Conditions: Otosclerosis

What is otosclerosis?

Otosclerosis is a condition that affects the tiny bones and surrounding bone of the ear, leading to gradual hearing loss. It happens when the bone that encases the inner ear (called the otic capsule) undergoes abnormal remodeling—cycles of bone being broken down and rebuilt in a disorganized way.

The most common site affected is around a small bone called the stapes, one of three tiny bones in the middle ear that carry sound vibrations from the eardrum to the inner ear. When new abnormal bone forms, it can lock the stapes in place so that it can no longer vibrate freely. Because sound can no longer pass efficiently into the inner ear, hearing is reduced. This type of hearing loss, caused by a mechanical block, is called conductive hearing loss.

In some cases the abnormal bone growth extends deeper, toward the hearing organ of the inner ear (the cochlea). When this happens, it can also damage the delicate structures responsible for sensing sound, adding a second type of hearing loss called sensorineural hearing loss. A person may then have a combination of both, known as mixed hearing loss.

Otosclerosis is one of the most common causes of hearing loss in adults that is not related to aging or noise exposure. It often starts in one ear but eventually involves both ears in the majority of people—roughly 70 to 85 percent of cases.

Causes and risk factors

The exact cause of otosclerosis is not fully understood. It is generally considered a complex condition resulting from a combination of genetic and environmental factors. Known and suspected contributors include:

• Family history and genetics. More than half of people with otosclerosis have a family member who is also affected. It often appears to run in families, and many genes involved in bone formation have been linked to it, though no single cause explains every case.

• Sex. Women are affected about twice as often as men.

• Ancestry. It is most common in people of European (Caucasian) descent and less common in people of African or Asian ancestry.

• Age. Symptoms most often begin in early to middle adulthood, generally between the ages of about 15 and 45, and most commonly in a person’s thirties.

• Hormonal factors. Changes during pregnancy, puberty, and menopause have been suggested as possible triggers or times when the condition may progress, though this is not fully proven.

• Viral infection. Prior measles infection has been proposed as a possible contributing factor.

Having one or more of these factors does not guarantee that a person will develop otosclerosis, and the condition can also occur in people with no known family history.

Symptoms

The main symptom of otosclerosis is slowly progressive hearing loss. Because it develops gradually, often over years, it may not be noticed at first. Common features include:

• Gradual hearing loss, frequently starting in one ear and later affecting both. Difficulty hearing is often more noticeable with lower-pitched sounds early on.

• Tinnitus, a ringing, buzzing, or humming sound in the ear.

• Difficulty following conversations, especially in quieter settings. Some people notice they actually hear better in noisy environments.

• Dizziness or balance problems (vertigo), which are less common but can occur.

How is otosclerosis diagnosed?

Diagnosis usually begins with a review of a person’s symptoms and family history, followed by an ear examination and hearing tests. Key parts of the evaluation include:

• Hearing tests (audiometry). A hearing specialist (audiologist) measures how well sounds of different pitches and volumes are heard. Otosclerosis typically produces a characteristic pattern of conductive hearing loss.

• Tympanometry. This test measures how the eardrum and middle ear respond to sound and pressure, helping to assess movement of the middle ear structures.

• Ear examination. The eardrum usually looks normal on examination, which helps distinguish otosclerosis from other ear problems.

• Imaging. In selected cases, a high-resolution CT scan of the temporal bone (the part of the skull that houses the ear) can show the abnormal bone and help rule out other conditions. MRI may also be used in certain situations.

In some cases, the diagnosis is only fully confirmed during surgery, when the surgeon can directly see and test whether the stapes bone is fixed in place.

Possible complications and associated conditions

• Progressive and mixed hearing loss. Without treatment, hearing loss tends to worsen over time. In some people the disease extends into the inner ear, causing sensorineural or mixed hearing loss, which is harder to fully correct.

• Profound hearing loss. In a minority of people, the condition advances to severe or profound hearing loss.

• Tinnitus and dizziness. These can persist and, for some people, affect quality of life.

• Both ears affected. Most people eventually develop the condition in both ears.

• Links to bone and skeletal traits. Research suggests otosclerosis shares some biological pathways with other conditions involving bone growth and remodeling, reflecting its underlying nature as a bone disorder.

How is otosclerosis treated?

Treatment options generally fall into three categories: monitoring the condition over time, using hearing aids to amplify sound, and surgery to replace the fixed stapes bone with a small prosthesis (an operation called stapedotomy or stapedectomy). In advanced cases with significant inner ear involvement, a cochlear implant may be considered. Certain medications have also been studied as a way to slow disease activity. Treatment choices are individualized. Additional detail is available on the page about otosclerosis treatments.