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Hearing Disorders
The most common hearing disorders are those
that affect hearing sensitivity. When a sound is
presented to a listener with a hearing sensitivity
disorder, one of 2 things may occur:
1. The listener with a HS disorder may be unable
to detect the sound.
2. The sound will not be as loud to that listener
as it would be to a listener with normal hearing.
Note: Vision is different. The most common
vision disorders affect acuity, not sensitivity to
light. Acuity is the ability to resolve differences.
Eyeglasses and contact lenses improve acuity,
not sensitivity to light. Hearing aids are just the
opposite – they improve sensitivity to sound by
amplifying it – but do not improve acuity.
Important: This sensitivity vs. acuity distinction
is not quite so simple with hearing (or vision):
hearing loss of any significance nearly always
involves problems of both sensitivity and acuity
– sounds are harder to hear (sensitivity) and they
are nearly always distorted (acuity). More about
this later.
The Audiogram
Most common way to measure hearing sensitivity is
to measure pure-tone (sinusoid) thresholds.
Threshold: Sound level required to barely detect a
Audiogram of a Listener with
sound.
Thresholds in the Normal Range
125
250
500
1000
2000
4000
8000
-10
0
Red: right ear
10
Intensity (dB HL)
20
Audiogram
for a listener
w/ thresholds
in the normal
range.
30
40
50
60
70
80
90
100
110
Frequency (Hz)
Mild high-frequency loss
125
250
Audiogram of a Listener with a
Mild High-Frequency Hearing Loss
500
1000
2000
4000
8000
-10
0
Red: right ear
10
Intensity (dB HL)
20
30
40
50
60
70
80
90
100
110
Frequency (Hz)
Moderate-to-severe bilateral loss
Severe Loss Left, Ear Moderate Loss Right Ear
125
250
500
1000
2000
4000
8000
-10
0
10
Severe loss
in left ear,
moderate
loss in right
ear.
20
Intensity (dB HL)
30
40
50
60
70
80
90
100
110
Pure Tone Average (PTA)
Frequency (Hz)
Average thresholds at 500, 1000, 2000 Hz – the frequencies
most important for speech understanding. From the
audiogram above:
Pure-tone Average, Left Ear:
Pure-tone Average, Right Ear:
93 dB
50 dB
Terminology
Normal Hearing:
PTAs < 25 dB
Hearing Impairment: PTAs 25-92 dB
Deaf:
PTAs > 92 dB
The term deafness is reserved for cases in which
“ … the handicap for hearing everyday speech …
[is] … total” (Davis & Silverman, 1979).
Despite these conventions: (1) there is no sharp
dividing line between hearing impairment and
deafness, and (2) degrees of deafness are
meaningful; e.g., there is a difference between
PTAs of 110 and 95.
Types of Hearing Disorders
Many ways to classify hearing disorders
1. Nature of the loss:
Sensitivity vs. Acuity
 Dysacusia – Deficit in discrimination or
interpretation of sound: “Don’t shout, I can
hear you just fine. I just can’t understand
what you’re saying.” Disacusia is a good
term that isn’t in very common use.
 Acuity deficits sometimes due to disorders
of the central auditory
system.
 Disorders of sensitivity and acuity are not
mutually exclusive.
2. Functional Classification
 Conductive – Disorders involving the
conduction of sound to the cochlea.
 Sensori-neural – Disorders involving the
cochlea (usually the hair cells) or 8th N.
 Central – Disorders affecting the CNS (brain
stem or auditory cortex).
Two related terms:
Peripheral – Not central; i.e., conductive or
sensorineural.
Retrocochlear – Disorders involving anatomical
structures beyond the cochlea; i.e., 8th N, brain
stem, auditory cortex.
3. Cause or Etiology of the Disorder
Hearing disorders can be classified on the basis of
the cause of the disorder. Some examples:
 Ototoxic drugs
 Noise exposure
 Old age (presbycusis)
 Otitis media
 8th N tumors
 Meniere’s Disease
In this review, we will proceed by functional
subsystem (conductive, sensorineural, central), and
by etiology within each subsystem.
Conductive Hearing Disorders
1. External Ear
 Congenital malformations. There are many
of these. Most serious is congenital atresia
– collapse or closure of the EAM (ear
canal). May occur in isolation, but typically
associated congenital malformations of the
middle ear as well.
 Impacted wax (cerumen) – results in mild
hearing loss; easily treated by removal of
the wax.
2. Middle Ear
a. Otitis Media
 By far the most common cause of conductive
hearing loss.
