Auditory neuropathy is a hearing disorder in which sound successfully reaches the inner ear, but for one or more reasons, the signals are not successfully transmitted from the inner ear to the brain.
The process of hearing has many integrated parts by which hearing loss or disorders may occur. Auditory neuropathy (AN) is a disorder that has several proposed causes. One belief is that the disorder starts after the stimulation of hair cells in the inner ear at either the cochlear or vestibulocochlear nerve (associated with hearing and balance). Belief in this cause also brought about a change in the disorder name to auditory dyssynchrony (AD). Often the two are used interchangeably or together as AN/AD (another term used is auditory neuropathy spectrum disorder or ANSD). Other beliefs focus around damage to the hair cells themselves that result in faulty transmission of electrical impulses (converted from sound waves) to the auditory nerves. There is still a great need for research in understanding the causes and treatments of this disorder.
Risk Factors for Auditory Neuropathy\Auditory Dyssynchrony
One risk factor associated with AN\AD relates to prenatal and perinatal circumstances. Some findings suggest that adults that discover that they have AN\AD may have late presenting symptoms of the disorder they had from birth. Risk factors include:
- jaundice (also known as hyperbilirubinemia)
- premature birth
- low-birth weight
- family history of AN\AD
- other neurologic disorders: Charcot-Marie-Tooth syndrome, Friedrich ataxia, Stevens-Johnson syndrome, Ehlers-Danlos syndrome
Diagnosis of Auditory Neuropathy\Auditory Dyssynchrony
Newborns are screened after birth for AN/AD using the auditory brainstem response (ABR) test. This test alone however is not definitive for having the disorder. Adults usually seek medical attention due to symptoms. In adults, onset of symptoms is often progressive in nature. Symptoms differ from hearing loss in that there is not a consistent tone loss. Some individuals may hear all sounds and tones appropriately however are unable to understand what they are hearing, also regarded as poor speech-perception abilities. Other complaints may include sounds that fade in and out or hearing sounds out-of-synch with what would be expected. These symptoms may remain stable, have periods of exacerbation, or worsen over time.
The ABR test is performed by attaching monitoring electrodes to the person's head in order to measure electrical activity along the vestibulocochlear nerve. Another test that usually accompanies the ABR test is the otoacoustic emissions (OAE) test, which measures the function the hair cells within the inner ear. Current understandings of AN/AD suggest that an abnormal ABR test in the presence of a normal OAE test may indicate the disorder. While the ABR and OAE tests are the mainstream tests, other tests may include: pure tone audiogram testing, speech audiometry, and/or acoustic reflex (AR) measures, also known as the middle ear muscle reflex (MEMR) test. Bloodwork and MRIs appear to have no place in the diagnosis of AN\AD. CT scans only need to be performed if surgical interventions, like cochlear implantation, are planned.
Treatment of Auditory Neuropathy\Auditory Dyssynchrony
Currently no cure exists for AN\AD. All treatments are supportive therapies (treat symptoms). Different doctors will subscribe to different philosophies on treatment. Available therapies are listed below:
- hearing aids
- frequency modulation (FM) systems
- cochlear implants
- frequent parental interactions involving face-to-face communication and expressions
- sign language
- lip reading with Cued Speech and Signed Exact English
Living with Auditory Neuropathy\Auditory Dyssynchrony
Since AN\AD is sometimes difficult to pin down, early identification is important in dealing with the disorder. Initiating supportive therapies will help improve the quality of life of the child or adult. In order to get the appropriate therapies for the person, consultations may be needed to help manage AN\AD symptoms. Professional consults may include:
- speech pathologist
- pediatric neurologist
- genetic counselor
Getting the appropriate help will get the person on track to dealing with his disorder. Depending on the degree of the hearing loss, will determine how many therapies and to what extent coping will be needed in dealing with the disorder.
Nemours Foundation. Auditory Neuropathy Spectrum Disorder (ANSD). Accessed: March 25, 2009 from http://kidshealth.org/parent/general/eyes/ansd.html Starr, A., Picton, T.W., Sininger, Y., Hood, L.J., & Berlin, L.I. “Auditory Neuropathy” Brain 1996 119:741-753 http://brain.oxfordjournals.org/cgi/reprint/119/3/741
Nemours Foundation. Auditory Neuropathy Spectrum Disorder (ANSD). Accessed: March 25, 2009 from http://kidshealth.org/parent/general/eyes/ansd.html
Starr, A., Picton, T.W., Sininger, Y., Hood, L.J., & Berlin, L.I. “Auditory Neuropathy” Brain 1996 119:741-753 http://brain.oxfordjournals.org/cgi/reprint/119/3/741