Abstract
Objective:
To examine the effect of patient age on longitudinal speech understanding outcomes following cochlear implantation (CI) in bilateral hearing loss.
Study Design:
Retrospective cohort study.
Setting:
Tertiary academic center
Patients:
1105 adult patients with bilateral hearing loss receiving a unilateral CI between 1987-2022
Interventions:
None
Main Outcome Measures:
Post-operative speech recognition outcomes, including AzBio sentences, consonant-nucleus-consonant word (CNC-w), and Hearing in Noise Test (HINT) in quiet were analyzed at short- (<2 years), medium- (2-8 years) and long- (>8 years) term post-operative intervals.
Results:
86 very-elderly (>80 years), 409 elderly (65-80 years), and 709 non-elderly (18-65 years) patients were included. Short-term post-operative AzBio scores demonstrated similar magnitude of improvement relative to pre-operative scores in the very-elderly (47.6, 95%CI:[28.9-66.4]), elderly (49.0, 95%CI:[39.2-58.8]), and non-elderly (47.9, 95%CI:[35.4-60.4]). Scores for those >80 years of age remained stable after two years post-implant, but in those ≤80 years of age, scores continued to improve for up to eight years (elderly: 6.2, 95%CI: [1.5 – 12.4]; non-elderly: 9.9, 95%CI:[2.1-17.7]) post-implantation. Similar patterns were observed for CNC-w scores. Across all age cohorts, patients with pre-operative HINT scores between 40-60% had similar scores compared to those with pre-operative scores of <40%, at short-term (82.4, 78.9, 95%CI:[−23.1-10.0]) , medium-term (77.2, 83.9, 95%CI:[−15.4-8.2]), or long-term (73.4, 71.2, 95%CI:[−18.2-12.2]) follow-up.
Conclusions:
Patients over the age of 80 gain significant and sustained auditory benefit after CI, including those meeting expanded CMS criteria for implantation. Patients <80 years of age demonstrated continued improvement over longer periods than older patients, suggesting a role of central plasticity in mediating CI outcomes as a function of age.
Introduction
Hearing loss is associated with several adverse health outcomes including decreased physical functioning and mobility, increased rates of falls and hospitalizations, and increased rates of dementia and depression[1–5]. In 2019, the Center for Disease Control (CDC) estimated that approximately 13% of adults had difficulty hearing, and that these patients often presented with progressive, bilateral symmetric sensorineural hearing loss that is most pronounced at high frequencies[6]. Whereas assistive hearing devices such as hearing aids can help to amplify sound, patients often report difficulties with understanding speech despite sufficient loudness and intensity of sound[7]. By directly stimulating the distal cochlear nerve, cochlear implants (CI) can offer improved hearing outcomes including sound quality and speech perception.
Longitudinal data on speech perception outcomes in the elderly following CI is mixed. Rak et. al have shown stable long-term speech perception in adult patients, with gradual deterioration of hearing in noise in the elderly population [8]. Spitzer et. al likewise described overall stability of functional outcome over time, but with increased variance in long-term speech recognition that correlated with age [9]. Hilly et. al noted worse HINT outcomes in patients over age 70 within two years [10], while other groups have demonstrated age to only be a predictor of speech perception in the presence of background noise [11, 12]. As the number of CI procedures increases within the aging population, more longitudinal data is needed to appropriately counsel elderly patients.
Audiological candidacy for CI as defined by the Centers for Medicare and Medicaid Service (CMS) requires individuals to have bilateral moderate to profound sensorineural hearing loss and limited benefit from assistive devices such as hearing aids. Recently, the CMS expanded the candidacy profile from those with hearing test scores below 40% to those with scores below 60% in best-aided listening conditions[13]. This decision was based off review of multiple clinical studies suggesting that older adults with preoperative speech scores between 40 and 60% may also benefit from cochlear implantation[14–18], which will allow for an increasing number of Medicare patients to undergo CI surgery. However, it remains unclear if these improvements translate equivalently across the aging spectrum[19, 20]. In this study, we examine the effect of patient age and pre-operative speech perception scores on long-term auditory outcomes following CI, with a focus on the very elderly (>80) population.
