Otosclerosis

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Otosclerosis, also known as otospongiosis, is an abnormal growth of the spongy bone that causes conductive a-typical hearing loss. It usually begins in the labyrinth of the inner ear, and is diagnosed when the growth spreads to the middle ear. The most common presentation attaches the footpad of the stapedius to the oval window, which reduces the overall amplitude of vibrations transmitted to the inner ear. Bony growth may also spread to the stapedius crura and the oval window. It is less common to find the growth on the ossicles, or occupying a large amount of middle ear space.

Otosclerosis is generally not detectable by a physical examination of the pinna and ear canal. Occasionally the Schwartze sign, a vascular promontory, results in a rosy glow that can be seen through the tympanic membrane. The audiogram of a person with otosclerosis will show a low frequency air-bone gap consistent with conductive hearing loss. The bone conduction thresholds will be altered and they may appear to be 5dB poorer than the air conduction thresholds. Carhart’s notch, a dip in bone conduction threshold at 2000 Hz is frequently found with otosclerosis. Immittance tests will show a type As tympanogram due to reduced compliance and normal ear canal volume. No acoustic reflex will be present, because the growth attenuates all sounds. Additionally, all site-of-lesion tests will point to a middle ear abnormality.

Patients with otosclerosis will notice difficulties hearing sounds below their threshold level. However, increased intensity alone will not necessarily improve hearing due to the attenuation levels. Patients may complain of difficulties hearing while chewing. The bony growth directly attached to the ossicles will better transfer bone conduction vibrations, resulting in increased loudness for chewing noises. Additionally, most patients find that speech perception is better in a noisy environment. This effect is known as paracusis willisii. Due to the increased level of...
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