Long-term Follow-up of Auditory Performance and Speech Perception and Effects of Age on Cochlear Implantation in Children with Pre-lingual Deafness
Cochlear implantation (CI) has become a pivotal intervention for children with severe to profound hearing loss, particularly those with pre-lingual deafness. This study aimed to evaluate the long-term development of auditory and speech perception abilities in children who underwent CI before the age of 3 years and to explore the impact of age at implantation on these outcomes. The findings provide valuable insights into the optimal timing for CI and the trajectory of auditory and speech development post-implantation.
Background
Hearing loss is a significant global health issue, affecting approximately 466 million people worldwide, including 34 million children. In China, the prevalence of hearing loss is particularly high, with an estimated 120,000 children suffering from severe to profound hearing loss before the age of 7. For these children, CI offers a promising solution to improve auditory and speech abilities, facilitating their integration into mainstream society.
The development of auditory and speech perception abilities in children with hearing loss is influenced by various factors, with age at CI (CI age) being one of the most critical. Early CI is believed to capitalize on the brain’s plasticity during the sensitive period of auditory and speech development, which is most pronounced in the first three years of life. However, there is ongoing debate regarding the optimal age for CI, with some studies suggesting that earlier implantation leads to better outcomes, while others argue that the benefits of early CI are not significantly different from those of later implantation.
Methods
This study included 278 children with pre-lingual deafness (176 boys and 102 girls) who underwent CI between the ages of 6 and 36 months (mean age: 19 months). The children were followed up for 5 years post-implantation, with evaluations conducted at various intervals: pre-implantation, and 1, 3, 6, 12, 18, 24, 36, 48, and 60 months post-implantation.
Auditory performance was assessed using the Categorical Auditory Performance (CAP) scale, which classifies auditory perception ability on a scale from 0 to 7. Speech intelligibility was evaluated using the Speech Intelligibility Rating (SIR) scale, which rates speech intelligibility on a scale from 1 to 5. These scales were chosen for their wide application, high repeatability, and suitability for children of various ages and speech abilities.
Results
Development of Auditory Ability After CI
The auditory ability of the children showed the fastest development within the first 6 months post-implantation (k = 0.524, t = 30.992, P < 0.05). This rapid improvement was followed by a deceleration in the rate of development (k = 0.14, t = 3.704, P < 0.05), with a plateau reached by the 24th month (k = 0.03, t = 1.908, P < 0.05). The CAP scores continued to improve slowly and steadily until the 60th month post-implantation.
Development of Speech Intelligibility After CI
Speech intelligibility showed a different developmental trajectory compared to auditory ability. The fastest improvement in SIR scores occurred between the 12th and 24th months post-implantation (k = 0.138, t = 5.365, P < 0.05). The rate of improvement then decelerated (k = 0.026, t = 1.465, P < 0.05), with a plateau reached by the 48th month (k = 0.012, t = 1.542, P < 0.05). This pattern indicates that speech development lags behind auditory development in the early stages post-implantation.
Effects of CI Age on CI Outcomes
The study found that CI age had a significant impact on auditory and speech abilities in the early stages post-implantation. For the 6th-month follow-up, the mean CAP scores were significantly different (P month group in several divisions, particularly for implantation months 14 to 15 and 19 to 33. Similarly, for the 12th-month follow-up, significant differences were observed in the 7, 11 to 12, 20 to 24, and 26 to 31 implantation month divisions. For the 18th-month follow-up, significant differences were observed in the 10 to 30 implantation month divisions.
However, by the 24th-month follow-up, there were no significant differences (P > 0.05) in CAP and SIR scores between the ≤month group and the >month group for all divisions. This suggests that the initial advantages of earlier CI age diminish over time, with children who underwent CI at a younger age eventually catching up to those who underwent CI at an older age.
Optimal Cutoff Age for CI
The study identified 15 months as the optimal cutoff age for CI. Children who underwent CI at or before 15 months showed faster and more pronounced development of auditory and speech abilities, reaching full scores on the CAP and SIR scales by the 48th and 60th months post-implantation. In contrast, children who underwent CI after 15 months did not achieve full scores on these scales.
Discussion
The findings of this study highlight the importance of early CI for children with pre-lingual deafness. The rapid development of auditory ability within the first 6 months post-implantation underscores the critical role of early auditory stimulation during the sensitive period of auditory development. The slower and more prolonged development of speech intelligibility suggests that speech development requires a longer period of accumulation and practice.
The study also provides evidence that the initial advantages of earlier CI age diminish over time, with children who underwent CI at a younger age eventually catching up to those who underwent CI at an older age. This finding supports the recommendation for earlier CI, as it allows children to maximize their auditory and speech development during the critical period of brain plasticity.
The identification of 15 months as the optimal cutoff age for CI provides valuable guidance for clinicians and parents in making informed decisions about the timing of CI. Children who undergo CI at or before 15 months are more likely to achieve full auditory and speech abilities, facilitating their integration into mainstream society.
Conclusion
In conclusion, this study demonstrates that the auditory and speech abilities of children with pre-lingual deafness continuously improve over the 5 years following CI, with auditory development preceding speech development. Early CI, particularly before the age of 15 months, is recommended to maximize the benefits of auditory and speech development during the critical period of brain plasticity. The findings provide valuable insights for clinicians and parents in making informed decisions about the timing of CI and highlight the importance of long-term rehabilitation and follow-up for children with pre-lingual deafness.
doi.org/10.1097/CM9.0000000000000370
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