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R.NCS.T. Exam study materials
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R.NCS.T. Exam practice questions

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Question 1Nerve Conduction Studies

During a routine motor nerve conduction study, the active recording electrode is placed over the motor point of the muscle. What is the primary purpose of this placement?

  1. To measure the sensory nerve action potential amplitude directly
  2. To determine the F-wave latency independent of the M-wave
  3. To reduce stimulus artifact by grounding the limb
  4. To record the compound muscle action potential with the steepest initial negative deflection Correct answer.

Explanation

Placing the active electrode over the motor point yields a biphasic waveform with an initial negative (upward) deflection, which gives the most accurate onset latency and amplitude measurement of the compound muscle action potential.

Question 2Nerve Conduction Studies

Which parameter of a sensory nerve action potential is most directly used to calculate sensory conduction velocity?

  1. Area under the curve
  2. Peak-to-peak amplitude
  3. Total duration
  4. Onset latency Correct answer.

Explanation

Conduction velocity is calculated from the distance between stimulation and recording sites divided by the onset latency of the response. Onset latency marks the arrival of the fastest conducting fibers.

Question 3Nerve Conduction Studies

A technologist wants to minimize stimulus artifact obscuring the onset of a sensory response. Which adjustment is most appropriate?

  1. Reposition the ground electrode between the stimulator and recording electrodes Correct answer.
  2. Increase stimulus duration to 1 ms
  3. Decrease the amplifier sensitivity
  4. Move the ground electrode closer to the active recording electrode

Explanation

Placing the ground electrode between the stimulating and recording electrodes shunts current away from the recording site and reduces stimulus artifact.

Question 4Nerve Conduction Studies

In a standard motor nerve conduction study, supramaximal stimulation is defined as a stimulus intensity that:

  1. Produces a 50% reduction in the M-wave amplitude
  2. Produces a maximal compound muscle action potential amplitude that does not increase with further intensity increase Correct answer.
  3. Is just sufficient to produce a visible muscle twitch
  4. Equals the sensory threshold for the same nerve

Explanation

Supramaximal stimulation means the stimulus is strong enough that further increases in intensity do not increase the compound muscle action potential amplitude, ensuring all motor axons are activated.

Question 5Nerve Conduction Studies

Which nerve is most commonly studied for motor conduction in the upper limb by stimulating at the wrist and elbow while recording over the abductor pollicis brevis?

  1. Ulnar nerve
  2. Median nerve Correct answer.
  3. Musculocutaneous nerve
  4. Radial nerve

Explanation

The median motor study typically stimulates at the wrist and antecubital fossa and records over the abductor pollicis brevis, a thenar muscle innervated by the median nerve.

Question 6Nerve Conduction Studies

What does a prolonged distal motor latency most directly indicate?

  1. Loss of sensory axons
  2. Reduced number of motor units in the muscle
  3. Slowing of conduction in the proximal segment of the nerve
  4. Slowing of conduction in the segment between the distal stimulation site and the muscle Correct answer.

Explanation

Distal motor latency measures the time from distal stimulation to the onset of the compound muscle action potential, reflecting conduction through the distal nerve segment, neuromuscular junction, and muscle activation.

Question 7Nerve Conduction Studies

Which factor most increases nerve conduction velocity in a myelinated peripheral nerve?

  1. Higher limb temperature below 30 degrees Celsius
  2. Smaller axon diameter
  3. Increased myelin thickness relative to axon diameter Correct answer.
  4. Shorter internodal distance

Explanation

Conduction velocity in myelinated fibers increases with axon diameter and with myelin thickness relative to axon diameter, which improves saltatory conduction.

Question 8Nerve Conduction Studies

When performing a sensory nerve conduction study, which electrode configuration records an orthodromic response?

  1. Stimulating over the muscle belly and recording over the tendon
  2. Stimulating distally and recording proximally along the nerve Correct answer.
  3. Stimulating proximally and recording distally along the nerve
  4. Stimulating at two sites simultaneously

Explanation

An orthodromic sensory response is recorded when the nerve is stimulated distally and the response is recorded more proximally, following the natural direction of sensory conduction.

