Otosclerosis

What Is Otosclerosis?

Otosclerosis is a condition in which abnormal bone remodelling occurs within the middle ear, gradually restricting the movement of the tiny bones responsible for transmitting sound. The word itself comes from the Greek oto (ear) and skleros (hard) — reflecting the hardening of bone tissue that characterises the disease. Although it can affect any part of the bony labyrinth of the ear, otosclerosis most commonly targets the stapes (stirrup bone), the smallest bone in the human body, where it meets the oval window of the inner ear.

In a healthy ear, sound waves travel down the ear canal and cause the eardrum to vibrate. These vibrations are then passed along a chain of three tiny bones in the middle ear — the malleus (hammer), incus (anvil), and stapes (stirrup) — collectively known as the ossicular chain. The stapes sits against the oval window, a membrane-covered opening to the fluid-filled inner ear (cochlea). When the stapes vibrates, it creates pressure waves in the cochlear fluid, which stimulate the hair cells that convert sound into electrical signals for the brain.

In otosclerosis, abnormal spongy bone begins to grow around the base (footplate) of the stapes where it connects to the oval window. Over time, this new bone hardens and progressively fixes the stapes in place, preventing it from vibrating freely. The result is a conductive hearing loss — sound is physically blocked from reaching the inner ear at full strength. According to NICE clinical guidelines, otosclerosis is one of the most common causes of progressive conductive hearing loss in adults of working age, making early recognition and treatment particularly important.

Who Gets Otosclerosis? Prevalence and Demographics

Otosclerosis affects approximately 1-2% of the UK population, though histological studies (examining temporal bones after death) suggest that subclinical otosclerosis — present but not causing noticeable symptoms — may be far more common, occurring in up to 10% of people. The condition is the single most common cause of conductive hearing loss in young and middle-aged adults in the UK, according to data from ENT UK, the professional body for ear, nose, and throat specialists.

Several demographic patterns are well established:

• Age of onset: Otosclerosis typically develops between the ages of 15 and 45, with most people first noticing symptoms in their twenties or thirties. It is rare for symptoms to begin before puberty or after the age of 50.
• Sex: The condition is approximately twice as common in women as in men. This disparity is thought to be linked to hormonal factors — oestrogen receptors have been identified in otosclerotic bone tissue, and pregnancy is known to accelerate the progression of the disease. Women who have had multiple pregnancies are at greater risk of faster progression.
• Ethnicity: Otosclerosis shows a strong ethnic predisposition. It is most common in white European populations and relatively rare in people of African, East Asian, and South Asian descent. Research published by RNID (formerly Action on Hearing Loss) notes that the condition is approximately ten times more common in white populations than in Black populations.
• Genetic factors: There is a significant hereditary component. Approximately 50% of people with otosclerosis have a family history of the condition. It follows an autosomal dominant inheritance pattern with variable penetrance, meaning that carrying the gene does not guarantee developing symptoms. If one parent has otosclerosis, there is roughly a 25% chance that each child will develop the condition. Multiple genes have been implicated, and research continues to identify specific genetic markers.
• Viral associations: Some researchers have found evidence of measles virus RNA in otosclerotic bone, suggesting that persistent measles infection may play a role in triggering the condition in genetically susceptible individuals. The decline in measles cases following widespread MMR vaccination may partly explain an apparent reduction in otosclerosis incidence in recent decades, though this remains an area of active research.

Symptoms of Otosclerosis

The symptoms of otosclerosis develop gradually, often over months or years, and can be easy to dismiss in the early stages. Recognising the signs of hearing loss early is important because treatment is most effective when the condition is identified before significant hearing damage has occurred.

The hallmark symptoms include:

• Progressive hearing loss: This is the most common symptom, typically beginning in one ear before eventually affecting both (bilateral involvement occurs in approximately 70-80% of cases). The hearing loss is usually gradual and may initially be noticed as difficulty hearing whispered speech or low-pitched sounds.
• Paracusis of Willis: This is a distinctive and somewhat paradoxical feature of otosclerosis — people find they can hear better in noisy environments than in quiet ones. This occurs because background noise causes others to raise their voices, which compensates for the conductive hearing loss. If you find that you hear better at a busy restaurant than in a quiet room, this is a characteristic sign worth mentioning to your audiologist.
• Tinnitus: Many people with otosclerosis experience tinnitus, often described as a low-pitched buzzing, humming, or roaring sound. The tinnitus may fluctuate in intensity and can be particularly noticeable in quiet environments.
• Speaking quietly: Because bone conduction of your own voice remains intact (and may even be enhanced), your own voice can sound louder to you than it does to others, causing you to speak more softly without realising it.
• Balance disturbance: Some people experience mild dizziness or unsteadiness, particularly if the otosclerotic process extends beyond the stapes footplate. Significant vertigo is uncommon but should be reported to your specialist.

