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The speech perception skills during the first year of cochlear implant use improved significantly in the postlingually deafened children but progressed at a slower rate in prelingually deafened children. However, speech perception and speech production continued to improve in both groups over a 5-year follow-up, and some prelingually deafened children attained comparable or better speech understanding than postlingually deafened children.
While prelingual deafness is generally defined as loss of hearing before the acquisition of speech, there appears to be no consensus regarding a specific cutoff age, as it has been alternatively defined as onset of hearing loss before the age of 2 years, (Osberger et al., 1999) 3 years, (Nikolopoulos et al, 2004) or 6 years. (Quigley et al., 2000) If using the age of 3 years as the cutoff to distinguish prelingual from postlingual hearing loss, some data from the Nijmegen experience may apply to postlingually deafened children. Makhdoum et al. (1997) briefly reported their own experience at the St.
Radboud University Hospital (Nijmegen, The Netherlands) with 16 pediatric cochlear implantation recipients who acquired profound deafness at the age of 0.3 to 1.9 years (n=5), 2.0 to 2.9 years (n=6), or 3 years or older (n=5) and were compared with a large (number not reported) reference group of age-matched severely and profoundly deaf children who used hearing aids and were tested with the same speech perception test battery. Preoperatively, all of the cochlear implantation groups demonstrated poor speech perception scores that were equivalent to those obtained in children in the reference group who had a hearing loss greater than 125 dB. During follow-up, all of the cochlear implantation groups showed remarkable improvement, with the greatest improvement observed in the group acquiring deafness at age 3 years or older. At the 3-year follow-up, the 3 cochlear implantation groups, respectively, attained speech perception scores that were equivalent to those obtained in children in the reference group who had a hearing loss of 97, 78, and 72 dB. These limited data suggest that cochlear implantation in postlingually deafened children is likely to lead to improvements in speech perception and speech production that initially are greater and occur more rapidly than those in prelingually deafened children but subsequently may be comparable with those in prelingually deafened children. However, additional studies are required to demonstrate efficacy of cochlear implantation in this patient population.
American Speech-Language-Hearing Association (ASHA): According to a technical report approved by the ASHA, both prelingually and postlingually deafened children are candidates for cochlear implantation if they receive limited benefits from conventional amplification. (ASHA, 2004) Unilateral Cochlear Implantation in Children with Prelingual or Perilingual Hearing Loss Overall, clinical studies indicate that in children with prelingual perilingual hearing loss, cochlear implantation is likely to lead to significant and rapid improvement in speech perception and speech production and more gradual but progressive improvement in complex language/grammar in most cases. (Hocevar-Boltezar et al., 2005; Anderson et al., 2004; Calmels et al., 2004; Manrique et al., 2004) However, cochlear implantation results are variable; are likely to be significantly better with earlier versus later cochlear implantation, shorter versus longer duration of deafness, and oral versus total communication before cochlear implantation; but also may be influenced by other factors such as preimplant residual hearing, learning style, family structure/support, or cochlear implantation coding strategy.
Francis et al. (2004) demonstrated that outcomes with cochlear implantation after childhood meningitis can be highly positive provided that central nervous system effects of the meningitis are considered in designing the program of postimplant rehabilitation.
Cochlear Implants - Commercial Medical Management Guideline
Unilateral Cochlear Implantation in Children with Auditory Neuropathy: Auditory neuropathy describes an unusual form of sensorineural hearing loss where the outer hair cells are intact and functioning but the auditory nerves or inner hair cells are not. Otoacoustic emissions are present and recordable but the auditory brainstem response is absent. Providing a cochlear implant to some of these children has resulted in significant improvement in hearing and speech recognition.
(Jeong et al., 2007; Rance and Barker, 2008; Vlastarakos et al., 2008) Most of the available studies were small and uncontrolled. Larger studies are needed to determine optimal treatment for children with auditory neuropathy.
Bilateral Cochlear Implantation in Adults According to a Hayes review (Hayes, 2007), most studies involving bilateral CI were prospective case series studies and had small sample sizes, and, in most patients, bilateral CI was sequential such that performance after the second CI was compared with previous performance with a single CI. Most studies used a repeated measures study design such that each patient served as his or her own control after the second CI was implanted. The exception to this was the study by Summerfield et al. (2006) in which adult patients with a single CI were randomized to receive a second CI or to a 12month waiting period for second CI, thereby allowing comparison between the two groups. Interval between first and second CI varied substantially within and among studies, as did age at second CI. In the studies that included adults, most were postlingually deafened, whereas the pediatric studies generally involved children who were pre- or perilingually deafened.
Six of the reviewed studies evaluated bilateral CI in adults with postlingual hearing loss; one study was published in two different reports due to evaluation of different outcome measures in each report (Ramsden et al., 2005; Summerfield et al., 2006). This study included a randomized component that allowed for evaluation of quality of life (QOL) measures in patients with bilateral CI versus those with unilateral CI, reported by Summerfield et al. (2006). The study involved 28 adults who had been using a unilateral CI successfully for up to 6 years and who were candidates for a second CI.
Patients were randomly assigned to receive a second implant immediately (n=13) or to wait for a year before receiving the second CI (n=15). Questionnaires were used to assess sound localization and quality, impact of the second CI on ability to participate in conversation in noise, and QOL measures. At the 9-month follow-up, self-reported measures of spatial hearing, quality of hearing, and hearing for speech were significantly better for the bilaterally implanted group than for those in the wait group. However, QOL measures showed no significant improvement, and some of the patients who had received the second implant had lower QOL scores, possibly due to an increase in tinnitus.
