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EMG > EMG knowledge > Flashcards

EMG knowledge Flashcards

1
Q

Filter settings Sensory NCS

A

20Hz to 10 kHz

also listed as 20-2000Hz

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2
Q

Filter setting for Motor NCS

A

2Hz to 10kHz

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3
Q

Filter settings for EMG

A

20Hz to 10kHz

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4
Q

Sensory sweep speed ( X-axis)

A

5 msec

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5
Q

Sensory sensitivity (gain), Y-axis

A

10uV-20uV

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6
Q

Sweep speed motor

A

2msec

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7
Q

Sensitivity motor

A

5mV

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8
Q

EMG sweep speed

A

10 msec

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9
Q

EMG sensitivity

A

100uV for insertional activity

1mV for recruitment pattern analysis

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10
Q

Normal temp for upper limb

A

32 degrees

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11
Q

Normal temp for lower limb

A

30 degrees

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12
Q 
What happens to these parameters when electrodes are less than 4cm apart
Peak latency: ?
Amplitude:  ?
Duration:  ?
Rise time: ?
A

Peak latency: Decreased
Amplitude: decreased
Duration: Decreased
Rise time decreased

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13
Q

For SNAP:
Anatomy examined
Pertinent latencies
Amplitude measurements

A

Anatomy examined: sensory nerves
Pertinent latencies: Peak or onset
Amplitude measurements: peak to peak (uV)

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14
Q

For CMAP:
Anatomy examined
Pertinent latencies
Amplitude measurements

A

Anatomy examined: Motor nerve fibers, NMJ, muscle fibers
Pertinent latencies: onset latency
Amplitude measurements: Baseline to peak mV

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15
Q

H reflex formula

A

9.14 + .46 (leg length in centimeter from the medial malleolus to the popliteal fossa) + 0.1 (age)

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16
Q

H reflex normal value

side to side

A

28 to 30msec
Side to side difference 1.5 msec is significant
> 60 years: adds 1.8 msec
temp not an important factor as H-reflex the pickup is over a more proximal (and therefore warmer) muscle.

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17
Q

F wave:
Normal
Side to side difference

A

Normal:
Upper limb: 28 msec
Lower limb: 56 msec

Side to Side difference:
2 msecs in upper limb is significant
4 msec in the lower limb is significant
decreased persistence (occurrence) on repetitive stimulation correlates with a potential abnormality

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18
Q

Median motor

A

Amp >5

DL <4.2

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19
Q

Sural

A

Amp >5

DL <4.2

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20
Q

Median sensory

A

Amp > 15

DL <3.7

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21
Q

Ulnar motor

A

AMP> 4.6

DL <4

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22
Q

ulnar sensory

A

AMP> 12

DL <3.6

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23
Q

Combined sensory index

A

CSI: ringdiff+ thumbdiff+ palmdiff

CSI peak distal latencies > 1ms is abnormal

> 5ms difference from peak latencies is abnormal in each

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24
Q

Dorsal Ulnar cutaneous (bar)

A

Amp> 5

DL <2.9

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25
Q

Radial motor

A

Amp>2
DL <2.9

Amp>4.5
DL < 2.1

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26
Q

Radial sensory

A

Amp >15
DL <2.9

AMP>7
DL <2.8

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27
Q

MAC

A

AMP>4

DL <2.6

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28
Q

LAC

A

AMP >5

DL <2.5

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29
Q

peroneal motor

A

AMP>2

DL <6

30
Q

Tibial motor (medial plantar nerve)-AHB

A

AMP>4

DL <6

31
Q

Tibial motor (lateral plantar branch)-FDMB

A

Amp >6.1

DL <8.3

32
Q

femoral motor

A

AMP> 3

DL <7.4

33
Q

superficial peroneal sensory

A

AMP >15.1

DL <4.2

34
Q

Muscles innervated by PIN

A
  1. Supinator
  2. Extensor Carpi Radialis Brevis
  3. Extensor digitorum communis
  4. Extensor digiti minini
  5. Extensor carpi ulnaris
  6. aBductor pollicis
  7. extensor pollicis brevis
  8. Extensor pollciis longis
  9. extensor indicies
35
Q