Methods
Institutional Review Board (IRB00188251 Johns Hopkins School of Medicine) approval was obtained for this study. Retrospective chart review was performed for all adult patients who received a unilateral CI for bilateral hearing loss at a single academic medical center between 1987 and 2022. Patients who received concurrent bilateral implants and patients who underwent revision surgery were excluded. Speech recognition outcomes, including Hearing in Noise Test (HINT), consonant-nucleus-consonant word (CNC-w), and AzBio were collected during the pre- and post- implant timeframes by trained CI audiologists. Testing modality was determined by the audiologist at the time of assessment and therefore reflected institutional trends as testing modality changed with time. If the patient had more than one test modality applied during the post-operative period, the test-type which matched the pre-operative test modality was included, and others were excluded. Post-operative testing was organized into short-term (conducted between six weeks and two years post-operatively), medium-term (two years to eight years), and long-term (greater than eight years). Testing stimuli were presented at a sound pressure level of 60 to 70 dB in quiet to the implanted ear and the score under best-aided conditions was recorded. If more than one result was available for a particular time frame, then the highest score was used.
Demographics, clinical characteristics, and audiometric data were collected for all patients. Patient age was categorized into very-elderly (>80 years), elderly (65-79 years), and non-elderly (<65 years) based on time of CI[21]. These data were analyzed using descriptive statistics. Single sided ANOVA with group wise comparison were used to compare test results at the three post-operative time frames. Statistical analysis was performed on R Studio version 2022.12.0 (Vienna, Austria) and a significance level of p<0.05 was used for all analyses.
Results
1104 adult patients with eligible audiologic data were identified and compiled in a database. 535 (47.6%) of these patients were male. The majority of the patients (n = 709, 64.2%) were below the age of 65, 409 patients (37.0%) were between 65-80 years, and 86 (7.8%) were over 80. These data are summarized in Table 1.
Table 1.
Demographic and implant data of patient cohort
| Total cohort (n = 1104) | |
|---|---|
| Male sex | 535 (47.6%) |
| Age at implant | |
| Non-elderly (<65) | 709 (64.2%) |
| Elderly (65-80) | 409 (37.0%) |
| Very elderly (>80) | 86 (7.8%) |
| Right-sided implant | 564 (51.1%) |
Across all age ranges, the mean improvement from pre-operative AzBio scores in the short-term (up to 2 years) was: 48.1 (95%CI: [40.9-55.5]), in the medium-term (2-8 years): 54.2 (95%CI: [46.6-61.8]), and in the long-term (>8 years): 51.9 (95%CI: [43.1-60.7]). Improvement from pre-operative HINT scores was found to be 62.5 (95%CI: [56.7-68.2]), 66.2 (95%CI: [56.7-68.2]), and 54.9 (95%CI: [43.7-66.1]), in the short-, medium-, and long-terms, respectively. Improvement from pre-operative CNC-w scores were noted as 41.3 (95%CI: [36.2-46.7]) in the short-term, 48.8 (95%CI: [42.9-54.7]) in the medium-term, and 46.8 (95%CI: [38.0-55.7]) in the long-term (Table 2).
Table 2.
Improvement of post-operative AzBio, HINT, and CNC-w scores in the very elderly, elderly, and non-elderly after cochlear implant.
