Dizziness Handicap Inventory (DHI)
The top right panel of Figure 7 shows boxplots of DHI scores before implantation and 6 mo postactivation. The mean DHI scores was reduced by 4.6 points. A one-way RM ANOVA was performed on the DHI data, with test interval as the factor; complete results are shown in Table 9. There was no significant difference in DHI scores between baseline and 6 mo postactivation (p = 0.661).
The bottom panels of Figure 7 shows boxplots of SSQ scores before implantation and 6 mo postactivation for the Speech, Spatial, and Quality subtests of the SSQ. Mean scores improved by 2.3, 3.0, and 1.0 points for Speech, Spatial, and Quality, respectively. One-way RM ANOVAs were performed on the SSQ data, with test interval as the factor; complete results are shown in Table 9. Significant improvements were observed for the Speech (p = 0.003), Spatial (p < 0.001), and Quality subtests (p = 0.034).
Glasgow Hearing Aid Benefit Profile (GHAPB)
Figure 8 shows boxplots of GHABP scores 6 mo postactivation for each of the six listening scenarios: listening to the television with the volume adjusted for others in the room, conversation in a quiet room, conversation on the street, conversation in a group, Personal issue 1 (P1), and Personal issue 2 (P2). The top six panels show scores for listeners’ worry, difficulty with the CI off, and difficulty with the CI on for the various listening scenarios; for these panels, lower scores are better. Across all listening scenarios, mean scores were 3.3, 3.2, and 2.8 for worry, difficulty with the CI off, and difficulty with the CI on, respectively. A one-way RM ANOVA was performed on the difficulty data averaged across listening scenarios, with listening condition (CI off, CI on) as the factor; complete results are shown in Table 9. Difficulty was significantly reduced with the CI on (p = 0.015).
The bottom six panels of Figure 8 show scores for how much subjects used the CI for different listening scenarios, how helpful they felt they CI was for different listening scenarios, and how satisfied they were with the CI for different listening scenarios; for these panels, higher scores are better. Across all listening scenarios, mean scores were 4.4, 3.5, and 3.8 for CI use, helpfulness of the CI, and satisfaction with the CI, respectively.
Demographic factors age at CI and duration of deafness were compared with localization RMSE and to binaural SRTs in noise for the S0N0 and S0NNH conditions at baseline, 6 mo postactivation, and for the change in performance (6 mo – baseline). Pearson correlation analyses showed no significant relationship between either demographic factor and localization or binaural SRTs (p > 0.05 in all cases).
Behavioral performance was compared with subjective reports from questionnaire data at baseline, 6 mo postactivation, and for the change in performance. Tinnitus VAS scores were significantly correlated with TFI scores at 6 mo postactivation (r = 0.63; p = 0.033), but not at baseline (r = 0.24; p = 0.514). No significant correlations were observed between VAS or TFI scores and SRTs for the various spatial conditions, between HINT sentence recognition in quiet or SRTs in noise for the various spatial conditions, between localization or speech SRTs in noise and SSQ scores or GHABP scores (p > 0.05 in all cases)
While AEs were reported in five subjects, most were resolved within 4 weeks. One of the safety concerns for this study was the capacity of the CI ear to interfere with NH function. The PTA thresholds with the NH ear alone were not significantly affected after cochlear implantation, and PTA thresholds did not increase by more than 10 dB after implantation for any subject 6 mo postactivation. There was no significant change in SATs, CNC word recognition in quiet, and HINT sentence recognition in quiet with the NH ear alone before or after implantation (Table 4). The SRTs in noise for S0NCI and S0NNH with the NH ear alone were not significantly affected after cochlear implantation (Table 6). Surprisingly, there was a small but significant improvement for NH-only SRTs for the S0N0 condition at 6 mo postactivation (Table 6), possibly due to procedural learning or some unclear benefit of the CI on NH-only performance. The SRTs with the NH ear alone did not increase by more than 4 dB for any subject at 6 mo postactivation; the maximum decrement in SRT among all subjects was 0.17 dB after implantation. Thus, long-term experience with electric hearing did not significantly interfere with contralateral acoustic hearing function.
