Hearing aids to support cognitive functions of older adults at risk of dementia: the HearCog trial- clinical protocols

Hearing Loss and Dementia: Where to From Here?

Victorian era psychologists were the first to comment on associations between sensory and cognitive function. More recently, hearing loss has been shown as a marker of risk for dementia. However, it is not known whether this association represents a causal impact of hearing loss, nor whether treating hearing loss may help prevent dementia. Most studies on relationships between hearing loss and cognitive outcomes are observational, are at risk of confounding, and cannot reach conclusions about causation. A recent high quality randomized controlled trial, relatively uncommon in audiology, reported no impact of a comprehensive hearing intervention in mitigating cognitive decline in older adults. Although secondary analysis revealed potential benefits in a sub-sample of adults, this finding may be spurious. Encouraging policymakers, patients, and other health care practitioners to address hearing loss in terms of dementia prevention may be inappropriate on the grounds of both relevance at individual level and lack of clear evidence of benefit. In addition, advocating need to address hearing loss in terms of mitigating dementia risk may reduce the importance of addressing hearing loss in its own right. Linking hearing loss to dementia risk may also exacerbate the stigma of hearing loss, inadvertently discouraging people from seeking help for hearing. We suggest that treating hearing loss may have important benefits in preventing or delaying diagnosis of dementia via improving orientation and functioning in daily life, without changing the underlying pathology. Rather than linking hearing loss to dementia risk, we suggest a positive message focusing on the known benefits of addressing hearing loss in terms of improved communication, quality of life, and healthy aging.

Dementia Prevention and Treatment: A Narrative Review

Importance

Dementia affects 10% of those 65 years or older and 35% of those 90 years or older, often with profound cognitive, behavioral, and functional consequences. As the baby boomers and subsequent generations age, effective preventive and treatment strategies will assume increasing importance.

Observations

Preventive measures are aimed at modifiable risk factors, many of which have been identified. To date, no randomized clinical trial data conclusively confirm that interventions of any kind can prevent dementia. Nevertheless, addressing risk factors may have other health benefits and should be considered. Alzheimer disease can be treated with cholinesterase inhibitors, memantine, and antiamyloid immunomodulators, with the last modestly slowing cognitive and functional decline in people with mild cognitive impairment or mild dementia due to Alzheimer disease. Cholinesterase inhibitors and memantine may benefit persons with other types of dementia, including dementia with Lewy bodies, Parkinson disease dementia, vascular dementia, and dementia due to traumatic brain injury. Behavioral and psychological symptoms of dementia are best treated with nonpharmacologic management, including identifying and mitigating the underlying causes and individually tailored behavioral approaches. Psychotropic medications have minimal evidence of efficacy for treating these symptoms and are associated with increased mortality and clinically meaningful risks of falls and cognitive decline. Several emerging prevention and treatment strategies hold promise to improve dementia care in the future.

Conclusions and Relevance

Although current prevention and treatment approaches to dementia have been less than optimally successful, substantial investments in dementia research will undoubtedly provide new answers to reducing the burden of dementia worldwide.

Do hearing loss interventions prevent dementia?

Hearing loss has been identified as a potentially modifiable risk for dementia. This discussion paper reviews studies examining the impact of hearing loss interventions on cognitive decline and incident cognitive impairment, identified the challenges for research on the cognitive impacts of hearing interventions, and the likely benefits of hearing interventions for healthy aging and mental well-being.

The longitudinal relationship between hearing loss and cognitive decline in tonal language-speaking older adults in China

Introduction

Previous longitudinal studies indicate that hearing loss and cognitive impairment are associated in non-tonal language-speaking older adults. This study aimed to investigate whether there is a longitudinal association between hearing loss and cognitive decline in older adults who speak a tonal language.

Methods

Chinese-speaking older adults aged 60 years and above were recruited for baseline and 12 month follow-up measurements. All participants completed a pure tone audiometric hearing test, Hearing Impaired-Montreal Cognitive Assessment Test (HI-MoCA), and a Computerized Neuropsychological Test Battery (CANTAB). The De Jong Gierveld Loneliness Scale was used to measure loneliness, and the 21-item Depression Anxiety Stress Scale (DASS-21) was used to measure aspects of mental health. Associations between baseline hearing loss and various cognitive, mental and psychosocial measures were evaluated using logistic regression.

Results

A total of 71 (29.6%) of the participants had normal hearing, 70 (29.2%) had mild hearing loss, and 99 (41.2%) had moderate or severe hearing loss at baseline, based on mean hearing thresholds in the better ear. After adjusting for demographic and other factors, baseline moderate/severe audiometric hearing loss was associated with an increased risk of cognitive impairment at follow-up (OR: 2.20, 95% CI: 1.06, 4.50). When pure-tone average (PTA) was modeled continuously, an average difference of 0.24 in HI-MoCA scores for every 10 dB increase in BE4FA existed, and an average difference of 0.07 in the change of HI-MoCA scores in a 12 month period.

