EMG Nerve Conduction Studies

Question 1

Which nerve conduction parameter directly reflects the speed of the fastest-conducting motor nerve fibers between two stimulation points?

Accepted Answer

Nerve conduction velocity

Answer

Nerve conduction velocity is calculated by dividing the distance between two stimulation sites by the difference in their latencies, reflecting the fastest-conducting myelinated motor fibers.

Question 2

What does a reduced compound muscle action potential (CMAP) amplitude on motor nerve conduction studies primarily indicate?

Accepted Answer

Loss of functioning motor axons

Answer

CMAP amplitude reflects the number of functional motor axons contributing to the compound response; a reduced amplitude indicates axonal loss rather than demyelination.

Question 3

In adults, the H-reflex is most reliably and consistently obtained from which nerve-muscle pair?

Accepted Answer

Tibial nerve / soleus

Answer

The H-reflex is most consistently elicited by stimulating the tibial nerve and recording from the soleus, serving as the electrophysiologic equivalent of the Achilles tendon reflex via the S1 reflex arc.

Question 4

A prolonged F-wave latency with a normal distal motor latency and normal nerve conduction velocity most likely suggests:

Accepted Answer

Proximal conduction slowing or nerve root pathology

Answer

F-waves travel the full length of the motor nerve proximally and back distally; a prolonged latency with normal distal NCS indicates pathology in the proximal segment, such as radiculopathy or proximal plexopathy.

Question 5

In carpal tunnel syndrome, which NCS finding is typically the earliest and most sensitive indicator?

Accepted Answer

Prolonged median sensory peak latency across the wrist

Answer

Prolonged median sensory latency across the wrist is the most sensitive NCS indicator of carpal tunnel syndrome, as sensory fibers are more vulnerable to compressive ischemia than motor fibers.

(EMG) Electromyography Certification Practice Test

(EMG) Electromyography Certification Practice Test

EMG Nerve Conduction Studies