Areas of Capsaicin-Induced Secondary Hyperalgesia and Allodynia Are Reduced by a Single Chiropractic Adjustment: A Preliminary Study

INTRODUCTION: The aim of the study was to investigate the hypoalgesic effects of a single spinal manipulation treatment on acute inflammatory reactions and pain induced by cutaneous application of capsaicin. METHODS: Twenty healthy subjects participated in the experiment, which consisted of 2 sessions. In both sessions, following control measurements, topical capsaicin was applied to the right or left forearm to induce cutaneous inflammatory reactions. The cream was removed after 20 minutes. Then subjects received either spinal manipulation treatment (SMT) or "nonspinal manipulation treatment" (N-SMT), respectively. In control as well as pretreatment and posttreatment intervals, the following tests were performed: measurement of the areas of mechanical hyperalgesia and stroking allodynia, assessment of spontaneous pain, and measurement of blood flow. RESULTS: The results confirmed that topical capsaicin induced inflammatory reactions based on occurrence of hyperalgesia and allodynia, augmented pain perception, and increased blood flow following capsaicin application compared with the control session. When compared with N-SMT, spontaneous pain was rated significantly lower post-SMT (P <.014). In addition, areas of both secondary hyperalgesia and allodynia decreased after SMT (hyperalgesia: P <.007; allodynia: P <.003). However, there was no significant treatment effect for local blood flow. CONCLUSION: These results suggest hypoalgesic effects following a single SMT. As local vascular parameter was not affected by the single SMT, the hypoalgesic effects appear to be due to central mechanisms.