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Single-sided Deafness Cochlear Implantation

Candidacy, Evaluation, and Outcomes in Children and Adults

Friedmann, David R.; Ahmed, Omar H.; McMenomey, Sean O.; Shapiro, William H.; Waltzman, Susan B.; Roland, J. Thomas Jr.

doi: 10.1097/MAO.0000000000000951
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Objectives: Although there are various available treatment options for unilateral severe-to-profound hearing loss, these options do not provide the benefits of binaural hearing since sound is directed from the poorer ear to the better ear. The purpose of this investigation was to review our center's experience with cochlear implantation in such patients in providing improved auditory benefits and useful binaural hearing.

Study Design: Retrospective chart review.

Methods: Twelve adult patients and four pediatric patients with unilateral severe-to-profound hearing loss received an implant in the poorer ear. Outcome measures performed preoperatively on each ear and binaurally included consonant–nucleus–consonant (CNC) monosyllabic words and sentences in noise. The mean pure-tune average in the better ear was within normal range.

Results: Test scores revealed a significant improvement in CNC and sentence in noise test scores from the preoperative to most recent postoperative evaluation in the isolated implant ear. All adult subjects use the device full-time.

Conclusions: The data reveal significant improvement in speech perception performance in quiet and in noise in patients with single-sided deafness after implantation. Performance might depend on factors including length of hearing loss, age at implantation, and device usage.

Department of Otolaryngology–Head and Neck Surgery, NYU School of Medicine, New York, NY, U.S.A.

Address correspondence and reprint requests to David R. Friedmann, M.D., NYU Langone Medical Center, New York, NY 10016, U.S.A.; E-mail: drf249@nyumc.org

Invited article presented at Proceedings of 14th Pediatric CI Symposium, Nashville, TN, U.S.A., December 2014.

S.O.M., J.T.R., and W.H.S. are on the advisory boards for Cochlear Corp. J.T.R. is also on the advisory board for AB Corp. The remaining authors disclose no conflicts of interest.

Single-sided deafness (SSD) refers to an asymmetric condition in which a patient has one ear with severe-profound sensorineural hearing loss with normal hearing in the contralateral ear. The impact of unilateral hearing loss may be variable and considerations in children are different from those in adults. Nevertheless, they experience a substantial hearing deficit.

In typical listening situations, sound reaching one ear differs from the sound that reaches the opposite ear in two ways: because of the head shadow effect, there is a difference in the intensity of the sound at each ear and there is a variance between the times when the sound reaches each ear. One of the most important uses of these differences is to allow the listener to know the direction from which a sound, including speech, originates. Moreover, these abilities allow the listener to separate speech from background noise. Since the lack of ability to discriminate and understand speech in the presence of competing sounds reduces an individual's competence and effectiveness in personal and professional interactions, the loss of binaural hearing can significantly affect socioeconomic and quality-of-life functions.

Studies in children reveal that unilateral hearing impairment may negatively affect language development, social interactions, and academic performance (1,2). Some adults with postlingual SSD seem only minimally bothered by the loss and do not pursue further treatment, whereas others possibly related to occupational or social considerations seek assistive listening technologies.

Still the benefits of binaural hearing, especially in aiding with difficult listening situations, are clear and have been well described elsewhere for both normal hearing listeners (3) and those with bilateral cochlear implants (4). These include improved speech understanding in quiet and in noise, better localization, and the ability to hear at greater distances. In addition to the objective benefits of binaural hearing there are numerous subjective advantages including a more “balanced” and less tiring listening experience.

Most rehabilitative options for SSD route sound to the contralateral cochlea resulting in only unilateral auditory stimulation either with transmission via cross-routing of sound (CROS) amplification devices or osseointegrated devices such as bone anchored hearing aids (BAHA). Although both of these approaches provide the patients with some access to sound, the configurations do not restore hearing to the deaf ear but rather route the signals so that the benefits of binaural hearing are not maximally achieved as previously demonstrated (5). Even with such technology, improved hearing in difficult listening situations and the ability to localize sound remain elusive to most patients with SSD (6) and may actually make listening more difficult with certain signal-to-noise ratios incident on the unaffected ear. Cochlear implants for SSD were first introduced in the setting of intractable tinnitus (7), but have since been shown to have benefits far beyond tinnitus suppression (8,9).

