T2076 Visceral Hypersensitivity in Patients With Irritable Bowel Syndrome is Significantly Associated With Increased Contractility of the Rectum in Response to Balloon Distension

Abstract

Background: Visceral hypersensitivity (VH) is considered a pivotal pathogenic factor in the irritable bowel syndrome (IBS). VH is believed to reflect increased conscious perception of gut stimuli and may be assessed by reduced pain thresholds (≤ 32 mmHg; [1]) during rectal balloon distension. On the other hand, in some patients, rectal balloon distension may also induce contractile responses. Whether the occurrence of contractions is associated with reduced pain thresholds has not been investigated. Aim: To investigate in IBS patients whether VH is associated with increased contractile responses to rectal balloon distension. Methods: 84 consecutive IBS patients underwent a series of rectal isobaric balloon distension tests with stepwise pressure increase from 0 to 48 mmHg using an electronic barostat. Pain thresholds were assessed by recording the patients' rectal sensations (ranging from 0=”no sensation” to 7=”pain”) in response to each distension. An investigator blinded to the pain thresholds visually analyzed the occurrence of marked contractions of the rectum wall determined by volume depressions in the pressure-volume curves. Statistics included ChiSquareand T-tests. Results: Overall, 38% (n=32) of patients had VHwith rectal pain thresholds ≤32 mm Hg. The proportion of patients producing distension-induced contractions was 27% (n= 23) of the entire cohort. There was a highly significant association between the occurrence of contractions and the presence of VH: 15% of patients with normal pain thresholds had contractions compared to 47% of hypersensitive patients (p<0.002). Conversely, 65%of patients with contractions had VH (p<0.002). Moreover, rectal pain thresholds were significantly lower in patients with contractions compared to those without (31.8±8.8 vs. 38.1±9.3mmHg; p<0.007). Conclusion: In this population of IBS patients, VHdetermined by reduced rectal pain thresholds was significantly associated with the occurrence of increased rectal contractility in response to balloon distension. These findings suggest 1) increased motor reflex responses as component of VH; and/or 2) an important contribution of these contractions to visceral pain generation. Indeed, recent observations indicate deformationincreased activity of mechanosensitive neurons even at constant wall tension [2]. Hence, contractile intestinal wall deformations following distension might per se increase pain perception in a subgroup of patients. These findings could have potential future diagnostic and therapeutic implications. 1. Bouin et al. Gastroenterology 2002;122:1771-1777 2. Mazzuoli & Schemann. J Physiol 2009;587:4681-94