Final Review Flashcards
(25 cards)
Do summating potentials come from the inner hair cells?
Yes
They don’t show up at low intensity levels, why we need to present ECochG at high intensities
Difficult to identify with people with HF HL
Does most clinical evidence indicate that there is no difference in waveforms in awake vs natural sleep for ECochG?
Yes
The least affected potential
Attention also have little or no affect
Not influences by sedatives, relaxants, barbiturates, or anesthesia
What is the preferred stimulus for ECochG?
Click
Alternating polarity (generally cancels out CM)
What is the epoch for ECochG?
5-10 ms
What is the electrode montage for ECochG?
Transtympanic - through TM (near field)
Extratympanic - outside TM
What are the two outcomes for ECochG?
Little or no response under typical clinical measurement conditions (most common cause is cochlear pathology; particularly in the HF)
Clear SP and AP components but SP amplitude is atypically large (menieres)
Was ECochG discovered prior to ABR?
Yes
Was used in young children and difficult to test patients to determine hearing threshold
Recording technique utilized in ECochG yields increased amplitude wave I; sometimes more robust than wave V as intensity decreased to threshold
When should you optimize wave I?
Useful with patients with SNHL, especially HFSNHL to distinguish cochlear vs neural auditory dysfunction
AP amplitude decreases with hearing loss in the 2kHz-8kHz range; no affect on SP
Permits calculation of interpeak latencies for neurodiagnostic ABR to rule out retrocochlear or brainstem involvement
Good for patients with neurological disorders (retrocochlear) where waves III or V are not identifiable
Can ECochG be useful in diagnosing ANSD and monitoring cochlear function of those with suspected ANSD?
Yes
Estimated up to 10% of permanent hearing loss in infants associated w/ ANSD
Combined w/ other electrophysiological tests, distinct patterns have emerged
How do you use ECochG for diagnosing menieres?
Common electrophysiologic pattern with MD is a large SP amplitude relative to AP amplitude
Best seen when patients are symptomatic especially experiencing aural fullness and hearing loss
Diagnostic specificity of this test is poor from 20%-65% in the literature
Variability exists due to episodic nature of the disease, differences in protocols and especially recording electrode locations
What variables affect recording?
ECochG is best as a recording of near field response so the closer to the generator site (hair cells of cochlear) the more robust and reliable
Montage used
What is the normative data for SP/AP ratios?
Tiptrodes > 50% = Abnormal
Tympanic Membrane Electrode > 35% = Abnormal
Transtympanic Needle Electrode > 30% = Abnormal
AP latency condensation – Rarefaction: > 0.38 msec
What are some tips and tricks for recording ECochG?
With moderate to severe HFSNHL, record ECochG with TM electrode (tiptrode adequate for detection of AP-wave I if attempting to enhance for neuro evaluation)
Use horizontal montage to enhance wave I
Impedance values should be below 5 kOhms and within 3 kOhms of each other
Always record pre-stimulus (10% of timebase) to determine level of background noise, will see CM immediate w/ stimulation
SP is more prominent using high frequency Tonebursts (1kHz or 2kHz)
High pass filtering important for recording SP (1, 3, 5)
Increase intensity to maximum level to ensure greatest opportunity of recording CM, SP and AP (SPs cannot be recorded below 50 dB)
SP can be affected by intensity
Add rarefaction and condensation averages together – CM and stimulus artifact will disappear; SP and AP easier to identify
SNHL negates SP/AP ratio rules
If the SP is not identifiable, increase the stimulation rate to 91.1; AP disappears but SP remains
What is the coding and billing for ECochG?
CPT 92584
Once per date of service
What is the stimulus for ASSR?
Continuous tone with variation in amplitude and frequency modulation
How is ASSR measured?
ASSR averaging time is locked to a period of time and sustained neural activity
Do ASSRs with faster modulation rates look more like ABRs?
Yes
Tests more of the brainstem than the cortex
Is there limited information behind bone conduction ASSR?
Yes
Spurious responses occur due to stimulus artifact and possibility of vestibular response at frequencies below 1000 Hz (SAL technique recommended to overcome effects)
High frequency BC thresholds improve with age; Low frequency BC thresholds worsen with age
Can ASSR be done in the sound field?
Yes
Better stimulus for sound field – less distortion with speakers and amplification
Benefit of sound field ASSR for infants with hearing aids when behavioral data is not possible
Studies support reasonable correlation between aided ASSR thresholds and behavioral data
Why was stacked ABR done?
Make it more sensitive to small lesions
Look at amplitude changes rather than latency
Is ENOG similar to EMG?
Yes
Recording electrode may also be used to pick up the electrical activity of a muscle innervated by that nerve
When is the facial nerve response in ENOG?
8 ms
Masseter response is at 5 ms
What are the CPT codes for ENOG?
92516 facial nerve function studies
(Approx reimbursement is $70 per exam/per DOS)
