Otosclerosis: Causes, Symptoms, Diagnosis, and Treatment

Otosclerosis is a condition involving abnormal bone remodeling in the ear that can cause gradual hearing loss. It most commonly affects the stapes, one of the three tiny bones in the middle ear. When abnormal bone growth restricts the stapes from vibrating properly, sound cannot travel efficiently to the inner ear, resulting in hearing loss.

Otosclerosis often develops in early or middle adulthood and may affect one or both ears. It is more common in women than men and can run in families. In some cases, abnormal bone remodeling also affects the inner ear, potentially causing sensorineural hearing loss or, less commonly, balance-related symptoms.

Although otosclerosis can progress over time, treatments such as hearing aids and surgery can help many people manage the resulting hearing difficulties.

How the Ear Works

Image credit: National Institute on Deafness and Other Communication Disorders (NIDCD), NIH.

To understand how otosclerosis affects hearing, it helps to understand how the ear works. The ear has three main parts: the outer ear, middle ear, and inner ear. Each plays a specific role in converting sound waves into signals the brain can interpret.

Sound waves enter the outer ear and travel through the ear canal to the eardrum. The eardrum vibrates in response, transferring these vibrations to the middle ear, which contains three tiny bones called the ossicles: the malleus, incus, and stapes.

These bones transmit and amplify sound vibrations. The stapes, the smallest of the three ossicles, pushes against the oval window, an opening that transfers vibrations into the fluid-filled cochlea of the inner ear.

Movement of the fluid stimulates tiny sensory cells called hair cells. These cells convert mechanical vibrations into electrical signals, which travel along the auditory nerve to the brain, allowing us to perceive sound.

Think of the middle ear as a mechanical linkage. Each part must move properly to transmit vibrations efficiently. If one of the bones becomes stiff or fixed, less sound energy reaches the inner ear.

This is what happens in otosclerosis when abnormal bone remodeling restricts the movement of the stapes. The resulting hearing loss is typically conductive, meaning sound is not transmitted efficiently through the outer or middle ear.

What Is Otosclerosis?

Otosclerosis is a condition in which abnormal bone remodeling affects the bony structures of the ear. It most commonly involves the stapes, which becomes progressively fixed near its connection to the oval window.

Courtesy: MEDINDIA

According to the National Institute on Deafness and Other Communication Disorders (NIDCD), otosclerosis involves abnormal bone remodeling that can prevent the stapes from moving properly, interfering with sound transmission and causing hearing loss.

In a healthy ear, the stapes moves freely to pass sound vibrations into the inner ear. When otosclerosis restricts its movement, sound transmission becomes less efficient, leading to conductive hearing loss.

In some cases, the condition also affects the bone surrounding the cochlea. When the inner ear is involved, a person may develop sensorineural hearing loss or mixed hearing loss, which combines conductive and sensorineural components.

The exact cause of otosclerosis is not fully understood. Genetic factors appear to play a role, and researchers have investigated possible links with viral infections, including measles. However, these proposed contributing factors do not establish a single cause for the condition.

Otosclerosis usually develops gradually. Some people also experience tinnitus, dizziness, or balance difficulties, particularly when the inner ear is involved.

Characteristics of Otosclerosis

• Gradual progression: Hearing loss often develops over several years.

• One or both ears affected: The condition can begin in one ear and later affect the other.

• Stapes fixation: Abnormal bone remodeling can restrict the movement of the stapes.

• Potential inner-ear involvement: Some cases produce sensorineural or mixed hearing loss.

• No typical external signs: The condition does not usually cause visible changes to the outer ear, and pain is not a typical symptom.

• Specialized testing required: Hearing tests help identify the pattern of hearing loss, while imaging may be used in selected cases.

Symptoms of Otosclerosis

The most common symptom of otosclerosis is gradually worsening hearing. It may initially affect one ear, with the other becoming affected over time.

Some people first notice difficulty hearing soft voices or low-pitched sounds. Others struggle to follow conversations, especially when background noise makes speech harder to distinguish.

Other symptoms may include:

• Tinnitus: Ringing, buzzing, humming, or roaring sounds without an external source.

• Difficulty hearing in noisy environments: Following conversations becomes harder when several people are speaking.

• Paracusis of Willis: Some people with conductive hearing loss report that they hear speech relatively better in noisy surroundings because other people may speak louder to be heard. This is not a reliable diagnostic sign.

• Dizziness or balance difficulties: These symptoms can occur in some cases, particularly when the inner ear is involved.

• No obvious ear pain: Hearing changes may occur without pain or visible changes to the ear.

Because symptoms often develop slowly, otosclerosis can be mistaken for other causes of hearing loss, including age-related hearing changes or earwax buildup.

A hearing assessment is an important step in determining the type and degree of hearing loss. An ear specialist can then investigate whether otosclerosis or another condition is responsible.

Understanding the Audiogram

An audiogram is a chart that shows how well a person hears sounds at different frequencies and volumes. It is an essential part of a hearing assessment and helps distinguish between conductive, sensorineural, and mixed hearing loss.

In otosclerosis, an audiogram may show an air-bone gap. This occurs when hearing thresholds measured through air conduction are poorer than thresholds measured through bone conduction.

Air conduction tests the entire hearing pathway, including the outer and middle ear. Bone conduction bypasses much of the outer and middle ear by delivering vibrations through the skull to the inner ear.

When the stapes is fixed, sound transmission through the middle ear becomes less efficient. As a result, air conduction thresholds may be poorer than bone conduction thresholds.

Another finding sometimes associated with otosclerosis is Carhart's notch, a dip in bone conduction thresholds around 2,000 Hz. This pattern can occur when the stapes is fixed and reflects altered mechanical behavior of the middle ear. It is not, by itself, proof of otosclerosis or a definitive measure of inner-ear damage.

