EMG

Question 1

EMG provides

___ info about muscle

____ info about nerve

Answer 1

• Direct info about muscle

* Indirect info about nerve

Question 2

name 5 clinical indications for EMG/NCS

Answer 2

Muscle weakness
Muscle atrophy
Numbness
Reduced reflexes
Neuropathic pain?

These only apply as indications if there is a specific question to be answered.. Don’t just order to verify what you already know
Extension of physical exam
Good for any objective neurological finding, less useful for subjective complaints

Pain not picked up on this exam (unless other neuro deficits) b/c needle EMG doesn’t test the small unmyelinated nerves

Question 3

6 benefits from EMG

Answer 3

Establish correct diagnosis
Localize the lesion
Establish severity of lesion
Approximate timeline
Prognostic value
Assess therapeutic benefit of treatment`

Question 4

3 precautions/contraindications for EMG/NCS

2 safety/risk considerations

Answer 4

Precautions/Contraindications
Anticoagulation (INR > 3.0*)
Bleeding disorders
Active infection

Safety/Risks
AICD is safe for needle portion of exam
Risk of pneumothorax/hematoma/nerve damage

Question 5

in ____% of individuals, lung apex rises above the clavicle where it may be puncured laterally

Answer 5

20

Question 6

which muscle places the patient at highest risk of PTX

Answer 6

SS

The supraspinatus muscle lies in the supraspinous fossa. Needle electromyographic examination of this muscle may be complicated by pneumothorax if sampling is near the midpoint where the supraspinous fossa is narrowest ( A). If the needle is placed deep above point A (area marked by *), there is a risk of pleural puncture. The muscle can be more safely sampled medially in the supraspinous fossa ( B).

Question 7

What is the peripheral nervous system components hat make up that which is tested on EMG (5)

Answer 7

1. AH cell
2. DR ganglia
3. NMJ
4. muscle fiber
5. axon

Question 8

Define a motor unit

Answer 8

Motor unit:

• one axon
• anterior horn cell
• all connected muscle fibers and neuromuscular junctions.

Motor neuron, neuromuscular junction, and muscle fiber

A nerve fiber action potential normally always results in depolarization of all the muscle fibers of the motor unit creating an electrical potential known as the motor unit action potential (MUAP)

Question 9

what is wallerian degeneration:

Answer 9

degeneration of the nerve distal to the site of injury

Axon and myelin death = muscle atrophy and muscle membrane irritability (so spontaneous depolarizations can occur) and voluntary contractions can become uncoordinated

Question 10

spontaneous recordings:

What location?

Fasciculation
Myokymia
Tetany
Cramp
Neuromyotonia

Answer 10

Motor neuron/axon

Question 11

spontaneous recordings:

What location?

end plate sike

Answer 11

terminal axon

Question 12

spontaneous recordings:

What location?

complex repetitive discharge

Answer 12

multiple muscle fibers

Question 13

spontaneous recordings:

What location?

fibrillation
PSW
myotonia

Answer 13

single muscle fiber

Question 14

spontaneous recordings:

What location?

end-plate noise

Answer 14

NMJ

Question 15

Which needle?

less interference
more painful

Answer 15

concentric

Question 16

which needle?

larger amplitude
more polyphasia

Answer 16

monopolar

Question 17

which needle?

active electrode runs as a small wire through the needle center and the shaft serves as the reference electrode

Answer 17

concentric

Question 18

which needle?

needle is Teflon coated (less painful). Additional electrode is needed as the reference electrode (G2). Insulated shaft, so less artifact.

Answer 18

monopolar

To Remember: ‘Mono’ = one so still need a second electrode to serve as the reference

Question 19

which needle?

reference electrode (G2), whereas the active electrode (G1) runs as a very small wire through the center of the needle and is exposed at the needle tip, which is beveled.

recording field?

Answer 19

concentric

“teardrop” configuration

• monopolar has much larger recording area

Question 20

The more muscles you test, the more ____ the results are (more likely to find pathology).

Answer 20

sensitive

Question 21

5 components to pay attention to during the EMG exam

Answer 21

Insertional activity
Muscle at rest
Muscle during gentle contraction
Recruitment
Interference pattern 

• Establish consistent sequence for EACH muscle so nothing is forgotten

Question 22

EMG screen

_____ = vertical boxes

_____ = horizontal boxes

Answer 22

Gain = vertical boxes (200uV)

Sweep = horizontal boxes (10ms)

Question 23

____ = intensity of signal

Answer 23

gain

Question 24

____ = time of signal

Answer 24

sweep

Question 25

what are the standard setings for EMG? Sweep Gain

Answer 25

Sweep 10ms/Division Gain 50uV for spontaneous activity 100-500uV for motor unit analysis

Question 26

describe how each is measured in waveform analysis ``` amplitude: duration: Rise time Negative deflection positive deflection ```

