EMG Flashcards
EMG provides
___ info about muscle
____ info about nerve
- Direct info about muscle
- Indirect info about nerve
name 5 clinical indications for EMG/NCS
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
6 benefits from EMG
Establish correct diagnosis
Localize the lesion
Establish severity of lesion
Approximate timeline
Prognostic value
Assess therapeutic benefit of treatment`
3 precautions/contraindications for EMG/NCS
2 safety/risk considerations
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
in ____% of individuals, lung apex rises above the clavicle where it may be puncured laterally
20
which muscle places the patient at highest risk of PTX
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).
What is the peripheral nervous system components hat make up that which is tested on EMG (5)
1.AH cell
2. DR ganglia
3. NMJ
4. muscle fiber
5. axon
Define a motor unit
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)
what is wallerian degeneration:
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
spontaneous recordings:
What location?
Fasciculation
Myokymia
Tetany
Cramp
Neuromyotonia
Motor neuron/axon
spontaneous recordings:
What location?
end plate sike
terminal axon
spontaneous recordings:
What location?
complex repetitive discharge
multiple muscle fibers
spontaneous recordings:
What location?
fibrillation
PSW
myotonia
single muscle fiber
spontaneous recordings:
What location?
end-plate noise
NMJ
Which needle?
less interference
more painful
concentric
which needle?
larger amplitude
more polyphasia
monopolar
which needle?
active electrode runs as a small wire through the needle center and the shaft serves as the reference electrode
concentric
which needle?
needle is Teflon coated (less painful). Additional electrode is needed as the reference electrode (G2). Insulated shaft, so less artifact.
monopolar
To Remember: ‘Mono’ = one so still need a second electrode to serve as the reference
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?
concentric
“teardrop” configuration
- monopolar has much larger recording area
The more muscles you test, the more ____ the results are (more likely to find pathology).
sensitive
5 components to pay attention to during the EMG exam
Insertional activity
Muscle at rest
Muscle during gentle contraction
Recruitment
Interference pattern
- Establish consistent sequence for EACH muscle so nothing is forgotten
EMG screen
_____ = vertical boxes
_____ = horizontal boxes
Gain = vertical boxes (200uV)
Sweep = horizontal boxes (10ms)
____ = intensity of signal
gain
____ = time of signal
sweep
what are the standard setings for EMG?
Sweep
Gain
Sweep
10ms/Division
Gain
50uV for spontaneous activity
100-500uV for motor unit analysis
describe how each is measured in waveform analysis
amplitude:
duration:
Rise time
Negative deflection
positive deflection
Amplitude: peak to peak
Duration: baseline to baseline
Rise Time
Negative deflection (upward)
Positive deflection (downward)
Technique for needle exam
- test ___ of the muscle
- Move from ___ to __ in each section
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.
With each needle movement, normal insertional activity is brief and usually lasts _____.
Increased insertional activity can be seen in ____
300 ms or less
in both neuropathic and myopathic disorders
Which of the following abnormal spontaneous activities is generated by a single muscle fiber?
Fasciculation potential
Myokymic potential
Neuromyotic potential
Myotonic potential
Cramp
d
spontaneous activity generated by the muscle (4
- fib potentials
- PSW
- myotonic discharges
- CRDs
Spontaneous activity generated by the nerve (6
- myokymic discharges
- cramps
- neuromyotonic discharges
- tremors
- multiples (MUAPs, ie doublets, triplets)
- *fasciculations (can be muscle or neve generated)
myokymic discharge is often associated with ____
radiation plexopathy
Which activity starts and stops abruptly?
A) fibrillation potential
B) positive sharp wave
C) complex repetitive discharge
D) Myotonic discharge
E) Myokymic discharge
c
PSW fire at what freq?
regular?
0.5-10hz
yes
PSW and fibs are graded on a scale of _____
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
CRDs
Indicates:
Firing frequency:
Start and stop ____
___ sound
Indicates chronic pathology
Firing frequency 10-100Hz
Start and stop abruptly
Same complex fires repetitively and quickly
Machine sound
Myotonic discharges
- fire freq:
seen clinically as:
sounds like _____
in _____ morphology
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
Myokymic discharge
Firing pattern:
sounds like:
Firing pattern = regular bursts of groups of motor units
Sounds like soldiers marching
Neuromyotonia
sounds like:
____ firing pattern
Frequency:
Ping sound
Waning firing pattern
Very high frequency (150-250 Hz)
The following are in order from lowest to highest of what?
fasciculations
doublets,triplets,multiplets
myokymia
cramps
neuromyotonia
frequency and number of potentials
Endplate spikes:
Firing pattern:
occurs when?
Initial ______
sounds like:
Irregular, sporadic firing pattern
Occurs when needle tip is near an endplate zone
Initial negative deflection
Cracking, buzzing, sputtering sound
endplate noise
sounds like:
‘Seashell’ sound
Theses areas are often painful for patient
4 components to pay attn to on MUAP
Amplitude (height)
Duration (length)
Phases
Rise time
___ refers to the waveform that is generated by voluntary contraction of the muscle during EMG testing
muap
(not SNAP or CMAP during nerve conduction)
Type of needle dictates normative values (amplitude, duration, phases)
what happens with reinnervation and fiber group typing in neuropathic process
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
normal amplitudes
concentric needle:
monopolar:
Concentric needle < 4mV
Monopolar needle < 7mv
Varies greatly on needle position
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
needle position
amplitude
duration
Concentric:
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
normal duration:
Long duration means:
Short duration means:
Normal 5 – 15 msec
Long duration = asynchronous firing (i.e. reinnervation from neuropathic disease)
Short duration = due to fewer muscle fibers
_____ The number of times the same motor unit fires per one second
firing frequency
Helps identify source of waveform
- regular vs irregular
- slow, fast, really fast
how do you calculate firing frequency?
number of times MUAP fires per second.
calculated by dividing 1000 by the interspike interval
increased force of muscle contraction is generated in 2 ways:
- Faster firing frequency (activation)
- Recruiting additional units (recruitment)
____ is The orderly addition of motor units to increase the force of muscle contraction
recruitment
two methods of recruitment analysis that can be used
- Noting firing frequency of first unit when 2nd unit is recruited (normal is around 5-10Hz)
- Recruitment Ratio
* Normal = 5
* Neuropathic > 8
* Myopathic < 3
recruitment ratio =
= Fasting Firing Frequency/total number of units
- 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 - 17Hz/4 = 4.25
- RR = 4.25
