Download Causation of Permanent Unilateral and Mild Bilateral Hearing Loss

Causation of Permanent Unilateral and
Mild Bilateral Hearing Loss in Children
Trends in Amplification
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Anne Marie Tharpe, PhD, and Douglas P. Sladen, PhD
Children with permanent unilateral or mild hilateral hearing loss have heen a focus of concern hy audiologists, educators, and physicians for at least 2 decades. These
c hildren are know n to he at risk for psychoeducational difficulties. However, despite this concern, little has heen
learned ahout the causative factors of these hearing losses
and how those factors might he contrihuting to child
development. Ihis review of known causes of permanent
unilateral and mild hilateral hearing loss in children is
meant to draw attention to the importance ofthe search for
etiologic factors. iTiat is, the identification of the hearing
loss should not signal the end of the diagnostic process
hut, rather, the heginning of a search for causation. With
the comhined efforts of audiologists, otolar\ngologists,
pediatricians, geneticists, and other medical professionals,
we may enhance our understanding of the primary causes
of unilateral and mild hilateral hearing loss and, jx-rhaps,
create links hetween causative factors and ¡wychosocial
and psychoeducational outcomes.
nilateral (UHL) and mild bilateral (MBHL)
permanent hearing loss have long heen implicated for putting children at risk for academic
difficulty,'"^ For purposes of this article, the term
"mild" hilateral hearing loss may include v\hat are
often termed "minimal" degrees of loss. Bess et al**
defined minimal degrees of hearing loss as (1) unilateral sensorineural hearing loss, defined as av crage airconduction thresholds (O.S, 1.0, 2.0 kHz) 20 dB HL
or more in the impaired ear and an average air-hone
gap no greater than 10 dB at LO, 2.0, and 4.0 kHz
and average air-conduction thresholds in the normal
hearing ear of IS dB I IL or less; (2) hilateral sensorineural hearing loss, defined as average pure-tone
thresholds hetween 20 and 40 dB HL hilaterally with
average air-hone gaps no greater than 10 dB at frequencies 1.0, 2.0, and 4.0 kHz; and (3) highfrequency sensorineural hearing loss defined as airconduction thresholds greater than 25 dB HL at 2 or
more frequencies ahcne 2 kHz (ie, 3.0, 4.0, 6.0, or 8.0
kll/) in I or hoth ears with air-hone gaps at .T.O and
4.0 kHz no greater than 10 dB. On average, children
with these losses have high academic failure rates as
compared v\ith those of their normal hearing
peers.'^'' The psychoeducational and psychosocial
implications of UHI and MBHL are rcviev\ed earlier
in this issue hy Tharpe.^ Despite considerahle interc st
in the effects of these losses on child development, little attention has heen paid to the underlying etiologies. In fact, contemporary reports of causes of LHL
are no more illuminating than reports from the 1960s
through the 1980s—hefore newhorn hearing screening. That is, earlv reports indicated that hetween 359r
and 65% of children with UHL had unknown etiologies.'•''•"' More tecentiv, in reports from the 1990s,
unknown etiology was again reported to ¡lecount for
approximately 3S% to 60% of cases of Ulli ."•'- Ihis
is indeed surprising given the recent completion of
the sequencing ofthe human genome and other medical advances that have improved our ahility to identify genetic, metaholic, and viral causes of hearing
loss in infancy, lhe most commonly reported known
etiologies of UHL include viral complications
(approximately 25%),'•'"'•'" meningitis (approximatelv
15%),''"'head trauma (approximately S^ to 12%),"'
prenatal or perinatal disorders (12%),^ and genetic
disorders.
U
From tho \andcrbill Hill Wilkerson Center,
University Medical Center. Nashxillc. Tennessee.
Vanderbilt
Address correspondence to: Anne Marie Tharpe, PhD,
Vanderbilt I5ill Wilkerson Center, 121 S 21st A\e Soulb. #8.^10,
Meiiical Center Last, Soutb Tower, Nashville, I N .^72^2-8242;
e-mail: [email protected].
