Hearing impairment

A hearing impairment is a decrease in one's ability to hear (i.e. perceive auditory information). While some cases of hearing loss are reversible with medical treatment, many lead to a permanent disability (often called deafness).

Causes

There are four major causes of hearing loss: genetic, disease processes affecting the ear, medication and physical trauma.

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Genetic

Hearing loss can be inherited. Both dominant and recessive genes exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. If a family had genetic hearing impairment caused by a recessive gene it will not always be apparent as it will have to be passed onto offspring from both parents.

Related Topics:
Dominant - Recessive gene

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Dominant and recessive hearing impairment can be syndromic or nonsyndromic. Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness.

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• The most common type of congenital hearing impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness.
• The most common dominant syndromic forms of hearing impairment include Stickler syndrome and Waardenburg syndrome.
• The most common recessive syndromic forms of hearing impairment are Pendred syndrome, Large vestibular aqueduct syndrome and Usher syndrome.

Disease or illness

• Measles may result in auditory nerve damage
• Meningitis may damage the auditory nerve or the cochlea
• Autoimmune disease has only recently been recognised as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Wegener's granulomatosis is one of the autoimmune conditions that may precipiate hearing loss.
• Presbyacusis is deafness due to loss of perception to high tones, mainly in the elderly. It is considered a degenerative process, and it is poorly understood why some elderly people develop presbyacusis while others do not.
• Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).
• Adenoids that do not disappear by adolescense may continue to grow and may obstruct the Eustachian tube, causing conductive hearing impairment and nasal infections that can spread to the middle ear.
• AIDS and ARC patients frequently experience auditory system anomalies.http://library.gallaudet.edu/dr/faq-etiol.html
• HIV (and subsequent opportunistic infections) may directly affect the cochlea and central auditory system.http://library.gallaudet.edu/dr/faq-etiol.html
• Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.http://library.gallaudet.edu/dr/faq-etiol.html
• Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.http://library.gallaudet.edu/dr/faq-etiol.html
• Premature birth results in sensorineural hearing loss approximately 5% of the time.http://library.gallaudet.edu/dr/faq-etiol.html
• Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.http://library.gallaudet.edu/dr/faq-etiol.html
• Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.

Medications

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamycin).

Related Topics:
Aminoglycoside - Gentamycin

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Various other medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics.

Related Topics:
Diuretic - Aspirin - NSAID - Macrolide

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Physical trauma

• There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.
• People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent.
• Exposure to very loud noise (90 dB or more, such as jet engines at close range) can cause progressive hearing loss. Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent hearing loss.

Noise Exposure

• Noise-induced hearing loss is the second most common form of sensorineural hearing deficit, after presbycusis (age-related hearing loss)
• Exposure to high levels of noise (>85 dB or more) for extended periods of time can cause a permanent, sensorineural hearing loss.
• Noise-Induced Hearing Loss (NIHL) typically begins at 4,000 Hz and spreads downward and upward.
• Earplugs or earmuffs can help to reduce the noise that reaches the ear.
• The louder the noise is, the shorter the safe amount of exposure is. For example, the safe exposure amount at 85 dB is 8 hours, while the safe exposure at 90 dB is only 2 hours, 31 minutes (National Institute for Occupational Safety and Health, 1998)
• Personal electronic audio devices, such as iPods, can produce powerful enough sound to cause significant Noise-Induced Hearing Loss