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Brad 4th Ed Part 1 > Ch. 9 Electrodiagnostic medicine I: Fundamental Principles > Flashcards

Ch. 9 Electrodiagnostic medicine I: Fundamental Principles Flashcards

1
Q

What is saltatory conduction?

A

Action potential jumps from one node of Ranvier to another

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2
Q

What kind of voltage-gated channels do myelinated nerves lack and contain?

A

Voltage-gated potassium channels

Only contain voltage-gated Na channels

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3
Q

What are the differences in nerve AP b/w men and women?

A

Women have inc antidromic sensory nerve amp in median and ulnar nerves
Women have great NCV for upper and lower limbs

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4
Q

How is SNAP affected by age?

A

CV declines 1-2m/s per decade
Duration 10-15% longer in 40-60 yo and 20% longer in 70-88 yo
Amp 1/2 in 40-60 yo and 1/3 in 70-88 yo

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5
Q

Newborn’s motor NCV are ___ that of adults

A

1/2

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6
Q

When do children’s NCV reach that of adults?

A

3-5 yo

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7
Q

What happens to NCV after 50 yo?

A

Fastest motor fibers decline by 1-2m/s per decade
Inc in distal motor latency
Dec in motor amp

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8
Q

How does height affect NCV?

A

Slower lower limb NCV in taller patients

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9
Q

What is the most influencing factors on NCV?

A

Temperature

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10
Q

How does temperature affect NCV?

A

As temp lowers the amount of current required to generate an AP inc and reduces NCV

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11
Q

How does temperature affect CMAP and SNAP?

A

Inc Amp, duration, rise time and area

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12
Q

With every __ drop in temperature there is a ___ decrease in conduction velocity

A

1 deg C temp dec 2.4 m/s dec in CV

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13
Q

What should the minimum temperature of limbs be when doing NCS?

A

32 deg C in upper

30 deg C in lower

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14
Q

What is an antidromic technique?

A

Induced neural impulse propagates along the nerve in a direction opposite to its physiologic direction

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15
Q

What is an orthodromic technique?

A

Impulses propagate in direction along the nerve in physiologic direction

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16
Q

What is a mixed nerve repsonse?

A

Component of both othrodromic and antidromic responses

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17
Q

What is the shape of a SNAP waveform?

A

Biphasic negative-positive potential

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18
Q

How can distance b/w active and recording electrodes change SNAP?

A

Distance <40 mm amp dec and peak latency shortens

Distance > 40 mm neg peak amp will not grow but terminal + phase will change configuration

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19
Q

What is normal insertional activity?

A

Inserting needle into muscle results in brief bursts of electrical potentials

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20
Q

What is decreased insertional activity?

A

Few or no electrical waveforms when needle inserted in fibrous or electrically inexcitable tissue

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21
Q

What is increased insertional activity?

A

Insertional activity persists after needle movememnet cessation

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22
Q

What is a miniature end-plate potential?

A

Waveform is short duration (0.5-2 ms), small (10-50uV), irregularly occuring (1/~5 sec per axon terminal) monophasic negative waveform

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23
Q

What do miniature end-plate potential represent?

A

Random release of Ach vesicles

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24
Q

What doe miniature end plate potentials (MEPPs) sound like?

A

Seashell murmur

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25
Q

What is an end-plate spike?

A

Short duration (3-4 ms) of moderate amp (100-200uV) irregularly firing and biphasic with initial negative deflection when needle placed near the end-plate region

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26
Q

How can one differentiate a PSW from an end-plate spike?

A

PSW and fibs have a regular firing rate and slowly trail off

End-plate spikes are irregular

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27
Q

What is a motor unit?

A

One anterior horn cell, its axon and the single musce fibers supplied by that nerve

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28
Q

What is a motor unit action potential (MUAP)?

A

Electrical activity from all muslce fibers summates together

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29
Q

What is the MUAP amplitude?

A

maximum peak to peak CRT trace displacement

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30
Q

What is the rise time of a MUAP?

A

Temporal aspect of a potential’s peak

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31
Q

What is the duration of a MUAP?

A

Depature from and return to baseline

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32
Q

What are phases of MUAP?

A

Number of baseline crossings plus one

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33
Q

What is peak-to-peak MUAP amp arised from?

A

<12 single muscle fibers located w/in 0.5 mm of needle electrode

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34
Q

What is the shape of a MUAP?