Keywords: unilateral; mild hilateral; children; hearing
loss; etiology
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Trends in Amplifitution I Vol, 12. No. 1, Marc h 2008
Even less is known about the etiology of permanent MBHL primarily because moderate to profound
degrees of hearing loss are targeted in our newborn
screening programs'^ thus, lesser degrees of loss are
often not identified until school age. The late age of
identification of iMBHL'^ may contribute to our lack
of knowledge about causative factors. That is. in some
cases, a delay in identification of hearing loss may
limit our ability to interpret etiologic evaluations reliabl\ (eg, cytomegalovirus) or may affect parental
memory of possible illnesses or injuries that could
account for tbe loss. For these reasons, much of \\ hat
we know about etiologs of hearing loss in children is
related to moderate or greater degrees of loss.
Ho\\e\er, for everx child with bilateral profound bearing loss, 1 or 2 are born witb lesser degrees of bilateral
or UllL. Ibe US National Health and Nutrition
Examination Suney III revealed that l.S'i of schoolaged children bad bilateral low-frequency bearing loss,
and greater than ?>'r bad bilateral high-frequency loss
of slight to mild degree''*; therefore, tbe large numbers
of children witb MBHL warrant closer examination of
etiologic factors, fable I provides a listing of known
causes of Ul IL and MBHL and their prevalence.
Common Etiologies
Although information regarding tbe etiologies of
permanent UHL and MBHL is limited, it is reasonable to sus]iect tbat in addition to tbe few know n etiologies of MBHL and UHL some of tbe same factors
that result in more severe degrees of bearing loss
can also cause lesser degrees of loss. Tbe following
re\ iev\ includes tbe currently documented causes of
permanent UHL and MBHL in children.
Prematurity
Prematurity (ie, preterm births less tban 37
weeks) represents a constellation of possible etiologies, and frequently, we are unable to distinguisb tbe
various contributing factors to bearing loss in these
infants. Morbidity associated with prematurity
includes birtb asphyxia, intracranial bemorrbage,
ot()l()\ic medications, and bronchopulmonary dysplasia, among others.
Several limitations prevent tbe determination of
tbe prevalence of MBHL or UHL in premature
babies. As discussed hy Ross et al'^ earlier in tbis
issue, newborn screening programs are designed to
identify bearing losses tbat are of moderate degree
or greater. As such, tbe equipment and protocols
used for newborn screening (ie, tor measuring otoacoustic emissions and auditor) brainstem responses)
are designed to identify losses greater tban ajiproximately 40 dB HL; tberefore, if data are obtained from
traditional newborn screening protocols, reports on
tbe prevalence of bearing loss in premature babies
will typically not reflect accurate estimations of
MBHL and UHL.
One of tbe few studies reporting on bearing loss hy
degree in bigb-risk populations avoided these limitations by conducting bebavioral testing w ben tbe infants
were 8 to 12 montbs of age.'*"* Tbe iNational Institutes
of Health Identification of Neonatal Hearing
Impairment project examined \\oil-baby nursery graduates witb risk factors and neonatal intensive care unit
infants (including premature infants) and identified
UHL in 3.4'^f and bilateral bearing loss in l.l'r of
babies vAth bigb risk factors. Of tbose with bilateral
loss, approximately ()^'( were of mild degree; bowex er.
tbose numbers may have included infants witb conductive as well as permanent loss. Of tbose infants predicted to ba\e permanent bilateral bearing loss, tbere
were appro.ximatek equal numbers of ears having mild,
moderate, severe, and profound degrees of loss."*
Herrgârd et al' prospectively followed S8 premature (<32 weeks) infants until S years of age.
Tbey found approximately Vr of these infants bad
permanent MBHL or UHL.
Genetic
Connexin. More tban ISO genes for syndromic
and nonsyndromic deafness have been "mapped" to
cbromosomal regions, and of tbese, at least 80 b;ne
been identified. However, by far, connexin mutations are tbe most common cau.se of genetic bearing
loss in the United States. Mutations involving tbe
GJB2 gene tbat encodes tbe gap junction protein
connexin 26 are tbe commonest form of deafness in
many populations, accounting for ^O'^i- to -^0% of
genetic cases.''^•^'' Members of tbe connexin gene familv are tbougbt to participate in tbe recycling of potassium back into tbe cocblear endolympb, a critical step
in tbe physiology of sound perception."
