Hearing%20Disorders - PowerPoint PPT Presentation

View by Category
About This Presentation
Title:

Hearing%20Disorders

Description:

If OM lasts more than 2-3 months, the condition is known as chronic otitis media. ... Hearing loss is often more severe than serous OM. ... – PowerPoint PPT presentation

Number of Views:213
Avg rating:3.0/5.0
Slides: 60
Provided by: SPPA
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Hearing%20Disorders


1
  • 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
  • The listener with a HS disorder may be unable to
    detect the sound.
  • The sound will not be as loud to that listener as
    it would be to a listener with normal hearing.

2
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.
3
The Audiogram Most common way to measure hearing
sensitivity is to measure pure-tone (sinusoid)
thresholds. Threshold Sound level required to
barely detect a sound.
Red right ear
Audiogram for a listener w/ thresholds in the
normal range.
4
Mild high-frequency loss
Red right ear
5
Moderate-to-severe bilateral loss
Severe loss in left ear, moderate loss in right
ear.
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
93 dB Pure-tone Average, Right Ear 50 dB
6
Terminology Normal Hearing PTAs lt 25 dB Hearing
Impairment PTAs 25-92 dB Deaf PTAs gt 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.
7
  • 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 Dont shout, I can hear
    you just fine. I just cant understand what
    youre saying. Disacusia is a good term that
    isnt in very common use.
  • Acuity deficits sometimes due to disorders of the
    central auditory system.
  • Disorders of sensitivity and acuity are not
    mutually exclusive.

8
  • 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.

9
  • 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
  • Menieres Disease
  • In this review, we will proceed by functional
    subsystem (conductive, sensorineural, central),
    and by etiology within each subsystem.

10
  • Conductive Hearing Disorders
  • 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.

11
  • 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.
  • Well talk about it later.

12
  • 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

13
  • 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.

14
  • 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) at this stage, the fluid is sterile
    (not infected).
  • Suppurative or Purulent Otitis Media As the
    disease progresses, the fluid can become infected
    and thickens into (eck) pus.

15
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.
16
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 its
treated, then it returns This gets old after a
while but is pretty common.
17
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?
18
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.
19
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. (But most SLPs do not know the
literature.) 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.
20
  • 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.

21
  • 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)

22
prosthetic stapes
incus
23
  • 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.

24
From http//www.ohsu.edu/ent/ear/chol.html Chol
esteatomas 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).
25
  • 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.
  • Presbycusis
  • Hearing loss associated with aging
  • Most common cause of SN HL and most common
    cause of HL overall.

26
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
27
  • Moral We all have a long, slow slide ahead of
    us. Dont 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, theyre gone for good.
  • One last point Presbycusis listed here under the
    SN category since it is clear that this is the
    dominant component. However
  • 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 ).

28
  1. There may also be a conductive component due to
    age-related changes in the mobility of tissues in
    the middle ear.
  2. 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 patients primary complaint.

29
  • 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 exposuresBad
    news
  • Low levels x brief exposuresNot so bad
    news

30
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
  • Dip or notch at 3-6 kHz
  • Typical progression shows the notch broadening
    (especially on the high frequency side) and
    deepening
  • High frequencies more affected than lows

31
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 Its a reasonable alternative
to mortality.)
32
ANTIBIOTICS WITH GOOD EVIDENCE FOR OTOTOXICITY
Drug Vestibulotoxicity Hearing Toxicity Toxic Level
Erythromycin   yes High IV doses only
Gentamicin 8.6 minor Usually 2 weeks
Streptomycin very toxic minor  
dihydrostreptomicin minor toxic very toxic  
Tobramycin Yes minor in 6 Less toxic than Gentamicin
Netilmicin   2.4  
Amikacin not toxic 13.9  
Neomycin minor very toxic In topical ear drops
Kanamycin minor very toxic  
Etiomycin moderate    
Vancomycin nontoxic none to moderate synergistic with gentamicin
Metronidizole toxic (rarely) unknown  
Capreomycin   yes  
Table from http//www.tchain.com/otoneurology/dis
orders/bilat/ototoxins.html See other classes of
ototoxic drugs on the same web site.
33
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.  
34
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).
35
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)
36
  • d. Menieres 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
  • Periodic episodes of rotary vertigo (the
    sensation of spinning) or dizziness (the
    Menieres attack)
  • Fluctuating, progressive, low-frequency hearing
    loss
  • Tinnitus
  • A sensation of "fullness" or pressure in the ear

37
  • (1) Rotary Vertigo
  • This is easily the most disruptive and
    debilitating symptom of Menieres. 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

38
  • (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 OR WORSE

39
  • (4) Sensation of fullness
  • Like the weird sensation you get on an airplane
    or elevator before your ears pop except it
    cant be cleared. (Cause of fullness sensation
    unrelated to M.E. function)
  • Cause of Menieres
  • 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).

40
Normal Ear Ear with
Endolymphatic

Hydrops
Note bulging of membranous labyrinth
(www.tchain.com/otoneurology/disorders/menie
res/men_eti.html)
41
Age and Sex Distribution MD is an
Equal-Opportunity Disease
Moral The disease strikes all ages and both
sexes.
42
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.
43
  • 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

44
  • (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

45
(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.
46
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 barsNo. of attacks/month Light
barsDuration 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. 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.
Fischer van Elferen (1985)
47
  • Prognosis
  • According to one source, vestibular symptoms can
    be controlled (not prevented) in about 70 of
    patients, meaning that attacks of vertigo 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.

48
  • 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.

49
  • 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.

50
  • 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

51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
  • 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

55
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. Theres hardly
anything thats not on the list of anoxia
consequences. SN HL is on the list. (c) Many
other etiologies that are less common
56
  • (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.

57
  • (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)

58
  • 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

59
Treacher-Collins Syndrome
Waardenburg Syndrome
Klippel-Feil Syndrome
About PowerShow.com