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BR 3rd Ed > Ch 5 - EDX: NCS > Flashcards

Ch 5 - EDX: NCS Flashcards

1
Q

What does onset latency reflect in sensory fibers?

A

Fastest fibers

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2
Q

What does the peak latency represent?

A

Initiation of conduction along the majority of axons. Recorded from stimulus to peak waveform

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3
Q

What is conduction velocity?

A

Speed an impulse travels along a nerve dependent on myelin sheath

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4
Q

What are the age variations in conduction velocity?

A

Newborns 50% of an adult
1 yo 80% of adults
3-5 yo equal to adults
Dec 1-2 m/s per decade >50yo

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5
Q

What is considered a normal limb temperature for NCS?

A

Upper: 32 deg C
Lower: 30 deg C

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6
Q

How does temperature affect CV?

A

Dec 2.4 m/s per 1 deg C drop

5% dec for each 1 deg C below 29 deg C

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7
Q

What is amplitude?

A

Max voltage diff b/w two points reflecting # of nerve fibers activated and synchronicity of firing

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8
Q

How is amplitude measured?

A

Peak-to-peak or baseline-to-peak

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9
Q

How is duration measured?

A

Initial deflection from baseline to return

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10
Q

What is the duration?

A

Summation and firing rate of numerous axons

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11
Q

What is latency of activation?

A

Time b/w initiation of electrical stimulus and beginning of saltatory conduction
<0.1 ms

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12
Q

What is conduction?

A

Saltatory conduction of an AP along myelinated axons to terminal branches, unmyelinated twigs and NMJ

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13
Q

What is Synaptic transmission?

A

Chemical transmission of signal across the NMJ to initiate a single fiber AP
0.2-1.0 ms

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14
Q

What are normal values for CV?

A

Upper: >50 m/s
Lower: >40 m/s

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15
Q

What is the area?

A

Both amp and duration of the waveform

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16
Q

What is temporal dispersion?

A

Range of CV of fastest and slowest nerve fibers

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17
Q

How does temporal dispersion change with proximal to distal stimulation?

A

Waveform spreads out with proximal compare to distal stim

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18
Q

What is phase cancellation?

A

Comparing proximal to distal stim, drop in amp and inc duration occurs

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19
Q

When is phase cancellation most notable?

A

SNAP due to short duration

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20
Q

When accounting for phase cancellation what is a normal drop of SNAP when moving proximal?

A

50%

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21
Q

When accounting for phase cancellation what is a normal drop of CMAP when moving proximal?

A

15%

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22
Q

What is a SNAP?

A

Sensory nerve study representing conduction of an impulse along sensory nerve fibers

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23
Q

What is SNAP useful for localizing a lesion to?

A

DRG

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24
Q

What happens to SNAP with lesions proximal to the DRG?

A

SNAP is preserved as axonal transport from cell body to peripheral axon intact

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25
Q

What are SNAPs more sensitive than CMAP in detection of?

A

Incomplete nerve injury

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26
Q

What are advantages of antidromic studies over orthodromic studies?

A

Easier to record
More comfortable
Require less stim intensity
Larger amp due to nerve more superficial at distal recording sites

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27
Q

What happens to motor and sensory responses with Postganglionic injuries?

A

CMAP and SNAP diminished or absent

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28
Q

What happens to motor and sensory responses with Preganglionic injuries?

A

CMAP diminished or absent

SNAP normal

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29
Q

What happens to the waveform when reference and recording electrodes are <4 cm apart?

A

Decreased peak latency, amp, duration and rise time

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30
Q

What do CMAPS or M waves represent?

A

Conduction of an impulse along motor nerve fibers of a motor unit

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31
Q

When can CMAP be ABN with a normal SNAP?

A

Lesion proximal to the DRG

Lesion affecting a purely motor nerve

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32
Q

Describe the typical waveform of a CMAP.

A

Biphasic with initial negative deflection

33
Q

Why would a CMAP have an initial positive deflection?

A

Inappropriate placement of active electrode to motor point
Volume conduction from other muscles or nerves
Anomalous innervation

34
Q

What can contribute to a falsely decreased amp and inaccurate latency for CMAP?

A

Act and Ref electrodes too close
Submaximal stim
Stim over callous or edema

35
Q

What is an H-reflex?

A

NCS late response is an electrically evoke analogue to a monosynaptic reflex

ex) Achilles reflex

36
Q

How is an H-reflex stim?

A

Submaximal stim for 1.0ms activates IA afferent nerve fibers causing an orthodromic sensory response to the SC and then orthodromic motor resonse back to recording electrode

37
Q

What is H-reflex used to monitor?

A

C7 or S1 radiculopathy

38
Q

What locations are stim to find the H-reflex?

A

FCR: Median nerve: C7
Soleus: Tibial nerve: S1

39
Q

How can H-reflex be potentiated and inhibited by muscle contraction?

A

Potentiated: agonist muscle
Inhibited: antagonist muscle

40
Q

What are limitations of the H-reflex?