Most connexin deafness reported thus far hiis
been profound in degree, but tbe murine model
(mice used as a disease model) provides a clear
precedent for reported nonpenetrance at birtb,^'
stiggesting tbe opportunity for less severe degrees of
bearing loss. Furtbermore, Wake et al"" found a
Causation of Hearing Loss in Children / Tfiarpc, Shuicii
Table 1.
Caus(
Cienclic
Connexin
Mitochondrial
Enlarged vestibular
aqueduct
Sudden
Auditory neuropathy-
Noise induced
\ iral/bacterial
Mumps
Otitis media
Congenital C.M\
Meningitis
Prematurity
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Known Causes of UHL or MBHL and Prevalence Estimates
Krequeiuy of Occurrence
Accounts for 3()'>i to 4()'> of all genetic hearing loss; 1% to 16^r of
these cases are estimated to result in MRHL.
Accounts for less than \9c of prelingual deafness and 5'f of postlingual,
nonsyndromic hearing loss; 21% of these cases are MHIIL.
Accounts for S% to y^r of all cases of unknown etiology; M<'¡ ol children with tVA have MBHL, an additional unknown number will have
LI IL.
Three percent to Ví of all cases occur in children; as many as 98%
have UHL.
Accounts for less than }% of all pédiatrie hearing loss; appro.vimatelx
ii'r of cases have borderline normal, MBHL. and there ha\e been
(c\\ reports of UHL,
Approximately lO'i of all children in the United States have
noise-induced hearing loss; approximately 2i)'i of these arc \IBHL.
Accounts for approximately 2% of childhood hearing loss; HO'r to 4S';
of these cases are UHL.
Five percent to 2()'r of all cases of otitis media will result in SNHL; the
majority of these cases are bilateral, high-frequency SNHL, with some
reports of LHL.
Thirteen percent to 24'r of all children with asymptomatic CM\ and
up MYi of children with symptomatic CM\' will haxe SNHL; 17'; of
the asymptomatic and 12% ofthe symptomatic cases are MBHL; S2'r
ofthe asymptomatic cases and ^^'r ofthe symptomatic cases are
LHL
Ten percent of all children with bacterial meningitis are left with
SNHL; 4'r to Mn of these are LHL; 14'ï arc- MBHL.
Five percent of premature infants have MBHL or UHL.
Reference
Liu et al"-"
Wake et a l "
Marazita et a l "
Jacobs et aP"
C allison and Horn""
.^rjmand and Webber"
Wynn et aP"
I'oiTsl et al*'
Madden et aP"
Mskar et aP'
Unala et aP'
Mutlu vl aT'
Arnold et al'"'
Vartiainen and Karjalainen"'
Ogawa et al"^
Fowler et al"'
Dahle et al'"
Fortnum and l)a\is
Herrgard et al''
Note: MlîHL = mild bilateral hearing loss; SNHL = sensorineurai hearing loss; UHl = unilateral hearing loss.
large proportion (16'f) of their cohort of Asian children w ith slight to mild bilateral sensorineurai hearing loss were homozygous for the V37I change in the
GJB2 gene. They concluded that this change is a
mutation associated with hearing loss and is a common cause of slight to mild sensorineurai hearing
loss in Asian children. Similarly, Kenna et al~'
reported on a cohort of children «ith biallelic (ie,
both alternative forms of the gene) Cx26 mutations
(M.Í4T or V37I) and found that they had a slightly
higher incidence of mild degrees of hearing loss
(including UHL) than previous studies indicated.
Others haw reported hearing loss resulting from
GJB2 mutations in the mild hearing loss range,
including high-frequency hearing loss (4 to 8 kH/).-^
Mitochondrial 12S ribosomal (rRNA). In the
United States. 10*^* ofthose with hearing loss resulting from pharmacologie ototoxicity have mutations
involving the mitochondrial 12S ribosomal (rRNA)
gene, including the A15S5G substitution, which is
associated with extreme sensitivity to aminoglycoside
ototoxicity.^' This mutation is very common in China,
accounting for up to a third of all patients with
aminoglycoside ototoxicity.-'' Individuals with these
mutations have a higher susceptibility to aminoglycosides at low t r dosages than the av erage population.
