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

Late, bilateral response mediated through the lateral medulla

Answer

Bilateral response mediated through a polysynaptic medullary pathway

Answer

Response generated solely by optic nerve activation

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

Short latency, ipsilateral only, oligosynaptic pontine pathway

Answer

Short latency, bilateral, monosynaptic brainstem pathway

Answer

Longer latency, ipsilateral only, cerebellar pathway

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

Incrementing response greater than 100% amplitude increase

Answer

No change in compound muscle action potential amplitude

Answer

Initial decrement followed by full repair at the fifth stimulus

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

Myasthenia gravis

Answer

Botulism presenting acutely

Answer

Congenital myasthenic syndrome type 1

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

Lateral medulla (Wallenberg syndrome)

Answer

Ipsilateral facial nerve distal to the stylomastoid foramen

Answer

Contralateral motor cortex

Question 6

What is the diagnostic significance of post-exercise facilitation in repetitive nerve stimulation testing?

Accepted Answer

It identifies presynaptic disorders like LEMS by demonstrating marked amplitude increase after brief exercise

Answer

It confirms a postsynaptic acetylcholine receptor defect in myasthenia gravis

Answer

It differentiates myasthenia gravis from congenital myasthenic syndromes

Answer

It indicates motor neuron disease with functional reserve

Question 7

When performing repetitive nerve stimulation to evaluate suspected myasthenia gravis, which muscle group provides the highest diagnostic sensitivity?

Accepted Answer

Trapezius or facial muscles (proximal or bulbar)

Answer

Abductor pollicis brevis (median nerve, distal)

Answer

Abductor digiti minimi (ulnar nerve, distal)

Answer

Extensor digitorum communis (radial nerve, distal)