Relationships between Hearing Loss, Hearing Aids and Trajectories of Regional Cerebral Metabolism in Subjects with Mild Cognitive Impairment

Introduction: While the impact of hearing loss and use of hearing aids upon risk of developing dementia has been studied previously, the cross-comparison between subjects with hearing loss and subjects with hearing aids and differential relationships to changes over time in brain metabolism have not yet been elucidated. In this study, we report findings using longitudinal [F-18]fluorodeoxyglucose (FDG) PET scan data and neuropsychological assessments among subjects diagnosed with hearing loss, with and without the use of hearing aids.

Methods: From the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database, 1647 subjects were identified to have mild cognitive impairment, or a global Clinical Dementia Rating (CDR) of 0.5, at baseline screening. Out of this pool, 351 subjects were identified to have hearing impairments. The subjects were further narrowed by assessing those whose only sensory impairment was hearing loss and those with multiple FDG-PET brain scans archived after baseline. Subjects (n=31) were then categorized into three different groups, including those with untreated hearing loss and treated hearing loss/hearing aids (total n=14), and a demographically matched group having no diagnosed hearing impairment (n=17). Brain metabolism from each of 47 standardized volumes of interest (sVOI) normalized to whole-brain activity were quantified in each PET scan and compared after one and two years to baseline scans in one-tailed paired t-tests, and a longitudinal analysis of the inter-group difference of those intra-group differences was conducted using two-tailed unpaired t-tests.

Results: There was no statistically significant difference in age or education between the hearing loss, hearing aids, and control groups. Over one year, in the difference of differences analysis, the most significant differential metabolic decline occurred in the left superior frontal gyrus when comparing the control group against the untreated hearing loss group (p=0.004). The hearing aids group against the control group yielded a significant differential decline in left superior frontal gyrus as well (p=0.02), while the hearing loss group declined 1.5 times faster than the hearing aids group. After two years, the untreated hearing loss group had significant declines against the control group in the right mid-frontal gyrus (p=0.007), the right posterior inferior frontal gyrus (p=0.01), and left inferior frontal gyrus (p=0.04). In contrast, during the same period of time, the hearing aids group had no significant decline in metabolic rate in these or any other of the 47 sVOI’s examined.

Conclusions: The use of hearing aids by subjects with mild cognitive impairment at baseline was associated with less cerebral metabolic decline than was observed in subjects with untreated hearing loss relative to control subjects with no diagnosed hearing loss, primarily in frontal cortical regions that are known to decline with normal aging. These results suggest that while hearing loss may accelerate the aging process occurring in cerebral metabolism, that this acceleration may be ameliorated by the use of hearing aids.