Hardening of bone in the inner ear, limiting movement of one of the ossicles which transmit sound vibrations to the inner ear and resulting in hearing difficulties. This disorder often occurs shortly after puberty, is now more common in women than men, and is sometimes worse during pregnancy. Sound enters the ear through the auditory canal, and is then transmitted to the tympanic cavity, which contains the three auditory ossicles: the hammer, the anvil and the stapes. The ossicles transmit sound to the inner ear, where the vibrations stimulate nerves. In otosclerosis hardening of the bone in Otosclerosis is stiffening of the auditory ossicles, the small bones in the middle ear, causing hearing loss. The inner ear prevents the stapes from moving, thus hindering the passage of sound to the inner ear. The patient becomes hard of hearing, usually in both ears; the condition is sometimes stable for a period, and then suddenly deteriorates, frequently followed by another stable period. Total deafness caused by otosclerosis is rare. Ringing in the ears (particularly a fluting tone) frequently occurs, and the patient sometimes complains of slight dizziness and an unsteady feeling similar to drunkenness, because the balancing mechanism of the inner ear is affected. Women are more troubled by ostoscle-rotic dizziness during menstruation. Many other disorders can cause hearing difficulties, including congenital deformation of the ossicles and adhesions and malformation caused by inflammation of the middle ear. In otosclerosis hearing difficulties occur gradually and it often runs in families. The family doctor should include the eardrum in his examination. In the case of otosclerosis the eardrum looks normal, which is not so in the case of most other disorders associated with hearing difficulties, or when the inner ear is inflamed. Hearing shows characteristic abnormalities. Whispered speech from a certain distance can be understood, particularly the higher tones; the difficulty is usually related to low tones (bass deafness). In the early stages of the disorder the patient can still understand well, even when surrounded by a lot of noise, because the low tones are suppressed but the high ones are heard. The family doctor can also test hearing with tuning forks. Examination of this kind can distinguish between hearing difficulties caused by abnormalities in the auditory canal, the eardrum and the middle ear and the auditory ossicles, as opposed to difficulties caused by damage to the auditory nerves. An intricate examination, which cannot usually be performed by the family doctor, is audiometry. Tones at various frequency are transmitted to the patient by headphones, and he says at what volume he cannot hear a particular frequency. The cause of the bone hardening which restricts the movement of the stapes is not known, and it is also not clear why hearing difficulties can increase during pregnancy. The disease can be transmitted to children who have mothers suffering from otosclerosis, but the likelihood of this is also unknown. Treatment of otosclerosis can be by surgery, to loosen the restricted stapes, but results are often disappointing, and many patients benefit more from a hearing aid.