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Benefits of Cochlear Implantation for Single-Sided Deafness

Data From the House Clinic-University of Southern California-University of California, Los Angeles Clinical Trial

Galvin, John J. III1,2; Fu, Qian-Jie2; Wilkinson, Eric P.1,3; Mills, Dawna3; Hagan, Suzannah C.3; Lupo, J. Eric3; Padilla, Monica4; Shannon, Robert V.4

doi: 10.1097/AUD.0000000000000671
Clinical Trials
Open

Objectives: Cochlear implants (CIs) have been shown to benefit patients with single-sided deafness (SSD) in terms of tinnitus reduction, localization, speech understanding, and quality of life (QoL). While previous studies have shown cochlear implantation may benefit SSD patients, it is unclear which point of comparison is most relevant: baseline performance before implantation versus performance with normal-hearing (NH) ear after implantation. In this study, CI outcomes were assessed in SSD patients before and up to 6 mo postactivation. Benefits of cochlear implantation were assessed relative to binaural performance before implantation or relative to performance with the NH ear alone after implantation.

Design: Here, we report data for 10 patients who completed a longitudinal, prospective, Food and Drug Administration–approved study of cochlear implantation for SSD patients. All subjects had severe to profound unilateral hearing loss in one ear and normal hearing in the other ear. All patients were implanted with the MED-EL CONCERTO Flex 28 device. Speech understanding in quiet and in noise, localization, and tinnitus severity (with the CI on or off) were measured before implantation (baseline) and at 1, 3, 6 mo postactivation of the CI processor. Performance was measured with both ears (binaural), the CI ear alone, and the NH ear alone (the CI ear was plugged and muffed). Tinnitus severity, dizziness severity, and QoL were measured using questionnaires administered before implantation and 6 mo postactivation.

Results: Significant CI benefits were observed for tinnitus severity, localization, speech understanding, and QoL. The degree and time course of CI benefit depended on the outcome measure and the reference point. Relative to binaural baseline performance, significant and immediate (1 mo postactivation) CI benefits were observed for tinnitus severity and speech performance in noise, but localization did not significantly improve until 6 mo postactivation; questionnaire data showed significant improvement in QoL 6 mo postactivation. Relative to NH-only performance after implantation, significant and immediate benefits were observed for tinnitus severity and localization; binaural speech understanding in noise did not significantly improve during the 6-mo study period, due to variability in NH-only performance. There were no correlations between behavioral and questionnaire data, except between tinnitus visual analog scale scores at 6 mo postactivation and Tinnitus Functional Index scores at 6 mo postactivation.

Conclusions: The present behavioral and subjective data suggest that SSD patients greatly benefit from cochlear implantation. However, to fully understand the degree and time course of CI benefit, the outcome measure and point of comparison should be considered. From a clinical perspective, binaural baseline performance is a relevant point of comparison. The lack of correlation between behavioral and questionnaire data suggest that represent independent measures of CI benefit for SSD patients.

1Auditory Implants Department, House Ear Institute, Los Angeles, CA, USA

2Department of Head and Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, CA, USA

3House Clinic, Los Angeles, CA, USA

4Department of Otolaryngology-Head & Neck Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.

Received April 26, 2018; accepted September 5, 2018.

The authors have no conflicts of interest to disclose.

Address for correspondence: John Galvin, House Ear Institute, 2100 West Third Street, Suite 100, Los Angeles, CA, USA 90057. E-mail: jgalvin@hei.org

