Objective: Mixed evidence exists regarding whether irritable bowel syndrome (IBS) patients show increased somatic pain perception compared with controls. The current study used a deep, tonic somatic pain stimulus (ischemic pain) to evaluate somatic hypersensitivity in IBS patients. [This is deep pain associated with decreased blood flow owing to obstruction or constriction.]
Methods: A total of 27 diarrhea-predominant and 15 constipation-predominant IBS patients, and 29 controls participated in the study. The modified submaximal effort tourniquet procedure was performed to induce ischemic arm pain, and the time required to reach pain threshold and pain tolerance were recorded in seconds. All subjects completed the Functional Bowel Disease Severity Index (FBDSI) scale as well as several psychosocial instruments. Group differences for threshold and tolerance were determined using a series of one-way ANOVA tests followed by Tukey comparisons.
Results: IBS patients had a shorter time to ischemic threshold (F = 34.606, P < 0.001) and tolerance (F = 38.656, P < 0.001) compared with controls; however, the groups did not differ on ratings of pain at the time of tolerance. IBS patients had a higher rating on the FBDSI scale compared with controls (P < 0.001), and ischemic pain threshold was negatively correlated with the FBDSI score.
The results of this study suggest that a widespread alteration in central pain processing in IBS patients may be present as they display hypersensitivity to ischemic arm pain, and ischemic pain threshold was associated with clinical symptoms.
These findings could reflect a dysfunction in inhibitory pain systems in IBS patients, as ischemic (deep) pain may be under tonic inhibitory control. [Tonic control refers to nerve impulses that maintain tone or level of activity in muscles or other ‘effector’ organs, as in the GI tract.]
Source: Pain Medicine, Nov 2010;11(11):1619-27. PMID: 21029350, by Zhou Q, Fillingim RB, Riley JL, Verne GN. Department of Medicine, The Ohio State University, Columbus, Ohio; College of Dentistry, University of Florida, Gainesville, Florida; North Florida/South Georgia Veteran Health System, Gainesville, Florida; Research Service, Cincinnati VAMC, Cincinnati, Ohio, USA.