Not surprisingly, aided PTA thresholds, SATs, word recognition in quiet, and sentence recognition in quiet in the CI ear alone greatly improved 1 mo postactivation, beyond which there were no significant changes (Table 4). Mean recognition of CNC words in quiet with the CI ear alone was 51.1% correct at 6 mo postactivation, comparable with mean CI-only CNC scores in some SSD-CI studies (e.g., 47.3% correct in Firszt et al., 2012; 55.4% correct in Friedmann et al., 2016; 55.0% correct in Dillon et al., 2018), but slightly higher than in others (e.g., 40.8% correct in Holder et al., 2017; 44.7% correct in Sladen et al., 2017b). Mean recognition of HINT sentences in quiet with the CI ear alone was 84.0% correct at 6 mo postactivation, better than reported in some previous studies that used the more difficult AzBio sentences (e.g., 67.0% correct in Zeitler et al., 2015; 66.0% in Sladen et al., 2017b), but poorer than in others (e.g., 95.0% correct in Friedmann et al., 2016).
The reduction in tinnitus severity was the strongest benefit of cochlear implantation. Note that severe tinnitus was not part of the inclusion or exclusion criteria for this study. Cochlear implantation significantly reduced tinnitus VAS scores (Table 8), consistent with previous studies that also used a VAS (Punte et al., 2011; Mertens et al., 2013, 2016). One-third of the subjects reported baseline Tinnitus VAS scores ≤2, and two-thirds of subjects reported scores ≤5. This distribution is somewhat different from previous studies where fairly high tinnitus severity was part of the inclusion criteria (Van de Heyning et al., 2008; Buechner et al., 2010; Punte et al., 2011; Mertens et al., 2016a). At 6 mo postactivation, the mean VAS score was 2.3 with the CI on, comparable with scores from previous SSD CI studies (e.g., 2.3 in Van de Heyning et al., 2008; 2.8 in Punte et al., 2011; 2.2 in Punte et al., 2011), lower than in others (e.g., 3.4 in Mertens et al., 2013).
Cochlear implantation also significantly reduced TFI scores (Table 9), consistent with previous studies that used other tinnitus questionnaires (Van de Heyning et al., 2008; Mertens et al., 2016a; Dillon et al., 2018). At 6 mo postactivation, the mean TFI score was 25.2. Note that most previous SSD CI studies used the similar Tinnitus Handicap Inventory (Newman et al., 1996), making it difficult to directly compare the present TFI scores to Tinnitus Handicap Inventory scores from previous studies. For one-third of the subjects, baseline TFI scores were <21, indicating only a “small” problem with tinnitus (Henry et al., 2014). However, baseline TFI scores ranged from 75 to 96 in one-third of subjects, indicating “big” to “very big” problems with tinnitus. Six months postactivation, six of 10 subjects reported tinnitus severity <21, and four of 10 reported tinnitus severity between 41 and 66. Thus, 40% of subjects still reported “moderate” to “big” problems with tinnitus even after 6 mo of implant use. Still, for these subjects, the mean reduction in tinnitus severity was substantial (23 points). There was a significant correlation between VAS and TFI scores only at 6 mo postactivation (p = 0.033), but no correlation at baseline (p > 0.05) or between the changes in VAS and TFI scores (p > 0.05). This suggests that at 6 mo postactivation, the acutely measured VAS scores were indicative of tinnitus severity subjects experienced during the previous week.