A

Triphasic: positive-negative-positive

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35
Q

What are polyphasic potentials?

A

MUAPs with 5 or more phases

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36
Q

What are satellite potentials?

A

Late waves linked to the rest of the waveform

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37
Q

What is collateral sprouting?

A

Denervated muscle fibers induce nearby terminal axons of intact nerves to send out neural projections to reinnervate orphaned muscle fibers

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38
Q

What do neurogenic diseased MUAPS look like?

A

Larger amplitude, longer-duration and highly polyphasic MUAPs

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39
Q

What do myopathic MUAP’s look like?

A

Shorter-duration, highly polyphasic, low-amplitude

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40
Q

Where is a muscle’s end-plate or motor point located?

A

Midway b/w muscles origin and insertion where active electrode is placed to record a CMAP

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41
Q

Where is the reference electrode placed to record a CMAP?

A

On or distal to the tendinous insertion of the muscle

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42
Q

What does a positive deflection preceding the negative phase of a CMAP mean?

A

The active electrode is off of the motor point

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43
Q

What are fibrillation potentials?

A

Regularly firing spontaneous depolarization of denervated a single muscle fiber

44
Q

What do fibrillation potentials look like?

A

<5 ms duration
<1 mV amp
Fire b/w 1-15 Hz

45
Q

What do fibrillation potentials sound like?

A

Rain on a tin roof

46
Q

What are PSW?

A

Waveforms recorded from a single muscle fiber w/ unstable resting membrane potential secondary to denervation or intrinsic muscle disease

47
Q

What does a PSW look like?

A

Large primary sharp deflection followed by a small neg potential
Duration of 100 ms or longer

48
Q

What doe PSW sound like?

A

Regular firing rate (1-15Hz) and a dull thud sound

49
Q

Where can transient runs of “PSW appearing potentials” be found?

A

Paraspinal, hand and foot intrinsic muscles

50
Q

What is a complex repetitive discharge?

A

Spontaneously firing group of action potentials that stop abruptly

51
Q

What do complex repetitive discharges look like?

A

Continuous run of simple or complex spike patterns that repeat at 0.3-150 Hz

52
Q

What doe complex repetitive discharges sound like?

A

Heavy machinery or idling motorcycle

53
Q

What cannot effect CRDs?

A

Curare or nerve blocks

54
Q

What do CRD’s indicate?

A

Chronic process of a group of muscle fibers becoming separated from their NMJ’s

55
Q

What is myotonia?

A

Delayed muscle relaxation after muscle contraction

56
Q

What is percussion myotonia?

A

Delayed muscle relaxation after activation with a reflex hammer

57
Q

What does “warm up” do to myotonia?

A

Continued muscle contraction lessens myotonia

58
Q

What is a fasciculation?

A

Visible contraction of a portion of a muscle

59
Q

What is a fasciculation potential?

A

Electrically summated voltage of depolarzing muscle fibers belonging to all or part of one motor unit

60
Q

Describe fasciculation potentials

A

Discharge 1Hz to many/min
Irregular and random
No under voluntary control
Influenced by mild contraction of agonist or antagonist muscles

61
Q

Fasciculation potentials occur in ___

A 
Normal foot intrisics or gastrosoleus muscles
Motor neuron disorders
Radiculopathies
Entrapment neuropathies
Cervical spondylotic myelopathy
Metabolic disturbances
62
Q

What is myokymia?

A

Rippling movement or “bag of worms” movement of the skin

63
Q

What is a myokymic discharge?

A

Bursts of normal appearing group of motor units with interburst intervals of electrical silence

64
Q

Describe myokymic discharges

A

Firing rate 0.1-10 Hz in semirhythmic pattern

65
Q

What do myokymic discharges sound like?

A

Sputtering of a low-powered motorboat engine

66
Q

What can facial myokimc potentials be seen in?

A

Multiple sclerosis

Brainstem neoplasm

67
Q

What can segmental myokymic discharges be seen in?

A

Syringomyelia

Radiculopathies

68
Q

What can generalized myokymic discharges be seen in?

A

Uremia
Thyrotoxicosis
Inflammatory polyradiculoneuropathy
Issac’s syndrome

69
Q

What can limb myokymic discharges be seen in?

A

Radiation plexopathy

Chronic compressive neuropathies

70
Q

What is seen on EMG in stiff man syndrome?

