October - December 2002: Auditory Neuropathy/Dys-Synchrony. II. Management

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1. Introduction

In this second part of our editorial devoted to Auditory Neuropathy/Dys-Synchrony (AN/AD), we would like to address several issues regarding its management. As it is not until recently that this specific kind of deafness was identified, several aspects of its management are still under investigation. However, the follow-up of dozens of patients seen at Kresge Lab allows us to give some insights about the main directions that need to be taken.

2. Background Information

AN/AD patients have:

(1) evidence of poor auditory function, with difficulty hearing in at least some situations or for some stimuli;

(2) evidence of poor auditory neural function, with absent or elevated auditory brain-stem reflexes (either middle ear muscle reflex or olivocochlear reflex) and an abnormal auditory brainstem response (ABR);

(3) evidence of normal outer hair cell function, demonstrated by the presence of either or both otoacoustic emissions (OAEs) and cochlear microphonic (CM). A patient with this hearing disorder can have an audiogram of 90dBHL but still have OAEs. Alternately, a patient with AN/AD can have an audiogram in which all thresholds fall within the normal range of hearing, yet have no ABR.

In AN/AD patients the exact site of the problem cannot be specified. Based on audiologic test results, the anatomic site of lesion of AN/AD lies somewhere in the auditory pathway between the outer hair cells and the afferent neurons of the auditory nerve. Locating the exact site of lesion is complicated by the likelihood that AN/AD has more than one etiology and by the tendency for secondary degenerative effects to occur as a result of damage to one part of the peripheral auditory system (Harrison, 2001).

First of all, it is important to know that neither "correcting the audiogram" nor predicting hearing and speech behaviors based on ABR is useful for such patients. The ABR, while required for identification, is not predictive of future speech and language development in these patients. Some AN/AD patients develop speech and language skills despite the lack of an ABR. Also, pure tones do not give an accurate reflection of hearing in AN/AD patients. Pure tone test results may fluctuate, and range from normal thresholds to profound loss with many configurations. The predictive value of the pure tone results merits further study in terms of prognosis for the patient. There is also no significant correlation between CM amplitude and the presence or absence of transient evoked otoacoustic emissions (TEOAEs) with the degree of pure tone hearing loss (Starr et al., 2001).

3. Hearing Aids

The potential benefit from hearing aids appears limited for most patients with AN/AD. Hearing aids may provide greater awareness to environmental sounds, and observation as well as aided sound field audiograms can reflect this. However, the experiences of the patients known to Kresge Lab indicate that hearing aids do not help in development of auditory communication or language acquisition, and this is a primary reason that we do not routinely recommend the use of hearing aids for AN/AD patients. Most patients with AN/AD reject the amplification of a dys-synchronous signal that can create a frustrating listening condition.

If patients or professionals feel that a hearing aid trial is necessary for newly identified AN/AD patients, one ear can be aided and the OAEs of the other ear can be monitored to follow the status of AN/AD (Berlin, 1998).

4. Cochlear Implants

Cochlear implants were not considered at first for AN/AD patients because of the suspected abnormality of the eighth nerve, which seemed counterintuitive for cochlear implant management. Given appropriate family and patient history, cochlear implants are a viable management option for AN/AD patients. Children usually show significant improvements in speech perception abilities, communication skills, and sound detection. A few adults with AN/AD have also been implanted.

We now make our decision on a case-by-case basis, looking at the history of the patient and the desires for future outcomes of the patient and family. Not knowing how a patient will develop makes it difficult to offer a single management plan. Therefore, the age of the patient, current language ability, and extent to which the condition is affecting their life should be considered. Implants are not the only management option but rather may be a strong possibility after careful consideration of the individual's background.

5. Changes over time

Over time, AN/AD may improve, remain unchanged, or become worse. In a few rare cases, the condition seems to have improved over time. In our sample group of 100, seven patients began to develop age appropriate speech and language without amplification, and further intervention was not required for them to function in the hearing and speaking world (Berlin et al., 2001). However, they still no showed no synchronous ABR. Those infants that worsen tend to lose their emissions and become indistinguishable from sensory hearing loss patients. In these cases, early identification can be helpful; it may assist in understanding future behaviors such as sporadic evidence of hearing seen by good prosody, vocal monitoring, word use, awareness to environmental sounds, or a strong rejection of hearing aids.

