On this page
Otosclerosis
This condition leads to progressive hearing loss when the stapes, a small ear bone, becomes fixed and can no longer vibrate properly. It typically affects adults, often with a genetic predisposition.
Overview
Otosclerosis is a condition of the middle ear characterised by abnormal bone growth, primarily around the stapes bone. This tiny, stirrup-shaped bone is essential for transmitting sound vibrations from the eardrum to the inner ear. When otosclerosis causes the stapes to become fixed, it can no longer vibrate freely, leading to a type of hearing loss called conductive hearing loss [PMID:33678505]. In some cases, the condition can also affect the inner ear, leading to sensorineural hearing loss or a mixed hearing loss.
This condition typically develops in young to middle-aged adults, often beginning with mild hearing loss that gradually worsens over time. While the exact cause is complex and not fully understood, a combination of genetic and environmental factors is thought to play a role. It is estimated to affect around 2% of the Caucasian population, though its prevalence can vary across different ethnic groups [PMID:24606764].
Symptoms & clinical features
The primary symptom of otosclerosis is a gradual, progressive hearing loss, which typically begins in one ear but can often affect both ears over time. This hearing loss is usually conductive, meaning sound waves are not effectively transmitted through the middle ear. People with otosclerosis might find it difficult to hear low-pitched sounds or soft speech. They may also notice that their own voice sounds unusually loud to them.
Another common symptom associated with otosclerosis is tinnitus, which is the perception of ringing, buzzing, or hissing sounds in the ears [PMID:33678505]. Some individuals may also experience dizziness or balance problems, particularly if the condition affects the inner ear. Symptoms often worsen during pregnancy, which suggests a possible hormonal influence on the condition's progression.
Video: Genetics 101
Affected organs
Otosclerosis primarily affects the middle ear, specifically the ossicular chain, which consists of three small bones: the malleus, incus, and stapes. The stapes bone is most commonly affected, becoming rigid and unable to vibrate properly. The abnormal bone growth occurs in the bony capsule of the labyrinth, the part of the inner ear that houses the cochlea (for hearing) and vestibular system (for balance).
In some instances, the abnormal bone remodelling can extend beyond the stapes to involve the inner ear structures, leading to sensorineural hearing loss. This is sometimes referred to as cochlear otosclerosis. The auditory nerve, which carries sound signals to the brain, is not directly affected, but its function can be impaired by changes within the inner ear.
Risks & severity
The severity of hearing loss in otosclerosis can vary significantly between individuals, ranging from mild to severe. It is typically a progressive condition, meaning that the hearing loss tends to worsen over many years. The age of onset usually falls between 15 and 45 years, though it can manifest outside this range. Women are generally more affected than men, and symptoms sometimes accelerate during pregnancy.
While otosclerosis itself is not life-threatening, the progressive hearing loss can significantly impact quality of life, communication, and social interaction. There are no known specific lifestyle risk factors, but a family history of otosclerosis increases an individual's likelihood of developing the condition, highlighting a strong genetic component.
Genetic causes
Otosclerosis is considered a complex or polygenic condition, meaning that it is influenced by multiple genes working together, along with environmental factors. Research suggests that several genes may contribute to an individual's susceptibility. Among these, genes like COL1A1 (collagen type I alpha 1 chain) and RELN (reelin) have been studied.
COL1A1 is vital for the formation of type I collagen, a fundamental protein found in bones and connective tissues throughout the body. While variants in COL1A1 are well-known causes of conditions like osteogenesis imperfecta, certain changes in this gene may also play a role in the abnormal bone remodelling seen in otosclerosis. RELN is involved in neuronal migration and brain development, but it is also expressed in the inner ear, and some studies indicate its involvement in bone remodelling processes [PMID:34771216]. Pathogenic variants in these genes might disrupt the normal bone formation and breakdown processes within the middle ear, leading to the characteristic changes of otosclerosis.
Inheritance pattern
Otosclerosis typically shows a complex or polygenic inheritance pattern. This means that multiple genes contribute to an individual's susceptibility to the condition, rather than a single gene being solely responsible. Additionally, environmental factors are thought to interact with these genetic predispositions.
While a family history of otosclerosis is common and increases the risk, the pattern of inheritance does not follow simple Mendelian rules (like autosomal dominant or recessive). This implies that even if one parent has otosclerosis, predicting the exact chance for their children to develop the condition is challenging, as it depends on the interplay of many genetic and non-genetic factors. Genetic counselling can provide more personalised risk assessments for families.
