EMG and NCV Flashcards
What is an EMG
- 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
EMG
What is normal Insertional activity?
and what is abnormal?
- 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
EMG
at rest
what should you see vs what could be seen
- should see electrical silence (flatish line)
other findings:
- positive sharp waves
- fibrillation potentials
- complex repetitive discharge
- myotonic discharge
refer to lecture slides for pictures
repetitive discharge is seen in what type of disorders
- seen in disorders involving anterior horn cells, and some myopathies
EMG - muscle contraction
- 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
Other findings on an EMG during muscle contraction
- 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
Large/giant motor unit action potential
- collateral sprouting
Short duration, low amplitude
- sign of myopathy (Clinical weakness)
Nerve degeneration vs regeneration
- positive short wave = degeneration
- regeneration = asked person to contract; polyphasic = sign of regeneration
Other EMG finding: jitter
- sign of myasthenia gravis
- repeated contraction amplitude gets smaller
- dont contract as smoothly
Nerve conduction velocity
- an evoked test: the tester is evoking a response via a stimulus
- tests sensory and motor
- looks at integrity of the nerve
recording electrode
- used in a NCV test
- distal muscle placement
- look at what happens distally
Motor NCV
what is it looking for and how is this test conducted
- proximal stimulation => distal recording
- orthodromic testing
- looking for a motor response
Sensory NCV
how is this done
- proximal stimulation => distal recording
- antidromic testing
- looking for sensory response
Goes opposite the direction the sensory info usually travels
Reasons for NCV studies: neuropathy Focal
- carpal tunnel syndrome
- peroneal neuropathy
- ulnar neuropathy
Reasons for NCV: generalized neuropathy
- diabetic neuropathy
- guillian-barre syndrome
reasons for NCV studies: axonal neuropathy
- diabetic neuropathy
- nerve transection
Reasons for NCV: demyelinating neuropathy
- guillian barre syndrome
- carpal tunnel syndrome
Reasons for NCV: other conditions
- radiculopathy
- disorders at the neuromuscular junction: myasthenia gravis, lambert-eaton muscle syndrome
- motor neuron disease: ALS
- sensory neuronopathy: Sjogren’s syndrome
EMG: what should be seen for insertional activity:
- normal
- LMN lesion
- UMN lesion
- myopathy
- normal activity (not flat line)
- increased activity
- normal activity
- normal activity
EMG: what should be seen at rest
- normal
- LMN lesion
- UMN lesion
- myopathy
- flat line
- fibrillation
- flat line
- flat line
EMG: what should be seen for minimal voluntary contraction
- normal
- LMN lesion
- UMN lesion
- myopathy
- Normal
- giant amplitude
- normal
- small amplitude
EMG: what should be seen for Max Voluntary contraction
- normal
- LMN lesion
- UMN lesion
- myopathy
- full recruitment pattern
- low firing rate
- low firing rate
- full recruitment pattern (low amplitude)
*look at picture
NCV testing results
Sensory Nerve testing
- Sensory Nerve Action Potential (SNAP)
- latency: time it takes
- amplitude
- velocity: speed
NCV testing results
Motor Nerve testing
compents of the results
- compound muscle action potential
- latency
- amplitude
- velocity
NCV
F-wave
- used to look fo signs of demyelination, radiculopathy
- stimulate motor unit
- antidromic stimulation: distal muscle to alpha motor neuron
- stimulus reaches alpha MN, travels back down to muscle
- decreased speed indicates proximal nerve pathology
- stimulate nerve at least 10 times
- in lower extremity, average should be 60 seconds or less
only motor portion
NCV
F-wave results
For radiculopathy and demyelinating disease
Radiculopathy:
- demyelinating nerve root compression: may be prolonged (less myelin)
- axonal loss: may disappear/decreased amplitude
Demyelinating disease
- early: may see no change
- mid-course: delay in F-wave latency
- Late/severe: no F-wave
NCV
H reflex
- electrically induced stretch reflex
- stimulates sensory nerve
- stimulation should travel through nerve root, stimulate alpha motor neuron, travel down motor nerve and cause contraction
- decreased speed indicates NR pathology
- most often used to look at S1 NR by stimulating tibial nerve
H reflex results
- typical latency for S1 reflex: 35 ms
- increased latency indicates proximal sensory or motor damage: radiculopathy, avulsion (use with medical history)
- good to do and compare both sides
Information from nerve conduction studies: latency
- increased latency = more time
- increased latency implies less myelin
- NCV affected by number of axons and myelin
Information from nerve conduction studies: amplitude
- affected by number of axons
- M-wace/CMAP/MAP (motor NCS)
- SNAP sensory (NCS)