Sites of compression of PIN

A
  1. Arcade of Froshe
  2. supinator muscle
  3. extensor carpi radialis brevis muscle
  4. Leash of henry (recurrent radial vessels that fan out across the PIN at the level of the radial neck)
  5. Fibrous tissue anterior to the radiocapitellar joint
36
Q

Diabetic Amyoptrophy

A

Also known as: proximal diabetic neuropathy, diabetic lumbosacral radiculoplexus neuropathy, and diabetic polyradiculopathy.

occurs in patients with diabetes (Type II>Type 1), Usually involves weakness followed by wasting of muscles, and excruciating pain in the muscles of thigh, hip, and buttocks. Symptoms sudden in onset. The weakness involves the thigh and the leg so patients have difficulty getting out of chairs and often require cane or crutches.

37
Q

ALS symptoms classically do not include

A

loss of extraoccular control, bowel/bladder dysfunction, or dementia

38
Q

ALS most likely inherritance pattern

A

ALS runs in families, most likel autosomal dominant

39
Q

A family history in a second- or third-degree relative or a family history of frontotemporal dementia should also be regarded as strong evidence in support of a diagnosis of?

A

Familial ALS

40
Q

What needle type is best for isolated MUPs

A

bipolar needle

41
Q

The onset latency

A

represents the conduction speed of the fastest fibers

42
Q

EMG myopathy findings

A

low amplitude, short duration, polyphasic motor units with early recruitment.

43
Q

On needle electromyography (EMG), normal motor units have a duration of:

A

5-15msec
Duration is the time from the initial baseline departure to the final return to baseline. Normal duration is about 5 to 15 msec or approximately one horizontal division with a commonly used sweep speed of 10 msec/division. It represents the degree of synchrony in the firing of the individual motor fibers that contribute to the motor unit. With reinnervation, there is asynchrony of firing of individual muscle fibers due to immature myelin. Therefore, duration of a motor unit increases with reinnervation and can be seen in chronic neuropathic processes. Decreased duration may be seen in myopathic disorders.

44
Q

In the newborn, nerve conduction velocities are approximately what percentage of adult values?

A

At birth, most of the myelination is incomplete. Conduction velocities are about 50% of adult values. By 1 year of age, the velocity is about 75%. Myelination is usually complete by age 3 to 5 years.

45
Q

Rich Canau anastomosis

A

anastmosis between deep ulnar branch and reccurent medial nerve

46
Q

CRDS

A

CRDs are usually noted in longstanding disorders (of more than 6 months). They represent groups of spontaneously firing action potentials with an affected area of muscle electrically stimulating an adjacent muscle fiber. This produces a local muscular arrhythmia. The patterns repeat regularly with a frequency of 10 to 100 Hz. They have the sound of a motorboat misfiring. They can be seen in chronic neurogenic or myopathic disorders. As the needle study would be normal in a sensory neuropathy (only the motor fibers are tested with needle testing), CRDs would not be noted in a sensory peripheral neuropathy.

47
Q

EMG findings in spinal stenosis

A

In spinal stenosis, there is narrowing of the vertebral canal, which is usually exacerbated by extending the spine (standing) and relieved with flexion of the spine (sitting). Pain may radiate from the back down to the extremities, especially with extension of the spine. SNAPs are normal as the dorsal root ganglion (DRG) is located outside the spinal canal. CMAPs should not be affected as the distal portion of the nerve is not affected. There may be abnormal spontaneous potentials at rest (positive sharp waves [PSW] or fibrillations) or chronic motor unit action potential (MUAP) changes (polyphasic potentials) that are often bilateral. Bilateral paraspinals and extremities should be tested for EMG abnormalities.

48
Q

Denervation can be found

A

in neuropathic or myopathic processes.