 By far the most common health problem in
children.
Disease Process – OM involves a very specific
chain of events revolving around the abnormal
functioning of the Eustachian tube.
 Begins with an ordinary upper respiratory infection
(head cold) involving, among other things, the
nasopharynx.
 Nasal secretions infect the Eustachian tube.
 The Eustachian tube, which is normally closed,
becomes inflamed and can no longer open upon
swallowing, yawning, etc. This means that pressure
can no longer be equalized between the middle ear
and the ambient air.
**** This is the key to the whole deal ****
 Oxygen in the ME cavity is consumed by
ordinary metabolic processes. Ordinarily, this
oxygen is re-supplied through the Eustachian
tube. With a plugged ET, this cannot occur.
 The absorption of oxygen without re-supply
results in a partial vacuum (i.e., lower than
normal pressure) in the ME.
 The pressure drop sucks the TM inward into
the ossicular chain, reducing its mobility.
Consequences: hearing loss and pain – often
quite intense.
 Partial vacuum creates another problem:
Recall that the entire ME cavity is lined with
mucous membrane. The pressure drop causes
clear fluid to be sucked out of the mucosal
lining of the ME. This accumulation of fluid
contributes to the conductive hearing loss.
Condition is called serous otitis media or
nonsuppurative otitis media. Defining features:
(1) clear, thin, watery fluid, (2) fluid is sterile
(not infected).
 Suppurative or Purulent Otitis Media: As the
disease progresses, the fluid can become
infected and thickens into (eck) pus.
Consequences
The major consequences of OM are
hearing loss and pain.
The hearing loss is typically mild (usually
20-30 dB) and often fluctuating.
The pain varies quite a bit but is often
quite severe. It is not unusual for the
pressure drop in the ME to become
severe enough to cause the TM to
rupture.
Some Additional Terminology
Acute vs. Chronic OM: A specific bout of OM
with pain, accumulation of fluid, sometimes
fever, etc., is called acute otitis media. If OM
lasts more than 2-3 months, the condition is
known as chronic otitis media.
Recurrent OM: Frequent bouts of OM: OM is
treated successfully, then returns, then it’s
treated, then it returns … This gets old after a
while but is pretty common.
Treatment of Otitis Media
Most common treatment by far: Antibiotics (especially
amoxicillin)
Common treatment for recurrent or chronic OM: PE
Tubes (PE = pressure equalization). This is a small
plastic tube inserted into the TM. Why would such a
tube be expected to treat OM?
Two More Terms
Otitis Media with Effusion (OME): Otitis media
characterized by the accumulation of fluid.
Mucoid or Mucous Otitis Media (“Glue Ear”):
Fluid in middle ear is thick and gooey rather than
thin and watery. Hearing loss is often more
severe than serous OM. Seen in some cases of
recurrent OM – purulent OM is treated, killing the
infection, but fluid does not drain.
Speech and Language Delay??
Evidence is mixed and still controversial, even
after many years of study, but there is some
research suggesting that frequent bouts of OM
(i.e., recurrent OM) can result in delays in
acquiring speech and language.
Most SLPs believe that there is a link between
recurrent OM and speech & language delays.
Evidence is mixed, but if you focus on the
studies that are the most thorough and with the
best experimental designs, the evidence for this
link is weak. Some well designed studies show
an effect at ~age 4 that disappears as kids get
older. The issue is still not entirely settled.
b. Otosclerosis (note: topic here is still conductive HL,
sorted by cause)
 Begins as a soft, spongy growth of new bone –
may appear anywhere in the ME, but most often
near the oval window.

Later hardens (i.e., becomes sclerotic)

In 90% of cases: No symptoms
In the unlucky 10%: Growth reduces mobility of
stapes, causing a conductive HL.
Otosclerosis is a progressive condition, beginning
in childhood. For that unlucky 10%, HL typically
begins in late teens or early 20s.
 Maximum HL seldom worse than ~50-60 dB.
 Treatment: Stepedectomy (removal of stapes and
replacement with an artificial stapes)
incus
prosthetic stapes
c. Cholesteatoma
 Cyst that invades the ME
 Usually grows rapidly
 Can: (1) destroy the ossicular chain, (2) invade the
cochlea, or (3) break through the thin shelf of bone that
forms the superior surface of the ME cavity, invading the
meninges.
 HL usually mild and not really the major concern.
