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PM&R > Electrodiagnostics > Flashcards

Electrodiagnostics Flashcards

1
Q

How do newborn nerves compare to adults? At what age do they equal adults?

A

Newborns nerves are half as fast as adults. They equal adults at 3-5 years.

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2
Q

Describe the Sunderland Classification of Nerve Injury

A
  1. Neurapraxia (conduction block)
  2. Axonotmesis (Axon damage(
  3. Axon and Endoneurium injury
  4. Axon, Endoneurium, and Peineurium injury (only Epineurium intact)
  5. Neurotmesis (complete nerve transection)
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3
Q

How does axonal degeneration differ from Wallerian degeneration?

A

Axonal degeneration starts distally and ascends whereas with Wallerian the nerve degenerates distally from the site of the lesion.

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4
Q

How does nerve conduction velocity change with age?

A

decreases by 2 m/s per decade past age 50

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5
Q

How does putting electrodes closer than 4cm affect NCS parameters?

A

decreases peak latency, duration, amplitude, and rise time

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6
Q

How does a decrease in temperature affect sodium channels?

A

colder temperature causes a delay in opening and closing of the sodium channel gates which can increase amplitude and prolong conduction

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7
Q

How long does it take axons to regrow if connective tissue remains intact?

A

1mm/day or 1 inch/month

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8
Q

How long does it take median nerve stimulation at the wrist to reach Erb’s point? How long to reach the cortex?

A

9 msec and 20 msec respectively

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9
Q

How will lowering the high frequency filter affect the waveform?

A

It will decrease amplitude but prolong latency

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10
Q

How would a 5 deg C drop in temperature affect conduction velocity and distal latency?

A

It would increase distal latency by 1 msec and decrease conduction velocity by 10 m/s

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11
Q

If you suspect a low amplitude median CMAP is due to a Riche-Cannieu anastomosis, what should you do to confirm?

A

stimulate the ulnar nerve at the wrist and elbow

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12
Q

In general, what is the high-frequency filter set at?

A

10kHz

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13
Q

In order to increase the signal-to-noise ratio by a factor 3, how many averages need to be preformed?

A

9

S:N = (signal amplitude x square rt of # of averages preformed)/noise amplitude

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14
Q

name two causes of myokymic discharges

A

radiation plexopathy, rattlesnake venom

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15
Q

Normal duration, amplitude, and phases of a motor unit action potential?

A
  • Duration: 5 - 15 ms
  • Amplitude: up to 2 mV
  • Phases: 2-4 (equal to # of baseline crossings + 1)
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16
Q

On EMG, what types of abnormal sponteneous activity are generated by muscle fibers?

A

Myotonia, CRDs, FIBs, PSWs

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17
Q

Please describe the A band, H Zone, and I band

A
  • A band: Myosin
  • H zone: Myosin not overlapped with Actin
  • I band: Actin not overlapped with Myosin
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18
Q

What allows for muscle fiber relaxation?

A

ATP powering Ca++ being pumped back into the sarcoplasmic reticulum allowing tropomyosin to block actin’s active sites

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19
Q

What are normal conduction velocities for upper and lower limbs?

A
  • Upper: 50 m/s
  • Lower: 40 m/s
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20
Q

What are three NCS findings that could indicate a Martin-Gruber anastomosis?

A
  • decreased distal amplitude of median nerve CMAP compared to proximal
  • initial positive deflection of median nerve CMAP
  • artifically fast CV
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21
Q

What diagnosis would you suspect if you see conduction block at non-entrapment sites?

A

GBS

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22
Q

What disorders are associated with myotonic discharges?

A
  • Myotonic conditions
  • Polymyositis
  • Acid-maltase deficiency
  • Hyperkalemic periodic paralysis
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23
Q

What does an A- (Axon) Wave represent?

A

collateral sprouting following nerve damage

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24
Q

What is Ohm’s Law?

A

V = I x R (voltage = current x resistance)

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25
Q

What is the definition of innervation ratio?

A

number of muscle fibers innervated per alpha motor unit (huge muscles have huge innervation ratio)

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26
Q

What is the normal latency for R1 and R2 in a blink reflex?

A
  • R1 < 13
  • ipsilateral R2 < 41 msec
  • contralateral R2 < 44 msec

Source: Preston and Shapiro

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27
Q

What is the shortcoming of using needle electrodes with NCS?

A

CV cannot be assessed as only a few fibers are sampled

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28
Q

What makes up a motor unit?

