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This material should not be used as a basis for treatment
decisions, and is not a substitute for professional consultation
and/or peer-reviewed medical literature.
Conductive Hearing Loss
Conductive hearing loss results from a problem with the outer or
middle ear.
This means that there is something preventing sound from being conducted
through the outer and middle ear to the inner ear.
In conductive hearing loss, the sensory and neural components of
the inner ear are completely functional. Common causes of conductive
loss include ear canal blockage (by a foreign object) , scarring
of the ear drum , congenital malformation of the outer or middle
ear structures, and ossicular discontinuity.
Treatment for conductive hearing loss depends on the cause and the
extent of the loss, and may include surgery or hearing aids, while
antibiotics are usually indicated for ear infections.
Sensorineural Hearing Loss
Synonyms: Sensorineural deafness, perceptive hearing loss, perceptive
deafness.
Sensorineural hearing loss results from either damage to the cochlea
or the auditory nerve.
This type of loss is sometimes referred to as "nerve"
loss, although this term is usually inaccurate since most sensorineural
hearing loss is sensory, not neural.
Inside the cochlea are thousands of sensory haircells that translate
sound into the neural language that is transmitted to the brain
so we hear.
Disease or degeneration most often damages the haircells, not the
nerve.
When hearing is tested, both sensory and neural hearing loss patterns
appear the same way.
Thus, the term sensorineural hearing loss is used to describe both
types of loss.
Most sensorineural hearing loss is permanent and cannot be treated
medically or surgically except in certain circumstances, for example,
sudden hearing loss, and .
Sensory loss from cochlear damage can occur with , ingestion of
ototoxic medications, and some immune diseases.
Hearing loss that is present at birth is usually sensorineural,
but also can be conductive especially in patients born with facial
deformities. Aging causes the most common sensory hearing loss.
This is called presbycusis.
By the age of 65, one-third of all people have significant
Ultimate success with hearing aids may be influenced by a person's
ability to recognize words.
Some people's ears with sensorineural hearing loss are like radios
that aren't quite tuned in.
Speech may be loud enough but not clear. Unfortunately, if a person's
ears create distortions that cause poor word recognition, hearing
aids may not accommodate this deficit. That is, the sound that is
delivered through the hearing aid may be crystal clear, but that's
not the way the way it sounds to the ear with the distortions!
Individuals with bilateral profound sensorineural hearing loss may
be candidates.
On the next page Sudden sensorineural hearing loss (SSNHL)
Sudden sensorineural hearing loss
SSNHL is a hearing loss that is greater than 30 dB in three contiguous
frequencies and that occurs over a period of less than 3 days.
The incidence is estimated at 20/100000 persons per year, increasing
with advancing The natural history of SSNHL is that about 65% of
patients recover their hearing spontaneously.
Negative prognostic factors are thought to be: age less than 15
years or older than 65 years and a hearing loss in the opposite
ear.
Positive prognostic factors are: seeking medical treatment within
10 days of onset, mid-frequency or upsloping hearing loss.
The severity of the hearing loss is inversely proportional to the
rate of recovery.
Signs & Symptoms SSNHL is usually unilateral and accompanied
by tinnitus (70%) and often vertigo (50%).
Degree of hearing loss is variable.
Patients often report that they awaken in the morning and notice
a hearing loss.
"Acoustic trauma" is defined as sudden aural damage resulting
from short term intense exposure or even a single exposure.
The types of loud noise considered in this category include: fireworks,
small arms fire, gunfire, grenade fire, exploding mines, and major
explosions.
Most literature does not specify the range of noise levels likely
to occur with any of these types of explosions.
Noise levels are probably well in excess of 120 dB.
Extremely loud noises can rupture the ear drum and damage the ossicles.
Less intense acoustic trauma may produce ear pain or a sensation
of burning, temporary threshold shift or permanent threshold shift,
and tinnitus.
The severity of the loss varies with the magnitude of the explosion
and proximity to the blast.
Both tinnitus and sensorineural hearing loss are known complications
of treatment with salicylates, such as aspirin.
The symptoms appear at serum levels of 300 mg/litre or higher, and
are almost always reversible once therapy is ceased and serum levels
fall below this level.
Whereas permanent tinnitus may be an occasional sequelae of toxicity,
there is marginal evidence that it leads to permanent sensorineural
hearing loss.
Otosclerosis
primarily causes progressive conductive deafness (usually bilateral),
most often between the ages of 11 to 30 years.
A small proportion occurs before 10 years of age, and an even smaller
proportion after the age of 50.
In 70 per cent of cases, the disease is familial and in 30 per cent
it is of sporadic onset.
Progress is inexorable but may be uneven. When sensorineural hearing
loss develops it almost invariably follows the onset of the conductive
component.
It is unknown if sensorineural disease can occur in the absence
of a conductive component. There is some support for the notion
that otosclerosis may be the cause of otherwise unexplained sensorineural
hearing loss in young to middle-aged adults.
Whilst the cause of otosclerosis is unknown, early detection and
treatment often serves to ameliorate the effects of the disease,
and few cases, if treated late, are remediable.
Acceleration of the hearing loss is known to occur with pregnancy,
menopause, and with chronic stress reactions associated with major
trauma.
Aggravation by exposure to one of the ototoxic drugs is possible.
Where SNHL is thought to be due to otosclerosis the contribution
is only likely to be through the aggravation of the primary disease.
Known viral causes of sensorineural hearing loss are mumps, measles,
pertussis, rubella, and varicella-zoster.
These mainly cause sensorineural hearing loss in early childhood.
Less certain associations exist for poliovirus, influenza B, cytomegalovirus,
coxsackie virus, Epstein-Barr virus (infectious mononucleosis),
and herpes simplex virus.60
In view of the uncertainties referred to above, all of the above
viruses are considered to be possible risk factors for sensorineural
hearing loss but only mumps, measles, pertussis, rubella, and varicella-zoster
are likely and then only when a close temporal relationship exists.
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