ANSD Flashcards
Define ANSD
A disorder involving a dys-synchronous neural response and present otoacoustic emissions
(Starr et al., 1996; Cardon & Sharma, 2013)
Why do the different etiologies of ANSD matter?
These different etiologies result in different presentations of the disorder.
What is consistent among all ANSD patients?
- Present OAEs
- Difficulty with speech understanding in noise that is worse than expected by their audiogram
(Cardon & Sharma, 2013)
What does the speech understanding difficulty in noise stem from for patients with ANSD?
A disruption in temporal processing resulting from the dys-synchronous neural response of the auditory nerve.
Synchrony is necessary for speech perception in noise!
(Cardon & Sharma, 2013)
What physiologic tests are used in the diagnosis and investigation of ANSD? What are the results from each of these tests?
- OAEs–> Present but may disappear over time
- Tympanometry–> Normal (Rance, 2005)
- Audiogram–> normal to profound SNHL (Rance, 2005)
- Speech-in-noise–> Poor (Rance, 2005)
- Acoustic Reflexes–> Abnormal or absent (Rance, 2005)
What electrophysiologic measures measures are used in the diagnosis and investigation of ANSD?
1) ABR with reversed polarity of click stimulus
2) EcochG
3) P1 CAEP
What is the cochlear microphonic?
A receptor potential that resembles the sound stimulus and mainly reflects receptor potentials produced at the apical end of the outer hair cells when they are mechanically activated.
What does the cochlear microphonic look like in a normal hearing individual?
Inverted when the polarity of the click stimulus is reversed while the rest of the waveform does not invert
What does the presence of a cochlear microphonic indicate?
Intact cochlea/hair cells
How is the diagnosis of ANSD made using all of the tests?
If the patient has robust CM, inverted condensation and rarefaction waveforms, and flat or absent alternating waveforms
When would you use EcochG?
If the patient doesn’t have OAEs but the ABR is abnormal.
Why would you use EcocG?
For further visualization of the cochlear microphonic.
If the patient doesn’t have OAEs but the ABR is abnormal, want to do an EcochG to rule out cochlear dysfunction by looking at the cochlear microphonic.
What is the P1 cortical auditory evoked potential (CAEP)?
- A slower, post-synaptic potential that requires less synchrony than an ABR
- With increasing age, P1 latency decreases reflecting maturation of the central auditory pathways
What is the P1 CAEP used for?
As a management tool to assess maturation of the auditory system and predict benefit from amplification b/c P1 CAEP has been correlated with P1 CAEP in ANSD children with hearing aids (Cardon & Sharma, 2013)
Why are CI’s proposed for use for ANSD patients?
Cochlear implants deliver a signal directly to the auditory nerve. This direct stimulation of the auditory nerve has been proposed as a way to re-establish synchrony in the firing of the auditory nerve.
