EMG and NCV

Question 1

What is an EMG

Answer 1

• Electromyography
• volitional activities: patient must be able to follow directions
• patient generates (or attempts) muscle contraction
• assessment of muscle activity and signs of muscle damage

Question 2

EMG

Insertional activity

Answer 2

• should be some signs at insertion
• there should be some resistance
• increased activity: muscle degeneration, nerve injury
• decreased activity: significant atrophy, non-viable muscle tissue

Question 3

EMG

at rest

what should you see vs what could be seen

Answer 3

• should see electrical silence (flatish line)

other findings:

• positive sharp waves
• fibrillation potentials
• complex repetitive discharge
• myotonic discharge

refer to lecture slides for pictures

Question 4

repetitive discharge is seen in what type of disorders

Answer 4

• seen in disorders involving anterior horn cells, and some myopathies

Question 5

EMG - muscle contraction

Answer 5

• single motor unit action potention (normal = biphasic or triphasic)
• slight contraction: recruit 1 motor unit
• maximal contraction: are they able to recruit more motor units (full interference pattern)
• repeated contractions
• amplitude (m wave) - stronger muscle = larger amplitude

Question 6

Other findings on an EMG during muscle contraction

Answer 6

• polyphasic waves: sign of muscle disease or muscle recovery after injury
• large or giant motor unit action potentials: occur with collateral sprouting

refer to pictures

Question 7

Large/giant motor unit action potential

Answer 7

• collateral sprouting

Question 9

Short duration, low amplitude

Answer 9

• sign of myopathy (Clinical weakness)

Question 10

Nerve degeneration vs regeneration

Answer 10

• positive short wave = degeneration
• regeneration = asked person to contract; polyphasic = sign of regeneration

Question 11

Other EMG finding: jitter

Answer 11

• sign of myasthenia gravis
• repeated contraction amplitude gets smaller
• dont contract as smoothly

Question 12

Nerve conduction velocity

Answer 12

• an evoked test: the tester is evoking a response via a stimulus
• tests sensory and motor
• looks at integrity of the nerve

Question 13

recording electrode

Answer 13

• used in a NCV test
• distal muscle placement
• look at what happens distally

Question 14

Motor NCV

Answer 14

• proximal stimulation => distal recording
• orthodromic testing
• looking for a motor response

Question 15

Sensory NCV

Answer 15

• proximal stimulation => distal recording
• antidromic testing
• looking for sensory response

Question 16

Reasons for NCV studies: neuropathy Focal

Answer 16

• carpal tunnel syndrome
• peroneal neuropathy
• ulnar neuropathy

Question 17

Reasons for NCV: generalized neuropathy

Answer 17

• diabetic neuropathy
• guillian-barre syndrome

Question 18

reasons for NCV studies: axonal neuropathy

Answer 18

• diabetic neuropathy
• nerve transection

Question 19

Reasons for NCV: demyelinating neuropathy

Answer 19

• guillian barre syndrome
• carpal tunnel syndrome

Question 20

Reaons for NCV: other conditions

Answer 20

• radiculopathy
• disorders at the neuromuscular junction: myasthenia gravis, lambert-eaton muscle syndrome
• motor neuron disease: ALS
• sensory neuronopathy: Sjogren’s syndrome