Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone.

As the lesions reach the stapes the bone is resorbed, then hardened (sclerotized), which limits its movement and results in hearing loss, tinnitus, vertigo or a combination of these.

The word otosclerosis derives from Greek ὠτός (ōtos), genitive of οὖς (oûs) "ear"[5] + σκλήρωσις (sklērōsis), "hardening".

[12] While the disease is considered to be hereditary, its penetrance and the degree of expression is so highly variable that it may be difficult to detect an inheritance pattern.

Also there is mounting evidence that measles virus is present within the otosclerotic foci, implicating an infectious etiology (this has also been noted in Paget's Disease).

[15] Conductive hearing loss (CHL) in otosclerosis is caused by two main sites of involvement of the sclerotic (or scar-like) lesions.

Additionally the cochlea's round window can also become sclerotic, and in a similar way impair movement of sound pressure waves through the inner ear ("acoustic coupling").

The most common location of involvement of otosclerosis is the bone just anterior to the oval window at a small cleft known as the fissula ante fenestram.

The fissula is a thin fold of connective tissue extending through the endochondral layer, approximately between the oval window and the cochleariform process, where the tensor tympani tendon turns laterally toward the malleus.

There are certainly a few well documented instances of sclerotic lesions directly obliterating sensory structures within the cochlea and spiral ligament, which have been photographed and reported post-mortem.

Otosclerosis is traditionally diagnosed by characteristic clinical findings, which include progressive conductive hearing loss, a normal tympanic membrane, and no evidence of middle ear inflammation.

Post-mortem studies show that as many as 10% of people may have otosclerotic lesions of their temporal bone, but apparently never had symptoms warranting a diagnosis.

In clinical practice otosclerosis is encountered about twice as frequently in females as in males, but this does not reflect the true sex ratio.

In pure-tone audiometry, this manifests as air-bone gaps on the audiogram (i.e. a difference of more than 10 dB between the air-conduction and bone-conduction thresholds at a given test frequency).

However, medial fixation of the ossicular chain impairs both the inertial and osseotympanic modes of bone conduction, increasing the bone-conduction thresholds between 500 Hz and 4 kHz, and reducing the size of air-bone gaps.

[19] Tympanometry measures the peak pressure (TPP) and peak-compensated static admittance (Ytm) of the middle ear at the eardrum.

If the mobility of the stapes is reduced due to otosclerosis, then stapedius muscle contraction does not significantly decrease the admittance.

[26] There are numerous side-effects to both pharmaceutical treatments, including occasional stomach upset, allergic itching, and increased joint pains which can lead to arthritis.

A stapedectomy consists of removing a portion of the sclerotic stapes footplate and replacing it with a middle ear implant that is secured to the incus.

A modern variant of this surgery called a stapedotomy, is performed by drilling a small hole in the stapes footplate with a micro-drill or a laser, and the insertion of a piston-like prothesis.