Otosclerosis

What is otosclerosis?

Otosclerosis, also known as otospongiosis, is a disease that leads to progressive deafness due to abnormal bone growth in the middle ear. It generally occurs in one ear initially, however eventually affects both ears. Sometimes the condition is associated with an impaired sense of balance (dizziness) and tinnitus (the sensation of hearing sounds that are not there, e.g. ringing or buzzing sounds). This occurs when the abnormal bone growth extends to the inner ear. Paracusis is an additional symptom that may be experienced, in which the individual hears better in a noisy environment.

Otosclerosis may cause either a conductive hearing loss or a mixed conductive and sensorineural hearing loss.

At what age does it begin?

The age of onset is typically from 20-30 years. However, childhood onset has been noted as well as late adult onset.

How does the condition lead to hearing loss?

The ear consists of three major sections, the outer ear, middle ear and inner ear. Sound waves in the environment enter your body through the outer ear. The sound waves then strike eardrum (tympanic membrane), causing it to vibrate. The eardrum is connected to tiny bones in themiddle ear called the ossicles (the malleus, incus and stapes are the names of these bones). The vibrations of the eardrum cause these bones to vibrate which in turn makes the fluid in the inner ear move. The movement of fluid within the inner ear results in tiny hair cells bending that trigger electrical impulses to be carried towards the brain in the auditory nerve. Once these nerve impulse reach the brain we perceive sounds. In short, sound waves set parts of our hearing system into motion that eventually trigger electrical signals to be carried from the ear to the brain.

otosclerosis and hearing loss

In otosclerosis, the bones in the middle ear grow abnormally (usually the stapes), impairing their ability to transmit sound waves through the ear. Without treatment the bones may eventually become fixed and lead to deafness.

What causes the condition?

Currently researchers are unsure what triggers the condition, however there are a number of risk factors associated with otosclerosis. Below is a list of risk factors that increase the likelihood of having otosclerosis.

Otosclerosis Risk factorDescription
GenderWomen are almost twice as likely to develop otosclerosis in comparison to men
Family historyApproximately 2/3 people with the condition have a family history of otosclerosis
PregnancyPregnancy has been found to worsen the condition
CaucasianWhite people have a higher prevalence
Drinking non-fluoridated waterSome research indicates drinking water without fluoride may be a risk factor for developing otosclerosis
MeaslesContracting measles may increase the likelihood of developing the condition
Osteogenesis imperfecta: a disease in which bones are very brittlePeople with osteogenesis imperfecta are more likely to develop otosclerosis
OtherSome individuals without any of these risk factors may also develop the condition

How is it diagnosed?

If you suffer from difficulty hearing, tinnitus or balance problems you should see your doctor or audiologist. Your audiologist will take a comprehensive case history by asking you questions about your hearing difficulties and your medical history. The audiologist will use an otoscope (an instrument used to look inside the ear) to visualise the ear canal and the eardrum. People with otosclerosis will usually have a normal ear canal and eardrum.

The audiologist will then conduct a number of hearing tests to determine the degree of hearing loss and the cause. The selection of hearing tests used will depend on your individual circumstances but may include audiometry, immittance tests and otoacoustic emissions testing.

Audiometry involves hearing sounds of varying pitches and loudness levels through headphones that you have to respond to by either pressing a button or raising your hand. This test yields valuable information regarding the degree of hearing loss, whether it is bilateral (in both ear) or unilateral (in one ear). It also allows the audiologist to determine whether the hearing loss is  conductive (when the problem lies in the outer ear or middle ear), sensorineural (when the problem lies in the inner ear or in the nervous system) or mixed. Usually hearing loss caused by otosclerosis is a conductive hearing loss.

Immittance testing

Immittance testing involves inserting a probe into the ear that emits sounds and controls the air pressure in the outer ear. The probe then measures the sound waves that bounce back off your ear drum. These measurements help an audiologist identify a hearing loss and determine the cause of hearing loss. Acoustic reflex testing may also be a component of immittance testing. In acoustic reflex testing a loud sound is played and the audiologist can evaluate whether the muscles within the middle ear contracted in response to the loud noise by measuring the sound waves that bounce back off the eardrum.

In addition to the hearing tests conducted it is sometimes necessary to undergo medical imaging. Your audiologist will refer you to a suitable specialist if this is required.

Can it be treated and if so how?

Yes, the condition can be treated. Treatment options include surgery, the use of hearing aids and some research suggests that taking fluoride supplements may slow the progression of the disease.

Surgery

The surgical option involves removing the stapes (one of the bones within the middle ear) and replacing it with a prosthetic device. This procedure is termed a stapedectomy and may return hearing to normal, however does carry risks like any surgical procedure.

Hearing aids

Surgery may not be appropriate for everyone and hearing aids may be a more suitable option. Hearing aids amplify sound to a degree that is safe and sufficiently loud for the wearer. For more information regarding the different types of hearing aids available click here.