EMG

Question 1

what is an EMG?

Answer 1

• assesses the fxn and integrity of the PNS
• NCS (n conduction studies)
• EMG (electromyography)
• special tests (repetitive n stimulation)

Question 2

N conduction studies

Answer 2

• peripheral n’s are stim w a controlled electrical stimulus

- responses are recorded

Question 3

N conduction studies- basic elements

Answer 3

• motor n conductions
• sensory n conductions
• late responses

Question 4

N conduction studies- measured parameters

Answer 4

• motor latency (conduction time from stim across a n segment thru the NMJ to initial act of m fibers)
• motor amplitude (# of activated m fibers)
• sensory latency (conduction time of AP from stim across a n segment)
• sensory amplitude (# of activated sensory axons)
• conduction velocity

Question 5

Needle electromyography

Answer 5

• needle electrode inserted into the m
• m is studied at rest and at diff levels of sustained, voluntary contraction
• electrical shape and pattern of response can distinguish b/w n and m disease

Question 6

Needle electromyography- parameters evaluated

Answer 6

• insertional activity
• spontaneous activity
• motor unit configuration
• motor unit recruitment
• interference pattern

Question 7

Needle electromyography- Insertional activity

Answer 7

• burst of electrical activity as needle is inserted into m
• due to disruption of m fiber membranes
• prolonged w denervation, some m dz’s

Question 8

Needle electromyography- denervation

Answer 8

• fibrillations, positive sharp waves, fasciculations

- hallmark of denervation, m membrane irritation

Question 9

Grading of spontaneous activity

Answer 9

• 0: no fibs, PSWs (+ sharp waves)
• +/-: fibs/PSWs are not persistent
• 1+: persistent in at least 2 areas
• 2+: persistent of moderate #’s in 3 or more areas
• 3+: persistent of large #’s, but not obscuring baseline
• 4+: base obliterated

Question 10

motor unit configuration

Answer 10

• diff force levels act m
• single motor units are assessed (motor axon and its m fibers)
• motor unit configuration- amplitude, duration, morphology

Question 11

motor unit recruitment

Answer 11

-pattern of motor unit activation w increasing volitional activation

Question 12

interference patterns

Answer 12

-motor unit pattern w full voluntary activation

Question 13

Needle electromyography- this neurogenic motor unit demonstrates what?

Answer 13

• reduced recruitment
• inc amplitude
• inc duration
• polyphasia (turns over baseline)

Question 14

EMG pearls

Answer 14

• supplement to, and NOT a replacement for hx and PE
• results- time-dependent
• studies are not “standardized”