Every day I work with adults receiving cochlear implants (CIs). Choosing an implant is a major decision, so, quite understandably, recipients and their families want to know how much benefit they can expect to get. Unfortunately, this is not a straightforward question to answer.
With a cochlear implant, even if everything goes right, we still cannot predict how well an adult will hear. There is a vast range of speech perception outcomes. Some users will be able to use the telephone easily and obtain 100 percent on a sentence test without lipreading, others will be unable to understand any speech without lipreading, and still others will find themselves somewhere in between.
The question is, would it be easier for adults to make the decision to have an implant if we could even roughly predict how well they may hear afterward?
Pre-, Per-, and Postoperative Factors Affecting Performance of Post-Linguistically Deaf Adults Using Cochlear Implants: A New Conceptual Model over Time
Lazard DS, Vincent C, et al PLOS ONE 2012;7(11):e48739.
With this thought always in my mind, a recent multicenter collaboration published in an international, peer-reviewed, open-access, online publication caught my eye. It is a retrospective study testing the effect of multiple factors on cochlear implant speech performance in quiet and noise. The authors also wanted to design a model of predicted auditory performance using the factors that were found to be significant. A strength of the paper is the large sample size: 2,251 patients implanted since 2002 at 15 international centers.
The authors describe the factors that are already known to influence postoperative speech perception performance: duration of severe to profound hearing loss, age at implantation, age at onset of severe to profound hearing loss, duration of implant experience, and etiology. However, these factors only explain a very small percentage of the large variability seen in results. In this paper, the authors wanted to examine the effect of 15 other factors.
Speech perception testing in the clinic is not the only way to measure cochlear implant benefit, and many patients comment that it does not reflect real-life performance. However, it is a measure used by almost all cochlear implant centers and at least must be a rough estimate of the ability that most patients want to achieve—to understand speech in their lives.
The difficulty with speech perception measures in an international multicenter study is that different tests are often used in each country, as the patients are tested in their home language. In addition, there are differences in pre-sentation level and speech material, such as phonemes, monosyllabic words, disyllabic words, and sentences. In this study, all centers provided an open-set speech perception test in quiet and in noise without lipreading. A percentile rank for each patient within each center was calculated to try and remove differences in clinical practice between centers.
The Table shows the 15 factors the authors evaluated and whether or not they were found to have a significant effect on performance. Because of the large number of data points in the analysis, the researchers identified P < 0.001 as the threshold for statistical significance. When P was less than 0.05 but greater than 0.001, the factor was considered marginally significant.
It is encouraging to see that implanting the better or worse ear, defined using audiometric criteria, did not have any effect. Choosing which ear to implant is often a difficult clinical decision. These results may show that speech performance with a cochlear implant relies not on the peripheral structures of the implanted ear but more on the integrity of central processing, the authors wrote. Whichever ear is implanted, what matters is that the brain was not deprived of sound preoperatively.
Hearing aid use had a strong effect on performance; not using a hearing aid seemed to accelerate the degeneration caused by auditory deprivation. Although the effect of preoperative speech perception score was significant, it was found, not surprisingly, to be highly influenced by other factors—age at onset of severe to profound hearing loss, pure-tone average of the better ear, and hearing aid use.
I was particularly interested and surprised to see that the cochlear implant brand had a significant effect on the speech perception score with the implant. At my center—in common with others, I expect—we counsel patients that their outcome will be similar whichever device they choose. Four brands of CIs were included: Advanced Bionics, Cochlear, MED-EL, and Neurelec. However, in order to avoid the use of these data for commercial advantage, the authors decided not to say which implant device was which. I can understand this reasoning, but of course it does make it difficult to counsel patients. Although the performance differences were significant between the highest and the two lowest brands, the mean scores of the highest and lowest differed by only 14%.
The authors found additional factors that may affect performance with a cochlear implant. However, this new model only accounted for 22% of the variance in performance, meaning that 78% of the variance is still unexplained. So when we counsel patients about how well they may do with an implant, we perhaps have a few more clues to help us, but there still are a lot of unknown factors.