Berlin et al. (2001) suggested that AN/AD encompasses a continuum of possible outcomes from living in Deaf culture to only minimal difficulty hearing in noise. AN/AD is not limited to children; adults have also been diagnosed with it, though it is not known if the condition developed late, gradually grew worse, or was present but unidentified since infancy. To date, there is no means to accurately predict which course an AN/AD patient may take, whether improving, remaining the same, or progressively worsening.

The variation in AN/AD is particularly represented in adult patients. Some of those seen at Kresge Lab have been able to manage quite well with visual input such as lip reading, closed captioning or by using their own compensation strategies. Some AN/AD adults obtain success with cochlear implants, while others function well in the Deaf community and use sign language as their primary means of communication. A few patients show only mild functional effects of the AN/AD.

6. Other considerations

With the development of newborn screening programs many AN/AD patients are identified at a young age. From the sample of 100 AN/AD patients (Berlin et al., 2001), the largest group was two years old or younger. For infants, management can mean watchful waiting. While this can seem frustrating for parents, it is necessary to ensure the best course of action. During the waiting period, visual language in the form of cued speech and some method of signs (e.g., baby signs, signed English, ASL) should be used with the infant to avoid language delays (Berlin et al., 2002).

The watchful waiting period can vary, though a general guideline used at the Kresge Lab is no more than 18-24 months of age. During this time, methods of visual language training are used, and the child should be monitored for presence of emissions, synchrony in the ABR, and development of language. The family should determine what they want for the child's future in terms of functioning in the hearing world.

AN/AD is not limited to the pediatric population. Some patients do not discover that they have AN/AD until later in life when difficulty in school or work is encountered. Some of these patients may also have associated conditions such as Charcot-Marie-Tooth disease, other neurological degenerative conditions, or visual deficits that require careful scrutiny. Current language level and function should be examined in this population. Even though language may develop, our experience is that AN/AD patients have little or minimal word or sentence recognition in the presence of competing noise. This can have a significant effect on educational and vocational achievement.

7. Conclusions

The evolution of AN/AD continues to present a challenge to audiologists and other professionals because there are many variables to consider in its diagnosis and management. Rather than one path, AN/AD presents many facets and several possible outcomes for patients. The use of physiologic tests, MEMRs, ABR, OAEs, are critical to an accurate diagnosis. Age is not a limiting factor in the identification of new AN/AD patients. Rather than treating the audiogram, audiologists should match the management with the physiology and the needs of the patient and the family. This may mean not recommending hearing aids even though the audiogram might suggest that they are appropriate. In terms of outcome, there are many variations on the theme of AN/AD, which complicates the choices that families must make. Options should be explored based on patient history, including birth history and the possibility of peripheral neuropathy, and whether there is a desire to enter the hearing and speaking world. Cochlear implants have been found to be successful in many patients with AN/AD, and are one, though not the only, option. With the proliferation of screening programs using ABR, the detection of AN/AD is likely to increase markedly. Therefore we recommend watchful waiting so long as the patient's speech and language develops on target.

8. References

Berlin, C.I., Hood, L.J., Cecola, P., Jackson, D.F., & Szabo, P. (1993). Does type I afferent neuron dysfunction reveal itself through lack of efferent suppression? Hearing Research, 65, 40-50.

Berlin, C.I., Hood, L.J., Hurley, A., & Wen, H. (1996). Hearing aids: Only for hearing impaired patients with abnormal otoacoustic emissions. In C.I. Berlin (Ed.), Hair cells and hearing aids. San Diego: Singular Publishing Group, Inc., 99-111.

Berlin, C.I., (1998). Auditory Neuropathy. Current Opinions in Otolaryngology & Head and Neck Surgery, 6, 325-329.

Berlin, C. (1999). Auditory neuropathy: Using OAEs and ABRs from screening to management. Seminars in Hearing, 20(4), 307-315.