A

Eval long neural pathway so hinder specificity of lesion

Can be normal with incomplete lesions

Doesn’t distinguish b/w acute and chronic

Once ABN, always ABN

41
Q

What is a F-wave?

A

Small later pure motor response occurring after the CMAP

42
Q

How is a F-wave produced?

A

Short duration, supramaximal stim initiates an antidromic motor response to the anterior horn cells in the SC which produces an orthodromic motor response to the recording electrode

43
Q

Why is a F-wave not a true reflex?

A

No synapse along the nerve pathway being stim

44
Q

Why do configuration and latency of an F-wave change with each stim?

A

Due to activation of different groups of anterior horn cells with each stim

45
Q

What can F-wave be useful for detecting?

A

Polyneuropathies and plexopathies

Not radiculopathies

46
Q

Where can F-wave be obtained?

A

Any muscle

47
Q

What are limitations of F-waves?

A

Eval long neural pathway and hinders specificity of injury

Only accesses motor fibers

48
Q

What is a significant side to side difference in H-reflex latency?

A

0.5-1 ms

49
Q

What is a significant side to side difference in F-wave latency?

A

Upper limb: 2.0 ms

Lower limb: 4.0 ms

50
Q

How can an A-wave be obtained?

A

Evoked during CMAP with submaximal stim and abolished with supramaximal stim

51
Q

Where does an A-wave typically occur?

A

b/w CMAP and F-wave at a constant latency

52
Q

What does an A-wave represent?

A

Collateral sprouting following nerve damage

53
Q

What is the blink reflex?

A

NCS is an electrically evoked analogue to the corneal reflex

54
Q

How is a blink reflex initiated?

A

Stim supraorbital branch of the trigeminal nerve→ pons and branches to lateral medulla→ ipsi and contralateral orbicularis oculi via the facial nerve

55
Q

What responses are evaluated during the blink reflex?

A

Ispilateral R1

Bilateral R2

56
Q

Which response is the blink associated with?

A

R2 response

57
Q

What is the afferent pathway of the blink reflex?

A

Sensory branches of CN V (trigeminal nerve)

58
Q

What is the efferent pathway of the blink reflex?

A

Motor branches of CN VII (facial nerve)

59
Q

What is the course of the R1 (early) response?

A

Through the pons

60
Q

What is the course of the R1 (late) response?

A

Through the pons and lateral medulla

61
Q

What lesions affect the R1 response?

A

Trigeminal nerve
Pons
Facial nerve

62
Q

What lesions affect the R2 response?

A 
Consciousness level
Parkinson's disease
Lateral medullary syndrome
Contralateral hemisphere
Valium
Habituation
63
Q

How is NCS of CN VII (facial nerve) performed?

A

Stim distal to the stylomastoid foramen at the angle of the mandible

Response recorded over nasalis muscle

64
Q

How does a patient with peripheral facial nerve injury present?

A

Equal weakness in upper and lower facial muscles

65
Q

How does a patient with a lesion rostral to the facial nucleus present?

A

Lower facial muscles more severely affected than upper

66
Q

What is Synkinesis?

A

Aberrant regeneration of axons in facial nerve injuries leading to reinnervation of inappropriate muscles

67
Q

How can Synkinesis present?

A

Lip twitching when closing an eye

Crocodile tears when chewing

68
Q

What is facial NCS useful for monitoring injury for?

A 
Bell's palsy
Neoplasms
Fractures
Middle ear infection
DM
Mumps
Lyme disease
69
Q

What indicates outcomes of facial nerve injury?

A

Demylinating better than axonal injury

No evoked potential for 7 days indicates poor prognosis

70
Q

What are treatments of facial nerve injury?

A

Prednisone
Massage
Electrical stim

71
Q

What does a somatosensory evoked potential (SSEPs) evaluate?

A

Time-locked responses of the nervous system to an external stim

72
Q

Describe the ascending sensory pathway of an afferent potential during SSEP.

A

Peripheral nerve→ plexus→ root→ SC (posterior column)→ contralateral medial lemniscus→ thalamus→ somatosensory cortex

73
Q

How is SSEP initiated?

A

Repetitive submaximal stim of sensory nerve, mixed nerve or dermatome recorded from spine orscalp

74
Q

What are the MC nerves used to test SSEP?

A

Median and tibial nerve

75
Q

What is SSEP useful for monitoring for?

A

Peripheral nerve injury
CNS lesions (MS)
Intraoperative monitoring of spinal surgery

76
Q

ABN SSEP in MS are most likely to be seen in____.

A

Lower limb prolonged interpeak latencies

77
Q

What can indicate nerve injury during spinal cord surgery?

A

Loss of tibial nerve potentials with preservation of median nerve

78
Q

What are advantages of SSEP?

A

Eval sensory PNS and CNS

Eval d/o CNS, dorsal nerve roots and peripheral nerves

ABN results present immediately

79
Q

What are disavantages of SSEP?

A

Only eval fibers sensing vibration and proprioception

Limited in ability to localize lesion

Affected by sleep and anesthesia

BR 3rd Ed (92 decks)

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