EVIDENCE FOR 2 DISTINCT PERCEPTUAL ALTERATIONS IN IRRITABLE-BOWEL-SYNDROME

Background and aims-Visceral hyperalgesia has been implicated as a fac tor contributing to symptom generation in irritable bowel syndrome (IB S). However, previous studies using intestinal balloon distension have used psychophysical procedures which do not provide adequate and unbi ased measures of visceral sensitivity. Methods-Three psychophysical ta sks were examined in 45 patients with IBS (positive Rome criteria) and 14 controls using rectal balloon distension with a computerised diste nsion device. Discomfort threshold and tolerance were assessed during an ascending series of phasic pressure stimuli and during an interacti ve threshold tracking procedure. In addition, stimulus response functi ons were generated from intensity and unpleasantness ratings of the re ctal distensions.Results-Discomfort threshold and tolerance for the as cending stimuli were significantly lower for the patients with IBS com pared with the controls. In contrast, discomfort thresholds during the tracking procedure and stimulus response curves for the ascending ser ies were not different between the groups. A factor analysis of the ps ychophysical data was consistent with the presence of two distinct and unrelated perceptual alterations related to rectal distension: hyperv igilance for visceral stimuli, manifested as lowered response criteria for using the descriptor ''discomfort''; and rectal hypersensitivity, manifested as a lower discomfort threshold and left shift of the stim ulus response curves. Conclusions-Patients with IBS as a group have a greater propensity to label visceral sensations negatively and show a lower tolerance for rectal balloon distension. A subgroup of patients also have baseline rectal hypersensitivity, assessed by unbiased measu res of discomfort threshold and stimulus intensity judgements.