Question 9Nerve Conduction Studies

A motor nerve conduction study shows an M-wave amplitude of 6 mV at the distal site and 3 mV at the proximal site, with normal distal latency and normal conduction velocity. What is the most likely interpretation?

  1. Temperature-related slowing of conduction
  2. Axonal loss affecting the entire nerve
  3. Normal temporal dispersion without significance
  4. Conduction block in the segment between the two stimulation sites Correct answer.

Explanation

A greater than 50% drop in amplitude between distal and proximal stimulation, with preserved distal latency and velocity, indicates conduction block in the intervening segment.

Question 10Nerve Conduction Studies

Which change in nerve conduction parameters is expected when limb temperature falls from 34 to 28 degrees Celsius?

  1. Decreased conduction velocity and prolonged latency Correct answer.
  2. Decreased amplitude with unchanged velocity
  3. Shortened distal latency with increased amplitude
  4. Increased conduction velocity and decreased latency

Explanation

Cooling slows the kinetics of ion channels and membrane depolarization, reducing conduction velocity and prolonging latencies.

Question 11Nerve Conduction Studies

During an ulnar motor study, the active electrode is over the abductor digiti minimi and stimulation is at the wrist and below the elbow. Which additional stimulation site is needed to assess for conduction block across the elbow?

  1. At the mid-forearm
  2. At the axilla
  3. Above the elbow Correct answer.
  4. At the palmar crease

Explanation

Comparing responses from stimulation below and above the elbow allows assessment of the ulnar nerve segment across the elbow, where entrapment commonly occurs.

Question 12Nerve Conduction Studies

A sensory study of the median nerve yields an onset latency of 3.0 ms over a distance of 140 mm. What is the approximate sensory conduction velocity?

  1. 140 m/s
  2. 4.7 m/s
  3. 23 m/s
  4. 47 m/s Correct answer.

Explanation

Velocity equals distance divided by latency: 140 mm (0.14 m) divided by 0.003 s equals approximately 47 m/s.

Question 13Nerve Conduction Studies

Which finding best distinguishes a demyelinating from an axonal process on nerve conduction studies?

  1. Prolonged distal latency with normal velocity
  2. Uniformly reduced amplitudes with mildly reduced velocity
  3. Reduced sensory amplitude with normal motor velocity
  4. Markedly reduced conduction velocity with preserved amplitude in some segments Correct answer.

Explanation

Demyelination characteristically produces marked slowing of conduction velocity, prolonged latencies, and conduction block, often with relatively preserved amplitudes in unaffected segments.

Question 14Nerve Conduction Studies

What is the primary reason for measuring the distance between stimulation sites along the course of the nerve rather than as a straight line between surface landmarks?

  1. To increase the amplitude of the response
  2. To improve accuracy of calculated conduction velocity Correct answer.
  3. To reduce stimulus artifact
  4. To shorten the distal latency

Explanation

Conduction velocity is derived from the true length of the nerve segment traveled; measuring along the nerve course improves the accuracy of the calculated velocity.

Question 15Nerve Conduction Studies

An F-wave study is performed on the median nerve. Which statement best describes the physiologic basis of the F-wave?

  1. It is produced by direct muscle stimulation
  2. It is a sensory response recorded from muscle
  3. It represents a monosynaptic reflex arc through the spinal cord
  4. It results from antidromic activation of motor axons followed by anterior horn cell backfiring Correct answer.

Explanation

The F-wave arises when supramaximal stimulation antidromically activates motor axons, causing anterior horn cells to fire and send an orthodromic volley back to the muscle.

Question 16Nerve Conduction Studies

A patient has a prolonged median distal motor latency with a normal median sensory response and normal ulnar studies. Which condition is most consistent with this pattern?

  1. Generalized demyelinating polyneuropathy
  2. Ulnar neuropathy at the elbow
  3. Carpal tunnel syndrome Correct answer.
  4. Radiculopathy at C6

Explanation

Focal prolongation of the median distal motor latency with relative sparing of other nerves is characteristic of median nerve compression at the wrist, as in carpal tunnel syndrome.

Question 17Nerve Conduction Studies

Which electrode is used as the reference in a standard motor nerve conduction study?

