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.
a Department of Anaesthesia, General Intensive Care and Pain Management, Medical University of Vienna, Vienna, Austria
b Institute of Neurology, Medical University of Vienna, Vienna, Austria
c Section 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.