A

anterior horn cell, axon, NMJ, and all muscle fibers innervated by that axon

29
Q

What median muscles are affected with entrapment at the Ligament of Struthers (present in 1% of population)?

A

all of them can be affected

30
Q

What muscle can be used for H-reflex in the upper extremity? Which pathway is tested?

A

Flexor carpi radialis for C7 pathway

31
Q

What nerve fibers are stimulated to trigger the H-reflex?

A

Ia sensory afferent nerves

32
Q

What nerve innervates the adductor magnus?

A

obturator and sciatic (tibial portion)

33
Q

What nerves are most commonly used for SSEP studies?

A

median and tibial

34
Q

What nerve innervates the brachialis muscle?

A

musculocuteneous and radial (dual innervation)

35
Q

What temperatures should be limbs be kept at for NCS?

A
  • Upper limbs: above 32 C
  • Lower limbs: above 30 C
36
Q

What type of nerve fibers do EDX studies evaluate?

A

Ia (large, myelinated)

37
Q

What type of nerves take longer to undergo Wallerian degeneration?

A

Sensory (11 days vs the 7 days with motor axons)

38
Q

Will changing the low-frequency filter affect the onset latency?

A

No

39
Q

With blink reflex study, how is R2 response generated?

A

CN V sensory to Vs nucles in the medulla to bilateral VII nuclei in the pons to bilateral orbicularis oculi muscles via CN VII nerves.

40
Q

With blink reflex study, how is the R1 response generated?

A

CN V sensory to Vm nucleus in the pons to ipsilateral VII nucleus in the pons to ipsilateral orbicularis oculi via CN VII

41
Q

What type of neuropathy does diabetes cause?

A

axonal

42
Q

What is seen on NCS studies in GBS?

A

conduction block and temporal dispersion at non-entrapment sites

43
Q

What differentiates critical illness neuropathy from critical illness myopathy?

A

numbness

44
Q

Genetic cause of CMT1A

A

PMP-22 duplication

45
Q

What is the genetic cause of HNPP?

A

PMM-22 deletion

46
Q

What does CMT2 cause?

A

axonal polyneuropathy

47
Q

What surgery can improve weakness in myasthenia gravis?

A

thymectomy

48
Q
A
49
Q

How does NCS differ between myasthenia gravis and Lamber-Eaton?

A

Routine NCS studies are normal in MG but Lambert Eaton has low amplitude CMAPs

50
Q

How do you detect NMJ disease with RNS?

A

NMJ disease will show a greater than 10% decrement in amplitude between the 1st and 4th waveforms with low rate RNS (2-3 Hz)

51
Q

What is seen with high rate (10 - 50 Hz) RNS in NMJ disease?

A

In general, CMAP repair but huge increase (300%) if Lambert Eaton

52
Q

What is Post-Exercise Facilitation?

A

Same as high rate RNS, see repair after maximal muscle contraction for 60 seconds.

53
Q

What is post-exercise exhaustion?

A

Continue doing low rate RNS q 5 minutes to try to bring out the decrement

54
Q

What is Werdnig-Hoffman Disease?

A

SMA 1: floppy infant that never sits and dies early of respiratory failure

55
Q

What is Kugelberg-Welander Disease?

A

SMA3: can walk independently, normal life expectancy

56
Q

What is the genetic cause of SMA?

A

mutation of the SMN1 (Survival Motor Neuron) gene

57
Q

Pharmcologic treatment for SMA?

A

nusinersen

58
Q

What clinical findings are notably absent in ALS?

A

bowel and bladder abnormalities

59
Q

What type of muscle fibers are affected in steroid myopathy?

A

type II

60
Q

What type of dermatomyositis is due to cancer?

A

type III

61
Q
A
62
Q

How long does it normally take the Tibial SSEP to reach the cortex?

A

45 msec

63
Q

Carpal tunnel syndrome symptoms of what duration indicate a poor prognosis?

A

greater than 10 months

64
Q

What amino acid is a norepinephrine precursor?

A

tyrosine

65
Q

Three causes of axonal sensorimotor neuropathies

A

alcohol, amyloidosis, sarcoidosis

66
Q

what is a normal amount of jitter in single fiber EMG?

A

less than 60 usec (micro second)

67
Q

what myopathy is associated with malignant hyperthermia?

A

central core disease

68
Q

what muscle most commonly shows EMG abnormalities in polymyositis and dermatomyositis?

A

paraspinals

PM&R (21 decks)

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