The Use of Hearing Aids and Transcranial Direct Current Stimulation (tDCS) for Tinnitus Management

Abstract

Background/Aim: Tinnitus is a perception of sound in the absence of an external sound source. Millions of people world-wide experience some form of tinnitus and for approximately 5% of them, tinnitus can have catastrophic effects on their quality of life. There are currently no effective pharmacological cures, but many therapies that attempt to reduce tinnitus perception or reaction through a combination of counselling and sound therapy or neuromodulation exists. The primary objective of this doctoral thesis was to explore a novel approach for tinnitus management combining hearing aids (sound therapy) and transcranial direct current stimulation (tDCS). Methods: Five studies were undertaken as a part of this doctoral thesis. 1. A retrospective analysis, of the audiometric and tinnitus test records of 192 participants suffering from chronic tinnitus was undertaken to investigate the best audiometric predictor of tinnitus pitch. 2. A scoping literature review, investigating the role of hearing aids in tinnitus management was undertaken. Out of 277 shortlisted studies, data was charted for 29 studies (18 research studies and 11 reviews) based on their relevance to the topic of investigation. 3. An exploratory pilot study was completed by 25 participants with chronic tinnitus and aidable hearing loss to study the impact of variation of the desired sensation level input/output [DSL(I/0) v5.0] hearing aid prescription procedure of hearing aid output on tinnitus. 4. A dose-response tDCS trial aimed to optimise the intensity and duration of anodal tDCS of the left temporoparietal area (LTA) for suppressing tinnitus in 25 participants with chronic tinnitus. 5. A double-blind sham controlled randomised clinical trial (seven month duration) of tinnitus treatment in which multi-session tDCS of the LTA was used along with hearing aids in 40 participants with chronic tinnitus and aidable hearing loss. Results and Discussion: The best predictor of tinnitus pitch was found to be the frequency at which the hearing threshold was approximately 50 dBHL. This was proposed to be the point of transition from predominantly outer hair cell damage to the threshold of inner hair cell damage resulting in deafferentation triggered tinnitus. The scoping review supported the use of hearing aids for tinnitus management; however more quality evidence and randomised control trials documenting the effectiveness of hearing aids for tinnitus management was recommended. The exploratory study of hearing aid prescription revealed DSL(I/0) v5.0 as a good starting point for prescribing hearing aid gain for tinnitus management. The most effective tDCS settings for transient tinnitus suppression were 2mA current intensity and 20 minutes duration. Hearing aids can significantly improving tinnitus related quality of life irrespective of tDCS. tDCS lead to positive effects on the minimum masking levels however no effect on tinnitus questionnaires. Conclusions: High frequency audiometry should be an integral part of tinnitus assessment. Hearing aids (sound therapy) are effective in managing tinnitus. Further research is needed to explore whether sound therapy may be improved by methods priming the auditory system.