Evoked Potentials & Late Response Studies Flashcards
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The H-reflex is most commonly elicited from which nerve-muscle combination?
Answer: Tibial nerve - soleus
The H-reflex is most reliably elicited by stimulating the tibial nerve and recording from the soleus, representing the S1 monosynaptic reflex arc.
Which of the following best describes the physiological basis of F-waves?
Answer: Late motor responses due to antidromic activation of motor neurons followed by orthodromic discharge
F-waves result from antidromic activation of alpha motor neurons, causing a small percentage to 'backfire' orthodromically and produce a late muscle response.
What does prolonged F-wave latency most commonly indicate in electrodiagnostic studies?
Answer: Proximal motor nerve demyelination or radiculopathy
Prolonged F-wave latency indicates slowing in the proximal segment of the motor nerve, suggesting proximal demyelination, polyradiculopathy, or Guillain-Barré syndrome.
H-reflex latency in adults is most significantly influenced by which factor?
Answer: Limb length and patient height
H-reflex latency is primarily determined by limb length (and patient height), since longer limbs require greater conduction distance for the same reflex arc.
Bilateral absent H-reflexes at rest in an adult most strongly suggests which diagnosis?
Answer: Diffuse peripheral neuropathy
Bilateral absent H-reflexes suggest diffuse peripheral neuropathy affecting the S1 arc bilaterally, whereas radiculopathy typically causes unilateral H-reflex changes.
What stimulus rate is most appropriate for eliciting F-waves during a nerve conduction study?
Answer: 0.5-1 Hz
F-waves are elicited at slow rates (0.5-1 Hz) to prevent suppression of the F-wave response by preceding motor neuron discharges.
In F-wave analysis, 'F-wave persistence' refers to which measurement?
Answer: The percentage of stimuli that successfully elicit an F-wave response
F-wave persistence is the percentage of delivered stimuli that produce an F-wave, with normal persistence typically ≥80-90% for most commonly tested nerves.