How Otosclerosis Is Diagnosed

If your GP suspects otosclerosis based on your symptoms and history, they will refer you to an audiologist or ENT (ear, nose, and throat) specialist. Diagnosis involves a combination of hearing tests and, in some cases, imaging:

• Pure tone audiometry: This is the primary diagnostic test. It measures your hearing thresholds for both air conduction (sound travelling through the ear canal) and bone conduction (sound transmitted directly through the skull bones to the inner ear). In otosclerosis, air conduction is reduced while bone conduction remains relatively normal, creating a characteristic air-bone gap on the audiogram. This gap confirms the conductive nature of the hearing loss.
• The Carhart notch: A classic audiometric finding in otosclerosis is a dip in bone conduction thresholds at 2000 Hz (sometimes also at 500 Hz and 4000 Hz). This artefact — known as the Carhart notch — is caused by the mechanical effect of stapes fixation on the resonance of the ossicular chain, rather than by actual inner ear damage. It typically improves or disappears after successful surgery.
• Tympanometry: This test measures the movement of the eardrum in response to pressure changes. In otosclerosis, the tympanogram often appears normal or shows a slightly reduced peak (low compliance), which helps distinguish the condition from other causes of conductive hearing loss such as middle ear fluid or eardrum perforation.
• CT scanning of the temporal bone: High-resolution CT imaging may be used to visualise the otosclerotic foci — areas of abnormal bone around the oval window and cochlea. CT is particularly useful when considering surgery, as it helps the surgeon assess the extent of disease and plan the approach. It is also important for identifying cochlear otosclerosis (see below).
• Differential diagnosis: Your specialist will also consider and rule out other conditions that can mimic otosclerosis, including ossicular discontinuity (a break in the bone chain), superior semicircular canal dehiscence, and congenital fixation of the stapes.

Treatment Options

Treatment for otosclerosis depends on the severity of hearing loss, whether one or both ears are affected, your overall health, and your personal preferences. The three main approaches are hearing aids, surgery, and medical therapy. Many people begin with hearing aids and later consider surgery, while others opt for surgery early. Your audiologist or ENT consultant will discuss the options in detail so that you can make an informed decision.

Hearing Aids

Hearing aids are an effective and entirely non-invasive way to manage the conductive hearing loss caused by otosclerosis. Modern digital hearing aids can be precisely programmed to amplify the specific frequencies affected, and many people achieve excellent results with well-fitted devices.

Hearing aids are particularly suitable for people with mild to moderate hearing loss, those who prefer to avoid surgery, people with medical conditions that increase surgical risk, and cases where only one ear is significantly affected. The NHS provides digital behind-the-ear hearing aids free of charge through NHS audiology services, while private providers such as Boots Hearingcare, Specsavers Audiology, Hidden Hearing, THCP, and Scrivens offer a wider range of styles and technology levels. A proper hearing aid fitting and regular aftercare appointments are essential for getting the most from your devices. For practical advice on daily use, see our guide to getting the most from your hearing aids.

Stapedectomy and Stapedotomy

Surgery is the definitive treatment for otosclerosis and offers the possibility of permanently restoring hearing without the need for a hearing aid. Two closely related procedures are used:

• Stapedectomy: The fixed stapes bone is removed entirely and replaced with a tiny prosthetic piston (usually made of Teflon or titanium) that connects the incus to the oval window membrane, restoring the transmission of sound vibrations to the inner ear.
• Stapedotomy: A small hole is created in the fixed stapes footplate using a laser or micro-drill, and a prosthetic piston is inserted through it. This is the more commonly performed technique today, as it involves less disruption to the oval window and may carry a slightly lower risk of complications.

Both procedures are performed through the ear canal (no external incision), usually under local anaesthetic with sedation as a day case — meaning you go home the same day. The operation typically takes 60-90 minutes. According to ENT UK and NICE, stapes surgery achieves hearing improvement in over 90% of cases, with many patients experiencing dramatic results within the first few weeks. The air-bone gap is typically closed to within 10 dB, and the Carhart notch usually resolves.

As with any surgery, there are risks to be aware of:

• Taste disturbance: The chorda tympani nerve (which carries taste sensation from the front of the tongue) runs through the middle ear and may be stretched during surgery. Temporary taste changes on one side of the tongue are common but usually resolve within weeks to months.
• Tinnitus: Pre-existing tinnitus may improve, remain unchanged, or occasionally worsen after surgery.
• Dizziness: Mild dizziness or unsteadiness is common in the first few days after surgery and usually settles quickly. Prolonged vertigo is uncommon.
• Sensorineural hearing loss: In rare cases (approximately 1-2%), surgery can cause permanent damage to the inner ear, resulting in a sensorineural hearing loss that cannot be corrected with a hearing aid. In very rare instances, this can lead to total deafness in the operated ear.
• Perforation of the eardrum: This is uncommon and usually heals on its own.

