Hearing Problems

Auditory Neuropathy Spectrum Disorder

Auditory Neuropathy Spectrum Disorder (ANSD) has previously been referred to in the literature as Auditory Neuropathy (AN) and Auditory Dys-synchrony (AD). ANSD is a relatively complex type of hearing loss that is believed to be due to abnormalities at the synapse of the inner hair cell and auditory nerve, and/or the auditory nerve itself. ANSD can cause problems on two fronts:

1. Hearing levels: it can result in a hearing loss of any degree (mild, moderate, severe or profound).

2. Speech discrimination: it can result in speech sounding very distorted. In some instances a person with ANSD can have a relatively mild hearing loss demonstrated on an audiogram but speech sounds so distorted to them that they experience severe problems when trying to understand conversation on a day-to-day basis.


Diagnosing ANSD

The key characteristics of ANSD are evidence of normal/near normal cochlear hair cell function together with abnormal/absent auditory nerve function. To test these we need to do the following:

  • Cochlear hair cell function: We can test cochlear function using otoacoustic emissions (OAEs) or looking for the cochlear microphonic (CM) using a 'click' evoked auditory brainstem response (ABR). If OAE's and/or the CM are present we have evidence that there is normal/near normal cochlear hair cell function.
  • Auditory nerve function: To test auditory nerve function we use the auditory brainstem response (ABR). When there is ANSD the waveforms are poorly formed or absent.

Causes of ANSD

ANSD is most commonly seen in babies who have required neonatal intensive care and suffered from hypoxia but it has also been seen in full-term healthy babies.

There has been at least one gene associated with ANSD called the OTOF (otoferlin) gene. This gene codes for the inner hair and spiral ganglion cells within the cochlea.

ANSD can develop later in life. In these instances it is often associated with a syndrome that includes other peripheral neuropathies such as Charcot-Marie-Tooth disease.


Hearing aids & Cochlear Implants for ANSD

Children and adults with ANSD experience varied results with both hearing aids and cochlear implants. This occurs for a number of reasons:

  • Hearing aids: If the person with ANSD doesn't find speech very distorted they can do very well with hearing aids. It is often still helpful for them to use an FM-system in noisier environments but overall they can cope quite well. However, if they do find speech very distorted they may find that the hearing aids just amplify the distortion and they can't communicate effectively without the help of visual cues and/or sign language. In these instances it's worth considering a cochlear implant even if the degree of the hearing loss is not considered to be severe enough to fit the typical cochlear implantation criteria.
  • Cochlear implants: If the ANSD is due to dysfunction of structures within the cochlear a cochlear implant can bypass the problem. If implanted early these patients can do very well with a cochlear implant. However, if MRI-scanning shows that the auditory nerve has not developed properly it may be difficult for the signal from the cochlear implant to get through to the brain so that it can be heard. In these cases the patient may find that the cochlear implant helps them to be more aware of sounds around them but they still have difficulty understanding speech if they can't face the speaker and/or have access to sign language.

Further Reading:

1. Berlin CI, Morlet, Hood LJ: Auditory neuropathy/dyssynchrony: Its diagnosis and management. Pediatr Clinics North Amer 2003;331-340.

2. Gibson PR, Graham JM: Editorial: Auditory neuropathy and cochlear implantation-myths and facts. Coch Implants Int 2008 (published online in Wiley InterScience, www.interscience.wiley.com).

3. Starr A, Picton TW, Kim R: Pathophysiology of auditory neuropathy. In Sininger Y, Starr A. eds., Auditory Neuropathy: A New Perspective on Hearing Disorders. San Diego: Singular Press, 2001: 67-82.

4. Buchman C, Roush P, Teagle H, et al.: Auditory neuropathy characteristics in children with cochlear nerve deficiency. Ear Hear 2006;27:399-408.

5. Rance G: Auditory neuropathy/dys-synchrony and its perceptual consequences. Trends Amplif 2005; 9:1-43.

6. Rance G, Barker E, Mok M, et al.: Speech perception in noise for children with auditory neuropathy/ dys-synchrony type hearing loss. Ear Hear 2007;28: 351-360.

7. Cone-Wesson B, Rance G, Sininger YS: Amplification and rehabilitation strategies for patients with auditory neuropathy. In Sininger Y, Starr A, eds., Auditory Neuropathy: A New Perspective on Hearing Disorders. San Diego: Singular Thompson Learning, 2001: 233-249.

8. Rance G, Barker EJ: Speech perception in children with auditory neuropathy/dyssynchrony managed with either hearing aids or cochlear implants. Otol Neurotol 2008;29:179-182.