From http://www.ohsu.edu/ent/ear/chol.html:
Cholesteatomas are benign growths of skin in the
middle ear and mastoid. These "skin cysts" can and do cause
many problems in the ear. Cholesteatomas commonly cause
hearing loss and infections. The only treatment available to
cure a cholesteatoma is surgery. The surgery that is typically
performed is tympanoplasty with or without mastoidectomy.
Cholesteatomas left untreated can go on to cause serious and
sometimes life threatening health problems, such as
meningitis or brain abscess. Cholesteatomas can develop in
both children and adults. Surgery is usually done as day
surgery (outpatient).
Sensori-Neural Hearing Loss
General: By far the most common underlying cause
of SN HL is damage to the hair cell transducers. In
these most common cases, the auditory nerve and
central auditory pathway are intact, but stimulation
of the auditory nerve is abnormal due to damaged
hair cells. There are many possible reasons for the
hair cells to become damaged. The various
etiologies of SN HL consist mainly of a catalog of
different causes of hair cell damage.
a. Presbycusis
• Hearing loss associated with aging
• Most common cause of SN HL – and most
common cause of HL overall.
Begins in adolescence! This figure shows data for men
(top) and women (bottom) at different ages. A little
discouraging?
Men
High frequencies are more
strongly affected than lows.
(We will see this again when
we talk about noise-induced
HL.) Any guesses about why
high-frequencies are more
vulnerable?
Women
Moral: We all have a long, slow slide ahead of us.
Don’t squander the hearing you have by needlessly
exposing yourself to long periods of loud noise.
Wear ear plugs or muffs when mowing the grass,
snow-blowing, etc., and use some sense in
listening to music. Once hair cells are damaged,
they’re gone for good.
One last point: Presbycusis listed here under the
SN category since it is clear that this is the
dominant component. However:
(1)The SN component may not be due exclusively to
hair cell loss. Changes in the elasticity of the
basilar membrane and metabolic changes in the
stria vascularis may also play a role (Davis, H. and
Silverman, S. Richard, 1978, Hearing and Deafness, New York: Holt, Rinehart & Winston ).
(2) There may also be a conductive component due
to age-related changes in the mobility of tissues
in the middle ear.
(3) There is sometimes a central component due to
the loss of neurons in the CNS, (related primarily
to arteriosclerosis). The result of this CNS
damage is a reduction in acuity and speech
perception abilities. The resulting deficit in
speech perception ability is sometimes referred
to as phonemic regression. In some cases it is
this problem rather than a loss of hearing
sensitivity that is the patient’s primary
complaint.
b. Noise-Induced Hearing Loss
Exposure to high levels of noise can damage HCs and cause SN HL.
Two types:
Acoustic trauma:
 Injury due to brief exposure to very intense sounds such as gun
shots, artillery fire, explosions, etc.
 HL may be severe and permanent, but substantial recovery is
common.
Long-term noise exposure (more common):
 Damage results from long-term exposure to high levels of noise.
 Common in some occupational settings – heavy manufacturing and
agriculture being the most common.
 Amount of inner-ear damage depends on the combination of:
Intensity of the noise
Length of exposure
Pretty simple: High levels x long exposures=Bad news
Low levels x brief exposures=Not so bad news
Audiometric Pattern is distinctive (audiogram on right shows more
advanced progression than left)
Image from http://www.aafp.org/afp/20000501/2749.html (American Academy of Family Physicians)
Note:
(1) Dip or “notch” at ~3-6 kHz
(2) Typical progression shows the notch broadening (especially on the
high frequency side) and deepening
(3) High frequencies more affected than lows
c. Ototoxic Drugs
Certain drugs can cause SN HL. Toxicity effects
vary from mild and temporary to severe and
permanent.
Some very common drugs such as aspirin
(especially in large doses) can cause hearing
loss (and/or tinnitus), but not in most people,
and the loss is typically mild and temporary.
An especially important group of antibiotics are
notoriously ototoxic. Examples include
neomycin, streptomycin, kanamycin.
Since this is well known, why might these drugs
ever be administered? (A: It’s a reasonable alternative to
mortality.)
