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:
- Hearing loss of some degree varying from mild to profound loss
- The degree of hearing loss is not predictable from other tests such as Auditory Brainstem Response (ABR) or speech perception testing
- Hearing that appears to fluctuate from day-to-day or even from hour-to-hour
- Difficulty understanding speech, especially with high levels of background noise
- Speech understanding difficulties that are worse than would be predicted from other tests of hearing function
- Other neuropathies that may affect coordination for activities like writing, running or talking
What Causes ANSD?
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:
- Premature birth
- Lack of oxygen (anoxia) at birth
- Hyperbilirubinemia, possibly requiring blood transfusion, associated with severe jaundice during the newborn period
- Ototoxic drug exposure (exposure to drugs or chemicals that damage the inner ear)
- Infectious disease (mumps, etc)
- Immune disorders (Guillain-Barre, etc)
- Non-syndromic dominant autosomal, recessive autosomal, X-linked, or mitochondrial genetic conditions
-
Neurological disorders
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.
How Is Auditory Neuropathy Spectrum Disorder Diagnosed?
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:
- Tympanometry and Acoustic Reflexes
- Auditory Brainstem Response (ABR)
- Otoacoustic Emission (OAEs)
- Behavioral Audiogram (if the child is older than 5 to 6 months of age)
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.
What Are The Treatment and Management Options for ANSD?
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
hearing aids,
cochlear implants or
frequency modulated (FM) systems.
Hearing Aids for Children with ANSD
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.
Cochlear Implants for Children with ANSD
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.
Frequency Modulated (FM) Systems
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.
How Does A Child With ANSD Learn To Talk and Understand Others?
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.
- Some children benefit from teaching that focuses only on learning to listen and speak
- Some children have great difficulty understanding what is heard and benefit more from visual communication approaches (i.e., sign language or Cued Speech)
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.
- Teachers, SLPs, early interventionists, audiologists and other team members can help families to decide whether or not an approach is working
- Once successful approaches are identified the child should make steady progress
- Successful approaches can be modified to enhance outcomes
- Communication and understanding should improve over time, and frustration due to communication challenges should lessen
- This gives families increasing confidence and success in communicating with their child