| Very elderly (95% CI) | Elderly (95% CI) | Non-elderly (95% CI) | All age-ranges (95% CI) | |
|---|---|---|---|---|
| AzBio | ||||
| Short-term | 47.6 (28.9-66.4) | 49.0 (39.2-58.8) | 47.9 (35.4-60.4) | 48.1 (40.9-55.5) |
| Medium-term | 41.0 (20.6 – 61.4) | 54.1 (44.1 – 64.2) | 57.8 (44.9 – 70.7) | 54.2 (46.6-61.8) |
| Long-term | 38.1 (−1.6 – 77.9) | 47.0 (34.1 – 59.9) | 55.3 (41.5 – 69.2) | 51.9 (43.1-60.7) |
| HINT | ||||
| Short-term | 57.5 (35.2-63.7) | 68.5 (60.7-76.4) | 61.2 (51.9-70.4) | 64.5 (56.7-68.2) |
| Medium-term | 61.5 (45.4-79.6) | 69.7 (60.7-78.7) | 64.1 (53.3-74.8) | 66.2 (56.7-68.2) |
| Long-term | 40.3 (13.2-67.4) | 58.2 (43.3-73.2) | 56.1 (37.8-74.4) | 54.9 (43.7-66.1) |
| CNC-w | ||||
| Short-term | 37.8(14.9-40.7) | 41.1(34.8-48.1) | 45.0(36.9-53.1) | 41.3 (36.2-46.7) |
| Medium-term | 36.1 (11.3-40.8) | 48.6 (40.5-56.7) | 54.8 (45.6-64.1) | 48.8 (42.9-54.7) |
| Long-term | 12.2(−22.1-46.6) | 39.3(28.3-16.0) | 58.1(44.0-72.2) | 46.8 (38.0-55.7) |
When stratified by age range, short-term post-operative AzBio scores demonstrated similar magnitude of improvement relative to pre-operative scores in the very-elderly (47.6, 95%CI: [28.9-66.4]), elderly (49.0, 95%CI: [39.2-58.8]), and non-elderly (47.9, 95%CI: [35.4-60.4]). On group-wise comparison of longitudinal performance, there was no improvement between medium-term and short-term, or long-term and medium-term scores in the very elderly age groups. However, patients under 80 years of age continued to demonstrate improvement through the medium-term follow-up period (Elderly: 6.2, 95%CI: [1.5 – 12.4]; non-elderly: 9.9, 95%CI:[2.1-17.7]) and remained stable in the long-term. This is shown in Figure 1. When age was analyzed as a continuous variable, patients above 76 years of age did not show statistically significant improvement in AzBio scores between short- and medium- term follow-up.
Figure 1.
Pre- and post-operative cochlear implant AzBio test scores. Very Elderly: >80 yrs, Elderly: 65-80 yrs, Non-elderly: <65 yrs. Short term: 0.5-2 yrs, Medium term: 2-8 yrs, Long term: >8yrs
Similar relationships are observed for CNC-w scores. There is comparable magnitude of improvement in the short-term for very-elderly (37.8.6, 95%CI: [14.9-40.7]), elderly (41.1, 95%CI: [34.8-48.1]), and non-elderly (45.0, 95%CI: [36.9-53.1]). Again, there was no sequential improvement in the very elderly after the short-term, but the elderly group (7.5, 95%CI: [2.2 – 14.1]) and non-elderly group (9.8, 95%CI: [6.2 – 15.5]) continued to experience improvement from short- to medium- term (Figure 2). When age was analyzed as a continuous variable, patients above 75 years of age did not show statistically significant improvement in CNC-w between short- and medium- term follow-up. There was also trend towards continued improvement between medium- and long-term in the non-elderly group, although statistical significance was not reached. In contrast, in the elderly and very-elderly groups, there was a trend towards decline in scores at the long-term assessment. For HINT, there was a smaller improvement during the short-term in the very elderly (57.5, 95%CI: [35.2-63.7]) compared to the elderly (68.5, 95%CI: [60.7-76.4]) and non-elderly (61.2, 95%CI: [51.9-70]) and across all ages, there was no improvement between medium-term and short-term, or long-term and medium-term (Figure 3). These data are organized in Table 2.
Figure 2.
Pre- and post-operative cochlear implant CNC-w test scores. Very Elderly: >80 yrs, Elderly: 65-80 yrs, Non-elderly: <65 yrs. Short term: 0.5-2 yrs, Medium term: 2-8 yrs, Long term: >8yrs
Figure 3.
