March 2020 The Hearing Journal

Low uptake of cochlear implants (CIs) among adults with hearing loss has been a longstanding but understudied issue. Less than five percent of adults with an appropriate audiological profile for CIs in the United States actually use them, compared with the approximately 50 percent CI utilisation rate among children. This discrepancy reflects the reality that most CI-related studies have focused on the paediatric rather than adult population. In one study examining the barriers to CI access in the United Kingdom and Australia, the misconception that CIs are only for children was cited as one deterrent.

Now researchers from the University of Miami and the University of Michigan suggest that the lack of uniform guidelines on testing for adult CI candidacy is another factor that contributes to the low number of adult CI users. Sandra Prentiss, PhD, CCC-A, an assistant professor of otolaryngology at the University of Miami Miller School of Medicine, and colleagues wrote that while evidence of CI benefits for those who can't benefit from traditional amplification like hearing aids has pushed the U.S. Food and Drug Administration to expand CI indications to include even those with lesser degrees of hearing loss, no national or international consensus or clinical practice guideline statement on the delivery of care specific to preoperative and postoperative audiologic evaluation for CI exists.

Meanwhile, the revised Minimum Speech Test Battery (MSTB) recommended by leading CI manufacturers Cochlear, Med-EL, and Advanced Bionics in 2011 for assessing adult CI candidacy is neither supported by evidence nor does it represent a consensus of commissioned experts, Prentiss and her colleagues wrote. The new MSTB consists of the AzBio sentences presented in quiet and in noise, an adaptive speech-in-noise (SIN) test known as the Bamford-Kowal-Bench SIN, and a monosyllabic word test that uses consonant-vowel nucleus-consonant stimuli. The testing conditions, testing materials, and definitions of “best aided” listening conditions, however, are poorly defined. Prentiss and her colleagues hypothesised that the resulting ambiguity may lead to inconsistency across clinics, and that is exactly what they found.

They sent out a 65-question survey through the American Cochlear Implant Alliance to its members to study audiology practice patterns in testing adult candidates for CIs. Prentiss said audiologists in almost all of the centres used the same tests but employed different methods to determine candidacy. “I wasn't expecting the methods to vary so significantly,” she said. One problem with having such variability in assessment practices is inconsistency in access to cochlear implants, Prentiss said. “While we can argue that having some flexibility in testing methods may be beneficial, what we gathered from our study is that the testing methods are likely missing potential candidates with testing methods that are too conservative or not truly testing realistic listening scenarios,” she said. “Additionally, if two centres are using different testing or candidacy criteria, a patient may qualify for a cochlear implant at one centre and not at another. This creates confusion and mistrust in the process that is already difficult and stressful for the patient.”

One example where differences in practice may hinder CI access is the lack of clarity regarding the use of hearing level (HL) and sound pressure level (SPL) in test administration. Seventy-four percent of those who used MSTB testing materials employed an SPL scale and the other 26 percent an HL scale at various decibel levels. Previous research has demonstrated that presentation at 60 dB HL results in an SPL of approximately 72 dB, which has been shown to be vocally unsustainable and may falsely inflate sentence and word discrimination scores.  Despite existing evidence that 70 dB SPL is not representative of real-world situations and the fact that 60 dB SPL is recommended in MSTB instructions, some clinics in the study still presented test materials at inappropriate levels that may exclude potential candidates who could benefit from CIs.

The industry-wide impact of this variability in testing practices is demonstrated in the 8.3 percent penetration rate into the CI market, Prentiss said. She is working with the American Cochlear Implant Alliance to establish guidelines to streamline preoperative testing methods. In the meantime, she urges audiologists to refer appropriate cases for CI evaluation. “If anyone has a patient that is not perceiving benefit from a hearing aid, the patient can be referred for a cochlear implant evaluation,” Prentiss said. “An evaluation does not necessarily mean the patient will undergo surgery, but rather learn if they are a candidate and be aware of all treatment options for his/her hearing loss and make an informed decision for treatment. No referral is a bad referral!”

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