Sensorineural hearing loss facts for kids

Quick facts for kids Sensorineural hearing loss
Cross section of the cochlea.
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Sensorineural hearing loss (SNHL) is a type of hearing loss that happens when there's a problem with your inner ear or the special nerve that sends sound signals to your brain. This nerve is called the vestibulocochlear nerve (or cranial nerve VIII). SNHL is the most common type of hearing loss, making up about 90% of all reported cases.

This kind of hearing loss is usually permanent. It can be mild, meaning you only miss very quiet sounds, or it can be very severe, where you can barely hear anything at all. Sometimes, it affects certain sound pitches more than others, like high-frequency sounds.

Sensory hearing loss often happens when the tiny hair cells inside your cochlea (a part of your inner ear) are damaged or don't work right. These hair cells might be abnormal from birth, or they can get damaged later in life. Things that can damage them include infections, certain medicines that are bad for hearing (called ototoxic drugs), and even your genes. A very common cause of SNHL is being around loud noise for a long time, which is called noise-induced hearing loss. Even a single very loud noise, like a gunshot or a bomb, can cause this. Listening to headphones too loudly or being in noisy places often, like concerts or loud workplaces, can also put your hearing at risk.

Neural hearing loss happens when the cochlear nerve itself is damaged. This damage can stop the nerve from sending sound signals correctly to your brainstem.

Most people with SNHL notice their hearing slowly getting worse over many years. Sometimes, it can affect a large range of sounds. You might also experience other symptoms like ringing in your ears (tinnitus) or feeling dizzy (vertigo). The most common types of SNHL are related to age (presbycusis) and noise exposure.

If you have SNHL, you might find it hard to hear people talking when there's a lot of background noise. Understanding conversations on the phone can be tough. Some sounds might seem too loud or sharp. You might also struggle to understand certain speech sounds, like "s" or "f." It can also be hard to tell where sounds are coming from, especially high-pitched ones. People might seem to mumble when they talk. These symptoms can also happen with other types of hearing loss, so a hearing test is needed to find out for sure.

Doctors usually find SNHL by doing a pure tone audiometry test, also known as an audiogram. This test measures how well you hear sounds through bone. Other tests like Tympanometry and speech audiometry can also help. An audiologist is the professional who performs these tests.

There isn't a known cure for SNHL right now. However, there are ways to manage it, like using special communication strategies and hearing aids. For very severe or total deafness, a cochlear implant can be used. This is a special device that can help restore some hearing. You can also help prevent SNHL by avoiding loud noises, certain chemicals and drugs, and head injuries. Treating or getting vaccinated against diseases like meningitis can also help.

What are the Signs of Sensorineural Hearing Loss?

Since doctors can't directly see inside your inner ear, they rely on what you tell them about your symptoms and on hearing tests. Most people with SNHL say their hearing is worse. Many also report a "plugged" feeling in their ear or a ringing sound (tinnitus). About half of them also experience dizziness or balance problems (vertigo).

To help check for symptoms, there's a survey called the Hearing Handicap Inventory for Adults (HHIA). It has 25 questions about how hearing loss affects your daily life.

What Causes Sensorineural Hearing Loss?

SNHL can be something you're born with (called congenital) or something you get later in life (called acquired). Acquired causes can include diseases, loud noise, or injuries. Many cases are simply due to getting older.

Genetic Causes

Sometimes, hearing loss runs in families. More than 40 different genes have been linked to deafness. There are also over 300 syndromes (groups of symptoms) that include hearing loss, and each syndrome can have its own genetic causes.

Causes from Birth (Congenital)

• Infections:
  • Congenital rubella syndrome happens when a pregnant mother gets the rubella virus. This can affect the baby's hearing. Vaccines like MMR have helped control this.
  • Cytomegalovirus (CMV) infection is a common cause of hearing loss that gets worse over time in children. It's a virus easily spread through body fluids. If a pregnant woman gets CMV, it can affect her baby's development, including hearing.
  • Toxoplasmosis is a parasite that can cause SNHL in babies before they are born.
• Inner Ear Problems: Sometimes, the auditory nerves or the cochlea (inner ear part) don't develop normally. This can happen in some genetic syndromes.
• GATA2 Deficiency: This is a group of disorders caused by a problem with the GATA2 gene. This gene is important for the development of blood and other cells. When it doesn't work right, it can affect the fluid-filled spaces around the inner ear, leading to SNHL.

Age-Related Hearing Loss (Presbycusis)

Presbycusis is when your hearing slowly gets worse as you get older. This can start as early as age 18, often affecting high-pitched sounds first. It's more common in men than women. This type of hearing loss might not be very noticeable until much later in life. It's the most common cause of SNHL in many parts of the world.

