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Buss et al. (2008) evaluated 26 postlingually deafened adult patients who were followed up for 1 year. Patients received Cochlear Implants - Commercial Medical Management Guideline MED-EL COMBI 40+ devices bilaterally. Benefits of bilateral electrical stimulation were observed under conditions in which the speech and masker were spatially coincident and conditions in which they were spatially separated. Both the "head shadow" and "summation" effects were evident from the outset. Benefits consistent with "binaural squelch" were not reliably observed until 1 year after implantation. The investigators concluded that the study results support a growing consensus that bilateral implantation provides functional benefits beyond those of unilateral implantation. Longitudinal data suggest that some aspects of binaural processing continue to develop up to 1 year after implantation. The squelch effect, often reported as absent or rare in previous studies of bilateral cochlear implantation, was present for most subjects at the 1 year measurement interval.
Verschuur et al. (2005) demonstrated that bilateral cochlear implantation (Nucleus 24 device) in 20 patients provided significant improvement in horizontal plane localization abilities compared with unilateral cochlear implant use.
Schleich et al. (2004) investigated the impact of bilateral cochlear implant use on speech perception in noise in bilateral users of the MED-EL COMBI 40/40+ cochlear implants. Speech reception thresholds were measured in 21 subjects (20 were post-lingually deafened, 1 pre-lingually) using the Oldenburg sentence test. The 18 subjects from whom a complete data set could be obtained showed a significant head shadow effect and summation effect for all test conditions, whereas the squelch effect was significant for noise from the left side only. Effect sizes were not correlated with duration of deafness.
A prospective case-control study was conducted on 23 bilateral cochlear implant patients with the Mark III health utility index. This study found an improvement in quality of life and a favorable cost-utility associated with bilateral cochlear implantation in patients with profound hearing loss. These patients showed additional improvements in quality of life after they received their second implant. (Bichey and Miyamota, 2008) Dunn et al. (2008) compared speech recognition and localization performance of patients who wear bilateral cochlear implants (CICI) with patients who wear a unilateral cochlear implant (true CI-only). A total of 73 subjects participated in this study. The study results demonstrated significantly greater benefit on words and sentences in quiet and localization for listeners using two cochlear implants over those using only one cochlear implant.
Grantham et al. (2007) evaluated 22 adults, all postlingually deafened who were bilaterally fitted with MED-EL COMBI 40+ cochlear implants and were tested in a modified source identification task. Subjects with bilateral cochlear implants localized sounds in the horizontal plane when using both of their devices, but they generally could not localize sounds when either device was deactivated.
Nopp et al. (2004) investigated sound localization with bilateral and unilateral cochlear implants in 20 bilaterally implanted MED-EL COMBI users and found that bilateral cochlear implants offer a substantial benefit in sound localization to late-deafened, late-implanted subjects.
Ricketts et al. (2006) compared speech recognition in noise for bilateral and unilateral modes within 16 postlingually deafened, adult bilateral cochlear implant recipients. The results of study demonstrated a small but significant bilateral speech-recognition-in-noise advantage for cochlear implant recipients in an environment with multiple noise sources.
There is minimal data in peer-reviewed medical literature regarding the use of bilateral cochlear implants for prelingual bilateral sensorineural hearing loss in adults. Well-designed studies are needed to evaluate the potential advantages of bilateral cochlear implants and to identify which patients would benefit from this procedure.
Bilateral Cochlear Implantation in Children Hayes also reviewed studies evaluating bilateral CI in children with pre- or perilingual bilateral hearing loss. (Hayes,
2007) Ages of the children enrolled in the studies varied from under 1 year of age to over 16 years, and sample size
Cochlear Implants - Commercial Medical Management Guideline
varied from 11 to 39. Kuhn-Inacker al. (2004) studied sequential bilateral CI in 39 children, who were then followed for a period of 6 to 24 months. In this study, most children demonstrated better word discrimination in the bilateral condition, compared with monaural, although intensive training was required to achieve acceptable performance of the second CI.
The older children and those with a longer interval between first CI and second CI required more training than younger children or those with a short interval between implants. This study is limited by relatively small sample size, variable duration of follow-up, and heterogeneity in patient characteristics.
Galvin et al. (2007) studied 11 children who had previously undergone unilateral CI and were then implanted with a second CI several years later. At 6 months after the second CI, 8/10 patients showed benefit in speech perception when noise was presented ipsilateral to the first implant, with no benefit when noise was contralateral to the first implant. None showed a significant difference in sound localization for bilateral versus monaural CI, and the improvement in overall functionality was questionable. This study was limited by the very small sample size and short duration of follow-up.
Peters et al. (2007) reported on a prospective multicenter study of sequential bilateral CI in 30 children, age 3 to 13 years, who had received their first CI before 5 years of age. Results were stratified by age at time of second CI. While all age groups demonstrated improved speech perception with bilateral CI, younger patients appeared to receive more benefit and the performance of the ear that received the first CI showed improvement, in addition to the overall improvement in speech perception found in the bilateral mode. However, definite conclusions regarding the effect of age cannot be drawn from the small numbers of patients in each age group.
Scherf et al. (2007) also investigated sequential bilateral CI in children (n=33); 17 were younger than 6 years of age at second CI, while 16 were older. All children in this study had significantly higher hearing thresholds in the bilateral condition compared with either unilateral condition, and speech recognition scores in quiet were superior in the bilateral condition. However, in the noise condition, the second CI provided a benefit only in the younger age group. This report provided results from testing at 18 months after second CI; this study is still ongoing and may eventually provide longterm follow-up on these children.