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INTRODUCTION

Adult patients with single-sided deafness (SSD) often experience poor sound source localization, reduced speech understanding in noise, reduced quality of life (QoL), and debilitating tinnitus (Van de Heyning et al., 2008; Vermeire & Van de Heyning, 2009; Beuchner et al. 2010; Arndt et al., 2011; Jacob et al., 2011). Noninvasive interventions include contralateral routing of signal (CROS), in which a microphone on the deaf side routes the acoustic signal to the contralateral hearing ear, and bone conduction devices (BCDs), in which a microphone on the deaf side stimulates the contralateral hearing ear via bone conduction. The CROS and BCD systems may improve speech understanding when speech is presented to the deaf ear. However, speech understanding may be reduced when noise is presented to the deaf ear due to the loss of head shadow benefit. Localization may be reduced as bilateral signals are mixed together and routed to a single ear. Neither system is effective for tinnitus relief, presumably because the deaf ear is not stimulated. While the CROS and BCD systems have been shown to provide some acoustic benefit in SSD patients (Faber et al., 2013), other studies have shown patient acceptance to be poor (Linstrom et al., 2009; Yuen et al., 2009; Martin et al., 2010).

Cochlear implantation has been shown to significantly improve localization, speech understanding in noise, and QoL, and significantly reduce tinnitus severity in adult SSD patients (e.g., Van de Heyning et al., 2008; Vermiere & Van de Heyning, 2009; Arts et al., 2012; Firszt et al., 2012; Cadieux et al., 2013; Nawaz et al., 2014; Tokita et al., 2014; Vlastarakos et al., 2014; Härkönen et al., 2015; Mertens et al., 2015, 2016ab, 2017; Távora-Vieira et al., 2013, 2015; Zeitler et al., 2015; Cabral Junior et al., 2016; Friedmann et al., 2016; Grossman et al., 2016; Hoth et al., 2016; Kitoh et al., 2016; Rahne & Plontke, 2016; Arndt et al., 2017; Dillon et al., 2017, 2018; Finke et al., 2017; Sladen et al., 2017abc). Cochlear implantation has also been shown to benefit pediatric SSD patients (e.g., Arndt et al., 2015; Sharma et al., 2016; Greaver et al., 2017; Polonenko et al., 2017; Sladen et al., 2017c; Thomas et al., 2017). Cochlear implants (CIs) have also been shown to be a better intervention for SSD patients than the CROS or BCD systems in terms of tinnitus relief, localization, QoL, and speech understanding in noise under some spatial conditions (Arndt et al., 2011; Tokita et al., 2014; Vlastarakos et al., 2014; van Zon et al., 2015). Because the CI stimulates the deaf ear, it allows for some restoration of binaural hearing. This is especially beneficial for localization and speech understanding when speech and noise are spatially separated. Stimulation of the deaf ear also appears to reduce tinnitus severity, though the mechanism of benefit is unclear.

Most of the above SSD CI studies were conducted in Europe. Early studies primarily targeted reduction of tinnitus severity via cochlear implantation. Later studies showed significant improvements in localization, speech understanding in noise, and QoL. While there are a number of SSD CI users in the United States, most have been implanted “off label” and CIs are currently not approved for SSD patients. Recently, there have been several Food and Drug Administration (FDA)–approved and investigator-initiated clinical trials for cochlear implantation in SSD patients in the United States. Clinical trials are necessary to demonstrate the risks and benefits of cochlear implantation for SSD patients. FDA approval would allow SSD patients in the United States to experience the benefits of cochlear implantation demonstrated in previous European studies.

