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Age and Outcome of Cochlear Implantation for Patients with Bilateral Congenital Deafness in a Cantonese-Speaking Population

Tong, Michael C. F.; Leung, Eric K. S.; Au, Albert; Lee, William; Yue, Virgil; Lee, Kathy Y. S.; Chan, Vanessa S. W.; Wong, Terence K. C.; Cheung, Dilys M. C.; van Hasselt, C Andrew

doi: 10.1097/AUD.0b013e31803150b4
Research Articles

Objective: To evaluate the effect of age at implantation by assessment of speech perception in cochlear implant users with bilateral congenital deafness.

Design: A retrospective cohort analysis of 60 cochlear implant users (age at implantation, 1.01 to 22.0 yr) who have at least 2 yr of experience. Their outcome performance was defined by the change in i) speech perception category (SPC) score based on postoperative assessment results and ii) the type of education attended after implantation. The association of age at implantation with SPC scores was analyzed at different ages at implantation (2, 3, 4, 5, and 6 yr old). The SPC scores for a particular age at implantation were compared at 6, 12, and 24 mo after implantation. The impact of age at implantation on choice of education was evaluated by analyzing the transition from a school for the deaf to mainstream education for the 45 children who were operated on before the age of 10, because older children are less likely to make such a change.

Results: Children implanted at the ages of 2, 3, 4, 5, and 6 yr all obtained significant improvements in SPC scores 24 mo after implantation. The greatest improvement was noted at 24 mo after implantation among those operated on before age 3. For all age groups, improvement at 24 mo after implantation is greater than at 12 mo, whereas the latter is greater than the improvement noted at 6 mo after implantation. Comparison of children implanted before the age of 3 and between ages 3 and 10 showed a significant difference in the choice of education after implantation. Children who were implanted before the age of 3 were more likely to attend mainstream education after implantation.

Conclusion: Results from the present study are consistent with the current belief that implantation at a younger age provides greater benefit. The proportion of children attending mainstream education was significantly higher for those implanted before age 3, which may be a potential benefit to early implantation for relieving the burden of governments in providing special education.

The Chinese University of Hong Kong, Hong Kong, China.

Address for correspondence: Michael C. F. Tong, Division of Otorhinolaryngology, Department of Surgery, CUHK, 6/F, Clinical Sciences Building, Prince of Wales Hospital, New Territories, Hong Kong SAR, China. E-mail: mtong@surgery.cuhk.edu.hk

Received December 15, 2005; accepted May 17, 2006.

The current trend in pediatric cochlear implantation is, undeniably, decreasing age of implantation. Implementation of universal newborn hearing screening makes early detection of hearing impairment possible; advancing surgical techniques allow infants under the age of 12 mo to be implanted safely (James & Papsin, 2004), and improvement in neural response telemetry facilitates initial programming of speech processors, providing auditory stimulation for infants (Gordon, Gilden, Ebinger, et al., 2002). Evidence in favor of early implantation is numerous, the most important evidence is that early implantation entails better performance outcome. Speech perception ability (Manrique, Cervera-Paz, Huarte, et al., 2004a; 2004b; Svirsky, Teoh, & Neuburger, 2004; Zwolan, Ashbaugh, Alarfaj, et al., 2004), onset of babbling (Schauwers, Gillis, Daemers, et al., 2004), and plasticity of the central auditory system (Sharma, Dorman, & Spahr, 2002) have been proven to be correlated with age at implantation. Such advantages have been reported in Western studies, but substantiation in a Cantonese-speaking population is limited. This paper aims to evaluate the effect of age at implantation on speech perception performance in a Cantonese-speaking population.

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Materials and Methods

Subjects

This is a retrospective cohort study. Sixty patients (32 males and 28 females; age at implantation, 1.01 to 33.0 yr) who received cochlear implants at Prince of Wales Hospital for at least 2 yr were selected. All subjects had bilateral congenital deafness and were implanted unilaterally with Nucleus 24 or 22 devices with full electrode insertion. Residual hearing, taken as average preoperative hearing thresholds at 0.5, 1, and 2 KHz on the side to be implanted, ranged from 97 to 125 dB HL, with a mean of 113 dB HL.

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Outcome Measure

Outcome was defined by change in speech perception category (SPC) scores and change in the type of education opted for (mainstream school versus school for the deaf) after implantation. SPC scores were based on adult and pediatric versions of the Hong Kong Speech Perception Test Manual (Cochlear Implant Working Group, 2000), which were used for all pre- and postoperative assessments. A longitudinal set of data containing preoperative assessments and postoperative assessments at 6, 12, and 24 mo was collected. Scores of the Hong Kong Speech Perception Test Manual tests, including seven-sound detection, syllable identification, vowel and consonant identification, open-set sentence, and word recognition, were used to determine the SPC scores, which ranked from 0 to 7. Patients are granted a score of 0 for no sound detection; 1 for sound detection; 2 for suprasegmental perception; 3 for vowel identification; 4 for consonant identification; 5 for minimal open-set word recognition; 6 for >20% score in open-set word recognition; and 7 for >50% score in open-set word recognition. Similar classification systems have been used in other Western studies (Mondain, Sillon, Vieu, et al., 1997).

