Quiz 3 (ANSD) Flashcards
what is ANSD
disruption of neural synchrony
define ANSD
characterized by disruption to temporal coding of acoustic signals in the auditory n causing impairment of auditory perceptions relying in temporal cues
the phenotype of ANSD reults from
selective loss/damage of synaptic junctions of IHCs
NT release disorder by IHC synapses
injury to spiral ganglion
demyelinatioin/damage to myelin sheath, cell body or axon of CN VIII → can spread to BS
auditory n hypoplasia/absence
improve sound detection
OHCs
what is present in ANSD
pre-neural & cochlear OHC
in tact OAEs
CM
why are OAEs in tact with ANSD
because OAEs relate to OHC fxn and these are in tact with ANSD but they may disappear in later stages
what creates cochlear microphonics
OHCs
temporal resolution is not affected in ansd but frequency resolution is
false
temporal resolution is affect & frequency res is not
what do ABR results look like in ANSD
absent or abnormal
becauase ABR is generated by neural structures → neural integrity of 8th n & lower BS pathways are affected
ECochG and ARTs also are absent because of
CN VIII N involvement
critical for sound discrimination
IHC
what are ribbon synapses
highly specialized, encode sound w/ sub-millisecond temporal precision, mediated by calcium channels
vesicles that contain NTs
synapse w/ VIII N fibers
IHCs
DFNB9 & its relation to ANSD
AR
deafness gene that results in mutation in OTOF gene
what does OTOF gene do
encodes for protein otoferlin
why is otoferlin important
calcium sensor for vesicle fusion & pool replenishment at IHC ribbon synapses
what is research showing with mic.e without otoferlin
they are profoundly deaf because sound evoked NT fails to release at IHC synapse even with normal sensory epithelium structure of the IHC
site of lesion of ANSD
spectrum disorder due to multiple sites of lesions
what is auditory/cochlear synaptopathy
loss of synchrony of neural firing causing loss of temporal resolution
could be at dorsal cochlear nucleus because of synaptic damage at IHC and/or at level of spiral ganglion
adversely affects fine speech structure decoding & speech perception especially in noise
also seen in ANSD
Majority of NICU babies had a _____ hearing loss but ~ 20% had a ______ hearing loss
bilateral, unilateral
what is etiology of ANSD
idiopathic, genetic, or environmental
sound audibility & auditory perception are different. What does this mean
children w/ ANSD present w/ common pattern of electrophysiologic & electroacoustic results BUT auditory capabilities can vary vastly
PT population is heterogeneous for
etiology, presentation & management outcomes
Sensory IHCs & CN VIII N fibers in tact with this condition
DFNB9
nosology for ANSD
auditory neuropathy
presynaptic & postsynaptic n disorder
auditory neuropathy/dys-synchrony
auditory synaptopathy
more recently → cochlear synaptopathy or hidden hearing loss
incidence of ANSD
10-15% of deaf population
more babies in nicu
Majority of NICU babies had a bilateral hearing loss but ~ 20% had a unilateral hearing loss
etiology of ANSD
idiopathic genetic or environmental
what are genetic based ANSD’s
non syndromic
syndromic
mitochondrial
non syndromic genetic ANSD
AR → mutations of Connexin 26 & Otoferlin (DFNB9)
otoferlin is localized to IHC & often with synapse of IHC to VIII N fibers
syndromic genetic ANSD
associated w/ peripheral neuropathies
Charcot Marie Tooth & Friedrich’s ataxia
mitochondrial genetic ANSD
comes from mom 100% (all m and f affected)
will males transmit the gene?
no because they shed their cytoplasm that contains the mitochondria
Leber’s hereditary optic neuropathy
immune disorders deafness typical to ANSD
Guillian-Barre syndrome
affects proximal nerve roots & portions of VIII N
deafness & paralysis w/ lengthy recovery period
metabolic disorders & ANSD
diabetic neuropathy → typically acquired in adults
environmental based ANSD
viral infections
if VIII N primarily affect for any reason, clinical picture is
ANSD
if arterial supply unaffected,
OAEs CM & sometimes wave 1 of ABR can be identified
if arterial supply affected,
both neural & cochlear receptor elements are disrupted
OHCs affected & OAEs & ABR may be absent which confuses clinical picture of ANSD
what are peripheral neuropathies?
