EEG Evoked Potentials 2 ā Questions and Answers
Question 1: A unilaterally prolonged P100 latency on visual evoked potential testing is most characteristically associated with which condition?
- Retinal detachment
- Demyelinating optic neuritis (multiple sclerosis) (Correct answer)
- Glaucoma
- Cataracts
Correct answer: Demyelinating optic neuritis (multiple sclerosis)
Demyelinating optic neuritis, most commonly seen in multiple sclerosis, slows conduction along the optic nerve, resulting in a prolonged P100 latency that may persist even after clinical recovery.
Question 2: In a BAEP recording, absent Wave I with relatively preserved Waves III and V most likely indicates pathology at which level?
- Cochlea or cochlear nerve peripheral to the brainstem (Correct answer)
- Cochlear nucleus in the lower brainstem
- Superior olivary complex
- Inferior colliculus
Correct answer: Cochlea or cochlear nerve peripheral to the brainstem
Wave I reflects the distal cochlear nerve action potential; its absence with central waves preserved indicates peripheral auditory dysfunction (cochlea or nerve), not brainstem pathology.
Question 3: During intraoperative neurophysiological monitoring, a sudden 50% decrease in SSEP amplitude or a 10% increase in latency should prompt what immediate action?
- Increase stimulus rate to improve signal averaging
- Alert the surgical team immediately (Correct answer)
- Switch to a different stimulation site
- Increase the number of averages collected
Correct answer: Alert the surgical team immediately
The '50/10 rule' is the standard alert criterion: a >50% amplitude drop or >10% latency increase warrants immediate notification of the surgeon to allow corrective intervention before permanent injury.
Question 4: What is the upper limit of normal for the interpeak latency IāV (IPL IāV) in BAEPs recorded from a typical adult?
- Less than 2.0 ms
- Less than 3.0 ms
- Less than 4.4 ms (Correct answer)
- Less than 6.0 ms
Correct answer: Less than 4.4 ms
The IPL IāV, representing total brainstem conduction time, normally does not exceed approximately 4.4 ms; values beyond this suggest central conduction slowing.
Question 5: Bilateral prolongation of SSEP cortical latencies with normal peripheral nerve and plexus responses most strongly suggests pathology at which level?
- Bilateral peripheral neuropathy
- Bilateral brachial plexopathy
- Cervical spinal cord (myelopathy) (Correct answer)
- Bilateral carpal tunnel syndrome
Correct answer: Cervical spinal cord (myelopathy)
Normal peripheral potentials with delayed cortical responses imply a central conduction abnormality; bilateral symmetric involvement points to the cervical cord rather than unilateral brain pathology.
Question 6: The N20 component of the median nerve SSEP is primarily generated by which brain structure?
- Thalamus (ventral posterior lateral nucleus)
- Primary somatosensory cortex (Area 3b, S1) (Correct answer)
- Supplementary motor area
- Parietal association cortex (Area 7)
Correct answer: Primary somatosensory cortex (Area 3b, S1)
N20 reflects the initial thalamocortical volley arriving at primary somatosensory cortex (Brodmann area 3b) on the posterior bank of the central sulcus.
Question 7: Which technical factor most directly degrades SSEP and BAEP signal quality by introducing 60 Hz noise and poor signal-to-noise ratio?
- High patient body temperature
- High electrode impedance (Correct answer)
- Slow stimulus repetition rate
- Low number of trials averaged
Correct answer: High electrode impedance
High electrode impedance increases susceptibility to capacitively coupled electrical interference (60 Hz), which obscures the small far-field potentials and cannot be fully corrected by averaging.
EEG Evoked Potentials 2
A unilaterally prolonged P100 latency on visual evoked potential testing is most characteristically associated with which condition?