Nerve Conduction Studies & Electromyography Flashcards
7 cards from real ABEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Nerve Conduction Studies & Electromyography flashcards as text
Which parameter is most affected by limb temperature cooling during nerve conduction studies?
Answer: Conduction velocity
Cooling slows sodium channel kinetics, prolonging action potential duration and reducing conduction velocity by approximately 2 m/s per degree Celsius.
A patient presents with median nerve mononeuropathy. On NCS, the distal motor latency is prolonged but conduction velocity across the forearm segment is normal. This pattern is most consistent with:
Answer: Focal demyelination at the carpal tunnel
Focal demyelination at the carpal tunnel produces prolonged distal latency while leaving proximal conduction velocity intact.
On EMG, which finding most specifically indicates active denervation rather than chronic reinnervation?
Answer: Fibrillation potentials and positive sharp waves
Fibrillation potentials and positive sharp waves reflect spontaneous activity of denervated muscle fibers and indicate active denervation.
In ulnar neuropathy at the elbow, inching technique is used to:
Answer: Localize the exact site of focal conduction slowing
Inching stimulates at 1–2 cm intervals across the elbow to pinpoint the site of maximal conduction slowing or conduction block.
Which EMG finding is characteristic of myotonic dystrophy type 1?
Answer: Myotonic discharges waxing and waning in amplitude and frequency
Myotonic discharges classically wax and wane in both amplitude and frequency, producing the 'dive bomber' sound on EMG.
The H-reflex predominantly tests which nerve root when recorded from the soleus muscle?
Answer: S1
The soleus H-reflex traverses the tibial nerve, travels through S1 afferents, and returns via S1 motor fibers to the soleus.
Which of the following best describes a complex repetitive discharge (CRD) on EMG?
Answer: A high-frequency uniform discharge beginning and ending abruptly without waxing or waning
CRDs are high-frequency, uniform discharges with abrupt onset and cessation, created by ephaptic activation between adjacent muscle fibers.