What is Sensorineural Hearing Loss? An Audiologist Explains

old woman with white hair trying on a hearing aid

Sensorineural hearing loss is the most common type of chronic hearing loss, accounting for 90 percent of adult cases. But what is it? This guide will cover the causes, symptoms, diagnosis and treatment of sensorineural hearing loss.

Defining Sensorineural Hearing Loss

Medical jargon like “sensorineural” might seem intimidating, so let’s break it down. The root words are “sensory” and “neural.” Sensorineural hearing loss is caused by damage to the parts of your hearing mechanism that sense sound and transmit it to the brain, namely the inner ear and the auditory nerve.

Sensorineural is one of the two main types of hearing loss. The other is conductive hearing loss, which occurs when the outer ear or middle ear cannot properly channel sound to the inner ear. When you have both types, it’s called mixed hearing loss.

The Hearing Mechanism

To better understand sensorineural hearing loss, we need to go over the basics of how hearing works:

  • After sound passes through the ear canal into the middle ear, it vibrates the eardrum.
  • Sound vibrations are transmitted via bones in the middle ear to the inner ear.
  • The inner ear converts sound waves to electrical signals that are sent via the hearing nerve to the brain.

The Sensorineural Component of Hearing

Next, let’s take a closer look at the different parts of the inner ear and related components of the nervous system to learn more about the role they play in hearing:

  • Cochlea: The cochlea is a snail-shaped organ inside the inner ear. It’s filled with fluid and lined with tiny hair cells, delicate sensory organs that pick up vibrations from sound waves.
  • Hair cells: Tiny hair cells line the organ of Corti within the cochlea. The outer hair cells act as amplifiers of sound from the middle ear. The inner hair cells convert sound waves to electrical impulses and transfer them to the auditory nerve. Hair cells do not regenerate once damaged.
  • Auditory nerve: The eighth cranial nerve is also known as the “hearing nerve.” It carries information about hearing and balance to the brain.

The hair cells in the inner ear act as a transducer and convert sound energy to electrical energy. This is picked up by the nerve and then processed in the brain.

Subtypes of Sensorineural Hearing Loss

Sensorineural hearing loss can be further categorized based on factors like onset and whether it only exists or is more pronounced in one ear.

Unilateral sensorineural hearing lossMost sensorineural hearing loss is bilateral, meaning it occurs in both ears. However, conditions like tumors, Meniere’s disease, and trauma can cause sensorineural hearing loss in only one ear.
Sudden sensorineural hearing lossSensorineural hearing loss is typically progressive. It presents slowly and gets gradually worse over time. In rare cases, head trauma, viral infections, and other causes can produce sudden hearing loss that appears instantly or over a few days.
Acute sensorineural hearing lossWhile hearing loss caused by age or noise is chronic and irreversible, some sensorineural hearing loss lasts less than 72 hours and is considered acute.

Causes of Sensorineural Hearing Loss

Anything that harms the auditory nerve or the inner ear can cause sensorineural hearing loss. The most common causes are age and noise, but genetic syndromes, infections, head trauma, and toxic substances can also cause sensorineural hearing loss.

Age-Related Hearing Loss

As people grow older, the nerve endings inside the ear start to break down.

About one in three people over 65 have hearing loss and might benefit from a hearing aid, according to the National Institute on Deafness and Other Communication Disorders website.

Chronic conditions acquired late in life and lifetime exposure to loud noises can aggravate the natural tendency of inner ear components to degrade with age.

Noise-Induced Hearing Loss

Prolonged exposure to sounds louder than 85 decibels damages the inner ear.

Noise-induced hearing loss is common in industries like construction and heavy manufacturing that involve daily exposure to loud noises for hours at a time. Extended use of headphones at unsafe volumes is another risk factor.

Loud sounds like explosions and gunshots can cause acute hearing loss, while repeated loud noise exposure leads to permanent hearing loss.

Other Causes

While noise and age account for the vast majority of sensorineural hearing loss cases, there are several other potential causes, including.

  • Genetic disorders: Around 400 syndromes can cause genetic sensorineural hearing loss. Waardenburg syndrome is the most common, but hearing loss can also result from Usher syndrome, Pendred syndrome, Lange-Nielsen syndrome and others.
  • Viral infections: A viral ear infection can cause hearing loss. For example, prenatal rubella infection is the most common non-genetic cause of congenital hearing loss.
  • Trauma: A head injury can damage the inner ear or the auditory nerve. Trauma from sudden changes in air pressure can cause both sensorineural and conductive hearing loss. This is most common in divers and pilots.
  • Cardiovascular Disease:  Your inner ear doesn’t have a backup blood supply, so any condition that affects blood flow can cause hearing loss, including stroke, high blood pressure, and peripheral artery disease.
  • Toxic chemicals and drugs:  More than 700 drugs have harmful effects on the ear, including nonsteroidal anti-inflammatory drugs, antimalarials and some anti-cancer medications. Solvents, paint thinners and other industrial chemicals can also harm your ear.
  • Autoimmune inner ear disease: This is a rare inflammatory condition where your body’s immune response attacks the ear. It often starts in one ear and progresses to the other over a few weeks to a month.

Sensorineural hearing loss is tied to around 400 different genetic syndromes, of which the most common is the Waardenburg syndrome.

