ABEM Nerve Conduction Studies & Electromyography 4

Question 1

The blink reflex R1 response primarily assesses which pathway?

Accepted Answer

Trigeminal sensory — facial motor via the pons (oligosynaptic)

Answer

The R1 response is an oligosynaptic reflex traversing the trigeminal afferent and facial efferent within the pons.

Question 2

In a patient with suspected thoracic outlet syndrome, which NCS finding is most diagnostically helpful?

Accepted Answer

Reduced medial antebrachial cutaneous SNAP

Answer

Reduced medial antebrachial cutaneous SNAP amplitude reflects lower trunk/medial cord involvement characteristic of neurogenic thoracic outlet syndrome.

Question 3

Which feature distinguishes a fasciculation potential from a fibrillation potential on EMG?

Accepted Answer

Fasciculations have the morphology of MUAPs and fire irregularly; fibrillations are small and fire regularly

Answer

Fasciculations represent spontaneous discharge of entire motor units and have MUAP morphology with irregular firing; fibrillations are single muscle fiber potentials with regular firing.

Question 4

In Lambert-Eaton myasthenic syndrome (LEMS), high-frequency repetitive stimulation (50 Hz) or brief maximal voluntary contraction characteristically produces:

Accepted Answer

Increment >100% in CMAP amplitude

Answer

LEMS is a presynaptic disorder where high-frequency stimulation causes calcium accumulation and acetylcholine release, producing >100% CMAP increment.

Question 5

A patient has weakness and numbness in the lateral forearm after shoulder dislocation. Which nerve is most likely injured?

Accepted Answer

Musculocutaneous nerve

Answer

The musculocutaneous nerve innervates the biceps, coracobrachialis, and provides the lateral antebrachial cutaneous sensory nerve, commonly injured with shoulder dislocation.

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

ABEM Nerve Conduction Studies & Electromyography 4