49
Q

Alcoholic neuropathy

A

sensory & motor axonal neuropathy

50
Q

Paraneoplastic syndrome***

A

sensory axonal neuropathy

51
Q

Guillain-Barré syndrome

A

segmental demyelination

52
Q

Diabetic neuropathy

A

sensory and motor, axonal and demyelinating peripheral polyneuropathy.

53
Q

flexor pollicis brevis

A

the median and ulnar nerves

54
Q

Normal amplitude for a MUAP

A

Normal amplitude of a motor unit using a monopolar needle is about 1 to 7 mV in amplitude.

55
Q

adductor magnus is innervated by

A

This muscle has dual innervation from both the Obturator nerve and the Tibial division of the Sciatic nerve.

56
Q

A-waves

A

seen in chronically injured nerves and represent regeneration or collateral sprouting of a nerve, as the orthodromic response is diverted along a collateral neural branch to circumvent the conventional path. This alternative path has a constant latency and is seen between the M- and the F-wave, with Submaximal stimulation.

57
Q

CSI

A

Thumb diff, ring diff, palm diff. f the added differences total more than 0.9 msec, CTS is confirmed.

58
Q

SSEPs

A

may be helpful in diagnosing problems in sensory nerves (such as in meralgia paresthetica, also known as lateral femoral cutaneous nerve injury) that are not accessible to routine electrodiagnostic testing. SSEPs are not the test of choice in assessing for a radiculopathy, as only the sensory pathway is tested and the pathway is very long. Problems anywhere along the pathway may affect latency and amplitude. They are not at all useful in assessing motor nerves (anterior interosseous nerve injury). The pathway is too long to be of use in a sacral plexopathy.

somatosensory-evoked potentials can also assess autonomic nerves

59
Q

Hereditary neuropathies

A

uniform-demyelinating neuropathies. They will therefore show uniformly slowed conduction velocity without temporal dispersion. Temporal dispersion would be seen in segmental demyelination, where some fibers are conducting much slower than others.

60
Q

Critical illness neuropathy

A

sensorimotor axonal neuropathy.

Latencies and conduction velocities remain normal to borderline normal. Should test at least 3 limbs.

(If the fastest axons are affected, latency may be mildly increased, and conduction velocities mildly decreased. However, the axonal loss (amplitude) is out of proportion to the slowing.)

61
Q

Acquired neuropathies

A

are usually more distal or segmental then hereditary neuropathies. Temporal dispersion is a feature of an acquired neuropathy.

62
Q

paraneoplastic syndrome.

A

A patient who has low-amplitude sensory nerve action potentials with preserved compound motor action potential amplitudes (and relatively normal conduction velocities and latencies) should be suspected of having a paraneoplastic syndrome.

63
Q

What errors would decrease NCS amplitude

A

not stimulating over the nerving

not giving enough stimlation

64
Q

What error would result in the latencies being delayed

A

reversing the anode and cathode

If the anode and cathode were reversed on the stimulator, there would be an extra 3 to 4 cm in length between the stimulator and the active electrode.

65
Q

SDSA

A

In myopathies, motor units usually have low amplitude (less than 1 mV when using a monopolar needle), short duration, polyphasicity, and early recruitment.

66
Q

The X-axis (sweep) represents

A

time, which is usually in milliseconds per division.

67
Q

During repetitive nerve stimulation in a patient with myasthenia gravis, what should be seen?

A

In repetitive nerve stimulation, a greater than 10% decrease in CMAP amplitude from the first to the fifth stimulation is considered significant for pathology at the neuromuscular junction.

68
Q

To assess whether a patient has a peripheral neuropathy, it is necessary to?

A

test sensory AND motor nerves in three limbs

69
Q

The rise time is measured as

A

time from the peak of the initial positive deflection to the subsequent negative upward peak

70
Q

H-reflex elicited in any muscle besides the gastrocnemius-soleus or the flexor carpi radialis is considered…

A

pathological and may indicate an upper motor neuron lesion.

71
Q

when the gain is set at 100 mcV/division you can better assess

A

fibs, positive sharp wave (PSW), or an end-plate potential

EMG (6 decks)

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