Hearing impairment refers to the difficulty that a person perceives due to a hearing loss. Hearing loss or deafness is decreased or absent ability to perceive auditory information. While some cases of hearing loss are reversible with medical treatment, many lead to a permanent disability. Of vital importance are the age at which the hearing loss occurred, as this may interfere with the acquisition of spoken language. Hearing aids and cochlear implants may alleviate some of the barriers caused by hearing impairment, but are often insufficient. Persons with difficulty hearing, especially those who develop a hearing problem later in life, often require social acceptance and support, as well as technical adaptations, as part of the rehabilitation process.
Causes:
There are four major causes of hearing loss: genetic, disease processes
affecting the ear, medication and physical trauma. There are three major
types of hearing loss: conductive, neural, or a combination. Treatment
depends upon the type of hearing loss that is present.
Genetic:
Hearing impairment 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 be
expressed 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 manifest as it will have to be passed onto offspring
from both parents.
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.
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.
HIV (and subsequent opportunistic infections) may directly affect the
cochlea and central auditory system.
Chlamydia may cause hearing loss in newborns to whom the disease has been
passed at birth.
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.
Premature birth results in sensorineural hearing loss approximately 5%
of the time.
Syphilis is commonly transmitted from pregnant women to their fetuses,
and about a third of the infected children will eventually become deaf.
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).
Various other medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics.
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.
