Treatment of chronic tinnitus with repeated sessions of prefrontal transcranial direct current stimulation: outcomes from an open-label pilot study

Tinnitus is the perception of sound in the absence of an environmental sound source. Abnormal activity in central auditory pathways is considered as the neuronal correlate of tinnitus. However, there is increasing evidence from neuroimaging studies for an additional involvement of the frontal cortex in the pathophysiology of tinnitus, especially concerning its attentional and emotional aspects. Recently, in a subgroup of tinnitus patients, temporary reduction of tinnitus intensity and tinnitus-related distress has been reported after bifrontal tDCS with the anode over the right and the cathode over the left dorsolateral prefrontal cortex (DLPFC). The aim of this study was to investigate whether repeated application of bifrontal tDCS results in longer-lasting reduction of tinnitus and may represent a potential treatment approach. Thirty-two patients with chronic and treatment-resistant tinnitus received six sessions of bifrontal tDCS (1.5 mA, 30 min, two sessions per week) with the anode over the right and the cathode over the left DLPFC. Treatment outcome was assessed with several standardized tinnitus questionnaires, numeric rating scales, and a depression scale. In the entire group, beneficial effects of bifrontal tDCS on tinnitus were found for numeric rating scores of loudness, unpleasantness, and discomfort, but not in tinnitus or depression scales. Exploratory analysis revealed an effect of gender on treatment effects with female patients demonstrating a better response in several scores. Our open-label pilot study suggests some beneficial effect of bifrontal tDCS (anode right and cathode left) in the treatment of severe tinnitus, warranting further controlled studies.