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What Is Otosclerosis?

May is Better Hearing Month, and it’s the perfect time to take stock of your hearing health. Hearing loss can come from many sources. Prolonged exposure to loud noises is the most common, but there are many others you might not have considered: medical conditions, certain medications, ear blockages and even problems with the tiny bones in your ears. Otosclerosis is an example of the last category. 

The human ear is exceedingly complex, with dozens of structures that work together to enable you to hear. If any of these structures are damaged or not working incorrectly, hearing loss can be the result. While the bones affected by otosclerosis are very small, the condition can have a big effect on your hearing.

What Is Otosclerosis?

Otosclerosis is abnormal bone growth in the middle ear that causes improper function of the structures within the middle ear and can result in hearing loss—in some cases, severe. Otosclerosis may affect one or both ears, though both ears being affected is much less common.

The stirrup, or stapes, is the last bone in the middle ear and is usually the bone affected by otosclerosis. This bone rests on the entrance to the middle ear and the abnormal bone growth interferes with the sound waves passing into the inner ear.

Otosclerosis is a progressive condition. Without treatment, it gets worse. The condition affects more than three million Americans.

Anatomy of the Middle Ear

There are three main parts of the ear – the outer, middle and inner ear. Sound waves enter the ear through the outer ear and proceed to the middle ear, causing the ear drum to vibrate. Three tiny bones in the middle ear called ossicles work together as a lever system to transmit these vibrations to the inner ear. The three ossicles are:

  • Hammer (malleus) – One end is attached to the eardrum and the other end forms a lever hinge with the anvil.
  • Anvil (incus) – One end is hinged to the hammer and the other end is fused to the stirrup, allowing the anvil and stirrup to act as one bone.
  • Stirrup (stapes) – The stirrup is loosely connected to an opening in the inner ear (cochlea) called the oval window, using a piston-like action to transmit sound vibrations into the fluid of the inner ear. This fluid is contained in the snail-shaped part of the inner ear containing hair cells.

The movement of the stirrup signals to the brain that there is a sound event. The inner ear then translates the vibrations in the fluid of the inner ear into electrical impulses transmitted via the auditory nerve, which sends them to the brain.

Without the middle ear bones, less than one percent of sound would be transmitted to the inner ear. Once otosclerosis progresses to the point where the stapes becomes immovable, it can no longer transmit sound waves.

Symptoms of otosclerosis

Hearing loss is the most common symptom of otosclerosis, which develops gradually. The inability to hear low-pitched sounds is usually the first symptom noticed. Other symptoms may include:

  • Dizziness
  • Tinnitus (ringing, roaring, buzzing, hissing in ears or head)
  • Balance problems

Causes and risk factors

The exact cause of otosclerosis is unknown, though a hereditary link may be involved. If a parent has otosclerosis, there is a 25 percent chance that their child will develop the disorder. If both parents have otosclerosis, the risk rises to 50 percent. Otosclerosis is the most common cause of hearing loss in young adults.

Other risk factors—suggested but not proven by research—associated with otosclerosis include:

  • Age—The risk of otosclerosis rises as age increases
  • Ethnicity—Caucasians are more often affected than other ethnicities
  • Gender—Women are at higher risk than men
  • Hormonal changes due to pregnancy
  • Viral infections, measles in particular (due to recent U.S. outbreaks of measles, vaccination is the best prevention method for this cause of otosclerosis)

Treatment of otosclerosis

An audiologist (hearing care professional) will first conduct an examination to diagnose otosclerosis and rule out other health problems or diseases that may be causing hearing loss. A variety of tests are used.

Otosclerosis most often causes conductive hearing loss, which is a blockage of sound into the inner ear. This type of hearing loss is treatable. However, sometimes otosclerosis can cause sensorineural hearing loss or mixed hearing loss. Sensorineural hearing loss occurs when the hairs of the inner ear that transmit sound are damaged. This type of damage is irreversible. Mixed hearing loss is a combination of conductive and sensorineural hearing loss.

Because otosclerosis most commonly causes conductive hearing loss, surgery is available in many cases. All or part of the stapes is removed and a prosthetic device is implanted to bypass the abnormal bone and pass the sound waves to the inner ear. A total replacement of the stapes is called a stapedectomy, and a partial removal is called a stapedotomy. Though usually successful, all surgeries carry risks and complications. In rare cases, hearing loss can worsen after surgery.

Surgery may not be required when mild hearing loss is present. In these cases, hearing aids are the best treatment option. However, patients with mixed hearing loss due to otosclerosis may not achieve a successful result with hearing aids.

Treatment with hearing aids

For people with mild hearing loss, hearing aids can be a useful treatment option, though not all patients will have success using a hearing aid. Hearing aids work by magnifying sound vibrations entering the ear. Patients with a hearing loss of 60 dB or less and with only conductive hearing loss may benefit the most from hearing aids. For these individuals, hearing aids are usually easy to fit and generally have the power to override the hearing loss.

Your audiologist will discuss treatment options with you and provide the best hearing aid options for each individual case. Hearing aid options vary based on many factors, including the degree of hearing loss, the type, and the patient’s individual conditions.

If you suspect you have hearing loss or know you have a family history of otosclerosis, contact one of our specialists today to discuss diagnosis and treatment options.