  1. The active electrode over the motor point
  2. The ground electrode on the limb
  3. The stimulating cathode
  4. The electrode placed over the tendon or a distant site Correct answer.

Explanation

In motor studies the reference electrode is placed over the tendon or a relatively inactive distant site, while the active electrode sits over the motor point.

Question 18Nerve Conduction Studies

During a nerve conduction study, the amplifier's low-frequency filter is set to 2 Hz and the high-frequency filter to 10 kHz. What is the main effect of raising the low-frequency filter to 20 Hz?

  1. It prolongs the onset latency
  2. It increases the amplitude of the sensory response
  3. It reduces stimulus artifact entirely
  4. It removes slow baseline wander but may distort the late components of the response Correct answer.

Explanation

The low-frequency filter removes slow potentials such as baseline wander; raising it too high can attenuate slower components of the waveform.

Question 19Nerve Conduction Studies

Which nerve conduction finding is most characteristic of an early, mild axonal neuropathy?

  1. Prolonged F-wave latency with normal amplitudes
  2. Conduction block across a focal segment
  3. Reduced response amplitudes with relatively preserved conduction velocity Correct answer.
  4. Markedly slowed conduction velocity

Explanation

Axonal loss reduces the number of conducting fibers, lowering amplitudes while conduction velocity remains relatively preserved because surviving fibers conduct normally.

Question 20Nerve Conduction Studies

What does the term temporal dispersion describe in a motor nerve conduction study?

  1. Artifact from inadequate grounding
  2. Desynchronization of the compound muscle action potential due to differing conduction velocities among fibers Correct answer.
  3. Slowing of conduction due to cooling
  4. Loss of motor axons between stimulation sites

Explanation

Temporal dispersion results from varying conduction velocities among fibers, causing the response to broaden and lose amplitude as it travels over a longer segment.

Question 21Nerve Conduction Studies

A technologist records a median sensory response with an onset latency of 2.0 ms and a peak latency of 2.8 ms. Which latency value is conventionally used for calculating sensory conduction velocity?

  1. The difference between peak and onset latencies
  2. Peak latency
  3. The average of onset and peak latencies
  4. Onset latency Correct answer.

Explanation

Onset latency marks the arrival of the fastest conducting fibers and is conventionally used for calculating conduction velocity.

Question 22Nerve Conduction Studies

A patient's median motor study shows normal distal latency and normal conduction velocity, but the compound muscle action potential amplitude is markedly reduced. Which process best explains this finding?

  1. Cooling of the limb
  2. Focal demyelination at the wrist
  3. Loss of motor axons or muscle fibers Correct answer.
  4. Temporal dispersion across a long segment

Explanation

A reduced compound muscle action potential amplitude with preserved latency and velocity reflects loss of motor axons or muscle fibers rather than a conduction abnormality.

Question 23Nerve Conduction Studies

Which technical factor most directly affects the reliability of a calculated motor conduction velocity across a limb segment?

  1. The duration of the amplifier sweep
  2. The size of the ground electrode
  3. The color of the recording electrodes
  4. The accuracy of the surface distance measurement between stimulation sites Correct answer.

Explanation

Conduction velocity depends on the measured distance and the latency difference; errors in surface distance directly alter the calculated velocity.

Question 24Nerve Conduction Studies

A study shows a 40% drop in compound muscle action potential amplitude between distal and proximal stimulation sites, accompanied by waveform broadening but no significant latency change. What is the most likely explanation?

  1. Partial conduction block
  2. Normal variation
  3. Temporal dispersion Correct answer.
  4. Complete axonal transection

Explanation

A modest amplitude drop with waveform broadening and preserved latency is characteristic of temporal dispersion from varying conduction velocities rather than true conduction block.

Question 25Nerve Conduction Studies

When comparing the H-reflex to the F-wave, which statement is accurate?

  1. The F-wave requires submaximal stimulation to be recorded
  2. The H-reflex is a monosynaptic reflex best recorded from the soleus with tibial nerve stimulation Correct answer.
  3. The H-reflex is recorded from the thenar eminence after median stimulation
  4. The F-wave is abolished by voluntary contraction

Explanation

The H-reflex is a monosynaptic stretch reflex, classically recorded from the soleus after submaximal tibial nerve stimulation, whereas the F-wave is a late motor response requiring supramaximal stimulation.