Studies have shown that people who live in quiet places without much loud noise tend to have better hearing as they age compared to those in noisy, industrial areas. However, genes might also play a role. It's important to remember that hearing loss caused by things other than normal aging (like noise) isn't considered presbycusis, even if it gets worse with age. About one in three people have significant hearing loss by age 65, and by age 75, it's one in two. Age-related hearing loss cannot be prevented or reversed.

Noise-Induced Hearing Loss

Most people living in modern society have some permanent noise-induced hearing loss (NIHL). This happens when the hearing parts of the inner ear are overloaded and damaged by loud noise. NIHL often shows up as a dip in hearing around 4000 Hz on a hearing test. Both how loud the noise is and how long you're exposed to it can cause damage. The louder the noise, the shorter the time you can safely be exposed.

NIHL can be temporary or permanent. For example, if you go to a loud concert, your ears might ring, and your hearing might be dull for a while. This is a temporary shift. Noise levels as low as 70 dB (about twice as loud as normal conversation) can cause damage if you're exposed for a long time (like 24 hours a day). Sounds above 125 dB (a loud rock concert is around 120 dB) can cause instant and permanent ear damage.

Noise and aging are the main reasons for presbycusis, which is the most common type of hearing loss in industrial societies.

Many organizations have set rules for safe noise levels in workplaces and other environments. Sound intensity is measured in decibels (dB). Here are some examples:

An increase of 6 dB means the sound energy doubles, which means it's twice as likely to damage your ears. Our ears hear sound in a special way, so it takes a 10 dB increase for a sound to seem twice as loud. But ear damage depends on the actual sound intensity, not just how loud it feels to you. So, don't rely on how loud a sound seems to judge its danger.

Safe exposure times get shorter very quickly as noise levels go up. For example, you can safely be exposed to 85 dB for 8 hours a day. But at 94 dB (like a nightclub), the safe exposure time is only 1 hour!

• Noise in Your Environment: People living near airports, train stations, busy highways, or factories are often exposed to noise levels between 65 and 75 dBA. If they spend a lot of time outdoors or with windows open, this noise can damage their hearing over time.
• Personal Music Players: Devices like iPods can play music very loudly (115 decibels or more), which is strong enough to cause significant NIHL.
• Acoustic Trauma: A single, extremely loud event, like an explosion or a very loud music concert, can cause immediate temporary or permanent hearing loss.
• Workplace Noise: Many countries have rules about noise levels in workplaces. For example, 90 dB(A) for 8 hours is often considered the maximum safe level to protect workers' hearing.

Diseases or Disorders

• Inner Ear Inflammation: Infections or inflammation of the inner ear can cause SNHL.
• Diabetes: Recent studies show that hearing loss is twice as common in people with diabetes. It's thought that high blood sugar levels might damage the tiny blood vessels in the inner ear, similar to how diabetes can affect eyes and kidneys.
• Tumors: Growths near the brainstem, like an Acoustic neuroma (a non-cancerous tumor on the vestibulocochlear nerve), can press on the hearing nerve and cause SNHL.
• Ménière's disease: This rare condition causes SNHL, usually in low-pitched sounds. It also involves sudden attacks of dizziness, ringing in the ears, and a feeling of fullness in the ear.
• Bacterial meningitis: This serious infection can damage the cochlea. Hearing loss is a common side effect, especially in young children.
• Viral Infections:
  • AIDS can sometimes affect the auditory system.
  • Mumps can cause severe SNHL, often in one ear.
  • Measles can damage the auditory nerve, sometimes causing mixed hearing loss (SNHL plus conductive).
  • Ramsay Hunt syndrome type II (shingles affecting the ear) can also cause SNHL.

Head Trauma

A head injury can damage the ear itself or the brain pathways that process sound. People who have head injuries, especially concussions from contact sports like football or hockey, can experience temporary or permanent hearing loss or tinnitus.

Problems Around Birth (Perinatal Conditions)

These issues are more common in babies born too early, especially those under 1500 grams (about 3.3 pounds). Problems like lack of oxygen, jaundice, bleeding in the brain, or meningitis can lead to SNHL in premature babies.

Iodine Deficiency / Hypothyroidism

Not getting enough iodine can be linked to hearing loss. If a pregnant mother doesn't have enough iodine, it can affect the baby's inner ear development, leading to SNHL. This used to be a problem in some parts of the world, but adding iodine to salt has helped prevent it.

Brain Stroke

A Brain stroke in areas of the brain that handle hearing can also cause deafness.

