Author: Azpiroz F.

Institution: Digestive System Research Unit, Hospital General Vall d'Hebron, Autonomous University of Barcelona, Barcelona, Spain. AZPIROZ@HG.HEBRON.ES

Summary: Growing evidence suggests that symptoms in patients with irritable bowel syndrome (IBS) may be due to a visceral sensory dysfunction. Specifically, it has been shown that patients with IBS have hypersensitive responses to distension of the rectum, whereas their tolerance to somatic stimuli is normal or even increased.

Furthermore, patients with IBS have hypersensitivity of the small bowel, which selectively affects mechanosensitive afferents, with normal perception of electrical stimulation of the gut. Sensory dysfunctions may also be associated with altered reflex activity, which may contribute to the clinical symptoms. Normally, a series of mechanisms at different strata of the nervous system modulate visceral afferent input and determine conscious perception.

Conceivably, a dysfunction of these regulatory mechanisms may alter sensitivity in clinical conditions. To date, neither the origin nor the clinical significance of visceral hyperalgesia has been elucidated. However, it seems likely that the sensory and reflex dysfunctions of the gut in IBS may combine to different degrees, and their interaction may explain the clinical pleomorphism of the syndrome.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10202202&query_hl=22&itool=pubmed_docsum

Authors: Drewes AM, Petersen P, Rossel P, Gao C, Hansen JB, Arendt-Nielsen L.

Institution: Dept. of Medical Gastroenterology, Aalborg Hospital, Denmark. drewes@smi.auc.dk

Background: Hyperalgesia to visceral stimuli is a biological marker of the irritable bowel syndrome (IBS). Abnormal pain processing is probably of most importance, but biomechanical abnormalities of the gut wall may also contribute to the findings. In the current study, we investigated the sensation of the gut to electrical stimuli as well as the distensibility of the rectum and sigmoid colon in IBS patients and a control group.

Results: The pain detection thresholds to electrical stimuli at the rectosigmoid junction were 12.5 (range 7-39) mA in controls and 7.5 (range 0.75-12) mA in IBS patients (P = 0.03). The calculated pressures at the pain detection threshold in the sigmoid colon were lower in the IBS patients (31.5 (range 5-58) versus 5 cm (range 5-25) water; P = 0.03), otherwise no differences were seen in sensation rating to the different distension pressures. The CSA was slightly higher in controls to the different pressures, whereas no differences between the groups were seen in strain and tension of the rectum and sigmoid colon.

Conclusion: The visceral hypersensitivity in IBS seems to be related to alterations in the nervous system rather than biomechanical parameters such as the tension and strain of the gut wall. Treatment of pain in IBS should therefore be based on drugs with documented action on the nociceptive pathways in the central nervous system.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11495078&query_hl=20&itool=pubmed_docsum

Authors: Verne GN, Price DD.

Institution: University of Florida, Malcolm Randall VAMC, Department of Medicine, Gastroenterology Section (IIIC), 1601 SW Archer Road, Gainesville, FL 32608-1197, USA. vernegn@medicine.ufl.edu

Summary: Animal models of neuropathic pain have significantly advanced our knowledge of abnormalities in central pain processing mechanisms in chronic pain disorders. New neuroimaging techniques using functional magnetic resonance imaging and positron emission tomography scanning are beginning to provide insight into cortical participation in the processing of pain. Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders seen by physicians.

Visceral hypersensitivity or decreased pain thresholds to distension of the gut is considered to be a biologic marker for IBS and is present in most patients with this gastrointestinal disorder. Patients with IBS also have many extraintestinal symptoms consistent with a central hyperalgesic state. Recent studies suggest that patients with IBS may also have cutaneous hyperalgesia similar to that seen in other chronic pain disorders such as fibromyalgia. This suggests that abnormalities of central nociceptive processing are present in IBS.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12126584&query_hl=17&itool=pubmed_docsum

Authors: Tillisch K, Mayer EA.

Institution: Center for Neurovisceral Sciences and Women's Health, David Geffen School of Medicine, University of California-Los Angeles, 11301 Wilshire Boulevard, Los Angeles, CA 90073, USA. ktillisch@mednet.ucla.edu

Summary: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by chronic abdominal discomfort or pain in the absence of detectable organic disease. IBS is common and is associated with a significant impairment in health-related quality of life.

Enhanced perception of visceral stimuli ("visceral hypersensitivity") appears to be an important pathophysiological mechanism. Early IBS studies using functional brain imaging techniques suggest an alteration in central pain modulation circuits, rather than an increased sensitivity of peripheral visceral pain pathways. The frequent comorbidity with psychiatric disorders suggests the possibility of shared pathophysiological mechanisms and etiologic factors.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16273016&query_hl=14&itool=pubmed_docsum