Irritable Bowel Syndrome

Last Updated: November 21, 2006
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Synonyms and related keywords: IBS, irritable bowel disease, IBD, functional bowel disease, irritable colon, mucous colitis, nervous bowel, spastic bowel, spastic colitis, postprandial abdominal pain, stomach pain, mucorrhea, Manning criteria, abdominal pain, abdominal colic, Rome criteria, altered bowel habits, postprandial urgency, constipation, diarrhea, bloating, colonic dysmotility, colon motility disturbances
AUTHOR INFORMATION Section 1 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

Author: Jenifer K Lehrer, MD, Staff Physician, Department of Internal Medicine, University of Pennsylvania
Coauthor(s): Gary R Lichtenstein, MD, Director of Inflammatory Bowel Disease Center, Professor, Department of Internal Medicine, University of Pennsylvania


Jenifer K Lehrer, MD, is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, American Society for Gastrointestinal Endoscopy, and Pennsylvania Medical Society
Editor(s): Rajeev Vasudeva, MD, FACG, Clinical Professor of Medicine, Consultants in Gastroenterology, University of South Carolina School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Douglas M Heuman, MD, FACP, Director of Hepatology, McGuire Veterans Affairs Medical Center, Professor, Department of Internal Medicine, Division of Gastroenterology, Virginia Commonwealth University School of Medicine; Alex J Mechaber, MD, FACP, Associate Professor, Department of Internal Medicine, Division of General Internal Medicine, University of Miami Miller School of Medicine; and Julian Katz, MD, Clinical Professor of Medicine, Drexel University College of Medicine; Consulting Staff, Department of Medicine, Section of Gastroenterology and Hepatology, Hospital of the Medical College of Pennsylvania

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INTRODUCTION Section 2 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography
Background: Irritable bowel syndrome (IBS) is a functional GI disorder characterized by abdominal pain and altered bowel habits in the absence of specific and unique organic pathology. Osler coined the term mucous colitis in 1892 when he wrote of a disorder of mucorrhea and abdominal colic with a high incidence in patients with coincident psychopathology. Since that time, the syndrome has been referred to by sundry terms, including spastic, irritable, and nervous colon.

Traditionally, IBS is a diagnosis of exclusion. No specific motility or structural correlates have been consistently demonstrated, so IBS remains a clinically defined illness. Manning and associates established 6 criteria to distinguish IBS from organic bowel disease. Although historically important, these criteria are insensitive (58%), nonspecific (74%), and less reliable in men.

The Manning criteria to distinguish IBS from organic disease are as follows:

Onset of pain associated with more frequent bowel movements
Onset of pain associated with looser bowel movements
Pain relieved by defecation
Visible abdominal bloating
Subjective sensation of incomplete evacuation more than 25% of the time
Mucorrhea more than 25% of the time
More recently, a consensus panel created and then updated the Rome criteria to provide a standardized diagnosis for research and clinical practice.

The Rome III criteria (2006) for the diagnosis of IBS require that patients must have recurrent abdominal pain or discomfort at least 3 days per month during the previous 3 months that is associated with 2 or more of the following:

Relieved by defecation
Onset associated with a change in stool frequency
Onset associated with a change in stool form or appearance
Supporting symptoms include the following:

Altered stool frequency
Altered stool form
Altered stool passage (straining and/or urgency)
Mucorrhea
Abdominal bloating or subjective distention
Four bowel patterns may be seen with IBS. These patterns include IBS-D (diarrhea predominant), IBS-C (constipation predominant), IBS-M (mixed diarrhea and constipation), and IBS-A (alternating diarrhea and constipation). The usefulness of these subtypes is debatable. Notably, within 1 year, 75% of patients change subtypes, and 29% switch between constipation-predominant IBS and diarrhea-predominant IBS.

Pathophysiology: Traditional theories regarding pathophysiology may be visualized as a 3-part complex of altered GI motility, visceral hyperalgesia, and psychopathology.

