Activating endogenous visceral pain modulation: a comparison of heterotopic stimulation methods in healthy controls

All sensory input underlies modulation by endogenous central nervous system pathways. Dysfunctional endogenous pain modulation has been demonstrated in central sensitization and in several pain syndromes, including Irritable Bowel Syndrome (IBS) Activation of endogenous visceral pain modulation by heterotopic stimulation was compared using different methods. Rectal electrical or distension pain alone or with simultaneous (i.e. heterotopic) noxious hand or foot cold stimulation were investigated in randomized sequence in 14 male and 1 female healthy subjects. Mean pain intensities on a visual analogue scale of 0-100 (95% CI) during tonic rectal electrical and distension stimulation alone were 64 (52-76) and 55 (39-71), respectively. Rectal distension pain decreased by 36% (18-55) with simultaneous hand and by 45% (24-66) with simultaneous foot cold pain. Rectal electrical pain decreased by 45% (29-61) during hand and by 46% (28-64) during foot cold pain. Facilitation, i.e. increased rectal pain during heterotopic stimulation was observed in only 1 of 60 stimulation runs. Potent and consistent activation of endogenous visceral pain inhibition was achieved with heterotopic cold pain limb stimulation. Somato-visceral convergence did not affect the effectiveness of induction of endogenous visceral pain inhibition in healthy subjects, as hand and foot heterotopic stimulation resulted in similar pain inhibition. Pain facilitation, as shown earlier in IBS patients, was not evident in healthy controls.