ABEM Evoked Potentials & Late Response Studies 2 — Questions and Answers
Question 1: Following median nerve stimulation, which SSEP peak represents activation at the level of the brachial plexus (Erb's point)?
- N9 (Correct answer)
- N13
- N20
- P25
Correct answer: N9
N9 represents the nerve action potential volley arriving at the brachial plexus, recorded from the ipsilateral supraclavicular fossa (Erb's point).
Question 2: What is the primary clinical application of brainstem auditory evoked potentials (BAEPs)?
- Diagnosing carpal tunnel syndrome and median neuropathy
- Evaluating auditory pathway integrity and detecting acoustic neuromas or brainstem lesions (Correct answer)
- Assessing brachial plexus root avulsion injuries
- Measuring cortical motor function and connectivity
Correct answer: Evaluating auditory pathway integrity and detecting acoustic neuromas or brainstem lesions
BAEPs evaluate conduction through the auditory pathway from the cochlea through the brainstem, making them sensitive for acoustic neuromas and demyelinating brainstem lesions.
Question 3: In pattern-reversal visual evoked potentials (VEPs), the P100 wave is generated primarily by which structure?
- Optic chiasm
- Lateral geniculate nucleus of the thalamus
- Primary visual cortex (occipital cortex, V1) (Correct answer)
- Optic nerve proximal segment
Correct answer: Primary visual cortex (occipital cortex, V1)
The P100 is a positive deflection at approximately 100 ms recorded over the occipital scalp, reflecting activation of the primary visual cortex (V1).
Question 4: A unilaterally delayed P100 latency with preserved amplitude on VEP testing is most characteristic of which condition?
- Diabetic retinopathy with macular involvement
- Multiple sclerosis with a history of optic neuritis (Correct answer)
- Bilateral cataracts reducing stimulus contrast
- Macular degeneration with central scotoma
Correct answer: Multiple sclerosis with a history of optic neuritis
Demyelination of the optic nerve from multiple sclerosis characteristically prolongs the P100 latency, often with preserved amplitude, reflecting slowed rather than lost conduction.
Question 5: Which wave of the brainstem auditory evoked potential (BAEP) is generated by the distal cochlear nerve?
- Wave I (Correct answer)
- Wave III
- Wave V
- Wave VII
Correct answer: Wave I
Wave I is generated by the distal portion of the eighth cranial nerve (cochlear nerve), representing the most peripheral auditory generator in the BAEP series.
Question 6: The I-V interpeak latency in BAEP studies primarily reflects conduction through which segment?
- Peripheral auditory pathway from cochlea to cochlear nerve
- Brainstem conduction from the cochlear nerve (Wave I) to the inferior colliculus (Wave V) (Correct answer)
- Cortical processing of auditory information in temporal lobe
- Middle ear ossicular chain transmission time
Correct answer: Brainstem conduction from the cochlear nerve (Wave I) to the inferior colliculus (Wave V)
The I-V interpeak latency measures conduction time through the brainstem from Wave I (cochlear nerve) to Wave V (inferior colliculus/lateral lemniscus).
Question 7: In median nerve SSEPs, which peak represents the initial cortical response recorded over the contralateral scalp?
- N9
- N13
- N18
- N20 (Correct answer)
Correct answer: N20
N20 is the first cortical response recorded over the contralateral somatosensory cortex (C3' or C4'), representing thalamocortical activation reaching primary somatosensory cortex.
ABEM Evoked Potentials & Late Response Studies 2
Following median nerve stimulation, which SSEP peak represents activation at the level of the brachial plexus (Erb's point)?