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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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Keywords:Copyright © 2016 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company
Pediatric and adult cochlear implantation; Single-sided deafness