Beecham.

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Irritable Bowel Syndrome (IBS): Examining New Findings and Treatments: Defining and Diagnosing IBS


Defining and Diagnosing IBS

For many years, the pathogenesis of functional GI disorders (FGIDs), including IBS, was associated with a psychosomatic paradigm. Consequently, the use of FGID as a diagnosis has acquired a pejorative aura. Current thinking defines IBS as a GI disorder of function (GIDF), connoting a clinical condition that can be measured and recorded, and therefore, in this sense, can be visualized.

  • Pathogenesis/Symptoms of IBS

    Figure 1.

    Pathogenesis/Symptoms of IBS

    (Enlarge Slide)

IBS: Differences Between Patients' Experiences and Doctors' Perspectives

  • The psychosomatic paradigm that for years has been associated with FGIDs appears to pervade the thinking of many present-day physicians. This becomes apparent when the doctors' perspective of IBS is compared with the patients' experiences. A UCLA survey of approximately 3,000 respondents illuminated how IBS had a strong negative effect on patients' quality of life:


    1. 40% reported intolerable abdominal pain
    2. 65% plan their day-to-day schedule based on the anticipated use of bathroom facilities
    3. 53% of patients with IBS declared that their health limited their activity whereas only 26% of individuals without IBS felt the same way.

    Overall, the patients' experiences illustrated the debilitating nature of IBS.

    In contrast, the majority of doctors interviewed about IBS underappreciated the seriousness of the condition -- 33% felt that IBS was primarily a manifestation of a psychopathology. However, this appears to be an oversimplified conclusion based on data from a study comparing psychological indices applied to normal individuals, lactose malabsorbers (LMAs), and individuals with IBS in the general community who do not seek medical attention, versus LMAs and individuals with IBS who do seek healthcare.[1] In this study, the higher rate of neuroticism noted among LMAs and patients with IBS who sought medical assistance suggests that psychopathology among IBS sufferers is associated with healthcare-seeking behavior.

  • In contrast to findings indicating that the average patient visits 3 doctors over 3 years before obtaining a diagnosis of IBS, 58% of doctors declared that IBS was easy to diagnose. This is perplexing in light of reports that only 20% of doctors are familiar with the guidelines for the diagnosis of IBS, and 80% of those physicians do not use the guidelines. The current Rome II criteria[2] indicate that a diagnosis of IBS is likely when abdominal discomfort/pain is present along with 2 of 3 specified features relating to altered bowel habits.

  • Comparison of Community and Clinic Samples

    Figure 2.

    Comparison of Community and Clinic Samples

    (Enlarge Slide)

Physiological Differences in IBS Patient Subgroups

  • The gastrocolic reflex, a partly neurogenic process, refers to an increase in colonic motility induced by feeding. Postprandial deviations from the normal motility patterns lead to altered bowel habits. For example, a spastic colon (eg, diarrhea-predominant IBS [D-IBS]) is characterized by an exaggerated motility response to food intake. This exaggerated postprandial response also occurs in response to intraluminal distention or to an injection of cholecystokinin (CCK -- a hormone released in the duodenum) in patients with IBS.

  • Contractions of Sigmoid Colon After a Meal (Normal Human)

    Figure 4.

    Contractions of Sigmoid Colon After a Meal (Normal Human)

    (Enlarge Slide)
  • Contractions of Sigmoid Colon After a Meal (Spastic Colon Syndrome)

    Figure 5.

    Contractions of Sigmoid Colon After a Meal (Spastic Colon Syndrome)

    (Enlarge Slide)
  • Smooth muscles in the colon can impede and/or facilitate the movement of intraluminal contents. Haustral contractions impede stool movement; high-amplitude propagating contractions (HAPCs) are sweeping propulsive motor events that are typically clustered around bowel movements. The frequency of HAPCs is increased in D-IBS. In contrast, HAPCs are fewer and segmental impeding contractions are more frequent in constipation-predominant IBS (C-IBS). In summary, C-IBS is characterized by postprandial rectal relaxation, blunted gastrocolic response, and lower rectal discomfort threshold. On the other hand, D-IBS is characterized by a postprandial increase in rectal tone, an enhanced gastrocolic response, and hypersensitivity to rectal distention.

  • Effects of Balloon Distention on Rectosigmoid Motility

    Figure 6.

    Effects of Balloon Distention on Rectosigmoid Motility

    (Enlarge Slide)

Diagnosis of IBS

  • The following clinical findings do not support a diagnosis of IBS: (1) symptom onset in old age; (2) a steady but aggressive course; (3) frequent awakening by symptoms; and (4) indicators of inflammation, fever, weight loss, rectal bleeding, steatorrhea, obstruction, or dehydration.

    The following laboratory tests should be performed when screening for IBS:


    • Blood tests
    • Stool hemoccults (~20% of IBS patients may bleed)
    • Flexible sigmoidoscopy
    • Lactose tolerance evaluation

    Other tests may be necessary depending on the medical history. For example, small bowel x-rays are recommended when Crohn's disease is a possible diagnosis. Colonoscopy and biopsies may be necessary to test for organic diseases. To differentiate between secretory and osmotic diarrhea, inpatient fasting for 72 hours, with intravenous electrolyte administration, should be implemented; the resolution of diarrhea within this period suggests an osmotic (nonsecretory) mechanism.

  • Recommended Laboratory Investigations

    Figure 8.

    Recommended Laboratory Investigations

    (Enlarge Slide)