Sensorineural hearing loss (SNHL) results from damage to cells or nerve fibers in the inner ear. It affects the auditory nerve, which carries sound signals to the brain. It can appear over time, occur suddenly, or be present from birth.
According to a 2019 article, SNHL is the cause of over 90% of hearing loss cases in adults.
The ear has three parts — the outer, middle, and inner ear. SNHL occurs when there is damage to the inner ear or issues with the auditory nerve that conducts messages between the inner ear and brain.
This article discusses SNHL, its symptoms, causes, and treatment options.
SNHL is a type of hearing loss that occurs as a result of inner ear damage.
It can develop when tiny hairs — stereocilia — become damaged and die off. These hairs are in a part of the inner ear called the cochlea. People may not notice any hearing loss until more than
It can also happen if:
- the auditory nerve becomes damaged
- there is trauma to the structures of the inner ear
- there is atypical development of the cochlea or inner ear structures during fetal development
SNHL can be acquired, sudden, or congenital:
- Acquired: There are many causes of acquired SNHL. For example, a person can acquire SNHL over time due to exposure to loud noises. Exposure to sounds above
85 decibels (dB)can start to damage a person’s hearing over time. This is the equivalent to city traffic from inside the car, gas-powered lawnmowers, and leaf blowers.
- Sudden: Sudden SNHL has a variety of causes, such as infection, head trauma, or other medical conditions.
- Congenital: For approximately
1–3 people in every 1,000, the cause is genetic, and they are born with a predisposition toward hearing loss. Research to determine if cochlear damage is repairable in children who develop SNHL early in life has so far shown inconclusiveresults.
Degrees of hearing loss
Depending on how much damage has occurred, SNHL can range from mild hearing loss to profound hearing loss. According to the American Speech-Language-Hearing Association (ASHA), an audiologist bases this on how loud a sound needs to be for a person to hear it.
The following table outlines the degrees of hearing loss:
|Hearing loss degree||Hearing loss in decibels (dB HL)|
Depending on the cause, a person may experience sensorineural hearing loss in one or both ears:
- Bilateral hearing loss: This occurs when there is hearing loss in both ears. It can be hereditary or develop as a result of medication and noise exposure.
- Unilateral hearing loss: This is partial or total hearing loss in one ear. It can be hereditary or develop due to head trauma or viral or bacterial infections.
- Asymmetrical hearing loss: This refers to hearing loss that affects both ears. However, one side is more affected than the other. This occurs when there is more than a difference of 15 dB hearing range between the ears. Asymmetrical hearing loss can develop due to head injury, medications, aging, noise, or genetic causes.
According to the
Conductive hearing loss might develop as a result of:
An individual can have both conductive and sensorineural hearing loss, called mixed hearing loss.
The symptoms of SNHL can be gradual or sudden.
Some symptoms include:
- muffled sounds
- difficulty understanding speech
- gradual or sudden hearing loss
- a full sensation in the ear
- ringing in the ear
If a person notices symptoms of SNHL, they should make an appointment with a doctor or audiologist for a hearing evaluation.
There are many different causes of SNHL.
Some environmental factors can
- infection, such as:
- premature birth
- low birth weight
Acquired SNHL can develop as a
- presbycusis, which is the gradual hearing loss that develops as a person ages
- exposure to loud noises
- head injury
- Ménière’s disease
- infections, such as meningitis
- autoimmune inner ear disease
- vestibular schwannoma, which is a benign tumor that presses against the auditory nerve
- medications, such as loop diuretics and some types of chemotherapy
- barotrauma, which refers to damage that occurs as a result of abrupt changes in air or water pressure
Sudden SNHL has a variety of causes. However, only
Causes of sudden SNHL include:
- head trauma
- autoimmune conditions
- conditions affecting blood circulation
- neurological conditions, such as multiple sclerosis
- Ménière’s disease
should considersudden SNHL to be a medical emergency. People should contact a doctor as soon as possible if they experience sudden hearing loss.
A doctor or audiologist may perform the following tests to diagnose SNHL:
- Rinne test: An audiologist strikes a tuning fork and places it against the mastoid bone behind the ear. They will do this until a person is no longer able to hear the sound. They will then move the tuning fork in front of the ear canal until a person can no longer hear the sound. If the sound was better when the audiologist held the tuning fork in front of the ear canal, they may have SNHL.
- Weber test: An audiologist strikes a tuning fork and places it against a person’s forehead. If the sound is louder in the affected ear, the hearing loss is conductive. If it is louder in the unaffected ear, a person has SNHL.
- Pure tone audiogram: This measures the ears’ ability to hear different tones and sounds conducted through the air and the bones of the skull.
A healthcare professional will perform the Rinne and Weber tests together.
- tympanometry to assess the function of the middle ear
- otoacoustic emissions test, which checks the inner ear’s response to sound
- electrophysiological tests to measure the activity of the nervous system
- speech audiometry to test the impact of the hearing loss on a person’s ability to communicate
- CT scans and MRI scans
A doctor may also perform acoustic reflexes. This tests the reflex contraction of the muscles in the middle ear.
They may also perform other laboratory tests depending on the potential cause of SNHL.
The doctor will devise a treatment plan based on the underlying cause, the level of hearing loss, and the potential for restoring any hearing.
Hearing aids are the
Depending on the cause, other treatment options may include:
- corticosteroids to treat sudden hearing loss
- continued observation, including hearing tests
- medication with corticosteroids to reduce swelling following loud noises
- surgery to fit a type of hearing device called a cochlear implant
If the cause is Ménière’s disease, a doctor may suggest diuretics and a low sodium diet. If this does not work, they may administer transtympanic steroid injections or perform a procedure called endolymphatic sac decompression.
Acquired SNHL typically progresses slowly, and a person is able to manage the condition with hearing aids and regular appointments with an audiologist. If a person is eligible, cochlear implants can help to improve hearing loss, even if it is profound.
For those with sudden SNHL, the outlook depends on:
- when it developed
- a person’s age
- whether a person has vertigo
- the degree of hearing loss
The outlook tends to be poorer in older adults and those with vertigo or severe hearing loss. For a better outlook, it is important for people to seek treatment quickly.
People should contact a doctor if they have any symptoms of SNHL. However, it is particularly important to seek medical help if a person experiences sudden SNHL.
This is because the cause may be a medical emergency, such as head trauma or infection.
SNHL is a common cause of hearing loss, particularly as people age. It can cause sounds to be quieter, muffled, and distorted, and voices can be difficult to distinguish in loud environments.
There are several causes of SNHL, including age, medications, disease, infection, tumor, head trauma, and loud noise. All of these can cause the tiny hairs in the cochlea to die off, or damage the auditory nerve, resulting in hearing loss.
SNHL is usually irreversible, and treatment involves assistive listening devices.