Irritable Bowel Syndrome

Irritable Bowel Syndrome

• A functional bowel disorder characterized by abdominal pain or discomfort and altered bowel habits in the absence of detectable structural abnormalities.

Pathophysiology of IBS

• Poorly understood• Proposed factors include:– Abnormal gut motor and sensory activity– Central neural dysfunction– Psychologic disturbances– Stress– Luminal factors

Pathophysiology of IBS

• Abnormal gut motor activity• Colonic motor abnormalites are more prominent

under stimulated conditions• IBS patients may exhibit increased rectosigmoid

motor activity for up to 3 hours after eating. • The motility index of high-amplitude propagating

contractions in diarrhea-prone IBS patients were greatly increased compared to healthy subjects.

Pathophysiology of IBS

• Abnormal Gut Sensitivity– IBS patients frequently exhibit exaggerated sensory

responses to visceral stimulation.– Postprandial pain has been temporally related to

entry of the food bolus into the cecum of 74 % of patients.

– IBS px’s have an increased area of referred pain. This is suggestive of postprandial symptoms occuring due to a nutrient-dependent exaggerated sensory component of the gastrocolonic response.

Pathophysiology of IBS

• Proposed mechanisms for gut hypersensitivity:– Increased end-organ sensitivity with recruitment of

“silent” nociceptors– Spinal hyperxicitability with activation of nitric oxide and

possibly other neurotransmitters– Endogenous modulation of caudad nociceptive

transmission– Possible development of long term hyperalgesia due to

development of neuroplasticity, resulting in permanent or semi permanent changes in neural response to visceral stimulation.

Pathophysiology of IBS

• CNS Factors– The association of emotional disorders and stress

with IBS symptom exacerbation and therapeutic response to cerebral cortical therapy.

– Mid-cingulate gyrus shows greater activation on MRI in IBS patients

– IBS patients show preferential activation on of the prefrontal lobe, which contains a vigilance network concerned with alertness

Pathophysiology of IBS

• Psychologic Disturbances– Abnormal psychiatric features are recorded in up

to 80 % of IBS patients.– No single psychiatric diagnosis predominates.– Prior sexual and physical abuse has also shown a

link with the development of IBS.– Psychological factors influence pain thresholds as

stress alters sensory threshold.

Pathophysiology of IBS

• IBS and infection– 544 patient study with confirmed bactierial

gastroenteritis• 1/4 of the patients had subsequent IBS• Microbes involved: Campylobacter, Salmonella, and

Shigella• Patients w/ campylobacter infxn who are toxin positive

are more like to develop IBS

Pathophysiology of IBS

• Serotonin and IBS– A link between the postprandial symptoms of IBS

patients and serotonin– Serotonin containing enterochromaffin cells in the

colon are increased in a subset of IBS-D patients. – Plasma 5-HT levels were significantly higher in this

group then the control groups.