Diagnosis & testing
The diagnosis of otosclerosis typically begins with a detailed medical history and a physical examination of the ear by a specialist, such as an Ear, Nose, and Throat (ENT) surgeon or an audiologist. Audiometry, a hearing test, is crucial for assessing the type and degree of hearing loss. Characteristic audiometric findings, such as conductive hearing loss with specific patterns, can suggest otosclerosis.
Imaging techniques, such as high-resolution Computed Tomography (CT) scans of the temporal bone, can sometimes reveal the abnormal bone growth associated with otosclerosis, particularly in more advanced cases. Genetic testing is not routinely used for diagnosing otosclerosis in the NHS, as it is a complex condition with multiple genetic factors rather than a single causative gene. Referrals for audiology and ENT assessment are usually made by a GP. For specific R-codes and further information on genetic testing pathways, clinical genetic services or the NHS Genomic Medicine Service can provide guidance, though otosclerosis is not typically diagnosed through a single genetic test.
Management & lifestyle
Management of otosclerosis aims to improve hearing and manage associated symptoms. For conductive hearing loss, treatment options often include hearing aids, which amplify sound and help overcome the sound transmission issues. Surgical intervention, known as stapedectomy or stapedotomy, is another common treatment. This procedure involves removing the fixed stapes bone and replacing it with a prosthetic device to restore sound conduction. Surgical success rates are generally high, but like any surgery, it carries potential risks.
In cases where sensorineural hearing loss is present or develops, hearing aids may still be beneficial, and sometimes cochlear implants are considered for severe sensorineural components. For tinnitus, various management strategies can be employed, including sound therapy, cognitive behavioural therapy, or medication. Regular audiological assessments are important to monitor hearing changes and adjust management plans as needed within the NHS care pathway. Genetic counsellors can provide support regarding the hereditary aspects of the condition and guide families to appropriate services.
UK care pathway
In the UK, individuals suspected of having otosclerosis would typically first consult their General Practitioner (GP). The GP may then refer them to an Audiology service for hearing tests and assessment, or directly to an Ear, Nose, and Throat (ENT) specialist. ENT specialists are typically responsible for confirming the diagnosis, discussing treatment options like hearing aids or surgery, and managing the condition.
While otosclerosis is a complex genetic condition, genetic testing through the NHS Genomic Medicine Service (GMS) is not routinely offered for its diagnosis due to its polygenic nature. However, if there is a strong family history or other unusual features, a referral to Clinical Genetics may be considered to discuss the genetic aspects and potential implications for family members. Genetic counsellors within these services can provide invaluable support and information.
Frequently asked questions
Is otosclerosis always inherited?
Otosclerosis often runs in families, indicating a strong genetic component. However, it typically has a complex or 'polygenic' inheritance pattern, meaning multiple genes and environmental factors are involved, rather than a single gene being passed down simply.
Can otosclerosis affect both ears?
Yes, otosclerosis can affect one ear (unilateral) or both ears (bilateral). It often begins in one ear and may later develop in the other, or it can start in both ears simultaneously. The severity of hearing loss might also differ between the two ears.
What treatments are available for otosclerosis?
Common treatments include hearing aids to amplify sound and surgery (stapedectomy or stapedotomy) to replace the affected stapes bone with a prosthesis. Your ENT specialist will discuss the most suitable option based on your specific condition and hearing loss.
Will my hearing loss get worse over time with otosclerosis?
Otosclerosis is generally a progressive condition, meaning the hearing loss tends to worsen gradually over many years. Regular audiological assessments are important to monitor changes and adjust your management plan as needed.
Is pregnancy a risk factor for otosclerosis progression?
Some studies suggest that otosclerosis symptoms, particularly hearing loss, can worsen or accelerate during pregnancy. The exact reasons are not fully understood, but hormonal changes are thought to play a role. If you have otosclerosis and are planning a pregnancy, discuss this with your ENT specialist.
References
- Moumoulidis I, Axon P, Baguley D. A review on the genetics of otosclerosis. Clinical otolaryngology : official journal of ENT-UK ; official journal of Netherlands Society for Oto-Rhino-Laryngology & Cervico-Facial Surgery. 2007. PMID: 17651264