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.
- Slowly progressive 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