Irritable Bowel Syndrome : Diagnostic Symptom Criteria and Impact of Rectal Distensions on Cortisol and Electrodermal Activity

Abstract: In a population prevalence questionnaire study we demonstrated that constipation and fecal incontinence are common problems in the general Swedish population with a similar magnitude as in other Western countries. 95.6% of the population had between three bowel movements per day and three per week. Constipation was mostly defined by “hard stools” and “the need of using laxatives”.Irritable Bowel Syndrome (IBS) is characterized by abdominal pain/discomfort and abnormal bowel habits. The diagnostic criteria of IBS are based on clinical symptoms. Division of IBS patients into symptom subgroups appears important as their bowel symptoms are characterized by heterogeneity. International criteria to subgroup IBS (Rome II) are based on expert consensus and not on evidence. We investigated the variation of stool consistency and defecatory symptoms in 135 IBS patients by symptom diary cards. Most patients hadalternating stool consistency. When subgroups were based on stool consistency, all kinds of defecatory symptoms (straining, urgency, and feeling of incomplete evacuations) were frequently present in all subgroups. Stool frequency was in the normal range in the majority of patients. We propose that IBS subgroups should be based on stool consistency. We suggest that Rome II supportive criteria must be reconsidered as the determination of presence or absence of specific symptoms does not work as an instrument for categorization of IBS patients into diarrhoea- and constipation-predominant. We also propose that abnormal stool frequency should be excluded to define subgroups of IBS. Alternating stool consistency and presence of different defecatory symptoms, regardless of stool consistency should be included as criteria for IBS.Stress is known to play an important role in the onset and modulation of IBS symptoms. From experimental studies there is evidence for a stress-dependent alteration of visceral sensitivity. The biological mechanisms responsible for the causal link between stress and IBS symptoms are not completely understood, but the hypothalamic-pituitary-adrenocortical axis and the autonomous nervous system seem to play a prominent role in the pathophysiology of IBS. We investigated visceral sensitivity and the effect of repeated maximal tolerable rectal distensions on salivary cortisol levels and skin conductance in patients with IBS, chronic constipation and healthy volunteers.We found that the expectancy of the experimental situation per se (provocation of bowel symptoms by rectal distensions) compared to non-experimental days at home measured as salivary cortisol had a high impact on the level of arousal in IBS. IBS patients had higher skin conductance values than controls in the beginning of distension series and lower rectal thresholds for first sensation, urge and discomfort than healthy controls and constipation patients. IBS patients demonstrated habituation to repeated subjective maximal tolerable rectal distensions according to sympathetic activity although patients continued to rate their discomfort as maximal. Constipation patients had lower sympathetic activity than IBS patients before and during repeated rectal distensions. None of the groups demonstrated a significant increase in cortisol after repetitive rectal distensions.We conclude that Rome II supportive criteria for IBS should be reconsidered according to our findings. IBS patients are more sensitive to pre-experimental stress than healthy controls and patients with constipation. This should be considered in the design of experimental IBS studies. IBS patients habituated to subjective maximal tolerable, repetitive rectal distensions with decreasing sympathetic activity. Since responses to repeated stimuli of close-to-pain intensities are resistant to habituation this finding could be caused by psychological influences on perception, that is, perceptual response bias.