Hearing impairment tied to Parkinson’s disease

Individuals with a reduced sense of hearing are at increased risk of Parkinson’s disease, as shown in a study.

Analysis of data from the UK Biobank showed that each 10-dB increase in speech-reception threshold (SRT) at baseline was associated with a 57-percent higher risk of incident Parkinson’s disease (hazard ratio [HR], 1.57, 95 percent confidence interval [CI], 1.018–2.435; p=0.041). [Parkinsonism Relat Disord 2024;doi:10.1016/j.parkreldis.2024.107219]

Similar results were obtained in a sensitivity analysis adjusted for only age, where an excess risk of incident Parkinsons’s disease was seen per 10-dB increase in SRT (HR, 1.64, 95 percent CI, 1.006–1.098; p=0.025). However, this association disappeared when hearing impairment was defined according to categorical UK Biobank SRT norms, with neither ‘insufficient’ (p=0.163) nor ‘poor’ (p=0.074) hearing showing any association with Parkinson’s disease compared with ‘normal’ hearing.

“The lack of congruence between the primary and exploratory findings, may in part be explained from a statistical perspective. Specifically, the primary analysis drew upon continuous SRT data, whilst the additional exploratory analysis drew upon a categorical variable computed from the continuous SRT data,” the authors noted.

“It is accepted that transforming a continuous variable into a categorical one can lead to the masking of potentially meaningful variability in the data thus, leading to a loss of information and statistical power. Therefore, it may be that the conflict between the primary and exploratory analyses results, arises from this arbitrary categorisation, rather than hearing impairment not being related to Parkinson’s,” they added. [Neuro-Oncol Pract 2022;9:87-90]

According to the authors, the study contributes to the growing evidence on hearing impairment as a risk factor for Parkinson’s disease, with prior research having also shown an association between hearing impairment and a 1.18- to 1.73-fold risk increase over 2–10 years of follow-up. [JAMA Neurol 2022;79:359-369; Eur J Neurol 2014;21:752-757]

Hearing loss care

“These findings are incredibly important; first, this is one of the first studies to look at how hearing impairments may increase risk for Parkinson’s or be an early warning sign of Parkinson’s,” according to lead study author Dr Megan Readman from Lancaster University in Lancaster, Lancashire, UK.

“Second, as our findings suggest, hearing loss is intricately related to Parkinson’s, so it may be beneficial for auditory functioning and the management of auditory impairment to be considered at the time of diagnosis and follow-up care,” Readman said.

How hearing impairment may be related to Parkinson’s disease seems to involve dopaminergic neurotransmission, which is crucial in auditory processing across various regions, such as the inner ear, brainstem, and higher-order auditory centres, according to Readman and colleagues. This hypothesis is further supported by animal studies demonstrating that dopaminergic depletion, as observed in D2 receptor knockout mice and MPTP-treated bats, leads to significant auditory deficits, they added. Given the well-established role of dopaminergic dysfunction in Parkinson’s disease, the authors pointed out that these available research provide some evidence of a mechanistic link between dopaminergic depletion and hearing impairment in this condition. [Mov Disord 2020;35:537-550; Neuroreport 2021; 32:125-134; Front Neural Circuits 2021:15:624563; J Neurosci 2012;32:344-55]

The analysis included 159,395 individuals (mean age 56.61 years, 54.53 percent female) who underwent the Digit Triplet Test and were free from Parkinson’s disease at the point of assessment. According to the UK Biobank SRT norms, 111,295 individuals had ‘normal’ hearing, 6,096 had ‘poor’ hearing, and 42,004 had ‘insufficient’ hearing. A total of 810 cases of probable Parkinson’s disease were reported over a median follow up of 14.24 years.

Readman emphasized the importance of conducting further analyses in alternative populations to validate the finding before clinical recommendations can be made.