Dr. McCreery is an associate director of audiology and staff scientist at Boys Town National Research Hospital in Omaha, NE.
A major challenge when treating children with auditory neuropathy spectrum disorder is that the auditory brainstem response and otoacoustic emissions assessments, vital for identifying the disorder, do not provide clinicians with information about what patients can do with what they hear. Pure-tone audiometric data vary from the normal range to profound hearing loss, and speech recognition abilities cannot be accurately estimated based on the degree of hearing loss or audibility. (Int J Audiol 2010;49:30; Trends Amplif 2005;9:1.) Results from functional assessments and outcome measures are critical, and can guide the intervention process for children with auditory neuropathy spectrum disorder (ANSD).
An excellent evidence-based systematic review of audiological management of ANSD was recently published by experts from the University of North Carolina at Chapel Hill and the American Speech Language Hearing Association's National Center for Evidence-Based Practice. (Amer J Audiol 2011;20:159.) The stepwise management protocol that we use in our clinic at Boys Town National Research Hospital in Omaha is outlined in another publication from the UNC group. (Ear Hear 2010;31:325.) The core components of the stepwise process are that every child with ANSD receives a trial with appropriately fit amplification based on his audiogram and children who do not show improvements in auditory behavior or skill development with hearing aids should be evaluated for cochlear implantation.
Referral to early intervention after ANSD diagnosis must occur as it would for any child with hearing loss. The next steps for most infants with hearing loss are taking ear impressions and initiating amplification. Issues relate to our inability to predict behavioral thresholds from the significantly abnormal auditory brainstem response in ANSD, so the initiation of amplification for children with ANSD must not occur until some behavioral threshold data have been obtained using a reliable assessment method, such as visual reinforcement audiometry (VRA).
The obvious downside to waiting for behavioral threshold data is that this approach will often significantly delay the provision of amplification beyond our typical goals for early intervention. This delay does not mean that we simply send the family on its way and tell them to return when the child can sit up well enough for VRA. Instead, the family will need support and counseling about the wide range of auditory skills that can occur with ANSD. Outcome measures can provide early indications about the infant's functional auditory skills, such as the Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS) or LittlEARS. Some children with ANSD have comorbid developmental concerns that may further delay the ability to perform hearing assessment behaviorally and initiate amplification. These delays can be frustrating for parents and audiologists.
Audiologists should focus on ear- and frequency-specific data to facilitate hearing aid fitting once the child is developmentally able to participate in a behavioral hearing assessment. Ideally, a high- and low-frequency threshold in each ear would be preferable as the basis for hearing aid fitting. Research suggests that approximately 50 percent of children with ANSD and some residual hearing may experience improvements in speech recognition with hearing aids. (Ear Hear 2002;23:239.) Unfortunately, the benefit from amplification cannot be predicted on audibility, so the only way to determine if hearing aids will be beneficial for a child with ANSD is to provide them while closely monitoring their auditory behavior and skill development. Loaner hearing aids should be provided, if available, until the degree of benefit from hearing aids can be determined. Parents should be extensively counseled on the wide range of potential outcomes that can occur with hearing aids for children with ANSD. The fitting should be completed using real ear or real-ear-to-coupler difference measurements to verify that speech is audible and that the maximum output is safely controlled, using a standardized prescriptive method such as the desired sensation level. (Trends Amplif 2005;9:159.) Providing audibility does not guarantee a positive outcome for children with ANSD, but no other method can determine the potential for improvement without amplification at this time.
The continued use of developmentally appropriate outcome measures during a trial with amplification can provide important supplemental evidence to estimate hearing aid benefit. Children who experience improvements in auditory skills and communication development with hearing aids should continue to use them. Cochlear implant candidacy should be evaluated for children who do not experience improvements in auditory awareness or other skills during an amplification trial. Cochlear implant candidacy for children with ANSD should include a realistic discussion of the range of potential outcomes and medical and radiological evaluations to determine the integrity of the auditory nerve because some children with ANSD may have an absent or severely deficient auditory nerve. (Ear Hear 2006;27:399.) Children with ANSD and cochlear nerve deficiency may have poorer functional outcomes than children with ANSD who have an intact auditory nerve. (Ear Hear 2010;31:325.)
It is likely a child will need to use hearing assistance technology in concert with his device to ensure communication access in a wide range of acoustic environments, such as in classrooms and public places, regardless of whether he uses a hearing aid or a cochlear implant for auditory access. Assessing a child's functional auditory skills and outcomes should continue as he develops and his listening needs and environments become more varied and complex. The University of Western Ontario Pediatric Audiological Monitoring Protocol can be helpful in documenting the child's progress in auditory development and identifying specific areas of difficulty. (Trends Amplif 2010;15:57.) Children with ANSD can have the best opportunity to reach their potential with ongoing monitoring and evaluation.
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