Tourniquet constriction exacerbates hyperalgesia-related pain induced by intradermal capsaicin injection

Background When capsaicin is injected intradermally, hyperalgesia develops around the injection site. The authors observed that volunteers report pain ful sensations in the skin remote from the injection site during tourniquet constriction of the affected extremity. Methods: Each volunteer received an intradermal injection of capsaicin on t he volar forearm, followed by intermittent tourniquet constriction of the e xtremity. In some participants, the tourniquet position was rotated between different sites on the upper extremities. Laser Doppler measurements were made in the skin to measure capillary blood now during pain magnification. Results: Hyperalgesia developed in the volunteers who were tested after the capsaicin injection. Blood now increased three times in the dermal capilla ries remote from the injection site after capsaicin injection. The tourniqu et-induced pain reached peak intensity soon after tourniquet inflation. Tou rniquet constriction of the arm on the affected side reliably induced painf ul exacerbation in each person tested. The quality of the sensation was des cribed as burning and extended across the arm in most volunteers. Only when pinprick hyperalgesia was detectable did the volunteers experience the dif fuse, immediate pain sensation. The pain initiated by the tourniquet constr iction likely is related to changes in skin capillary blood flow. Conclusions: Low cutaneous blood perfusion is related to the intensity of o ngoing, spontaneous pain when secondary hyperalgesia is present. The specif ic trigger(s) have yet to be identified.