How Sensorineural Hearing Loss Happens (Pathophysiology)

Sensory hearing loss happens when the tiny hair cells inside the cochlea don't work right. Neural hearing loss happens when the eighth cranial nerve (the vestibulocochlear nerve) or the hearing pathways in the brainstem are damaged. If the problem is higher up in the brain, it's called central deafness.

Cochlear Hair Cells

Figure 3: Cross-section of the cochlea.

The Organ of Corti inside your cochlea has two types of hair cells: outer hair cells (OHCs) and inner hair cells (IHCs). There are about 12,000 OHCs in each ear, arranged in rows. Each OHC has tiny "hairs" called stereocilia on top.

Both OHCs and IHCs are like tiny sensors. IHCs are mainly responsible for sending sound information to your brain. They turn the mechanical movements of sound into electrical signals that your nerves can understand. When the stereocilia on IHCs move, an electrical current flows, creating signals in the connected nerves.

OHCs are special because they actually help the cochlea work actively. They receive vibrations and turn them into electrochemical signals. The stereocilia on OHCs touch a membrane called the tectorial membrane. When the basilar membrane (where the hair cells sit) vibrates, the stereocilia bend. How they bend affects how often the hearing nerves connected to them fire.

OHCs can also contract and expand. This ability helps them fine-tune the basilar membrane and make it very sensitive to quiet sounds. This active process is very important for good hearing, but the cochlea is easily damaged.

Hair Cell Damage

SNHL is most often caused by damage to the OHCs and IHCs. Hair cells can die, or their stereocilia can become damaged. This can happen from viral infections, chemicals that are toxic to the ear, or loud noise.

When OHCs are damaged, the cochlea's active mechanism doesn't work as well, or at all. This means your ear loses its sensitivity to quiet sounds, especially in the 2–4 kHz range. To hear these sounds, they need to be made louder (amplified). IHCs are tougher, but if they get damaged, you'll have a general loss of hearing sensitivity across all sounds. Even damage to just the first row of OHCs can cause a loss of sensitivity to quiet sounds.

How is Sensorineural Hearing Loss Diagnosed?

Case History

Before any tests, your doctor will ask you questions about your hearing, your medical history, and your family's health. This helps them understand your situation.

Otoscopy

The doctor will look inside your ear canal and at your eardrum using a special lighted tool called an otoscope. This helps them check the condition of your outer and middle ear.

Differential Testing

These tests are most helpful if you have hearing loss in only one ear. They help tell the difference between SNHL and conductive hearing loss (problems in the outer or middle ear). They use a tuning fork (usually 512 Hz) to compare how you hear sounds through the air and through your bones.

• Weber test: A tuning fork is placed on the middle of your forehead. If you have SNHL in one ear, the sound will seem louder in your normal ear.
• Rinne test: This test compares how well you hear through the air versus through the bone behind your ear. With SNHL, both air and bone conduction are reduced equally, so the difference between them stays the same.

Table 1. A table comparing sensorineural to conductive hearing loss

Other, more complex tests are needed to figure out the exact type of hearing loss.

Tympanometry

A tympanogram is a test that checks how well your middle ear works and how much your eardrum moves. It can help tell if your hearing loss is due to a problem in the middle ear (conductive hearing loss) or if it's SNHL.

Audiometry

An audiogram is the result of a hearing test. The most common type is pure tone audiometry (PTA). It shows how well you hear different sound pitches (frequencies) between 250 and 8000 Hz. There's also high-frequency audiometry for sounds up to 20,000 Hz. PTA helps tell the difference between conductive, sensorineural, and mixed hearing loss. Hearing loss can be described by how severe it is (mild, moderate, severe, profound) or by its shape on the audiogram (e.g., high-frequency, low-frequency, notched).

Other types of audiometry test how clearly you hear speech (speech audiometry) or how well your hearing nerves transmit signals (evoked response audiometry).

Magnetic Resonance Imaging (MRI)

MRI scans can show big structural problems that cause hearing loss. They are used for hearing loss from birth to see if the inner ear or hearing nerve has an unusual shape. They are also helpful if a tumor is suspected or to check damage from infections or autoimmune diseases. MRI scans are not useful for age-related deafness.

How to Prevent Sensorineural Hearing Loss

While age-related SNHL (presbycusis) can't be prevented, and we don't yet have cures for inherited SNHL, many other causes of acquired SNHL can be avoided. This means staying away from loud environmental noise and very loud sounds like those at rock concerts or nightclubs. Using ear plugs is a good idea in noisy places. You can also learn about the noise levels you're exposed to using special apps. Reducing the time you spend in loud environments also helps lower your risk.

Noise Exposure Limits

How is Sensorineural Hearing Loss Treated?

Currently, there are no approved or recommended cures for SNHL because it's usually a permanent change in the ear. Treatments focus on managing the hearing loss.