Ototoxicity is the ability of a chemical or drug to
cause damage to the inner ear or, on rare occasions,
the central auditory pathway. The mechanism for
how aminoglycosides get into hair cells remains
unknown, but it is possible to have hair cell loss without associated hearing loss. The hearing loss assoc iated with ototoxicity is typically high frequency and
bilateral.
Enlarged Vestibular Aqueduct Syndrome
A well-known cause of UHL and MBHL in children is
enlarged vestibular aqueduct (EVA) syndrome. The
vestibular aqueduct is the bony canal extending from
20
I ri'nds in Amplification/\o\.
12. No. 1, March 2008
the vestibule to the endolymphatic sac in the temporal
bone and contains the membranous endolymphatic
duct. Along with the endolymphatic sac, the \cstihular
aqueduct is thought to help regulate the concentration
of ions in the cochlear fluids. It is speculated that an
E\A will result in the expansion of the endolymphatic
sac and duct. Such an enlargement may result in a
chemical imbalance, causing hearing loss.
Ixpically. the diameter of the \cstibular aqueduct at its midpoint ranges between 0.5 and 1.4
mm. .\ commonly accepted definition of KV A syndrome is a diameter greater than 1.5 mm at the midpoint. The diagnosis of l:\ A is achieved with the use
of computed tomography imaging of the temporal
bones and magnetic resonance imaging.
This particular cause of hearing loss has been
reported to account for 5% to 7^r of hearing loss that
has previously been classified as having unknown c tiology" •"** and is the most common form of inner oar
malformation associated with scnsorineuial hearino
loss.^*^ .\ recent study found EVA in M'/f of children
with sensorineural hearing loss in their cohort^".
llowi'Ncr. these authors defined a large vestibular
aqueduct as one in which both of its widths were
iib()\c' the •^»Sth percentile (>1.9 mm at the operciilum
and/or >0.9 mm at the midpoint) of the control group,
a definition that is not yet widely accepted and may
overestimate the incidence of FA A. IA A malformations have been linked to Pendred Syndrome, branchiootorenal syndrome, CHARGI Association, and
Waardenburg Syndrome.^'
Hearing loss that occurs with l:\A has a sudden
onset or gradual progression. The disorder is twice as
likely to be bilateral than unilateral and will often
result in some degree of hearing loss ranging Irom
minimal to profound." Children who have been diagnosed with E\A are strongly encouraged to protect
their remaining hearing by taking precautions against
damaging the delicate structures of the \estibular
aqueduct. Such precautions include a\<)iding contact
sports and extreme changes in barometric pressure.
Sudden Idiopathic
Sudden hearing loss has been characterized as hearing thresholds of 30 dB or greater at 2 or 3 consecutive frequencies.""^"* Anecdotally. patients with
sudden hearing loss report a decrease in hearing
oN'ernight or a rapid progression in hearing loss over
sexeral days. Furthermore, the hearing loss typically
occurs in only I ear. Only 2% of patients with sudden hearing loss are affected bilaterally. The exact
cause of sudden hearing loss is only found in approximately lO'^ir of patients,^"" with the rest being categorized as sudden idiopathic. For those w ho receive
a definiti\e diagnosis, viral and vascular factors,
membrane puncture, and autoimmune disease are
most often implicated. *•*
The prevalence of sudden hearing loss in children
is lower than in adults. Specifically, only S'^ of all
cases of sudden hearing loss occurs in patients under
21 years of age.^*" and only 3.5% occurs in patients
under 14 years of age.^ Ireatment options for sudden
hearing loss are limited because the exact etiology is
often unknowtT; hov\t\cr. common treatments include
the use of vasodilators, steroids, diuretics, and anticoagulants. Spontaneous recoser) is common among
patients with sudden hearing loss. In fact, the rate of
spontaneous recovery has been reported to occur in
as many as 65'r of patients with sudden loss.^** Roman
et al" reported that partial hearing reco\ery occurred
in approximately 29'r of their small sample of children
v\ith sudden hearing loss. Of those, half had their
hearing loss imprcne to a lc\el of a mild degree of loss.