A

Normal MUAPs producing a sustained discharge pattern in agonist and antagonist muscles

71
Q

What can induce cramps?

A

Hyponatremia
Hypocalcemia
Vitamin deficiency
Peripheral neuropathies

72
Q

How can cramps be induced in the calf muscles of normal patients?

A

Exercises
Abnormal positioning
maintained fixed position for a prolonged period

73
Q

What is seen on EMG in a cramped muscle?

A

Multiple motor units firing b/w 40-60 Hz up to 20-300 Hz

74
Q

What is tetany?

A

Spontaneous muscle twitiching, cramps and carpopedal spasm

75
Q

What is Chvostek’s sign?

A

Inducing tetany by tapping the facial nerve

76
Q

What is the peroneal sign?

A

Inducing tetany by tapping the peroneal nerve at the fibular head

77
Q

What is Trousseau’s sign?

A

Placing BP cuff around arm for 3 minutes inducing hand tetany

78
Q

Describe a motor unit potential in tetany

A

Fires rapidly with inderdischarge interval of 2-20 ms
Doublet: fires twice
Triplet: fires 3 times
Multiplet: fires >3 times

79
Q

How does Seddon classify nerve injury?

A

Combo of functional status and histologic appearance

80
Q

How is neurapraxia?

A

Mild degree of neural insult that results in conduction block of impulse across the affected segment

81
Q

Describe EMG in neurapraxia

A

No fibs should be seen as axon is intact and muscle innervation maintained

82
Q

What is axontmesis?

A

Only axon is disrupted w/ preserved perineurium and epineurium causes wallerian degeneration

83
Q

What is the prognosis of axontmesis?

A

Good with axonal regeneration

84
Q

What is neurotmesis?

A

Complete disruption of axon and all supporting CT structures.

85
Q

What is the prognosis of neurotmesis?

A

Poor prognosis for complete recovery and requires surgery

86
Q

How does Sunderland classify nerve injury?

A

Trauma with respect to the axon and supporting CT

87
Q

What does compression neuropathy cause?

A

Thinning of myelin and widening of nodes of Ranvier, causing slowing of latency and velocity on NCS

88
Q

What are the two types of electrodes used in EMG/NS?

A

Surface and needle

89
Q

Describe a monopolar needle

A

Solid, stainless steel shaft coated in Teflon except bare metal tip which acts as the recording surface

90
Q

Describe a concentric needle

A

Hollow, stainless steel hypodermic needle with central platinum or Nichrome-silver wire surrounded by expoxy resin

91
Q

Where are the ground and reference in the monopolar needle?

A

Separate from needle

92
Q

Where are the ground and reference in the concentric needle?

A

Ground is separate and reference in cannula

93
Q

Describe pros and cons of the monopolar needle

A

Wider recording territory
Distant reference makes recording “noisy”
Teflon coating dec patient discomfort

94
Q

Describe pros and cons of the concentric needle

A

Active and reference electrodes close together making them quieter
More discomfort

95
Q

Describe motor units found with concentric needles compared to monopolar

A

Smaller amp
Fewer phases
Comparable duration
Less distant motor unit activity

96
Q

Describe a single-fiber electrode

A

Modified modified concentric needle with small 25 um recording port opposite of electrodes bevel

97
Q

What is an amplifier?

A

Device w/ ability to magnify wanted signals and minimize unwanted signals or noise

98
Q

Which amplifier is connected to the active electrode?

A

Noninverting amplifer

99
Q

Which amplifier is connected to the reference electrode?

A

Inverting amplifier

100
Q

What does a high-frequency filter do?

A

Eliminates frequencies higher than its numeric designation and permits lower frequencies to pass

101
Q

What does a low-frequency filter do?

A

Eliminates frequencies lower than its numeric designation and permits higher frequencies to pass

102
Q

Is the stimulating cathode negative or positive?

A

Negative

103
Q

Is the stimulating anode negative or positive?

A

Positive

104
Q

Describe the optimal condition of the patients skin during EMG/NCS

A

Dry without perspiration, lotion, make up or other surface conductors

105
Q

Where should the ground electrode be placed?

A

Between active and reference electrodes

106
Q

What is the most effective what to reduce stimulus artifact?

A

Rotate anode about cathode

Brad 4th Ed Part 1 (36 decks)

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