EEG Evoked Potentials 4 — Questions and Answers
Question 1: Which VEP component is most commonly used clinically to detect demyelinating disease of the optic nerve?
- N75
- P100 (Correct answer)
- N145
- P200
Correct answer: P100
The P100 component of the VEP is the most clinically relevant peak; a delayed latency (>115 ms) strongly suggests optic nerve demyelination.
Question 2: In brainstem auditory evoked potentials (BAEPs), Wave V originates primarily from which structure?
- Cochlear nucleus
- Superior olivary complex
- Lateral lemniscus/inferior colliculus (Correct answer)
- Medial geniculate body
Correct answer: Lateral lemniscus/inferior colliculus
Wave V of the BAEP is generated by the lateral lemniscus and inferior colliculus region of the upper brainstem.
Question 3: What does a prolonged I–III interpeak interval in BAEPs indicate?
- Cochlear pathology
- Pontine lesion between cochlear nucleus and superior olive (Correct answer)
- Cortical auditory processing disorder
- Midbrain compression
Correct answer: Pontine lesion between cochlear nucleus and superior olive
The I–III interpeak interval reflects conduction time through the lower brainstem (caudal pons), so prolongation indicates a lesion in that segment.
Question 4: During intraoperative monitoring with somatosensory evoked potentials, which change should prompt immediate surgical notification?
- 10% amplitude decrease
- 50% amplitude decrease or 10% latency increase (Correct answer)
- Any waveform variability
- Baseline drift only
Correct answer: 50% amplitude decrease or 10% latency increase
The universally accepted alarm criterion for intraoperative SSEP is a ≥50% amplitude decrease or ≥10% latency increase from baseline.
Question 5: Pattern-reversal VEPs are preferred over flash VEPs in clinical practice primarily because they:
- Are faster to perform
- Require less patient cooperation
- Produce more consistent waveforms with smaller normal variance (Correct answer)
- Do not require specialized equipment
Correct answer: Produce more consistent waveforms with smaller normal variance
Pattern-reversal stimuli generate highly reproducible P100 components with tight normative ranges, making subtle latency delays more detectable than with flash VEPs.
Question 6: Which evoked potential modality is most useful for monitoring spinal cord function during scoliosis correction surgery?
- Visual evoked potentials
- Brainstem auditory evoked potentials
- Somatosensory evoked potentials (Correct answer)
- P300 event-related potentials
Correct answer: Somatosensory evoked potentials
SSEPs monitor the dorsal column sensory pathways of the spinal cord, making them the primary tool for detecting cord compromise during spinal instrumentation.
Question 7: In a patient with absent BAEPs bilaterally, which condition is LEAST likely to be the cause?
- Bilateral profound sensorineural hearing loss
- Brain death
- Technical artifact from poor electrode impedance
- Cortical stroke sparing the brainstem (Correct answer)
Correct answer: Cortical stroke sparing the brainstem
BAEPs reflect subcortical (brainstem) generators; a cortical stroke that spares the brainstem would preserve all BAEP waves.
EEG Evoked Potentials 4
Which VEP component is most commonly used clinically to detect demyelinating disease of the optic nerve?