Wolfe et al. (2007) reported on a retrospective case series of bilateral sequential CI in 12 children who had undergone first CI at or before 3 years of age. All patients showed improvement in speech recognition in noise in the bilateral condition at 12 months after activation of the second CI. The very small sample size of this study and limited reporting of test results precludes definitive statements about the overall benefit of bilateral CI in children.
Litovsky et al. (2006b) evaluated the functional benefits from bilateral stimulation in 20 children ages 4-14; 10 used two CIs and 10 use one CI and one hearing aid. Results show that both groups perform similarly when speech reception thresholds are evaluated. However, there appears to be benefit (improved minimum audible angle (MAA) and speech thresholds) from wearing two devices compared with a single device that is significantly greater in the group with two CI than in the bimodal group.
Litovsky et al. (2006c) evaluated localization acuity in 13 children with prelingual deafness who received bilateral cochlear implants and 6 children with a cochlear implant and a hearing aid in the nonimplanted ear. The results of the study demonstrated that many children perform better on measures of localization acuity with bilateral implants compared with children using the cochlear implant plus a hearing aid. However, the investigators indicated that these results should be interpreted with caution because the long-term benefits of bilateral cochlear implants are not yet fully understood.
According to a Hayes review (Hayes, 2007), data from studies suggest that compared with unilateral CI, bilateral CI led to improvement in speech perception and sound localization in noise conditions in most of the adults and many of the children who underwent either simultaneous or sequential bilateral implantation. However, intensive training can be required to achieve these benefits, response was variable, and one study (Summerfield et al., 2006) reported a negative or
Cochlear Implants - Commercial Medical Management Guideline
neutral impact on QOL measures. Additionally, it was difficult to determine if the improvements reported under the test conditions translated into functional improvements in daily activities involving conversations in a variety of setting.
Although small sample sizes and short duration of follow-up in most of these studies preclude definitive statements about bilateral CI, the data suggest that results are best when there is a short interval between the first and second implantation, and younger children seem to attain more benefit than do older children.
The following studies were not reviewed by Hayes:
Grieco-Calub et al. (2008) evaluated two groups of children with chronological ages ranging from 26 to 36 months: 1) children with normal hearing (n = 8) and 2) children with severe-to-profound sensorineural hearing loss (n = 18). Of the children who are deaf, 10 used bilateral CIs, and 8 used unilateral cochlear implants. Preliminary results show that localization acuity is emerging in toddlers with bilateral CIs but not in toddlers with unilateral cochlear implants.
Beijen et al. (2007) compared 5 bilaterally implanted children (mean age at testing, 3 yr 7 mo) with 5 unilaterally implanted children (mean age at testing, 5 yr 3 mo). Meningitis was the cause of deafness in all of the children. The bilaterally implanted children had significantly better scores on the localization test than the children with unilateral cochlear implants. The scores of the children with bilateral cochlear implants were also significantly higher on the spatial domain of the Speech, Spatial and Qualities of Hearing Scale (SSQ), which concerns localization. No significant differences were found in the speech and quality of hearing domains and the total scores on the SSQ between the two groups.
According to a systemic evidence review of 37 studies conducted by Murphy and O'Donoghue (2007), the available evidence indicates that bilateral cochlear implantation confers material benefits not achievable with unilateral implantation, specifically in terms of sound localization and understanding of speech in noise. However, well-designed prospective studies of sufficient size are needed to precisely quantify these benefits, to validate outcome measures, especially in children, and to define the criteria for intervention.
Longitudinal data demonstrate the beneficial effects of cochlear implantation in improved access to mainstream educational settings for implanted children with severe-to-profound sensorineural hearing loss. (Beadle et al., 2005;
Cheng et al., 2000; Francis et al., 1999) In a retrospective review, 43 children (age, less than 18 years) and 22 adults underwent sequential bilateral implantation with at least 6 months between surgeries. Study results revealed sequential bilateral implantation leads to significantly better speech understanding. On average, patients improved, despite length of deafness, time between implants, or age at implantation. (Zietler et al., 2008) Schafer et al. (2007) used a meta-analytic approach to examine sixteen peer-reviewed publications related to speechrecognition performance in noise at fixed signal-to-noise ratios for participants who use bilateral cochlear implants (CIs) or bimodal stimulation. Two hundred eighty-seven analyses were conducted to compare the underlying contributions of binaural summation, binaural squelch, and the head-shadow effect compared to monaural conditions (CI or hearing aid).
The analyses revealed an overall significant effect for binaural summation, binaural squelch, and head shadow for the bilateral and bimodal listeners relative to monaural conditions. In addition, all within-condition (bilateral or bimodal) comparisons were significant for the three binaural effects, with the exception of the bimodal condition compared to a monaural CI. No significant differences were detected between the bilateral and bimodal listeners for any of the binaural phenomena.
National Institute for Health and Clinical Excellence (NICE) NICE has published guidance on the use of cochlear implants for severe to profound deafness in children and adults.
Unilateral cochlear implantation is recommended as an option for those with severe to profound deafness who do not receive adequate benefit from acoustic hearing aids. Simultaneous bilateral cochlear implantation is recommended as an
Cochlear Implants - Commercial Medical Management Guideline