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). more...

If the hearing loss occurs at a young age, it may interfere with the acquisition of spoken language and social development. Hearing aids and cochlear implants may alleviate some of the problems caused by hearing impairment, but are often insufficient. People who have hearing impairments, especially those who develop a hearing problem later in life, often require support and 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.

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.

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 adolescence 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.

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