Our purpose in this article was to review our institutional experience with selecting appropriate SSD pediatric and adult patients to receive a cochlear implant for various indications and their subjective and objective outcomes to date to determine if 1) there is a functional increase in word and sentence recognition in quiet and in noise and 2) the binaural advantage can be restored by placing a cochlear implant in the poorer ear.

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METHODS

Subjects

This retrospective chart review was approved by our institutional review board (IRB) and included 12 adult patients and 4 children with SSD. All patients had unaidable hearing in the affected ear. There were no strict hearing criteria in the better and all patients were evaluated on an individual basis but the average PTA in the better hearing ear was 12.7 (SD 7.0). All patients contributing data had at least 1 year of CI use.

See Table 1 for adult demographic factors. Most subjects were deaf as a result of sudden sensorineural hearing loss (SSNHL) (67%), and did not have any pathology in their normal hearing ear (83%). The PTA of the deaf ear among all subjects was 87.0 (SD 8.3). The mean age at diagnosis among adult patients with SSD was 47.3 years (SD 12.4) and on average they were implanted 3.1 years (SD 5.7) later. Eleven adult patients received Cochlear Nucleus (Englewood, CO, U.S.A.) devices and one received Advanced Bionics (Valencia, CA, U.S.A.) devices. All four children received Cochlear Nucleus devices. Intraoperatively, all patients had full insertions of the electrode array without perioperative or postoperative complications.

TABLE 1

TABLE 1

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Speech Perception

Patients were evaluated according to our institutional SSD protocol (Table 2). Before the availability of direct connect, a “plug and muff” technique was used to minimize/eliminate the role of better hearing ear (n = 4) in a sound-proof booth using recorded material. To ensure that the poor ear was completely isolated from the “good” ear on the nonimplanted side, the good ear was plugged and muffed using E.A.R. foam earplugs (3 M Co., St. Paul, MN, U.S.A.) and TASCO sound shield over-the-head earmuff Model #2900. (TASCO Corp, Riverside, RI, U.S.A.). For the plug, the mean attenuation for frequencies 125 to 8000 Hz was 42.3 dB with a noise reduction rating (NRR) of 29. The muff had a mean attenuation of 33.9 dB for frequencies 125 to 8000 Hz with an NRR of 29.

TABLE 2

TABLE 2

Later in our experience, a manufacturer-specific direct connect system to the cochlear implant sound processor was used to allow isolation of the CI ear for testing with an insert earphone in the unaffected ear. Direct connect (DC) audiometric testing (Cochlear Americas), via electrical cable connection, to the cochlear implant processor allows testing of each ear in isolation or together (binaurally) using tones or speech. This allows elimination of the inadvertent role of the better hearing ear in sound field testing and allows for hearing in noise testing with spatially separated competing signal and sound localization without the need for multispeaker arrays. The generalizability of this system has been validated elsewhere including precise timing and level cues (10–12). The signals are processed via a head-related transfer function (HRTF) so that it is equivalent to sound field presentation and the software provides calibration to ensure that the signals are delivered at the desired presentation levels.

Speech perception both pre- and postoperatively was measured in quiet using consonant–nucleus–consonant (CNC) words as well as AzBio sentences and administered at 60 dB A.

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Hearing in Noise

Hearing in background noise with various signal-to-noise ratios (SNR) was also tested with speech from the front and noise incident from the front, the better hearing ear, and the CI ear. Bamford–Kowal–Bench sentence-in-noise (BKB-SIN) (Etymotic Research 2005, Elk Glove Village, IL, U.S.A.) testing was administered for four adult subjects, whereas adaptive hearing in noise test (HINT) testing was administered for the remaining six adult subjects.

BKB-SIN is designed to assess sentence recognition in noise and consists of 36 lists of sentences presented in 4-talker babble noise. The sentences are presented at 65-dB SPL and the level of the noise is varied in 3 dB steps at fixed SNR beginning at +21 dB SNR (easy) descending to −6 dB SNR (hard) to obtain a speech reception threshold where the subjects can repeat key words 50% of the time (SNR-50); therefore, a lower score is indicative of better performance. The test was performed in the sound field in each ear individually and in the sound field in three conditions: speech front/noise front, speech front/noise right, speech front/noise left (n = 4) or using Direct Connect (n = 6) as noted above. Scores are indicated as dB SNR. In those patients tested in both sound field and using Direct Connect, results were found to be equivalent.

