Hearing Impairment in Parkinson’s Disease: Expanding the Non-Motor Phenotype

Objective To evaluate hearing impairment in patients affected by Parkinson’s disease as compared with hearing scores observed in normal age and sex matched controls Methods 118 consecutive patients with clinical diagnosis of Parkinson’s disease were screened. Severity of motor symptoms and staging were measured with the Unified Parkinson’s Disease Rating Scale (section III) and the Hoehn and Yahr scale. Audiometric evaluation consisted of a comprehensive audiologic case history and questionnaire, visual otoscopic examination, acoustic immittance measures (tympanogram and acoustic reflexes), pure tone audiometry and measurement of brainstem auditory evoked potentials. Healthy age- and sex-matched subjects were selected as control group. Results 106/118 patients were enrolled. Pure tone audiometry revealed age-dependent high-frequency hearing loss in patients with Parkinson’s disease as compared with both normative values and healthy age- and sex-matched controls (75/106, 71%; χ2= 5.959; p=0.02 and 92/106 (86.8%) vs 60/106 (56.6%); χ2= 23.804; p<0.001, respectively). Pure tone audiometry scores correlated with Hoehn and Yahr scale scores (p<0.05). Brainstem auditory evoked potentials were normal in all patients. Conclusion Our patients with Parkinson’s disease showed age-dependent peripheral, unilateral or bilateral hearing impairment. Whether these auditory deficits are intrinsic to Parkinson’s disease or secondary to a more complex impaired processing of sensorial inputs occurring over the course of illness remains to be determined. Because α-synuclein is located predominately in the efferent neuronal system within the inner ear, it could affect susceptibility to noise-induced hearing loss or presbycusis. It is feasible that the natural aging process combined with neurodegenerative changes intrinsic to Parkinson’s disease might interfere with cochlear transduction mechanisms thus anticipating presbycusis.