Overview 

Otosclerosis also referred to as otospongiosis, is an ear condition where there is abnormal bone growth in the middle ear. The origin of the word derives from the Greek language, where otós means “ear” and skerós means “hardening”.¹ Otosclerosis is caused by an abnormal growth of the bones in the ear, specifically the stapes (also called the stirrup bone, see Figure 1 and 2).^1,2 It prevents the movement of the chain of bones, which disrupts the ability of sound to vibrate the stapes, affecting the transmission of sound waves. In other words, it obstructs the transmission of sound through the bones to the inner ear, where it is interpreted by the brain.² Otosclerosis, in most people, affects both ears.

Otosclerosis is a progressive disorder, which means it tends to get worse over time, and it can result in conductive hearing loss. People with otosclerosis often report progressive hearing loss, accompanied by tinnitus. 

Prevalence 

This disorder is fairly common, occurring in approximately 1 out of every 200 individuals, and is responsible for hearing impairment in adults. It usually begins between the ages of 20 and 45, and is believed to be the principal cause of hearing loss in young adults. Recognising the causes and symptoms of Otosclerosis is essential for its early diagnosis and treatment.³

What are the causes of otosclerosis?

The exact cause of otosclerosis remains unclear, but several factors are thought to play a role in its development. These factors include genetic predisposition, viral infections, hormonal factors, and autoimmune responses.

Genetic factors 

Otosclerosis has a significant hereditary component, with around 50-60% of affected individuals having a family history of the condition. Research has pinpointed several genes that might contribute to the development of otosclerosis, although the specific genetic mechanisms are not yet fully understood. The condition is typically inherited in an autosomal dominant pattern, which means that if one parent has otosclerosis, there is a 50% chance that their children will inherit it.^2,3 Otosclerosis is hence not preventable.

Viral infections 

Evidence suggests that viral infections, particularly measles, might contribute to the onset of otosclerosis. Research has found an association between measles virus RNA in the stapes footplate and otosclerosis⁴. However, the exact connection between measles and otosclerosis is still not clear.

Hormonal factors 

Hormonal changes, especially those associated with pregnancy, are believed to impact the progression of otosclerosis. Many women experience a worsening of their hearing loss during or after pregnancy. The hormones oestrogen and progesterone, which rise during pregnancy, are thought to influence bone metabolism, possibly speeding up the bone remodelling process that characterises otosclerosis³.

Autoimmune responses 

Autoimmune mechanisms are also thought to play a role in the development of otosclerosis. Some studies suggest that immune system dysfunction may contribute to abnormal bone growth in the middle ear. However, more research is needed to prove an association.^1,3

Demographic factors

Although research is not able to fully explain them, there are some demographic factors that seem to be associated with higher likelihood of developing otosclerosis: 

• Statistically, people assigned female at birth (AFAB) are more prone to develop it than people assigned male at birth (AMAB) 
• Caucasian people are more affected by the disease than other races.³

When to suspect otosclerosis

Otosclerosis typically manifests with a variety of symptoms that can vary in severity. The progression of these symptoms is usually gradual and early signs may be subtle. The main symptoms include hearing loss, tinnitus (ringing in the ears), balance problems, and, in rare cases, dizziness or vertigo:

Hearing loss 

The main symptom of otosclerosis is conductive hearing loss, which occurs due to the immobilisation of the stapes bone in the middle ear. This immobilisation disrupts the efficient transmission of sound waves to the inner ear. Initially, the hearing loss may be mild and primarily affects lower-pitched sounds, such as car engines, thunder and men’s deep voices.¹ In fact, most people with otosclerosis first notice that they struggle to hear low-pitched sounds or whispers. Some people find it easier to hear when there is background noise (a phenomenon called Willis paracusis or false paracusis) or may speak in a low tone as their voice seems too loud to them. As the condition progresses, it can lead to more significant hearing impairment, eventually affecting higher-pitched sounds as well.

In some instances, otosclerosis can also cause sensorineural hearing loss if the abnormal bone growth extends into the cochlea, impacting the sensory cells of the inner ear.² This combination of conductive and sensorineural hearing loss can make diagnosis more difficult.

Tinnitus 

Another symptom of otosclerosis is tinnitus (ringing or buzzing in the ears). This noise can be constant or intermittent, and its pitch and intensity tend to vary. The mechanism in which tinnitus appears in otosclerosis isn't fully known, but it is thought to be linked to changes in the mechanics of the middle ear and possibly the inner ear as well.^1,2

Balance issues 

Some individuals with otosclerosis might experience balance problems or a sense of unsteadiness. The stapes fixation can impact the vestibular system, which is crucial for maintaining balance and spatial orientation. While these balance issues are typically mild, they can still impact life quality for some people.^1,2

Dizziness and vertigo 

Although less common, dizziness or vertigo can occur in otosclerosis, especially if the condition affects the inner ear structures. Vertigo is marked by a sensation of spinning or motion when there is no actual movement, and it can be severe in some cases, significantly impacting the quality of life.^1,2

How is otosclerosis diagnosed and is there a cure?

Diagnosing Otosclerosis involves a combination of medical history review, physical examination, hearing tests that measure hearing sensitivity (audiogram) and middle-ear sound conduction (tympanogram), and imaging studies such as computed tomography (CT) scans. These evaluations are typically performed by an audiologist (healthcare professional specialised in hearing conditions) or an otorhinolaryngologist (also known as otolaryngologist or ENT, a doctor that is specialised in ear, nose, neck and throat) to confirm the diagnosis and staging of the condition.

While there is no cure for Otosclerosis, there is a panoply of treatments available to manage the symptoms and improve hearing. These include hearing aids, Cochlear implants and surgical interventions, particularly stapedectomy (minor surgery to remove the stapes and replace them with a prosthesis that improves sound conduction; see Figure 3)⁴. There are also a number of medications that may be used, such as Sodium Fluoride and Bisphosphonates, that have been proven to slow down disease progression.⁶

When should I see a doctor?

If you notice a gradual decline in your hearing, whether it is in one ear or both, particularly if you have a family history of OtosclerosisIf you have a persistent ringing, buzzing, or other unusual noise you experience balance issues background noise helps you hear better

Can I live a normal life with otosclerosis?

Most people with otosclerosis can maintain a good quality of life. Early diagnosis and intervention are vital. With adequate treatment, most people can achieve good management of symptoms and substantially improve their hearing.

• Some lifestyle changes are beneficial in reducing the impact of certain symptoms. For example, tinnitus may be reduced by avoiding loud noises, such as construction work or loud music, and managing stress 
• Eating foods rich in calcium can be beneficial as well as it may reduce bone deterioration 
• Additionally, some people find that their hearing improves after discontinuing the use of the contraceptive pill, so it might be worth discussing it with your gynaecologist 
• It is generally safe to swim, dive, and fly, but you should be cautious if you have a middle ear infection.^2,3 It is important to check with your doctor as they will be able to advise which activities are safe for you
• Due to the emotional and psychological distress caused by hearing impairment, it may also help looking for support groups (they can be found online, some examples are the National Deaf Children’s Society and The Royal National Institute for Deaf People). Some people also find counselling useful. In the UK, you can usually get it for free through the National Health System by self-referring on your GP surgery website

Summary

• Otosclerosis is a chronic condition caused by abnormal growth of the bones in the middle ear
• It leads to progressive hearing loss, tinnitus (ringing in the ear) and balance impairment
• The exact cause of Otosclerosis remains unknown, but some risk factors are family history, race, gender, and viral infections
• Treatment may include medication, surgery and hearing aids
• Early detection and treatment are vital to achieve a good life quality