Altered GI motility includes distinct aberrations in small and large bowel motility.
The myoelectric activity of the colon is composed of background slow waves with superimposed spike potentials. Colonic dysmotility in IBS manifests as variations in slow-wave frequency and a blunted, late-peaking, postprandial response of spike potentials. Patients who are prone to diarrhea demonstrate this disparity to a greater degree than patients who are prone to constipation.
Small bowel dysmotility manifests in delayed meal transit in patients prone to constipation and in accelerated meal transit in patients prone to diarrhea. In addition, patients exhibit shorter intervals between migratory motor complexes (the predominant interdigestive small bowel motor patterns).
Current theories integrate these widespread motility aberrations and hypothesize a generalized smooth muscle hyperresponsiveness. They describe increased urinary symptoms, including frequency, urgency, nocturia, and hyperresponsiveness to methacholine challenge.
Visceral hyperalgesia is the second part of the traditional 3-part complex that characterizes IBS.
Enhanced perception of normal motility and visceral pain characterizes IBS. Rectosigmoid and small bowel balloon inflation produces pain at lower volumes in patients than in controls. Notably, hypersensitivity appears with rapid but not gradual distention.
Patients who are affected describe widened dermatomal distributions of referred pain.
Sensitization of the intestinal afferent nociceptive pathways that synapse in the dorsal horn of the spinal cord provides a unifying mechanism.
Psychopathology is the third aspect.
Associations between psychiatric disturbances and IBS pathogenesis are not clearly defined.
Patients with psychological disturbances relate more frequent and debilitating illness than control populations.
Patients who seek medical care have a higher incidence of panic disorder, major depression, anxiety disorder, and hypochondriasis than control populations.
An Axis I disorder coincides with the onset of GI symptoms in as many as 77% of patients.
A higher prevalence of physical and sexual abuse has been demonstrated in patients with IBS.
Whether psychopathology incites development of IBS or vice versa remains unclear.
Recently, microscopic inflammation has been documented in some patients. This concept is groundbreaking in that IBS had previously been considered to have no demonstrable pathologic alterations.
Both colonic inflammation and small bowel inflammation have been discovered in a subset of patients with IBS as well as in patients with inception of IBS after infectious enteritis (postinfectious IBS). Risk factors for developing postinfectious IBS include female gender, longer duration of illness, the type of pathogen involved, an absence of vomiting during the infectious illness, and young age.
Laparoscopic full-thickness jejunal biopsy samples revealed infiltration of lymphocytes into the myenteric plexus and intraepithelial lymphocytes in a subset of patients. Neuronal degeneration of the myenteric plexus was also present in some patients.
Patients with postinfectious IBS may have increased numbers of colonic mucosal lymphocytes and enteroendocrine cells.
Enteroendocrine cells in postinfectious IBS appear to secrete high levels of serotonin, increasing colonic secretion and possibly leading to diarrhea.
Recently, small bowel bacterial overgrowth has been heralded as a unifying mechanism for the symptoms of bloating and distention common to patients with IBS. This has led to proposed treatments with probiotics and antibiotics.
Frequency:

In the US: Population-based studies estimate the prevalence of IBS at 10-20% and the incidence of IBS at 1-2% per year. Of people with IBS, approximately 10-20% seek medical care. An estimated 20-50% of gastroenterology referrals relate to this symptom complex.
Internationally: Incidence is markedly different among countries.
Mortality/Morbidity:

This is a chronic relapsing condition. Physicians must be forthcoming with patients because knowledge may help allay undue fears as their disease waxes and wanes. IBS does not increase mortality or the risk of inflammatory bowel disease or cancer.
The principal associated physical morbidities include abdominal pain and lifestyle modifications secondary to altered bowel habits.
Work absenteeism resulting in lost wages is more frequent in patients with IBS.
Race:

American and European cultures demonstrate similar frequencies of IBS across racial and ethnic lines. However, within the United States, survey questionnaires indicate a lower prevalence in Hispanics in Texas and Asians in California.
Populations of Asia and Africa may have a lower prevalence.
The role of different cultural influences and varying health care–seeking behaviors is unclear.
Sex: In Western countries, women are 2-3 times more likely to develop IBS than men, although males represent 70-80% of patients with IBS in the Indian subcontinent. Women seek health care more often, but the IBS-specific influence of this occurrence remains unknown. Other factors, such as a probably greater incidence of abuse in women, may confound interpretation of this statistic.

Age:

Patients often retrospectively note the onset of abdominal pain and altered bowel habits in childhood.
Approximately 50% of people with IBS report symptoms beginning before they were aged 35 years.
The development of symptoms in people older than 40 years does not exclude IBS but should prompt a closer search for an underlying organic etiology.


