Sensorineural Hearing Loss (SNHL) occurs when there is damage to the inner ear, auditory nerve (the nerve that runs from the ear to the brain) or to the brain itself. When inner ear nerves become damaged and do not properly transmit their signals to the brain. Sensorineural hearing loss not only reduces the intensity of sound, but it might also introduce an element of distortion resulting in sounds being unclear even when they are loud enough. Sensorineural hearing loss is the most common type of hearing loss among adults (occurs in 80 percent of adult cases).
Sensorineural hearing loss is typically permanent and cannot be corrected medically or surgically. In most cases, the symptoms can be significantly managed with hearing aids. Hearing aids can help treat the symptoms of sensorineural hearing loss, however they cannot perfectly reverse symptoms like eyeglasses do.
Degree of Hearing Loss
Degree of hearing loss refers to the severity of the loss. There are seven categories that are typically used. The numbers are representative of the patient’s thresholds, or the softest intensity that sound is perceived.
Normal = 0 dB to 20 dB
Mild loss = 20 dB to 40 dB
Moderate loss = 40 dB to 60 dB
Severe loss = 60 dB to 80 dB
Profound loss = 80 dB or greater
Sensorineural Hearing Loss Symptoms
In adults, hearing loss may be very gradual, for example in age-related hearing loss. The person may start to find it difficult to hear and understand people when in a noisy place. Hearing loss can also be very sudden, for example if it’s caused by a viral infection of the inner ear.
- Sounds heard are quieter, distorted and less clear
- Difficult to understand the speech if there is background noise
- Ringing or buzzing sound in the ears (tinnitus)
- In case of an infection – symptoms such as earache and discharge from ears
- Other people may appear to mumble or can hear, but do not understand, what is being said
- Vertigo (spinning sensation) may indicate a problem with the nerves in the ear or brain
- Usually Bilateral (both ears) Hearing loss
- Feeling of being off-balance or dizzy
Sensorineural Hearing Loss Causes
The ear is made up of 3 main parts: 1) the outer ear, 2) the middle ear, and 3) the inner ear (cochlea). The outer ear extends from the part of the ear you can touch to the ear drum. The outer ear acts like a funnel to direct sound to the eardrum. The eardrum separates the outer ear and the middle ear. Behind the ear drum is the middle ear, which is normally filled with air.
( Image Credit : BUPA UK )
When sound hits the ear drum, the tiny bones are set in motion which activates the cochlea. Inside the cochlea there are thousands of tiny nerve endings called hair cells. These hair cells change the sound waves into electrical impulses that travel along the auditory (hearing) nerve to the brain. The brain processes these impulses and changes the sounds into something meaningful to you.
Sensorineural hearing loss occurs when something damages the inner ear, the auditory (hearing) nerve, or the parts of the brain that process sound.
- Sensory hearing loss occurs when the cochlea or the tiny hair cells are damaged
- Neural hearing loss occurs when damage occurs to the hearing nerve or the part of the brain responsible for hearing
Sensorineural deafness that is present at birth (congenital) is most often due to :-
- Genetic syndromes
- Infections that the mother passes to her baby in the womb
Sometimes it is hard to tell whether the problem is sensory, neural, or both. That is why we often use the general term sensorineural hearing loss. Sensorineural hearing loss usually starts in the high frequencies (high pitches). As more damage occurs, the hearing in the lower frequencies may also become worse.
Main Causes of Sensorineural Hearing Loss:
The most common types of chemotherapy that cause hearing loss are the platinum drugs or compounds. It usually happens because the Chemotherapy drug has been absorbed into the fluid that surrounds the hair cells. This causes damage to the hair cells which cannot send signals to the brain, making it harder to hear certain sounds.
- Radiotherapy or Radiation
Radiation can cause sensorineural hearing loss in 2 different ways :-
- Radiation may damage the hair cells, like chemotherapy does
- Radiation may also damage the area of the brain that changes sound into meaning or the nerves that transmit electronic signals between the hair cells and the brain.
- Surgery or Tumors
The areas of the brain that process sound can be damaged during brain surgery. The auditory (hearing) nerve can be bruised or even cut. Swelling or a tumor pressing on the nerve can keep the nerve from working properly.
- Age-related hearing loss (presbycusis)
The aging process is a very common cause of sensorineural hearing loss. As we get older, the inner ear nerves and sensory cells gradually die.
- Heredity/Family history
- Injury at birth
- Certain syndromes or diseases like meningitis, scarlet fever, measles
- Certain drugs (prescription as well as illegal) that are toxic to the auditory system
- Head injury
- Regular exposure to loud noises, for example if you work in a noisy place or listen to a lot of loud music
Sensorineural Hearing Loss Treatment
Sensorineural hearing loss is permanent. Usually, it cannot be treated medically. However, it can be treated with hearing aids. Depending on the level of hearing loss and the pitches that are affected, the audiologist may suggest that the patient try hearing aids. Unfortunately, hearing aids are not like glasses, in the sense, they will not give a patient normal hearing. Hearing aids may help make some sounds easier to hear that they may not have heard well before. With hearing aids, speech may still sound distorted to the patient, because hearing loss affects the inner ear in different ways. Making sound loud enough for a patient to hear does not always make sound easier to understand.
The goal of any treatment is to improve your hearing. The following are considered helpful :
- Hearing aids
- Telephone amplifiers and other assistive devices
- Sign language (for those with severe hearing loss)
- Speech reading (such as lip reading and using visual cues to aid communication)
A cochlear implant may be recommended for certain people with very severe hearing loss. Surgery is done to place the implant. The implant makes sounds seem louder, but does not restore normal hearing.
- U.S. National Library of Medicine
- St. Jude Children’s Research Hospital
- American Speech-Language Hearing Association
If you, or your friends and family, think that your hearing is getting gradually worse, see your doctor immediately. Take care and you would be safe from Sensorineural hearing loss .