In this study, we report the outcomes of an FDA-approved clinical trial “Cochlear Implants for Adults with Single-sided Deafness” (NCT02259192). This prospective, investigational device exemption study was a collaborative effort among the University of Southern California, the University of California, Los Angeles, and the House Clinic. The MED-EL Corporation provided the CI devices, covered all clinical expenses during the study, and provided research support. The primary objective of the study was device safety in terms of cochlear implantation and its effect on hearing function in the contralateral normal-hearing (NH) ear. Device safety was assessed in terms of the number of unexpected serious adverse events associated with the surgical procedure and everyday use of the CI. The effect of cochlear implantation on NH function was assessed by comparing baseline (before surgery) pure-tone average (PTA) thresholds across 0.5, 1.0, and 2.0 kHz in the NH ear to PTA thresholds 1, 3, and 6 mo after activating the CI speech processor; an increase in unaided PTA threshold >10 dB in the nonimplanted ear would indicate a hearing loss AE. The capacity of the CI to interfere with the NH ear was also assessed in terms of speech understanding in noise when speech and noise were presented directly in front of the subject. Speech understanding in noise was quantified as the speech reception threshold (SRT), defined as the signal-to-noise ratio (SNR) needed to produce 50% correct recognition of words in sentences in noise (Plomp & Mimpen, 1979). An increase in the SRT >4 dB in the NH ear alone at 6 mo postactivation (relative to the baseline) was deemed as substantial interference by the CI on NH ear function. In Nilsson et al. (1994), the 95% confidence interval for NH listeners was ±1.96 dB. It was unclear at the time of the study design how much this variability might increase for SSD patients. As such, a 4-dB decrement in the SRT in the NH ear was considered to be large enough to be outside of the potential variability across SSD subjects, test runs, and test intervals.

The study also included a number of secondary objectives. The efficacy of cochlear implantation for SSD patients was assessed in terms of clinical audiological measures (PTA thresholds, word and sentence recognition in quiet), localization, speech understanding in noise with and without spatial cues, tinnitus severity, and QoL. These longitudinal measures provided some estimate of the time course of adaptation to the CI. While previous studies with bilaterally deaf CI users have shown that most adaptation to electric hearing occurs during the first 3 to 6 months of CI use (Waltzman et al., 1986; Spivak & Waltzman, 1990; Holden et al., 2013; Sladen et al., 2017a), the time course of adaptation may be longer for SSD CI users (Mertens et al., 2017).

As noted above, many previous studies have shown benefits of cochlear implantation for SSD patients. In some studies, CI benefits were assessed relative to performance before implantation (e.g., Arndt et al., 2011; Punte et al., 2011; Kitoh et al., 2016; Dillon et al., 2017). In others, CI benefits were assessed relative to NH-only performance after implantation (e.g., Firszt et al., 2012; Mertens et al., 2015, 2017; Távora-Vieira et al., 2015; Grossman et al., 2016; Döge et al., 2017). In this study, CI benefits were assessed relative to each of these reference points over the study period. Different from some previous studies (e.g., Arndt et al., 2017; Mertens et al., 2015, 2017), patients were required to have normal hearing in the nonimplanted ear, which might limit CI benefits for some outcome measures, compared with patients with mild-to-moderate hearing loss in the nonimplanted ear. Finally, these data are from a prospective, longitudinal FDA clinical trial and as such, represent important evidence for consideration of revised indications for cochlear implantation for adult, postlingual, unilaterally deaf patients in the United States.

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METHODS

Subjects

Subjects were recruited from the House Clinic in Los Angeles CA, and in response to the study announcement on clinicaltrials.gov. Table 1 shows the inclusion and exclusion criteria for the study. Eleven SSD patients enrolled in the study. One patient withdrew before cochlear implantation because the patient decided to pursue a different CI device (rather than the MED-EL device, which was the only one available for this study). This left 10 subjects (5 male, 5 female) who completed the study. The mean age at implantation was 57.6 ± 10.3 years, and the mean duration of deafness was 3.2 ± 2.1 years. No subject had previous experience with CROS or BCD devices. Demographic information for the 10 subjects who completed the study is shown in Table 2. All subjects provided written informed consent, in accordance with the local institutional review board of record (St. Vincent’s institutional review board no. 14–019).