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CLINICAL Section 3 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography
History: A meticulous history is the key to diagnosis. The Rome criteria provide the construct upon which questions are based (see Background). Symptoms consistent with IBS include the following:

Altered bowel habits
Constipation variably results in complaints of hard stools of narrow caliber, painful or infrequent defecation, and intractability to laxatives.
Diarrhea usually is described as small volumes of loose stool, with evacuation preceded by urgency or frequent defecation.
Postprandial urgency is common.
Alternating habits are common. Characteristically, one feature predominates in a single patient, but significant variability exists among patients.
Abdominal pain
Descriptions are protean. Pain frequently is diffuse without radiation. Common sites of pain include the lower abdomen, specifically the left lower quadrant.
Acute episodes of sharp pain are often superimposed on a more constant dull ache.
Meals may precipitate pain, and defecation commonly improves pain. Defecation may not fully relieve pain.
Pain from presumed gas pockets in the splenic flexure may masquerade as anterior chest pain or left upper quadrant abdominal pain. This splenic flexure syndrome is demonstrable by balloon inflation in the splenic flexure and should be considered in the differential of chest or left upper quadrant abdominal pain.
Abdominal distention
Patients frequently report increased amounts of bloating and gas. Quantitative measurements fail to support this claim.
People with IBS may manifest increasing abdominal circumference throughout the day, as assessed by CT scan. They may also demonstrate intolerance to otherwise normal amounts of abdominal distention.
Clear or white mucorrhea of a noninflammatory etiology is commonly reported.
Noncolonic and extraintestinal symptoms
Epidemiologic associations with dyspepsia, heartburn, nausea, vomiting, sexual dysfunction (including dyspareunia and poor libido), and urinary frequency and urgency have been noted.
Symptoms may worsen in the perimenstrual period.
Fibromyalgia is a common comorbidity.
Stressor-related symptoms
These symptoms may be revealed with careful questioning.
Emphasize avoidance of stressors.
Inconsistent symptoms must alert the physician to the possibility of an organic pathology. Symptoms not consistent with IBS include the following:
Onset in middle age or older
Acute symptoms: IBS is defined by chronicity.
Progressive symptoms
Nocturnal symptoms
Anorexia or weight loss
Fever
Rectal bleeding
Painless diarrhea
Steatorrhea
Lactose and/or fructose intolerance
Gluten intolerance
Physical:

The patient has an overall healthy appearance.
The patient may be tense or anxious.
The patient may present with sigmoid tenderness or a palpable sigmoid cord.
Causes: Causes remain poorly defined, but they are being avidly researched.

Postulated etiologies
Abnormal transit profiles and an enhanced perception of normal motility may exist.
Local histamine sensitization of the afferent neuron causing earlier depolarization may occur.
Causes related to enteric infection (See Pathophysiology for more detail.)
Colonic muscle hyperreactivity and neural and immunologic alterations of the colon and small bowel may persist after gastroenteritis.
Psychological comorbidity independently predisposes the patient to the development of postinfectious IBS.
Psychological illness may create a proinflammatory cytokine milieu, leading to IBS through an undefined mechanism after acute infection.
Central neurohormonal mechanisms
Abnormal glutamate activation of N-methyl-D-aspartate (NMDA) receptors, activation of nitric oxide synthetase, activation of neurokinin receptors, and induction of calcitonin gene-related peptide have been observed.
The limbic system mediation of emotion and autonomic response enhances bowel motility and reduces gastric motility to a greater degree in patients who are affected than in controls. Limbic system abnormalities, as demonstrated by positron emission tomography, have been described in patients with IBS and in those with major depression.
The hypothalamic-pituitary axis may be intimately involved in the origin. Motility disturbances correspond to an increase in hypothalamic corticotropin-releasing factor (CRF) production in response to stress. CRF antagonists eliminate these changes.
As discussed in Pathophysiology, Pimental and colleagues have proposed that small bowel bacterial overgrowth provides a unifying mechanism for the common symptoms of bloating and gaseous distention in patients with IBS.
Bloating and distention may also occur from intolerance to dietary fats. Reflex-mediated small bowel gas clearance is more impaired by lipids (fat) ingestion in patients with IBS versus patients without IBS.