Objective: In this preliminary study we aimed to investigate the nature of the differences in auditory function between patients with PD (N=25 with Hoehn and Yahr stages ranging from 1-3) and matched healthy controls (HC) (N=20).

Background: There is convincing clinical evidence of alterations in auditory function in Parkinson’s disease (PD), although the nature of these alterations has not been clarified sufficiently. Auditory function involves a number of structures in the brainstem. According to the Braak and Braak hypothesis synuclein pathology affects caudal brainstem structures early in the premotor stages of PD. The question therefore is if brainstem nuclei involved in auditory processing are affected in these early stages and if the investigation of auditory function could serve as a biomarker for premotor PD.

Methods: Pure tone audiometry (PTA), speech audiometry (SA) and otoacoustic emissions (OAE) were evaluated in a silent room and using conventional methods.

Results: No differences could be found between PD patients and HC in PTA and SA in silence and using background noise. There were only minor differences between the on and off-stage in PD patients. However, significant differences were detected for OAE between HC and PD in the off condition, as well as between PD off and PD on, with PD off demonstrating significantly disinhibited OAE. The difference between PD on and HC was nonsignificant.

Conclusions: The amplitude of the OAE is higher in PD patients in the off medication condition. OAE amplitudes are inhibited by the olivocochlear efferent system, which connects the superior olivary nucleus with hearing cells in the Corti organ of the inner ear. Our results indicate a dysfunction of this inhibitory system. The differences between PD on and PD off suggest an inhibitory effect of dopamine on the OAE amplitude. Further investigation concerning the changes in OAE in the early stages of PD is warranted.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-auditory-biomarker-for-parkinsons-disease/