Determining the effects of transcranial direct current stimulation on tinnitus and tinnitus-related outcomes: protocol for a systematic review

INTRODUCTION: Tinnitus is the awareness of a sound in the ear or head in the absence of an external source. It affects around 10%–15% of people. About 20% of people with tinnitus also experience symptoms such as depression or anxiety that negatively affect their life. Transcranial direct current stimulation (tDCS) is a technique involving constant low-intensity direct current delivered via electrodes on the head. It is postulated to modulate (suppress or enhance) neural activity in the region between electrodes. As such, it represents a potential treatment option for tinnitus, as well as comorbid depression or anxiety. This systematic review will estimate the effects of tDCS on outcomes relevant to tinnitus. In addition, it will determine whether there is any relationship between stimulation parameters (electrode montage, current intensity, and length and frequency of stimulation sessions) and the effect of tDCS on these outcomes. METHODS AND ANALYSIS: Electronic searches for peer-reviewed journal articles will be performed in the Cochrane Register of Studies online (the Cochrane Ear, Nose and Throat Disorders Group Register and CENTRAL, current issue), PubMed, EMBASE, CINAHL, LILACS, KoreaMed, IndMed, PakMediNet, CNKI, AMED, PsycINFO, Web of Science, ClinicalTrials.gov, ICTRP and Google Scholar using the following search terms: transcranial Direct Current Stimulation OR tDCS AND tinnitus OR depression OR anxiety OR quality of life OR adverse effects OR neurophys*. Searches were not limited by date. Methods are reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P). Randomised controlled trials will be included if they report at least one of the following outcomes: tinnitus symptom severity, anxiety or depression as measured by relevant validated instruments. Where available, data on quality of life, adverse effects and neurophysiological changes will also be reviewed. In addition to an analysis of the effect of each parameter, an analysis will be performed to uncover any interactions between parameters. Where appropriate, meta‐analyses will be performed. ETHICS AND DISSEMINATION: This systematic review will make use of secondary data only. As no data will be obtained from participants directly, ethical approval has not been sought. No other ethical issues are foreseen. Findings will be submitted for peer-reviewed publication and presented at academic conferences. The results of this review will inform future research. PROSPERO REGISTRATION NUMBER: CRD42020185567.