Discussion

The results revealed a significant longitudinal relationship between age-related hearing loss and cognitive decline in this cohort of tonal language-speaking older adults. Steps should also be taken to incorporate hearing assessment and cognitive screening in clinical protocols for older adults 60 years and above in both hearing and memory clinics.

Cortical thickness of the left parahippocampal cortex links central hearing and cognitive performance in aging

Hearing impairment is considered a leading modifiable risk factor of cognitive decline and dementia. While most evidence has been established on clinical assessment of peripheral hearing loss, understanding of how central hearing in real-world conditions is associated with cognitive aging is limited. This study analyzed the data of 473 unrelated healthy adults aged 36-100 years old from the Lifespan Human Connectome Project in Aging. Central hearing was evaluated using the Words-in-Noise decibel threshold. Cognitive functions were evaluated by the performance on cognitive tests, and cortical thickness was estimated from magnetic resonance imaging (MRI) data. Here, we show that a higher hearing threshold was associated with a lower performance on immediate and delayed episodic memory retrieval, switching aspect of executive function, working memory, reading decoding, and vocabulary comprehension. Cortical thickness in the left parahippocampal cortex (lPHC) was negatively associated with the hearing threshold and acted as a significant partial mediator in the association of central hearing with immediate recall, switching, reading decoding, and vocabulary comprehension. These findings suggest that cortical thickness in the lPHC, an early target of dementia, partially links central hearing and performance in multiple cognitive domains in aging.

Hearing and vision difficulty and sequential treatment among older adults in India

Aging not only affect biomarker-related processes, but it also affects the physiological processes of the human body. Of all the physiological processes, hearing and vision are of utmost importance to a human. Therefore, this study examines the prevalence and factors associated with hearing and vision difficulty and their sequential treatment among older adults in India. Utilizing data from Building a Knowledge Base on Population Aging in India, study used two sets of outcome variables; firstly, self-reported hearing and vision difficulty and secondly, treatment-seeking for hearing and vision difficulty. A total of 9541 older adults aged 60+ years from seven major regionally representative states were selected. Descriptive statistics were used to perform preliminary analysis. Additionally, the study employed the Heckprobit selection model. It is a two-equation model. This model is used in order to accommodate the heterogeneity (i.e., shared unobserved factors) among older adults and then address the endogeneity (between hearing and vision loss problems and their treatment-seeking behaviour) for older adults in India, the model offers a two-step analysis and deals with the zero-sample issue. Around 59% and 21% of older adults reported vision and hearing difficulty, respectively. Only 5% of older adults suffering from hearing difficulty reported utilizing hearing aids. Lifestyle factors (smoking tobacco and chewing tobacco) significantly affect hearing and vision difficulty; various chronic diseases were also found to be associated with high levels of hearing and vision difficulty among older adults. Results from Heckprobit model shows that older adults with 11+ years of education had higher probability to use visual [β = 0.54, 95% confidence interval (CI): 0.37, 0.70] and hearing aids [β = 0.6, 95% CI: 0.18, 1.02]. The use of hearing and vision aids was lower among poor older adults, older adults from Scheduled Caste, and older adults in rural areas. The study indicates that more than half of older adults face vision difficulty and almost one-fourth face hearing difficulty in rural India, education and lifestyle appear to be the main driver of health-seeking behaviour. Additional attention shall be given to understand the strategies that may advocate a higher use for hearing aids among older adults.

Can cochlear implantation prevent cognitive decline in the long-term follow-up?

