Otosclerosis refers to abnormal bone growth of the bony labyrinth, primarily at the oval window. It manifests at the stapes, which becomes increasingly fixated to the oval window. This process leads to progressive conductive hearing loss because the ossicle's ability to vibrate becomes increasingly limited. Frequently, the other ear is also affected. Left untreated, the disease can progress to deafness. Audiometry reveals decreased air conduction and a characteristic Carhart's notch in the bone conduction curve. Replacement of the upper part of the stapes with a prosthesis (stapedotomy) is the treatment of choice.
- The exact mechanism is unknown.
- 50% of cases show autosomal dominant inheritance with incomplete penetrance, while the rest occur sporadically.
- Nests of unossified cartilaginous cells in the enchondral layer of the bony labyrinth (otic capsule) give rise to spongy bone (active otosclerotic focus) → otosclerosis
- Stapedial otosclerosis (most common site) → fixation of stapes to oval window → conductive hearing loss
- Slowly progressive conductive hearing loss with the 2nd ear affected in ∼ 70% of patients as the disease progresses
- Mild vertigo (approx. 25%) 
- Paracusis willisii: patients hear better in noisy rather than quiet surroundings.
- Quiet speech
- Schwartze sign: a red-blue hue seen through tympanic membrane
Symptoms may increase during pregnancy or following menopause because of hormonal changes.
Pure tone audiometry
- ↓ Air conduction (especially for lower frequencies)
- Carhart notch: an increase in the bone conduction threshold at 2,000 Hz (which is seen as a dip in the bone conduction curve)
- Impedance audiometry: absent stapedius reflex
- The progression of otosclerosis cannot be significantly influenced by conservative therapy.
- Surgical procedures
- The stapes is partly (stapedotomy; ) or completely (stapedectomy) replaced by a prosthesis.
- Cochlear implant: in the case of bilateral deafness