PEDIATRICS Vol. 118 No. 4 October 2006, pp. 1350-1356 (doi:10.1542/peds.2006-0502)
ARTICLE |
Does Cause of Deafness Influence Outcome After Cochlear Implantation in Children?
a Department of Otorhinolaryngology, Athens University, Hippokration Hospital, Athens, Greece
b Nottingham Pediatric Cochlear Implant Programme, Nottingham, United Kingdom
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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OBJECTIVES. The objective of this study was to evaluate long-term speech perception abilities of comparable groups of postmeningitic and congenitally deaf children after cochlear implantation.
METHODS. This prospective longitudinal study comprised 46 postmeningitic deaf children and 83 congenitally deaf children with age at implantation of 
5.6 years. Both groups were comparable with respect to educational setting and mode of communication and included children with additional disabilities.
RESULTS. Both postmeningitic and congenitally deaf children showed significant progress after implantation. Most (73% and 77%, respectively) could understand conversation without lip-reading or use the telephone with a known speaker 5 years after implantation, whereas none could do so before implantation. At the same interval, the postmeningitic and congenitally deaf children scored a mean open-set speech perception score of 47 (range: 0–91) and 46 (range: 0–107) words per minute, respectively, on connected discourse tracking. The respective mean scores at the 3-year interval were 22 and 29 correct words per minute, respectively. None of these children could score a single correct word per minute before implantation. The progress in both groups was statistically significant. When the 2 groups were compared, there was no statistically significant difference.
CONCLUSION. Postmeningitic and congenitally deaf children showed significant improvement in their auditory receptive abilities at the 3- and 5-year intervals after cochlear implantation. There was no statistically significant difference between the outcomes of the 2 groups, suggesting that, provided that children receive an implant early, cause of deafness has little influence on outcome. Although the prevalence of other disabilities was similar in both groups, for individual children, their presence may have profound impact. The study supports the concept of implantation early in life, irrespective of the cause of deafness.
Key Words: cochlear implant • speech perception • children • auditory perception • outcome • meningitis • congenital • etiology • results
Abbreviations: PMD—postmeningitic deaf • CD—congenitally deaf • CDT—connected discourse tracking • CAP—categories of auditory performance
When pediatric cochlear implantation began, considerable doubts were expressed about the advisability of implantation for congenitally deaf children. In 1989, Shannon1 suggested that, because of lack of auditory input, the central auditory neural mechanisms of congenitally deaf children may be incompletely developed. He added that in such cases, the electrical stimulation of the auditory pathways might not result in interpretable sensations. Two years later, in 1 of the major clinical trials that influenced Food and Drug Administration approval of pediatric cochlear implantation, Staller et al2 reported that prelingually deaf children with acquired deafness tended to obtain higher scores on speech perception than congenitally deaf children. Boothroyd et al3 also suggested that prelingually deaf children who had experienced auditory input before acquiring profound deafness would derive more benefit from a cochlear implant than those who were congenitally deaf.
On the basis of these theoretical assumptions and the results of early clinical trials, the prevalent view for several years was that postmeningitic deaf (PMD) children children who received an implant would outperform the congenitally deaf (CD). Eventually, a considerable number of studies4–14 attempted to compare the functional outcome of PMD and CD children with implants. However, robust statistical data to support any hypothesis are lacking, with reported results often being contradictory. Most studies comprised heterogeneous groups of children, varying widely in age from the very young to adolescents. Typically, the numbers of subjects at the long-term intervals after implantation were far too small to allow meaningful statistical analysis. No study that was based on a calculation of statistical power to determine the minimum numbers of children needed in each group to allow valid comparisons existed. The aim of the present article was to compare in a prospective, longitudinal manner the long-term speech perception of comparable groups of PMD and CD children in the long term after cochlear implantation.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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The study comprised 46 PMD children and 83 CD children who fulfilled the required inclusion criteria, which were as follows:
- Prelingually deaf children who were deafened by meningitis. The children were defined as having prelingual deafness when they were deafened before the age of 3, as used in the literature.15,16
- Children who were CD.
- Bilateral profound deafness with hearing thresholds >95 dB across the speech frequencies before implantation.
- Age at implantation of 5.6 years. Children in the United Kingdom usually start school between 5 and 6 years of age. Therefore, upper age limit for implantation at
5 years and 6 months usually includes all preschool children.
- Fifteen or more intracochlear electrodes.
- Implantation with the same implant system (the Nucleus device).
