Hearing loss occurs when some part of the hearing system is not working as it should. Hearing loss commonly falls into two categories – conductive or sensorineural.
Hearing loss can be described as mild, moderate, severe or profound, depending on the level of the quietest sound a child can hear.
Auditory neuropathy spectrum disorder (sometimes called auditory neuropathy or auditory dys-synchrony) are terms used to describe a particular type of hearing problem when sounds may be transmitted normally through the middle ear and the cochlea but then do not transmit normally from the cochlea, or along the auditory nerve. This means that the child may be hearing something, but this is probably very distorted.
The number of children affected by this condition is not yet fully known, but it is estimated that up to one in 10 profoundly deaf children have this condition.
An ‘otoacoustic emissions’ (OAE) test shows whether the outer hair cells of the cochlea are responding normally. An ‘auditory brainstem response’ (ABR) measures the function of the auditory nerve and its connections in the lower part of the brain. A cochlea microphonic (CM) test also shows evidence of how the cochlea’s hair cells are working. All of these tests are harmless and painless. These tests measure how well parts of the hearing system are working but they do not directly measure hearing itself.
This means that although the ear is picking up sound correctly, the hair cells within the cochlea or the hearing nerve itself may not be passing the sound on to the brain correctly.
Usually the auditory brainstem response will closely match the levels at which a child responds to sound. However, when a child has auditory neuropathy spectrum disorder, the auditory brainstem response will not match the level at which the child responds to sounds. Very often, there will be no auditory brainstem response even though the child does respond to some sounds.
The auditory brainstem response test measures the function of the auditory nerve. In some babies, particularly those born prematurely, the auditory nerve may not be fully developed and the results of the auditory brainstem response test will be poor because of this delay in development. For this reason, very young babies will have their tests repeated when their hearing system has had time to develop.
What can my child hear?Although a child with auditory neuropathy spectrum disorder is hearing something, it may be very distorted and difficult for the brain to make sense of. The hearing loss measured (by hearing responses to sound) with this type of hearing problem varies greatly from child to child, from normal to profound hearing loss. For some children with this condition, their hearing problem will seem to change from time to time or their hearing will be better on some days than others. Sometimes the hearing loss can be progressive (get worse with time), and in some children their hearing has improved with time.
These unusual test results are creating new challenges for families and professionals working with these children. A diagnosis of auditory neuropathy spectrum disorder warns professionals that a child may not act or respond as a typical deaf child. The child will need to be monitored closely as they grow up.
Auditory neuropathy spectrum disorder will affect a child’s ability to understand speech and is often worse than would be predicted by the level of hearing loss measured. Hearing aids may be recommended to help improve a child’s hearing to a level where they can hear quieter sounds. Because professionals cannot rely on the auditory brainstem response test results as they would with other babies, the fitting of hearing aids may be delayed until further tests have been carried out when the child’s hearing system is more developed. This might be after six months of age, depending on the development of the baby. It is vital that hearing aids are of a high quality and are fitted at the earliest opportunity in order to give the child the best chance of learning to understand speech sounds. The guidance of a speech pathologist may be recommended.
Auditory neuropathy spectrum disorder is not yet fully understood, but it probably has more than one cause. Children with this condition have often had significant health problems during or shortly after their birth. They may have been born very prematurely, had a low birth weight, had jaundice or not had enough oxygen. It is possible that auditory neuropathy spectrum disorder runs in some families and may have a genetic cause.
Your child will be assessed regularly by various members of a team made up of different professionals. This team may include specialists from audiology, audiological medicine, paediatrics, ENT, neurology, genetics, and neonatal care as well as speech pathologists and teachers of deaf children. Parents are the most important members of this team and their involvement is vital. There are no general rules or advice for children with auditory neuropathy spectrum disorder. By using continuous assessments and sharing observations and test results, team members will base their advice on the individual child. These professionals are there to support you and your child.
Background noise is a common problem for children with any hearing problem, including auditory neuropathy spectrum disorder. It is important to try to improve your child’s listening environment in order to help them make the most of the speech that they hear. You can do this by using soft furnishings, as well as wall and floor coverings. (Sound will bounce off hard surfaces, creating an echo effect, and soft surfaces reduce this.) Try to reduce background noise as much as possible (for example, turning off the television or radio) when talking together. Toddlers and children at school often benefit from using a personal FM system. The teacher or parent wears a microphone and the child picks up the voice directly through the hearing aids.
Soundfield systems, where the teacher’s voice is fed through a loudspeaker, may also be helpful in the classroom. These systems help to raise the speaker’s voice to a comfortable listening level above the background noise.
It is possible that some children with auditory neuropathy, even those wearing good-quality hearing aids, cannot make enough use of speech sounds to develop speech. Children with this condition are likely to benefit from learning a manual system of communication (for example, a sign language) especially in the early years. This helps to ease the frustration of not being able to communicate when they are very young.
The tests described above are now routinely used for testing newborn babies. The results of the otoacoustic emissions and the auditory brainstem response tests, and other tests, need to be interpreted together in order to get an accurate diagnosis. In the past babies were not necessarily tested in this way and may only have had one or the other, or a hearing test where the health visitor records your child’s responses to sounds behind them. In children with this condition, their response to the otocoustic emissions test may naturally reduce or disappear altogether with time. For this reason, the way in which auditory neuropathy spectrum disorder is diagnosed in an older child may differ, but do talk to your consultant or audiology department for further advice.
If your child has a severe or profound hearing loss for which they get no or limited benefit from their hearing aids, they may be offered an assessment for a cochlear implant. A cochlear implant is a device that is surgically fitted. It stimulates the auditory nerve. The outcomes for children with auditory neuropathy spectrum disorder compared with other types of profound hearing loss are similar.
If you have any worries, discuss them with your doctor, audiologist or another member of your support team.
You can also get further information from the following websites
Information provided by National Deaf Children’s Society. Reproduced with permission.
Disclaimer: The information contained on this website is not intended as a substitute for independent professional advice.
