Prof. Dr. Gerhard Hesse
Ohr- und Hörinstitut, Tinnitus-Klinik am KH Bad Arolsen
Hidden hearing loss following moderate noise exposure
In general noise trauma results in the damage of outer hair cells, mostly in the 4-6 kHz frequency range (Hesse 2016). However, latest research hints to the fact, that noise exposure can also lead to lesions in the first synapse and other neuronal changes, either additionally or even with intact hair cells (Liberman 2016). There is little data available supporting this diagnosis for humans. However the fact that lesions can persist or even exist with normal audiometric findings has a high medico-legal and socio-economic impact.
Even if a noise trauma initially can lead to outer hair cell injury, after recovery (supported by steroid therapy) hearing loss can persist due to retrocochlear lesions regarding the synaptic communication between sensory inner hair cells and subsets of cochlear nerve fibres (Liberman and Kujawa 2017). In animal models this has been proven (Liberman 2016, Liberman, Epstein et al. 2016), for humans this could only be detected after high level noise exposures (Prendergast, Millman et al. 2017).
One reason for this „hidden hearing loss“ could be, that noise trauma can lead to damage of retrocochlear structures and mainly the extremely fast and vulnerable synapses between inner hair cells and the first neurone, resulting in high and highest frequency hearing loss. Possibly this hearing loss can recover after proper acoustic stimulation.