Question 26Nerve Conduction Studies

Which nerve is most commonly studied to assess the motor component of the median nerve?

  1. Median nerve Correct answer.
  2. Ulnar nerve
  3. Peroneal nerve
  4. Radial nerve

Explanation

The median nerve is assessed by recording over the abductor pollicis brevis. The ulnar nerve is assessed over the abductor digiti minimi, and the radial nerve over the extensor indicis.

Question 27Nerve Conduction Studies

What is the typical active electrode placement for a sensory nerve conduction study of the median nerve?

  1. Over the proximal phalanx of the index finger Correct answer.
  2. Over the muscle belly
  3. Over the distal phalanx of the thumb
  4. Over the wrist crease

Explanation

For median sensory studies, the active electrode is placed over the proximal phalanx of the index finger, and the reference is placed distally. This configuration records the orthodromic sensory response.

Question 28Nerve Conduction Studies

Which parameter is most directly affected by the distance between the stimulating and recording electrodes in a motor nerve conduction study?

  1. Duration
  2. Amplitude
  3. Distal latency Correct answer.
  4. Conduction velocity

Explanation

Distal latency is the time from stimulation to the onset of the compound muscle action potential and is directly proportional to the distance between the stimulation and recording sites. Conduction velocity is calculated using distance and latency, but it is not the parameter directly measured.

Question 29Nerve Conduction Studies

Which filter setting is most appropriate for a routine motor nerve conduction study?

  1. Low-frequency filter 2 Hz, high-frequency filter 2 kHz
  2. Low-frequency filter 20 Hz, high-frequency filter 2 kHz
  3. Low-frequency filter 10 Hz, high-frequency filter 10 kHz
  4. Low-frequency filter 2 Hz, high-frequency filter 10 kHz Correct answer.

Explanation

Motor nerve conduction studies typically use a low-frequency filter of 2 Hz and a high-frequency filter of 10 kHz to capture the full frequency content of the compound muscle action potential. Sensory studies often use higher low-frequency filters (e.g., 20 Hz) to reduce noise.

Question 30Nerve Conduction Studies

Which nerve conduction study finding is most consistent with a demyelinating neuropathy?

  1. Normal distal latency with reduced sensory nerve action potential amplitude
  2. Prolonged distal latency with normal amplitude Correct answer.
  3. Normal conduction velocity with prolonged F-wave latency
  4. Reduced compound muscle action potential amplitude with normal conduction velocity

Explanation

Demyelinating neuropathies are characterized by slowing of conduction, which manifests as prolonged distal latency, reduced conduction velocity, and prolonged F-wave latencies. Axonal loss primarily reduces amplitudes.

Question 31Nerve Conduction Studies

During a nerve conduction study, which electrode is placed over the muscle belly to record the compound muscle action potential?

  1. Ground electrode
  2. Active electrode Correct answer.
  3. Stimulating electrode
  4. Reference electrode

Explanation

The active electrode (G1) is placed over the motor point of the muscle to record the compound muscle action potential. The reference electrode (G2) is placed over a relatively inactive area, such as a tendon.

Question 32Nerve Conduction Studies

Which artifact is most likely to be reduced by adjusting the ground electrode?

  1. Stimulus artifact
  2. 50/60 Hz electrical noise Correct answer.
  3. Physiologic tremor
  4. Movement artifact

Explanation

The ground electrode helps to reduce electrical noise, particularly 50/60 Hz interference, by providing a common reference. Stimulus artifact is minimized by adjusting stimulus parameters and electrode placement.

Question 33Nerve Conduction Studies

What is the primary purpose of supranaximal stimulation in motor nerve conduction studies?

  1. To minimize patient discomfort
  2. To ensure all motor axons are activated Correct answer.
  3. To prevent temporal dispersion
  4. To reduce stimulus artifact

Explanation

Supranaximal stimulation ensures that all motor axons in the nerve are activated, producing a maximal compound muscle action potential. This is necessary for accurate amplitude and latency measurements.