As DC was integrated into our evaluations, we began using adaptive HINT testing in place of BKB-SIN for evaluating hearing in noise sentences on all new patients as well as for subsequent evaluations of previously implanted patients.

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Localization

Localization testing was performed with the Direct Connect system as described above for five adult patients. A broadband noise from 1 of 12 virtual locations in the rear hemifield with locations numbered 1 through 12 on a response sheet, from right to left, and positioned to represent an arc from 97.5 degrees (on the right) to 262.5 degrees (on the left) with 15 degrees separations between source locations. The task involves a verbal response corresponding to the perceived location of the sound. Localization testing is reported as the degrees root mean squared (RMS) error.

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RESULTS

Adult Subjects, n = 12

Postoperative data were available for 10 adult patients (Table 3) as one transitioned care to another center whereas another was not a native English speaker. Data from most recent postoperative evaluation (3.4 yr ± 1.8) were used for performance comparison relative to preoperative data. Table 4 demonstrates individual subject outcomes data.

TABLE 3

TABLE 3

TABLE 4

TABLE 4

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Speech Perception

There was significant improvement in CNC word scores in the implanted ear with an average benefit of 54% (SE ± 8.4), p = 0.001 in seven adult patients who underwent this test. Improvement in sentence scores on AzBio in quiet relative to the SSD ear was on average 82.5% (SE ± 14.5); however, this was not statistically significant (p = 0.11) as there were only two matched pairs. Sound field and direct connect results were equivalent in all patients.

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Hearing in Noise

Speech-in-noise using binaural hearing BKB-SIN or adaptive HINT tests demonstrated that when noise was presented to the SSD/CI ear (speech front), the signal-to-noise ratio significantly decreased with an average reduction of 2.0 dB SNR (SE ± 0.8), p = 0.047 in nine adult patients tested. When noise was presented to the better hearing ear (speech front), the signal-to-noise ratio significantly decreased with an average reduction of 4.6 dB (SE ± 1.0), p = 0.005.

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Localization

No significant difference in sound localization was found when comparing preoperative data to 1-year postoperative data with regards to root mean square (RMS) error values (n = 4 matched pairs, p = 0.61). Furthermore, no difference was found when comparing preoperative data to postoperative data from more than 1 year after surgery (n = 2 matched pairs, p = 0.21).

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Subjective Assessment

All adult subjects were able to integrate the signal from the implanted ear (electrical) with the acoustic signal, without deterioration in speech understanding in their better hearing ear. All patients with tinnitus reported suppression since device activation.

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Pediatric Subjects (n = 4)

Our institutional experience consists of four pediatric SSD patients implanted to date. The first child was implanted at the age of 10, and is now 14 years old. She has enlarged vestibular aqueduct (EVA) and a long duration of deafness in her left ear. Preoperatively, she obtained 0% on CNC words in the effected ear alone. Her score at the 1-year post-op interval was 18% but has since dropped to 6% by year three. Concurrently, there has been a progressive decline in the nonimplanted ear alone from 98 to 80% at her most recent evaluation. At 3 months and 1 year, BKB-SIN scores were significantly improved in all three conditions compared with preoperative values, but have since declined to poorer than preimplant scores. Although she initially wore the device regularly, she now wears it only in school—though she does report subjective benefit during use as duly noted by her parents and teachers. Evidence from our experience with SSD patients after cochlear implantation is that although the quality of the auditory percept may not be acceptable, as they lose hearing in the nonimplanted hearing ear (as expected in patients of EVA, for example), they begin to better integrate and interpret the CI signal. This has not been the case to date with this patient as she has been wearing her device with less regularity over time. When questioned, she seems too focused over concern for her declining acoustic hearing to recognize the long-term benefit of using her implant more regularly.

