Reducing transcranial direct current stimulation-induced erythema with skin pretreatment: considerations for sham-controlled clinical trials.

OBJECTIVES: Transcranial direct current stimulation (tDCS)-induced erythema (skin reddening) has been described as an adverse effect that can harm blinding integrity in sham-controlled designs. To tackle this issue, we investigated whether the use of topical pretreatments could decrease erythema and other adverse effects associated with tDCS. MATERIALS AND METHODS: Thirty healthy volunteers were recruited, and four interventions were applied 30 min prior to tDCS in a Latin square design: placebo, ketoprofen 2%, hydroxyzine 1%, and lidocaine 5%. TDCS was applied for 30 min (2 mA, anode and cathode over F3 and F4, respectively) in two active sessions with a minimum 1-week interval. The Draize erythema scoring system scale was used to assess erythema intensity; a tDCS questionnaire was used to assess other adverse effects (e.g., tingling, itching, burning sensation, and pain). RESULTS: We found that ketoprofen (but not hydroxyzine or lidocaine) significantly attenuated tDCS-induced erythema regarding intensity and duration, with a medium effect compared with placebo. Erythema was overall mild, short-lived (lasting 18-24 min after tDCS ending), and more intense under the anode. Subjects with darker skin color also tended to present less intense tDCS-induced erythema. The prevalence of other adverse effects was low and did not differ between dermatological groups. CONCLUSIONS: Ketoprofen 2% topical pretreatment might be an interesting strategy to reduce tDCS-induced erythema and might be useful for blinding improvement in further sham-controlled tDCS trials.