The mean RMSE with binaural listening at 6 mo postactivation was 34.1 degrees, slightly higher than in other SSD CI studies (e.g., 28.0 degrees in Dorman et al., 2015; 26.6 degrees in Kitoh et al., 2016; 27.6 degrees in Grossman et al., 2016; 30.0 degrees in Zeitler et al., 2015; 28.0 degrees in Dillon et al., 2017; 29.2 degrees in Litovsky et al., 2018). Note that there were differences among studies in terms of the number of speakers, spacing between speakers, placement of the speakers (in front of the listeners or behind the listener, as in this study), etc. With binaural listening, localization did not significantly improve relative to binaural baseline until 6 mo postactivation (Table 5). There was great variability in terms of improvement in binaural localization; relative to baseline binaural, reductions in RMSE ranged from 1.5 to 27.6 degrees. Note that some subjects had some low-frequency hearing in the ear to be implanted that might have aided in baseline binaural localization. It is unclear whether this residual acoustic hearing was preserved after cochlear implantation. Unfortunately, binaural localization with the CI off (with no plugging or muffing of the CI ear), which would have been directly comparable with baseline binaural, was not measured.
Relative to NH-only performance, the mean CI benefit for localization at 6 mo postactivation was 18.2 degrees, less than in some SSD CI studies (e.g., 26.1 degrees in in Távora-Vieira et al., 2015; 35.4 degrees in Grossmann et al., 2016; 27.4 degrees in Litovsky et al., 2018). There was great variability in CI benefit relative to the NH-ear alone, ranging from 4.7 to 27.8 degrees. It is unclear why the CI benefit relative to NH-only performance, while significant, was poorer in this study than in some previous studies. Again, differences in experimental setups and patient populations (e.g., normal hearing versus mild-to-moderate hearing loss in the nonimplanted ear) may have contributed to differences in CI benefit.
Speech Understanding in Noise
At 6 mo postactivation, the SRT for HINT sentences in noise with binaural listening for S0N0 was −4.2 dB, comparable with SRTs for Oldenburg Sentence Test sentences in Rahne and Plontke (2016; −4.4 dB), but better than reported in some SSD CI studies (−3.0 dB for Leuven Intelligibility Sentence Test sentences in Vermiere & Van de Heyning, 2009; −1.6 dB for Oldenburg Sentence Test sentences in Grossmann et al., 2016; −2.4 for Bamford-Kowal-Bench sentences in Friedmann et al., 2016). A significant improvement in SRTs was observed at 1, 3, and 6 mo postactivation, relative to binaural baseline. However, NH-only performance also significantly improved during this period and may have contributed to the better binaural performance. When speech and noise were spatially separated (S0NNH), binaural SRTs significantly improved at 3 and 6 mo postactivation, relative to binaural baseline. The mean SRT was −2.6 dB, comparable with previous studies (e.g., −2.0 dB for BKB sentences in Távora-Vieira et al., 2013; −2.5 dB for BKB sentences in Friedmann et al., 2016; −3.1 dB for OLSA sentences in Grossmann et al., 2016).
Relative to NH-only, there was no significant CI benefit for any of the spatial conditions and no significant CI benefits were observed for head shadow, squelch, summation, or SRM. This finding is in agreement with some previous studies (e.g., Vermiere & Van de Heyning, 2009; Arndt et al., 2011; Mertens et al., 2015; Döge et al., 2017). However, Mertens et al. (2017) found significant CI benefits for head shadow and SRM for SSD CI patients with normal hearing in the contralateral ear over a longer time period, suggesting that such benefits for speech understanding in noise may take a longer time to emerge than the 6-mo period in this study.
Quality of Life
The mean scores for the Speech, Spatial, and Quality subtests of the SSQ at 6 mo postactivation were 5.7, 5.5, and 6.8, respectively; the total SSQ score was 5.0. The total SSQ score was somewhat less than observed in some previous SSD CI studies (e.g., 6.1 in Vermiere & Van de Heyning, 2009; 7.0 in Dillon et al., 2018; 5.4 in Louza et al., 2017; 5.9 in Mertens et al., 2015). It is unclear why postactivation SSQ scores would be lower in this study. It is possible that differences in patient groups across studies may have contributed to differences in SSQ scores. In this study, patients were required to have normal hearing in the nonimplanted ear and were not required to have tinnitus. In other SSD CI studies, patients were often allowed to have mild-to-moderate hearing loss in the nonimplanted ear and severe tinnitus was part of the inclusion criteria.