TABLE 1

TABLE 1

TABLE 2

TABLE 2

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Project Timeline

Figure 1 shows the project timeline for each subject. After screening patients for potential candidacy during standard clinical appointments, potential candidates were informed of the study and, if interested, were contacted to discuss the study further. If the subject wished to enroll in the study, informed consent was obtained in writing. An initial evaluation followed that included obtaining medical history, neuro-otological testing, videonystagmography (VNG) testing, administration of vaccines, computed tomography scan of the internal auditory canal, and a physical examination. Baseline audiological measures were also collected for each ear, including pure-tone thresholds and word and sentence recognition in quiet. If the subject met the candidacy requirements, the subject was scheduled for CI surgery within 6 mo of the audiological evaluation. During this time, baseline localization, speech understanding in noise, and tinnitus severity were measured; subjects also completed questionnaires relating to tinnitus, dizziness, and QoL. Approximately 1 mo after surgery, the CI processor was activated and audiological measures were re-collected. Audiology, localization, speech understanding in noise, and tinnitus severity were re-measured at 1, 3, and 6 mo postactivation of the CI; questionnaires were also re-administered at 6 mo postactivation. A neuro-otological examination and caloric VNG testing were performed at 6 mo postactivation.

Figure 1

Figure 1

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Audiological Measures

To determine candidacy (and to serve as baseline measures after enrollment in the study), air conduction and bone conduction pure-tone thresholds were measured for each ear at 0.125, 0.25, 0.5, 1.0, 2.0, 4.0, and 8.0 kHz. Inclusion criteria were PTA thresholds across 0.5, 1.0, and 2.0 kHz ≥70 dB HL in the ear to be implanted, and PTA thresholds ≤25 dB HL in the NH ear with no audiometric frequency ≥35 dB HL. Speech audibility thresholds (SATs) in quiet were also measured. Recognition of Hearing in Noise Test (HINT; Nilsson et al., 1994) sentences and consonant-nucleus-consonant (CNC; Peterson and Lehiste, 1962) words was measured in quiet at 60 dBA. The HINT sentences, rather than AzBio sentences, were used because at the time of the original development and submission of this study (in 2011), the AzBio sentences had not yet been validated (Spahr et al., 2012) and HINT sentences were still used as part of the standard clinical evaluation for CI candidacy. Inclusion criteria were HINT sentence recognition ≤40% correct in the ear to be implanted, and HINT and CNC word recognition ≥80% correct in the NH ear.

For baseline measures, audiometric thresholds and SATs were measured using ER3A insert earphones; to measure performance in the ear to be implanted, 40 dB contralateral masking noise was delivered to the NH ear. Baseline word and sentence recognition were measured in sound field; to measure performance in the ear to be implanted, 55–60 dB of masking noise was delivered to the NH ear via insert earphone. After activating the speech processor, audiological measures were re-collected separately for the NH ear and CI ear (aided). Note that unaided thresholds with the CI ear were not collected after implantation.

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Sound Source Localization

Localization was measured in sound field using a 12-speaker array and stimuli and methods similar to Chan et al. (2008). Localization was measured before CI surgery and again at 1, 3, and 6 mo postactivation. Performance was measured with NH ear alone and with both ears (binaural). To reduce potential contributions of contralateral low-frequency acoustic hearing in the CI ear, the CI processor was turned off and the CI ear was plugged (Hearos extreme protection series; NRR = 33) and muffed (Dave Clark model 27/27S; NRR = 22 dB), which when combined nominally provided 55 dB of attenuation. Note that in the binaural baseline condition, the ear to be implanted was not plugged or muffed.

Loudspeakers were at ear level and spaced 15 degrees apart behind the subject, and spaced 1 m from the center of the subject’s head. The stimulus was a broadband impulse sound (gunshot) presented at 65 dBA; the presentation level from trial to trial was roved by 6 dB to reduce the availability of loudness cues for localization. Before formal testing in each condition, subjects were given a preview playing the stimulus from each of 12 sound source locations in order. During testing, a sound source (loudspeaker) was randomly selected (without replacement), and the stimulus was delivered from that source. The subject responded by clicking on one of the loudspeakers shown on a computer screen that mirrored the speaker locations, after which a new stimulus was presented. Subjects were instructed not to move their head during testing. Stimuli were presented twice from each sound source (24 trials in each test block). Localization accuracy was quantified in terms of root mean square error (RMSE). A minimum of two test runs were conducted for each listening condition; if the difference in RMSE between the two test runs was greater than 10 degrees, a third test run was conducted. The mean RMSE was calculated across test runs.

