Children with severe hearing loss who were under the age of five years and underwent cochlear implantation had better improvement in comprehension and spoken language expression that would be predicted from their pre-implantation language scores, with earlier age at implantation linked to greater improvements, according to a study reported in the April 21 issue of JAMA (Journal of the American Medical Association).

According to background information in the article "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 traditional amplification devices (hearing aids). More than half of such children are treated with cochlear implantation."

Cochlear implant systems includes an externally worn microphone and a microprocessor programmed to extract intensity, frequency, and timing cues from acoustic signals, which are then 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. The authors write "With experience, children understand speech, environmental sounds, and music with varying degrees of success". However, 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 team evaluated spoken communication development over a 3-year period in children who had undergone cochlear implantation before the age of 5 years (n = 188) and hearing children of similar ages (n = 97) from 2 preschools. Follow-up was completed between November 2005 and May 2008. The Reynell Developmental Language Scales was used to assess spoken language comprehension and expression.

The scientists found that the children who had undergone 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. The younger the cochlear implantation recipients were, the steeper were their rate of increases in comprehension (1.1 points per year younger) and expression (1.0 points per year younger).

The authors wrote "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."

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.

The scientists concluded "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."

"Spoken Language Development in Children Following Cochlear Implantation"
John K. Niparko, MD; Emily A. Tobey, PhD; Donna J. Thal, PhD; Laurie S. Eisenberg, PhD; Nae-Yuh Wang, PhD; Alexandra L. Quittner, PhD; Nancy E. Fink, MPH; for the CDaCI Investigative Team
JAMA. 2010;303(15):1498-1506.
Link to abstract