ANTIBIOTICS WITH GOOD EVIDENCE FOR OTOTOXICITY
Drug
Vestibulotoxicity
Erythromycin
Hearing
Toxicity
Toxic Level
yes
High IV doses only
Usually 2 weeks
Gentamicin
8.6%
minor
Streptomycin
very toxic
minor
dihydrostreptomicin
minor toxic
very toxic
Tobramycin
Yes
minor in 6%
Netilmicin
2.4%
Amikacin
not toxic
13.9%
Neomycin
minor
very toxic
Kanamycin
minor
very toxic
Etiomycin
moderate
Vancomycin
nontoxic
none to
moderate
Metronidizole
toxic (rarely)
unknown
Capreomycin
Less toxic than Gentamicin
In topical ear drops
synergistic with gentamicin
yes
Table from: http://www.tchain.com/otoneurology/disorders/bilat/ototoxins.html See other classes of ototoxic drugs on the same web site.
List below from: www.lhh.org/hrq/22-2/ototoxic.htm
A. Salicylates
1. aspirin and aspirin-containing products
2. salicylates & methyl-salicylates (linaments)
B. Non-Steroidal Anti-Inflammatory Drugs (NSAIDS)
1. diclofenac (Voltaren)
2. etocolac (Lodine)
3. fenprofen (Nalfon)
4. ibuprofen (Motrin, Advil, Nuprin, etc.)
5. indomethacin (Indocin)
6. naproxen (Naprosyn, Anaprox, Alleve)
7. piroxicam (Feldene)
8. sulindac (Clinoril)
(Toxic effects are dose related and are almost always reversible once medications are discontinued).
C. Antibiotics
1. aminoglycosides
a. amikacin (Amakin)
b. gentamycin (Garamycin)
c. kanamycin (Kantrex)
d. neomycin (Found in many over-the-counter antibiotic ointments)
e. netilmicin (Netromycin)
f. streptomycin
g. tobramycin (Nebcin)
(Of particular interest is that topical ear drop medications containing gentamycin or neomycin do not appear to be ototoxic in
humans unless the tympanic membrane (ear drum) is perforated. When a solution of an aminoglycoside antibiotic is used on the
skin together with an aminoglycoside antibiotic used intravenously, there is a risk of an increase of the ototoxic effect, especially
if the solution is used on a wound that is open or raw, or if the patient has underlying kidney damage.
Neomycin is the drug that is most toxic to the structure involved in hearing, the cochlea, so it is recommended for topical use
only. But even topical therapy has resulted in hearing loss when large areas were treated which allowed for large amounts of the
drug to be absorbed into the body. Hearing loss caused by this class of antibiotics is usually permanent).
2. erythromycin
a. EES
b. E-mycin
c. Ilosone
d. Eryc
e. Pediazole
f. Biaxin
g. Zithromax
(Usually ototoxic when given in intravenous doses of 2-4 grams per 24 hours, especially if there is underlying kidney failure).
3. vancomycin (Vancocin) (Similar to aminoglycosides in that it may be ototoxic when used intravenously in life- threatening
infections. To further exaggerate the problem is the fact that aminoglycosides and vancomycin are often used together
intravenously when treating life-threatening infections).
4. minocycline (Minocin) (Similar to erythromycin).
5. polymixin B & amphotericin B (Antifungal preparations).
6. capreomycin (Capestat) (Anti-tuberculosis medication).
D. Diuretics
1. bendroflumethazide (Corzide)
2. bumetadine (Bumex)
3. chlor-thalidone (Tenoretic)
4. ethacrynic acid (Edecrin)
5. furosemide (Lasix)
(These are usually ototoxic when given intravenously for acute kidney failure, acute hypertensive crisis, or acute pulmonary
edema/congestive heart failure. Rare cases of ototoxicity have been found when these medications are taken orally in high doses
by people with chronic kidney disease).
E. Chemotherapeutic Agents
1. bleomycine (Blenoxane)
2. bromocriptine (Parlodel)
3. carboplatinum (Carboplatin)
4. cisplatin (Platinol)
5. methotrexate (Rheumatrex)
6. nitrogen mustard (Mustargen)
7. vinblastin (Velban)
8. vincristine (Oncovin)
(The ototoxic effects can be minimized by carefully monitoring blood levels).
F. Quinine
1. chloroquine phosphate (Aralen)
2. quinacrine hydrochloride (Atabrine)
3. quinine sulfate (Quinam)
(The ototoxic effects are very similar to those of aspirin).
G. Mucosal Protectant
1. misoprostol (Cytotec)
d. Meniere’s Disease
Serious, often debilitating disease of hearing and
balance of unknown/uncertain cause.
MD affects a single ear in about 75% of cases.