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Speech Understanding in Noise

Speech understanding in noise was measured in sound field, with and without spatial cues. Speech performance was measured before CI surgery and again at 1, 3, and 6 mo postactivation. Performance was measured with NH ear alone (CI off, CI ear plugged and muffed) and with both ears (binaural). Speech (S) was always presented directly in front of the listener. Noise (N) was presented to the CI ear (S0NCI), in front of the listener (S0N0), or to the NH ear (S0NNH). Note that in the binaural baseline condition, the ear to be implanted was not plugged or muffed.

Speech understanding in noise was quantified in terms of the SRT. Speech materials consisted of HINT sentences produced by a single male talker (Nilsson et al., 1994); steady state noise was filtered to match the spectrum across all sentences. The SRT were adaptively measured by adjusting the noise level according to the correctness of the response using Rule 3 from Chan et al. (2008). During each test run, a sentence was randomly selected (without replacement) from the 260-item stimulus set and presented from the front speaker at 60 dBA; noise was presented at the target SNR to one of the three loudspeakers, depending on the spatial condition. The initial target SNR was 0 dB for the S0NCI condition and 6 dB for the S0N0 and S0NNH condition. If the subject repeated 50% or more of the words correctly, the noise level was increased by 2 dB; if the subject repeated less than 50% of the words correctly, the noise level was reduced by 2 dB. The final six reversals in SNR were averaged as the SRT. A minimum of two runs were completed for each listening and spatial condition. If the difference in SRTs between the first two runs was more than 2 dB, a third SRT was measured. SRTs were averaged across test runs.

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Tinnitus Severity

Tinnitus severity was measured using a visual analog scale (VAS) with the CI on and off, as in previous SSD CI studies (Van de Heyning et al., 2008; Punte-et al., 2011). Tinnitus VAS scores were collected at baseline (before CI surgery) and at 1, 3, and 6 mo postactivation. Subjects were asked to mark the tinnitus severity on a 10-cm line anchored with the extreme labels “No tinnitus at all” and “Worst tinnitus imaginable.” For the CI off condition, subjects were given approximately 30 min to acclimate to NH-only listening, which allowed time for the tinnitus (which is often reduced while wearing the CI) to recover in intensity. Subjects anecdotally reported that the tinnitus returned to baseline levels within a few minutes of turning off the CI.

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Questionnaires

To estimate the impact of cochlear implantation on SSD patients’ everyday life, a number of questionnaires were administered before implantation and 6 mo postactivation, including:

  • Tinnitus Functional Index (TFI). The TFI (Meikle et al., 2012) is a validated subjective, self-reported rating of the impact of tinnitus on patients’ everyday life over the previous 10 days. The TFI contains 25 questions, each of which is answered on a 10-point scale. A score of 100 indicates maximum tinnitus severity and impact and a score of 0 indicates no tinnitus.
  • Dizziness Handicap Inventory (DHI). The DHI (Jacobsen and Newman, 1990) is a validated, self-reported rating of the impact of dizziness on a respondent’s everyday life. The DHI contains 25 questions that the respondent must answer according to “Never” (0 points), “Sometimes” (2 points), and “Always” (4 points). A score of 100 indicates maximum dizziness severity and impact and a score of 0 indicates no dizziness.
  • Speech, Spatial, and Qualities of Hearing scale (SSQ). The SSQ was originally developed as an assessment tool for hearing aid fitting and associating hearing impairment with the subjective level of disability (Gatehouse and Noble, 2004). The 50-item questionnaire assesses the respondent’s perceptual abilities for three subtests: Speech, Spatial, and Quality. Each question is answered according to a 10-point scale, and the scores were averaged within each subtest, resulting in a range from 0 (poorest) to 10 (best).
  • Glasgow Hearing Aid Benefit Profile (GHABP). The GHABP (Gatehouse, 1999) consists of several questions each associated with four general and two patient-specified listening situations (Personal Issue 1 and Personal Issue 2). Responses range from 0 to 5. The GHABP was administered only at 6 mo postactivation because most of the questions were related to the effect of the CI on the listening situation.
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RESULTS

