Auditory neuropathy spectrum disorder (ANSD) is a condition that affects the inner ear. People with ANSD have difficulties understanding speech, although their capacity for detecting other sounds may be unaffected.

Learning spoken language can be challenging for children with this condition. However, certain technologies can help restore some hearing.

This article provides an in-depth introduction to ANSD. After describing the condition and its prevalence, it explains the symptoms, causes, diagnosis, and treatment options.

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ANSD is a hearing disorder that affects a person’s inner ear.

The ears of someone with ANSD may have a typical capacity to detect sounds. However, hearing also involves the ear sending information about these sounds to the brain. ANSD diminishes the ear’s capacity to do this.

It can affect one ear or both and develops in people of all ages. However, doctors diagnose most cases at birth. If a person develops ANSD later in life, it is often due to diabetic neuropathy or conditions that cause nerve cells in the brain or peripheral nervous system to lose function over time.

Common features

People with ANSD have difficulties understanding speech. This occurs even if someone has very little general hearing loss or none at all.

Additionally, people with ANSD may experience speech sounds fading in or out or being out of sync. Some children with ANSD may find it challenging to acquire spoken language skills.

Scientists once considered ANSD a rare disease. However, that opinion has now changed.

According to a 2020 review of the literature about the condition, certain studies estimate 1–10% of people with hearing impairments may have ANSD, and it may affect 10–15% of all deaf people.

The National Deaf Children’s Society (NDCS) states that ANSD can manifest in many ways.

It is a spectrum disorder because its symptoms are highly varied and can differ in intensity. Signs of ANSD include:

  • difficulty with speech comprehension, which may worsen with background noise or fast speech
  • difficulty with speech comprehension that does not match general hearing ability
  • low hearing ability
  • improvement, deterioration, or fluctuation of hearing ability, possibly on a day-to-day basis

In some cases, children with ANSD may have worse hearing when they experience changes in body temperature.

Scientists are still determining the exact reasons why people develop ANSD. Possible causes include:

  • problems with the ear’s inner hair cells, which function to convert certain sounds into information for the brain
  • problems with the auditory neurons that function to transmit this information to the brain
  • problems with the connection between the inner hair cells of the ear and these neurons

The above problems may arise from inherited genetic mutations, damage to the ear, or a combination of both.

Ear damage in newborns may occur due to:

  • infection
  • severe jaundice
  • oxygen deprivation
  • some medications to treat neonatal infections

Diagnosing ANSD can be a complex task.

Doctors use two main diagnostic tests. Both are painless and safe to perform on children and infants.

To perform an auditory brainstem response (ABR) test, doctors place electrodes on the head and, sometimes, the ears. They may also use headphone inserts. This test monitors brain wave activity in response to sound.

An otoacoustic emissions (OAE) test involves placing a tiny, highly sensitive microphone into the ear canal. This microphone can detect the very faint sounds that the ear’s outer hair cells can produce as a response to sound.

ANSD does not affect the ear’s outer hair cells. For this reason, an atypical ABR test result can indicate ANSD if it comes with a typical OAE reading.

Other diagnostic tests include:

  • A cochlear microphonic test: This measures how the cochlear outer hair cells are functioning.
  • Tympanometry and stapedial reflex testing: This tests how well the moving parts of the middle ear function.
  • Behavioural audiometry: This involves using toys and play as a part of the hearing assessment to diagnose the condition in those over 5–6 months old.

Doctors may also perform imaging studies to look at the inner ear and auditory nerve.

In newborns, ANSD can spontaneously improve within 1–2 years. However, without treatment, many people with ANSD will not experience improvements in their condition.

What technologies can help?

Although scientists cannot yet cure ANSD, certain interventions may restore some hearing capabilities.

In particular, the National Organization for Rare Disorders (NORD) lists some assistive listening devices that may help people with ANSD, including:

  • frequency modulation systems
  • cochlear implants
  • hearing aids

An individual’s healthcare team will discuss the most appropriate technologies for their specific case of ANSD.

Healthcare professionals who can help

As NORD explains, treating ANSD and its complications sometimes requires an interdisciplinary team of healthcare professionals. This team may include:

  • audiologists, who are licensed to diagnose and evaluate hearing loss and other related conditions
  • otolaryngologists, who specialize in treating disorders of the ear, nose, and throat
  • neurologists
  • speech therapists
  • genetic counselors

Children who have ANSD from birth may require lifelong attention from this team.

Because ANSD affects a person’s ability to process speech sounds, the condition can make it harder for children to develop spoken language skills. Even with assistive listening devices, some children with ANSD will never learn to speak.

However, the NDCS states that most children with ANSD will acquire spoken language skills.

ANSD can make spoken communication between children and their caregivers difficult or even impossible, at least temporarily.

The NDCS notes some techniques and technologies that can help with communication:

  • using sign language or cued speech, a visual communication system that uses eight hand shapes in four different positions
  • reducing background noise
  • trying assistive devices, such as hearing aids or cochlear implants

Children and their caregivers may also benefit from the advice of a speech therapist.

ANSD is a condition that affects the ear’s ability to process speech sounds. It occurs due to problems with the inner ear and can affect adults and children. While some people are born with ANSD, infections and neurologic conditions can also cause it.

Doctors cannot cure this condition. However, various assistive hearing devices may help with speech-sound processing.

Children with ANSD may find it challenging to acquire spoken language skills. Speech therapy could prove highly useful in these cases. Some children with ANSD may also benefit from learning nonverbal communication skills, such as sign language.