Pre- and post-operative cochlear implant HINT test scores. Very Elderly: >80 yrs, Elderly: 65-80 yrs, Non-elderly: <65 yrs. Short term: 0.5-2 yrs, Medium term: 2-8 yrs, Long term: >8yrs
We then specifically evaluated the impact that expanded CMS criteria would have in this study cohort. Within our population, 956 (86.6%) patients had pre-operative scores of less than 40%, while 83 (7.5%) had scores in the 40 – 60% range (Supplemental Table 1). Overall, patients who scored <40% and those who scored 40-60% on preoperative testing achieved similar short-term post-operative scores across all three speech perception tests: AzBIO (75.4 vs. 68.9, t-test 95%CI:[−23.1-10.0]), HINT (90.6 vs. 82.9, t-test 95%CI:[−18.1-8.1]), CNC-w (54.2 vs. 51.3, t-test 95%CI: [−12.5-17.2]). Given the higher pre-operative scores in the 40-60% cohort, the absolute improvement in scores was smaller compared to the improvement in the <40% cohort (AzBIO: 62.1 vs. 24.5, t-test 95%CI:[36.5–51.2]). This finding was consistent across all three tests (HINT: 78.3 vs.41.3, t-test 95%CI:[28.9-42.1], CNC-w: 44.7 vs. 7.2, t-test 95%CI:[28.8-39.2]) . In age-wise analysis, HINT was the only test with a sufficient sample size to make meaningful comparisons across all three age groups. There was no significant difference in the medium-term scores between patients with pre-operative scores less than 40% compared to those between 40-60% in the very elderly cohort (73.8 vs. 74.2, 95%CI: [−8.9 – 11.1]), the elderly cohort (82.2 vs. 76.6, 95%CI: [−5.6 – 9.1], or the non-elderly cohort (78.9 vs. 75.1, 95%CI: [−10.2 – 7.2]). Similarly, there was no statistically significant difference in long-term scores between pre-operative score cohorts within the very elderly (52.8 vs. 62.1, 95%CI: [−12.2 – 3.6], the elderly (85.2 vs. 76.2, 95%CI: [−11.4 – 5.2]), or the non-elderly (72.5 vs. 74.5, 95%CI: [−3.5 – 4.2]) (Figure 4).
Figure 4.
Pre- and post-operative HINT scores stratified by pre-operative scores and age. Very Elderly: >80 yrs, Elderly: 65-80 yrs, Non-elderly: <65 yrs. Short term: 0.5-2 yrs, Medium term: 2-8 yrs, Long term: >8yrs
Discussion
There is a growing body of literature investigating the effectiveness of CIs in the elderly population[12, 21]. Numerous studies have suggested that this population may not derive as much benefit as younger cohorts[11, 22]; however, more recent data has shown that there is a comparable improvement in audiometric and quality of life outcomes in the short-term [8]. There are fewer studies that have tracked longitudinal, long-term outcomes in the elderly patient population. Our current work shows that both very elderly (>80 years) and elderly (65 – 80 years) patients receive clinically meaningful and statistically significant improvement in speech understanding after CI, and that this change remains stable at more than eight years after surgery. Furthermore, our data shows that these improvements are consistent across a range of pre-operative speech perception test scores, which is important given the expanded CMS criteria for CIs.
Within our study, we found that patients across all age ranges demonstrated significant improvement in speech perception scores following CI in the short-term post-operative period. When stratified by age, there was no difference in the magnitude of improvement between patients below 65 and those above 65. Further analysis of the very elderly (>80 years) showed similar increases in AzBio and CNC-w scores after CI compared to both elderly (65-80 years) and patients below 65. These findings parallel recent studies demonstrating comparable improvements in speech perception scores over different patient age ranges [23, 24]. Within HINT, the magnitude of improvement in the short-term was smaller in the very elderly compared to younger cohorts. Hilly et. al found similar trends in elderly patients when evaluating speech perception during short-term follow-up using HINT under quiet conditions [10]. However, when taking into account pre-operative scores, there was no difference in absolute scores between the age groups at short-term HINT testing.
Research on longitudinal speech perception in adults has shown improvement in scores continue up until five years after implant, then plateau through the first decade[8, 25, 26]. In our large cohort, we find an age-dependent effect on post-implant trajectories. There is continued increase in AzBio and CNC-w scores between two to eight years for patients under age 80, and even beyond 8 years for patients under age 65 when tested by CNC-w (Fig. 2). In contrast, these scores for the very elderly do not demonstrate improvement through the medium-term and for both elderly and very-elderly groups, may even decline past 8 years. Interestingly, we do not see a similar pattern of continued improvement for HINT testing, even in younger patients. These differences can likely be attributed to known differences in dynamic range between test types. The ceiling effect of HINT testing may limit the recognition of continued improvement from short- to medium- term, whereas the larger dynamic range of AzBio and in particular, CNC-w, continues to capture subtle changes through this period[27, 28]. Outside of test characteristics, the continued improvement seen in patients under 80 in both AzBio and CNC-w may represent both age-related decline in cognitive function related to processing of speech intelligibility and/or decreased auditory cortex plasticity. Moberly et. al have previously found that decreased working memory function is implicated in lower speech perception scores, independent of hearing ability [29–31]. Tests requiring increased executive function, such as AzBio, may be depressed in the very elderly, which may partially explain the absence of improvement through the medium-term. Additionally, given the putative relationship between CI function and neural plasticity, these tests could also be capturing subtle, ongoing changes to the auditory cortex in a younger population that may not be fully realized in the short-term[32]. Outside of these subtle differences in improvement, we noted that across all test-types, patients’ long-term scores demonstrated significant improvement from pre-operative tests, and were stable relative to medium-term assessment, even in the very elderly.
