Can Hearing “Nerve Damage” Be Fixed? Exploring Sensorineural and Retrocochlear Hearing Loss.

I’ve had a query from someone who was diagnosed with hearing loss following chicken pox. At the time, some 20+ years ago, they were told it was “nerve damage, nothing can be done”.

"Nothing can be done" is not correct, as the hearing loss can be helped with amplification. What ENT surgeons usually mean is "it's not reversible" (true, if too much time has passed). With certain other types of middle-ear damage, an operation may be possible to improve hearing.

The term “nerve damage” was often used for sensorineural hearing loss - which is where the damage is located in the cochlea (inner ear) and/or the nerves beyond the cochlea.

Now we would more commonly say "sensorineural" to refer to cochlear damage. The term “retrocochlear” more accurately describes damage beyond the cochlea.

Image copyright: www.centerforacousticneuroma.com

Left to right on the above image shows: ear canal, eardrum (in pink), middle ear bones, semicircular canals and cochlea (spiral shape) and the bundle of nerve fibres leading off to the brain.

Sensorineural hearing loss refers to damage in the cochlea. This is where sound is sensed mechanically and turned into nerve signals.

Retrocochlear damage refers to the nerve fibres and their pathway inside the brain. Any part of that pathway can be damaged, by virus, stroke, tumour etc.

Noise exposure, for instance, can causes damage to the synapses (junctions between the nerve cells) along this retrocochlear pathway. This type of retrocochlear damage is called cochlear synaptopathy. It causes problems with defining and understanding speech in background noise, and it doesn’t show up on a hearing test.

Neuropathy is a degradation of the nerves themselves, or the myelin sheaths that allow them to send signals quickly along their length.

Tumours are another retrocochlear issue, causing hearing loss by compressing the bundle of nerve fibres leading from the inner ear. Lesions can form from strokes or other damage.

The reality for most people is that they will accumulate hearing damage during their life. A scarred eardrum, viruses, noise damage, genetic, and perhaps a blood flow/stroke issue later on. Hence why people in later life can have very different hearing problems, even when their hearing test results are similar. They have a mix of all these elements, some affecting the middle ear, some cochlear and some retrocochlear.

Back to our patient who had “nerve damage”. This could be the ENT surgeon’s short way of saying sensorineural hearing loss, or the surgeon may have known for sure that there was nerve (retrocochlear) damage. A virus like chicken pox can cause both.

Today, a patient who appears with sudden hearing loss might have immediate steroid therapy and oxygen treatment to slow/reverse damage and support the body during the virus’ assault. Investigative tests may be done to determine which areas of the retrocochlear pathway is damaged (audiologists do brainwave pattern studies with electrodes to narrow this down). These investigations are only useful if you think there is a treatment that will work, e.g. removing a tumour or lesion in the brain. Imaging such as MRI is carried out for new asymmetric loss to identify tumours and blood vessel abnormalities in this region.

Most people who were diagnosed with 'nerve damage' historically would not benefit from having investigations, but they would benefit from hearing aids. The treatment pathway for this patient is the same as it is for someone today. Hearing aids, possibly with advanced features and/or auditory training (listening exercises) if synaptopathy is suspected.

Audiologists can conduct speech in noise testing to identify if there are particular problems with hearing in background noise. This is usually quicker and easier than extensive testing to find the exact location and type of damage, and it leads to exactly the same outcomes.

Given the 20+ year timescale, I have advised this patient to go direct to either an NHS or an experienced private audiologist. Hearing aids will give them the better hearing and compensate for the damage caused by the virus. If the high-frequency hearing loss is severe, frequency lowering technology can bring those sounds into their audible range.