Four major symptoms:
(1)Periodic episodes of rotary vertigo (the
sensation of spinning) or dizziness (the
“Meniere’s attack”)
(2)Fluctuating, progressive, low-frequency hearing
loss
(3)Tinnitus
(4) A sensation of "fullness" or pressure in the ear
(1) Rotary Vertigo
This is easily the most disruptive and debilitating
symptom of Meniere’s. Similar to the mild vertigo you get
from too many beers, or from spinning around on a
playground swing. Some major differences:
 Dramatically more severe
 Often accompanied by nausea, vomiting, sweating
 Onset is usually sudden
 Typically persists for hours or even days
 Patient has little or no ability to control it
 Condition often leaves the patient confined to a bed
and as stationary as possible for long periods of time,
until the symptoms subside. Even small head
movements can greatly exacerbate the symptoms
(2) SN Hearing Loss
 Fluctuating
 Initially affects low-frequencies more than highs, but may
spread to highs as the disease progresses
 Progressive (i.e., gets worse with time)
 Hearing may be completely lost in the affected ear
 Usually unilateral
 Sounds may appear “tinny” (low-freq loss) & distorted
 Loudness intolerance is common (abnormal sensitivity to
intense sounds)
(3) Tinnitus
 Ringing, roaring, or buzzing sensation, fluctuating in
intensity, but does not abate
 Pretty annoying
(4) Sensation of “fullness”
Like the weird sensation you get on an airplane or elevator
before your ears pop – except it can’t be cleared. (Cause of
fullness sensation unrelated to M.E. function)
Cause of Meniere’s
 The proximate (i.e., immediate) cause of MD is excessive
and fluctuating pressure in the endolymphatic fluid in the
membranous labyrinth (cochlea and vestibular) systems.
This causes the membranous labyrinth to bulge.
 Condition is known as endolymphatic hydrops.
 Result is progressive damage to the hair cells
responsible for both hearing and balance.
 Underlying cause of fluid imbalance not known for sure.
Likely suspects – viral infection or autoimmune disorder
affecting production or absorption of endolymph (duh).
Normal Ear
Ear with Endolymphatic
Hydrops
Note bulging of membranous labyrinth
(www.tchain.com/otoneurology/disorders/menieres/men_eti.html)
Age and Sex Distribution:
MD is an Equal-Opportunity Disease
Moral: The disease strikes all ages and both sexes.
Incidence (number of new cases diagnosed per
year)
Estimates vary, but probably somewhere
between 100 and 200 new cases per year per
million (see citations below).
TJ Wilmot. Ménière's disorder. Clinical Otolaryngology 1979 4: 131-43.
J Stahle, C Stahle, K Arenberg. Incidence of Ménière's disease. Archives of Otolaryngology 1978 104: 99-102.
I Watanabe. Incidence of Ménière's disease, including some other epidemiological data. Ménière's Disease: A Comprehensive
Appraisal, ed WJ Oosterveld. 1983 J Wiley & Sons.
P Wladislavosky-Waserman, GW Facer, B Mokri, LT Kurland. Ménière's disease: a 30-year epidemiological and clinical study
in Rochester MN, 1951-1980. Laryngoscope 1984 94: 1098-1102.
D Celestino, G Ralli. Incidence of Ménière's disease in Italy. American Journal of Otology 1991 12: 135-8.
Prevalence (number of cases present at any
given time)
2,182 per million
P Wladislavosky-Waserman, GW Facer, B Mokri, LT Kurland. Ménière's disease: a 30-year epidemiological and clinical study
in Rochester MN, 1951-1980. Laryngoscope 1984 94: 1098-1102.
Treatment
Numerous: Everything from diet to medications
(aimed at treating nausea and vertigo) to surgery.
Considerable debate about the effectiveness of
various treatments.
A few surgical treatments deserve mention:
(1) Endolymphatic shunt
 Plastic tube installed to drain excessive fluid
and reduce pressure
 Quite a bit of controversy about
effectiveness – some have called it a
“placebo” surgery
(2) Vestibular Nerve Resection
 Vestibular branch of 8th N is cut, leaving
cochlear branch intact (therefore
preserving residual hearing)
 Vertigo abates, but balance problems
may persist
(3) Destruction of the Affected Ear
In some severe (usually unilateral) cases of MD
that are unresponsive to other treatment,
complete ablation of the labyrinth is
recommended: removal of the incus and stapes,
and removal of the sensory tissue in the
labyrinth. In some cases the 8th N is cut as well.
This surgery is extreme – good indication of how
debilitating MD can be in severe cases.
******************
To my knowledge, there have been no
randomized clinical trials of any of the surgical
treatments for MD.
