Abstract

Background and objective: Non-motor symptoms (NMS) of Parkinson's disease (PD) are still underestimated and causative of disability and poor quality of life. Recently, it has been suggested that hearing impairment could be included into the spectrum of NMS, although both mechanisms and phenomenology are unclear. In this study we investigated the peripheral auditory pathway of PD, in patients with asymmetric rest tremor (ART) without dopaminergic denervation, and comparison with healthy controls (HC), aiming to detect differential alterations of cochlear functioning and medial olivocochlear system (MOC).
Methods: 23 PD patients, 9 with ART and 19 HC were assessed for auditory functions with clinical examination and Transient-evoked otoacoustic emissions (TEOAEs). PD and ART groups were also evaluated with Unified Parkinson's Disease Rating Scale (UPDRS) II-III and Hoehn and Yahr scale. One-way ANOVA analysis and Pearson's test were performed to measure differences between groups and correlations.
Results: TEOAE responses in PD patients were significantly lower compared to HC at 3 and 4 kHz, bilaterally. PD patients showed statistically significant lower TEOAEs at the same frequencies compared to ARTs. In addition, a MOC dysfunction in PD patients was observed. Conversely, no difference was found between ART and HC in all tests performed.
Conclusion: PD patients, differently from both ART patients and HC, show abnormalities of basal TEOAEs at the highest frequencies. Auditory dysfunction correlates to motor disturbances, suggesting an underlying dopaminergic pathogenic mechanism. Early recognition of hearing impairment may represent a tool for patient assessment and help in the differential diagnosis in ART patients.

Keywords: Non-motor symptoms; Parkinson’s disease; Asymmetric rest Tremor; Hearing impairment; OAEs; Cochlear function; Medial olivocochlear system