Significant improvements were observed for Speech, Spatial, and Quality subtests of the SSQ (Table 9), similar to previous studies with SSD CI patients (Vermiere and Van de Heyning, 2009; Arndt et al., 2011; Távora-Vieira et al., 2015; Dillon et al., 2018). Not surprisingly, the largest mean improvement was for the Spatial section (3.0 points) and the smallest was for the Quality section (1.0 point). Note that the range of improvement was quite large (0.8–5.8 points for Speech; 0.9–5.9 points for Spatial; −0.7 to 4.2 points for Quality). While localization and the Spatial subtest from the SSQ both significantly improved, there was no significant correlation between these measures at baseline or at 6 mo postactivation, or between the amount of improvement across measures. Similarly, while CI-only sentence recognition in quiet, binaural SRTs in noise (S0N0 and S0NNH), and the Speech subtest from the SSQ all significantly improved, there were no significant correlations between behavioral and subjective measures. This result is different from Dillon et al. (2018), who reported a significant correlation between sentence recognition in noise and the Speech subtest of the SSQ at 12 mo postactivation. Note that different sentence materials (AzBio), larger number of subjects (n = 20), and a longer study period were used in the study by Dillon et al. In this study, even though behavioral and subjective measures showed significant CI benefits, they appeared to capture different aspects of perception, with the questionnaire data reflecting long-term performance for more varied listening conditions than the acute behavioral measures in the lab.
When data were averaged across all listening scenarios, mean GHABP scores at 6 mo postactivation were 3.2 for “worry,” 3.3 for “difficulty with the CI off,” 2.4 for “difficulty with the CI on,” 4.3 for “how much the CI was used,” 3.4 for “how helpful the CI seemed,” and 3.7 for “how satisfied with the CI.” These scores were substantially higher than those reported by Louza et al. (2017), both in terms of perceived difficulty and perceived benefit. When averaged across all listening scenarios, the perceived difficulty was significantly reduced with the CI on (Table 9), consistent with Dillon et al. (2018) who used a similar test. Different from Dillon et al. (2018), there was no significant correlation between SRTs in noise and difficulty with the CI on, CI off, or the reduction in difficulty with the CI on. Note that different speech materials, a slightly different questionnaire, and a larger number of subjects were used in Dillon et al. (2018). The GHABP data also showed that subjects used the CI for most of the listening conditions and exhibited moderate-to-good satisfaction with the device. There was no correlation between perceived difficulty with the CI on or off from the GHABP and the Speech data from the SSQ, suggesting that these questionnaires captured different aspects of the subjective hearing experience.
The mean total DHI score at 6 mo postactivation was 18.6. Relatively few SSD CI studies have included dizziness severity as part of outcome measures. Doobe et al. (2015) reported a significant reduction in DHI scores for SSD patients with Ménière’s disease 6 mo after undergoing simultaneous labyrinthectomy and cochlear implantation; the total DHI score was reduced from 18 to 1. While not administering the DHI as part of their study, Hansen et al. (2013) found that simultaneous labyrinthectomy and cochlear implantation effectively eliminated vertigo in patients with Ménière’s disease. In this study (right top panel of Fig. 7), there was no significant change in dizziness severity between baseline and 6 mo postactivation. At baseline, six out of the 10 subjects exhibited no handicap (0–15 score), two exhibited a mild handicap (16–34 score), one exhibited a moderate handicap (36–53 score), and one exhibited a severe handicap (>54 score). At 6 mo postactivation, five out of the 10 subjects exhibited no handicap, four exhibited a mild handicap, and one exhibited a moderate handicap (36–53 score). Five of the subjects reported slightly increased dizziness severity at 6 mo postactivation; while elevated, scores generally remained within the same category of dizziness severity. Note that the subject who initially reported a severe handicap (88 score) at baseline reported no handicap (2 score) at 6 mo postactivation.
