Auditory Neuropathy Spectrum Disorder (ANSD), or Auditory Neuropathy is a term used to describe hearing loss caused by abnormal auditory nerve function. In today’s post, we’ll discuss what Auditory Neuropathy is, what causes ANSD and how it’s treated.
People suffering from Auditory Neuropathy have a normal cochlea or inner ear function, but experience hearing loss from the abnormal transmission of the sound along the auditory pathway. Simply put: There is a problem with sending sound from the ear to the brain.
When this occurs, it can lead to hearing loss and distortion of sound. Those who experience Auditory Neuropathy may be able to hear alright under normal circumstances but have trouble hearing in noisy environments.
In a normally hearing ear, sounds enter via the ear canal, vibrating the eardrum and moving the tiny bones in the middle ear cavity. These vibrations are then sent through to the cochlea or inner ear where the vibrations stimulate tiny nerve fibres. The signals from the nerve fibres are then transmitted to the auditory nerve which sends the signal along the auditory nerve to the brain for us to make sense of the sound.
In ANSD the sounds reach the cochlea normally but the transmission along the hearing nerve is altered. The functional abnormality is believed to lie in either the connection between cochlea and the auditory nerve, the auditory nerve fibres or a combination of both. The degree of hearing loss varies but is often associated with distortion of sound and therefore poor speech discrimination.
Symptoms of Auditory Neuropathy
Auditory Neuropathy can affect one ear or both ears. The level of hearing loss in people with ANSD can vary from mild to profound. Behavioural responses of infants and young children with Auditory Neuropathy fluctuate which can make it difficult for parents to spot and later manage. Symptoms may vary from person to person. Only a diagnostic hearing assessment with your trusted audiologist can reveal whether or not your child has Auditory Neuropathy.
Auditory Neuropathy Symptoms include:
Auditory neuropathy in babies may occur in association with specific conditions such as extreme prematurity, hyperbilirubinemia and hydrocephalus, or it may present in infants without obvious underlying factors.
Later onset ANSD in adults may develop along with age-related hearing loss. Some ANSD is related to neurological disorders that also cause problems outside of the hearing system. Examples of such disorders are Charcot-Marie-Tooth disease and Friedreich’s Ataxia.
Possible causes of Auditory Neuropathy:
Diagnosing ANSD is complex and requires expertise in analysing electrophysiological hearing tests. An ‘auditory brainstem response’ (ABR) test assesses the function of the auditory nerve and can accurately diagnose a hearing loss in babies as young as a day old. In an ear with ANSD, the ABR response is often absent at a high level (usually 80dB) or not repeatable.
Another test which can help define whether the hearing loss is sensorineural or due to ANSD is the otoacoustic emissions (OAE) test. An OAE is a low-level sound emitted by the cochlea, either spontaneously or evoked by an auditory stimulus, related to the function of the outer hair cells by the cochlea.
In a significant sensorineural hearing loss, OAEs are absent due to the poor function or absence of cochlea hair cells. In some cases of ANSD, OAEs will be present but have been noted to be absent in 30 per cent of ears with ANSD.
All babies in Australia have a hearing screening assessment at birth. Babies with ANSD are not expected to pass this assessment as it is an automated ABR screening test. Babies with ANSD have absent or abnormal ABR, therefore should not pass the assessment. Following the screening test, the baby may be referred for further diagnostic hearing assessment with a paediatric Audiologist.
Click here to learn more about hearing screening in newborns and young children.
The Audiologist will perform a number of tests to investigate the degree and type of hearing loss. They will often repeat the assessment in a month or so to confirm the diagnosis.
Later onset ANSD can be diagnosed in older children or adults when hearing difficulties are reported with or without hearing loss. Often hearing aids are not helpful and sounds are reported as distorted or unclear. A definitive diagnosis is made with ABR testing looking for the cochlear microphonic in the presence of abnormal ABR which does not match the behavioural hearing test results.
Once a diagnosis of ANSD is made by the Audiologist, further investigations are recommended. This will often be by an Ear, Nose and Throat Specialist, a paediatrician and sometimes a geneticist. In cases of unilateral ANSD, MRI scans are often recommended to assess the integrity of the auditory nerve on the affected side.
The child will also be referred for hearing aid or assistive listening device fitting. This will be on a trial and error basis as some children with ANSD will benefit from hearing aid fitting whilst others won’t. Some children may be referred for cochlear implantation candidacy if hearing aids are not beneficial.
Enabling a child to hear in order to develop speech and language is the ultimate goal of the team looking after the ANSD child. ANSD does affect the way children hear but it is difficult to predict how much from the hearing test results.
Oftentimes, the guidance of a speech pathologist combined with behavioural hearing assessments can determine the level of amplification required for the child. Regular hearing assessments will be necessary along the way to monitor and evaluate their progress.
If you have concerns about your child’s hearing, do not delay booking a children’s hearing test with your Audiologist. Our qualified team at Attune Hearing works with children of all ages from infants to teenagers. Untreated hearing problems can slow down your child’s development, so do waste time! To book an appointment today visit our website or give us a call at 1300 736 702.