Auditory Neuropathy Spectrum Disorder (ANSD)
ANSD is a type of sensorineural deafness.
Sensorineural deafness happens when there is a fault in the inner ear or the auditory (hearing) nerve that carries sound signals to the brain. Sensorineural deafness is permanent.
In ANSD, sounds are received normally by the cochlea but become disrupted as they travel to the brain. This makes it difficult to recognise and process sounds including speech.
What she can hear depends on the situation. Sometimes she can hear the doorbell or a dog barking, but sometimes she can’t. The problem was that we didn’t actually know what was going on because it was difficult to understand her diagnosis. It’s a new world for us, there’s no history of deafness in our family.
Olha is mum to Anna (8) who's profoundly deaf and has ANSD.
Understanding ANSD
ANSD affects about one to two babies in every 10,000 born. Around one in 10 children with sensorineural deafness have ANSD.
Children with ANSD usually find it harder to understand speech and distinguish one sound from another, especially when there’s background noise. A child with ANSD could have the same hearing levels as a child with sensorineural deafness but find it much harder to understand sounds.
Imagine speaking on a mobile phone with poor reception. The phone itself might work normally, but the sound is distorted. Even with typical hearing levels, you’d struggle to understand what’s being said. It would be even harder to understand if you were in a busy place with lots of background noise. Hearing with ANSD can feel similar.
Listen to a simulation of how different levels of ANSD might sound (YouTube).
ANSD is called a spectrum disorder because it affects children in different ways. Some children with ANSD find it almost impossible to recognise and process speech. Others hear in a similar way to another child with ‘typical’ sensorineural deafness.
Typical features of ANSD include:
- hearing that may vary from normal hearing thresholds to profound deafness
- hearing that may change over time: it may improve, deteriorate (be progressive), or fluctuate on a day-to-day basis
- difficulty understanding speech, especially with background noise
- speech recognition that is worse than predicted for the child’s level of hearing
- difficulty in hearing rapid changes in speech (such as following a conversation)
Some children with ANSD find that changes to their body temperature (such as having a fever) can affect their hearing.
How ANSD affects hearing
The cochlea contains thousands of sensitive ‘inner’ and ‘outer’ hair cells.
The outer hair cells help amplify the sound vibrations which travel from the middle ear to the inner ear.
The inner hair cells convert these vibrations into electrical signals.
The electrical signals travel along the auditory (hearing) nerve as impulses to the brain.
The brain interprets these impulses as sound.
In ANSD, the outer hair cells appear to function normally. ANSD can affect one or more parts of the hearing system beyond the outer hair cells. This may include having an underdeveloped or absent auditory (hearing) nerve.
Imagine a group of runners on a race track, carrying a banner with a message. The track is the auditory nerve. The runners are electrical signals. All the runners need to start running at the same time, run at the same speed, and cross the finish line at the same time so that the banner can be read clearly. This is similar to how typical auditory nerves fire.
Then picture the runners starting at different times, running at varying speeds, not running at all or changing direction. This becomes quite chaotic. The runners will arrive at the finish line at different times, the banner will likely be torn and not all of the message will reach the finish line. This is like ANSD, where the auditory nerves fire out of sync and send mixed and jumbled signals to the brain.
ANSD usually affects both ears (bilateral ANSD) but can also affect one ear only (unilateral ANSD).
Causes of ANSD
Spending time in neonatal intensive care units (NICU)
ANSD happens more frequently in babies who have spent time in NICU. It’s particularly common in babies born extremely prematurely (less than 28 weeks’ gestation).
Babies who have spent time in NICU are at higher risk of having ANSD because they are more likely to have had:
- low birth weight
- infections
- severe jaundice (hyperbilirubinaemia)
- lack of oxygen, difficulty breathing or a period of using a ventilator
Some drugs used to treat neonatal infections are known to be ototoxic (can cause damage to the inner ear). This could cause deafness and ANSD.
Genetics
ANSD may be genetic (inherited), even when there is no family history of deafness. The Otoferlin gene, which is necessary for hearing, is affected with ANSD. This can be inherited.
There also appears to be a link between the Connexin 26 gene (one of the most common causes of congenital sensorineural deafness) and ANSD.