In the PMD group, the age at implantation ranged from 1.3 years to 5.5 years (mean: 3.3 years; median: 3.4 years). In the CD group, age at implantation ranged from 1.4 years to 5.6 years (mean: 3.6 years; median: 3.6 years). There was no statistically significant difference in the age at implantation or in the duration of device use between the 2 groups. All children received their implant between 1989 and 1999. Age of diagnosis was not routinely recorded in the files of CD children, but universal newborn hearing screening was not in existence at that time and average age of diagnosis was between 12 and 18 months.
Although every attempt was made to evaluate prospectively all of the children at the 3- and 5-year intervals after implantation, a few children were not assessed with both outcome measures at both intervals for various reasons, including pressure on parental or tester time, missed follow-up appointments, illness, etc. However, such omissions were few; for example, in the PMD group, at the 5-year interval, only 2 children were not assessed with categories of auditory performance (CAP) and 6 with connected discourse tracking (CDT).
To assess whether mode of communication or educational placement affected the comparisons in the 2 groups, we explored the distribution of all children according to these factors (Table 1). Educational placement and mode of communication were collected annually by the teachers of the deaf at the implant program, in liaison with parents and local teachers. Educational placement was categorized as mainstream school, a unit or special class in a mainstream school, or a school for the deaf. The children were categorized into 1 of 2 communication modes: those who were using oral communication and those who were using signed communication to whatever degree. Those in the oral category were using spoken language at home and at school, and those in the signing category included those who were using Signed Supported English, as well as those who were using British Sign Language. It is recognized that this categorization does not describe comprehensively the full range of communication methods used by the children, but it does provide an accurate overall description of their mode of daily communication. There was no statistically significant difference between PMD and CD children regarding mode of communication and educational placement at the final (5-year) interval.
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Eleven (24%) of 46 PMD children had 1 or more additional needs (language or communication disorders, autism, and cognitive disorders). In the CD group, 19 (23%) of 83 children had similar difficulties. There was no statistically significant difference in the prevalence of additional disabilities between the 2 groups (P > .05).
Outcome Measures
The 2 outcome measures used in the study were the CAP and CDT.17 These were chosen because they provide robust measures of auditory receptive abilities and can be readily used in a range of settings and with children over a wide age span.
CAP
CAP is a global outcome measure that assesses the auditory performance of deaf children. It comprises a nonlinear, hierarchical scale of auditory receptive abilities; the lowest level describes no awareness of environmental sounds, and the highest level is represented by the ability to use a telephone with a known speaker.18–20 CAP is not a closed-set laboratory-type test but a measure of everyday auditory performance and thus reflects the "real life" progress of children in the developing use of audition. It is appropriate for use in both very young and older children and can be used over an extended time frame without encountering floor and ceiling effects.21 Furthermore, the interobserver reliability of this scale has been validated formally.18
CDT
CDT measures open-set speech perception. Simple stories are written specifically in 3 levels of linguistic difficulty, and the 1 that is appropriate for each child is chosen. The story is read, phrase by phrase, to the child, who is asked to repeat it verbatim. The relative position of the reader and the child precludes lip-reading. The exercise, sometimes called speech tracking, is timed, and the number of words that are repeated correctly per minute is calculated. CDT was selected because it has no ceiling effects and closely simulates real-life situations in which children need to understand speech in conversation.10,22–25 Poor performers or children who scored 0 were included at each test interval.
Statistical Power Analysis
A power analysis revealed that at least 80 children (40 in each group) were needed to find, at the P = .05 level of statistical significance, with 80% certainty, a difference of at least 16 words per minute in CDT between the 2 groups. Student's t test, Mann-Whitney U test, paired Student's t test, Wilcoxon signed rank test for paired observations, and 
2 were used for the statistical comparisons of the data. Statistical significance was accepted at the .05 level.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Tables 2 and 3 outline the CAP and CDT outcomes of the 2 groups. The majority of the children could understand conversation without lip-reading or use the telephone 3 and 5 years after implantation, whereas none of them could do so before implantation. Seventy-three percent of the PMD children and 77% of the CD children could understand conversation without lip-reading or use the telephone with a known speaker by 5 years after implantation. Statistical analysis revealed that the progress in both PMD and CD groups was statistically significant from before implantation to the 3-year interval (P < .001) and from the 3-year interval to the 5-year interval after implantation (P
.001).
