ABEM Equipment Operation & Data Interpretation 3

Question 1

A conduction block is defined in nerve conduction studies as a reduction in compound muscle action potential (CMAP) amplitude or area between proximal and distal stimulation sites of at least:

Accepted Answer

50%

Answer

A CMAP amplitude or area reduction of 50% or more between proximal and distal stimulation sites (with stable distal CMAP) is the accepted criterion for conduction block.

Question 2

In repetitive nerve stimulation (RNS) studies for myasthenia gravis, a decremental response is considered significant when the amplitude decrement exceeds:

Accepted Answer

10%

Answer

A decrement greater than 10% between the first and fourth or fifth response at 2–3 Hz stimulation is considered diagnostic of a postsynaptic NMJ disorder.

Question 3

Which filter setting change would INCREASE the duration of a recorded CMAP waveform?

Accepted Answer

Lowering the high-frequency filter from 10 kHz to 2 kHz

Answer

Lowering the high-frequency filter removes fast-rise components and rounds the waveform, artificially prolonging its apparent duration.

Question 4

The H-reflex latency is used clinically to assess which nerve root level in the lower extremity?

Accepted Answer

S1

Answer

The H-reflex recorded from the soleus via tibial nerve stimulation primarily evaluates the S1 afferent and efferent pathway.

Question 5

In needle EMG, fibrillation potentials are best characterized as:

Accepted Answer

Spontaneous, regular, biphasic or triphasic potentials with amplitude 20–300 µV indicating denervated muscle fibers

Answer

Fibrillation potentials are spontaneous discharges of individual denervated muscle fibers, characteristically small (20–300 µV), regular, and biphasic or triphasic.

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

ABEM Equipment Operation & Data Interpretation 3