Otosclerosis is a rare condition that causes hearing loss. It happens when a small bone in your middle ear, usually the one called the stapes, gets stuck in place. Most of the time, this happens when bone tissue in your middle ear grows around the stapes in a way it shouldn't.

Your stapes bone has to vibrate for you to hear well. When it can't do that, sound can't travel from your middle ear to your inner ear. That makes it hard for you to hear.


Faulty bone formation

Bone is a living tissue and contains cells that make, mold and take back up (resorb) bone. Normally bone is continually being broken down and re-modelled. In otosclerosis, it seems that the remodeling process of the stirrup (stapes) - one of the tiny bony ossicles in the middle ear - becomes faulty. New bone is not made properly and abnormal bone forms. However, the reason why this occurs mainly in the stapes (and sometimes the cochlea) is not entirely clear.


Hereditary (genetic) factors seem to be important because a tendency for otosclerosis can be inherited. About 2 out of every 3 people with otosclerosis have other family members who also have this condition. However, some people with otosclerosis have no family history.


It is also thought that a virus may play a part and the measles virus has been suggested. Indeed, the number of people diagnosed with otosclerosis seems to have decreased since the measles virus vaccination has been given. It may be that a genetic tendency to develop otosclerosis is inherited by some people. Then a trigger, such as a viral infection, actually causes the condition to develop.

Low levels of fluoride

It is also possible that low levels of fluoride may have something to do with the development of otosclerosis. The number of cases of otosclerosis in the UK went down after fluoride was routinely added to drinking water. However, this possible link with low levels of fluoride is controversial.


Most people with otosclerosis notice hearing problems in their 20s or 30s. One or both ears can be affected.

Symptoms of otosclerosis include:

  • hearing loss that gets gradually worse over time
  • particular difficulty hearing low, deep sounds and whispers
  • speaking quietly because your voice sounds loud to you
  • finding it easier to hear when there's background noise (unlike many other types of hearing loss)
  • hearing sounds, such as buzzing or humming, that come from inside your body (tinnitus)
  • dizziness (though this is rare)

The symptoms of otosclerosis can be hard to tell apart from other causes of hearing loss.


  • A hearing test (audiometry/audiology) may help determine the severity of hearing loss.
  • A special imaging test of the head called a temporal-bone CT may be used to look for other causes of hearing loss.

Note: Evaluate hearing impairment, and complications such as labyrinthitis, tinnitus, facial nerve paralysis, or bone loss of skull, separately.

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