Skin lesions induced by transcranial direct current stimulation (tDCS).

For several years, at the Institute Guttmann Neurorehabilitation Hospital (Barcelona, Spain), we have been applying Transcranial direct current stimulation (tDCS) for the management of Neuropathic pain after spinal cord injury. TDCS has been established as useful therapeutic option for patients with neuropathic pain [1]. Several recent studies demonstrate its efficacy, good tolerance and minimal side effects [2,3]. Our accumulated experience spans to having treated more than 100 patients, using always the same standardized protocols. Direct current is delivered with a batterydriven, constant current stimulator (NeuroConn, Ilmenau, Germany) and two surface sponge electrode pads (7 5 cm, 35 cm2) soaked with a saline solution (0.9% NaCl; 308 mosm/l). The anode is placed over C3 or C4 (EEG 10/20 system) aiming to target the motor cortex, and the cathode over the contralateral supraorbital area [4,5]. The electrodes were fastened into position by using two rubber polyester headbands (70 cm 3 cm). For patients with asymmetric pain, the anode is placed contralateral to the afflicted body part, while for patients with symmetric pain, the anode is placed over the dominant hemisphere. A constant current of 2 mA intensity is applied in daily sessions of 20 min (Current was rampedup for 15 s until it reached 2 mA; and finally the device was turned-off with a ramp-down of 15 s) during a period of 2 weeks (from Monday to Friday; total of 10 treatment sessions). After each session and patient, the material was replaced and cleaned with soap and water. Here we report on three cases of skin burns during this tDCS treatment. All three affected patients were men with little hair on their scalp. The three were stimulated with the same parameters getting values of impedance of 3e4.5 kU. Their skin’s surface was not cleaned with alcohol because the impedance levels were correct. All reported a usual tingling and itching sensation under the electrodes, but none experienced significant discomfort or pain. Following our standard operating procedures, constant electrode’s moistness, electrode position and impedance levels were controlled and stable during stimulation sessions. All patients showed a mild redness of the skin under the central part of the electrodes after the tDCS session but it disappeared after few minutes without discomfort. However, in all three instances, the skin lesions occurred under the cathode (supraorbital region) at the end of the sessions. By separating the electrodes from the skin they presented small skin lesions, which resembled red burns, with small blisters (Fig. 1). The extension of the lesions ranged from 2 to 3 mm up to 1.5 cm. Lesions appeared after the second stimulation session in one patient, while for the other two, they appeared between the eighth and tenth sessions. None of the patients had a skin lesion before the start, skin disease or a history of any pathological skin disorder.