Graphic showing silhouettes of two individuals pointing at a constellation with a galaxy in the background. The constellation shows IBS symptoms: constipation, abdominal pain, straining, bloating, urgency, diarrhea, abdominal discomfort, and fecal incontinence
Graphic showing silhouettes of two individuals pointing at a constellation with a galaxy in the background. The constellation shows IBS symptoms: constipation, abdominal pain, straining, bloating, urgency, diarrhea, abdominal discomfort, and fecal incontinence

THE SCIENCE OF IBS:
IBS HAS MANY CONTRIBUTING FACTORS

IBS has long been considered to have a multifactorial pathophysiology, with a complex array of contributing factors1-4

    • Genetic predisposition
    • Psychosocial factors
    • Gut immune activation
    • Microbiome, bile acids
    • Gut permeability
    • Diet

ALTERED FUNCTIONS5-7

VISCERAL HYPERSENSITIVITY AND ALTERED CORTICAL PERCEPTION IN IBS5-7

Infographic showing intestines on one side and a brain on the other, with arrows going back and forth between them.Infographic showing intestines on one side and a brain on the other, with arrows going back and forth between them.Infographic showing intestines on one side and a brain on the other, with arrows going back and forth between them.

IBS is thought to be associated with visceral hypersensitivity and pain caused by hyperactivity of colonic pain fibers located in the submucosa of the gut. These fibers signal to the pain-sensing regions of the brain, causing a disconnect between brain-gut communication that results in the brain perceiving gut signals more strongly than usual and sending signals to the gut that disturb intestinal functioning. 5-7

GI MOTILITY MECHANICS8

GI motility function is one factor that contributes to GI dysfunction causing either constipation or diarrhea. It is driven by smooth muscle contractions of the gut, causing extensive mixing and propulsion of gut contents through the system. The efficacy of mixing and propulsion depend on the spatiotemporal characteristics of the contractions, including frequency, amplitude, and duration.

Graphic depicting the difference between RPCs and GMCs.Graphic depicting the difference between RPCs and GMCs.Graphic depicting the difference between RPCs and GMCs.

GI MOTILITY IN IBS-C8

Chart showing strength and frequency of gut contractions in the duodenum and jejunum in a healthy subject.Chart showing strength and frequency of gut contractions in the duodenum and jejunum in a healthy subject.Chart showing strength and frequency of gut contractions in the duodenum and jejunum in a healthy subject.
Chart showing strength and frequency of gut contractions in the duodenum and jejunum in an IBS-C patient.Chart showing strength and frequency of gut contractions in the duodenum and jejunum in an IBS-C patient.Chart showing strength and frequency of gut contractions in the duodenum and jejunum in an IBS-C patient.

In IBS-C, it appears the overall ability of the colon to contract and expand to push gut contents forward is slowed. As removal of water from the fecal slurry is time dependent and actively regulated, the stool that remains in the colon longer becomes drier.11 This, combined with a reduction in RPCs and GMCs, causes contents to harden and build up over time as fluid is absorbed by the intestinal wall. Patients may experience an urge to defecate based on accumulation of feces in the sigmoid colon or rectum due to rectal motor function signals rather than gut motor function signals.8

IBS-C is also associated with intestinal secretion dysfunction; particularly associated with the amine serotonin (5-hydroxytryptamine [5-HT]), the main mediator of intestinal secretion. Synthesized primarily in the GI tract, 5-HT mediates intrinsic reflexes such as stimulation of propulsion, segmentation motility, epithelial secretion, and vasodilation. This dysfunction is correlated with high platelet 5-HT levels and decreased postprandial release of 5-HT, both of which appear to be associated with increased colonic transit time.11

GI MOTILITY IN IBS-D8

Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in healthy subjects.Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in healthy subjects.Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in healthy subjects.
Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in IBS-D patients.Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in IBS-D patients.Chart showing strength and frequency of gut contractions from the splenic exure to the rectum in IBS-D patients.

Patients with IBS-D exhibit far more spontaneous giant motility contraction (GMC) activity than the general population. These spasms result in faster transit through the intestines, shortening the time between ingestion and defecation by several-fold and causing diarrhea, urgency, and abdominal cramping. Not only do patients with IBS-D experience more GMCs, the GMCs are stronger, which may increase pain and account for cramping. A measurement performed after meal ingestion showed that GMC amplitude in IBS-D patients was more than twice that of normal controls.8

Another contributing factor to IBS-D is intestinal secretion dysfunction. Intestinal secretion is mainly mediated to the amine serotonin (5-hydorxytryptamine [5-HT]). The increase in circulating 5-HT reflects a primary deficiency in serotonin expression in gastrointestinal mucosa, resulting in the induction of loose bowel movements.11

IBS TRIGGERS

The visceral hypersensitivity, altered cortical perception, and abnormal gut motility associated with IBS can be triggered by numerous other factors, including certain foods, lack of sleep, menstrual cycle, and pregnancy.1-4

Help patients understand IBS pathophysiology

ROME IV
IBS CRITERIA

CHARACTERIZING IBS10

The Rome criteria was originally developed by an international group of gastroenterology experts to guide research. Over time, the criteria have been revised and updated to make them clinically relevant and useful.

ROME CRITERIA FOR DIAGNOSING IBS10

Recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, associated with 2 or more of the following criteria*:
  1. Related to defecation
  2. Associated with a change in frequency of stool
  3. Associated with a change in form (appearance) of stool

ROME IV IBS SUBTYPE CRITERIA

IBS-C10

Simple icon of the gut in painSimple icon of the gut in painSimple icon of the gut in pain

Abdominal pain related to defecation

Simple icon of small, hard, lumpy stoolsSimple icon of small, hard, lumpy stoolsSimple icon of small, hard, lumpy stools

>25% Bristol stool form 1 or 2

Simple icon of a loose, watery stoolSimple icon of a loose, watery stoolSimple icon of a loose, watery stool

<25% Bristol stool form 6 or 7

IBS-D10

Simple icon of the gut in painSimple icon of the gut in painSimple icon of the gut in pain

Abdominal pain related to defecation

Simple icon of a loose, watery stoolSimple icon of a loose, watery stoolSimple icon of a loose, watery stool

>25% Bristol stool form 6 or 7

Simple icon of small, hard, lumpy stoolsSimple icon of small, hard, lumpy stoolsSimple icon of small, hard, lumpy stools

<25% Bristol stool form 1 or 2

SATELLITE RESOURCES FOR IBS

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An open dialogue with patients may help reduce treatment delays and improve quality of life. The resources here are designed to help start the conversation and help with patient education and counseling.

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