Visceral pain perception in patients with irritable bowel syndrome and healthy volunteers is affected by the MRI scanner environment

Background: The MRI scanner environment induces marked psychological effects, but specific effects on pain perception and processing are unknown and relevant to all brain imaging studies. Objectives and methods: We performed visceral and somatic quantitative sensory and pain testing and studied endogenous pain modulation by heterotopic stimulation outside and inside the functional MRI scanner in 11 healthy controls and 13 patients with irritable bowel syndrome. Results: Rectal pain intensity (VAS 0-100) during identical distension pressures increased from 39 (95% confidence interval: 35-42) outside the scanner to 53 (43-63) inside the scanner in irritable bowel syndrome, and from 42 (31-52) to 49 (39-58), respectively, in controls (ANOVA for scanner effect: p=0.006, group effect: p=0.92). The difference in rectal pain outside versus inside correlated significantly with stress (r=-0.76, p=0.006), anxiety (r=-0.68, p=0.02) and depression scores (r=-0.67, p=0.02) in controls, but not in irritable bowel syndrome patients, who a priori had significantly higher stress and anxiety scores. ANOVA analysis showed trends for effect of the scanner environment and subject group on endogenous pain modulation (p=0.09 and p=0.1, respectively), but not on somatic pain (p>0.3). Conclusion: The scanner environment significantly increased visceral, but not somatic, pain perception in irritable bowel syndrome patients and healthy controls in a protocol specifically aimed at investigating visceral pain. Psychological factors, including anxiety and stress, are the likely underlying causes, whereas classic endogenous pain modulation pathways activated by heterotopic stimulation play a lesser role. These results are highly relevant to a wide range of imaging applications and need to be taken into account in future pain research. Further controlled studies are indicated to clarify these findings.