Auditory neuropathy
- Article
- 2021-03-02
What is Auditory Neuropathy?
Auditory neuropathy is a hearing disorder in which the inner ear successfully detects sound but has problems transmitting sound from the ear to the brain. It can affect people of all ages from infancy to adulthood. The number of people with auditory neuropathy is unknown, but current information suggests that auditory neuropathies play a substantial role in hearing impairment and deafness.
When their hearing sensitivity is tested, people with auditory neuropathy can have normal hearing or hearing loss ranging from mild to severe. They always have poor speech intelligibility, which means they have difficulty understanding speech clearly. People with auditory neuropathy have a greater deterioration in speech perception than hearing health experts would predict based on their degree of hearing loss based on a hearing test. For example, a person with auditory neuropathy can hear sounds but still have trouble recognizing spoken words. For these individuals, sounds may fade in and out or appear out of sync.
What Causes Auditory Neuropathy?
Researchers report several causes of auditory neuropathy. In some cases, the cause may be damage to the inner hair cells - specialized sensory cells in the inner ear that send information about sounds through the nervous system to the brain. In other cases, the cause may be damage to the hearing neurons that send sound information from the inner hair cells to the brain. Other possible causes include inheriting genes with mutations or damage to the auditory system, both of which can result in faulty connections between the inner hair cells and the auditory nerve (the nerve that leads from the inner ear to the brain), or damage to the brain. auditory nerve itself. In some cases, a combination of these problems can occur.
What are the roles of the outer and inner hair cells?
Outer hair cells help amplify sound vibrations that enter the inner ear from the middle ear. When hearing is functioning normally, the inner hair cells convert these vibrations into electrical signals that go to the brain as nerve impulses, where the brain interprets the impulses as sound.
While outer hair cells - hair cells in addition to and more numerous than inner hair cells - are generally more susceptible to damage than inner hair cells, outer hair cells appear to function normally in people with auditory neuropathy.
Are There Any Risk Factors for Auditory Neuropathy?
There are several ways that children can get auditory neuropathy. Some children diagnosed with auditory neuropathy had special health problems before or during birth or as a newborn. These problems include inadequate oxygen supply during or before birth, preterm birth, jaundice, low birth weight, and dietary thiamine deficiency. In addition, some drugs used to treat pregnant women or newborns can damage the baby's inner hair cells and cause auditory neuropathy. Adults can also develop auditory neuropathy along with age-related hearing loss.
Auditory neuropathy runs in some families, and in some cases scientists have identified genes with mutations that compromise the ear's ability to transmit sound information to the brain. Thus, inheritance of mutated genes is also a risk factor for auditory neuropathy.
Some people with auditory neuropathy have neurological conditions that cause problems outside the auditory system. Examples of such conditions are Charcot-Marie-Tooth syndrome and Friedreich's ataxia.
How is auditory neuropathy diagnosed?
Health professionals - including otolaryngologists (ear, nose, and throat doctors), pediatricians, and audiologists - use a combination of methods to diagnose auditory neuropathy. These include auditory brainstem response (ABR) and otoacoustic emissions (OAE) tests. The hallmark of auditory neuropathy is an absent or very abnormal ABR measurement along with a normal OAE measurement. A normal OAE measurement is a sign that the outer hair cells are working normally.
An ABR test uses electrodes placed on a person's head and ears to monitor brainwave activity in response to sound.id. In an OAE test, a small, highly sensitive microphone is inserted into the ear canal to monitor the faint sounds produced by the outer hair cells in response to auditory stimulation. ABR and OAE tests are painless and can be used on newborn babies and infants, as well as older children and adults. Other tests can also be used as part of a comprehensive evaluation of a person's hearing and speech perception.
Does auditory neuropathy ever get better or worse?
Some newborn babies diagnosed with auditory neuropathy improve and begin hearing and speaking within a year or two. Other babies stay the same, while some get worse and show signs that the outer hair cells are no longer functioning (abnormal otoacoustic emissions). In people with auditory neuropathy, hearing sensitivity may remain stable, get better or worse, or progressively deteriorate depending on the underlying cause.
What treatments, devices, and other approaches can help people with auditory neuropathy communicate?
Researchers are still looking for effective treatments for people with auditory neuropathy. Meanwhile, hearing professionals differ on the potential benefits of hearing aids, cochlear implants, and other technologies for people with auditory neuropathy. Some professionals report that hearing aids and personal listening devices such as frequency modulation (FM) systems are helpful for some children and adults with auditory neuropathy. Cochlear implants (electronic devices that compensate for damaged or non-working parts of the inner ear) can also help some people with auditory neuropathy. However, no tests are currently available to determine whether a person with auditory neuropathy could benefit from a hearing aid or a cochlear implant.
The best ways to teach and improve communication skills in infants and children with hearing impairments such as auditory neuropathy are also debated. One approach favors sign language as the child's first language. A second approach encourages the use of listening skills - along with technologies such as hearing aids and cochlear implants - and spoken language. A combination of these two approaches can also be used. Some health professionals believe that it can be particularly difficult for children with auditory neuropathy to learn to communicate through spoken language alone, as their ability to understand speech is often severely affected. Adults with auditory neuropathy and older children who have already developed spoken language may benefit from learning to speak speech (also known as lip reading).
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