Question 34Nerve Conduction Studies

A motor nerve conduction study of the median nerve shows a distal latency of 4.5 ms (normal <4.2 ms) and a conduction velocity of 52 m/s (normal >50 m/s). What is the most likely interpretation?

  1. Normal study
  2. Demyelinating neuropathy
  3. Carpal tunnel syndrome Correct answer.
  4. Axonal loss

Explanation

A prolonged distal latency with normal conduction velocity in the forearm is characteristic of carpal tunnel syndrome, where demyelination occurs at the wrist. Axonal loss would reduce amplitude, and a demyelinating neuropathy would typically slow conduction velocity.

Question 35Nerve Conduction Studies

Which nerve conduction study parameter is most sensitive for detecting early diabetic neuropathy?

  1. Median motor distal latency
  2. Peroneal motor velocity
  3. Sural sensory amplitude Correct answer.
  4. Ulnar sensory latency

Explanation

The sural sensory nerve action potential amplitude is often the first parameter to become abnormal in early diabetic neuropathy, reflecting distal axonal loss. Motor parameters may remain normal until later.

Question 36Nerve Conduction Studies

During an F-wave study, which parameter is most commonly measured?

  1. Amplitude
  2. Duration
  3. Minimal latency Correct answer.
  4. Chronodispersion

Explanation

The minimal F-wave latency is the most reliable and commonly measured parameter, reflecting conduction along the entire motor axon. Amplitude and duration are highly variable and less useful.

Question 37Nerve Conduction Studies

Which factor most significantly affects the amplitude of a sensory nerve action potential?

  1. Distance between stimulating and recording electrodes
  2. Filter settings
  3. Number of sensory axons activated Correct answer.
  4. Skin temperature

Explanation

The amplitude of a sensory nerve action potential is directly proportional to the number of sensory axons that are activated and conduct synchronously. Distance, temperature, and filters affect latency and other parameters but have less direct effect on amplitude.

Question 38Nerve Conduction Studies

A patient has a prolonged H-reflex latency in the tibial nerve with normal F-wave latency. What is the most likely explanation?

  1. Sciatic nerve lesion
  2. Peripheral neuropathy
  3. Lumbosacral plexopathy
  4. S1 radiculopathy Correct answer.

Explanation

The H-reflex assesses the S1 reflex arc, and a prolonged latency with a normal F-wave suggests a lesion affecting the sensory root or the reflex pathway, such as an S1 radiculopathy. Peripheral neuropathy would typically affect both H-reflex and F-wave.

Question 39Nerve Conduction Studies

Which nerve conduction study finding is most indicative of a conduction block?

  1. Prolonged distal latency
  2. Drop in amplitude between proximal and distal stimulation Correct answer.
  3. Temporal dispersion
  4. Reduced conduction velocity

Explanation

Conduction block is defined as a significant drop in compound muscle action potential amplitude or area when stimulating proximal to the site of block compared to distal stimulation. This indicates failure of action potentials to propagate past the lesion.

Question 40Nerve Conduction Studies

What is the effect of cooling the limb on sensory nerve conduction velocity?

  1. Variable effect
  2. Decreases velocity Correct answer.
  3. Increases velocity
  4. No effect

Explanation

Cooling decreases nerve conduction velocity in both motor and sensory fibers. This is why limb temperature should be maintained and monitored during nerve conduction studies.

Question 41Nerve Conduction Studies

Which parameter is used to calculate motor nerve conduction velocity?

  1. Area under the curve
  2. Latency difference between two stimulation sites Correct answer.
  3. Amplitude ratio
  4. Duration of the compound muscle action potential

Explanation

Motor conduction velocity is calculated by dividing the distance between two stimulation sites by the difference in latency between those sites. This avoids the influence of the distal latency.

Question 42Nerve Conduction Studies

In a nerve conduction study, which electrode arrangement is used for orthodromic sensory studies?

  1. Stimulating proximally, recording distally
  2. Stimulating and recording at the same site
  3. Stimulating distally, recording proximally Correct answer.
  4. Stimulating over the muscle belly

Explanation

Orthodromic sensory studies involve stimulating the nerve distally and recording proximally, following the normal direction of sensory conduction. Antidromic studies stimulate proximally and record distally.

