Auditory neuropathy: What is it and what can we do about it

Original Material From The Hearing Journal
Volume 51, Number 8, August, 1998

By Linda J. Hood, Ph.D.
Louisiana State University Health Sciences Center
Department of Otorhinolaryngology and Biocommunication and the Kresge Laboratory

lhood@lsuhsc.edu

Phone Int + , Fax Int

16. Are there situations where auditory neuropathy could be misdiagnosed?

Yes. Identification of auditory neuropathy presents a particular diagnostic problem in infants and children where the incidence of otitis media is higher than in older children and adults. If middle ear problems prevent evaluation of otoacoustic emissions, then it may be possible to evaluate outer hair cell function using cochlear microphonic measurement since this response appears less vulnerable to mild middle-ear problems than are OAEs (Berlin et al., 1998). In addition to the complicating factor of middle ear problems, it is conceivable that a patient could have a co-existing peripheral hearing loss which could affect the ability to measure otoacoustic emissions.

As an additional technical/procedural note, we always complete OAE testing prior to completing ABR testing in patients who are sedated. During deep sleep, the middle ear may develop positive pressure over time which could alter middle ear mechanics and reduce otoacoustic emission amplitude.

17. Do patients with auditory neuropathy have trouble communicating in everyday situations?

Yes. Our adult patients with auditory neuropathy display some awareness of sound around them, but generally are unable to discriminate speech sounds sufficiently to understand speech. In some patients, this difficulty may be related to neural timing problems (e.g., Starr et al., 1991) that may limit the ability to follow rapid transitions of normal speech. Patients with either some residual hearing ability or later-onset progressive auditory neuropathies tend to rely heavily on lipreading to supplement whatever auditory information is available to them. While reception of speech is difficult, patients generally have normal sounding speech and vocal qualities, suggesting an intact monitoring system.

A major dilemma involves the development of communication abilities in infants and young children identified with auditory neuropathy. These children do not have the advantage of accurate auditory information to help them discriminate and learn appropriate speech and language patterns. Since speech and language develop largely through repetition of heard patterns, active intervention, as discussed below, is critical.

18. What recommendations can I make about appropriate management for these patients?

In infants and young children who have not developed speech and language through auditory channels, the most important consideration is facilitation of the development of language. Since input to the auditory system and processing of auditory stimuli is most likely compromised, alternative input methods may be most helpful.

We recommend use of a visual communication system that follows the grammatical structure of English such as signed English or cued speech (Berlin et al., 1998). The choice of method is usually related to local resources. The goal is to expose children to conversation as it normally occurs in the home and in daily activities by allowing them to "eavesdrop" on all conversations among family members. The selection of a visual communication method that follows English, rather than of American Sign Language, is based on the possibility that auditory function may improve. If the ability to utilize auditory information does improve, then spoken language can be assimilated into a language system that already follows English language structure.

In patients who have already developed spoken language, the goal is to maximize the available auditory information and provide supplementary cues to speechreading. Since some patients are able to understand some speech in quiet surroundings but generally show much difficulty in background noise, enhancing the signal-to-noise ratio may be helpful. Training to improve speechreading skills may also be beneficial.

In addition to auditory and speech-language considerations, patients should be evaluated by a neurologist or pediatric neurologist to identify and manage any neurological abnormalities. And, of course, close collaboration with the patient's otolaryngologist, pediatrician, and/or general physician are important components of comprehensive care of these patients.

19. Do hearing aids, FM systems, or cochlear implants help?

Until the underlying etiologies of auditory neuropathy are better understood, the appropriateness of using hearing aids and cochlear implants is difficult to determine. Adult patients with auditory neuropathy generally report that hearing aids are of little or no benefit. Some patients find FM systems helpful in situations where enhancement of signal-to-noise ratios allow use of residual hearing for speech understanding.

Hearing aids are being tried to a limited extent in some children with auditory neuropathy. If the clinician or a parent strongly wishes to try a hearing aid to enhance awareness of sound, then we recommend high quality, low gain, wide dynamic range compression hearing aids. This approach is intended to minimize any deleterious effects of amplification on otoacoustic emissions until the importance of maintaining otoacoustic emissions in these patients is better understood. Use of more powerful hearing aids for limited time periods or in one ear only is being tried by some centers where trial with stronger amplification is desired. If hearing aids are tried, frequent monitoring of otoacoustic emissions for either temporary or permanent effects on OAEs should be part of the management program.

The potential benefit of cochlear implants is still an open question. If the underlying etiology of the auditory neuropathy in a particular patient is cochlear in origin (i.e., the inner hair cells and/or the hair cell-nerve juncture) and neural function is intact, then a cochlear implant may be potentially beneficial. In cases where the underlying etiology involves neural function, then the anticipated results with a cochlear implant may be less predictable based on current experience.

Unfortunately, we do not yet have a way to determine the specific involvement of either cochlear (inner hair cell) or neural sites in individual patients. Until the underlying etiology of a patient's auditory neuropathy can be determined and performance with cochlear implants or hearing aids is better understood, we take a cautious approach to their use in auditory neuropathy patients.

20. Do patients with auditory neuropathy ever get better ..... or worse?

In adult patients, hearing generally seems to either remain stable, show fluctuation (as in cases of temperature sensitivity or auto-immune disorders), or progressively worsen (as in some patients with HMSN).

In infants, both decline in hearing and improvements in auditory function have been observed (e.g., Berlin et al., 1998; Stein et al., 1996). Some newborns who display normal OAEs and absent ABRs may show improvement if neuromaturation is the underlying problem. In these cases, as the neural system matures, the ABR may improve. Other cases have been reported where auditory function, reflected in development of speech and language, develops over a longer period of time. Still other infants and young children have shown a progressive decrease in auditory responsiveness.

Until the etiologies underlying auditory neuropathy can be identified and distinguished clinically, it will be impossible to make accurate predictions about changes in auditory ability. For now, changes - either improvement or decline - can be ascertained only through long-term follow-up.<

Acknowledgments:

Support for studies related to auditory neuropathy research at Kresge Hearing Research Laboratory has been provided by NIH National Institute on Deafness and Other Communication Disorders, Kam's Fund for Hearing Research, American Hearing Research Foundation, National Organization for Hearing Research, Deafness Research Foundation, Kleberg Foundation, Oberkotter Foundation, and Louisiana Lions Eye Foundation.

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