EMG/NCV

Question 1

Define EMG

Answer 1

Recording of spontaneous and voluntary motor unit activity to examine the integrity of muscle and nerve.

Question 2

Define Nerve Conduction Velocity (NCV)

Answer 2

Measurement of the speed of transmission of a motor or sensory impulse along a nerve.

Question 3

Define motor unit

Answer 3

Single motor neuron and all the muscle fibers that innervate it

Question 4

In what order are the musle fibers being recorded in an EMG?

Answer 4

Muscle fibers closer to the electrodes will be recorded first, the ones away will be recordings further out

Question 5

Motor Unit potential characteristics: Typically single Motor unit potentials are which wave forms: __ and __

Answer 5

biphasic or triphasic, one phase for each time the potential crosses the baseline

Question 6

Motor Unit potential characteristics: What does it represent?

Answer 6

It represents the activity of the muscle fibers of a single motor unit

Question 7

Motor Unit potential characteristics: The entire duration is on the scale of what?

Answer 7

milliseconds

Question 8

What factors influence the size, shape and duration of the MUAP? Name 6 of them.

Answer 8

1) Distance between electrodes
2) Location of electrodes
3) Size of electrodes
4) Size of motor unit and dispersion of fibers
5) Depth of motor unit and distance from electrodes
6) Asynchrony of contraction of muscle fibers in MU.

Question 9

Normal EMG: What do you expect with insertion activity?

Answer 9

• Disruption of muscle membrane
• Some insertional activity is normal
• Duration up to 300 msec

Question 10

Normal EMG: After the insertion activity, what happens next?

Answer 10

Electrical silence at rest in normal motor units

Question 11

Normal EMG: After electrical silence at rest, what next?

Answer 11

-Have patient perofrm a minimal contraction “think about contracting your muscle”

Question 12

Normal EMG parameters: Amplitude, Duration, Frequency, type of waves (name a % for one type of the waves) with minimal voluntary contraction?

Answer 12

Amplitude - 300 uV - 5mV
Duration: 3-16 msec
Freq. - 5-15 /sec
Biphasic or triphasic (<10% polyphasic)

Question 13

Normal EMG parameters: After a single motor unit-minmal effort, what comes next?

Answer 13

-moderate effort-recruitment

Question 14

Normal EMG parameters: In a moderate effort-recruitment, why does the interference pattern start to fill in and the amplitude starts increasing?

Answer 14

• More units are being recruited -> larger ones
• firing frequency increases
• some summation is happening as some units are firing at the same time as others

Question 15

Normal EMG parameters: When does the normal interference pattern become full?

Answer 15

Becomes full with maximum effort

Question 16

Name 3 causes of neuropathies

Answer 16

1) Acquired, genetic
2) Metabolic, age-related
3) Traumatic, compressive, stretch, cut

Question 17

Abnormal EMG: How does the Insertion Activity look like? Why?

Answer 17

Prolonged because muscle membrane becomes unstable so with the stimulation of the needle there is excessive exchange of ions across the muscle membrane

Question 18

Abnormal EMG: At rest, what is the EMG portion called?

Answer 18

-Spontaneous potentials

Question 19

Abnormal EMG: Spontaneous Potentials-What are the two types of waves and which direction do they go?

Answer 19

1) Fibrillation potentials -> up (- direction)

2) Postive sharp waves -> down (+ direction)

Question 20

Abnormal EMG: Spontaneous Potentials-What does the wave represent? What are these waves caused by?

Answer 20

• The wave represents depolarization of single muscle fibers, not whole motor units.
• These potentials are probably caused by spontaneous release of Ach.

Question 21

What are Fasiculations?

Answer 21

Wave forms that represent contraction of a group of muscle fibers.

Question 22

Fasciculations: When can they occur? What % of observed potentials are these seen?

Answer 22

• Can occur in normal, fatigued muscle

- Can be present in normal individuals in a relatively small number (<10% of observed potentials)

Question 23

Fasciculations: Increased # of fasiculations can be a sign of what?

Answer 23

-SIgn of pathology in certain disease states

Question 24

Fasciculations: They are a diagnostic finding in which disease?

Answer 24

• Amyotrophic lateral sclerosis (ALS)

- both the upper motor neurons and the lower motor neurons degenerate or die, and stop sending messages to muscles.

Question 25

Denervated Muscle: Will you see any activity in a partially denervated muscle with minimal contraction?

Answer 25

Yes, you may see some normal MUAP with minimal contraction, but will see fewer

Question 26

Denervated Muscle: How will the interference pattern look like with a max contration in a partially denervated muscle moderate contraction?

Answer 26

- You will have incomplete interference | - There will be gaps in it and the amplitude may not be normal

Question 27

Myopathies: Primary disease is located where?

Answer 27

In the muscle, not the nerve

Question 28

Myopathies: How will the presentations by for a myopathy?

Answer 28

Presentations may vary depending on the exact nature of the myopathy

Question 29

Myopathies: What 2 types of waves are seen in myotonic dystrophies?

Answer 29

- High Frequency Discharges | - Myotonic discharge

Question 30

Reinnervation: What will you see as a the nerve recovers and reinnervation of muscle starts to happen? As the reinnervation continues, what will you see and how is it quantified?

