EMG EMG Clinical Applications & Pathology 2

Question 1

Which electrodiagnostic feature is most helpful in distinguishing axonal Charcot-Marie-Tooth (CMT2) from demyelinating CMT (CMT1)?

Accepted Answer

Markedly reduced CMAP amplitudes with relatively preserved conduction velocities in CMT2 versus uniformly slowed velocities in CMT1

Answer

CMT2 is axonal, producing reduced amplitudes with near-normal velocities, while CMT1 is demyelinating with uniformly slowed conduction velocities (often below 38 m/s in the upper limbs).

Question 2

In myasthenia gravis, which electrodiagnostic test is most sensitive for confirming neuromuscular junction dysfunction?

Accepted Answer

Single-fiber EMG (SFEMG) measuring jitter

Answer

Single-fiber EMG measuring jitter is the most sensitive electrodiagnostic test for neuromuscular junction dysfunction, detecting abnormalities even when RNS is normal.

Question 3

Which finding on needle EMG is most characteristic of Lambert-Eaton Myasthenic Syndrome (LEMS)?

Accepted Answer

Small baseline CMAP that markedly increases (>100%) after brief exercise or high-frequency stimulation

Answer

LEMS shows a small baseline CMAP with dramatic post-exercise or high-frequency facilitation (>100% increment) due to calcium-mediated acetylcholine vesicle release.

Question 4

A patient with fatigable weakness, ptosis, and diplopia undergoes RNS testing showing a 12% CMAP decrement at 3 Hz. What is the most likely diagnosis?

Accepted Answer

Myasthenia gravis

Answer

A >10% CMAP decrement at low-frequency (3 Hz) repetitive nerve stimulation in the clinical context of fatigable ptosis and diplopia is consistent with myasthenia gravis.

Question 5

Which EMG pattern is most consistent with inclusion body myositis (IBM)?

Accepted Answer

Mixed myopathic and neurogenic MUPs with fibrillations, affecting distal muscles (finger flexors, foot extensors) early

Answer

IBM characteristically shows a mixed myopathic-neurogenic pattern with both short and long MUPs, fibrillation potentials, and early distal involvement of finger flexors and foot extensors.

(EMG) Electromyography Certification Practice Test

(EMG) Electromyography Certification Practice Test

EMG EMG Clinical Applications & Pathology 2