Benefit of Cochlear Implantation: Binaural Performance Over Time Versus Binaural Benefit
The degree and time course of CI appeared to depend on the outcome measure and the point of comparison. Here, two points of comparison were considered: (1) binaural performance before versus after implantation (as in Arndt et al., 2011; Punte et al., 2011; Kitoh et al., 2016; Mertens et al., 2016b, 2017; Dillon et al., 2017), or (2) binaural performance after implantation versus NH-only performance after implantation (as in Firszt et al., 2012; Mertens et al., 2015, 2017; Távora-Vieira et al., 2015; Grossman et al., 2016; Döge et al., 2017). Binaural performance before and after implantation is clinically relevant, but the variability in NH-only performance after implantation (whether due to procedural leaning, reduction of tinnitus, reduction of stress, etc.) may also contribute to binaural performance.
In this study, NH-only performance was measured by plugging and muffing the CI ear, which attenuated any residual low-frequency hearing. For example, mean baseline RMSE for localization was 6.9 degrees better with binaural than with NH-only listening. For subjects S2, S4, and S7, who had low-frequency thresholds of 70 dB HL, baseline RMSE was more than 36.4, 10.8, and 20.0 degrees better with binaural than with NH-only listening, suggesting the plug and muff greatly attenuated the acoustic hearing in the ear to be implanted. For these subjects, binaural performance was better than NH-only performance at 1, 3, and 6 mo postactivation, but it is difficult to know if this advantage was due to the CI or to residual acoustic hearing that might have been preserved after surgery. Unfortunately, unaided thresholds in the CI ear were not re-measured after implantation. Data from these subjects suggest that the CI benefit for localization may differ when compared with baseline binaural or to NH-only performance and may depend on the availability of acoustic hearing in the implanted ear.
Immediate (i.e., 1 mo postactivation) and significant CI benefits were observed for tinnitus VAS scores, relative to baseline measures or to postimplantation measures with the CI off (Table 8). Immediate and significant CI benefits were also observed for localization relative to NH-only performance after implantation; relative to baseline binaural performance, localization did not significantly improve until 6 mo postactivation (Table 4). As noted above, residual acoustic hearing in the ear to be implanted may have contributed to better baseline binaural localization.
The point of comparison strongly affected the degree of CI benefit for speech understanding in noise. Relative to binaural baseline, significant reductions in binaural SRTs were observed as soon as 1 mo postactivation for the S0N0 condition and 3 mo postactivation for the S0NNH condition (Table 6). However, relative to NH-only performance after implantation, there were no significant CI benefits for any of the spatial conditions. As noted above, NH-only performance was significantly better at 6 mo postactivation for the S0N0 condition; though not significant, improvements in mean NH-only SRTs were observed for other spatial conditions and test intervals (top panels in Fig. 4). The source of this variability in NH-only performance is unclear. It is possible that some procedural learning may have occurred. Alternatively, cochlear implantation may have reduced overall stress or tinnitus, even when the implant was off. Mertens et al. (2013) found that NH-only SRTs improved when the tinnitus in the contralateral ear was reduced by turning on the CI. In a related study, Mertens et al. (2015) found that median NH-only SRTs for S0N0 improved from −2.33 dB at 12 mo postactivation to −5.84 dB at 36 mo postactivation. In this study, NH-only SRTs were measured after a short period of adaptation after turning off the CI. Subjects generally reported that the tinnitus returned immediately after turning off the CI, but the tinnitus may not have returned to maximum levels.
Methodological Issues and Limitations to This Study
In this study, word and sentence recognition in quiet with the CI only (bottom right panels of Fig. 2) were measured in sound field using contralateral masking noise presented to the NH ear via insert earphone. Performance was 0% correct at baseline for both measures, suggesting that the 55 to 60 dB of contralateral masking noise was sufficient. Performance with the CI only was significantly and substantially better at 1, 3, and 6 mo postactivation. While the masking noise may have been sufficient to block the NH contribution to performance in sound field, it is unclear whether it may have affected CI-only performance. Continuous noise at a sufficient level in the NH ear may increase tinnitus or may have a central masking effect, either of which might affect CI-only performance.
