Introduction: Knowledge of long-term outcomes in sequential implantation is needed for optimum candidacy selection and patient counselling. Studies to date describe speech outcomes up to two years post 2nd implant only. Up to this point results are asymmetrical across ears, with 1st-implanted ears providing better speech reception thresholds (SRTs), and less spatial release from masking (SRM) experienced if noise is closest to the 1st-implanted ear. Objective: To extend knowledge of clinical outcomes beyond 2 years post 2nd implant we compare results at 2 and 4 years post 2nd implant to test the following hypotheses: Hypothesis 1: Monaural SRTs in quiet will improve in both 1st and 2nd implanted ears. Hypothesis 2: Binaural SRTs in noise will improve. Hypothesis 3: SRM will improve. Hypothesis 4: SRM will become more symmetrical. Methods: This is a longitudinal study where children act as their own controls. From our caseload we identified 17 sequentially implanted children who by two years post 2nd implant were optimally programmed users of both implants, tested at both intervals. They participated in the McCormick Toy Discrimination Test with toy names presented from 0° azimuth, monaurally in quiet and binaurally with pink noise presented from 0°, -90°, and +90°. SRTs were calculated using an adaptive procedure to find the 71% correct level. SRM was calculated from SRTs in noise. Data were analysed via two-level hierarchical regression models with measurement and subject as levels one and two respectively. Results: Hypothesis 1: Both ear and test interval had a significant effect on SRTs in quiet (p<0.05 and p<0.0001 respectively) with 1st-implanted ears performing better. 1st-implanted ears improved by a mean value of 6.4dB and 2nd-implanted ears by 8.1dB over the two year period, however the difference in improvement was not significant. Hypothesis 2: Noise location and test interval both had a significant effect on binaural SRTs in noise (p<0.0001). Noise and speech from 0° was the most challenging condition and noise 90° towards the 2nd-implanted side was the easiest. There was also a significant interaction (p<0.01) showing that the change over time was dependent on the direction of the noise. While SRTs with noise from 0° improved by 2.7dB, larger improvements of 7.2dB and 5.7dB were seen for noise presented 90° towards 1st and 2nd-implanted ears respectively. Hypothesis 3: SRM significantly improved over time (p<0.001). This improvement was not dependent upon noise location. Hypothesis 4: Analysis of the change in absolute differences in SRM with noise at +90° and -90° found a small but non-significant increase in symmetry over time. Conclusion: Our findings support hypotheses 1, 2 and 3, i.e. monaural SRTs in quiet, binaural SRTs in noise and SRM improved from 2 to 4 years post 2nd implant. However our results did not support hypothesis 4. This may be due to a persistent effect of auditory deprivation prior to 2nd implantation.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)