Cooling the skin to 20°C prevents pain from capsaicin 8% patch application, whereas EMLA does not. Cooling does not inhibit epidermal nerve fiber density reduction.
Topical capsaicin 8% was developed for the treatment of peripheral neuropathic pain. The pain reduction is associated with a reversible reduction of epidermal nerve fiber density (ENFD). During its application, topical capsaicin 8% provokes distinct pain. In a randomized, double-blind study analyzed with a block factorial analysis of variance, we tested whether cooling the skin would result in reliable prevention of the application pain without inhibiting reduction of ENFD. A capsaicin 8% patch was cut into 4 quarters and 2 each were applied for 1 hour on the anterior thighs of 12 healthy volunteers. A randomization scheme provided for 1 of the application sites of each thigh to be pretreated with EMLA and the other with placebo, whereas both application sites of 1 thigh, also randomly selected, were cooled by cool packs, resulting in a site temperature of 20°C during the entire treatment period. The maximum pain level given for the cooled sites (visual analogue scale [VAS] 1.3 ± 1.4) proved to be significantly lower than for the non-cooled sites (VAS 7.5 ± 1.9) (P < .0001). In contrast, there was no significant difference in application pain between the sites pretreated with EMLA or with placebo (VAS 4.1 ± 3.6 vs 4.8 ± 3.5, P = .1084). At all application sites, ENFD was significantly reduced by 8.0 ± 2.8 (ENF/mm ± SD, P < .0001), that is, 70%, with no significant differences between the sites with the different experimental conditions. In conclusion, cooling the skin to 20°C reliably prevents the pain from capsaicin 8% patch application, whereas EMLA does not. ENFD reduction is not inhibited by cooling.
aDepartment of Anaesthesia, General Intensive Care and Pain Management, Medical University of Vienna, Vienna, Austria
bInstitute of Neurology, Medical University of Vienna, Vienna, Austria
cSection for Clinical Biometrics, Medical University of Vienna, Vienna, Austria
*Corresponding author. Address: Department of Anaesthesia, General Intensive Care and Pain Management, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Wien, Austria. Tel.: +43 1 40400 4139; fax: +43 1 40400 6422.
1E.K. and M.Z. contributed equally to this work should be considered co-first authors.
Submitted February 8, 2013; revised July 22, 2013; accepted August 2, 2013.