When measuring localization and SRTs in noise with the NH ear only, the CI ear was plugged and muffed, which nominally provided 55 dB of attenuation. This was especially important for evaluating localization. As noted above, some subjects had small amounts of low-frequency hearing in the ear to be implanted (Table 3) that may have contributed to baseline localization, even with the plug and muff. It is unclear whether this acoustic hearing was preserved after cochlear implantation. Adequate attenuation of low-frequency hearing in the CI ear is needed to measure performance with the NH ear alone, which is important to fully characterize the CI benefit for localization.
We also attempted to measure SRTs in noise with the CI ear alone for the different spatial conditions. Unfortunately, plugging and muffing the NH ear was not sufficient to consistently reduce the contribution of the NH ear to CI-only performance, as performance with the CI ear alone was often comparable with that with the NH ear alone. Ideally, CI-only performance for SSD patients (and for bimodal CI patients) should be measured with direct connection to the CI processor (e.g., via direct audio input, or DAI). In such a scenario, it is important to calibrate the DAI to microphone input, and to disable mixing settings that blend some amount of the microphone input with the DAI signal. Such a calibrated DAI approach would be helpful to measure audiometric thresholds, everyday listening settings, and speech performance with the CI, which may be difficult to measure in sound field when there is substantial acoustic hearing.
The number of patients in this prospective FDA clinical trial (n = 10) somewhat limits the extent to which the findings can be generalized to the larger population. The inclusion criteria of normal hearing in the nonimplanted ear further limits generalizations; if patients with mild-to-moderate hearing loss were included, CI benefits would likely be larger, especially for speech perception in noise. Nonetheless, the present data show that the CI is safe for SSD patients, largely restores audibility and speech understanding in quiet to the deaf ear, greatly reduces tinnitus severity, greatly improves QoL, and significantly improves localization, with some improvements in speech understanding in noise under certain test conditions. These findings are line with many previous studies. As a clinical trial, these data should also encourage larger scale studies aimed at expanding indications for cochlear implantation to include SSD patients.
This prospective, longitudinal study provides a comprehensive view of CI benefits for SSD patients during the first 6 mo of implant use. Major findings include:
- All SSD patients benefitted from cochlear implantation in terms of localization, speech understanding, tinnitus severity, and QoL. The largest CI benefits were for tinnitus reduction and the smallest benefits were for speech understanding in noise.
- No surgical complications or serious adverse events were noted. Most AEs were resolved soon after surgery. No significant decrements in NH-only performance were noted after implantation, suggesting that the CI did not interfere with NH ear function.
- The degree and time course of CI benefit depended on the outcome measure and the reference point. Relative to baseline binaural measures, immediate benefits were observed for tinnitus severity and speech performance; localization did not significantly improve until 6 mo postactivation. Relative to NH-only performance after implantation, immediate benefits were observed for tinnitus severity and localization; however, no benefits were observed for speech performance in noise, due to the variability in NH-only performance. To more fully understand the benefits of cochlear implantation for SSD patients, both reference points should be considered.
- There were few correlations between behavioral and subjective outcome measures, suggesting that both are important to characterize the benefit of cochlear implantation for SSD CI patients.
The authors thank all the SSD patients who participated in this study. The authors thank Justin Aronoff and David Landsberger for their help with the initial design of this study, and Suzanne Gutierrez for coordination support during the study. The authors also thank three anonymous reviewers for helpful comments. MED-EL provided the cochlear implants and speech processors for the study, as well as support for research and publication costs.
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
Clinical trial; Cochlear implant; Dizziness; Localization; Single sided deafness; Speech; Quality of life; Tinnitus