ANSD Flashcards
What is ANSD?
Hearing disorder characterized by disruption of temporal coding of acoustic signals in auditory nerve fibers resulting in impairment of auditory perceptions relying on temporal cues
Disruption of neural synchrony
With ANSD, are pre-neural or cochlear OHCs affected?
No
Only neural is affected
Is frequency resolution affected?
No
Does the disordered auditory nerve function affect processing of auditory temporal cues?
Yes
It causes disruption of temporal resolution and neural timing
Leading to interference with language comprehension (especially in noise) and localization of sound sources and binaural perception
What is the operational definition of ANSD?
Intact otoacoustic emissions (OAEs) but an absent or markedly abnormal ABR response
Why are OAEs intact?
OAEs are present because OAEs are related to OHC function and OHCs are intact in ANSD
Although OAEs may disappear in later stages of the disease
The cochlear microphonic (CM) is present (sometimes even if OAEs are absent) because CM also shows activity from the OHCs
Why are are ABRs disrupted?
ABR is generated by neural structures, which are disrupted
Neural integrity of the eighth nerve and lower brainstem pathways are affected in ANSD
Are ECochG and ARTs also absent?
Yes
Due to VIII N involvement
Was there considerable controversy and gaps in knowledge regarding ANSD?
Yes
Including nosology/terminology, site of lesion, etiology, and management
Was ANSD initially thought to be rare?
Yes
But current estimates of ANSD prevalence in children with permanent hearing loss is ~ 7 to 10%
It is, therefore, imperative for every audiologist working with children to be able to identify the typical pattern of ANSD
When was ANSD discovered?
Case study posted in 1991 about an 11-year old boy
What are some of the names that ANSD has had?
Auditory neuropathy
Presynaptic and postsynaptic nerve disorder
Auditory neuropathy/dys-synchrony
Auditory synaptopathy
Auditory neuropathy spectrum disorder
What is ANSD referred to more recently?
cochlear synaptopathy or hidden hearing loss
What is cochlear synatopathy due to noise exposure?
Loss of synchrony of neural firing causing loss of temporal resolution
Possibly at the level of the dorsal cochlear nucleus because of synaptic damage at the inner hair cell
And/or at the level of the spiral ganglion
Is there gradual neural degeneration in synaptopathy?
Yes
Adversely affects fine speech structure decoding and hence speech perception, especially in noise, which also is seen in ANSD
What is the site of lesion for ANSD?
Selective loss/damage of synaptic junctions of IHCs
Disordered release of neurotransmitters by IHC synapses
Injury to the spiral ganglion
Demyelination/damage to myelin sheath, cell body, or axon of CN VIII, which can spread to portions of the brainstem
Auditory nerve hypoplasia/absence
Can multiple sites of lesion cause the same pattern?
Yes
What are IHCs crucial for?
Sound discrimination
Do IHCs synapse with VIII N fibers?
Yes
What are ribbon synapses?
IHCs synaptic vesicle
Contain NT
Mediated by calcium channels
How many well babies are diagnosed with ANSD?
1 in 300
How much of the deaf population has ANSD?
About 10 to 15%
Can ANSD present with unilateral hearing loss?
Yes, about 20%
Can ANSD occur with other conditions?
Yes
Can ANSD patients be cognitively intact but have medical, vision, motor, and other issues?
Yes
What can the etiology of ANSD be?
Idiopathic, genetic, or environmental
Can genetic-based ANSD be either non-syndromic or syndromic?
Yes
What mode of inheritance does genetic based non-syndromic ANSD have?
AR
What are some examples of genetic based nonsyndromic mutations that can cause ANSD?
Mutations of connexin 26 and otoferlin (DFNB9)
Is genetic based syndromic ANSD often associated with peripheral neuropathies such as charchot marie tooth and friedrichs ataxia?
Yes
Is there also a mitochondrial mode of inheritance for ANSD?
Yes
Moms will pass it down, but fathers will not
Can immune disorders be accompanied by deafness typical to ANSD?
Yes
Such as Guillian-Barre syndrome
Affects proximal nerve roots and proximal portion of 8th nerve
Can metabolic disorders also cause ANSD?
Yes
Such as diabetic neuropathy
Can environmental-based factors also cause ANSD?
Yes
Such as viral infections (mumps and measles can present as unilateral ANSD)
If the 8th nerve is primarily affected for any reason, ifs the clinical picture one of ANSD?
Yes
If the arterial blood supply is not affected by ANSD, can OAEs, CM, and sometimes the wave 1 of the ABR can be identified?
Yes
What happens if the blood supply is compromised?
Then both neural and cochlear receptor elements will be disrupted
OHCs are affected and OAEs may be absent along with the ABR
This confused the clinical picture of ANSD
Why is low birth weight more of a problem for ANSD?
Could lead to transient ANSD
Could go away within 2 years
Why are prolong stays in the NICU an indication for ANSD?
Possibly related to serious and complicated medical issues and/or low birth weight and prematurity
What are some general risk factors for ANSD?
Prematurity and very low birth weight
Prolonged stay in the NIC
Anoxia/hypoxia and accompanying metabolic acidosis
Seizures
Is hyperbilirubinemia a big risk factor for ANSD?