Pre-natal infections
ANSD may be associated with certain infections during pregnancy such as cytomegalovirus (CMV).
Post-natal infections
ANSD has also been associated with infections after birth such as measles, mumps and meningitis.
Neurological conditions
ANSD may develop later in childhood for the first time. This is rarer, but may be associated with neurological conditions such as Charcot-Marie-Tooth disease and Friedreich’s Ataxia.
It’s not always possible to find out why a child has ANSD, but lots of research is happening in this area.
Find out more about the genetic tests used to try and identify the cause of deafness.
'Understanding your child's hearing tests'
Order or download our free resource ‘Understanding your child’s hearing tests’ to learn more about medical tests used to identify the cause of deafness.
Testing for ANSD
ANSD is characterised by absent or abnormal auditory brainstem responses (ABR) in the presence of functioning outer hair cells.
A combination of hearing tests are used to diagnose ANSD. These tests are usually carried out for babies who do not pass their newborn hearing screen or who are considered at risk for ANSD.
Auditory brainstem response (ABR) test
The ABR test measures whether sound is being sent from the cochlea (inner ear) through the auditory (hearing) nerve to the brain. A child with ANSD will have an abnormal or absent ABR. This could be caused by:
- damage to or absence of the inner hair cells of the cochlea
- the inner hair cells not working together and sending a disordered message to the nerves
- a damaged or underdeveloped auditory nerve
Some babies, particularly premature babies, may have an underdeveloped auditory nerve. The ABR test should be carried out again once the baby’s hearing system has had time to develop.
Some babies are born with a condition called hydrocephalus (excess fluid on the brain) which can affect ABR results. The ABR test should be repeated once the fluid has been drained.
Otoacoustic emissions (OAE) test
Otoacoustic emissions (OAEs) are sounds that are generated from the outer hair cells in a healthy cochlea. OAE testing provides an indication as to how well the outer hair cells of the cochlea are working. With ANSD, the outer hair cells are not affected and so OAEs may be present.
However, OAEs are not always reliable for diagnosing ANSD. A significant proportion of individuals with ANSD do not have recordable OAEs and OAEs may disappear over time, even for children with normal hearing. It is not known why this can happen.
Cochlear microphonic (CM) test
Like the OAE test, a CM test also measures how well the cochlea’s outer hair cells are working. CM testing is carried out as part of the tests to diagnose ANSD.
The CM test is usually done at the same time as an ABR test, using the same equipment.
Tympanometry and stapedial (middle ear) reflex testing
This test checks how well the moving parts of the middle ear are working. The middle ear muscles contract in response to loud sounds, and this reflex can be measured as part of the hearing assessment. Where there is a problem with the hearing nerve, as with ANSD, the stapedial reflexes are often absent or elevated.
It’s important to check middle ear function because ANSD cannot be ruled out if OAEs and CMs are absent and the child has glue ear. A child with glue ear should be assessed again once the glue ear has resolved.
Behavioural audiometry
Behavioural hearing tests are used for children older than 5 or 6 months. These tests use toys and play as part of the hearing assessment. Your child will listen for a variety of sounds as part of a game. These tests will tell your audiologist more about what your child hears, processes and responds to.
Speech discrimination testing
Speech discrimination tests check how well the child can hear words at different listening levels. Depending on the child’s age and stage of development, the tester will ask the child to name a toy or picture, or to copy spoken words. The tester will assess the quietest level at which the child can correctly identify the words used.
This test helps to provide information about a child’s functional hearing skills (how well their brain interprets sound). The results can help to make decisions about how to manage ANSD.
Imaging studies
Imaging studies, such as an MRI, can be used to examine the anatomy of the inner ear and auditory nerve to see if there are any defects or abnormalities.
Diagnosing ANSD
Babies who have spent time in neonatal intensive care units (NICU) may be diagnosed soon after birth because both OAE and ABR testing is carried out as part of their routine hearing screening.
Babies who have not spent any time in special care or NICU usually have just OAE testing. OAE testing alone will not identify ANSD. If you have concerns about your baby’s hearing or speech development, you should raise this with your child’s doctor. They may refer you to an audiologist for further testing.
Delayed maturation/myelination
Some premature babies are diagnosed with ANSD but show improvement in their hearing over time.