Berlin, C.I., Taylor-Jeanfreau, J., Hood, L.J., Morlet, T., Keats, BJ (2001). Managing and renaming auditory neuropathy (AN) as part of a continuum of auditory dys-synchrony (AD). Abstracts of the 24th Annual Midwinter Research Meeting ,Association for Research in Otolaryngology, 486, 137.

Berlin, C., Hood, L., & Rose, K. (2001). On renaming auditory neuropathy as auditory dys-synchrony. Audiology Today, 13, 15-17.

Berlin, C.I., Li, L., Hood, L.J., Morlet, T., Rose, K., & Brashears, S. (In press,2002). Auditory Neuropathy/Dys-synchrony: After the diagnosis, then what? Seminars in Hearing.

Deltenre, P., Mansbach, A.L., Bozet, C., Christiaens, F., Barthelemy, Pl, Paulissen, D., & Renglet, T., (1999). Auditory neuropathy with preserved cochlear microphonics and secondary loss of otoacoustic emissions. Audiology, 38, 187-195.

Harrison, R.V. (1998). An animal model of auditory neuropathy. Ear & Hearing, 19, 355-361.

Harrison, R. (2001). Models of auditory neuropathy based on inner hair cell damage. In Y. Sininger & A. Starr (Eds.), Auditory Neuropathy: A new perspective on Hearing Disorders (pp. 51-66). San Diego, CA: Singular Publishing Group, Inc.

Hood, L.J., Berlin, C.I., Morlet, T., Brashears, S., Rose, K., & Tedesco, S. (In press, 2002). Considerations in the Clinical Evaluation of Auditory Neuropathy/Auditory Dys-synchrony. Seminars in Hearing.

Rance, G., Beer, D.E., Cone-Wesson, B., Shepherd, R.K., Dowell, R.C., King, A.M. Rickards, F.W., & Clark, G.M. (1999). Clinical findings for a group of infants and young children with auditory neuropathy. Ear and Hearing, 20, 238-252.

Rogers, R. Kimberling, W.J., Starr, A., Kirschhofer, K., Cohn, E., Keyon, J.B., & Keats, B. (2001). The genetics of audiory neuropathy. In Y. Sininger & A. Starr (Eds.), Auditory Neuropathy: A new perspective on Hearing Disorders (pp. 15-35). San Diego, CA: Singular Publishing Group, Inc.

Sawada, S., Mori, N., Mount, R.J., & Harrison, R.V. (2001). Differential vulnerability of inner and outer hair cell systems to chronic mild hypoxia and glutamate ototoxicity: insights into the causes of auditory neuropathy. The Journal of Otolaryngology, 30(2), 106-114.

Shallop, J.K., Peterson, A., Facer, C.W., Fabry, L.B., Driscoll, C.L. (2001). Cochlear implants in five cases of auditory neuropathy: postoperative findings and progress. Laryngoscope, 111, 555-62.

Sininger, Y., & Oba, S. (2001). Patients with auditory neuropathy: Who are they and what can they hear? In Y. Sininger & A. Starr (Eds.), Auditory Neuropathy: A new perspective on Hearing Disorders (pp. 15-35). San Diego, CA: Singular Publishing Group, Inc.

Starr, A., Picton, T.W., Siniger, Y., Hood, L.J., & Berlin, C.I. (1996). Auditory neuropathy. Brain. 119, 741-753.

Starr, A., Sininger, Y., Nguyen, T., Michalewski, H.J., Oba, S., & Abdala, C. (2001). Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy. Ear and Hearing, 22, 91-99.

Starr, A., Picton, T., & Kim, R. (2001). Pathophysiology of auditory neuropathy. In Y. Sininger & A. Starr (Eds.), Auditory Neuropathy: A new perspective on Hearing Disorders (pp. 67-82). San Diego, CA: Singular Publishing Group, Inc.

8. For more information

Linda J. Hood Ph.D or This email address is being protected from spambots. You need JavaScript enabled to view it. :
Kresge Hearing Research Laboratory of the South
Department of Otolaryngology and Biocommunication
Louisiana State University Health Science Center
533 Bolivar Street New Orleans, LA 70112-2234, USA