Cognitive function and hearing are known to both decline in older adults. As hearing loss is proposed to be one modifiable risk factor for dementia, the impact of auditory rehabilitation on cognitive decline has been gaining increasing attention. Despite a large number of studies, long-term data are still rare. In a large prospective longitudinal monocentric study, 50 adults (aged ≥ 50 years) with severe postlingual bilateral hearing loss received a cochlear implant (CI). They underwent comprehensive neurocognitive testing prior to implantation (T1), at 12 months (T2) and up to 65 months (T3) after implantation. Various cognitive subdomains such as attention, inhibition, working memory, verbal fluency, mental flexibility and (delayed) recall were assessed by the computer-based non-auditory test battery ALAcog^©. The observed trajectories of two exemplary cognitive subdomains (delayed recall and working memory) were then fitted over time using multilevel growth models to adjust for sociodemographic covariates and compared with 5-year longitudinal data from a sample of older adults from the representative Survey of Health, Aging and Retirement in Europe (SHARE) study. Postoperatively, auditory functions improved from 6.98% (SD 12.83) to 57.29% (SD 20.18) in monosyllabic speech understanding. Cognitive functions significantly increased from T1 to T3 in attention (p = 0.001), delayed recall (p = 0.001), working memory (OSPAN; p = 0.001), verbal fluency (p = 0.004), and inhibition (p = 0.002). A closer look at follow-up revealed that cognitive improvement could be detected between T1 and T2 and thereafter remained stable in all subtests (p ≥ 0.06). Additional longitudinal analysis confirmed these findings in a rigorous multilevel approach in two exemplary cognitive subdomains. In contrast to the SHARE data, there was no evidence for age-differential associations over time in CI recipients. This suggests that older adults benefit equally from cochlear implantation. CI users with worse preoperative cognitive skills experienced the most benefit (p < 0.0001). Auditory rehabilitation by cochlear implantation has a stimulating effect on cognitive functions beyond an improvement in speech understanding and an increased well-being. Large multicenter studies using standardized protocols have to be undertaken in the future to find out whether hearing restoration might help to prevent cognitive decline.

Understanding the Relationship Between Age-Related Hearing Loss and Alzheimer’s Disease: A Narrative Review

Evidence suggests that hearing loss (HL), even at mild levels, increases the long-term risk of cognitive decline and incident dementia. Hearing loss is one of the modifiable risk factors for dementia, with approximately 4 million of the 50 million cases of dementia worldwide possibly attributed to untreated HL. This paper describes four possible mechanisms that have been suggested for the relationship between age-related hearing loss (ARHL) and Alzheimer’s disease (AD), which is the most common form of dementia. The first mechanism suggests mitochondrial dysfunction and altered signal pathways due to aging as a possible link between ARHL and AD. The second mechanism proposes that sensory degradation in hearing impaired people could explain the relationship between ARHL and AD. The occupation of cognitive resource (third) mechanism indicates that the association between ARHL and AD is a result of increased cognitive processing that is required to compensate for the degraded sensory input. The fourth mechanism is an expansion of the third mechanism, i.e., the function and structure interaction involves both cognitive resource occupation (neural activity) and AD pathology as the link between ARHL and AD. Exploring the specific mechanisms that provide the link between ARHL and AD has the potential to lead to innovative ideas for the diagnosis, prevention, and/or treatment of AD. This paper also provides insight into the current evidence for the use of hearing treatments as a possible treatment/prevention for AD, and if auditory assessments could provide an avenue for early detection of cognitive impairment associated with AD.

The impact of hearing impairment and hearing aid use on progression to mild cognitive impairment in cognitively healthy adults: An observational cohort study

INTRODUCTION

We assessed the association of self-reported hearing impairment and hearing aid use with cognitive decline and progression to mild cognitive impairment (MCI).

METHODS

We used a large referral-based cohort of 4358 participants obtained from the National Alzheimer's Coordinating Center. The standard covariate-adjusted Cox proportional hazards model, the marginal structural Cox model with inverse probability weighting, standardized Kaplan-Meier curves, and linear mixed-effects models were applied to test the hypotheses.

RESULTS

Hearing impairment was associated with increased risk of MCI (standardized hazard ratio [HR] 2.58, 95% confidence interval [CI: 1.73 to 3.84], P = .004) and an accelerated rate of cognitive decline (P < .001). Hearing aid users were less likely to develop MCI than hearing-impaired individuals who did not use a hearing aid (HR 0.47, 95% CI [0.29 to 0.74], P = .001). No difference in risk of MCI was observed between individuals with normal hearing and hearing-impaired adults using hearing aids (HR 0.86, 95% CI [0.56 to 1.34], P = .51).

DISCUSSION

Use of hearing aids may help mitigate cognitive decline associated with hearing loss.

Hearing Loss and Incident Dementia: Claims Data From the New York SPARCS Database

OBJECTIVE

Age-related hearing loss (HL) may be a risk factor for incident dementia. The objective was to use population-based claims data from the New York Statewide Planning and Research Cooperative System (SPARCS) to establish if HL is associated with incident dementia.

STUDY DESIGN

Retrospective cohort study.

SETTING

Comprehensive all-payer data reporting system (2007-2017).

PATIENTS

Two hundred six thousand eight hundred one subjects more than 60 years (56,523 with HL, random sample of 150,278 without HL).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The main outcome was incident dementia, measured by initial dementia diagnosis (ICD-9/ICD-10 code) associated with a patient visit/insurance claim. The main exposure was HL, measured by at least two separate HL diagnoses associated with claims before dementia diagnosis. Cox proportional-hazards models were used to examine the relationship of baseline HL with incident dementia, adjusting for age, sex, cardiovascular disease, cerebrovascular disease, diabetes, and smoking.

