Evoked Potentials & Late Response Studies Flashcards
7 cards from real ABEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Evoked Potentials & Late Response Studies flashcards as text
In the blink reflex study, what are the characteristics of the R1 response?
Answer: Early, ipsilateral response mediated through an oligosynaptic pontine pathway
R1 is an early (approximately 10-13 ms) ipsilateral response mediated by a short oligosynaptic pathway through the pons, involving trigeminal and facial nerve nuclei.
Which features best characterize the R2 response in a blink reflex study?
Answer: Longer latency, bilateral, polysynaptic pathway through the lateral medulla
R2 is a longer-latency (approximately 28-41 ms) bilateral response mediated by a polysynaptic pathway through the lateral medulla, explaining its bilateral appearance.
Which pattern on 3 Hz repetitive nerve stimulation (RNS) is characteristic of myasthenia gravis?
Answer: Decrementing response greater than 10% amplitude decrease
Myasthenia gravis characteristically shows a decremental response (>10% amplitude decrease) at low-frequency RNS due to impaired postsynaptic acetylcholine receptor function.
Which condition characteristically demonstrates a marked incrementing response on high-frequency repetitive nerve stimulation or post-exercise testing?
Answer: Lambert-Eaton myasthenic syndrome (LEMS)
LEMS shows marked increment (often >100%) on high-frequency RNS because calcium accumulation at the presynaptic terminal increases acetylcholine vesicle release.
In the blink reflex, absence of R1 with preserved bilateral R2 on ipsilateral supraorbital nerve stimulation most likely indicates a lesion where?
Answer: Ipsilateral pontine trigeminal-facial pathway
Because R1 is mediated by an oligosynaptic pontine pathway, selective R1 absence with preserved R2 points to a lesion in the ipsilateral pons disrupting the short-latency arc.
What is the diagnostic significance of post-exercise facilitation in repetitive nerve stimulation testing?
Answer: It identifies presynaptic disorders like LEMS by demonstrating marked amplitude increase after brief exercise
Brief voluntary exercise causes marked post-exercise facilitation in LEMS because calcium mobilized during exercise temporarily enhances presynaptic acetylcholine release, a hallmark of presynaptic disorders.
When performing repetitive nerve stimulation to evaluate suspected myasthenia gravis, which muscle group provides the highest diagnostic sensitivity?
Answer: Trapezius or facial muscles (proximal or bulbar)
Proximal and bulbar muscles (trapezius, nasalis, orbicularis oculi) yield higher sensitivity for decremental responses in myasthenia gravis than distal hand muscles.