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Auditory Neuropathy - Causes, Symptoms, Diagnosis, and Management

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Auditory neuropathy is a hearing loss where the inner ear detects the sound but fails to transmit it to the brain. Read the article to know more.

Written by

Dr. Ruchika Raj

Medically reviewed by

Dr. Oliyath Ali

Published At October 5, 2022
Reviewed AtJune 28, 2023

Introduction:

The hearing mechanism involves the interpretation of sound waves by the cochlear cells and transferring electrical impulses from the inner ear to the brain. As the sound impulse enters the eardrum, it transfers to the middle ear, coupled with perilymph fluid. Once the perilymph fluid stimulates it, the impulse is transferred by the auditory nerve to the brain to interpret the sound. The disruption in this mechanism of transfer of nerve impulses from the inner ear to the brain is called “auditory neuropathy.”

What Are the Auditory Nerves?

Auditory nerves are the eighth cranial nerves that help to transfer sound from the inner ear canal to the brain. The primary function of the nerves is to transmit information from the cochlea (a part of the inner ear) to the brain. In addition, the auditory nerves convert the sound vibrations that strike the ear into electrical signals. When these signals reach the brain, the person hears different sounds. Numerous disorders can affect the functioning of the auditory nerves, resulting in hearing loss.

What Is Meant by Auditory Neuropathy?

Auditory neuropathy spectrum disorder (ANSD) is a condition where the ear detects the sound normally, but the problem occurs in sending it to the brain. People affected by this condition will have difficulty differentiating sounds and understanding speech. The sound heard may be in and out or totally out of sync. The extent of hearing loss due to this condition can vary greatly among the affected children. Some common features seen in affected children are

  • Inconsistent speech responses.

  • Difficulty in understanding speech, usually seen more in noisy places.

  • There will be alterations in the hearing regularly.

  • The affected children act as if they have hearing loss.

Some newborns affected by ANSD improve over time as they initiate to hear and speak within one or two years. Some affected newborns stay the same, or the hearing problem can become even worse.

What Are the Causes of Auditory Neuropathy?

The exact cause of auditory neuropathy is still unknown. Some factors supposed to be responsible for auditory neuropathy are

  • Premature birth.

  • Low birth weight.

  • Jaundice in newborns.

  • Vitamin B deficiency.

  • Lack of oxygen at birth.

  • Ototoxic drugs (drugs that are toxic to ears).

  • Intracranial hemorrhage (bleeding between the tissues of the brain and skull).

  • Head trauma.

  • Viral infections like mumps and measles.

  • Genetic mutation.

  • Hereditary (family history of vestibular neuropathy).

  • Neurological disorders (diseases affecting the auditory nerves like acoustic neuroma).

What Are the Signs and Symptoms of Auditory Neuropathy?

Signs and symptoms of auditory neuropathy are:

  • Hearing loss.

  • Reduced hearing intensity.

  • Difficulty in understanding speech.

  • Nervous disorders cause the inability to write, speak and talk.

  • The baby is not babbling or laughing by eight months of age.

  • The child cannot understand speech.

  • Babies cannot speak or learn words by one year of age.

  • Babies do not react or turn to the source of the sound by six months of age.

How To Diagnose Vestibular Neuropathy?

Various diagnostic criteria of vestibular neuropathy are:

  • Auditory Brain Response (ABR) Test: In this test, electrodes are attached to the back of the ears and scalp. The response of the brain to sound is measured, which helps identify defects in the auditory pathway and nerve disorders like acoustic neuroma.

  • An Otoacoustic Emission (OAE) Test: This test measures the response of hair cells in the cochlea to the sound produced in the ear canal by a mini speaker.

  • Middle Ear Muscle Reflex (MEMR): This test evaluates the ear's response to loud sounds. In healthy ears, loud sounds cause the muscles of the middle ear to contract, but in the case of vestibular neuropathy, this muscular reflex is either defective or absent.

  • Magnetic Resonance Imaging (MRI): It checks any defects in the vestibular nerve due to cancerous or non-cancerous soft tissue lesions compressing or involving the auditory nerve (eighth cranial nerve).

  • Pure Tone Audiogram Test: This test helps to measure the severity of hearing loss by measuring the ability of a person to hear various sounds at different frequencies or pitches.

  • Speech and Language Testing: The speech-language pathologist monitors the patient's speech and language.

  • Audiological Assessment: Complete audiological assessment of infants and children is done to evaluate middle ear reflexes and behavioral response to sound.

What Is the Treatment of Vestibular Neuropathy?

Currently, no permanent cure for auditory neuropathy is available. However, some treatment options are:

  • Hearing Aids: These are the small electronic devices worn in the ear, making the sound received very loud and clear. An ENT specialist conducts a test or trial to find a suitable or appropriate hearing aid, which is then advised to the patient.

  • Cochlear Implants: These are small electronic devices implanted in the inner ears of a person suffering from severe hearing loss. A part of the implant is surgically placed inside the skull, and other parts are in the inner ear. Patients with cochlear implants are then taught to listen and speak well.

  • Bone Anchored Hearing System: It is designed such that it transfers sound through bone conduction.

  • Assistive Listening Devices (ALD): Various assistive listening devices are available, like a hearing loop system, infrared system, and amplifiers. These devices help the person to hear the sound loud and clear, even with a lot of background noise.

  • Frequency Modulation (FM) Systems: It helps to reduce background noise and makes the speaker's voice louder.

  • Communication Skill Training: Training for kids or adults is given in vestibular rehabilitation centers for sign language, lip-reading, and audio-verbal therapy (hearing and listening skills).

What Is the Risk Factor Associated With Auditory Neuropathy?

There are various reasons for a child to get affected by this condition. Most of the affected children will experience health issues during or after birth, such as

  • Lack of oxygen during labor.

  • Premature birth.

  • Jaundice.

  • Low weight during birth.

  • Thiamine deficiency.

  • Drugs intaken by pregnant women can affect the inner hair cells of the infant.

What Research Is Ongoing to Detect Auditory Neuropathy?

Various scientific research is going on to identify the gene involved in auditory nerve disorder. Many studies are still ongoing to study the mechanism of how genetic mutation is causing defects in the auditory pathway.

How To Prevent Vestibular Neuropathy?

  • Females should ensure a healthy pregnancy.

  • All vaccination doses should be done on time for children.

  • Avoid using multiple Ototoxic drugs (drugs that are toxic to the ear) simultaneously. Try replacing it with the medicine of an alternate regimen.

  • Avoid exposure to very loud noises for a longer duration.

  • Get the treatment of underlying diseases like acoustic neuroma, any cancerous or non-cancerous growth compressing the vestibular nerve leading to slowly progressive hearing loss.

Conclusion:

Vestibular neuropathy is rare but can affect people at any age. Vestibular neuropathy can cause a mild to profound range of hearing loss in children and adults. Although many diagnostic approaches exist for vestibular neuropathy, the grade of hearing loss cannot be predicted based on these diagnostic tests. The presence of any symptoms, such as increased bilirubin levels, low birth weight, and viral infections, should be observed and treated on a priority basis by consulting an ENT specialist to stop the further worsening of the condition. Further research and studies are needed to be done for the early diagnosis of auditory neuropathy and to cure it completely.

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Dr. Oliyath Ali
Dr. Oliyath Ali

Otolaryngology (E.N.T)

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