Relationship Between Synaptopathy and Tinnitus: A Systematic Review

Abstract

Tinnitus is the most common health problem seen in all age groups. It is usually present with hearing loss. But recent studies have shown that tinnitus is present among individuals with normal audiometric thresholds. The cause which is highlighted in recent studies for tinnitus among normal-hearing individuals is cochlear synaptopathy. Therefore, a comprehensive measure is required to identify and diagnose early so that many individuals will benefit through early detection and intervention of cochlear synaptopathy. The aim was to systematically review the articles related to hidden hearing loss and cochlear synaptopathy. Initially, a review search was conducted in different databases. This resulted in 122 topic-related articles. Among these, fifteen articles met the inclusion and exclusion criteria that were included for the study. The quality and potential risk associated with each article were evaluated using the Newcastle-Ottawa Scale (NOS). Review of the literature focused on physiological, behavioural and electrophysiological tests to diagnose cochlear synaptopathy. The study revealed that extended high frequency is a good measure in identifying hidden hearing loss. The reason which is mentioned for the same is vascular damage in the basal cochlear region. OAEs are also a good tool, but ambiguous results were reported. Reduced amplitudes of OAEs are due to dysfunctional OHC, but on the other hand, if the OAE amplitudes are not reduced, then the cause reported is damage in the higher auditory structures or at the IHC. ECochG has a very good implication in detecting cochlear synaptopathy. Damaged IHC would lead to the increased summating potential altering SP/AP ratio leading to hidden hearing loss. This review provides the relationship between cochlear synaptopathy and tinnitus in individuals with normal hearing. Extended high-frequency audiometry and ECochG are good tools for measuring cochlear synaptopathy. The leading cause that is described in the literature for hidden hearing loss is damage in IHC or basal cochlear region.