Charcot Marie Tooth & Friedreich’s ataxia
audiologic findings (summary)
present OAEs for most unless cochlear blood supply is compromised
ABS ABR w/ present CM → confirmed w/ 2 polarity click stimulus at 70-90 dB nHL
Abnormal ARTs → also present with any test of CN VIII fxn
poor WRS in noise
audio can have varying severity & configuration → not a measure of neural dys-synchrony
PT vary in characteristics & management needs
some benefit with amp
some with CI’s
some with neither
what do OAEs show for ANSD
they are tests of cochlear hair cell fxn
can use TEOAE & DPOASE
present in early years of ANSD and can become absent when OHC blood supply is compromised
what does contralateral OAE suppression show
normally shows decrease in OAE amplitude when masking is in the contra ear
in ANSD, the involvement of efferent VIII N fibers doesn’t let the neural impulses reach the OHCs creating no suppresison = abnormal
what is a click evoked abr
test of auditory nerve function
ABR & CM
what normally happens with intensity and latency in ABR
as intensity decreases, intensity increases
amp also decreases
what is seen with ABR in ANSD
latency of wave 5 doesn’t increase
ansd mimics a true abr
present CM
no amplitude decrease of waves I, II, V
waht should be done with ABR once you identify ANSD
stop the abr becuase it is useless
what are risk factors for ANSD
premature & low birth weight
prolonged NICU stay
O2 deficiency
seizures
hyperbilirubinemia
why does hyperbilirubinemia raise the question how long ABR status should be monitored and when CI should be considered?
because in few cases of it with transient ANSD spontaneous improvement can occur within first 2 years of life but they do not know if neural synchrony at the brainstem level restores and results in normal auditory processing so they typically wait 2 years before considering CIs
describe hyperbilirubinemia in terms of ANSD
may be reversible & spontaneously improve w/in 2 yrs of life
primary site of lesion is NOT VIII N → damage in CANS & BS (primarily Cochlear nucleus) and descends to VIII N
bilirubin accumulates in auditory BS & VIII n ganglion cells
nerve death or dysfunction will occur but IHC unaffected
what tests will be abnormal with ANSD
any test involving 8th nerve
word, reflexes, echog, contralateral suppression w/ OAEs
what is the site of lesion for ANSD
synapse bw 8th nerve & IHC, 8th nerve, spiral ganglion?
what are used to diagnose ANSD
careful case history
OAEs
ABR
MEAR
behavioral assessment
speech audiometry
ECochG
vestib assessment if needed
questionnaires for young children
describe OAE findings with ANSD
present because it is test of OHC fxn which is peripheral to 8th n
can be absent later with compromised blood supply
Contralateral OAE suppression (a normal phenomenon) is absent because the signal has to cross to the other ear, which can’t happen if we have nerve damage in the efferent nerve system
describe ABR findings in ansd
performed at high level click stimulus (70-90 dB nHL) w/ 2 polarities - NO ALTERNATING)
CM reverses w/ polarity change, no latency increase with intensity decrease = ANSD
combo of what is essential for ANSD diagnosis
OAE & ABR w/ 2 polarities
why should alternating polarities not be used in suspected cases of ANSD?
Because it is the sum of condensation & rarefaction polarities so it will not show response reversal
what if CM is not present even with ANSD presence
due to clinician error or alternating polarity was used
describe MEAR findings in ansd
abnormal or absent even with normal/mild SNHL (we expect reflexes even with SNHL up to 60 dB HL)
why is MEAR absent with ANSD
reflexes require functioning 8th nerve so if it is affected reflexes will not happen
why do we use behavioral assessment with ANSD
because abr cannot be performed
describe behavioral assesment findings in ANSD
hearing sensitivity ranges from normal/mild to severe to profound SNHL w/ varying configurations
unilateral or bilateral
~ 30 to 40% show a rising configuration hearing loss
fluctuations in hearing can occur
can the audio tell us about ANSD
NO
it doesn’t give us anything about dys-synchrony
describe speech audiometry results in ANSD
significant impact no matter hearing thresholds due to IHC & CN VIII involvement
some may be functionally deaf & some may have some intact intelligibility in quiet but poor in noise
what is recommended with speech audiometry? why?
SPEECH IN NOISE
poor word rec scores worse in noise because there is neural involvement
describe echog findings with ANSD
abnormal becuase APs generate at VIII N which are affected
what if you didn’t do two polarities? can you still pick up ANSD?
yes because as intensity decreases latency should increase so if wave 5 only exists and it stays the same, indicative of ANSD
ANSD is a continuum/spectrum
true
how is ANSD a spectrum
some can have no auditory complaints
others can do poor in noise & MEMRs are absent, inconsistent auditory responses
or some can have total lack of sound awareness
what other assessments can be done with ANSD
otologic eval with imaging of cochlea & auditory n
genetic eal
ophthalmologic if perifpheral neuropathies
neurologic eval
communication assessment
what is important to keep in mind with ANSD & management
variable auditory capabilities
question is not how severe the HL is but how severe the dys-synchrony is
when are CI’s successful
when pathophysicology is either biochemical abnormality of NT substances or synaptic deficits bw IHC & auditory n
when are CI’s sometime successful
if neural integrity is compromised → loss of myelin, loss of neural elements (including VIII N)
how can ANSD be managed educationally
with auditory and visual stimulation
manual communication like cued speech or ASL
a formal education to facilitate literacy & self-dependence
how can ANSD be managed
HAs & FM systems trials
most successful is CI’s
gene therapy
how does gene therapy help ANSD
adeno-associated virus (AAV) carries version of human OTOF gene used to introduce gene back into the innner ear through surgery
deaf children reported hearing sounds & understanding speech
