ABEM Evoked Potentials & Late Response Studies 3

Question 1

In the blink reflex study, what are the characteristics of the R1 response?

Accepted Answer

Early, ipsilateral response mediated through an oligosynaptic pontine pathway

Answer

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.

Question 2

Which features best characterize the R2 response in a blink reflex study?

Accepted Answer

Longer latency, bilateral, polysynaptic pathway through the lateral medulla

Answer

R2 is a longer-latency (approximately 28-41 ms) bilateral response mediated by a polysynaptic pathway through the lateral medulla, explaining its bilateral appearance.

Question 3

Which pattern on 3 Hz repetitive nerve stimulation (RNS) is characteristic of myasthenia gravis?

Accepted Answer

Decrementing response greater than 10% amplitude decrease

Answer

Myasthenia gravis characteristically shows a decremental response (>10% amplitude decrease) at low-frequency RNS due to impaired postsynaptic acetylcholine receptor function.

Question 4

Which condition characteristically demonstrates a marked incrementing response on high-frequency repetitive nerve stimulation or post-exercise testing?

Accepted Answer

Lambert-Eaton myasthenic syndrome (LEMS)

Answer

LEMS shows marked increment (often >100%) on high-frequency RNS because calcium accumulation at the presynaptic terminal increases acetylcholine vesicle release.

Question 5

In the blink reflex, absence of R1 with preserved bilateral R2 on ipsilateral supraorbital nerve stimulation most likely indicates a lesion where?

Accepted Answer

Ipsilateral pontine trigeminal-facial pathway

Answer

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.

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

ABEM Evoked Potentials & Late Response Studies 3