Facts on Hearing Loss
To understand hearing loss it is important to understand how normal hearing takes place. There are 2 different pathways by which sound waves produce the sensation of hearing: air conduction and bone conduction.
- In air conduction, sound waves move through the air in the external auditory canal (the "ear canal" between the outside air and your eardrum). The sound waves hit the tympanic membrane (eardrum) and cause the tympanic membrane to move.
- The bones in the middle ear are connected to the tympanic membrane. When the tympanic membrane moves, this movement is transmitted to the bones. These 3 bones are called the malleus, the incus, and the stapes. Movement of the stapes causes pressure waves in the fluid-filled inner ear.
- The cochlea is an inner ear structure surrounded by fluid. It contains multiple small hairs. Pressure waves in the fluid cause the hairs to move. This movement stimulates the auditory nerve. Different frequencies of noises stimulate different hairs on the cochlea, which translate to the sensation of sounds of different pitch.
- Hearing by bone conduction occurs when a sound wave or other source of vibration causes the bones of the skull to vibrate. These vibrations are transmitted to the fluid surrounding the cochlea and hearing results.
What Causes Hearing Loss?
There are 2 basic types of hearing loss, which are called conductive and sensorineural.
- Conductive causes: Conductive hearing losses result from physical problems with the movement of the sound wave through the ear. A simple example is blockage of the ear canal.
- Obstructed external ear canal - Cerumen (wax) build-up, hematoma (blood collection), or foreign body in the ear canal. This is one of the most common causes of hearing loss and the easiest to fix.
- Perforated tympanic membrane - Caused by direct trauma such as a cotton swab, middle-ear infections (otitis media), or explosions (blast injury)
- Dislocated ossicle (malleus, incus, or stapes) - Usually from trauma to the ear
- Otitis media - Middle ear infection (probably the most common cause for conductive loss)
- Otitis externa - Infection of the ear canal that causes it to swell
- Retraction of the tympanic membrane (ear drum) toward the middle ear. This may be associated with a collection of skin called a cholesteatoma
- Sensorineural causes: Sensorineural causes are from damage to the hair cells or nerves that sense sound waves.
- Acoustic trauma - Prolonged exposure to loud noises causes the hair cells on the cochlea to become less sensitive.
- Barotrauma (pressure trauma) or ear squeeze - Usually in divers
- Head trauma - A fracture of the temporal bone can disrupt the nerves of the auditory system or the cochlea directly
- Ototoxic drugs - Certain drugs can affect hearing by damaging the nerves involved in hearing. Usually this occurs when large or toxic doses are used but may also occur with lower doses.
- Antibiotics including aminoglycosides (gentamicin, vancomycin), erythromycins, and minocycline
- Diuretics including furosemide and ethacrynic acid
- Salicylates (aspirin) and nonsteroidal anti-inflammatories (NSAIDs) such as ibuprofen and naproxen
- Antineoplastics (cancer drugs)
- Vascular diseases (problems with blood vessels) include sickle cell disease, diabetes, leukemia, polycythemia, and diseases in which excessive blood clotting occurs.
- Children and adults with kidney problems are more susceptible to sensorineural hearing loss.
- Ménière disease - A disease that affects hearing and balance. It is usually associated with tinnitus (ringing in the ears). It has a gradual onset and may progress to deafness and severe vertigo. The cause is unknown, but thought to be associated with fluid shifts in the inner ear.
- Acoustic neuroma - A tumor in the auditory nerve. Usually associated with ringing in the ears.
- Infections, include some occurring during pregnancy and soon after birth in neonates.
- Aging (presbycusis)
Medically Reviewed by a Doctor on 11/16/2016
Angelique S Kelly Campen, MD
Scott H Plantz, MD, FAAEM
Francisco Talavera, PharmD, PhD
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