This may happen when a very premature baby is born before the myelination of their auditory nerve has completed. Myelin is an insulating layer that forms around nerves, including the nerves in the hearing system. This myelin sheath allows nerve impulses to transmit quickly and efficiently along the nerve cells. Myelination of the auditory nerve happens between 26 to 29 weeks' gestation before birth.
If a baby is born before myelination is complete, their ABR test will not give an accurate recording of the function of the hearing nerve. As the nerve matures, some of these babies may show improvement in their hearing over time. This spontaneous improvement has been seen up to around two years of age.
It is therefore essential to monitor babies and young children with ANSD closely to distinguish ANSD from delayed maturation in premature babies where possible.
Almost all children with ANSD are identified as babies. It is less common for older child to be diagnosed. If your audiologist suspects your child may have ANSD, they will arrange ABR testing for your child.
Language and communication
Children with ANSD need support at an early age to help them develop language and communication skills.
Build communication through play
Use our tips to find different activities to help you build communication skills with your deaf baby or toddler.
Make communication visual
Children with ANSD are likely to benefit from using sign language, especially during the early years.
Most children with ANSD develop spoken language as they get older. However, some children with ANSD will not be able to distinguish speech sounds well enough to be able to develop or understand speech. Learning sign language from an early age will help these children to develop language and communication skills in an age-appropriate way.
Reduce background noise
All deaf children find it hard to hear over background noise, but it’s particularly hard for children with ANSD. Try to reduce background noise as much as possible when talking with your child. You can use soft furnishings and wall or floor coverings to reduce echoes.
Technology for children with ANSD
Hearing aids
Hearing aids work by making sound louder, but they don’t make it any easier to understand.
It’s very difficult to predict whether a child with ANSD will benefit from wearing hearing aids. About 50% of children with ANSD benefit from some form of amplification. Others find hearing aids unhelpful.
Because ABR thresholds are unreliable in children with ANSD, hearing aids are fitted based on behavioural hearing tests instead. This means your child’s hearing aid fitting may be delayed until they are developmentally ready to undertake a behavioural hearing test.
If a baby with ANSD is not showing any reactions to sound in the first few weeks of life, your audiologist may suggest fitting hearing aids straight away. The hearing aids may be programmed for a moderate hearing loss to start with, and gradually turned up over a few months depending on how the baby reacts.
Some parents and audiologists choose to wait to fit hearing aids until their child’s hearing threshold levels are stable and consistent.
The professionals working with your child will regularly check your child’s hearing levels when they are wearing their hearing aids. They will also check their understanding of speech and speech development.
Cochlear implants
If your child has an intact and developed auditory (hearing) nerve, but has not benefited from using hearing aids, then you may be offered an assessment for cochlear implants.
Cochlear implants can improve the signals the brain receives because they give direct electrical stimulation to the auditory nerves.
Children with ANSD usually get similar levels of benefit from cochlear implants as children with typical severe to profound sensorineural deafness.
Auditory brainstem implants (ABI)
Children born with very thin or absent auditory nerves may be considered for an ABI.
ABIs are still a very new development. They stimulate the auditory brainstem directly, bypassing the ear and auditory nerve to provide a sensation of hearing.
An ABI does not provide the same benefit or sound as that perceived by a cochlear implant. However, ABIs can help aid lip-reading and provide other clues used in spoken communication (for example, the rhythm and speed of speech).
Unilateral ANSD
Some children have ANSD in one ear only. This is called unilateral ANSD. Children with unilateral ANSD should be monitored closely to make sure it is not affecting their language, communication, educational and social development.
If a child has very poor speech discrimination abilities in the ear with ANSD, then they’re unlikely to benefit from using a behind-the-ear hearing aid but may find other technology useful, such as a bone conduction hearing device, a CROS hearing aid, a personal radio aid or a soundfield system. Some older children with ANSD choose to wear an earplug in the ear with ANSD because they find sound quality on that side distracting.
Other technology
Children with ANSD may benefit from a wide range of assistive listening technology.
Pre-school children and school-age children often benefit from using a radio aid system. Find out more about radio 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.
Full references for this webpage are available by emailing
informationteam@ndcs.org.uk