Objective: The aim was to determine whether lower visceral pain thresholds in IBS primarily reflect physiological or psychological factors.
Methods: First, 121 IBS patients and 28 controls underwent balloon distentions in the descending colon using the ascending methods of limits (AML) to assess pain and urge thresholds. Second, sensory decision theory analysis was used to separate physiological from psychological components of perception: neurosensory sensitivity (p(A)) was measured by the ability to discriminate between 30 vs. 34 mmHg distentions; psychological influences were measured by the report criterion, i.e., the overall tendency to report pain, indexed by the median intensity rating for all distentions, independent of intensity. Psychological symptoms were assessed using the Brief Symptom Inventory (BSI).
Results: IBS patients had lower AML pain thresholds (median: 28 vs. 40 mmHg; p<0.001), but similar neurosensory sensitivity (median p(A): 0.5 vs. 0.5; p=0.69; 42.6% vs. 42.9% were able to discriminate between the stimuli better than chance) and a greater tendency to report pain (median report criterion: 4.0 "mild" pain) vs. 5.2 ("weak" pain); p=0.003). AML pain thresholds were not correlated with neurosensory sensitivity (r=-0.13; p=0.14), but were strongly correlated with report criterion (r=0.67; p<0.0001). Report criterion was inversely correlated with BSI somatization (r=-0.26; p=0.001) and BSI global score (r=-0.18; p=0.035). Similar results were seen for the nonpainful sensation of urgency.
Conclusions: Increased colonic sensitivity in IBS is strongly influenced by a psychological tendency to report pain and urge rather than increased neurosensory sensitivity.
- irritable bowel syndrome
- pain threshold
- psychological bias
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