Answer 30

- There will continue to be increased insertional activity until all muscle fibers are reinnervated. - Until all muscle fibers are re-innervated you will still see some fibrillation potentials and PSW. - As reinnervation continues you will see fewer and fewer (they are often graded on EMG reports as +1, +2 or +3 depending on how many are seen. Same with insertional sctivity)

Question 31

Reinnervation: As the msucle fibers begin to reinnervate, during a minimal contraction, what type of units will you see? Describe how they look like

Answer 31

- nascent units (ust coming into existence and beginning to display signs of future potential) - These are very small amplitude, short duration polyphasic = asynchronous potentials

Question 32

Reinnervation: During this process, what can occur from adjacent axons in an effort to pick up denervated muscle fibers?

Answer 32

Collateral sprouting occurs

Question 33

Reinnervation: Collateral innervated muscle fibers can produce what type of waves? How long does it take? Is it faster or slower than nascent units?

Answer 33

These collateral innervated muscle fibers can produce polyphasic long duration MUAP at 6-8 weeks (sooner than nascent units would appear.)

Question 34

Reinnervation: What can sometimes occur with surviving axons or regenerated axons or the collateral innervations? How long does this take?

Answer 34

Pick up more than the normal number of muscle fibers and form giant motor units but the reorganization of the MU takes at least 12-18 months and may not reach their final size for years

Question 35

Insertional activity will (increase or reduce) to normal over time with reinnervation

Answer 35

Insertional activity will reduce to normal over time with reinnervation

Question 36

MUAP – In early recovery nascent units, (short or long) duration, (high or low) amplitude, (bi, tri or polyphasic) because few muscle fibers in reinnervated MU, not synchronized, terminals conducting at (same or different) velocities

Answer 36

MUAP – in early recovery nascent units, short duration, low amplitude, polyphasic because few muscle fibers in reinnervated MU, not synchronized, terminals conducting at different velocities

Question 37

__ __may form if some MU’s do not effective regrow but this is a long term development (12-18 mos)

Answer 37

Giant MU

Question 38

Unlike EMG that involves voluntary __ contraction, NCV requires stimulation of the __. What is the purpose of NCV?

Answer 38

Unlike EMG that involves voluntary muscle contraction, NCV requires stimulation of the nerve. The purpose is to calculate how fast action potentials are conducted down the axons of the nerve.

Question 39

NCV: Which responses can you record with NCV?

Answer 39

1) Motor response | 2) Sensory response

Question 40

NCV: Where are the electrodes typically placed?

Answer 40

Finger tips or toes where there are no muscles

Question 41

NCV: In a motor response, is the nerve orthodromically or antidromically activated?

Answer 41

orthodromically (runs along an axon in its normal or anterograde direction, away from the soma)

Question 42

NCV: In a sensory response, is the nerve orthodromically or antidromically activated?

Answer 42

antidromically (refers to conduction along the axon away from the axon terminal(s) and towards the soma)

Question 43

NCV: Define artifact

Answer 43

For each stimulation there is an artifact that identifies when the stimulus was applied to the nerve

Question 44

NCV: Define M wave

Answer 44

When the muscle contracts, it produces a wave called the M wave

Question 45

NCV: The M wave includes ALL or just PART of the contracting muscle fibers

Answer 45

Includes ALL the contracting muscle fibers

Question 46

NCV: What is the conduction time?

Answer 46

Time from the stimulus artifact to the very beginning of the M wave deflection

Question 47

NCV: How do you calculate NCV?

Answer 47

1) Measure the length of the 2 stimulation sites 2) Take the difference between latency of the distal segment and proximal segment 3) Divide distance/time

Question 48

NCV: How would a M wave look like with compressive neuropathy or in a partially reinnervated muscle? What is it called? Why?

Answer 48

- Loss of smooth curve associated with normal M wave, called M wave dispersion - Dips in the curve - Not all of motor units are not being innervated

Question 49

NCV: In nerve regeneration, more or less myelin segments?

Answer 49

More myelin segments

Question 50

NCV: In nerve regeneration, the increase in myelin segments results in slower or faster regenerated nerve?

Answer 50

slower in regenerated nerve

Question 51

What type of tests do you perfrom for a nerve root problem S1 - soleus muscle?

Answer 51

H Reflex and F response

Question 52

The H wave reflects function of __ __

Answer 52

reflex loop

Question 53

M Wave from (short or long) latency stimulation of muscle

Answer 53

short

Question 54

F response is a supramaximal or submaximal reponse?

Answer 54

supramaximal reponse

Question 55

F response, what type of neuron does it use and how is it activated (antidromically or orthodromically)?

Answer 55

- uses only alpha motor neuro | - Antidromically activated

Question 56

F response tests the dorsal, ventral, or both roots

Answer 56

ventral root

Question 57

Where can the F response be elicited?

Answer 57

Anywhere

Question 58

H tests sensory, motor, or both?

Answer 58

Both sensory and motor

Question 59

EMG evaluates (passive or active) qualities of __ and __

Answer 59

EMG evaluates passive qualities of nerve and muscle

Question 60

EMG also exams __ contraction on single MU level

Answer 60

EMG also exams voluntary contraction on single MU level

Question 61

EMG is only (motor or sensory) system exam

Answer 61

motor

Question 62

NCV always involves __ response

Answer 62

NCV always involves stimulated response

Question 63

NCV produces a __ __

Answer 63

NCV produces a composite potential

Question 64

NCV can examine __ separate from __

Answer 64

NCV can examine sensory separate from motor