For very severe or total hearing loss, cochlear implants might be an option. These are electronic devices surgically placed in the inner ear. Unlike hearing aids, which just make sounds louder, cochlear implants do the job of the damaged inner ear parts, sending sound signals directly to the brain. The sound quality is different from natural hearing, but it can help people understand speech and environmental sounds better. Because of the surgery and cost, implants are usually for severe hearing loss.

Managing SNHL also involves using strategies like lip-reading and improving communication. Hearing aids are often used to make sounds louder and clearer. They are specially adjusted for each person's specific hearing loss to provide the most benefit.

Research into Sensorineural Hearing Loss

New Medicines (Pharmaceuticals)

• Antioxidant vitamins: Some research suggests that a mix of high doses of vitamins A, C, and E, plus Magnesium, taken before and after noise exposure, might help prevent noise-induced hearing loss in animals.
• Tanakan: This medicine, made from Ginkgo biloba, is being studied for treating SNHL and tinnitus that might be caused by blood vessel problems.
• Coenzyme Q10: This vitamin-like substance has antioxidant properties and is being researched for its potential benefits.
• Ebselen: This synthetic drug acts like a natural enzyme in the inner ear that protects it from loud noise damage.

Stem Cell and Gene Therapy

Scientists are working on ways to regrow hair cells using stem cells and gene therapy. While this is still many years away from being available in clinics, studies are happening now. The first human trial approved by the FDA began in 2012.

Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSHL), also called sudden deafness, is a rapid and unexplained loss of hearing. It usually happens in one ear, either all at once or over a few days. Most people with SSHL lose hearing in only one ear. This condition is considered a medical emergency, and getting treatment quickly can make it more effective.

Experts believe about one in 100 people get SSHL each year, usually adults in their 40s and 50s. The actual number might be higher because it often goes undiagnosed.

How it Appears

Many people notice SSHL when they wake up in the morning. Others realize it when they try to use the affected ear, like on the phone. Some hear a loud "pop" just before their hearing disappears. People with sudden deafness often feel dizzy or have ringing in their ears (tinnitus).

Diagnosis

SSHL is diagnosed with a pure tone audiometry test. If the test shows a loss of at least 30 dB in three nearby frequencies, it's diagnosed as SSHL. For example, a 30 dB loss would make normal conversation sound like a whisper.

Causes of Sudden Hearing Loss

Only about 10-15% of SSHL cases have a clear cause. Most cases are called "idiopathic," meaning the cause isn't known. Most evidence points to some kind of inflammation in the inner ear as the most common reason.

• Infection: Viruses like cytomegalovirus, rubella, measles, mumps, HIV, herpes, and even COVID-19 have been linked to SSHL.
• Blood Flow Problems: Poor blood flow to the inner ear or the hearing nerve can cause SSHL.
• Perilymph fistula: This is a leak of fluid from the inner ear, usually due to a tear in the round or oval windows. It often causes dizziness or balance problems, and can happen after trauma or with changes in pressure (like straining or lifting).
• Autoimmune Conditions: Sometimes, the body's immune system attacks the inner ear, leading to SSHL.

Treatment for Sudden Hearing Loss

About 35-39% of people with SSHL recover their hearing completely, usually within one to two weeks. If they get treatment from an otolaryngologist (an ENT doctor), about 85% will recover some hearing.

Treatments can include:

• vitamins and antioxidants
• vasodilators (medicines that widen blood vessels)
• betahistine (a medicine for dizziness)
• hyperbaric oxygen therapy (breathing pure oxygen in a special chamber)
• Medicines that make blood thinner
• anti-inflammatory medicines, especially corticosteroids like prednisone. These can be taken by mouth or sometimes injected directly into the middle ear.

How Common is Sensorineural Hearing Loss? (Epidemiology)

About 10% of people worldwide have some form of hearing loss. In the United States, about 13.5 million Americans have SNHL. Roughly half of these cases are present from birth. The other half are due to infections (before or after birth), certain drugs, loud noise exposure, severe head injuries, and premature births.

At least 8.5 out of every 1000 children under 18 have SNHL. Hearing loss becomes much more common with age; at least 314 out of every 1000 people over 65 have hearing loss. Some things that increase the risk of SNHL include osteoporosis, certain surgeries, and high bilirubin levels at birth.

See also

In Spanish: Pérdida de audición para niños

• Conductive hearing loss, hearing loss caused mainly by problems in the middle ear
• Cortical deafness, another type of nerve deafness
• Hearing loss
• Inner ear, the deepest part of the ear that contains the hearing sensors
• Otosclerosis, a condition of the middle ear that can sometimes lead to SNHL
• Tinnitus, ringing in the ears, which often happens with SNHL