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Otosclerosis is a condition of the middle ear which causes hearing loss that gets worse over time. Unlike hearing loss resulting from damage to the inner ear, the hearing loss from otosclerosis is often reversible.
- The name otosclerosis comes from the Greek words for "hard" (scler-o) "ear" (oto)
- Otosclerosis is a disorder which causes a hardening of the bones of the middle ear.
To understand why otosclerosis causes hearing loss, it is important to understand how the ear works. The human ear is divided into three parts: the external, middle, and inner ear.
- The external ear consists of the part of the ear you can see (the auricle) and the ear canal
- The middle ear includes the eardrum (tympanic membrane) and the three bones of the middle ear, the malleus ("hammer"), incus ("anvil"), and the stapes (pronounced STAY-PEAZ, "the stirrup").
- The inner ear is a fluid-filled series of chambers. One of these chambers, the cochlea, is responsible for converting sound vibrations into nerve impulses. It is these nerve impulses that the human brain interprets as sound and what we call "hearing."
The inner ear also contains the semicircular canals which are responsible, in part, for sensing movement and maintaining balance.
Normally, sound is conducted from the outside environment through the ear canal. Sound waves vibrate the tympanic membrane and set the bones of the middle ear into motion. These vibrations are transmitted from malleus, to incus, to stapes, and finally to the fluid of the inner ear. When everything is working normally, the hearing is normal.
However, if the bones of the middle ear don't vibrate normally, the inner ear does not receive the full amount of sound vibration and hearing is decreased. This is exactly what happens in otosclerosis.
Most cases of otosclerosis involve the last, and smallest bone, the stapes. In otosclerosis, the bottom of the stapes becomes calcified or hardened by overgrowth of new bone. It is unknown why this occurs.
Symptoms
The primary symptom of otosclerosis is a slowly progressive hearing loss beginning anytime between the age of 15 and 45, although it usually starts around age 20. Approximately three quarters of patients with otosclerosis will also develop a ringing or rushing sound in the affected ear, also called tinnitus.
In 25-30% of patients, balance problems may also occur, including unsteadiness, dizziness, vertigo, or other sensations of motion. Otosclerosis affects both ears in 80% of patients.
Who gets otosclerosis?
Otosclerosis affects approximately 10% of the adult Caucasian population. However, only 1% of people will ever develop significant hearing loss as a result of this condition. The condition is less common in people of Japanese and South American descent. It is rare in African Americans.
- Otosclerosis affects women twice as often as men
- In female patients, hearing often worsens rapidly during pregnancy
- Otosclerosis runs in families in many cases, but the genetic cause is not clear
Diagnosis
A simple hearing test is usually all that is required to diagnose this condition. However, since there are a number of middle ear conditions that cause hearing loss, it's difficult to diagnose otosclerosis without actually looking into the middle ear. This must be done in operating room as a surgical procedure known as a middle ear exploration or exploratory tympanotomy.
Patients who have balance problems in addition to hearing loss may need additional balance tests prior to surgery.
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