Auditory System Hearing Disorders Auditory Neuropathy

Auditory neuropathy is a condition that affects the hearing mechanism at the level of the auditory nerve. In individuals with auditory neuropathy, the auditory system is unable to transmit nerve impulses along the auditory nerve to the brain. This interferes with the hearing process, despite the fact that most of the middle and inner ear structures remain intact.

What is Auditory Neuropathy?

Auditory neuropathy results in a type of sensorineural hearing loss. Sensorineural hearing loss occurs when the auditory system is impaired at the level of the cochlea or the auditory nerve; that is, that problem lies in the inner ear or beyond. In people with auditory neuropathy, the cochlea receives sounds normally, but the problem occurs when the auditory nerve transmits signals to the brain.

The severity of auditory neuropathy varies widely. Auditory neuropathy is sometimes referred to as Auditory Neuropathy Spectrum Disorder (ANSD) because of the wide variation of symptoms and problems that can occur with the condition. Difficulty understanding speech in noisy conditions and fluctuating hearing are hallmarks of auditory neuropathy. Children, in some cases, may recover from early auditory neuropathy. In others, however, the condition persists.

Causes of Auditory Neuropathy

More than one auditory neuropathy cause has been identified. Known causes include:

  • Genetic conditions, such as Friedreich’s Ataxia and certain immune disorders
  • Infection and illness, including mumps and hyperbilirubinemia (a metabolic condition associated with jaundice)
  • Lack of oxygen at birth (anoxia).

Auditory Neuropathy Diagnosis

Hearing test results and medical history information are essential for making a diagnosis of auditory neuropathy. If doctors suspect a patient has auditory neuropathy, the following tests can help to make a diagnosis:

  • Auditory Brainstem Response (ABR) tests the ability of the inner ear system to transmit sound information as nerve impulses to the brain.
  • Otoacoustic Emissions (OAE) plays a sound into the ear, and a sensitive microphone measures the sound that comes back out through the ear. This test determines the integrity of the cochlea’s outer hair cells.

In people with auditory neuropathy, OAE tests are normal (or near normal), while ABR are not. ABR testing looks at both the auditory nerve and the cochlea; however, normal OAE results indicate that the problem found in the ABR test lies in the auditory nerve and its ability to transmit sound information to the brain. In some cases, the cochlea’s inner hair cells (those responsible for transmitting nerve impulses) may be affected, but in many cases cochlear function seems to be intact.

Like other hearing problems, auditory neuropathy cannot be cured, but assistive devices can be used to help individuals to process environmental sound and to develop speech and language skills. Amplification devices, such as FM systems and hearing aids, as well as cochlear implants, may help to improve hearing. However, assistive devices show variable results for individuals with auditory neuropathy. It is important for you to discuss these options with your physician and/or audiologist to determine the best course of action for your particular case.

Resources

KidsHealth (n.d.). Auditory neuropathy spectrum disorder (ANSD). Retrieved February 7, 2010, from KidsHealth.com Web site: http://kidshealth.org/parent/general/eyes/ansd.html.

My Baby’s Hearing (n.d.). Causes of hearing loss: auditory neuropathy. Retrieved February 7, 2010, from My Baby’s Hearing Web site: http://www.babyhearing.org/HearingAmplification/Causes/Neuropathy.asp.

National Institute on Deafness and Other Communication Disorders (n.d.). Auditory neuropathy. Retrieved February 7, 2010, from National Institute on Deafness and Other Communication Disorders Web site: http://www.nidcd.nih.gov/health/hearing/neuropathy.asp.