Relationship Between Symptoms and Hypersensitivity to Rectal Distension in Patients With Irritable Bowel Syndrome

S.D. Kuiken; R. Lindeboom; G.N. Tytgat; G.E. Boeckxstaens

Disclosures

Aliment Pharmacol Ther. 2005;22(2):157-164. 

In This Article

Discussion

This study aimed to explore the possible associations between specific IBS symptoms and the presence of visceral hypersensitivity in patients with IBS. Our data confirm that hypersensitivity to painful rectal distension can be demonstrated in about one-half of patients with IBS. Visceral hypersensitivity was more prevalent in female, compared with male patients. The two subpopulations of IBS patients, defined by the presence or absence of visceral hypersensitivity, were comparable in terms of age and bowel habit predominance. Severe abdominal pain was more prevalent in hypersensitive patients, whereas the prevalence of individual gastrointestinal symptoms was similar in both groups. However, none of the specific IBS symptoms (including pain) could accurately distinguish hypersensitive from normosensitive subjects. Therefore, selection based on clinical parameters is unlikely to discriminate individual IBS patients with visceral hypersensitivity from those with normal visceral sensitivity.

Earlier studies have indeed suggested that rectal sensory characteristics may play a role in the predominant symptom patterns of patient subgroups. For example, IBS-C patients experienced decreased sensations of urge during rectal distension compared with IBS-D patients.[19] However in the present study, differences in bowel habit were not associated with the presence or absence of hypersensitivity to rectal distension. In addition, hypersensitivity has been linked to certain individual IBS symptoms, such as the feeling of incomplete evacuation and urgency.[6,20,21] Except for severe pain, we were unable to demonstrate such correlation. Severe pain was significantly more prevalent in hypersensitive patients. Similar findings have been reported in functional dyspepsia, where the presence of visceral hypersensitivity was associated with epigastric pain.[13] Furthermore, it was also shown previously that patients with pain predominant IBS were more susceptible to rectal sensitization in response to repetitive sigmoid distension, compared with non-pain predominant IBS patients.[22] These findings suggest that there may be an association between pain and visceral hypersensitivity. To evaluate the possible predictive value of this symptom, we performed an A-ROC curve analysis. This revealed that the rather weak association was unable to select individual IBS patients with hypersensitivity. The same was true for all other symptoms studied. Additionally, we compared the group of patients with the lowest discomfort/pain thresholds, excluding patients with intermediate sensitivity. Again, none of the symptoms could adequately distinguish hypersensitive from normosensitive patients, illustrating that IBS patients with visceral hypersensitivity cannot be identified solely based on clinical symptoms.

The discomfort/pain threshold to define hypersensitivity was ≤18 mmHg above MDP. Compared with previous studies, this cut-off is rather conservative.[6,7,8] Because distension protocols and laboratory conditions are not necessarily comparable, we defined the range of normality based on our own sample of healthy controls, rather than using an historical cut-off. In addition, it seems unlikely that a less stringent cut-off increases the differences between the subgroups.

The fact that hypersensitive and normosensitive IBS present with comparable, heterogeneous symptom patterns does not exclude that hypersensitive patients may have a different underlying pathophysiology. In view of the hypersensitivity concept, it is possible that visceroanalgesic drugs may be only effective in those patients. Patient selection based on other criteria, such as bowel habit and gender, has already been shown to be of great importance for the outcome of clinical trials evaluating the efficacy of several contemporary compounds for IBS, for example alosetron and tegaserod.[23,24] Our study indicates that until clear criteria or alternative methods have been established to select individual hypersensitive patients, evaluation of perceptual thresholds to gut distension is still required. We perceive that such an approach would be very demanding if not impossible in large scale clinical trials. However, a 'proof of principle' study for the definitive foundation of the hypersensitivity concept in IBS is certainly warranted.

In conclusion, hypersensitive and normosensitive IBS patients present with comparable, heterogeneous symptom patterns. Therefore, selection based on clinical parameters is unlikely to discriminate individual IBS patients with visceral hypersensitivity from those with normal visceral sensitivity.


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