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Three years after implantation, PMD children developed mean open-set speech tracking scores of 22 (range: 0–66) correct words per minute, which increased to a mean of 47 (range: 0–91) correct words per minute at the 5-year interval. Similarly, CD children scored a mean of 29 (range: 0–107) correct words per minute 3 years after implantation and a mean of 46 (range: 0–107) correct words per minute at 5 years (Table 3). All children scored 0 before implantation. Statistical analysis revealed that the progress in both groups was statistically significant from before implantation to the 3-year interval (P < .0001) and from the 3-year interval to the 5-year interval after implantation (P < .0001). Children with additional difficulties performed significantly poorer than those with deafness alone (P
.01; Table 4). When the 2 groups were compared, there was no statistically significant difference between the PMD and CD children in their auditory perception, as measured by CAP and CDT, 3 and 5 years after implantation (P > .05).
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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A review of the current literature on pediatric cochlear implantation does not allow a definite conclusion about the impact of the cause of deafness on subsequent outcome. Limitations in the design of the related studies, combined with relatively small series and short follow-up, have resulted in somewhat tenuous conclusions. Staller et al2 reported that prelingually deaf children with acquired deafness tended to obtain higher scores on speech perception than the CD children. However, this study involved children who had received implants at 23 different cochlear implant centers and therefore had high intrasubject variance and heterogeneity. Moreover, the authors mentioned that because of the diversity and the magnitude of the evaluation protocol, not all children were evaluated at each test interval. Therefore, when they actually compared the performance of the PMD and CD children, the numbers of children were small. Nonetheless, the study proposed that PMD children tend to do better than their CD counterparts, although no statistical confirmation was provided. Uziel et al9 agreed with the previous study and found a statistically significant difference in speech perception between 24 CD children and 12 with prelingual deafness (mainly as a result of meningitis), with the CD children having lower scores. However, this difference disappeared by 18 months after implantation. Their results are weakened by the ceiling effects of the closed-set tests and the very small numbers at the 3-year interval (3–5 children depending on the test and subgroup).
In contrast to the results of the previous studies, Gantz et al4 found higher mean speech perception scores in CD children compared with PMD children after implantation. On the basis of these findings, the authors suggested that factors that can accompany meningitis, such as neural degeneration, may account for this difference. Thus, the detrimental effects of meningitis on the central nervous system may negate any positive influence afforded by previous auditory experience. However, these claims were not supported by statistical analysis. In addition, the actual numbers of children varied at each test interval depending on the child's age and ability to complete the test. Tyler et al,8 in an additional study at the same cochlear implant center, found a statistically significant difference in speech perception between 18 CD children and 12 with acquired deafness. This difference was in favor of CD children and increased as a function of time. However, there were no comparisons beyond the 3-year interval, and because of the small numbers, the authors suggested that their results should be considered tentative. Yucel et al13 also found that PMD children exhibited a significantly lower performance after implantation than those who presented with other causative factors. Again, however, the number of subjects in the study was small (21 in total), the sample was heterogeneous (including 40-year-old adults with 9-year-old children), and included single-channel and multichannel implant recipients.
Waltzman et al5 reported no difference between CD children and those with acquired deafness and suggested that the issue of congenital versus acquired deafness does not seem to be a factor when all children receive an implant early. However, some study groups had 5 or fewer children even at the 2-year interval. Kiefer et al6 agreed with the previous study, but their results also were weakened by small numbers (only 6 children at the 3-year interval). Mitchell et al14 compared 70 CD children with 22 postmeningitic prelingually deaf children and found no significant difference in postimplantation speech perception. However, the analysis was based on data from the last available interval, and there were no comparisons at any specific follow-up interval. Francis et al,11 in a more recent study, also found no difference in the overall postoperative speech perception performance between PMD children and those who were deafened by other causes. However, their sample included postlingually deafened children, and the speech perception performance was assessed only within the first 2 years after implantation. In addition, all studies (the present 1 included) are subject to the selection bias and candidacy criteria of the implant center, for example, a center's willingness to accept children with additional disabilities.
