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PM&R Recap > Electrodiagnostics > Flashcards

Electrodiagnostics Flashcards

1
Q

What is the innervation ratio?

What is the difference in innervation ratios between glutes/extraoccular muscles?

A

IR = # muscle fibers / alpha motor neuron

Glutes (and other large powerful muscles) have HUGE innervation ratios

Extraoccular muscles (and other small muscles for fine motor movement) have small innervation ratios

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2
Q

Nerve anatomy:

The connective tissue surrounding each individual axon and its myelin sheath?

A

Endoneurium

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3
Q

Nerve anatomy:

The connective tissue connecting axons together into bundles (nerve fascicles)?

A

Perineurium

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4
Q

Nerve anatomy:

The connective tissue connecting fascicles together?

A

Epineurium

*Nerve transection = cut completely through the epineurium
*Crush injury –> intact epineurium; has better prognosis for regrowth

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5
Q

What generates miniature depolarizations (MEPPs) of the postsynaptic endplate?

A

Spontaneous release of quanta of ACh at regular intervals, to maintain the health of the NMJ

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6
Q

What is the effect of lower temperatures on nerve conduction studies?

A

increased amplitude with increased duration
prolonged latency
increased conduction time (slowed conduction velocity)

*channels stay open longer, causing beefier amplitude and longer time of depolarizing

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7
Q

What are the temperature minimums for upper extremity and lower extremity during NCS?

A

UE = 32 degrees C
LE = 30 degrees C

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8
Q

Effect of lowering the high-frequency filter?

A

decreased amplitude
prolonged onset and peak latencies

“I’m late because I was high”

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9
Q

Effect of raising the low-frequency filter?

A

decreased amplitude
shorten peak latency

“I peaked early at a low point in my life”

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10
Q

Normal conduction velocity for upper extremities?

A

At least 50m/s

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11
Q

Normal conduction velocity for lower extremities?

A

At least 40m/s

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12
Q

Effects of volume conduction on latency/conduction velocity?

A

May see falsely short latency or falsely fast conduction velocity

applying too much current will cause the current to diffuse along tissues other than nerve

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13
Q

Is the H reflex a true reflex?

Most common use?

A

Stimulating the 1a sensory afferent nerves and recording over the muscle (action potential travels up spinal cord, stimulate the spinal reflex arc, and travel back down the motor nerve to make the muscle contract.

Usually stimulate proximally in popliteal fossa –> plantar flexion/calf twitch (recording electrode on soleus)

True reflex

Used to assess for S1 radiculopathy (positive if prolonged latency on one side, non-specific finding)

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14
Q

Is the F wave a true reflex?

A
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15
Q

Is the F wave a true reflex?

A

No

Can obtain from any motor nerve. F wave is produced when recording from a muscle and stimulating the nerve of that muscle at a distal location in a proximal stimulation direction. This will sent the AP antidromically to the anterior horn, which will then cause depolarization of a random population of anterior horn cells, whose depolarization will travel back down the axons of the motor nerve.

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16
Q

What do prolonged/absent F waves indicate?

A

first sign of AIDP

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17
Q

If an A-wave is present, what does it indicate?

A
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18
Q

If an A-wave is present, what does it indicate?

A
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19
Q

Is the A wave a true reflex?

A

No

Very predictable/stable waveform that shows up somewhere between the F-wave and the the direct motor response when recording F-waves from a muscle (exact same waveform w/ same latency and amplitude with each stimulation)

20
Q

If an A-wave is present, what does it indicate?

A

There has been reinnervation of the nerve to that muscle (at some point in pt’s life, there was prior nerve damage)

21
Q

Which needle type has reference electrode attached to needle w/ small listening area?

A

Concentric needle

22
Q

Which needle type has a broad listening area w/ separate reference electrode?

A

Monopolar needle

23
Q

What sound doe MEPPs make on EMG?

A

seashell sound; indicates needle is close to endplate (which can be very painful for patient)

24
Q

What do fibrillations and positive sharp waves indicate?

A

Abnormal spontaneous activity

Active denervation (axonal loss)

25
Q

What is the source level for Fibs and sharps?

A

muscle fiber

26
Q

Fasciculations indicate what?

A

anterior horn cell disease

Can also be found in normal patients

27
Q

What sound doe MEPPs make on EMG?

A

seashell sound; indicates needle is close to endplate (which can be very painful for patinet)

27
Q

What is the source level of Fasciculations?

A

Motor neuron/axon

28
Q

What spontaneous abnormal activity indicates a motor unit that has been denervated, then reinnervated by another motor neuron, which then also becomes denervated?

A

Complex repetitive discharge

Involuntary, repetitive serrated discharges (complex in appearance)

29
Q

What do complex regional discharges indicated?

A

chronic radiculopathy, anterior horn cell disease, normal patients

30
Q

What is ephaptic transmission?

A

process by which muscle fibers fire regularly together (as seen in complex regional discharges)

31
Q

What is the source level for Complex Regional Discharges?

A

Multiple muscle fibers

32
Q

What abnormal spontaneous activity has an amplitude that steadily decreases as the muscle fiber continues to fire (sounds like a divebomber)

A

Myotonic discharge

33
Q

What does myotonia indicate?

A

Seen in anything with “myotonia” or similar in the name

Myotonic dystrophy, paramyotonia, myotonia congenita, hyperkalemic periodic paralysis, acid maltase deficiency

34
Q

What is the source level for Myotonia?

A

muscle fiber

35
Q

Are smaller or large motor units recruited first?

A

smaller motor units

Huge motor units, which often contain type II muscle fibers, are activated with maximal intensity

36
Q

Firing frequency

A

count how many single MUAPs are on the screen, multiple by 5

E.g. see the MUAP 4 times, firing about 20Hz

37
Q

What is a neuropathic recruitment pattern?

A

decreased recruitment, with increased firing of intact motor units who are taking up the extra slack –> indicated axonal loss

38
Q

When is a MUAP considered to be polyphasic?

A

when it crosses the baseline 5 or more times

39
Q

What is a myopathic recruitment pattern?

A

early recruitment, MUAPs w/ small duration, small amplitude

40
Q

What indicates primary demyelinating process on NCS?

A

prolonged latency, decreased conduction velocity

41
Q

What indicates primary axonal process on NCS?

A

decreased amplitude

42
Q

Conduction block definition?

A

Decrease in proximal CMAP > 20% compared to CMAP at distal stimulation site

43
Q

When is wallerian degeneration complete?

A

5 days = motor
10 days = sensory

44
Q

Which condition is associated w/ conductions blocks at non-entrapment sites?

A

AIDP

45
Q

Indication for blink study?

A

detect lesions of the trigeminal nerve, facial nerve, and pons/medulla

PM&R Recap (10 decks)

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