The second pediatric impatient was implanted at the age of six and had PBK-word scores of 20%, HINT-Q was 76% and HINT-N was 49% in implant only condition at 3-months poststimulation. Bimodal scores were 100% showing that the signal was not being degraded by the addition of an electrical stimulus to the normal hearing ear. Interestingly, despite the apparent increase in performance, he only wears the CI in school and sometimes complains that it “bothers” the good ear. More recently, his father reports he has not worn his implant at all over the last few months. Of note, family dynamics seem to play a role in this patient's device use.

The third pediatric patient was 3 years old at the time of implantation. As of the 3-month postoperative evaluation, PBK-word scores were 96% with the nonimplanted ear alone and 32% with the implant alone. In the bimodal condition the word score was 96% attributable to the ceiling effect from having one normal hearing ear. Importantly, the combined signal did not cause a decrement in performance. On the sentence test, with noise-front she scored 100% in the nonimplanted ear, 70% with the CI alone, and 100% in the bimodal condition. Her father reports that the patient no longer asks where sound is coming from and responds better to sound in general.

Overall, the children demonstrated varying degrees of open-set speech perception in the implanted ear and bilateral improvement in the presence of background noise. However, these few children introduce some of the issues related to expectations after a prolonged duration of deafness and the impact of device use on performance.

Most recently, a family presented with their 6-month old who was diagnosed with sensorineural hearing loss. The family had done extensive research and asked many appropriate questions. At their request, the child underwent a cochlear implant evaluation at our center. After extensive counseling, the family elected to proceed with cochlear implantation, at the age of 11 months. There are not yet any postoperative data available.

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DISCUSSION

Perhaps the least understood aspect of unilateral hearing loss is determining if and when treatment is indicated. Some patients have to the ability to adapt well without any intervention. Although adults who have experienced postlingual SSD can endorse certain deficits or listening difficulties, the same cannot be assumed of children. Experience suggests that some children benefit from noninvasive interventions; however, determining optimal treatment and timing for a given patient remains a challenge. Some children and adults also overcome such deficits without intervention.

The other available treatment options for SSD do not restore hearing to the affected ear and hence, lack the advantages of binaural hearing that require sound to arrive at each ear independently for the processing of timing and pitch differences to be integrated by the brain. It should be noted that both the CROS and bone-anchored hearing aids may have undesirable effects in certain listening situations including hearing in noise, especially when noise is present on the side with the implant and may be routed to the better hearing ear, worsening the signal-to-noise ratio and making listening more difficult. Cochlear implants may overcome these issues, but should not be expected to restore all of the benefits of binaural hearing.

Studies such as our own on SSD CI are hampered by our inability to fully measure the efficacy of the treatment. Subjective improvement of localization and speech understanding in difficult listening situations in real-life situations with the addition of the second ear after implantation may actually be more important than our ability to quantify this with currently available tools and methods. It is possible that the tests currently being used are not sensitive enough to accurately reflect subjective patient reports until a certain level of competence is reached. As we move forward with evaluating SSD candidacy for cochlear implantation, it will be important to devise measurement tools that can better reflect the binaural advantage in the sound field in the presence of a normal or near-normal ear. Next we consider the factors that we use to consider candidacy for SSD CI on the basis of our experience so far.

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Candidacy Considerations

As observed in Table 1, our patients were diverse in their baseline characteristics including both demographics and audiometric characteristics. In some patients, the better hearing ear was in the normal range, but threatened in some way as in the case of an inner ear malformation predisposing to progressive hearing loss or as yet minimally symptomatic retrocochlear pathology in an only-hearing ear. Patients differed significantly in their motivating factors for pursuing cochlear implantation be it tinnitus suppression, trouble in difficult listening situations, or anticipated hearing loss in an only-hearing ear. Many more patients with SSD have been evaluated for cochlear implantation at our center and this experience has allowed us to define the following parameters for SSD CI candidacy.

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Absolute Indication: Late Stage Unilateral Ménière's Disease

Patients with late stage Ménière's disease may struggle with intractable vertigo from an ear essentially nonfunctional from an auditory perspective. With a simultaneous labyrnthectomy and ipsilateral cochlear implant, patients can have definitive treatment of their vertigo while bringing their “ear back to life” all during an outpatient ambulatory procedure. In 2013, Hansen et al. reported on the results of cochlear implantation in patients with Ménière's disease who progressed to profound sensorineural hearing loss with one ear. They reported significant improvement in word and sentence scores, though ability to localize sound in this cohort showed much more modest improvement (13). We have had similar experience with our cohort and we think this provides a hopeful option for patients who have often had years of suffering with their disease to both alleviate their vertigo and rehabilitate their hearing.

