Deck 17: Electrophysiological Testing of Nerves and Muscles

Question 1

During an electromyography (EMG) exam of a patient there is a brief burst of electrical activity when the needle electrode is inserted into the muscle. Which of the following is the correct interpretation of this finding?

A) Neuromuscular junction disease
B) Myopathic disorder
C) Demyelination of the motor neuron
D) Normal response caused by movement of the needle electrode

Answer 1

D

Question 2

Which of the following are primary indicators of demyelination of a nerve?

A) Positive sharp waves and decreased sensory and muscle action potentials
B) Prolonged distal latencies and slowing of nerve conduction velocity
C) Decreased amplitude and blocked nerve conduction
D) Shorter distal latencies and increased nerve conduction velocity

Answer 2

B

Question 3

When reporting the results of an EMG exam the practitioner should refrain from which of the following statements?

A) There is a conduction block of the median nerve in the carpal tunnel.
B) The patient has segmental demyelination of the posterior tibial nerve.
C) The patient's symptoms are caused by a herniated disc at L4-5.
D) Results of the EMG are consistent with neuromuscular junction disease.

Answer 3

C

Question 4

A patient with a neuropathic disorder will have which of the following characteristic recruitment patterns during an EMG exam?

A) Decreased number of motor units firing at a faster than normal rate
B) Small-amplitude, short-duration polyphasic motor units accomplished with little effort
C) Increased number of fasciculations and miniature end-plate potentials
D) Reduced insertional activity and frequent end-plate spikes

Question 5

Results of electroneuromyography (ENMG) are best used for which of the following purposes?

A) Identifying the location of a neuromuscular impairment
B) Diagnosing impairments that lead to peripheral neuropathies
C) Indentifying the actual cause of a nerve or muscle impairment
D) Diagnosing anatomical anomalies that may compress a nerve

Question 6

Which of the following is a normal characteristic of a motor unit potential?

A) Amplitude of 10 to 50 mV
B) Duration of 5 to 15 msec
C) Usually has multiple phases (polyphasic)
D) Low frequency (usually 1 to 5 per second)

Question 7

Why must the temperature of the examination room be kept at a constant temperature and skin temperature monitored during nerve conduction studies?

A) Fluctuations in temperature will cause patients to be uncomfortable during the test.
B) Decreased temperatures will result in slowing of nerve conduction velocity.
C) Muscle response to stimulation will be altered if the temperature varies.
D) Decreased temperatures will result in faster nerve conduction velocities.

Question 8

Electrically generated action potentials propagate along a nerve

A) Only orthodromically
B) Only antidromically
C) In both directions
D) Orthodromically for sensory nerves and antidromically for motor nerves

Question 9

Which of the following muscles is most commonly examined in an NCS for possible axonotmesis of the median nerve?

A) Abductor digiti minimi
B) Flexor digitorum profundus
C) Abductor pollicis brevis
D) Extensor digitorum brevis

Question 10

A patient with a peripheral nerve injury has an NCS performed 2 days post-injury. Results demonstrate normal conduction below the level of the injury and no response across the injured axon. Which of the following nerve injuries is most likely?

A) Cannot be determined at this time
B) Neurapraxia
C) Axonotmesis
D) Neurotmesis

Question 11

Which of the following best describes a nerve conduction study (NCS)?

A) Recording resting membrane activity of peripheral axons
B) Measuring the speed of contraction of a muscle following electrical stimulation of a motorneuron
C) Recording evoked responses produced by electrically stimulating a motor or sensory nerve
D) Measuring the difference between nerve conduction velocities of motor and sensory nerves

Question 12

After insertion of a needle electrode during an EMG exam the examiner will cease needle movement for a period of time. Which of the following is a normal finding during this "rest" period?

A) Positive sharp waves
B) Fibrillations
C) Miniature end-plate potentials
D) Complex repetitive discharges

Question 13

An EMG exam for a patient with a neuropathic disorder demonstrates the presence of small-amplitude, polyphasic motor unit potentials. Which of the following statements is the best interpretation of this finding?

A) This is an abnormal finding indicating neuromuscular disease.
B) The patient may be recovering from the disorder.
C) Needle electrodes were not inserted near motor units in the muscle.
D) Surgery is necessary to repair the motor neuron lesion.

Question 14

Which of the following is a benefit of saltatory conduction of myelinated nerves?

A) Speed of conduction is significantly lower.
B) More space is needed for myelinated nerves to conduct impulses.
C) Conduction amplitudes are much greater and last longer.
D) Amount of energy needed to propagate a nerve impulse is considerably less.

Question 15

Which of the following patients will typically not benefit from a referral for ENMG testing?

A) Those with numbness and pain involving the sensory division of the peripheral nervous system
B) Those having weakness of the right arm and leg following a cerebrovascular accident (CVA)
C) Those having paresthesias in the left foot and toes involving the sensory division of the peripheral nervous system
D) Those having weakness of right hand grasp involving the motor division of the peripheral nervous system

Question 16

Why must an ENMG examination be delayed until about 21 days after an axonopathy?

A) Three weeks is the approximate amount of time needed for Wallerian degeneration of the nerve to proceed.
B) It takes about 3 weeks for axons to begin regeneration.
C) Anterior horn cells will restore axoplasmic flow after 21 days.
D) It takes about 3 weeks for post-injury inflammation to subside.

Question 17

An examiner performing an NCS on a patient notes that the upper extremity nerve conduction velocities are about 5 to 10 meters per second faster than the lower extremity nerves. What is the correct interpretation of this finding?

A) This indicates a neuropathy affecting only the upper extremity nerves.
B) This is an abnormal finding likely caused by practitioner error in performance of the test.
C) This indicates a neuropathy affecting only the lower extremity nerves.
D) This is a normal finding.

Question 18

Which of the following statements regarding the effect of age on the results of an NCS is true?

A) Values for children under age 7 are about twice the values of adults.
B) Values decline about 1 to 2 meters per second for each decade over age 60.
C) Age has a minimal effect on values in children and adults.
D) Normal adult values are not achieved until after age 18.

Question 19

Which of the following results of an NCS reflects a decrease in conduction velocity?

A) An increase in latency
B) Decreased compound muscle action potential (CMAP) duration
C) A decrease in latency
D) Increased CMAP amplitude

Question 20

Why are CMAPs significantly greater than sensory nerve action potentials (SNAPs)?

A) CMAPs are determined by antidromic rather than orthodromic stimulation.
B) SNAPs have fewer nerve fibers to activate compared with CMAPs.
C) Distal latencies of SNAPs are much shorter than those of CMAPs.
D) CMAPs are the summation of numerous muscle fiber action potentials.