Auditory Neuropathy/Dyssynchrony Spectrum Disorder (ANSD) is a hearing disorder in which the inner ear (or cochlea) seems to receive sounds normally, but the signals leaving the cochlea are disorganized or the hearing nerve itself does not process sound normally.
ANSD was first identified in the 1990s when advanced testing procedures became available to measure the action of the cells in the cochlea. There are some common features that are usually seen with auditory neuropathy, including:
There are multiple possible causes for auditory neuropathy spectrum disorder. It can be inherited genetically or caused by trauma or disease. The most common known causes and risk factors for ANSD are:
There are large individual differences among children with this hearing disorder. For some, hearing may improve over time. This appears to be most common when the disorder is associated with prematurity or hyperbilirubinemia.
The diagnosis of ANSD is based on a certain pattern of results from a number of different hearing tests. The hearing tests recommended to accurately and properly diagnose ANSD are:
A characteristic finding with ANSD is that
Otoacoustic Emissions (OAEs) are often normal. This means that hair cells in the inner ear are working normally. At the same time,
ABR responses are absent or very abnormal. This shows poor responses from the hearing nerve.
Depending upon what method is used for newborn hearing screening (OAEs or ABRs), some children with ANSD may pass an initial hearing screening conducted in the hospital. This may delay the identification of the hearing disorder. Parents and physicians may not suspect hearing loss right away if an infant's response to sound changes from day to day.
As children get older, more hearing information becomes available. Ongoing testing may show poorer than expected speech understanding and greater difficulty hearing in noisy backgrounds. A wide variety of hearing loss degrees and hearing loss shapes can be seen. Children with ANSD may also have hearing responses that fluctuate or worsen over time.
The location of the problem that causes auditory neuropathy differs from person to person. With commonly used clinical tests, it is not easy to determine the specific site of the problem in a given individual. Therefore, there is no medical treatment for ANSD currently available. Management options include
cochlear implants or
frequency modulated (FM) systems.
Audiologists vary in their opinions about using hearing aids for a child with ANSD. Some children with ANSD do benefit from hearing aids. However, many children with this disorder get limited hearing aid benefit or no benefit at all. An easy-to-use and reliable way to predict who will and will not benefit has not been firmly established.
Many children with the disorder benefit more from a cochlear implant than hearing aids. Many children with ANSD perform as well with cochlear implants as children with typical sensorineural hearing loss. In cases where the site of the hearing problem actually involves the auditory nerve, outcomes with the implant may be more limited.
FM Systems can assist with speech understanding in noisy situations and may be recommended either in combination with one of these devices or by themselves.
No single approach fits all children with ANSD. It is helpful to work closely with a team of professionals who have experience with this particular disorder. A team can help parents observe their child and determine what techniques bring about the best responses.
It is difficult to predict how any one child will do. It is important to be flexible. With guidance, families can try different approaches and evaluate outcomes over time.