In light of the 2022 memorandum by CMS detailing the changes in CI coverage criteria for Medicare beneficiaries, there will be an expanded pool of eligible, older patients in the near future. Within our database, we noted that 7.5% of our included patients met the new criteria of preoperative speech scores between 40-60%. Understandably, these patients demonstrated decreased absolute improvement compared to the patients with pre-operative scores below 40%, particularly when using the CNC-w test These patients may receive less subjective benefit and demonstrate lower satisfaction compared to patients who met the traditional, more stringent, criteria. However, it is important to note that both cohorts demonstrated clinically meaningful improvement, and there was no significant difference in speech perception scores at both short- and medium- term follow-up. When stratified by age, very elderly patients demonstrated similar audiometric trends as the 65-80 age group, suggesting that this cohort should also derive benefit from the expanded criteria. These longitudinal findings are important when considering patient frailty and perioperative risks associated with surgery in the very elderly[33, 34]. It may also play a role in patient counseling for this vulnerable population, particularly in guiding treatment decisions for marginal elderly patients Rather than waiting for a clinically detectable decrease in hearing, early implantation may help mitigate some of these medical and audiological concerns. Furthermore, the relationship between cognitive decline and hearing loss is particularly notable in this population[35]. The enduring improvement in speech perception within the very elderly, independent of pre-operative scores, suggests that early implantation may reduce the effect of hearing loss on these patients’ quality of life[36].
Although this large cohort study can provide important insights to general population trends, there are limitations inherent to the retrospective nature of the database. Due in part to the large scope of the study spanning nearly three decades of patients, there is notable variation in follow-up scheduling and test modalities. As such, we were unable to fully control for inter-subject variability, and pooled scores were used for analysis. Variations in follow-up also informed our decision to select the highest score in each test period as our outcome, as this mitigated the effect of within-patient repeat measurements due to, for example, changes to CI programming. With this in mind, given the advances in device hardware as well as the evolution of surgical technique over the past 20-30 years, further studies are needed to examine trends in speech perception scores over time. We recognized that there is both loss to follow-up and censoring in the long-term period, particularly in the very-elderly, which can introduce selection bias and artificially depress speech perception scores. We were also unable to account for variables impacting post-implantation speech perception scores, including duration of deafness, etiology of deafness, and cognitive scores. Finally, as data was collected prior to expanded CMS criteria, patients with pre-operative scores between 40-60% comprised less than 10% of our study population. Combined with the loss of patients to follow-up, the analysis is inadequately powered to detect differences at the long-term for AzBio and CNC-w in the very elderly. Despite these limitations, we believe that the findings from our study are largely generalizable and that the very elderly population can derive significant and sustained improvements in hearing following CI.
Conclusions
Following CI, very elderly patients (>80 years) derive similar improvements in speech perception scores as their younger counterparts. Although this increase tends to plateau earlier in the follow-up period, the overall changes are long-lasting and sustained for at least eight years. These longitudinal auditory benefits extend to all patients meeting the expanded CMS criteria for implantation. Given the relationship between global executive function and hearing loss, early implantation in the very elderly may have enduring auditory and cognitive benefits.
Supplementary Material
Support:
This work was supported in part by the NIDCD Grant No. 5T32DC000027-33
Footnotes
Conflicts of interest:
None
Meeting:
This work was accepted for a podium presentation at COSM 2023: Boston, MA. May 3 - 7, 2023
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