Question 43Nerve Conduction Studies

A patient's median motor study shows a normal distal latency and normal conduction velocity, but the compound muscle action potential amplitude is reduced. What does this suggest?

  1. Demyelinating neuropathy
  2. Normal variant
  3. Axonal loss Correct answer.
  4. Conduction block

Explanation

Reduced compound muscle action potential amplitude with normal latency and velocity suggests loss of motor axons (axonal loss). Demyelination would typically slow conduction and prolong latency.

Question 44Nerve Conduction Studies

What is the primary reason for using a supramaximal stimulus in nerve conduction studies?

  1. To prevent stimulus artifact
  2. To ensure consistent activation of all nerve fibers Correct answer.
  3. To reduce electrical noise
  4. To minimize patient discomfort

Explanation

Supramaximal stimulation ensures that all nerve fibers in the stimulated nerve are activated, providing a consistent and maximal response. This is essential for reliable amplitude and latency measurements.

Question 45Nerve Conduction Studies

Which nerve conduction study finding is most consistent with a sensory neuropathy?

  1. Reduced compound muscle action potential amplitude
  2. Prolonged motor distal latency with normal sensory studies
  3. Reduced sensory nerve action potential amplitude with normal motor studies Correct answer.
  4. Prolonged F-wave latency

Explanation

Sensory neuropathy primarily affects sensory fibers, leading to reduced sensory nerve action potential amplitudes, while motor studies remain normal. Motor neuropathies would affect motor parameters.

Question 46Nerve Conduction Studies

Which factor most affects the reliability of a calculated motor conduction velocity?

  1. The filter settings
  2. The duration of the stimulus
  3. Accurate measurement of the distance between stimulation sites Correct answer.
  4. The amplitude of the compound muscle action potential

Explanation

Motor conduction velocity is calculated by dividing the distance between two stimulation sites by the difference in latency. Therefore, accurate distance measurement is crucial for reliable velocity calculation.

Question 47Nerve Conduction Studies

A study shows a 40% drop in compound muscle action potential amplitude between distal and proximal stimulation sites, with normal conduction velocity. What is the most likely diagnosis?

  1. Demyelinating neuropathy
  2. Normal variation
  3. Axonal loss
  4. Conduction block Correct answer.

Explanation

A significant drop in amplitude between distal and proximal stimulation, with normal conduction velocity, indicates conduction block. This is a hallmark of focal demyelination, such as in compression neuropathies.

Question 48Nerve Conduction Studies

Which nerve conduction study parameter is most useful for differentiating a preganglionic from a postganglionic lesion?

  1. F-wave latency
  2. Compound muscle action potential amplitude
  3. Motor conduction velocity
  4. Sensory nerve action potential amplitude Correct answer.

Explanation

Sensory nerve action potential amplitude is preserved in preganglionic lesions (e.g., root avulsion) because the dorsal root ganglion is intact, while it is reduced in postganglionic lesions. This helps localize the lesion.

Question 49Nerve Conduction Studies

What is the effect of temporal dispersion on the compound muscle action potential?

  1. Increased amplitude and decreased duration
  2. Decreased amplitude and increased duration Correct answer.
  3. Decreased amplitude and decreased duration
  4. Increased amplitude and duration

Explanation

Temporal dispersion occurs when action potentials in different nerve fibers arrive at the recording electrode at different times, leading to phase cancellation and reduced amplitude, while the overall duration increases.

Question 50Nerve Conduction Studies

Which nerve conduction study finding is most characteristic of a severe axonal neuropathy?

  1. Conduction block with normal amplitude
  2. Prolonged distal latency with normal amplitude
  3. Markedly reduced compound muscle action potential amplitude with mild slowing of conduction velocity Correct answer.
  4. Prolonged F-wave latency with normal compound muscle action potential amplitude

Explanation

Severe axonal neuropathy results in loss of axons, leading to markedly reduced compound muscle action potential amplitude. Conduction velocity may be mildly slowed due to loss of the fastest fibers but is not severely reduced.