Effect of Spinal Cord Response on Changes in Pain Thresholds of Each Tissue Due to Electroacupuncture.

Background: Acupuncture enhances the endogenous analgesic system and reduces pain. However, its effect is not constant, and it has been reported that it varies depending on the endogenous analgesic system and spinal cord response. Therefore, we investigated whether there was a difference in the changes in pain thresholds in muscle and skin tissue due to differences in the spinal cord response when electroacupuncture was applied to healthy participants whose endogenous analgesic system works normally.

Methods: We included 29 healthy volunteers who gave consent to participate. The participants underwent psychological evaluations, pain thresholds assessment for muscle and skin tissue, temporal summation of pain (TSP), and conditioned pain modulation (CPM). The participants subsequently received 30 min of acupuncture (scalp + three limbs) as an intervention, and the pain thresholds of muscle and skin tissue were measured before, 30 and 60 min after intervention. Note that participants were grouped by TSP based on high and low spinal cord response.

Results: Analysis of participants grouped by spinal cord response showed no difference in CPM between high and low groups prior to the intervention, indicating that the endogenous analgesic systems were the same for the two groups. However, electroacupuncture intervention affected changes in muscle pain threshold (p = 0.03). A significant difference in pain threshold was noted in the high group, 60 min after intervention (p = 0.04).

Conclusion: When electroacupuncture is applied to healthy participants, those with higher spinal cord response may have higher muscle pain threshold.