In addition, an absence of recoNcry was significantly
correlated with 3 factors: severe initial hearing loss,
association of vertigo, and "downward" sloping audiometric curve.
Auditory Neuropathy/Dyssynchrony
Auditory neuropathy/dyssNnchrony (A.\/AD) is an
auditor) disorder in which patients typical!) demonstrate hearing loss for pure tones, impaired speech
perception that is out of proportion to pure tone loss,
ahsent or abnormal auditory brainstem responses,
and normal outer hair cell Function as measured by
otoacoustic emissions and cochlear microphonics.
The audiometric configurations associated with
AN/AD \ar) considerahly, from normal pure tone
sensitixit) to profound loss, and UllL and MIÎIIL
have been reported.^'*•"' In such cases, pure tone
thresholds are wry poor predictors of the degree of difficult) or handicap that a child may be experiencing.
However, on rare occasions, speech perception ability may be only minimal!) affected, at least in optimum acoustic conditions.^'
It appears that there ma) be many causative factors associated with AiN/AI), including mutations of
the otoferlin gene (OTOF),"*"^* hxporbilirubinemia,'**''^
aspli)\ia.^^"'^ and prematurit)."*^ Several possible sites
of lesion have been posited for AN/AD, including
abnormalit) of the peripheral auditory system localized
Causation of Hearing loss in Children / Tharpe, Shulcii
to the inner hair cells, the eighth nerve, or the synapse
of the inner hair cells and eighth nerve."*^
Noise Induced
Hearing loss caused b\ noise exposure is not limited to
the adult population. In fact, 5.2 million, 6 to 19 year
olds (or approximately lO'^^r of children sur\eycd in this
age range) have hearing loss related to noise exposure'*';
however, the authors do not indicate if these losses are
temporary or permanent in nature. In addition, evidence of high-frequency hearing loss in nearly one third
of a cohort of college students has been reported.**
Noise-induced hearing loss occurs as a result of
chronic or acute noise exposure.
Cienetic factors have also been implicated in tbe
susceptibility one bas to noise.^^"^ Cbronic exposure
bas been cbaracterized by prolonged exposure to
sounds that exceed 85 dP SPL for an 8-bour period,
and acute noise exposure occurs as tbe result of
events such as an explosion or gunshot close to tbe
ear. Acoustic trauma results in immediate bearing
loss, wbereas bearing loss from cbronic noise exposure occurs gradually over time.
Hearing loss of tbis nature is initially restricted
to tbe bigb-frequency regions (3 to 6 kHz) and e\entually, witb additional exposure, extends into tbe
lower frequencies. Hearing loss secondary to noise
exposure occurs as a result of damage to tbe bair
cells of tbe cocblea. Specifically, cbanges in sound
pressure create a sbearing force on tbe stereocilia of
tbe bair cells lining tbe basilar membrane of tbe
cocblea, wbicb leads to our perception of sound.
Hvcc'ssivc force caused by bigb levels of noise can
lead to cellular metabolic (nerload, cell damage, and
cell deatb resulting in bearing loss."*'
Possible environmental sources that may contribute to noise-induced bearing loss in children
include fireworks, lawn mowers, and IONS.'"'" In
fact, several popular toys sucb as bike borns, toy cell
pbones, and arcade games bavc been sbown to produce bigb enougb intensity levels to barm bearing." '" In addition to toys, cbildren may be at risk
for noise-induced bearing loss from prolonged use of
personal audio players and attending musical concerts.''" Portnuff and Fligor^' recently examined tbe
safety of listening to tbe popular iPod de\ice. By
using current Occupational Safety and Healtb standards,^^ they concluded tbat users can listen for 4.S
consecutive bours with tbe volume set at 70'^f witbout risk of bearing loss if using tbe stock ear pbones
tbat are supplied witb tbe device. Tbe allowable
11
number of safe listening hours was shown to
decrease with increased volume and witb dillerent
forms of beadpbones (ie, ear buds vs supra aural
beadpbones). Tbe authors encourage tbe data to be
interpreted witb caution because not everyone bas
tbe same risk of bearing loss from prolonged noise
exposure and tbere is no wav to predict tbose v\bo
bave more or less sensitive ears.
