1. The use of a restorative hearing aid in patients with hearing loss decreased the hazard of developing dementia by 19%.
2. Hearing aid use was associated with a 3% increase in cognitive test scores.
Level of Evidence Rating: 1 (Excellent)
Study Rundown: Hearing loss is a common and undertreated condition, particularly among elderly patients. It is a known risk factor for developing dementia, along with other conditions affecting perception. Due to technology such as cochlear implants and other hearing restorative devices, hearing loss is modifiable. This study sought to determine the effect of treating hearing loss on patients’ risk of developing dementia and cognitive change.
The original systematic search yielded 3243 studies, of which 31 eligible studies were included in the qualitative analysis and 18 in the quantitative meta-analysis. Eight studies were included in the meta-analysis of longitudinal (2-25 year) assessment of hearing loss and cognitive function. All studies favoured treatment of hearing loss with an overall pooled estimate of a 19% reduction in hazard. The use of restorative hearing devices was protective from cognitive decline, a new diagnosis of dementia, and a decline in cognitive function from mild impairment to dementia. Finally, analysis of studies assessing absolute cognitive test scores demonstrated a 3% increase in cognitive function from baseline in hearing-impaired patients after they started using a restorative hearing device.
The present study by Yeo et al. demonstrated a significant advantage to treating hearing loss using restorative devices with regards to protecting from cognitive decline. This work is important in quantifying the benefit of restorative hearing devices and may influence funding for this technology for patients with hearing loss. The study design and a considerable number of included studies are a major advantage with regard to the strength of reported results. A primary limitation of this study is the inability to compare the severity of hearing loss among included patients. As such, it is impossible to know whether the effect of hearing restorative devices differs based on baseline function. Future studies should seek to address the feasibility of implementing hearing aid solutions at a systems level.
Relevant reading: Hearing loss and the risk of dementia in later life
In-Depth [systematic review and meta-analysis]: A systematic review and meta-analysis study was conducted, registered a priori on PROSPERO. Three databases were searched (PubMed, Embase and the Cochrane Library) for any primary observational or randomized controlled studies pertaining to cognitive decline in patients with treated hearing loss. The primary outcomes of interest were diagnosis of dementia or generalized cognitive decline measured by standard tests. Risk of bias assessments was performed using the Ottawa-Newcastle scale, and overall publication bias was determined using funnel plots as well as the Egger statistical test.
Of the 31 included studies, 2 were randomized controlled trials, 16 were prospective cohort studies, and the remainder were retrospective or cross-sectional. Twenty-one studies had a moderate, and 10 had a low risk of bias. The severity of hearing loss was variable amongst included participants.
The hazard ratio for any cognitive decline amongst patients with treated hearing loss and longitudinal follow-up greater than 2 years was 0.81 (95% confidence interval 0.76-0.87). This estimate was based on 8 studies and a pooled group of 126,903 participants. This protective hazard ratio was steadfast even when controlling for a number of possible confounding factors. The meta-analysis also revealed that patients treated with restorative hearing devices were also protected from other forms of cognitive decline: any cognitive impairment (hazard ratio 0.79, 95% confidence interval 0.65-0.97), decline from moderate cognitive impairment to dementia (0.73, 0.60-0.88), a new diagnosis of dementia (0.83, 0.77-0.90). A pooled analysis of studies assessing absolute cognitive test scores demonstrated a 3% (ratio of means 1.03, 95% confidence interval 1.02-1.04) increase in cognitive function from baseline in hearing-impaired patients after they started using a restorative hearing device.
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