There are many different types of hearing loss. They can have different causes and a different impact on the individual. Some types of hearing loss occur when the ear drum or other internal organs of the ear are damaged. Other types of hearing loss occur when the sound isn’t transmitted correctly from the ear to the brain, as is the case with auditory neuropathy.
Not all individuals with auditory neuropathy have hearing loss, but they all have trouble understanding speech. Some may have normal hearing while others may have a range of hearing loss. However, in all cases, the ear does not correctly transmit sounds to the brain so that they can be translated and understood.
Auditory neuropathy causes problems in understanding speech. Individuals with the disorder may be able to hear the sounds emitted by speech but they are unable to recognize and decode the words. In some cases, the sounds created by speech fade in and out randomly. Auditory neuropathy can affect people of all ages, from newborns to seniors.
Causes are still being researched
Auditory neuropathy is a fairly new finding in the clinical world. Researchers1 discovered only recently, in 1996, that in some people with the disorder the ear functions normally but the brainstem responds abnormally to sound.
Research continues into the causes of auditory neuropathy but findings aren’t conclusive. To date, it is believed that some cases may be caused by damage to the hair cells in the inner ear. These cells are responsible for the transmission of sound from the ear to the brain. In other cases, the disorder may be caused when the connections between the hair cells and the nerves to the brain are defective. In yet other cases, auditory neuropathy may be caused by a combination of the two.
Risk factors for developing the disorder are also being researched. Scientists do know that it may be genetic because auditory neuropathy can be an inherited trait in some families. Some people with the disorder also have other neurological disorders that could contribute to the likelihood of developing it. Among them are Charco-Marie-Tooth syndrome2 (a group of disorders that affect peripheral nerves) and Friedreich’s ataxia3 (a rare inherited disease that causes damage to the nervous system).
Scientists believe that the disorder may occur at birth due to a number of factors:
- Jaundice at birth
- Premature birth
- Low birth weight
- Inadequate supply of oxygen during birth
- Drugs given to pregnant women
Diagnosis of auditory neuropathy
Auditory neuropathy is diagnosed using several tests including the auditory brainstem response test and the otoacoustic emissions test.
Auditory brainstem response test: In this test, electrodes are placed on the scalp and on each earlobe. Clicking noises are then sent through earphones. The electrodes track the brain’s response to the clicking noises and record the response on a graph.
Otoacoustic emissions test: A small microphone is placed in the ear. As a series of clicks are played, the microphone detects and monitors the sounds generated by the outer ear cells in response to the clicks.
The two tests are compared to determine if the ear functions normally to receive the sound, and whether the brain perceives and correctly translates it.
Can auditory neuropathy be treated?
Just as researchers are still trying to determine the causes and risks for auditory neuropathy, they are also trying to determine the best treatments. There is no consensus and no clinical indication on the best treatments for the disorder. Various opinions on effective treatments include the use of:
- Hearing aids
- Cochlear implants
- Sign language
- A combination of sign language, hearing aids and cochlear implants
If you or a loved one require testing to determine if auditory neuropathy is present, seek out a trained audiologist. He or she can conduct the appropriate tests that can lead to a diagnosis and discussion of treatment options. A trained audiologist can also provide other resources for support and education of the disorder.
References
1: https://emedicine.medscape.com/article/836769-overview
2: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Charcot-Marie-Tooth-Disease-Fact-Sheet
3: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Friedreichs-Ataxia-Fact-Sheet