Safety

All subjects were implanted without major surgical complications. Full insertion of the electrode array was reported in all subjects. Adverse events were reported in 5 of the 10 subjects. S1 experienced facial nerve stimulation on several electrodes at loud but comfortable levels. This was resolved during mapping by increasing the pulse duration. Subject S3 experienced periorbital edema that resolved spontaneously a few days postoperatively. Subject S5 experienced mild postoperative balance disturbance that persisted for several weeks but resolved spontaneously. Subject S8 reported postauricular pain as a result of wearing the Sonnet processor. Moleskin was added to the area of the processor that was producing the discomfort; however, the subject continued to report pain after prolonged use. Four months postactivation and approximately 2 mo before protocol requirements, she was fit with the Rondo in an effort to allow the subject to comfortably and consistently use her CI; this resolved the issue. Subject S10 reported taste disturbance that had not yet been resolved at his most recent medical follow-up at 6 mo postactivation.

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Audiology

Figure 2 shows boxplots of PTA thresholds, SATs, CNC word recognition scores in quiet, and HINT sentence recognition scores in quiet with the NH ear and the CI ear, as a function of test interval. Table 3 shows baseline audiometric thresholds for the ear to be implanted. Baseline preoperative PTAs and HINT scores for the CI ear were all within the inclusion criteria. The mean improvement for CNC word recognition relative to baseline was 66.8, 76.0, and 84.0 percentage points at 1, 3, and 6 mo postactivation, respectively. The mean improvement for HINT sentence recognition in quiet relative to baseline was 36.4, 40.7, and 51.1 percentage points at 1, 3, and 6 mo postactivation, respectively. A two-way repeated-measures analyses of variance (RM ANOVA) was performed for each audiological outcome measure, with ear (NH, CI) and test interval (baseline, 1, 3, and 6 mo postactivation) as factors; complete results are shown in Table 4. For all outcome measures at all intervals, NH performance was significantly better than CI performance (p < 0.05 in all cases). For all outcome measures, there was no significant difference in NH performance across test intervals (p > 0.05 in all cases). For all outcome measures, CI performance at 1, 3, and 6 mo postactivation was significantly better than baseline (p < 0.05 in all cases), with no significant difference among postactivation test intervals (p > 0.05 in all cases).

TABLE 3

TABLE 3

TABLE 4

TABLE 4

Figure 2

Figure 2

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Localization

The top two panels in Figure 3 show RMSE in localization with the NH ear alone (left) and with binaural listening (right), as a function of test interval. The bottom two panels show the change in RMSE with binaural listening relative to performance with the NH ear alone at each interval postactivation (left), or relative to baseline binaural performance (right); values <0 indicate better performance after cochlear implantation. Relative to the NH ear alone, mean RMSE was reduced by 15.1, 14.0, and 18.2 degrees at 1, 3, and 6 mo postactivation, respectively. Relative to binaural baseline, mean RMSE was reduced by 6.7, 7.6, and 11.5 degrees at 1, 3, and 6 mo postactivation, respectively. A two-way RM ANOVA was performed on the localization data, with listening condition (NH, binaural) and test interval (baseline, 1, 3, 6 mo postactivation) as factors; complete results are shown in Table 5. There was no significant difference in localization with the NH ear alone across test intervals (p > 0.05 in all cases). Binaural performance was significantly better than with the NH ear alone at 1, 3, and 6 mo postactivation (p < 0.05 in all cases). Binaural performance was significantly better than binaural baseline only at 6 mo postactivation (p < 0.05).

