Neurophysiological Testing Flashcards
what are NCVs used for?
help diagnose nerve damage or disease
what are EMGs used for?
help determine if there is myopathic involvement in the disease
List some broad disease categories that electrodiagnostic testing can be helpful in diagnosing
- Motor neuron disease
- Radiculopathy
- Plexopathy
- Neuromuscular junction disease
- Muscle diseases
- Neuropathies
- Weakness in ICU
how can you further divide the categeory of neuropathy?
mononeuropathy
polyneuropathy
what are the 3 classifications for a mononeuropathy?
- Neuropraxia
- Axonotmesis
- Neurotmesis
what is neuropraxia?
pressure, compression or stretch injury
distorts myelin sheath w/o Wallerian degeneration
what is axonotmesis?
demyelination that causes axonal damage
axonal regeneration will occur over time along w/sprouting
What is neurotmesis?
severe injury to the nerve
axon, schwann cell and endoneurium are completly disrupted (like a complete cut)
what are the outcome measures we look at when interpreting NCVs?
- amplitude
- latency (proximal and distal)
- conduction velocity
what is amplitude a measure of?
the strength of the AP
related to the # of axons in the nerve being tested
what is latency a measure of?
the time it takes the AP to travel
what is conduction velocity a measure of?
the velocity of the AP
takes the distance traveled by the AP and the latency into account
when performing an NCV would type of injury would most likely result in changes to latency?
demyelination in some capacity
what type of damage to a nerve will affect the conduction velocity?
both demyelination and axonal damage
T/F: you can only test motor nerves with NCVs?
FALSE
can test both sensory and motor nerves but the set up is a bit different
what is the name for an AP generated during motor nerve testing? sensory nerve testing?
- motor → CMAP (compound motor action potential)
- sensory → SNAP (sensory nerve action potential)
SNAPs can be either ____________ or ______________
Orthodromic
Antidromic
what does Orthodromic mean?
it is traveling in the natural direction of a sensory AP
what does antidromic mean?
testing and recording opposite direction of sensory AP
possible b/c the AP generated during testing will be propogated in both directions
If there is suspected proximal damage what tests would we want to do?
- F-wave
- H-reflex
what is an F-wave?
retrograde “rebound” motor impulse
AP that travels the full length of the motor axon and back
(measures the latency of the antidromic CMAP)
T/F: the F-wave can be done on both sensory and motor nerve fibers?
FALSE
just motor
what types of damage/diseases is F-wave helpful in diagnosing?
- proximal damage/demyelination
- GBS/CDIP
- Radiculopathies
- Peripheral neuropathies
What is an H-reflex?
stimualtes an AP that follows the muscle stretch reflex arc
what types of disorders would an H-reflex be helpful in diagnosing?
- evaluation of:
- nerve root lesions
- Upper motor neuron lesions
- commonly done on the S1 root
what types of diseases/disorders would an EMG test be most helpful in?
diseases that affect:
- the muscle (muscular dystrophies)
- the neuromuscular junction (myasthenia gravis)
- diffuse disorders that cause peripheal neuropathies
- disorders that affect the motor neurons in the spinal cord (ALS, ruptured spinal disc)
what does EMG asses?
the electrical activity (AP) of the muscle in several stages.
refer to the electical activity as a MUAP (motor unit action potential)
EMG will asses the electrical activity of a muscle in several stages, what are they?
- as the needle goes into the muscle (insertional activity)
- muscle at rest
- muscle with activation
what type of activity will be observed in a normal/healthy muscle during the at rest phase of an EMG?
- insertional activity (50-200 ms = very short)
- should be silent following the crisp static sound of insertional activity
- normal spontaneous acitivity may be observed
list some normal spontaneously activity types that can be observed during the EMG at rest
- MEPPs - mini end plate potential
- EPPs - end plate potentials
- EPSs - end plate spikes
what would be considered abdnormal muscle activity at rest during EMG (3)?
- decrease in normal insertional activity
- increase in normal insertional activity
- prolonged insertional activity
what can cause a decrease in insertional activity during EMG?
- loss of muscle fibers (fibrosis, muslce atrophy)
- some metabolic disordes
what can cause an increase in insertional activity during EMG?
- neuropathic disorders
- myopathic disorders
what can cause prolonged insertional activity during EMG?
- post acute denervation
- inflammatory muscle disorders
- muscular dystrophy
what types of abnormal activity can be observed during rest in EMG testing?
- Fibrillations
- Positive Sharp waves
- Fasciculations
- Complex regional discharge (CRD)
- Myokymic
- Myotonic
what is a fibrillation?
spontaneous discharge of one or a few muscle fibers
what are fibrillations associted with?
- muscle degeneration (myopathy)
- suggests a potential LMN problem (neuropathy)
- the size of the fibrillations usually directly correspond to the severity of the injury
what are fasciculations?
spontaneous, twitch like contraction
not necessarily indivitive of pathology (ex: eye twitch)
what types of disorders/diseases are fasciculations more common with?
- a disease involving alpha motor neurons
- chronic demyelination conditions
what might suggest to you that a fasciculation is normal rather than due to a disease?
it is singular in event, not multiple is short succession
what is a complex reptitive discharge (CRD)?
polyphasic waveforms with fairly fixed amplitudes that show up in a high but stable discharge rate
sounds like a machine gun
spontaneous discharge of multiple different muscle fibers that are asychonous
what types of conditions are CRDs observed in?
- neurogenic
- myopathic
- generally observed with chronic conditions
- hereditory neuropathic diseases
what are Myokymic discharges?
groups of recurring spontaneous MUAP that fire in a brief repetitive burst pattern
what are Myotonic potentials?
rhythmic electrical discharges that are arise from muscle fibers all over the place - super spontaneous
what types of disease are myotonic potentials related to?
myotonic diseases
an alternative way to group MUAPs observed at rest is by what?
whether they fire alone or in groups
what types of MUAPs fire alone at rest?
- EPSs
- Fibrillation potentials
- Myotonic Discharges
what types of MUAPs fire in groups?
- adjacent muscle fibers
- CRD
- insertional activity
- motor unit potentials
- fasciculation potentials
- myokymic discharges
- neurotonic discharges
how would you describe the shape of a normal MUAP during muscle activation EMG?
- biphasic
- triphasic
when a neurogenic injury occurs, what changes will be observed immediately in an EMG?
reduced recruitment
increase in firing rates of MUAPs
when a neurogenic injury occurs, what changes will be oberved after collateral sprouting has occured?
the shape of the MUAP will change from triphasic to polyphasic
(MUAPs will be out of sync)
what are polyphasic MUAPs indicative of?
neurogenesis
collateral sprouting has most likely occured following a neurogenic injury and the new branches of the nerves are trying to figure out how to fire in sync again, they are disoriented
after a long time has passed following a neurogenic injury (>6 months) what changes will be observed on an EMG?
shape is once again triphasic
amplitude will be greater (1 nerve with 2x as many muscle fibers = must fire at a higher amplitude)
myopathic = decrease in _________
number of viable muscle fibers