The other outcome indicator is the choice of mainstream school versus school for the deaf after implantation. The stream of school attended after implantation was analyzed for subjects implanted under the age of 10. The cutting point at age 10 is arbitrary, although older children, even after implantation, are less likely to be transferred from a school for the deaf to a mainstream school.

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Statistical Analysis

The data was first tested for normality by the Shapiro-Wilk test. For the nonnormally distributed data, the association of age at implantation with outcome was analyzed by the Mann-Whitney U test at different ages (i.e., ages 2, 3, 4, 5, and 6 yr). Under a particular age at implantation, the benefit was compared by the mean rank difference at 6, 12, and 24 mo after implantation. Other possible parameters such as gender, residual hearing, magnetic resonance imaging/computed tomography status of the implanted ear, and side of implantation were analyzed by chi-square test. The relationship between age at operation and likelihood of entering mainstream education was evaluated by chi-square and Fisher exact test.

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Results

Outcome Performance

Subjects were divided into five groups by their age at implantation: 2, 3, 4, 5, or 6 yr. All groups achieved a positive change in SPC score at 24 mo after implantation (Fig. 1). The Mann-Whitney U tests yielded significant differences (p < 0.05) in mean rank between groups of implantation at ages 3, 4, 5, and 6 yr. Improvement at 24 mo was greater than at 12 mo (Fig. 1), whereas improvement at 12 mo was greater than at 6 mo after implantation (Fig. 1). At 24 mo after implantation, the greatest rank difference of 19.28 was between age at implantation before versus after age 3, which also had a high significance of p < 0.001, as shown in Fig. 1.

Fig. 1. Six-, 12-, and 24-mo postoperation mean rank differences at different ages of implantation.

Fig. 1. Six-, 12-, and 24-mo postoperation mean rank differences at different ages of implantation.

No significant differences were demonstrated by the chi-square tests between different groups on sex, side of implantation, or computed tomography/magnetic resonance imaging findings on cochlear and residual hearing. These parameters were not statistically different between groups tested.

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Type of Postoperative Education

Forty-five subjects implanted before age 10 were analyzed for the stream of school attended after implantation. Comparison for subjects implanted before age 3 and between ages 3 and 10 by chi-square and Fisher exact test showed that the two groups had a significantly different score for the different types of postoperative education attended (Fisher exact test significant = 0.034). Five of 13 subjects (38.5%) implanted before age 3 made the transition to normal education after implantation, whereas 3 of 32 subjects (9.4%) of those operated on between ages 3 and 10 made the transition.

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Discussion

Children with bilateral congenital deafness can benefit significantly from cochlear implantation. Existing evidence suggests that implantation at younger age provides greater benefit (McConkey Robbins, Burton Koch, & Osberger, 2004; Manrique, Cervera-Paz, Huarte, et al., 2004; Nikolopoulos, Dyar, Archbold, et al., 2004; Pulsifer, Salorio, & Niparko, 2003). Early implantation maximizes auditory stimulation to the child during the critical period for language acquisition (Colletti, Carner, Miorelli, et al., 2005). Results of this study are consistent with current findings, demonstrating greater improvement in younger age groups compared with the older age groups at 24 mo after implantation. A possible limitation of this present study is the small sample size of the younger group when the cut point was at the extremity of age. With only six children implanted before age 2, a nonsignificant difference (p = 0.08) was demonstrated against subjects implanted after age 2. With more subjects in that age group and long-term follow-up studies, those who are implanted before the age of 2 are more likely to demonstrate higher SPC scores. Although no definite conclusion could be drawn about the critical age at which implantation provides the greatest benefit, the trend we found coincides with current understanding that implantation at a younger age can provide greater benefit.

The proportion of children entering mainstream education after implantation was significantly higher in those implanted before age 3 (38.5%) than in those implanted between ages 3 and 10 (9.4%), with p = 0.034 by the Fisher exact test. One potential benefit of earlier implantation is that it might relieve the burden on governments to provide special schooling.

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Conclusion

Our study confirms the benefits in terms of speech perception outcome in performing cochlear implantation in a younger age group in a Chinese population. We have further shown that a younger age of implantation is a favorable factor for mainstreaming in school age children.

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References

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