Children under 5 years of age with severe hearing loss who underwent cochlear implantation experienced greater improvement in comprehension and expression in spoken language than would be predicted from their pre-implantation language scores, with younger age at implantation associated with greater improvements, according to a study in the April 21 issue of JAMA.
"Young children who experience severe to profound sensorineural hearing loss (SNHL) face challenges in developing spoken language because of an inability to detect acoustic-phonetic cues that are essential for speech recognition, even when fitted with tradi¬tional amplification devices (hearing aids). More than half of such children are treated with cochlear implantation," according to background information in the article.
Cochlear implant systems consist of an externally worn microphone and a microprocessor programmed to extract intensity, frequency, and timing cues from acoustic signals, which are transformed into an electrical code. The transmitted code is relayed by a surgically implanted receiver to an implanted array of contacts in the cochlea to stimulate surviving auditory neurons. "With experience, children understand speech, environmental sounds, and music with varying degrees of success," the authors write. But the timing of cochlear implantation that may yield the best results is unclear.
John K. Niparko, M.D., of the Johns Hopkins University School of Medicine, Baltimore, and colleagues assessed spoken language development over a 3-year period in children who underwent cochlear implantation before 5 years of age (n = 188) and hearing children of similar ages (n = 97) from 2 preschools. Follow-up was completed between November 2005 and May 2008. Spoken language comprehension and expression was assessed using the Reynell Developmental Language Scales.
The researchers found that children undergoing cochlear implantation showed greater improvement in spoken language performance (10.4 points per year in comprehension; 8.4 in expression) than would be predicted by their preimplantation baseline scores (5.4, comprehension; 5.8, expression), although average scores were not restored to age-appropriate levels after 3 years. Younger age at cochlear implantation was associated with significantly steeper rate increases in comprehension (1.1 points per year younger) and expression (1.0 points per year younger).
"Significantly higher rates of comprehension and expression were noted in children undergoing implantation at younger than 18 months compared with children undergoing implantation at ages between 18 and 36 months and at older than 36 months. The majority of children who received implants prior to age 18 months revealed trajectories of improvement that paralleled those of hearing controls. Cochlear implantation after 18 months of age was associated with less favorable trajectories of improvement in performance and greater variability in measures of both comprehension and expression," the authors write.
Each 1-year shorter history of hearing deficit was associated with steeper rate increases in comprehension and expression. Also, greater rates of improvement in comprehension and expression were associated with greater residual hearing prior to cochlear implantation, higher ratings of parent-child interactions and higher socioeconomic status.
"Results from this study carry implications for the clinical management of children with severe to profound SNHL. Although not determinative, age at implantation and residual hearing were associated with rate increases in the acquisition of spoken language in children with cochlear implants. These findings underscore the need to develop objective tools that can monitor the benefit of amplification in supporting spoken language acquisition and guide timely intervention with cochlear implantation," the researchers conclude.