Auditory neuropathy

Auditory neuropathy is the functional disturbance of the hearing nerve. It is a clinical condition and not the name for a specific disease. In 2008 at a consensus meeting it was decided to change the term auditory neuropathy to auditory neuropathy spectrum disorder (ANSD), incorporating all the different types.

ANSD can originate in the inner hair cell, hair cell neuron junction, nerve or nerve sheath. Unfortunately it is currently not possible to pinpoint the exact site of dysfunction.

It is estimated that 7-10% of children may suffer from ANSD with some not even aware they have it. 70% of all children will have also have other medical problems of various severity. In the other 30% non-syndromic group a genetic cause may be present. In rare cases babies can be born with deficient cochlear nerves.

A large number of the known causes relate to peri natal conditions. These include kernicterus (hyperbilirubinaemia), low birth weight, shortage of oxygen and prematurity. Infections such as mumps and meningitis can cause auditory neuropathy. It is also associated with head trauma. Friedreich ataxia and Stevens-Johnson syndrome have been associated with auditory neuropathy in adults.

The hearing loss occurs due to a timing problem of the electric signals in the nerve. This desynchrony can occur in the presence of normal pure tone hearing thresholds but usually profound hearing loss is present. Some people do not even know they have it. There is usually disproportionate poor speech recognition as expected for the better pure tone hearing present. Patients experience fluctuation in hearing and difficulty understanding speech in back ground noise.

The diagnosis is made with electrophysiological testing. Auditory brainstem responses are abnormal or absent in the presence of normal cochlear function.
A magnetic resonance imaging (MRI) may show an abnormal or absent cochlear nerve.

Patient should be managed by a multidisciplinary team. The hearing can be improved with hearing aids or cochlear implantation. Developing special listening skills and visual communication through speech and sign language if necessary should be encouraged as early as possible.