Sensorineural Hearing Loss Symptoms

The most obvious sign of sensorineural hearing loss is a noticeable reduction in your ability to hear. You might notice one or more of the following:

  • You can’t hear high-pitched sounds.
  • Sounds seem muffled.
  • Conversations are difficult to understand, especially over the phone or in the presence of background noise.
  • Friends and family tell you to lower your voice or turn down the TV.

You may also experience other symptoms, such as:

  • Tinnitus
  • Loss of balance and dizziness
  • Ear pain
  • Facial paralysis

How Is Sensorineural Hearing Loss Diagnosed?

To accurately diagnose sensorineural hearing loss, you may need to see a series of medical professionals and undergo several exams.  

Physical Exam of the Ears

Your first step is to see a general practitioner or an ear, nose and throat doctor for a check-up. They will:

  • Review your medical history and medications list for potential causes
  • Ask you questions about your symptoms
  • Examine your ear to rule out conductive causes like a blockage or eardrum rupture
  • Screen you for underlying conditions and risk factors

If the doctor can’t make a definitive diagnosis based on this initial exam, they will refer you to a specialist for more examination.

Hearing Test

Even if your doctor is pretty sure about your diagnosis, they will probably send you to a hearing professional to learn more about your condition. A trained audiologist can use a battery of hearing tests to determine the type and severity of hearing loss.

  • Pure-tone audiometry: This hearing test uses a tone generator to play sounds at various frequencies and volumes. They note the softest sound you can hear at each frequency on a grid called an audiogram.
  • Bone-conduction test: The audiologist uses a tuning fork or a tone generator to play sounds into the ear and through the bone. You have conductive hearing loss if you hear sounds louder through the bone.
  • Speech audiometry: If the audiologist diagnoses you with hearing loss, they might conduct this hearing test to determine how it affects your communication ability. They’ll play sounds of people talking or individual words at various volumes to find the lowest level you can comprehend.
  • Otoacoustic emissions test: This objective hearing test measures sounds produced by the inner ear. It helps diagnose hearing loss in newborns and pre-verbal children. If the tiny hair cells inside the cochlea are damaged, they will not produce otoacoustic emissions.

Pure Tone Audiogram is an outpatient test that evaluates the conduction of sound through the air and the bone.

Other Tests

In most cases, the above tests will be enough to conclusively diagnose sensorineural hearing loss, but you might need to undergo other tests to explore the underlying causes:

  • Auditory Brainstem Response (ABR): This test checks how the brain and nerves respond to sound. It’s useful for detecting tumors and nervous system diseases like multiple sclerosis and syphilis. It can also diagnose hearing loss in children, babies and adults who cannot be conventionally tested.
  • Magnetic-resonance imaging (MRI): MRI scans can identify acoustic neuromas and other growths that could potentially cause hearing loss.
  • Blood tests: If your doctor suspects your hearing loss is due to an autoimmune disorder, infection or chronic systemic disease, they may order bloodwork to rule out these conditions as possible causes.

Treating Sensorineural Hearing Loss

Some forms of sensorineural hearing loss can be reversed by treating the underlying condition medically. For example, hearing loss caused by an autoimmune disorder can usually be treated with steroids.

If your hearing loss results from a toxic reaction to a medication, it can be reversed by switching to alternative drugs.

However, most kinds of sensorineural hearing loss are sadly irreversible. The tiny hair cells of the inner ear will not regenerate once damaged. The good news is that mild or moderate hearing loss can be treated with hearing aids.

Hearing Aids

A good set of hearing aids may not be able to fully restore normal hearing, but they can come close. Hearing aid technology has advanced considerably in the past few decades.

Hearing aids can be programmed based on the results of your hearing test.

For example, if you have greater hearing loss in a specific frequency range, a programmable hearing aid can boost sounds in that range so that you can hear more clearly.

Many hearing aids can filter out background noise and interface with your phone or other devices.

If caught in time, most people with sensorineural hearing loss do very well with hearing aids and conservative treatment.

Cochlear Implants

Hearing aids might not do much good for people with profound or severe hearing loss. Once you’ve reached this stage, you might consider cochlear implants. Also known as a “bionic ear,” a cochlear implant is surgically implanted behind the ear.

The outer part of the cochlear implant has a microphone and a sound processor. It captures sounds and converts them to electrical signals that are transmitted directly into the auditory nerve.

Preventing Sensorineural Hearing Loss

While some folks are especially prone to getting sensorineural hearing loss due to genetics or chronic conditions, there are a few simple steps you can take to reduce your risk:

  • Limit your exposure to loud noises
  • Listening to devices at 60 percent volume and give your ears a break every hour
  • Manage chronic conditions like diabetes and heart disease
  • Live a generally healthy lifestyle
  • Avoid chemicals that can harm your ear
  • Wear ear protection at concerts and on the job if you work around loud noises

Conclusion

Sensorineural hearing loss is the most common type of hearing loss. It results from damage to the inner ear or auditory nerve, and the most common causes are age and exposure to loud noise. Sensorineural hearing loss is seldom reversible but often manageable with the help of hearing aids.

If you have problems hearing, contact your doctor. They’ll examine you and provide medical advice about the next steps.

Citations

1.  Mattox DE, Lyles CA. Idiopathic sudden sensorineural hearing loss. Am J Otol. 1989 May;10(3):242-7.