COMPARISON OF INVASIVE VERSUS NON-INVASIVE ELECTRICAL EAR STIMULATION IN TINNITUS SUPPRESSION: LITERATURE REVIEW

Abstract

Background: This paper is a review of the literature on electrical stimulation of the ear to treat tinnitus. This method of treatment has been used since the 1970s and different techniques have been explored. The primary aim of this work was to review the litera- ture on electrical stimulation of the ear to suppress tinnitus, with a specific focus on the methods and stimulation parameters used so far and the efficacy of the different methods. A secondary aim was to formulate recommendations on electrical ear stimulation parame- ters that suppress tinnitus. Material and methods: Four databases were searched: PubMed, Ovid Embase, Web of Science, and Science Direct. Database searches were conducted during November 2018 using the search terms: tinnitus and electrical stimulation. Inclusion criteria: All research articles on inva- sive and non-invasive electrical stimulation of the ear for suppressing tinnitus were included. Other inclusion criteria were records in English and involving adult human participants. Exclusion criteria: Studies on intracochlear stimulation using cochlear implants and studies where stimulation extended beyond the ear (e.g. transcutaneous electrical nerve stimulation, TENS) were excluded. Results: Twenty publications met the inclusion criteria and were analysed in this review. A comparison was made between invasive and non-invasive electrical ear stimulation in terms of efficacy, type of current used, laterality of stimulation, intensity and frequency of the current, duration of tinnitus suppression, and adverse effects. Due to the non-standardised methodology of the studies, there was only a low level of evidence available in terms of the advantages of a particular technique or stimulation parameter. The difficulties in comparing the effectiveness of the studies were related to many factors, and these are discussed. One factor is the variability in outcome measures, including different definitions of treatment success and limited use of standardised or validated outcome measures. Conclusions: Based on the reviewed literature, it is concluded there is no clear advantage of one stimulation condition over the oth- er in terms of method, stimulation parameter, or effectiveness. This leads us to conclusion that the present body of evidence is insufficient to for- mulate definite recommendations for electrical ear stimulation.