TABLE 5

TABLE 5

Figure 3

Figure 3

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Speech Understanding in Noise

The top panels in Figure 4 show SRTs with the NH ear alone and the bottom panels show SRTs with binaural listening for each spatial condition, as a function of test interval. The top panels in Figure 5 show the change in SRTs with binaural listening relative to the NH ear alone at 1, 3, and 6 mo postactivation; the bottom panels in Figure 5 show the change in SRTs with binaural listening relative to binaural baseline. Values <0 indicate better performance after cochlear implantation.

Figure 4

Figure 4

Figure 5

Figure 5

Two-way RM ANOVAs were performed on the SRT data for each spatial condition, with listening condition and test interval as factors; complete results are shown in Table 6. Relative to binaural baseline, there was no significant improvement in binaural SRTs for S0NCI across test sessions; binaural SRTs were significantly better at 1, 3, and 6 mo postactivation for S0N0 (p < 0.05 in all cases), and significantly better at 3 and 6 mo postactivation for S0NNH (p < 0.05 in both cases). Relative to the NH-only performance after cochlear implantation, there was no significant improvement in SRTs for any test interval or spatial condition (p > 0.05 in all cases). Note that NH-only SRTs significantly improved at 6 mo postactivation, relative to baseline, which may have contributed to the improved binaural performance.

TABLE 6

TABLE 6

The top panels of Figure 5 also show binaural squelch (re: CI ear), summation, and head shadow (re: CI ear) for 1, 3, and 6 mo postactivation. One-way RM ANOVAs were performed on binaural squelch (re: CI ear), summation, and head shadow (re: CI ear), spatial release from masking (SRM) relative to the NH ear and to the CI ear, with test interval (baseline, 1, 3, and 6 mo postactivation) as the factor; complete results are shown in Table 7. There was no significant effect of test interval for head shadow, squelch, summation, or SRM (p > 0.05 in all cases).

TABLE 7

TABLE 7

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Tinnitus Severity VAS

The top panels in Figure 6 show tinnitus severity VAS scores with the CI off (left) and the CI on (right), as a function of test interval. The bottom panels in Figure 6 show the change in VAS scores with the CI on, relative to the CI off at each test interval postactivation (left), or relative to the baseline score with the CI off (right); values <0 indicate reduced tinnitus with the CI on. A two-way RM ANOVA was performed on the VAS data, with listening condition (CI off, CI on) and test interval as factors; complete results are shown in Table 8. The VAS scores were significantly lower with the CI on than with the CI off at 1, 3, and 6 mo postactivation (p < 0.05 in all cases). The VAS scores were also significantly lower with the CI on 1, 3, and 6 mo postactivation than with the CI off at baseline (p < 0.05 in all cases).

TABLE 8

TABLE 8

Figure 6

Figure 6

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Tinnitus Functional Index (TFI)

The top left panel of Figure 7 shows boxplots of TFI scores before implantation and 6 mo postactivation. The mean TFI scores was reduced by 22.9 points. A one-way RM ANOVA was performed on the TFI data, with test interval (baseline, 6 mo postactivation) as the factor; complete results are shown in Table 9. The TFI scores were significantly lower 6 mo postactivation (p = 0.010).

TABLE 9

TABLE 9

Figure 7

Figure 7

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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).

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SSQ

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).

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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).

Figure 8

Figure 8

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.

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Correlational Analyses

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)

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DISCUSSION

Safety

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.

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Audiology

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).

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Tinnitus Severity

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.

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Localization

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.

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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.

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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.

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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.

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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.

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CONCLUSIONS

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.
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ACKNOWLEDGEMENTS

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:

Clinical trial; Cochlear implant; Dizziness; Localization; Single sided deafness; Speech; Quality of life; Tinnitus

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