RESULTS

Dementia incidence rates per 1,000 person-years were 10.16 (95% confidence interval [CI] = 9.81-10.51; subjects with HL) and 5.43 (5.28-5.57; subjects without HL). Fewer (2-10) HL claims (n = 56,523), compared with no (0) HL claims, was associated with 1.10 (95% CI = 1.05-1.15, p < 0.001) times the hazard of incident dementia, adjusting for covariates. Greater (>10) HL claims (n = 3,414), compared with no (0) HL claims, was associated with 1.63 (95% CI = 1.42, 1.86, p < 0.001) times the hazard of incident dementia, adjusting for covariates.

CONCLUSIONS

HL diagnosis was associated with increased risk of incident dementia based on a comprehensive all-payer data reporting system. Individuals with a more established diagnosis of HL (more HL claims) demonstrated an increased hazard ratio.

The Relationship Between Hearing Loss and Cognitive Impairment in a Chinese Elderly Population: The Baseline Analysis

Objectives: The objective of the study was to investigate the association between untreated age-related hearing loss and cognitive impairment in Mandarin-speaking older adults living in China. Methods: Older adults (293; 111 males, M = 70.33 ± 4.90 years; 182 females, M = 69.02 ± 4.08 years) were recruited. All participants completed a pure tone audiometric hearing assessment, Hearing Impairment-Montreal Cognitive Assessment Test (HI-MoCA), and a computerized neuropsychology test battery (CANTAB). The Mandarin version of the De Jong Gierveld Loneliness Scale was used to measure the loneliness, and the Mandarin version of the 21-item Depression Anxiety Stress Scale (DASS-21) was used to measure the current severity of a range of symptoms common to depression, stress, and anxiety of the participants. Results: A multiple stepwise regression analysis showed that the average of four mid-frequency thresholds in the better ear was related to CANTAB Paired Associates Learning (β = 0.20, p = 0.002), and the global cognitive function score (HI-MoCA) (β = -0.25, p < 0.001). The average of three high frequencies in the better ear was significantly associated with CANTAB Delayed Matching to Sample (β = -0.16, p = 0.008), and Spatial Working Memory (β = 0.17, p = 0.003). Conclusion: The results revealed a significant relationship between age-related hearing loss and cognitive impairment in Mandarin-speaking older adults. These research outcomes have clinical implications specifically for hearing health care professionals in China and other populations that speak a tonal language, especially when providing hearing rehabilitation.

Effects of hearing impairment and hearing aid use on the incidence of cognitive impairment among community-dwelling older adults: evidence from the Taiwan Longitudinal Study on Aging (TLSA)

Background

Previous studies have reported associations between hearing impairment (HI) and cognitive impairment, but the evidence is not conclusive while considering concurrent geriatric syndromes. Especially, evidence from previous studies rarely came from Asian studies. This study aimed to evaluate the independent effects of HI and hearing aid use on the incidence of cognitive impairment while considering most geriatric confounders.

Methods

This population-based, propensity-score matched cohort study used cohort from Waves IV–VII (1999–2011) survey of the Taiwan Longitudinal Study on Aging (TLSA). Cognitive impairment was identified based on Short Portable Mental Status Questionnaire (SPMSQ) scores. The hazard ratio (HR) was calculated using the Cox proportional hazard regression adjusting for age, sex, comorbidities, socioeconomic status, Center for Epidemiologic Studies Depression (CES-D) scores, the instrumental activities of daily living scale, mobility condition and quality of life. In addition, social support and participation were also considered as confounders in the analysis. To assess the robustness of our findings, we conducted a sensitivity analysis designed to access unmeasured confounding factors by calculating E-values.

Results

After 1:1 propensity-score matching, we included 709 participants in both the HI and non-HI groups with a mean age of 73.4 years and 39.4% of participants were female. The mean follow-up was 8.9 ± 3.9 years. The HI group had a higher incidence of cognitive impairment than the non-HI group (74.5% vs. 69.1%, respectively), with an adjusted HR of 1.16 (95% confidence interval [CI], 1.03–1.32) based on a 12-year follow up. The E-value was 1.45 for the estimate, which provided evidence for this study’s robustness. Although, a subgroup analysis showed that hearing aid use was associated with lower incidences of cognitive impairment (66.3% vs. 75.6%) when compared to non-users in the HI group, the adjusted HR of 0.82 (95% CI, 0.61–1.09) revealed no significant differences.

Conclusions

HI was an independent risk factor of incident cognitive impairment on top of concurrent geriatric syndromes. Early HI detection may thus be effective for preventing cognitive decline. Further studies are needed to evaluate the effect of hearing aid use on the prevention of cognitive decline.