Yes
Can be reversible (transient)
For hyperbilirubinemia, what is the site of lesion for ANSD?
Damage begins in the CANS and the brainstem, primarily the cochlear nuclei, and then descends to the 8th nerve
Nerve death or dysfunction will ensue, but the IHCs are unaffected
Can ANSD caused by hyperbilirubinemia also improve within 2 years of life?
Yes
But it is unclear if restored neural synchrony at the brainstem level results in normal auditory processing
What percentage of ANSD caused by hyperbilirubinemia will recover spontaneously?
5%
How do you diagnose ANSD?
Case history
OAEs
ABR (combined use of OAEs and ABR with two polarities is essential)
Middle ear acoustic reflexes (abnormal/absent)
Behavioral assessment
Speech audiometry
Electrocochleography (ECochG) - involves the 8th nerve
Vestibular assessment (some may present as “clumsy”)
Functional assessment for young children (questionnaires)
If you don’t do two polarities of the ABR, what is another way that you can identify ANSD?
The latencies of wave V are the same (abnormal)
Do we know why OAEs tend to disappear later on for ANSD patients?
No
Typically seen if blood supply is compromised
What is the standard screening protocol for OAEs?
TEOAEs or DPOAEs
What is contralateral OAE suppression?
It is a normal phenomenon that shows a decrease in OAE amplitude with masking to the contralateral ear
What is contralateral OAE suppression mediated by?
The medial olivocochlear bundle via the efferent auditory pathways
What happens if contralateral suppression doesn’t occur?
Involvement of efferent VIII N fibers prevents neural impulses from reaching OHCs, i.e., no OAE suppression- abnormal
Are ABRs and CMs present for ANSD?
ABRs are not present
But cochlear microphonics are
What is the CM generated from?
Predominantly the OHCs
When do CMs occur?
They occur 1 ms after the presentation and follows the phase of the stimulus, occuring before wave 1 of the ABR
Does the CM move upward with condensation?
Yes, and then downward with rarefaction
Does the CM simulate an ABR response?
Yes, but it’s artifactual
Can continue over a few milliseconds (especially in infants)
Are behavioral assessments very important for ANSD?
Yes, to get pure tone thresholds because you cannot get thresholds from the ABR
Can hearing loss in ANSD be anything?
Yes, unilateral or bilateral
SNHL at any range
Does ANSD have a significant impact on speech perception even with normal or near-normal thresholds?
Yes
Why does ANSD have a significant impact on speech perception?
Due to IHC and CN VIII involvement
Is there a range of speech perception in those with ANSD?
Yes
Some might be functionally deaf
Others might have relatively intact speech perception in quiet and do poorly in noise
Is speech in noise testing important for those with ANSD?
Yes
Gives a broader idea of their speech perception abilities
Are ARTs present with ANSD?
They are abnormal
Reflex arc affected due to auditory nerve/synapse involvement
T/F: Typically, you can get present reflexes with a SNHL less than or equal to 50 to 60 dB HL
True
What is a characteristic of ARTs with cochlear hearing losses?
Low SL
Is ANSD associated with vestibulopathy?
Sometimes
They are just not well coordinated
Cannot be seen on imaging (functional issue)
Is the ECochG abnormal for ANSD?
Yes
APs generated by the VIII N are affected so they will be abnormal
Can imaging of the cochlea and auditory nerve be important for ANSD?
Yes
Majority of children with ANSD may have additional intra-cranial anomalies
Should ANSD patients have an ophthalmologic assessment?
Yes, to assess other associated peripheral neuropathies such as Charcot Marie tooth, Friedrich’s ataxia, Guillain Barre
Do hearing aids and FM systems provide benefit to those with ANSD?
Limited
What is the current recommendation for those with residual hearing and ANSD?
Trial of amplification (use of real-ear and prescriptive targets is recommended)
Trial of FM system to reduce effects of noise, distance, and reverberation, especially in a classroom setting
Is a communication assessment also recommended for ANSD patients?
Yes, to evaluate how much they can speak or communicate
What are some educational tools that are recommended for those with ANSD?
Auditory and visual stimulation
Manual communication
Formal education method to facilitate literacy/self-dependence
Currently, what is the most effective treatment for ANSD?
CI’s
Children who do not demonstrate good progress in speech recognition and language development should be considered for a CI regardless of thresholds
What percentage of implant patients have ANSD?
About 10%
When are CIs successful?
When the underlying pathophysiology is a biochemical abnormality of NT substances or synaptic deficits between the IHCs and the VIIIth N
When are CIs marginally successful?
If neural integrity is compromised, such as loss of myelin or loss of neural elements (including the VIIIth N)
Is gene therapy a management method for ANSD?
It is currently being trialed
Being done specifically on AR deafness caused by mutations of the otoferlin gene
Must have intact IHCs and VIIIth N fibers
What are the current results of the gene therapy?
Some have reported hearing sounds and understanding speech
Some adverse transient reactions were reported
What are they actually doing during this gene therapy?
They are introducing an adeno-associated virus carrying a version of the human otoferlin gene into the inner ear through surgery
Were there dose-limiting toxicities found with the gene therapy?
No
