Introduction

Definition of otosclerosis

Otosclerosis is a bone remodelling disorder of the human otic capsule that leads to progressive conductive and/or sensorineural hearing loss as a result of fixation of the stapes.

Explanation of bilateral and unilateral otosclerosis

Otosclerosis usually involves both ears; however, unilateral disease can occur in up to 15% of cases.

Unilateral otosclerosis means that the hearing loss occurs in one ear. It is less common, affecting 10-15% of people with otosclerosis, while bilateral otosclerosis occurs in both ears. Bilateral otosclerosis is more common, affecting up to 90% of people with otosclerosis. The severity of the condition can vary between the two ears, with one ear being more affected than the other.

Causes and risk factors

Genetic predisposition

Scientists believe that otosclerosis runs in families. A tendency to develop otosclerosis can be inherited. About half of all people with otosclerosis have a gene with the condition.

Environmental factors

Viral Infections

A virus may play a part in the development of Otosclerosis. Some research suggests that viral infections like flu and measles may trigger otosclerosis in some people.

Low levels of fluoride

Fluoride is important for bone health, and low levels of fluoride in drinking water may contribute to the development of otosclerosis.

Hormonal factors

Pregnancy

Hormonal changes during pregnancy may affect the inner ear and worsen otosclerosis symptoms. 

Menopause

Hormonal fluctuations during menopause may also affect the inner ear and contribute to otosclerosis.

Age

Otosclerosis usually starts when you're young. You are most likely to get it during your 20s. Symptoms generally are at their worst in your 30s.

Symptoms of otosclerosis

Hearing loss is the most frequently reported symptom of otosclerosis. It usually starts as unilateral hearing loss and then moves to bilateral hearing loss.

Some other possible otosclerosis symptoms include:

• Vertigo.
• Ringing in your ears (tinnitus), which may occur along with hearing loss.
• Dizziness
• Balance problems

Diagnosis

Audiometry

Audiometry is a hearing test that measures the capability to hear sounds of different frequencies and volumes.It identifies the type and severity of hearing loss, which can indicate otosclerosis by measuring hearing loss and hearing thresholds through assessment of air conduction (hearing through the ear canal) and bone conduction (hearing through the skull).

Imaging tests(CT Scans, MRI)

Imaging tests provide detailed images of the temporal bone and inner ear structures. It helps to visualise the inner ear and surrounding structures. Imaging tests help in the diagnosis of otosclerosis by showing;

• Abnormal bone growth in the middle ear
• Fixation of the stapes bones of the middle ear
• Other structural abnormalities in the inner ear

Clinical examination

Otosclerosis is diagnosed by health care providers such as an otolaryngologist (commonly called an ENT), an otologist (a doctor who specialises in diseases of the ears), or an audiologist (a healthcare professional trained to identify, measure, and treat hearing disorders). This set of people diagnoses otosclerosis by firstly ruling out other health diseases or health problems. Then, a comprehensive examination is carried out using the following;

• Otoscopy (examining the ear conduit and eardrum with a scope)
• Tympanometry(measuring the movement of the eardrum and the middle ear)
• Weber and Rinne tests(assessing hearing and bone conduction)
• Physical examination of the ear, head, and neck.

Treatment options

Hearing aids

Hearing aids can help manage hearing loss caused by otosclerosis, but they do not treat the underlying condition. Mild otosclerosis can be treated with a hearing aid.

Stapedectomy

A surgical procedure where a prosthesis (artificial bone) is placed on your middle ear to bypass the stapes bone, thus improving sound conduction and restoring hearing.

Stapedotomy

This is a less invasive surgical procedure where a small hole is made in the stapes bone and a prosthesis is inserted to improve sound conduction.

Cochlear implants

A cochlear implant bypasses your inner ear structures and creates a new pathway on which sounds can travel to your brain.

Prognosis

Recovery of hearing

Over the course of many years, otosclerosis usually gets worse slowly. However, the time frame varies from person to person. Without treatment, otosclerosis may get worse over time. In some cases, it can spread to your inner ear and cause cochlear otosclerosis.

Recovery of hearing after otosclerosis is possible with treatment. The effectiveness of treatment varies from person to person, and the degree of hearing recovery depends on several factors, including:

• Severity of hearing loss
• Duration of hearing loss
• Type of treatment (stapedectomy or stapedotomy)
• Skill and experience of the surgeon
• Individual healing process
• It's important to note that several months to a year or more after surgery
• Some individuals may experience residual hearing loss or tinnitus

Complications

Some complications of otosclerosis may include;

• Hearing loss: The most common complication, ranging from mild to profound sensorineural hearing loss.
• Tinnitus: Ringing, buzzing, or whistling sounds in the affected ear
• Vertigo and balance problems: Otosclerosis can affect the balance organs in the inner ear, leading to vertigo, dizziness, and balance issues
• Cholesteatoma: A cyst-like structure that can form in the middle ear, potentially causing further hearing loss and complications
• Hearing recovery may take several months. Facial nerve paralysis: In rare cases, the facial nerve can be affected, leading to weakness or paralysis of the facial muscles
• Sensorineural hearing loss: Otosclerosis can progress to sensorineural hearing loss, which is permanent and irreversible

Conclusion

Summary of differences between bilateral and unilateral otosclerosis

Hearing loss in Bilateral otosclerosis progresses easily and is often more severe, thus it requires careful management and treatment. Sometimes, bilateral otosclerosis may lead to complete hearing loss in both ears. However, the hearing loss in unilateral otosclerosis is typically less severe and may not significantly impact daily life, which makes the treatment options more flexible.

Importance of early diagnosis and treatment

Early diagnosis and treatment not only improve hearing outcomes but also;

• Reduce the risk of complications (e.g., sensorineural hearing loss, vertigo)
• Enhance quality of life
• Potentially prevent bilateral involvement (in unilateral cases)
• Improve treatment success rates (e.g., stapedectomy/stapedotomy)
• Reduce the need for more invasive or complex treatments