Editorial

OBJECTIVE:

Irritable bowel syndrome (IBS) is a common functional disorder characterized by enhanced perceptual sensitivity and hypervigilance toward afferent signals from the viscera. We hypothesize that the increased responsiveness of IBS patients is a generalized phenomenon applying to stimuli other than visceral and attempt to demonstrate increased responsiveness to sounds as measured by the P1 scalp potential.

METHODS:

Event-related potentials were recorded from IBS patients and control subjects in an auditory task requiring detection of rare pitch targets in a designated ear. Visual words served as targets in an additional block.

RESULTS:

Compared to control subjects, IBS patients displayed a robust increase in the amplitude of the P1 scalp potential elicited by both attended and unattended sounds.

CONCLUSIONS:

Enhanced P1 indicates preattentive central nervous system dishabituation in response to repeated sounds. A generalized preattentive increase in central nervous system reactivity may be a feature that IBS shares with several anxiety disorders that frequently co-occur in these patients.

Background & Aims: Comorbid or extraintestinal symptoms occur frequently with irritable bowel syndrome and account for up to three fourths of excess health care visits. This challenges the assumption that irritable bowel is a distinct disorder. The aims of this study were to (1) assess comorbidity in 3 areas: gastrointestinal disorders, psychiatric disorders, and nongastrointestinal somatic disorders; and (2) evaluate explanatory hypotheses. Methods: The scientific literature since 1966 in all languages cited in Medline was systematically reviewed. Results: Comorbidity with other functional gastrointestinal disorders is high and may be caused by shared pathophysiological mechanisms such as visceral hypersensitivity. Psychiatric disorders, especially major depression, anxiety, and somatoform disorders, occur in up to 94%. The nongastrointestinal nonpsychiatric disorders with the best-documented association are fibromyalgia (median of 49% have IBS), chronic fatigue syndrome (51%), temporomandibular joint disorder (64%), and chronic pelvic pain (50%). Conclusions: Multivariate statistical analyses suggest that these are distinct disorders and not manifestations of a common somatization disorder, but their strong comorbidity suggests a common feature important to their expression, which is most likely psychological. Some models explain the comorbidity of irritable bowel with other disorders by suggesting that each disorder is the manifestation of varying combinations of interacting physiological and psychological factors. An alternative hypothesis is that the irritable bowel diagnosis is applied to a heterogeneous group of patients, some of whom have a predominantly psychological etiology, whereas others have a predominantly biological etiology, and that the presence of multiple comorbid disorders is a marker for psychological influences on etiology.

GASTROENTEROLOGY 2002;122:1140-1156

OBJECTIVE:

Selective attention to GI sensations has been suggested as an important mechanism that affects symptom perception in patients with irritable bowel syndrome (IBS), but this hypothesis has not yet been tested empirically. Differential recall of words describing negative affect has been used to demonstrate that depressed patients selectively attend to negative affect words. This technique may be useful for examining selective attention to somatic sensations. The aim of this study was to determine whether patients with IBS demonstrate selective recall of GI sensations compared with neutral words and words describing respiratory sensations.

METHODS:

A total of 16 IBS patients, nine asthmatic patients (medical controls), and eight healthy controls were shown 10 GI sensation words or phrases, 10 respiratory sensation words or phrases, and 10 neutral words in random order for 3 s each. After a distraction task, subjects wrote down all of the words or phrases they could remember.

RESULTS:

As predicted, IBS patients were more likely to recall GI words than other categories. Asthmatic patients were more likely to recall respiratory words in comparison with healthy controls.

CONCLUSIONS:

IBS patients selectively recall words describing GI sensations; this suggests that they may selectively attend to GI sensations, thus supporting the cognitive-behavioral theory of IBS.

Alterations in activation of pain modulation systems may play a role in the pathophysiology of irritable bowel syndrome (IBS). However, little is known about the effects of exogenous opioids on the perceptual and autonomic responses to aversive visceral stimulation. The aim of the study was to evaluate the effect of the mu opioid-preferring analgesic fentanyl (FEN), given intravenously, on perceptual and autonomic responses to rectal distension. Ten IBS patients and ten normal subjects received, on separate days, either high dose (HD) fentanyl (112 μg bolus followed by 0.04 μg/kg per min infusion), low dose (LD) fentanyl (56 μg bolus followed by 0.02 μg/kg per min) or normal saline (SAL) (50 cc bolus followed by 45 cc/h infusion). Perception thresholds for discomfort and pain during rectal distension were assessed using a tracking paradigm. Intensity and unpleasantness ratings of the distensions, and cardiac autonomic parameters were assessed during randomly delivered rectal stimuli. Effects of FEN on rectal compliance and tone as well as mental status were also assessed. IBS patients had lower perceptual thresholds for discomfort and pain under control conditions. FEN dose-dependently increased the perception thresholds in both healthy control subjects and in IBS patients with a greater relative efficacy in IBS patients than in normal subjects. IBS patients used significantly higher unpleasantness ratings of rectal stimuli compared to healthy controls, but showed no difference in the sensory intensity rating of the stimulus. FEN decreased both intensity and unpleasantness ratings for IBS and normals. FEN lowered cardiosympathetic tone in normal subjects but had no effect on IBS patients. FEN had no effect on rectal tone or compliance. FEN dose-dependently attenuates the perception of phasic rectal distension and affects unpleasantness ratings during random fixed rectal distension, with a greater relative efficacy for this antinociceptive effect in IBS patients. These findings support the hypothesis that IBS patients may have an altered central release of endogenous opioids in response to visceral stimulation.