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Absolute Indication: An “At Risk” Only Hearing Ear

Though rare, a threatened only hearing ear, for example, an acoustic neuroma or other retrocochlear pathology, is an important consideration for a cochlear implant. These patients live in fear of the possibility of 1 day waking up suddenly deaf ill equipped to handle the communication challenges that arise and not having previous experience or need to comprehend manual communication. Depending on the etiology, these patients may still be candidates for CI after bilateral hearing loss, but pre-emptive implantation at an early age can limit the duration of deafness in the worse hearing ear and hence improve likely outcomes if the threatened ear is not viable for implantation.

Additionally, a cochlear implant can provide assurance that if and when the patient loses hearing in the threatened only hearing ear that they will not be completely “off line” with their cochlear implant. We have found this to be important in patients even in cases where the electric signal is not well integrated during the interval of persistent acoustic hearing as these patients quickly adapt to electric only hearing once further loss occurs.

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Absolute Indication: Pediatric Progressive Hearing Loss

Although criteria continue to be defined, cochlear implant candidacy for SSD is most favored in younger patients with progressive conditions such as enlarged vestibular aqueduct (EVA), genetic conditions, autoimmune inner ear disease, ototoxicity, and certain metabolic diseases. Since the good ear is likely to decline eventually, re-establishing hearing in the poorer ear avoids the untoward sequelae of long duration of deafness and total auditory deprivation.

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Counseling and Other Considerations

Just as in any family with children undergoing evaluation for a cochlear implant, an important part of the preoperative counseling includes ensuring patients and their families understand the range of possible outcomes as well as the considerable time and effort required for optimal performance with the device. Additionally, particular consideration should include discussion about subjective performance and progress over time, in addition to objective testing. An assessment of functional impairments may be more important than objective audiologic testing, most of which may be relatively normal with one hearing ear. For those children who are school age, one should inquire of the family whether they have noted difficulty in particular listening conditions, in social interactions, or in reports from teachers.

Another consideration is the very young child with SSD. With acknowledgement that some children with SSD grow up to be well-functioning adults and adapt well, these outcomes are difficult to predict. The developing brain is at maximal neuroplasticity at a young age and so a prolonged period of auditory deprivation may compromise ultimate auditory performance with treatment. By analogy to adults, there are some adults who have lived with SSD without perceived difficulty, whereas others have found it challenging and no factors have yet been identified to know which patients fall into which group. Unfortunately, attempting to clarify these unknowns introduces a paradox. Waiting until a child gets older may allow a better determination of the impact of the hearing loss on functioning and learning, but this wait introduces a longer duration of deafness, a negative relationship in predicting CI outcomes. A recent review of the experience in Freiburg, Germany, with pediatric SSD indicates that children with acquired hearing loss and a shorter duration of hearing loss outperformed those with a longer duration of SSD (14). It is important that the family understands all of these considerations when making the decision with the cochlear implant team.

Additionally, at this early stage of investigation, successfully obtaining financial reimbursement surrounding the surgery, the device and associated visits to the implant center represent an important obstacle to its wider adoption.

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Relative Contraindications

After a certain period of time, as yet undefined, one might expect the length of deafness to be too long for the benefits of cochlear implants to be realized. Until data clarify such a cut-off, implantation with proper counseling may be considered.

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CONCLUSIONS

SSD can have a significant impact on developmental spheres and various aspects of quality of life. An informed discussion to include all available therapies and their respective advantages and disadvantages with the family and CI team is essential to the decision-making process. Early experience with SSD CI recipients suggests that cochlear implantation, with appropriate preoperative assessment and counseling and postoperative management, may offer these patients the best opportunity to realize the benefits of binaural hearing. Although in our center, certain conditions seem like clear indications, further data will be necessary before this treatment modality is advocated more widely.

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REFERENCES

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Keywords:

Pediatric and adult cochlear implantation; Single-sided deafness

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