Cutaneous response to
capsaicin has been used to assess central sensitization in
pain research. This study compared the response to intradermal
capsaicin in the forearm and foot of
vulvar vestibulitis (
vestibulodynia)-afflicted cases and controls. We hypothesized that cases will experience greater spontaneous
pain, larger cutaneous areas of punctate
hyperalgesia and dynamic
allodynia, and greater vascular flow than controls. We also hypothesized enhanced post-injection
pain in the foot compared to the forearm based on dermatome proximity of the foot and vulva. Methods. Ten
vulvar vestibulitis syndrome (VVS) cases and 10 age and ethnically matched controls underwent two randomized, cross-over trials with intra-dermal
injections of
capsaicin or a saline placebo in the forearm and foot. Outcome measures included spontaneous
pain level, surface area of punctate
hyperalgesia, surface area of dynamic
allodynia, cutaneous blood flow, regional skin temperature and vital signs. Results. VVS cases experienced greater spontaneous
pain, punctate
hyperalgesia and dynamic
allodynia than
pain-free controls. Within the VVS group, post-
capsaicin spontaneous
pain, punctate
hyperalgesia and dynamic
allodynia were similar in the forearm and foot. Post-
capsaicin blood flow did not differ between cases and controls by anatomic site. Measures of depression and anxiety correlated with spontaneous
pain intensity but did not correlate with measures of
hyperalgesia,
allodynia, or blood flow. VVS cases had higher resting pulse rates and lower resting systolic blood pressures than in controls. Conclusion. VVS patients show enhancement of post-
capsaicin pain response extending far beyond the anatomic location of the primary complaint.