In otosclerosis, there is abnormal growth of bone around the stapes, one of the three tiny bones in the middle ear that transmit sounds to the inner ear.
The stapes gradually becomes immobilized, resulting in progressive loss of hearing. Usually both ears are affected.
As well as resulting in hearing loss, otosclerosis may also cause tinnitus (ringing in the ear).
In many cases, hearing can be improved through the use of a hearing aid.
For severe cases, hearing can usually be restored by surgery to replace the stapes with an artificial substitute.