Dysfunctional endogenous pain modulation in patients with functional dyspepsia

BackgroundEndogenous pain modulation (EPM) is central to the processing of sensory information. Visceral and somatic EPM are abnormal in irritable bowel syndrome, but have not been studied in functional dyspepsia (FD). MethodsVisceral EPM was assessed in 34 FD patients and 42 healthy controls. Gastric pain was induced with oral capsaicin and EPM was studied by adding heterotopic thermal foot stimulation or distraction by STROOP test. Somatic EPM was assessed using foot heat stimulation with heterotopic hand electrical stimulation. Key ResultsEndogenous pain modulation by distraction reduced mean gastric pain by 11.9 on the 0-100 visual analog scale (95% CI: 3.8-20.1) in controls (p=0.006) and by 2.0 (-6.18 to 10.44) in FD (p=0.6), with greater EPM in controls than in FD (difference -13.3 [-26.1 to -0.5]; p=0.04). Endogenous pain modulation by heterotopic foot stimulation reduced gastric pain by 6.5 (-0.7 to 13.6) in controls (p=0.07) and by 7.1 (-2.29 to 16.47) in FD (p=0.1), with no significant difference in EPM between controls and FD (-2.0 [-14.5 to 10.5]; p=0.75). In patients with prominent FD pain, greater pain correlated with decreased visceral EPM by distraction (r=0.51, p=0.04). Somatic EPM by heterotopic stimulation significantly decreased foot pain in controls (p=0.004), but not in FD (p=0.80). Conclusions & InferencesIn FD, visceral pain modulation by distraction was dysfunctional compared to controls. Somatic pain modulation was also decreased in FD. These data and the correlation of abnormal pain modulation by distraction with clinical pain in pain-predominant FD suggest a potential pathophysiological significance of abnormal pain modulation in FD.