Otosclerosis
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.
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.
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 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.