No previous studies in the literature had calculated statistical power to define the numbers of children needed in each group to underpin their conclusions with valid statistical analysis. Statistical power is the probability that one can detect a difference if there really is one. It is highly influenced by the effect size, the variability, and the number of subjects. A study that concluded that no difference existed between 2 groups (as in the present study) could easily be attributable to the use of sample sizes that simply were too small to allow detection of a difference that actually existed (type ß error). The numbers of children in the present prospective study were determined by a calculation of statistical power. Therefore, it can be concluded safely that the inability in the study to demonstrate a clinically important difference between the PMD and CD groups is true and not attributable to the study's being powered inadequately The present study did not exclude poor performers or "difficult to test" children; such practice artificially inflates group data and may give an erroneously optimistic impression of group performance. In our study, children who were either unwilling or unable to be tested at a particular interval were scored as 0, although we knew that this underestimated their actual performance; doing so adds rigor to our method and addresses the legitimate concerns of some critics of the implant literature.26
Histologic studies in adults have revealed that the mean spiral ganglion cell count (12000) in CD adults is almost the same as the respective count in postmeningitic adults (13000).27 However, the presence of a spiral ganglion cell at a light microscopic level does not guarantee normal function; moreover, the loss of dendritic fibers may greatly exceed loss of ganglion cell bodies.28 In other words, the function of the peripheral spiral ganglion cells, dendrites, and peripheral neurons of the auditory pathways may be entirely different from their anatomic status. A study that compared the electrical auditory brainstem responses that were evoked by promontory stimulation in a group of CD and PMD children suggested that this function may be more intact in CD children than in PMD children.29 The numbers of children with identifiable wave form components (eV, eIII, and eII) were significantly greater in the CD group. In addition, the amplitudes, latencies, and 4 parameters of the amplitudes' input/output functions were assessed. All of the statistically significant differences were in favor of better responses in the CD children. In addition, the central auditory pathways may be damaged after meningitis; it is widely known that meningitis may cause neurologic, motor, visual, and behavioral disorders.30 Therefore, the sequelae of meningitis very well may eliminate any beneficial effect of previous auditory experience in PMD children. Besides, the duration of such early auditory experience often is very short because meningitis most often strikes in the first year of life (26 of 46 children in the present study). Moreover, the entry criterion of prelingual deafness in the present study had excluded any children with long auditory experience.
Although the auditory and speech perception progress in both groups was statistically significant from before implantation to the 3-year interval and from the 3-year interval to the 5-year interval after implantation, supporting the effectiveness of cochlear implantation in profoundly deaf children, 17% of children still were unable to score on the task of CDT at the 5-year interval. These children were able to score on CAP, which is an observational measure of auditory perception, with scores ranging from 4 to 7, but were unable to carry out the tracking procedure, which is a demanding performance test that requires great cooperation and concentration from these children. We also should take into account that many of the children who could not carry out CDT at the 5-year interval had behavior and/or linguistic problems that made obtaining a score on such a performance task impossible.
It is recognized that up to 40% of deaf children have 
1 additional difficulties that may have an impact on the use of the implant system; in the studied children, it was the case that those with additional difficulties, whether PMD or CD, had poorer results on our measures than those without such difficulties. It is important that these children be evaluated fully before and after implantation by a multiprofessional team so that additional difficulties are identified and addressed; for example all deaf children should have a full visual assessment.31 In some children, their additional difficulty, such as autism or language impairment, may be identifiable only after implantation, once more emphasizing the need for ongoing monitoring by a multiprofessional team. For maximization of the benefits of implantation for these children, they need specialized follow-up care that will enable their additional needs to be met.
The implementation of newborn hearing screening programs is providing novel opportunities to intervene earlier than ever in the lives of young deaf infants to provide a major positive impact on their capacity to acquire language.32 One of these options that increasingly is considered in the first 2 years of life is cochlear implantation, and emerging evidence supports its efficacy in profoundly deaf children,33 taking into account the continuous improvement of device technology. A trial of conventional hearing aids is considered desirable before proceeding to implantation; this may be shortened after meningitis or in the presence of major cochlear malformation.
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CONCLUSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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The present prospective, longitudinal study found that there was no statistically significant difference in the auditory receptive abilities of PMD and CD children at 3 and 5 years after implantation. Both groups showed significant improvement at the 3- and 5-year interval after implantation. These results suggest that provided that children receive an implant early, cause of deafness has little influence on outcome. Although the prevalence of other disabilities was similar in both groups, for individual children, their presence may have profound impact. The study supports the concept of implantation early in life, irrespective of the cause of deafness.
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ACKNOWLEDGMENTS |
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We express our gratitude to Meningitis Research Foundation (Bristol, United Kingdom) for the financial support of this project through a research grant.
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FOOTNOTES |
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Accepted Jun 1, 2006.
Address correspondence to Thomas P. Nikolopoulos, MD, DM, PhD, 116 George Papandreou St, Nea Philadelphia, Athens 143-42, Greece. E-mail: thomas.nikolopoulos{at}nottingham.ac.uk
The authors have indicated they have no financial relationships relevant to this article to disclose.
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