In the same population of patients reported by Summerfield et al. (2006), Ramsden et al. (2005) described the results of the evaluation of 30 postlingually deafened adults who had received a second CI within 3 years of their first implantation;
results for the immediate and delayed implantation group data were pooled. When mean test values were analyzed, speech perception was better with bilateral CI compared with unilateral CI, although not for all patients, and, as reported by Summerfield et al., QOL was not improved.
The other five studies of bilateral CI in adults were small case series or prospective studies that used repeated measures to evaluate hearing acuity before and after implantation of the second CI. Gantz et al. (2002) evaluated bilateral cochlear implantation in 10 adults with severe-to-profound, postlingual hearing loss. Each patient received 2 Nucleus cochlear implantation systems in a single surgical procedure. At 3 months and 1 year after surgery, patients underwent left-right sound localization tests and speech perception tests (CNC [Consonant-Nucleus-Consonant] words, HINT [Hearing in Noise Test] sentences, and CUNY [City University of New York] sentences in quiet and CUNY sentences in noise). The findings at 1 year showed significantly better performance under the binaural condition versus either monaural condition for right-left sound localization in all patients (100%), for HINT sentences in 5 patients (50%), for CUNY sentences in quiet in 1 patient (10%), and for the more difficult test of CNC words in 2 patients (20%). The study findings suggest that compared with unilateral cochlear implantation, bilateral cochlear implantation may allow significant improvement in sound localization in all patients and in speech perception in quiet and in noise in many patients. However, it appears that these improvements may relate more often to the effect of head shadow (the physical barrier that the head creates
Cochlear Implants - Commercial Medical Management Guideline
between sounds emitted from one direction and the ear on the contralateral side of the head) than to the effect of binaural squelch (the result of the brainstem processing the different timing, amplitude, and spectral messages received by both ears and separating the sounds into auditory objects). Despite this, the study shows that binaural squelch can occur with bilateral cochlear implantation. The authors contend that the benefit of binaural squelch may require more listening experience, different types of speech processing for each cochlear implantation device, or some type of coordinated speech processing for both cochlear implantation devices.
In another study, Litovsky et al. (2004) assessed bilateral cochlear implantation (Nucleus systems) in 20 patients, including 17 adults with postlingual (n=14) or prelingual (n=3) hearing loss who received bilateral cochlear implantation in a single surgical procedure and 3 children with prelingual hearing loss who received cochlear implantation first in one ear and at a later date in the other ear. The study results suggest that in adults who receive bilateral cochlear implantation in a single surgical procedure, bilateral cochlear implantation may allow rapid improvement in sound localization, particularly in those with extensive experience using bilateral hearing aids, and may improve speech perception skills within 3 months in some, although improvement in this skill is variable and may occur more gradually after long-term deafness. In prelingually deafened children receiving unilateral cochlear implantation first and receiving cochlear implantation for the other ear several years later, bilateral cochlear implantation shows only slight improvement in sound localization, right-left sound discrimination, and speech perception within 3 months, compared with monaural conditions.
However, the 3-month follow-up may be insufficient to demonstrate the potential benefits of binaural hearing in prelingually deafened children and may be insufficient to show improvement in speech perception versus monaural conditions in any patients.
Litovsky et al. (2006a) investigated simultaneous bilateral CI in 37 adults with postlingual onset of bilateral, severe to profound hearing loss. Speech understanding in quiet (CNCs and HINT sentences) and in noise (BKB-SIN Test) was evaluated at 1, 3, and 6 months after implantation, with speech presented at 0° azimuth, and noise at either 0 degrees, 90 degrees right, or 90 degrees left in the horizontal plane. Testing was performed with each implant alone and in the bilateral mode. A self-assessment questionnaire was used to evaluate use of the CI for a 3-week period during which the study participants only used the CI that produced the best scores during unilateral testing, and then again with both CIs activated. Six months after CI, there was a significant advantage for speech understanding in quiet for the bilateral mode compared with either monaural modes. In a noise situation, the greatest benefit was found when the patient was able to take advantage of the head shadow effect. Patients reported that their ability to understand and localize speech was best in the bilateral mode. This study is limited by the relatively small number of patients and the short duration of follow-up.
Schoen et al. (2005) examined different aspects of sound localization in 12 adults with postlingual hearing loss who received bilateral cochlear implantation (MED-EL COMBI systems) in a single surgical procedure (n=3) or 2 sequential procedures (n=9) and had 3 or more months of experience with bilateral cochlear implantation. The study results suggest that in adults receiving bilateral cochlear implantation, either in a single surgical procedure or 2 sequential procedures, bilateral cochlear implantation may allow relatively accurate horizontal and lateral sound localization within 3 months of bilateral activation.
In a prospective study by Laszig et al. (2004), 15 adults underwent sequential bilateral CI, while 22 underwent simultaneous bilateral CI. All patients were postlingually deafened. The patients received the Nucleus 24 CI and were tested at 6 months after CI for changes in speech perception and comprehension and speech localization, with test results reported as matched pair data. In sequentially implanted patients, there was no difference between first and second CI in terms of performance, and there was a significant binaural head shadow benefit for both groups. Overall, bilateral CI improved speech comprehension and localization, and there were indications of binaural auditory processing. This study was limited by the small sample size and short duration of follow-up.
The following studies were not reviewed by Hayes: