ABEM Equipment Operation & Data Interpretation 4

Question 1

A patient's median motor NCS shows normal distal latency and CMAP amplitude but the conduction velocity is 35 m/s (normal >49 m/s). This pattern most suggests:

Accepted Answer

Diffuse demyelinating polyneuropathy

Answer

Diffusely slowed conduction velocity below 75% of the lower limit of normal, with preserved amplitude, suggests a demyelinating polyneuropathy affecting the entire nerve.

Question 2

Complex repetitive discharges (CRDs) in needle EMG are characterized by:

Accepted Answer

Regular, uniform discharges that start and stop abruptly with a 'machine-like' sound

Answer

CRDs are high-frequency (5–100 Hz), uniform, repetitive discharges of constant morphology that start and stop abruptly, producing a machine-like sound.

Question 3

During single-fiber EMG (SFEMG), 'jitter' is defined as:

Accepted Answer

The variability in interpotential interval between two muscle fiber action potentials from the same motor unit

Answer

Jitter is the variability (MCD – mean consecutive difference) in the time interval between action potentials of two muscle fibers belonging to the same motor unit.

Question 4

In somatosensory evoked potentials (SSEPs), the N20 component recorded over the scalp following median nerve stimulation represents:

Accepted Answer

Thalamo-cortical radiation or primary somatosensory cortex activation

Answer

The N20 is the first cortical response generated in or near the primary somatosensory cortex (area 3b) following median nerve stimulation.

Question 5

When performing near-nerve sensory recording (intraneural technique) compared to surface electrode recording, the primary advantage is:

Accepted Answer

Higher amplitude SNAPs enabling detection of small or absent responses

Answer

Near-nerve needle recording dramatically increases SNAP amplitude, allowing detection of responses too small to be recorded with surface electrodes.

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

(ABEM) American Board of Electrodiagnostic Medicine Practice Test

ABEM Equipment Operation & Data Interpretation 4