ANSD

What is Auditory Neuropathy Spectrum Disorder (ANSD)?

In my own words and, most importantly, those of a parent and layman (you may, like me, need to refer to the glossary page for clarification on some of the many acronyms):

Auditory Neuropathy Spectrum Disorder (ANSD) is a long-winded misnomer. It is the latest in a long line of long-winded misnomers which, thus far, takes the prize for being the longest and, in my opinion, the biggest misnomer.

I am sure there are plenty of experts out there rolling their eyes at me for saying this and I have, time and again, been reassured that given the ambiguities of the condition, it is the best name they can come up with at present (until the next one that is). The definition was coined at a recent conference where a consensus was reached on how to define the idiosyncratic symptoms which define the condition.

Herein lies the crux of the problem – ANSD is not a condition per se – it is a description of an anomalous set of symptoms and test results which define this type of hearing loss apart from more common sensoneural or conductive hearing losses.

ANSD – what does it mean? – it means that your child is not a normal deaf child, your child could go on to hear and develop speech and language (regardless of what their testing tells you) or it could mean your child is like Alice and can’t hear anything useful.

Make no mistake, a child with ANSD may be able to hear in windows, they may have good days and bad days, moments of hearing and moments of not.  As a parent we missed Alice’s hearing disability because we thought she could hear.  You are not mad, this condition is designed to confuse and confound.

What surprises me most about hearing loss is, beyond behavioural abnormalities in children, by which I mean it being apparent that they can’t hear, deafness is ‘diagnosed’ by the use of a number of standard testing procedures. The gold standards of these are behavioural tests, most commonly Visual Reinforcement Audiometry (VRA), as these give us information about the thresholds of hearing. The problem is, these give no clue to the underlying cause of the problem and, more importantly, in the case of ANSD, whether it is useful sound or just noise that is ‘heard’.

Various groups of men and women in white coats have discovered, over the years, a number of interesting behaviours of the ears themselves. Most notably, in 1948, Thomas Gold discovered the Oto-Acoustic emission (OAE). In short, this is an echo produced by the inner ear when it picks up sound. I am told that we still don’t really understand what it is or where it comes from but, and this is the key thing, the presence of OAEs is normally a sign of a healthy ear.

In most sensoneurally deaf children, OAEs are absent or very poor and in hearing children, they are present (for the benefit of any health professionals out there, please remember this is written by me for the benefit of other parents out there).

In addition to OAE testing, we are now able, through the use of clever machines, to measure whether the ear itself, the receptacle of sound, is able to translate sound waves into coherent messages which travel to the brain. This is done through Auditory Brainstem Response (ABR) and Cortical Auditory Evoked Potential (CAEP) testing. Most commonly ABRs are used which involve placing electrodes on the forehead and behind the ears of the patient and measuring electrical output of the auditory nerves when sound is played into the ears.

VRA, OAE and ABR testing are the commonplace testing regimes any parent of a ‘deaf’ child will soon become very familiar with.

In the majority of deaf children, part of the ear is either damaged or absent hence the absence of OAEs. VRA testing is then used to define at what levels and frequencies the patient can actually hear given the limited capability of the ear or associated nerves.

This is where ANSD comes in.

In patients with ANSD, which it is estimated make up around 10-15% of all deaf children, these tests produce a different and quite unique set of results. It is these results which define the ‘condition’.

In children with ANSD there are normal OAEs, but completely absent or abnormal ABRs. This suggests that the problem in transmitting sound from the ear to the brain lies either in the innermost workings of the ear itself or in an abnormality (or in rare cases complete absence) of the auditory nerves. In my addled brain, there are many potential causes of this.

  • Damage to or absence of the inner hair cells of the cochlea
  • The inner hair cells are not moving together and hence send a dyssynchronous message to the nerves.
  • A problem with the neurontransmitter at the synapse between the cochlea and the auditory nerves
  • Damage to or absence of the auditory nerves

Which all sounds to me like any number of different conditions, rather than just one and herein lies the problem.

If you are very, very lucky, you will find out, for sure, the route cause of your child’s ANSD. If not, you are left with a best guess.

This is the problem with the name. The cause may not be a neuropathy (problem with the nerve) at all. I preferred Auditory Neuropathy / Auditory Dyssynchrony (AN/AD) as it seemed to cover both the major causes of the symptoms, but I am told it was deemed too unwieldy and confusing. Hence, we got ANSD instead – explain that one. It will probably change again next year, so watch this space.

What seems to be consistent in ANSD patients is that they can ‘hear’ at certain levels (this may be moderate, profound etc.) but what they hear is largely distorted. I read somewhere that it is best described as like listening to a badly tuned radio. There is speech in there somewhere, but the white noise makes it very difficult to decipher. There is a simulation of this through the link at the bottom of this page.

Like many conditions, children (or adults) with ANSD sit somewhere on a normal distribution curve. Some have a reasonable grasp of speech and in situations where there isn’t too much background noise, can learn and use speech quite well. They may grow up in the mainstream without any assistance and, in some cases, go undetected. Some children (like Alice) exist at the other end of the spectrum and have no useful sound and hence develop no speech or language – everything to them is distorted. The majority sit somewhere in between.

So, in a manner of speaking, that is what ANSD is. So what can you do about it?

This is where ANSD converges with ‘normal’ deafness insomuch as the choices available to parents are limited to three things.

  • Embrace your child’s deafness and the opportunities and challenges this will bring and immerse them in the deaf world using sign or lip reading (or other non-sound-based modes of communication) as their primary tool to communicate with the rest of the world.
  • Conventional hearing aids (of which there are various types which I have neither the inclination nor expertise to describe here). In ‘normal’ deaf children, simple amplification, so long as the loss isn’t too profound, can solve the problem. The evidence seems to suggest that some ANSD children benefit from hearing aids as it refines the frequencies of spoken language, filtering out some of the distortion.
  • Cochlear implantation. Evidence suggests that success with a CI in ANSD patients is in line with that of ‘normally’ deaf children, although it does seem to be those ANSD children at the profound end of the scale who benefit most.

Beyond these ‘interventions’ what is most important is giving your child access to language. Be that through signing or, as is the best recommendation for children with ANSD, Cued Speech. I wont go into why that is here as it is covered elsewhere on the blog.

So what causes ANSD?

Your guess is as good as mine (and the majority of the health profession too). What we do seem to know is that there are a number of accepted causes which can lead to any one of the deficiencies in the functioning of the hearing pathway. These are:

  • Bad luck /  a freak of nature
  • Infection (CMV is increasingly being looked at as a potential cause)
  • Jaundice at birth
  • Premature birth (the ANSD can, in some cases, rectify itself as the nerves mature.)
  • Genetic Mutation – A mutation in a gene called Otoferlin has been highlighted as a cause of ANSD. Those children with this as a cause seem to present at the profound end of the scale.

So there you have it. Sit up at the back and any questions?

Some useful links: