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Flashcards in Electrodiagnosis Deck (46):
1

Myotonic discharges produce a distinctive sound on electromyography (EMG). This sound results
from

(a) spontaneous firing of motor unit action potentials (MUAPs).
(b) intermittent blocking of muscle fibers during voluntary activity.
(c) firing of just a few muscle fibers per motor unit during voluntary activity.
(d) spontaneous firing of muscle fibers

Answer: (d)
Commentary: The classic myotonic discharge of waxing and waning in frequency and amplitude is often described as either a dive-bomber or revving engine. The source generator of a myotonic potential is muscle fiber, and thus may take the form of either positive wave or a brief spike potential. Neuromyotonia and myokymia result in spontaneous firing of motor unit action potentials as opposed to muscle fiber action potentials. Intermittent blocking of some muscle fibers within a motor unit result in unstable MUAPs, which are characterized by changes in either amplitude or number of phases from potential to potential. Unstable MUAPs are seen in primary neuromuscular junction (NMJ) disorders or with new and immature NMJs, as can be seen in early reinnervation. Mypopathic MUAPs result from a decreased number of muscle fibers firing within a motor unit. These signals are seen as short-duration, small amplitude, and polyphasic potentials.


2013

2

One advantage of a concentric needle compared to a monopolar needle is its

(a) higher amplitude of motor unit action potentials(MUAPS).
(b) decreased likelihood of electrical interference.
(c) ability to vary the recording surface size.
(d) longer duration of the MUAPs.

Answer: (b)
Commentary: The shaft of a concentric needle serves as the reference electrode, whereas an additional electrode (typically a surface electrode) is needed as a reference when using a
monopolar needle. MUAPs recorded from monopolar needles are slightly longer in duration and have higher amplitude, since they record from the entire area around the needle tip rather than only from the fibers facing the bevel. Because the concentric needle shaft serves as the reference electrode, the recording surface size is fixed and interference from surrounding muscles is minimized.

2012

3

Which type of study best differentiates a severe polyradiculopathy from amyotrophic lateral
sclerosis (ALS)?

(a) Motor nerve conduction studies of upper and lower extremities
(b) Needle electromyography of thoracic paraspinals or bulbar muscles
(c) Sensory nerve conduction studies of upper and lower extremities
(d) Needle electromyography of multiple extremities


Answer (b)
Commentary: Sensory nerve conduction studies are normal in both radiculopathy and motor
neuron disease. Motor nerve conduction studies are also often normal in both diseases. Both
diseases may demonstrate abnormal needle examination in multiple extremities. Thoracic
paraspinals and bulbar muscle examinations are most helpful in differentiating severe
polyradiculopathy from amyotrophic lateral sclerosis (ALS), since one would expect these studies
to be normal in radiculopathy but may be abnormal in ALS

2011

4

In a patient with a neuromuscular junction disorder, which electrodiagnostic results for compound
muscle action potential (CMAP), motor unit action potential (MUAP) or nerve action potential
(SNAP) may be misleading if the limb is cold?

(a) Diminished CMAP decrement on repetitive nerve stimulation
(b) Diminished polyphasia of the MUAP
(c) Shortened distal latency of the CMAP
(d) Decreased amplitude of the SNAP


Answer (a)
Commentary: In neuromuscular junction (NMJ) disorders, compound muscle action potential
(CMAP) decrement may be diminished if the limb is cold, likely due to decreased functioning of
acetylcholinesterase. Cool temperatures may alter results by slowing nerve conduction velocity,
prolonging distal latency, increasing amplitude and duration of sensory nerve action potential
(SNAP) and CMAP and motor unit action potential (MUAP), increasing phases of MUAP.

2011

5

A 55-year-old overweight man presents to clinic with complaints of numbness in his left leg. He
reports that he does not exercise and has an office job. He is diagnosed with meralgia
paresthetica. Which of the following is consistent with this diagnosis?

a) Peroneal motor F-wave study is abnormal.
b) Sensory nerve conduction studies reveal decreased amplitude on the affected side.
c) Electromyography findings show denervation in the vastus lateralis.
d) Exam reveals decreased sensation in the medial thigh.


Answer: (b)
Commentary:
Meralgia paresthetica presents with paresthesias in the lateral thigh. Sensory nerve conduction
studies of the lateral femoral cutaneous nerve may show a drop in the sensory nerve action
potential (SNAP) amplitude on the affected side compared to the asymptomatic, contralateral
study. Symptoms are confined to below the inguinal ligament and above the knee. Peroneal motor
nerve conduction studies and F waves should be normal and needle electromyography should not
show acute or chronic axonal motor loss, because the lateral femoral cutaneous nerve is purely
sensory

2011

6

Myotonic discharges produce a distinctive sound on electromyography (EMG). This sound results from
(a) spontaneous firing of motor unit action potentials (MUAPs).
(b) intermittent blocking of muscle fibers during voluntary activity.
(c) firing of just a few muscle fibers per motor unit during voluntary activity.
(d) spontaneous firing of muscle fibers.

Answer: (d)
Commentary: The classic myotonic discharge of waxing and waning in frequency and amplitude is often described as either a dive-bomber or revving engine. The source generator of a myotonic potential is muscle fiber, and thus may take the form of either positive wave or a brief spike potential. Neuromyotonia and myokymia result in spontaneous firing of motor unit action potentials as opposed to muscle fiber action potentials. Intermittent blocking of some muscle fibers within a motor unit result in unstable MUAPs, which are characterized by changes in either amplitude or number of phases from potential to potential. Unstable MUAPs are seen in primary neuromuscular junction (NMJ) disorders or with new and immature NMJs, as can be seen in early reinnervation. Mypopathic MUAPs result from a decreased number of muscle fibers firing within a motor unit. These signals are seen as short-duration, small amplitude, and polyphasic potentials

2013

7

Which safety practice is the most appropriate when performing an electrodiagnostic study on a
patient in a hospital bed?

(a) The device should be turned on after the placement of electrodes on the patient.
(b) An insulated extension cord should be used to connect the power line.
(c) More than 1 ground electrode should be attached to the patient.
(d) All electrical devices in contact with the patient should share a common ground

Answer: (d)
Commentary: It is important to have all the electrical devices that are in contact with the patient
plugged into the same outlet to share a common ground. Similarly, only 1 ground electrode
should be used on the patient. To avoid power surges, the device should be turned on prior to the
application of any electrodes to the patient and turned off after the removal of electrodes.
Extension cords can increase leakage currents and should be avoided.

2010

8

Which characteristic best describes fasciculation potentials?

(a) Semirhythmic in their firing pattern
(b) Morphologically the same as motor unit potentials
(c) Produced by ephaptic conduction between single muscle fibers
(d) Randomly firing single muscle fibers

Answer: (b)
Commentary: Fasciculation potentials are spontaneously firing motor unit potentials with the
same morphologic characteristics as that of a motor unit or polyphasic action potential. They
have an irregular firing pattern usually and the site of origin is unclear. Ephaptic conduction
between single muscle fibers is thought to be the mechanism for complex repetitive discharges.
Single muscle fiber potentials are much smaller and represent units such as a fibrillation potential.

2010

9

A 37-year-old man is sent to you for electrodiagnostic assessment for right lumbosacral
radiculopathy. Nerve conduction studies of the right leg are normal. Needle exam shows the
following:

NEEDLE ELECTROMYOGRAPHY


Muscle -- Abnormal Spontaneous Activity -- Recruitment
Adductor longus 0 Normal
Vastus medialis 0 Normal
Tensor fascia lata 1+ Normal
Semimembranosus 1+ Normal
Biceps femoris (short head) 0 Normal
Tibialis anterior 2+ Reduced
Medial gastrocnemius 0 Normal
Lumbar paraspinals 1+

Which root is most likely injured?

(a) L2
(b) L3
(c) L4
(d) L5

Answer: D

Commentary: The common root among the affected muscles is L5. It is often difficult to narrow
the involvement to a single root level.


2010

10

One advantage of a concentric needle compared to a monopolar needle is its
(a) higher amplitude of motor unit action potentials(MUAPS).
(b) decreased likelihood of electrical interference.
(c) ability to vary the recording surface size.
(d) longer duration of the MUAPs.

Answer: (b)
Commentary: The shaft of a concentric needle serves as the reference electrode, whereas an
additional electrode (typically a surface electrode) is needed as a reference when using a
monopolar needle. MUAPs recorded from monopolar needles are slightly longer in duration and
have higher amplitude, since they record from the entire area around the needle tip rather than
only from the fibers facing the bevel. Because the concentric needle shaft serves as the reference
electrode, the recording surface size is fixed and interference from surrounding muscles is
minimized.

2012

11

In patients with steroid myopathy, the needle electromyographic study usually reveals
(a) small motor unit action potentials (MUAPs) with early recruitment.
(b) small MUAPs with reduced recruitment.
(c) positive waves and fibrillation potentials in proximal muscles.
(d) normal MUAPs and normal recruitment.

Answer: (d)
Commentary: Needle examination in patients with steroid myopathy usually reveals normal
insertional activity and no abnormal spontaneous activity. Motor unit potential morphology and
recruitment do not reveal any abnormalities. This combination occurs because in steroid
myopathy the type 2 muscle fibers are preferentially affected, in contrast to the first-recruited
type 1 fibers.

2012

12

78. Which finding would you expect in a 35-year-old man with type 1 hereditary motor sensory
neuropathy?
(a) Absence of ankle reflexes
(b) Pes planus
(c) Motor nerve conduction velocity slowing, with evidence of temporal dispersion
(d) Absence of electromyographic spontaneous activity

Answer: (a)
Commentary: Hereditary motor sensory polyneuropathy type 1 (HMSN-1, the demyelinating
form of Charcot-Marie-Tooth disease) presents in young adult life with insidious onset of distal
weakness and sensory loss. Clinically, it typically presents with pes cavus, hammertoes and foot
drop. Ankle reflexes are absent. Temporal dispersion would indicate an acquired, not hereditary,
process. Secondary axonal loss is expected, which would result in positive waves and
fibrillations.

2012

13

Cooling can produce physiological changes in the body. One of these changes is an increase in
(a) nerve conduction rate.
(b) stretch receptor sensitivity.
(c) elasticity of connective tissue.
(d) general sympathetic activity.

Answer: (d)
Commentary: Nerve conduction rate is slowed by cooling. The stretch receptor sensitivity in
muscles and tendons is reduced, and the elasticity of connective tissue diminishes with cooling.
The general sympathetic activity is increased with cooling of the body, and this may affect the
responses of the stretch receptors in a beneficial way.

2012

14

A 33-year-old woman who had a prolonged labor 6 weeks ago, reports pain in the groin radiating
along the medial aspect of the thigh. Needle electromyographic exam shows evidence of
denervation in the gracilis and adductor muscles. Most likely she has a lesion in the
(a) femoral nerve.
(b) obturator nerve.
(c) sciatic nerve.
(d) genitofemoral nerve.

Answer: (b)
Commentary: The nerve common to the affected muscles is the obturator nerve. There is some
innervation of the adductor magnus by a branch off the sciatic nerve, but the gracilis, adductor
brevis, and adductor longus are supplied by the obturator nerve. Injuries of the obturator nerve are
uncommon, but one cause in such cases is compression of the nerve between the fetal head and
the pelvic wall during prolonged labor.

2012

15

What do fibrillation potentials represent?

A. Spontaneous depolarization of the muscle fiber
B. Demyelination of peripheral nerves
C central nervous system pathology
d activation of the motor unit

A is correct

Fibrillation potentials are simply spontaneous depolarizations of a single muscle fiber seen in pathologic tissue and are often elicited with needle movement while performing electromyography (EMG). Fibrillation potentials are seen in neurogenic conditions with acute or chronic axonal loss, but also in myopathic disease. Fibrillations are not characteristic for central nervous system disease states or conduction block. Conduction block is evaluated on nerve conduction studies. However, fibrillations could be seen in cases of conduction block if axonal loss has occurred as well.

2014

16

A 35-year-old man presents with left foot drop due to a fracture of his left tibia in a motor vehicle crash. He is stable after reduction and plating. Since the surgery, he has weakness in his left leg and numbness along the dorsum of his foot. Electrodiagnostic testing yields the following results:

MOTOR NERVE CONDUCTION STUDIES (Normal values are in parentheses)

Nerve
Stimulation Site
Distal Latency (ms)
Amplitude (mV)
NCV (m/s)

L Peroneal (EDB)
Ankle
4.4 (≤ 5.5)
5.1 (≥ 3.5)
Below fibular head
4.8 (≥ 3.5)
46 (≥ 40)
Knee
2.1 (≥ 3.5)
34 (≥ 40)

L Tibial (AH)
Ankle
5.2 (≤ 6.0)
10.4 (≥ 3.5)
Popliteal fossa
9.8 (≥ 3.5)
45 (≥ 40)

R Peroneal (EDB)
Ankle
4.6 (≤5.5)
4.8 (≥ 3.5)
Below fibular head
4.7 (≥ 3.5)
44 (≥ 40)
Knee
4.7 distal latency
4.4 (≥ 3.5)
49 (≥ 40)

Abbreviations: EDB,extensor digitorum brevis; AH, abductor hallucis; NCV, nerve conduction velocity

SENSORY NERVE CONDUCTION STUDIES (Normal NCS values are in parentheses)

Nerve
Stimulation site
Recording Site
Distal Latency (ms)
Amplitude (µV)


L Superficial peroneal
Leg - 12 cm
Anterior ankle
3.3 (≤ 3.5)
4 (≥ 20)

R Superficial peroneal
Leg - 12 cm
Anterior ankle
3.2 (≤ 3.5)
21 (≥ 20)

L Sural sensory
Calf - 14 cm
Ankle
3.9 (≤ 4.4)
10 (≥ 8)

NEEDLE ELECTROMYOGRAPHY


Muscle
Abnormal Spontaneous Activity
Recruitment

L Tensor fascia lata
0
Normal

L Biceps femoris, long head
0
Normal

L Biceps femoris short head
0
Normal

L Anterior tibialis
2+
Reduced

L Peroneal longus
2+
Reduced

L Tibialis posterior
0
Normal

L Gastrocnemius
0
Normal

L Vastus medialis
0
Normal

L Lumbar paraspinals
0
Normal

R Anterior tibialis
0
Normal

R Gastrocnemius
0
Normal

R Vastus medialis
0
Normal

What injury do these test results reveal?

Option d is correct.

This patient presents with a left common peroneal mononeuropathy following a surgical procedure. There is evidence of focal slowing with partial conduction block at the fibular head and an abnormal superficial peroneal sensory NCS compared to the contralateral side. These findings would imply a compressive injury at the fibular head. Furthermore, needle EMG reveals abnormal spontaneous activity in muscles distal to the fibular head innervated by the branches of the left common peroneal nerve (superficial peroneal and deep peroneal nerves). The tibial nerve conduction studies are completely normal.

2014

17

Positive sharp waves and fibrillation potentials are most likely to be seen in which condition?

A Anterior horn cell disease
B Steroid myopathy
C Small fiber neuropathy
D Cerebellar ischemia

Option A is correct

Positive sharp waves (PSWs) and fibrillation potentials are seen in certain disorders of the muscles, neurogenic disease, and neuromuscular disorders. These may include but are not limited to inflammatory myositis, inclusion body myositis, rhabdomyolysis, anterior horn cell disorders, radiculopathies, plexopathies, peripheral neuropathies, myasthenia gravis, and botulism. Steroid myopathy does not result in muscle necrosis and thus abnormal spontaneous activity is not observed. Fibrillation potentials and PSWs are not characteristic for central nervous system pathology. Small fiber neuropathies will be undetected on needle EMG.

2014

18

Which statement is most correct regarding instrumentation for electrodiagnostic studies?

a. Signals pass from the filters to the amplifiers.
b.Cathode-ray tube subtracts common electrical activity.
c.Electrical signals are transmitted from 2 surface electrodes.
d Filters are used to increase the electrical noise.

Option c is correct.

Electrical signals are transmitted from skin surface electrodes or through a needle. These electrodes are referred to as E1 and E2 or the active and the reference. Differential amplifiers eliminate signal common to the 2 electrodes. Filters are used to remove excessive electrical noise after signal amplification. Cathode-ray tube permits the visual display of the electrical signal as a waveform.

2014

19

A 25 year old patient presents for electrodiagnostic testing after sustaining a right shoulder injury following a motorcycle crash 4 weeks ago. He has no active elbow, wrist or finger extension. The needle examination of the radial innervated muscles shows normal insertional activity, no abnormal spontaneous activity and absent motor recruitment. In the Sunderland classification system, this nerve injury is best described as?

a. myelin injury with no Wallerian degeneration
b. Wallerian degeneration with preservation of endoneurium
c. disruption of axon with intact perineurium
d complete discontinuity of the nerve

Option a is correct.

The injury described is limited to the myelin with preservation of the axon. This type of injury is classified as neurapraxia by the Seddon classification and as type 1 by the Sunderland classification. In axonal injury, one would typically observe positive sharp waves and fibrillation potential within 3 weeks after the injury. Sunderland type 2 and 3 are both forms of axonal injury and differ in their extent of injury to the supporting neural structures. Sunderland type 2 and 3 are classified as axonotmesis by the Seddon classification. Complete discontinuity of the nerve is classified as type 5 Sunderland and as neurotmesis by Seddon.

2014

20

Which electrodiagnostic finding is most consistent with neurogenic thoracic outlet syndrome?

(a) Small median motor response from the thenar muscles
(b) Abnormal response of the lateral antebrachial cutaneous nerve
(c) Abnormal median sensory responses
(d) Abnormal spontaneous activity in the pronator teres muscle

Answer: B
Commentary: Neurogenic thoracic outlet syndrome involves the lower trunk of the brachial
plexus; hence, sensory and motor loss develops in the C8–T1 distribution. Thumb abduction is
often affected. Sensory changes are usually in the distribution of the ulnar and medial
antebrachial cutaneous nerves

2009

21

Which electrodiagnostic criterion is included in the diagnosis of peripheral nerve demyelination?

(a) Conduction velocity reduced in at least 4 nerves
(b) Compound muscle action potential conduction block in at least 3 nerves
(c) Prolonged distal motor latencies in at least 4 nerves
(d) Prolonged F-wave latency or absent F wave

Answer: D
Commentary: The criteria require conduction velocity to be reduced in 2 or more nerves,
compound muscle action potential conduction block or abnormal temporal dispersion in 1 or more nerves, prolonged distal motor latencies in 2 or more nerves, and prolonged F wave or absent F wave. Three of these four criteria must be present.

2009

22

A 22-year-old woman with complaints of fluctuating weakness and abnormal fatigability that
improves with rest is sent for electrophysiologic testing. Which electrophysiologic finding on
routine testing would be most consistent with this clinical presentation?

(a) Small sensory nerve action potentials
(b) Slow motor nerve conduction velocities
(c) Variability in motor unit action potential amplitude
(d) Small compound muscle action potentials

Answer: C
Commentary: This patient’s presentation is most consistent with myasthenia gravis. The
incidence of this condition is bimodal and affects women more than men in the younger age
group. When one suspects myasthenia gravis the test of choice is repetitive stimulation.
However, it is still important to assess for other possible problems and routine nerve conduction
and needle electromyographic examination should be performed. The sensory component of the peripheral nervous system lacks a neuromuscular junction and hence the sensory responses
should be normal. Motor amplitudes can be small, but this is usually only in severe cases. Motor
conduction velocities are normal, since this study assesses the conduction along the motor fibers.
Motor unit action potential amplitude variability is a characteristic abnormality observed during
routine electromyography in patients with neuromuscular junction disorders. This finding is due
to the variability in the total number of single muscle fibers being activated at any single time.

2009

23

Following repair of a right distal biceps tendon rupture, a 31-year-old construction worker
presents with problems extending his fingers. He had noticed swelling in the arm and forearm
before his cast was removed about 4 weeks ago. He does not have any sensory complaints and the
right superficial radial sensory nerve action potential is normal. Needle exam shows these data:
 


Muscle

Abnormal
Spontaneous
Activity

Recruitment


R Triceps 0 Normal
R Biceps 0 Normal
R Brachioradialis 0 Normal

R Extensor digitorum
communis
2+ Reduced

R Extensor indicis
proprius
2+ Reduced

R Flexor carpi ulnaris 0 Normal
R 1st dorsal
interosseous
0 Normal

R Extensor carpi
radialis
0 Normal

R Supraspinatus 0 Normal
R Cervical paraspinals 0 --
 
This patient most likely has a right

(a) radial mononeuropathy at the elbow.
(b) posterior interosseous neuropathy.
(c) posterior cord plexopathy.
(d) C7 and/or C8 radiculopathy

Answer: B
Commentary: The electrophysiologic findings are consistent with involvement of the right
posterior interosseous nerve (PIN). Typically in PIN injuries the triceps, brachioradialis, and
extensor carpi radialis longus/brevis muscles are spared.

2009

24

A 14-year-old girl is sent to you for electrodiagnostic evaluation of a left foot drop. The mother reports that the left foot drop has been present for about 2 months and that her daughter has lost about 40 pounds in the last 6 months. Nerve conduction studies and needle electromyography show the following data:

MOTOR NERVE CONDUCTION STUDIES
Nerve
Stimulation Site
Distal Latency (ms)
Amplitude (mV)
NCV (m/s)

L Peroneal
Ankle
4.2
1
Below knee
0.5
35
Above knee
NR

R Peroneal
Ankle
4.5
5.4
Below knee
5.0
47
Above knee
4.8
52

L Tibial
Ankle
4.4
9
Knee
8.5
53

SENSORY NERVE CONDUCTION STUDIES
Nerve
Stimulation Site
Distal Latency (ms)
Amplitude (μV)

L Sural
Ankle - 14 cm
3.6
17

L Superficial peroneal
Ankle - 12 cm
NR

R Superficial peroneal
Ankle - 12 cm
3.1
15

Needle Electromyography
Muscle
Abnormal Spontaneous Activity
Recruitment

L Vastus medialis
0
Normal

L Semimembranosus
0
Normal

L Short head of biceps femoris
0
Normal

L Tibial anterior
3+
Reduced

L Medial gastrocnemius
0
None

L Peroneus longus
2+
Reduced

L Lumbar paraspinals
0
--

NCV = Nerve Conduction Velocity
NR = No response


The patient’s symptoms are most likely due to left
(a) peroneal nerve injury at the fibular head.
(b) deep peroneal nerve injury.
(c) sciatic nerve injury.
(d) lumbosacral plexopathy.

(a)
The electrophysiologic findings are consistent with common peroneal nerve compression at the fibular head. The normal study of the short head of the biceps femoris points to a lesion distal to the innervation of this muscle, and hence a lesion at or below the level of the knee. Lack of involvement of muscles innervated by other nerves points away from a plexopathy or sciatic nerve injury. Excessive weight loss can often be a factor in patients with peroneal nerve compression lesions.
Ref: Dumitru D, Zwarts MJ. Focal peripheral neuropathies. In: Dumitru D, Amato AA, Zwarts

2008

25

how do you determine duration of MUAP

(c)
The total duration of a motor unit is measured from the initial deflection from baseline to the final return to baseline.

2008

26

While recording an antidromic sensory nerve action potential, you increase the distance between the active and reference electrode from 1cm to 4cm by moving the reference electrode. What is the effect on the onset latency and peak latency?

Onset Latency
Peak Latency

(a)
No change
Increase
(b)
Increase
No change
(c)
Decrease
Decrease
(d)
Increase
Increase

(a)
Increasing the interelectrode distance from 1 cm to 4 cm does not alter the onset latency, but increases the peak latency and amplitude of the sensory response. The onset latency does not change because the active electrode position is not changed. The sensory nerve action potential amplitude increases because less of the information is eliminated by differential amplification. Similarly, the peak latency also is prolonged as less of the signal is eliminated.

2008

27

A 65-year-old man is sent to you for electrodiagnostic assessment of his right facial droop. He presented to his internist 4 weeks ago with right facial pain and weakness, and decreased hearing. He was treated with high dose steroids without any improvement. His nerve conduction studies are as follows:

Nerve
Distal Latency (ms)
Amplitude (mV)

R Facial
3.5
0.8

L Facial
3.2
2.2

Blink Reflex
Recording
R1 (ms)
R2 (ms)

R Trigeminal
Right
Absent
Absent
Left
--
33

L Trigeminal
Right
--
Absent
Left
11.5
35

R1 – early component
R2 – late component
These findings are most consistent with right
(a) facial nerve lesion.
(b) trigeminal nerve lesion.
(c) pons lesion.
(d) lateral medulla lesion.

(a)
The blink reflex study has two responses, an early component (R1) and a late component (R2). The absence of the right R1 and R2 responses, but normal left R2 responses suggests a lesion affecting the right facial nerve. Additionally, the small right facial nerve response with direct stimulation suggests distal facial nerve degeneration. In a lesion involving the trigeminal nerve both R2 responses would be abnormal. In a pons or lateral medulla lesion the direct facial nerve response would be normal.

2008

28

A 17 year old woman was involved in a motor vehicle crash 4 months ago. She suffered a shoulder dislocation. Electromyographic studies have confirmed a brachial plexus injury to her posterior cord and indicate nerve continuity (Sunderland 2 injury). Although she has completed 4 weeks of occupational therapy, she has had no improvement in her strength from baseline. Your next step would be to
(a) reassure the patient and continue to monitor for improvement.
(b) continue occupational therapy for 4 additional weeks.
(c) initiate neuromuscular electrical stimulation to the affected muscles.
(d) refer the patient to neurosurgery for exploratory surgery.

(d)
With closed nerve injury as described, early active and passive range of motion (ROM) therapy of the affected joints is begun. The value of electrical stimulation is uncertain. The purpose of surgical repair is to improve peripheral nerve recovery and eventual function. Therefore, surgery is done when the patient has an incomplete loss of function but shows no improvement over several weeks, or no return of function at 2 months for peripheral nerve and 4 months for a brachial plexus injury. Findings at the time of surgery help establish a prognosis. However, the chances of successful surgical repair begin to decline by 6 months after the injury. By 18--24 months, the denervated muscles usually are replaced by fatty connective tissue, making functional recovery impossible.

2008

29

In patients with radiculopathy, how long does it take for morphologic changes of increased duration and amplitude to occur in the motor unit action potentials?
(a) 1 day
(b) 1 week
(c) 3 weeks
(d) 6 weeks

(d)
Reduced recruitment may be seen day 1. Positive waves may be seen in the paraspinals as early as 1 week, and positive waves and fibrillations may be seen in the extremities by 3–5 weeks, but, because of reinnervation by axon sprouting, it takes at least 6 weeks to see increased amplitude and duration of muscle activity.

2008

30

High frequency electrical stimulation predominantly stimulates which type of muscle fiber?

(a) Type 1
(b) Type 2
(c) Type 3a
(d) Type 3b

(b) Low frequency electrical stimulation predominantly stimulates type 1 muscle fibers. High frequency
electrical stimulation predominantly stimulates Type 2 muscle fibers. There are no type 3 muscle fibers.

2008

31

When performing needle electromyography in someone therapeutically anticoagulated with
warfarin, which muscle would be the safest to examine?
(a) Tibialis posterior
(b) Paraspinal muscles
(c) Deltoid
(d) Flexor pollicis longus

Commentary: Although needle EMG is generally safe in patients taking warfarin, whenever
bleeding risk is increased it is best to limit the needle examination to a few superficial muscles,
where prolonged compression can be performed if necessary. The pronator teres and tibialis
posterior are deep muscles in which, theoretically, a hematoma could develop. It is also best to
avoid needle insertion into areas where possible hematoma could compress a nerve or artery, such
as exiting spinal nerves near paraspinals or the radial artery near the flexor pollicis longus.
2011

32

A 40-year-old man presents with a gradual onset of painful distal paresthesias while playing
soccer. He feels clumsy and is falling more frequently. He has no known significant past medical
history. Physical exam demonstrates normal symmetric strength throughout his upper and lower extremities, normal vibration sensation and normal Romberg testing. His electrodiagnostic exam
results are as follows:

MOTOR NERVE CONDUCTION STUDIES*
Nerve Stimulation Site Distal Latency(ms)
Amplitude(mV)
NCV (m/s)

R Fibular (Peroneal) Ankle 6.1 (≤ 6.5) 2.0 (≥2.0)
Below knee 1.9 41 (≥40)
Above knee 1.9 41

L Fibular (Peroneal) Ankle 6.0 (≤ 6.5) 2.1 (≥2.0)
Below knee 2.0 40 (≥40)

R Tibial Ankle 6.1 (≤ 6.1) 3.0 (≥3.0)
Knee 2.9 42 (≥40)

R Median Wrist 4.4 (≤ 4.4) 5.2 (≥4.0)
Elbow 5.2 49 (≥49)
R Ulnar Wrist 3.5 (≤ 3.5) 7.0 (≥6.0)
Below elbow 6.9 49 (≥49)
* Normal values are in parentheses
Abbreviation: NCV, nerve conduction velocity; R, right; L, left.

SENSORY NERVE CONDUCTION STUDIES*
Nerve Distal Latency (ms) Amplitude (μV)

R Sural NR NR
L Sural NR NR
R Median 3.9 (≤ 3.7) 12.0 (≥20.0)
R Ulnar 3.9 (≤ 3.5) 5.0 (≥15.0)
* Normal values are in parentheses
Abbreviations: NR, nonresponsive; R, right; L, left.

NEEDLE ELECTROMYOGRAPHY
Muscle Spontaneous
Activity
Recruitment
R Gluteus medius 0 Normal
RVastus medialis 0 Normal
R Tibialis anterior 0 Normal
R Medial gastrocnemius 0 Normal
R Extensor hallicus longus 1+ Normal
R First dorsal interosseous (Pedis) 2+ Reduced
L First dorsal interosseous (Pedis) 2+ Reduced
R Pronator teres 0 Normal
R Abductor pollicus brevis 0 Normal
R First dorsal interosseous (Hand) 0 Normal

In addition, F waves were mildly prolonged in all motor nerves tested. His history and exam is
most consistent with a diagnosis of sensorimotor neuropathy due to
(a) diabetes or glucose intolerance.
(b) uremic disease.
(c) chronic inflammatory demyelinating polyradiculopathy.
(d) hereditary motor sensory neuropathy

Answer: (a)
Commentary: Diabetic neuropathy electrophysiological exam may demonstrate sensory nerve
conduction study abnormalities with normal motor nerve conduction studies but positive
fibrillation potentials distally on needle examination. In this case, motor nerve conduction studies
are borderline normal. It is likely that had F waves been obtained they would be mildly
prolonged. A neuropathy due to uremic disease would likely demonstrate pronounced conduction
slowing and low amplitude responses in sensory and motor nerves, and likely would not be
undiagnosed prior to the presentation described in the scenario. Chronic inflammatory
demyelinating polyradiculopathy (CIDP) and hereditary motor sensory neuropathy (HMSN-1)
represent demyelinating processes, and there is no evidence of this finding in the results.

2011

33

Which description best localizes the extensor indicis proprius muscle (with the forearm fully pronated) for needle electrode examination?
(a) Junction of the upper and middle third of the forearm between the radius and ulna
(b) Four fingerbreadths proximal to the wrist and directly over the ulnar side of the radius
(c) Two fingerbreadths proximal to the ulnar styloid and just radial to the ulna
(d) Mid-forearm along the radial border of the ulna

(c) Answer (a) describes the location of the extensor digitorum communis muscle; answer (b) describes the location of the extensor pollicis brevis muscle; and answer (d) describes the location of the extensor pollicis longus

2007

34

Blink reflex studies can be useful in diagnosing which condition?
(a) Neuromuscular junction disorder
(b) Axonal neuropathy
(c) Motor neuron disease
(d) Midpontine lesion

(d) Blink reflex studies can help assess facial and trigeminal nerve lesions, as well as central lesions in the brain stem. Neuromuscular junction disorders are better assessed by repetitive studies. Axonal neuropathies rarely affect the blink reflex, but demyelinating peripheral neuropathy can affect all potentials of the blink reflex study. Motor neuron disorders such as amyotrophic lateral sclerosis do not typically affect the blink reflex

2007

35

A 55-year-old man presents with a 2-month history of progressive weakness. On examination he has mild proximal weakness in the upper and lower limbs. His muscle tone and bulk are normal and he has no facial weakness. Sensation is normal and deep tendon reflexes are 1+ and symmetrical. Which finding on electrodiagnostic testing is most consistent with this patient’s presentation?
(a) Prolonged or absent F waves
(b) Decreased recruitment ratio
(c) Motor unit potentials with amplitudes of 10 millivolts
(d) Normal number of phases of the motor unit potentials

(b) The clinical presentation is most consistent with a myopathic picture. In myopathies the recruitment ratio is usually lower (

36

A 17-year-old female was involved in a motor vehicle crash 4 months ago. She sustained a shoulder dislocation. Electromyographic studies have confirmed a brachial plexus injury to her posterior cord and indicate nerve continuity. Although she has completed 4 weeks of occupational therapy, she has had no improvement in her strength from baseline. Your next step would be to
(a) reassure the patient and continue to monitor for improvement.
(b) continue occupational therapy for 4 additional weeks.
(c) initiate neuromuscular electrical stimulation to the affected muscles.
(d) refer her to neurosurgery for exploratory surgery.

(d) With closed nerve injury as described, early active and passive range of motion exercise of affected joints is begun. The value of electrical stimulation is uncertain. Surgery is done when there is an incomplete loss of function but no improvement over several weeks or no return of function at 2 months for peripheral nerve and 4 months for a brachial plexus injury. The purpose of surgical repair is to improve peripheral nerve recovery and eventual function. Findings at the time of surgery help establish a prognosis. However, the chances of successful surgical repair begin to decline by 6 months after the injury. By 18 to 24 months, the denervated muscles usually are replaced by fatty connective tissue, making functional recovery impossible

2007

37

What parameter of the motor unit action potential (MUAP) is the most sensitive to the distance between the generator source and recording electrode?
(a) Amplitude
(b) Phases
(c) Firing rate
(d) Duration

(a) The amplitude is primarily influenced by the distance between the electrode’s recording surface and the electrical generator. The duration is a highly stable and reliable parameter of the motor unit. The other parameters are not affected by the distance

2007

38

Which muscle fiber is characterized by fast-twitch oxidative metabolic properties?
(a) Type 1
(b) Type 2a
(c) Type 2b
(d) Type 3

(b) Humans have 2 primary types of muscle fiber. They are divided according to many different characteristics, including speed of contraction and sources of fuel. Type 1 muscle fibers are slow-twitch with oxidative metabolic pathways. Type 2 muscle fibers are fast-twitch fibers. The type 2 fibers can then be further divided into fast-twitch oxidative (type 2a) and fast-twitch glyclolytic (type 2b). There are no muscle fibers designated as type 3.

2007

39

A 23-year-old man is sent to the electrophysiology laboratory for evaluation of bilateral foot drop.
His history is significant for recent treatment of Hodgkin’s lymphoma with surgery and
chemotherapy. Which electrophysiologic finding is most consistent with a polyneuropathy
secondary to vincristine use?
(a) Reduced conduction velocity of the motor nerves
(b) Absent sensory responses with preserved motor responses
(c) Small amplitude motor and sensory responses
(d) Motor and sensory conduction block

(c) Vincristine causes an axonal polyneuropathy that primarily affects the most distal aspects of thenerve and produces a sensorimotor polyneuropathy. Nerve conduction studies reveal small amplitude or absent motor and sensory responses

2006

40

A 10-year-old boy suffered a blunt injury to his arm with resultant wrist drop. Electrophysiologic
studies done on the day of injury show normal nerve conduction studies in the nerves in the affected
limb except for the radial nerve. The radial nerve responses are normal distally but with stimulation
proximal to the site of injury responses are absent. Which finding is most consistent with a good
prognosis for recovery?
(a) Normal radial motor response with stimulation distal to the injury on day 5
(b) Normal radial sensory response with stimulation distal to the injury on day 5
(c) Absence of fibrillation potentials in the radial innervated muscles on day 5
(d) Presence of fibrillation potential in the radial innervated muscles on day 15

(a) It is difficult to differentiate between neurapraxia (good prognosis for recovery) and axonotemesis (poorer prognosis for complete recovery) immediately postinjury using electrophysiologic testing.
The compound muscle action potentials (CMAPs) are normal with stimulation distal to the lesion initially for the first 2 to 3 days. In lesions involving the axons, the CMAPs drop significantly, reaching a nadir at about day 7. In contrast, the CMAPs remain the same size with distal stimulation in lesions that only produce conduction block. Similar changes are noted in the amplitudes of the
sensory nerve action potentials (SNAPs); however, the amplitudes are unaffected for the first 5days, and then progressively fall over the next 4 to 5 days. If axonal damage exists, the needleelectrode examination usually does not show fibrillation potentials until 2 to 3 weeks after the
injury.

2006

41

A patient with a history of cervical cancer treated with pelvic radiation is sent to the
electrodiagnostic laboratory for assessment of a suspected lumbosacral plexopathy (LSP). Which
feature would more likely be seen in recurrent neoplasm than radiation plexopathy as the cause of
the LSP?
(a) Membrane instability shown by needle electrode examination
(b) Weakness in the distal muscles of the affected limb
(c) Decreased amplitude of the sensory nerve action potentials
(d) Deep aching pain locally presenting within 3 months of treatment

(d) Neoplasm is a common cause of lumbosacral plexopathy (LSP). Usually it is from direct extension
of tumor from nearby regions. Patients with tumor extension usually present initially with pain, both locally and in a radicular pattern. Radiation induced LSP usually results in proximal weakness without any pain or with little pain and most commonly present years after treatment is completed. Membrane instability, distal weakness, and decreased motor and sensory responses can be seen
both in tumor recurrence and in radiation induced LSP.

2006

42

A 45-year-old woman presents with a 2-week history of left leg weakness and paresthesias in the left leg for about 1 month. Examination reveals 4/5 strength with left foot dorsiflexion and plantar
flexion, and 4+/5 strength with left knee flexion. Strength otherwise is 5/5 in the left lower
extremity. Her nerve conduction and needle examination findings are as follows.


MOTOR NERVE CONDUCTION STUDIES
Nerve Stimulation Site Distal Latency (ms) Amplitude (mV) NCV (m/s)

L Peroneal Ankle 4.5 4.4 ---
Below knee -- 4.1 48
Above knee -- 3.8 51

R Peroneal Ankle 4.2 5.9 --
Below knee -- 5.5 52
Above knee -- 5.1 55

L Tibial Ankle 4.4 7.0 --
Knee -- 6.5 53

R Tibial Ankle 4.6 8.6 --
Knee -- 8.1 55

SENSORY NERVE CONDUCTION STUDIES
Nerve Stimulation Site Distal Latency (ms) Amplitude (μV)

L Sural Ankle - 14 cm 3.6 8
R Sural Ankle - 14 cm 3.7 17
L Superficial peroneal Ankle - 12 cm 3.2 6
R Superficial peroneal Ankle - 12 cm 3.1 15

NEEDLE ELECTROMYOGRAPHY
Muscle
Abnormal
Spontaneous
Activity Recruitment

Adductor longus 0 Normal
Quadriceps femoris 0 Normal
Iliopsoas 0 Normal
Semimembranosus 1+ Reduced
Biceps femoris (shorthead) 1+ Reduced
Tibialis anterior 2+ Reduced
Extensor hallucis longus 2+ Reduced
Medial gastrocnemius 2+ Reduced
Tibialis posterior 2+ Reduced
bTensor fascia latae 0 Normal
Gluteus maximus 0 Normal
Lumbar paraspinals 0

These findings are most consistent with a lesion located
(a) in the spine.
(b) between the spine and hip.
(c) between the hip and distal thigh.
(d) between the distal thigh and ankle.

(c) The lesion is in the sciatic nerve affecting both the tibial and peroneal nerves. The lesion is distal to
the origin of the gluteal nerves. The femoral nerve is not involved. The left lower extremity motor
and sensory studies are normal but compared to the right side reveal small amplitude responses

2006

43

While performing an electrodiagnostic study for suspected carpal tunnel syndrome, you notice that the median, ulnar, and radial sensory NCS demonstrates prolonged peak latencies with increased sensory nerve action potential (SNAP) amplitudes and durations. What should be evaluated next?

A. Additional nerve conduction studies of the lower extremity
B. F responses on the median and ulnar nerves
C. Limb temperature
D. Needle electromyography (EMG)

C.

Prolonged peak (or distal) latency with increased SNAP (or CMAP) amplitudes may be an indicator of cool limb temperatures. This should not be confused with a demyelinating process affecting the peripheral nervous system. The effects of a cool limb include slow nerve conduction velocity, prolonged distal and peak latencies, increased amplitude and duration of SNAPs and CMAPs, and increased duration, amplitude, and phases of MUAPs. Distal limb temperatures should be recorded and ideally maintained between 33 and 34 degrees Celsius. Additional nerve conduction studies of the lower limb, F responses of the upper limb, or the needle electromyography (EMG) would not be the appropriate first intervention; however, these studies may be necessary if abnormalities exist even after temperature correction and if true peripheral nerve pathology is suspected.

2015

44

Which phenomenon occurs when an axon is depolarized?

a. The intracellular region becomes more negatively charged.
b. sodium channels open, allowing sodium to rush out of the axon.
c. large anions and potassium permeate into the axon.
d. sodium movement is driven by electrical and concentration gradients.

D

The resting potential is about -90 millivolts. With depolarization an influx of sodium occurs, driven by both an electrical and concentration gradient. This sodium influx results in the axon becoming more postively impermeable to sodium ions in the resting state. The concentration of sodium is higher outside the membrane, whereas the potassium concentration is higher inside.

2015

45

When comparing the CMAP latency with the latency of the F response, which finding is most likely to occur as you move the stimulating electrode to a more proximal location in the limb?

a. Both CMAP and F-response latency will decrease
b. Both CMAP and F-response latency will increase.
c. CMAP

c

The F response is a late response that becomes evident after the CMAP response. The F response is derived from an antidromic stimulation of a peripheral nerve that propagates an impulse proximally to the anterior horn cells of the spinal cord and returns an orthodromic response to the distal muscle. The F response is a pure motor response creating a small action potential representing 1% to 5% of the muscle fibers. Moving the stimulator proximally shortens the distance to the spinal cord's anterior horn cells. Consequently, the F response latency decreases as you increase the distance from the distal muscle pick up site, and the CMAP amplitude or direct motor potential latency increase.

2015.

46

Small muscle motor units:

a. are recruited after large motor units
b. have fewer muscle fibers
c. have a higher threshold of recruitment
d. have large cross sectional areas.

b

the muscle motor unit size principle states that smaller motor units are recruited prior to large motor units. Further, smaller motor units have fewer muscle fibers, lower threshold and recruitment and smaller cross sectional areas.

2015.