Exploring the genetic relationship between hearing impairment and Alzheimer's disease

ObjectiveTo examine whether neuropathologic burden is associated with hearing impairment.MethodsWe studied 2,755 autopsied participants ≥55 years of age from the National Alzheimer's Coordinating Center database. Participants had at least 1 clinical evaluation at US National Institute on Aging–funded Alzheimer's Disease Center no more than 2 years before death. Patients were classified as hearing impaired by clinician report at baseline. Common dementia neuropathologies included Alzheimer disease pathologic change (Consortium to Establish a Registry for Alzheimer's Disease neuritic plaque density, neurofibrillary degeneration Braak stage), Lewy body disease, gross infarcts, and microinfarcts. Logistic regression models predicted impaired hearing with adjustment for age at death, sex, race, education, center, and follow-up time. Relative risks were calculated with the use of marginal standardization.ResultsImpaired hearing was common (32%). In participants who were cognitively normal at baseline (n = 580), impaired hearing was associated with higher Braak stage (relative risk [RR] 1.33 per 2-stage increase, 95% confidence interval [CI] 1.06–1.66) but not other pathologies. In participants with dementia (n = 2,175), impaired hearing was positively associated with microinfarcts (RR 1.18, 95% CI 1.00–1.39) and inversely associated with neuritic plaque density (RR 0.91 per score increase, 95% CI 0.85–0.99). Development of impaired hearing in those with cognitive impairment was associated with neocortical Lewy bodies (1.26, 95% CI 1.02–1.55).ConclusionsImpaired hearing, reported before the onset of cognitive impairment, was associated with increased neurofibrillary tangle burden. Impaired hearing in those with cognitive impairment was associated with microinfarcts and neocortical Lewy bodies but not typical Alzheimer disease pathologic change. Functional hearing problems may be a preclinical marker of neurofibrillary neurodegeneration, although replication is needed.

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Systematic review protocol for assessing central auditory functions of Alzheimer’s disease and its preclinical stages

BMJ Open ◽

10.1136/bmjopen-2019-033342 ◽

2020 ◽

Vol 10 (6) ◽

pp. e033342

Author(s):

Dona M P Jayakody ◽

Hadeel Y Tarawneh ◽

Holly K Menegola ◽

Jessica M Yiannos ◽

Peter L Friedland ◽

...

Keyword(s):

Systematic Review ◽

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Hearing Impairment ◽

Auditory Processing ◽

Primary Data ◽

Central Auditory Processing ◽

Auditory Function ◽

Review Protocol ◽

Auditory Functions

IntroductionA number of studies have reported an association between peripheral hearing impairment, central auditory processing and Alzheimer’s disease (AD) and its preclinical stages. Both peripheral hearing impairment and central auditory processing disorders are observed many years prior to the clinical manifestation of AD symptoms, hence, providing a long window of opportunity to investigate potential interventions against neurodegenerative processes. This paper outlines the protocol for a systematic review of studies examining the central auditory processing functions in AD and its preclinical stages, investigated through behavioural (clinical assessments that require active participation) central auditory processing tests.Methods and analysisWe will use the keywords and Medical Subject Heading terms to search the following electronic databases: MEDLINE, PsychINFO, PubMed, Scopus, EMBASE and CINAHL Plus. Studies including assessments of central auditory function in adults diagnosed with dementia, AD and its preclinical stages that were published before 8 May 2019 will be reviewed. This review protocol will be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols guidelines. Data analysis and search results will be reported in the full review. This manuscript has designed the protocols for a systematic review that will identify the behavioural clinical central auditory processing measures that are sensitive to the changes in auditory function in adults with AD and its preclinical stages. Such assessments may subsequently help to design studies to examine the potential impact of hearing and communication rehabilitation of individuals at risk of AD.Ethics and disseminationEthical approval is not required as this manuscript only reports the protocols for conducting a systematic review as primary data will only be reviewed and not be collected. The results of this systematic review will be disseminated through publication and in scientific conferences.PROSPERO registration numberCRD42017078272.

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