If both ears are affected, surgeons typically operate on the worse-hearing ear first and wait at least six months before considering surgery on the second ear. This approach minimises risk and allows time to assess the outcome.

Sodium Fluoride Therapy

Sodium fluoride supplements have been used by some ENT specialists to slow the progression of otosclerosis, particularly in its active (otospongiotic) phase. The rationale is that fluoride promotes the maturation of abnormal spongy bone into denser, more stable bone, potentially halting or slowing stapes fixation. However, the evidence base for sodium fluoride in otosclerosis is limited, and it is not routinely recommended by NICE. It may be considered in specific circumstances, such as when surgery is not appropriate and the disease appears to be progressing rapidly.

Cochlear Otosclerosis

In some cases, the abnormal bone growth extends beyond the stapes footplate and into the bony capsule surrounding the cochlea — the inner ear organ responsible for converting sound vibrations into nerve signals. This is known as cochlear otosclerosis (or retrofenestral otosclerosis) and can cause a sensorineural hearing loss in addition to the conductive component. When both types of hearing loss are present, it is described as a mixed hearing loss.

Cochlear otosclerosis is more challenging to treat because the sensorineural component — caused by direct damage to the cochlear structures or disruption of the endolymph chemistry — cannot be corrected by stapes surgery alone. Hearing aids may still provide benefit, and in severe cases where hearing loss is profound, cochlear implantation may be considered. Research from major UK audiology centres has shown that cochlear implants can be highly effective in patients with otosclerosis, though the surgical approach may be more complex due to the abnormal bone.

CT imaging of the temporal bone is particularly important in suspected cochlear otosclerosis, as it can reveal areas of demineralisation (the "halo sign") around the cochlea that help confirm the diagnosis and guide treatment planning.

Prognosis and Long-Term Monitoring

Otosclerosis is typically a progressive condition, meaning that without treatment, hearing loss tends to worsen gradually over years. The rate of progression varies considerably between individuals — some people experience relatively slow deterioration over decades, while others, particularly women during or after pregnancy, may notice more rapid changes.

The good news is that otosclerosis is one of the most treatable forms of hearing loss. With appropriate intervention — whether through hearing aids, surgery, or a combination — the vast majority of people with otosclerosis can achieve excellent hearing outcomes and maintain their quality of life. Stapes surgery, when successful, can provide lasting hearing improvement for many years, though a small proportion of patients may require revision surgery if the prosthesis shifts or new bone growth occurs.

Regardless of treatment choice, regular audiometric monitoring is essential. The NHS and RNID recommend periodic hearing assessments to track any changes, adjust hearing aid settings if needed, and identify the development of cochlear involvement early. Your audiologist can advise on the appropriate frequency of follow-up — typically every 12-24 months for stable cases, and more frequently if the condition is progressing or following surgery. A standard hearing test at each visit allows your audiologist to compare results over time and ensure your treatment remains optimal.

Living with Otosclerosis

A diagnosis of otosclerosis can feel daunting, particularly for younger adults who may not have expected to face hearing difficulties. However, it is important to remember that this is one of the best-understood and most successfully treated conditions in audiology. With modern hearing aids and surgical techniques, most people with otosclerosis lead full, active lives with excellent hearing.

Practical steps that can help include:

• Learn about your condition: Understanding how otosclerosis works and what your treatment options are empowers you to make informed decisions. Our guides on understanding your audiogram and choosing hearing aids are good places to start.
• Seek support: Organisations such as RNID and the British Tinnitus Association offer information, support groups, and helplines for people living with hearing loss and tinnitus.
• Communicate your needs: Let family, friends, and colleagues know about your hearing loss. Simple strategies — such as facing the speaker, reducing background noise, and using visual cues — can significantly improve communication. Our guide to recognising hearing loss may help your loved ones understand what you are experiencing.
• Protect your remaining hearing: Avoid exposure to loud noise, and use ear protection in noisy environments. While noise exposure does not cause otosclerosis, it can cause additional damage to the inner ear on top of the existing condition.
• Stay proactive with appointments: Whether you use hearing aids or have had surgery, keeping up with regular follow-up appointments ensures that any changes are caught early and your care is adjusted accordingly.

If you are experiencing gradual hearing loss, particularly if it began in your twenties or thirties or you have a family history of otosclerosis, the first step is to get your hearing assessed. A standard hearing test can quickly determine whether otosclerosis may be the cause and set you on the path to effective treatment. Find an audiologist near you and book an appointment today.