In the audiogram shown below:

• The right ear, represented by circles, shows mild hearing loss with a sensorineural pattern.

• The left ear, represented by X symbols, shows moderate mixed hearing loss, with a dip around 2 kHz consistent with a possible Carhart's notch.

These findings may be compatible with otosclerosis, but the audiogram alone cannot confirm the diagnosis. The full test results, clinical examination, and other investigations must be considered together.

Otosclerosis is not the only middle ear condition that can cause conductive or mixed hearing loss. Cholesteatoma, for example, is an abnormal skin growth in the middle ear that can damage the eardrum and ossicles. It may also cause ear discharge, recurrent infections, or other complications. Unlike otosclerosis, cholesteatoma is not typically associated with Carhart's notch.

This is why hearing test results should always be interpreted alongside other clinical findings.

Diagnosis and Treatment

Diagnosing otosclerosis usually involves a combination of hearing tests and an assessment by an appropriate healthcare professional, such as an audiologist or an ear, nose, and throat (ENT) specialist.

How Is Otosclerosis Diagnosed?

Audiometry

A hearing test measures hearing thresholds at different frequencies. Conductive hearing loss, including an air-bone gap, may suggest a problem with sound transmission through the middle ear.

Tympanometry

Tympanometry measures how the eardrum responds to changes in air pressure. It helps assess middle ear function and can provide additional information when investigating hearing loss.

CT scan of the temporal bone

A CT scan may be recommended when the diagnosis is uncertain, when other conditions need to be ruled out, or when detailed imaging is needed for surgical planning. Not everyone with suspected otosclerosis requires a CT scan.

No single test confirms every case. An ENT specialist considers the hearing test results, symptoms, examination findings, and any necessary imaging before determining the likely cause.

Treatment Options for Otosclerosis

Treatment depends on the severity of hearing loss, its effect on daily life, and the individual's preferences and medical circumstances.

1. Hearing Aids

Hearing aids amplify sound to help people hear speech and everyday sounds more clearly. They are a nonsurgical option for managing hearing loss caused by otosclerosis.

They can be particularly useful for people who prefer to avoid surgery, are not suitable candidates for an operation, or want to manage their hearing difficulties with amplification.

For people diagnosed with mild to moderate hearing loss, Eara's Ascend Premium OTC hearing aids offer rechargeable hearing support, Bluetooth connectivity, and app-based sound adjustments.

However, hearing aids do not remove the abnormal bone growth or stop otosclerosis from progressing. The most appropriate hearing aid depends on the individual's hearing test results, so people with suspected or diagnosed otosclerosis should consult an audiologist or ENT specialist before choosing an over-the-counter device.

2. Stapedotomy or Stapedectomy

Surgery may be considered when conductive hearing loss significantly affects everyday communication.

A stapedotomy involves creating a small opening in the fixed stapes and placing a prosthesis to transmit sound vibrations to the inner ear.

A stapedectomy involves removing part or, in some cases, more of the stapes and using a prosthesis to restore sound transmission.

Both procedures aim to improve the movement of sound into the inner ear. They can improve conductive hearing loss in suitable patients, but outcomes vary, and surgery carries risks that should be discussed with an ENT surgeon.

Surgery may not fully correct any sensorineural component of mixed hearing loss.

3. Cochlear Implants

Cochlear implants may be considered in selected cases of severe or profound hearing loss, particularly when the inner ear is significantly affected and conventional hearing aids provide insufficient benefit.

They work differently from hearing aids. Rather than simply amplifying sound, a cochlear implant converts sound into electrical signals that stimulate the auditory nerve.

They are not a routine treatment for otosclerosis and require a specialist assessment to determine whether someone is a suitable candidate.

Can Otosclerosis Be Prevented?

There is currently no established way to prevent otosclerosis, and no medication has been proven to reliably stop the condition from progressing.

However, appropriate assessment and treatment can help people manage hearing loss and maintain communication in everyday life.

If you have noticed gradual hearing changes, arranging a hearing assessment can help establish the type and degree of hearing loss and guide the next steps.

Living With Otosclerosis

Otosclerosis can affect conversations, work, social activities, and confidence, particularly when hearing changes go unrecognized.

The condition may progress slowly, so people sometimes adapt to hearing difficulties without realizing how much their hearing has changed. Family members may notice that the television volume is increasing or that conversations need to be repeated more frequently.

If you are experiencing these changes, a hearing assessment can help identify whether hearing loss is present and whether further medical evaluation is needed.

If you experience sudden hearing loss, seek urgent medical attention rather than waiting for a routine hearing test. Sudden hearing loss can have causes that require prompt treatment.

For gradual hearing loss, an audiologist or ENT specialist can help determine whether the problem is related to otosclerosis, another ear condition, or a different cause.

You can also take a first step toward understanding your hearing with Eara's free online hearing test. It takes under four minutes, and your results can be emailed to you. The test can help you recognize possible hearing difficulties, but it cannot diagnose otosclerosis or replace a comprehensive hearing assessment.

The Bottom Line

Otosclerosis is a condition involving abnormal bone remodeling that can restrict the movement of the stapes and cause gradual hearing loss. Some people develop conductive hearing loss, while others may experience mixed hearing loss if the inner ear is also affected.

Although otosclerosis cannot currently be prevented, hearing aids and surgery can help many people manage its effects. Cochlear implants may be an option in selected cases of severe hearing loss.

If you are experiencing changes in your hearing, don't assume that they are simply part of getting older or that they will resolve on their own. A hearing assessment and, when necessary, an evaluation by an ear specialist can help identify the cause and determine the most appropriate next steps.