Objective: We evaluated hearing function in a population of PD patients to investigate: 1) the occurrence of hearing loss; 2) the possible lateralization of hearing impairment; and 3) the correlation with PD motor symptoms.

Background: Considering Non-Motor Symptoms Scale for Parkinson’s Disease (NMSS) spectrum, the possible involvement of sensory systems had scarcely investigated, although earlier studies reported an impairment in visual and auditory systems [1-3]. In the field of hearing researches, alterations in PD patients were observed in different frequency ranges, although the association with disease severity, motor symptoms and Quality of Life (QoL) impairment, had not fully defined [4-8]. Recent studies on PD also demonstrated impairment in central auditory processing [8] and reduction in distortion-product otoacoustic emission (DPOAE) levels [1], which reflect cochlear outer hair cell (OHC) function.

Method: Pure tone audiometry (PTA) and distortion product otoacoustic emissions (DPOAEs) were used as outcome variables in 86 patients (46/40 male/female; mean age 65 ± 8.8 years) and 50 controls (27/23 M/F; mean age 63 ± 11.7 years).

Results: Patients showed significantly lower hearing levels than controls and significant asymmetry in cochlear function, as DPOAE responses were worse in the ear ipsilateral to their more affected motor side. Audiological alterations showed no significant correlations with patients’ clinical features, including disease stage or levodopa treatment.

Conclusion: We confirmed an impairment in auditory function in PD patients via PTA and DPOAE testing. The relevant novelty of our findings was the asymmetry in DPOAE responses, which suggests that the impairment of cochlear function could represent a lateralized PD non-motor feature. Several pathophysiological mechanisms may be hypothesized to explain the asymmetric cochlear damage in PD, including the impairment of cochlear dopamine release and the involvement of extra-dopaminergic contralateral circuits, with cholinergic pathways as a likely candidate.

References: 1. Pisani V, Sisto R, Moleti A, et al. An investigation of hearing impairment in de-novo Parkinson’s disease patients: A preliminary study. Park Relat Disord. 2015;21(8):987-991. 2. Vitale C, Marcelli V, Abate T, et al. Speech discrimination is impaired in parkinsonian patients: Expanding the audiologic findings of Parkinson’s disease. Park Relat Disord. 2016;22 Suppl 1:S138-43. 3. Weil RS, Schrag AE, Warren JD, Crutch SJ, Lees AJ, Morris HR. Visual dysfunction in Parkinson’s disease. Brain J Neurol. 2016;139(11):2827-2843. 4. Folmer RL, Vachhani JJ, Theodoroff SM, Ellinger R, Riggins A. Auditory Processing Abilities of Parkinson’s Disease Patients. Biomed Res Int. 2017; 2017: 2618587. 5. Fradis M, Samet A, Ben-David J, et al. Brainstem auditory evoked potentials to different stimulus rates in parkinsonian patients. Eur Neurol. 1988;28(4):181-186. 6. Gawel MJ, Das P, Vincent S, Rose FC. Visual and auditory evoked responses in patients with Parkinson’s disease. J Neurol Neurosurg Psychiatry. 1981;44(3):227-232. 7. Shetty K, Krishnan S, Thulaseedharan JV, Mohan M, Kishore A. Asymptomatic Hearing Impairment Frequently Occurs in Early-Onset Parkinson’s Disease. J Mov Disord. 2019;12(2):84-90. 8. Vitale C, Marcelli V, Allocca R, et al. Hearing impairment in Parkinson’s disease: expanding the nonmotor phenotype. Mov Disord. 2012;27(12):1530-1535.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/asymmetrical-cochlear-dysfunction-as-a-lateralized-non-motor-feature-in-parkinsons-disease/