Drug Therapy: Betahistine
There have been several well designed randomized
clinical trials testing the effectiveness of a synthetic
histamine call betahistine hydrochloride in treating
vertigo/nausea. Results have been encouraging.
Dark bars=No. of attacks/month
Light bars=Duration of attacks
TJ Wilmot, GE Menon. Betahistine in Ménière's disease. Journal
of Laryngology and Otology 1976 90: 83340
IJC Frew, GE Menon. Betahistine hydrochloride in Ménière's
disease. Postgraduate Medical Journal 1976 52: 501-3.
Fischer & van Elferen (1985)
A Fischer, L van Elfren. Betahistine in the treatment of
paroxysmal attacks of vertigo. A double blind trial (transl.). TGO
tijdschrift voor Therapie, Geneesmiddel en Onderzoek. 1985 10:
933-7.
Prognosis
 According to one source, vestibular
symptoms can be controlled (not prevented)
in about 70% of patients, meaning that
attacks of vertigo will be will be reduced in
severity/frequency.
 Tinnitus seldom disappears.
 If treatment is started while a patient's
hearing is still fluctuating, it is sometimes
improved by medical management. In some
patients, however, hearing loss will continue
to worsen.
e. Infections
 Bacterial or viral infections that invade
the inner ear can cause SN HL and
disruptions of vestibular function.
 Generic term for infections that invade
the inner ear: labyrinthitis. Meningitis
can sometimes spread to the inner ear
and result in labyrinthitis.
 Other infectious diseases: Mumps,
measles, meningitis, encephalitis,
chicken pox, influenza, and syphilis can
also invade the inner ear and cause SN
HL and/or vestibular symptoms.
f. 8th N Tumors (acoustic neuroma)
 Benign (nonmalignant) tumor that exerts pressure on 8th N
 Almost always slow growing
 Most common symptom: hearing loss (mild initially), often
accompanied by tinnitus
 Vestibular problems may also occur
 Cause is unknown
 Continued tumor growth can be life threatening
 Treatment: Surgical removal or radiation
 Early detection is really important: Small tumors can be
removed with less risk of destroying the 8th N (and
sometimes the 7th N as well).
 Early diagnosis is tough – early symptoms are undramatic
g. Congenital Causes
Congenital: Present at (or before) birth
This is to be distinguished from acquired or adventitious
hearing loss.
Congenital etiologies may be hereditary or nonhereditary.
(1) Non-Hereditary Causes
(a) Maternal rubella (German measles)
When an expectant mother is exposed to rubella, the
mother is not in any great danger, but the fetus is –
especially in the 1st trimester. Effects can include:
 Heart defects, brain damage, various visual
impairments
 SN HL, often profound
Less common now since the development of a rubella
vaccine
A rubella vaccine was not available when the last rubella
epidemic occurred in 1964. A large proportion of the current
population of congenitally deaf adults lost their hearing as a
result of this epidemic. These folks are now in their 50s.
The incidence of congenital deafness has been greatly
reduced in recent years since maternal rubella has come
under better control.
(b) Anoxia (asphyxia)
Insufficient oxygen during birth/delivery can cause all sorts
of problems for the newborn.
There’s hardly anything that’s not on the list of anoxia
consequences. SN HL is on the list.
(c) Many other etiologies that are less common
(2) Hereditary Causes
Genetic factors are thought to cause more than 50% of all
incidents of congenital hearing loss in children (NIDCD,
1989).
Two patterns:
(a) autosomal dominant
 One parent has a dominant gene for SN HL (and
typically has a hearing loss).
 There is at least a 50% probability that the child will
also have a hearing loss.
 Probability is higher if both parents have the dominant
gene.
(b) autosomal recessive
 Both parents (typically with normal hearing) carry a
recessive gene for SN HL.
 Each child will have a 1 in 4 chance of inheriting the
bum gene.
Approximately 80% of inherited hearing loss is autosomal
recessive. This makes early detection tough since, with
both parents hearing normally, the children are not
considered at risk.
(www.asha.org/hearing/disorders/causes.cfm)
Syndromes:
Inherited hearing loss can also be associated with a
complex of inter-related symptoms in the form of a
syndrome. A few examples include:
Syndromes:
Inherited hearing loss can also be associated with a
collection of inter-related symptoms in the form of a
syndrome. A few examples include:
 Waardenburg Syndrome
 Treacher-Collins Syndrome
 Klippel-Feil Syndrome
Treacher-Collins Syndrome
Waardenburg Syndrome
Klippel-Feil Syndrome