Auditory neuropathy is a very rare and interesting form of hearing loss, whereby the nerve impulses are somehow disturbed within the inner ear or along the auditory nerve on their way to the brain. The cause is still unknown, and currently, there is no cure for the disorder. This type of hearing loss is likely to involve both ears and can be mild or severe, but usually, it's quite problematic to pick up spoken words with some background noise. However, some patients have been able to perceive speech using either hearing aids or cochlear implants.
Auditory Neuropathy
The symptomatology of the auditory neuropathy may differ from one person to the other and may also fluctuate. Some of the symptoms include mild to severe deafness, fading in and out of sounds, speech perception, normal hearing with poor speech perception, poor speech perception due to noise, and profound deafness.
These can overlap with symptoms of the more common kinds of hearing loss; hence, it makes diagnosis and management quite challenging. The condition may cause conductive or sensorineural damage to the auditory system.
How Hearing Works
To understand how auditory neuropathy works, it is essential to understand the very basic process of how the sounds are heard:
Outer Ear: Being the most exposed part of the ear, it collects sounds and then leads them into the middle ear. It essentially forms some kind of conductive lining that assists in channeling the waves of sound inwards.
Middle Ear: The impingement of the sound waves causes a thin membrane partitioning the outer ear from the middle ear, the eardrum, to vibrate. Further amplification of these is done by very small bones also located in the middle ear. The ossicles are then transferred to the inner ear.
Inner ear: The modulated pressure waves reach the cochlea spiral-shaped organ inside the inner ear. Small hair cells detect the vibration all along the cochlea and change the vibrations back into electrical impulses.
Brain: The cochlear nerve sends the impulses to the brain stem, where they get decoded as sound.
In such cases of auditory neuropathy, the structures may work perfectly, but there are disruptions in the transmission from the ear to the brain; hence, the sound gets distorted. At times this disorganization causes deafness due to lesions that affect the auditory pathways.
Causes of Auditory Neuropathy
Even though the true causes of auditory neuropathy have not been clearly known, several factors may lead to the condition:
This can happen because of the damaged hair cells in the inner ear, and then the sound is not conducted properly.
Issues in the connections between Hair Cells and the Cochlear Nerve: Transmission of Sound can also be hindered because of problems in the connections between hair cells and the Cochlear Nerve.
• Direct damage to the Cochlear Nerve itself can create a block in the way Sound is sent to the brain.
• Sensory neural: Damage to the eighth cranial nerve: the nerve which is the combination of Cochlear and vestibular nerves, may be damaged.
Disturbance in the Brain Stem Auditory Pathway: It can cause no syndromic neuropathy, auditory hyperexcitability, and awkwardness in sound interpretation in general.
Auditory Neuropathy: Risk Factors
While auditory neuropathy can occur at any time of life, the following certainly increase the risk of its early development in infants and children.
Complications in pregnancy: Low oxygenation to the fetus could provide increased potential for risk.
Medications: There are certain medications that, if taken during pregnancy, have the potential to selectively kill the inner ear hair cells of susceptible infants.
Birth complications: How risk factors such as premature birth, jaundice, or low birth weight may present a heightened risk.
Neurological Disorders: There seems to be a small number of cases caused by things like Charcot-Marie-Tooth disease or Friedrich's ataxia.
Genetic Factors: In some families, it turns out more common than one would expect from the general population; this factor would seem to indicate a genetic influence.
Infections: One such is the infection by pneumococcal bacteria, which may cause meningitis and result in a hearing problem.
Diagnosis of Auditory Neuropathy
The following are the diagnostic tests:
- Auditory Brainstem Response (ABR): The test is conducted by putting electrodes on the ears and head, which record the response of the hearing nerve to sound. In cases of auditory neuropathy, this response is either absent or abnormal.
- Otoacoustic Emissions: A very small microphone that is inserted into the ear canal, which transmits a response from cochlear hair cells. In most cases, people who have auditory neuropathy still have some remaining functional hair cells.
- Speech Recognition Tests: Tests one's ability to recognize speech, especially in very noisy conditions whereby the length of the noise is at far greater lengths than that of the tone.
Audiometry: An audiometer can deduce the degree of severity and the type of hearing loss, and it is recorded on an audiogram.
Other Tests: The audiologist may conduct a few other tests to rule out some disorders like multiple sclerosis or conduction hearing loss brought about by heavy impact trauma or bone fracture, which may share similar symptoms.
Treatments for Auditory Neuropathy
There can be no universal cure for auditory neuropathy, and the same differs from person to person. Some of the widely popular treatments include:
-Cochlear Implants: These devices get surgically implanted and stimulate nerves in the ear. Most people diagnosed with auditory neuropathy have claimed that they could hear speech more clearly with cochlear implants.
Frequency Modulation Systems: These are carried receivers used with the aid of headsets to amplify sounds without wiring.
- Hearing Aids: These devices amplify all sounds, but most adults with auditory neuropathy do not find them especially useful.
Communication Skills for People with Auditory Neuropathy
Communication skills are taught to children with auditory neuropathy, but this remains highly debated in medical circles. There are two major methods to this effect:
1. Sign Language: Signing method is taught as a supplement to communication.
2. Listening and Speaking Management: This would involve the use of hearing aids or cochlear implants, if required, in addition to proper spoken language development.
As most professionals say, both management approaches are recommended because of the unpredictability of the auditory neuropathy effects. A good enough hearing to understand spoken language is necessary to expose the language to the child. Supplemental cues are much easier to learn in an adult who has already become proficient in spoken language.
Although auditory neuropathy is an extremely complex hearing disorder, characterized by variability in manifested symptoms and outcome, it profoundly affects communication. However, basically many strategies of treatment and management techniques are being made for this issue. Strategies for the betterment of life by better speech perception are also implemented. Continuous research is going on, particularly in the area of the communication strategy and the treatment strategy for this complex condition.
One should also be aware of how to differentiate auditory neuropathy from other kinds of hearing loss, either conductive or sensorineural. Conductive hearing loss, for instance, varies in etiology: it may be caused by swimmer's ear, which is an acute infection of the ear because of an allergy or exposure to water; it may also be the result of vestibular schwannoma. The type and cause of hearing loss have to be determined because they dictate effective intervention and treatment management.
