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 two
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: 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 later.
The Audiogram
Most common way to measure hearing sensitivity is
to measure pure-tone (sinusoid) thresholds.
Threshold: Intensity required to barely detect a sound.
125
250
Audiogram of a Listener with
Thresholds in the Normal Range
500
1000
2000
4000
8000
-10
0
Red: right ear
10
Intensity (dB HL)
20
(red, round, right)
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
10
Red: right ear
Intensity (dB HL)
20
30
40
50
60
70
80
90
100
110
Frequency (Hz)
Moderate-to-profound bilateral loss
Severe Loss Left, Ear Moderate Loss Right Ear
125
250
500
1000
2000
4000
8000
-10
0
10
20
Intensity (dB HL)
30
40
50
60
70
80
90
100
110
Frequency (Hz)
Pure Tone Average (PTA)
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 an important 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 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,
sensori-neural, 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.
 Otitis media means inflammation of the middle ear.
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, 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
treated, then 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?
A Few Additional Terms
Otitis Media with Effusion (OME): Otitis
media characterized by the accumulation
of fluid. This term refers to any kind of fluid
-- sterile, infected, it doesn't matter.
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 controversial, but there is
some research suggesting that frequent bouts of
OM *may* result in delays in acquiring speech
and language.
Surprising to some since hearing loss is usually
relatively mild and fluctuating, with significant
periods of normal hearing in between bouts of
OM for most kids.
But, there is also clear evidence from other
sources indicating that kids need higher sound
levels to perceive speech with the same accuracy
as adults. [Elliott et al. (1979). Children’s understanding of monosyllabic nouns in quiet and in noise. J.
Acoust. Soc. Am. 66, 12-21.]
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 oval window.
 Later hardens (i.e., becomes sclerotic)
 In 90% of cases: No symptoms
In unlucky 10%: Growth reduces mobility
of stapes, causing a conductive HL.
Progressive. Beginning in childhood. For
that unlucky 10%, HL typically begins in
late teens, early 20s.
 Maximum HL seldom worse than ~50-60
dB.
 Treatment: Stapedectomy (removal of
stapes and replacement with an artificial
stapes)
Stapedectomy
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. This is extremely not good.
 HL is usually mild and not really the major concern.
From http://www.ohsu.edu/ent/ear/chol.html (read this on your own)
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).
Sensorineural 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
hair cell damage. The various etiologies
of SN HL consist mainly of a catalog of
different causes of HC damage.
a.Presbycusis
• Hearing loss associated with aging
• Most common cause of SN HL – and
most common cause of HL overall
• Presbycusis begins in adolescence.
Sad but true.
This figure shows data for men (top) and women
(bottom) at different ages. Not good.
Men
Note that high frequencies are
more strongly affected than lows.
(We’ll see this again when we talk
about noise-induced HL.) Any
guesses about why high-freqs are
more vulnerable?
(Answer: The traveling wave starts at the base [high freq] and
heads to the apex [low freq]. So, low freq sound stimulates
HCs at the low freq end and the high freq end, while high freq
sound stimulates HCs at the high freq end only. And if you look
back to the Rose et al. FRC data from the physiology lecture,
the spread of excitation is especially large on the low freq side.
So, for low freq sound HCs at both ends of the BM are
vulnerable, but for high freq sound only HCs at the basal end
are affected, preserving low freq HCs. Moral: If you’re a hair
cell, you’re better off at the apex.)
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
sound. 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 is 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., 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? (Answer: They’re used when death is the likely alternative.)
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.
For your reference. The list below is 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 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) Roaring or ringing tinnitus
(4) A sensation of "fullness" or pressure in the
ear
(1) Rotary Vertigo
This is often the most disruptive and debilitating symptom of Meniere’s. Similar to the mild
vertigo you get from too many beers, or that
you may remember as a kid from spinning
around on a playground. 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” (due to low-freq
loss) and distorted

Loudness intolerance is common (abnormal sensitivity to intense
 Loudness intolerance is common (abnormal
sensitivity to intense sounds)
(3) Tinnitus
 Ringing, roaring, or buzzing sensation
 Fluctuates 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 is unrelated to M.E. function)
Cause of Meniere’s
 The proximate (i.e., immediate) cause of MD
is thought by some to be excessive and
fluctuating pressure in the endolymphatic
fluid that courses through the membranous
labyrinth of the cochlea and vestibular
systems. This causes the membranous
labyrinth to balloon or dilate.
 Condition is known as endolymphatic
hydrops.
 Result is progressive damage to the hair
cells responsible for both hearing and
balance.
 Underlying cause of the fluid imbalance (if
that actually is what’s going on) is not
known. Likely suspects – viral infection or
autoimmune disorder affecting production
or absorption of endolymph (duh).
Normal Ear
Ear w/ 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
•
There is 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 (pray for no mix-ups)
In some severe (always or nearly always
unilateral) cases of MD that are unresponsive to
other treatment, complete ablation of the
labyrinth is recommended.
(Surgeon goes in through the EAM, removes the incus and stapes,
pokes a hole in the promontory, and removes the sensory tissue in
the labyrinth. In some cases the 8th N is cut as well.)
This surgery is pretty extreme – good indication
of how debilitating MD can be.
To my knowledge, there have been no
randomized clinical trials of any surgical
treatment for MD.
For your reference – 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 prevented or 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 (i.e., 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
f. 8th N Tumors (acoustic neuroma)
•
•
•
•
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).
But, early detection is difficult – early-stage
symptoms are not dramatic.
Acoustic neuromas sometimes run in
families (case in point to follow).
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 non-hereditary.
(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 mid-40s.
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 (autosome = not a sex chromosome)
 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:
 Waardenburg Syndrome
 Treacher-Collins Syndrome
 Klippel-Feil Syndrome
Waardenburg
Syndrome
Treacher-Collins
Syndrome