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.