Do Patients With Dementia Benefit From Cochlear Implantation?

Abstract

Dementia negatively impacts quality of life and is likely to become more prevalent in the rapidly aging population of the United States. It is estimated that the number of people living with dementia will triple by 2050 and care of these patients will cost approximately $1.5 trillion annually. In addition, dementia places an enormous emotional toll on a patient's family and loved ones. Targeting modifiable risk factors may delay further cognitive decline and help manage dementia, providing therapeutic, financial, and social benefit to the patient, their family, and the healthcare system. Hearing loss was recently identified as a major risk factor for dementia, with more severe hearing loss associated with higher rates of cognitive decline and impairment (Fig. 1). While previous studies demonstrate that cochlear implantation (CI) in the elderly is safe and effective in reversing hearing loss, newer studies assess the effect of CI on independent risk factors for dementia associated with hearing loss, including cognition, depression, social isolation, physical activity, and quality of life. In this Triological Society Best Practice, we review these studies to address whether patients with dementia benefit from CI (Supporting Table 1). In a prospective study in 2016, Castiglione et al. assessed the effects of auditory rehabilitation on neurocognition and depression in 105 hearing-impaired elderly patients compared to 20 normal hearing controls (median age 74 years).1 Fifteen of those hearing-impaired patients were rehabilitated with CI and assessed 1 year later. CI users experienced a statistically significant positive effect on cognition and reduction in depression after 1 year of CI use. In this investigation, cognitive performance of pre-implant users was similar to patients with mild cognitive impairment (MCI), a risk state for dementia; after 1 year of CI use, there was no statistical difference in neurocognition or depression between CI users and normal hearing controls. In a larger prospective study in 2018, Völter et al. assessed neurocognition and quality of life among 60 hearing-impaired elderly patients (mean age 66 years) prior to CI implantation, consisting of a computer-based test for short-term, long-term, and working memory, processing speed, inhibition, and attention as well as questionnaires for quality of life.2 Thirty-three patients were reassessed at 6 months and 20 were reassessed at 12 months. No cognitive domains worsened after 6 or 12 months while multiple domains significantly improved at both the 6- and 12-month assessments. CI users exhibited statistically significant improvement in their self-esteem, physical activity, and social interactions. Notably, older patients over 65 years demonstrated relatively more improvement from baseline when compared with their younger counterparts. Another prospective study in 2018, performed by Mosnier et al., compared neurocognitive performance among 70 hearing-impaired elderly patients (mean age 72 years) preoperatively and then after approximately 7 years of CI use.3 Patients were neurocognitively classified as normal, having MCI, or having dementia. Unique to this study, 45% of study participants were diagnosed with MCI preoperatively. While there were statistically significant neurocognitive declines after 7 years of CI use, the authors report this mild decline is consistent with aging. Furthermore, only 6% of MCI CI users developed dementia, a rate much lower than elderly normal controls (reported at 50% over the same time period). Furthermore, the authors reported the encouraging finding that 10% of participants with MCI improved to normal cognitive function after 7 years of CI use. A prospective study in 2019 by Sarant et al. assessed cognitive function and quality of life among 59 hearing-impaired elderly patients (mean age 72 years) preoperatively and 20 patients after 18 months of CI use.4 This study assessed cognition with the Cogstate battery test, a highly sensitive and reliable visually based computerized test, and then collected comprehensive data on other relevant risk factors. Correcting for these risk factors allowed for a granular view of the effects of CI in elderly patients after 18 months. For example, males without higher education and all patients with higher education exhibited statistically significant improvement in executive function after CI, while individuals older than 70 years additionally exhibited significant improvements in attention and quality of life. While there are no studies of perioperative outcomes after CI in patients with dementia at this time, a multicenter retrospective study by Fakurnejad et al. in 2020 analyzed perioperative complications of CI on 3,420 patients from 2003 to 2016.5 Patients were grouped by five cohorts based on age (0–18, 19–39, 40–59, 60–79, and >80) and perioperative complications within 30 days of CI were assessed. Despite an increase in frequency of CI, there was no statistically significant increase in perioperative complications in the elderly compared with younger cohorts. The above studies suggest that patients with dementia may benefit from CI. CI may slow the progression of dementia and even lead to clinical improvement among those with mild baseline impairment.3 Whether these improvements are a reflection of successful treatment of hearing loss itself with CI, or whether they reflect tangible improvement in an underlying causal process for dementia, is not known. Cognitive function, hearing loss, and dementia have multiple shared features and may occur in an independent or dependent fashion in a given individual. However, improving neurocognitive measures and delaying or reversing dementia will not only benefit patients, but may also yield significant tangible and intangible benefits to caregivers and families. Additional research is still needed to further delineate models for patient selection, determine which patients will most significantly benefit, and identify any postoperative rehabilitative measures that may further enhance those benefits. The exact mechanism linking hearing loss, hearing rehabilitation, and dementia remains elusive and requires further investigation at the basic science and clinical levels. It is also not yet known to what degree hearing loss may confound neurocognitive assessment in the elderly, and whether addressing hearing loss in the elderly in widespread fashion would yield lower rates of dementia from correction of prevalence attributable to overdiagnosis. CI in elderly patients generally leads to improvement in neurocognition, depression, social isolation, physical activity, and general quality of life, even within the first year of CI use. Although it has yet to be studied specifically among patients with dementia, CI in the elderly is safe with no increase to perioperative complication with an increasingly aging population and more frequent implantation among the elderly. Larger and longer prospective studies are needed to further develop our understanding of the complex and interrelated causal relationships between hearing loss, dementia, and their shared risk factors. The described studies range between level II and III evidence (Supporting Table 1). Supporting Table 1 Summary of Studies Cited in This Review. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.