Viral/Bacterial
Mumps. Tbe mumps virus was a common cause of
acquired UHL before tbe introduction of tbe mumps
vaccine in 1967. Most developed countries bave experienced a yO'f to 95% decrease in tbe incidence of
mumps as a result of tbe availability of immunizations'^. However, reports of recent outbreaks of mumps
bave appeared in tbe United Slates, tbe United
Kingdom, and oiber developed countries.""^""'
Histopatbologic examination of tbe temporal
bones from individuals vsbo suffered bearing loss
after infection witb mumps indicates a severe atropby of tbe organ of corti and stria vascularis.
Endolympbatic bydrops bave also been noted, along
witb damage to tbe endolympbatic duct and fibrous
tissue in tbe endolympbatic sac."'
Otitis media. ,\ rarely reported but viable cause of
acquired sensory UHL or MBHL is middle ear disease
witb effusion. Tbe mecbanism causing tbis drop in
bone-conduction tbresbold is unknown. However,
some bave speculated tbat bacteria travels Irom tbe
middle-ear space tbrougb tbe round windovx. causing
damage to tbe basal end of tbe cocblea.'**'*" It bas also
been proposed tbat tbe accumulation of fluid in tbe
middle space reduces oxvgen to tbe cocblea via tbe
round window affecting cocblear function.*''"'
An early bistory of ear disease in young cbildren.
especially w ben combined witb a bistory of multiple
sets of myringotoniy tube insertions, appears to be a
prerequisite to bearing loss in tbe bigb frequencies.''^"^ Mutlu et al*' found evidence of temporary
and permanent sensory bearing loss at I or 2 bigb
frequencies in ^)'f of a cobort of cbildren v\ itb otitis
media witb effusion. Tbe bearing loss was most frequently observed at 2 kHz, which is consistent witb
damage to tbe region of tbe cocblear basal turn.
Congenital cytomegalovirus. Congenital cytomegalovirus (Ci\I\ ) is tbe leading cause of nongenetic
sensory bearing loss and tbe leading cause ol unilateral prelinguistic bearing loss in cbildren.** C .M\ infc ctions var\ in frequency according to maternal age,
race, and socioeconomic status. Congenital infection
22
I r e m h in . \ m p l i ß c a ü o i i / \ o [ .
1 2 . N o . I. M a r c h 20()K
occurs in 0.2'^^ to 2.^"^/ of all live birtbs," witb an average
incidence of 1%. Tbis translates to approximately
10000 to 80000 infants born in tbe United States
eacb year witb congenital CM\ infection,****' making
CMV tbe most common congenital viral infection.^"
Initial C"M\' infection, wbicb may have few
symptoms, is always followed by a prolonged, inapparent infection during wbicb tbe virus resides in
cells witbout causing detectable damage or illness.'''
Sev ere impairment of tbe body s immune system by
medication or disease increases tbe likelibood tbat
tbe virus v\ill be reactivated from tbe latent or dormant state. Infectious CM\ can be sbed in tbe bodily fluids of any previously infected person and tbus
may be found in urine, saliva, blood, tears, semen,
and breast milk. Tbe sbedding of tbe virus may take
place intermittently, without any detectable signs
and witbout causing svinptoms. Becurrent disease
rarely occurs unless tbe immune system is suppressed as a result of tberapeutic drugs or disease.
Tberefore, for tbe vast majority of people, C \ l \ '
infection is not a serious problem. However, CMV
infection can be barmful to certain bigb-risk groups,
including tbe unborn babv during pregnancy.
Tbe bearing loss associated with CM\' can range
in degree, can be unilateral or bilateral, and can
have onset montbs or years after birth. ' " ' Only
approximately 14% of tbe infections are identified at
birtb, witb tbe remaining H(->'( being asymptomatic.-' In cases not recognized at birtb, it can be
dillicult to impossible to diagnose because of tbe
bigb incidence of postnatal infection. Nance** bas
speculated tbat tbe neurologic deficits associated
witb C M \ ' may be to blame for tbe poor academic
performance of cbildren v\itb UHL secondary to
infection, ratber tban tbe bearing loss per se.
