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.