Answer 26

``` Amplitude: peak to peak Duration: baseline to baseline Rise Time Negative deflection (upward) Positive deflection (downward) ```

Question 27

Technique for needle exam 1. test ___ of the muscle 2. Move from ___ to __ in each section

Answer 27

Represents brief burst of muscle fiber potentials thought due to shearing of muscle fibers When withdraw to change quadrants, come back to just below the surface of skin and redirect the needle slightly. Then, move from shallow to deep with quick bursts of the needle. Warn patient that you have to agitate the muscle.

Question 28

With each needle movement, normal insertional activity is brief and usually lasts _____. Increased insertional activity can be seen in ____

Answer 28

300 ms or less in both neuropathic and myopathic disorders

Question 29

Which of the following abnormal spontaneous activities is generated by a single muscle fiber? ``` Fasciculation potential Myokymic potential Neuromyotic potential Myotonic potential Cramp ```

Answer 29

d

Question 30

spontaneous activity generated by the muscle (4

Answer 30

- fib potentials - PSW - myotonic discharges - CRDs

Question 31

Spontaneous activity generated by the nerve (6

Answer 31

- myokymic discharges - cramps - neuromyotonic discharges - tremors - multiples (MUAPs, ie doublets, triplets) - *fasciculations (can be muscle or neve generated)

Question 32

myokymic discharge is often associated with ____

Answer 32

radiation plexopathy

Question 33

Which activity starts and stops abruptly? ``` A) fibrillation potential B) positive sharp wave C) complex repetitive discharge D) Myotonic discharge E) Myokymic discharge ```

Answer 33

c

Question 34

PSW fire at what freq? regular?

Answer 34

0.5-10hz yes

Question 35

PSW and fibs are graded on a scale of _____

Answer 35

``` Imply ongoing denervation Present in many conditions Graded on Scale 0-4 0 = none 1 = persistent single train of PSW in at least 2 areas 3 = moderate number in 3 or more areas 4 = full interference pattern of PSW ```

Question 36

CRDs Indicates: Firing frequency: Start and stop ____ ___ sound

Answer 36

``` Indicates chronic pathology Firing frequency 10-100Hz Start and stop abruptly Same complex fires repetitively and quickly Machine sound ```

Question 37

Myotonic discharges - fire freq: seen clinically as: sounds like _____ in _____ morphology

Answer 37

Firing frequency varies between 20 – 100Hz Clinically seen as delayed relaxation after a strong contraction Dive bomber sound or revving engine sound In PSW or fib morphology Can occur in many diseases Induced my needle movement

Question 38

Myokymic discharge Firing pattern: sounds like:

Answer 38

Firing pattern = regular bursts of groups of motor units Sounds like soldiers marching

Question 39

Neuromyotonia sounds like: ____ firing pattern Frequency:

Answer 39

Ping sound Waning firing pattern Very high frequency (150-250 Hz)

Question 40

The following are in order from lowest to highest of what? ``` fasciculations doublets,triplets,multiplets myokymia cramps neuromyotonia ```

Answer 40

frequency and number of potentials

Question 41

Endplate spikes: Firing pattern: occurs when? Initial ______ sounds like:

Answer 41

Irregular, sporadic firing pattern Occurs when needle tip is near an endplate zone Initial negative deflection Cracking, buzzing, sputtering sound

Question 42

endplate noise sounds like:

Answer 42

'Seashell’ sound Theses areas are often painful for patient

Question 43

4 components to pay attn to on MUAP

Answer 43

Amplitude (height) Duration (length) Phases Rise time

Question 44

___ refers to the waveform that is generated by voluntary contraction of the muscle during EMG testing

Answer 44

muap (not SNAP or CMAP during nerve conduction) Type of needle dictates normative values (amplitude, duration, phases)

Question 45

what happens with reinnervation and fiber group typing in neuropathic process

Answer 45

A large MUAP is recorded. In this case, a single active motor neuron is now innervating more muscle fibers. When it fires there will be more muscle fiber action potentials and thus a larger MUAP

Question 46

normal amplitudes concentric needle: monopolar:

Answer 46

Concentric needle < 4mV Monopolar needle < 7mv Varies greatly on needle position

Question 47

Of all MUAP parameters, amplitude is most dependent on _____. Only muscle fibers very close to the needle contribute to _______, as opposed to _____, wherein most muscle fibers contribute. Note change in amplitude as needle is moved to different locations within the same motor unit

Answer 47

needle position amplitude duration

Question 48

Concentric: <___% MUAPs can be polyphasic

Answer 48

Concentric: < 10% MUAPs can be polyphasic Monopolar: < 25% MUAPs can be polyphasic Some muscles can have more polyphasic units (i.e. deltoid) Represents desynchronized discharges

Question 49

normal duration: Long duration means: Short duration means:

Answer 49

Normal 5 – 15 msec Long duration = asynchronous firing (i.e. reinnervation from neuropathic disease) Short duration = due to fewer muscle fibers

Question 50

_____ The number of times the same motor unit fires per one second

Answer 50

firing frequency Helps identify source of waveform - regular vs irregular - slow, fast, really fast

Question 51

how do you calculate firing frequency?

Answer 51

number of times MUAP fires per second. calculated by dividing 1000 by the interspike interval

Question 52

increased force of muscle contraction is generated in 2 ways:

Answer 52

1. Faster firing frequency (activation) | 2. Recruiting additional units (recruitment)

Question 53

____ is The orderly addition of motor units to increase the force of muscle contraction

Answer 53

recruitment

Question 54

two methods of recruitment analysis that can be used

Answer 54

1. Noting firing frequency of first unit when 2nd unit is recruited (normal is around 5-10Hz) 2. Recruitment Ratio * Normal = 5 * Neuropathic > 8 * Myopathic < 3

Question 55

recruitment ratio =

Answer 55

= Fasting Firing Frequency/total number of units 1. Calculate frequency of the fastest firing unit: (in this case, the largest unit) 6 boxes x 10ms = 60ms 1 fire/60ms x (1000ms/1sec) = 17Hz 2. 17Hz/4 = 4.25 3. RR = 4.25