Meningitis. Hearing loss is tbe most common complication of bacterial meningitis among cbildren. Tbe
incidence of bearing loss witb streptococcus pneumoniae is greater tban neisseria meningitidis (35.9% and
23.9%. respectively).'' UHL occurs in 4% to 30%"''''
and MBHL in approximatelv 14% of tbose witb bacterial meningitis.'* Altbougb most cases of postmeningitic bearing loss are permanent, tbere are reported
cases of spontaneous recoven.^' In fact, one study
reported approximately 10% of subjects bad a rapid
recoven of bearing. ' lhe bearing loss is caused bv
cocblear damai;e earlv in tbe illness, witb at least one
report indicating tbat tbe bearing loss occurred vsithin
6 bours of tbe diagnosis.'^ lbe cocblear aqueduct,
wbicb links tbe seala tympani to tbe subaraebnoid
space, is tbe likely conduit lor transmission of bacteria
to tbe eocblea. Mtbougb viral meningitis is more common tban bacterial, bacterial is more often associated
witb bearing loss. •* Bacterial meningitis is also a more
serious infection and can be life tbreatening.
Unilateral Atresia or Microtia
Congenital aural atresia (C V\) or microtia is a birtb
defect occurring in approximately 1 per 10000 live
birtbs as a syndromic or nonsyndromic disorder."**
C'A \ pbenotypes range from mild symptoms (narrowing of tbe external auditory canal and bypoplasia
of tbe tympanic membrane and middle ear cavity) to
severe symptoms (including tbe entire absence of tbe
middle ear in combination witb anotia, bony atresia
of tbe external auditory canal, and hypoplasia of
inner ear structures)^** and is frequently associated
witb cbromosomal abnormalities, especially deletions on tbe long arm of cbromosome IS (I8q).*"'
Unilateral CAA occurs in approximately 70% of
cases and occurs sligbtly more often in boys tban in
girls,"" Surgical remediation of unilateral C AA for
purposes of improving tbe conductive bearing loss is
often not recommended at all or, in some cases, is
not recommended until adolescence or adulthood.
Such surgery is noted to be one of tbe most difficult
otologic surgeries and, on average, results in small
improvements in bearing sensitivitv.'*'^^
Future Needs
Despite tbe widespread implementation of newborn
bearing screening programs in tbe United States,
systematic etiologic evaluations, especially genetic
evaluation and counseling, bave not become routine"'. However, it is clear from a survey of parents
of cbildren witb bearing loss tbat tbey want information about tbe cause of tbeir cbilds bearing
loss.^"' In faet, etiology of tbeir cbild's bearing loss is
rated as tbe top question parents bave after notification of a bearing loss diagnosis.
Nance''' bas proposed tbat by screening all newborn infants for just 4 important causes of deafness
(DFNiBl, CM\, Pendred syndrome, and tbe mt I2S
rRiNA \155SG mutation) more tban balf of all
infants w itb normal bearing at birtb w bo are at bigb
risk for delayed onset bearing loss in infancy would
be detected in addition to detecting infants at birtb
wbo bave tbe commonest genetic, tbe commonest
C^ausation of Hearing Loss in Children / Tharpe, Sladett
environmental, and the commonest preventable
causes of deafness. As demonstrated by this rc\ie\\.
that recommended screening protocol is likely to
identify numerous cases of permanent L'HL and
MBHL that would typically not be identified
through newborn hearing screening programs that
target more severe degrees of hearing loss. As witb
any screening protocols, the benefits and limitations
of sucb recommendations will require careful consideration before implementation.
References
1. Bess FH, Tharpe AM. Case histor\ data on unilati-rally
hearing-impaired children. Ear Hear. I986;7:14-19.
2. Culbertson JL, Gilhert Lh. Children with unilateral sensorineural hearing loss. Ear Hear. l986;7:.-?8-42.
3. Oyier RF, Oyler AL. Matkin ND. Unilateral hearing loss:
demographics and educational impact. Lati^ ,S;> Hear
Sen-Schools. 1988;19:201 210.
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