Electrodiagnostic Testing Flashcards
What is electrodiagnostic testing used for? Who typically performs these tests?
- Used to asses function and integrity of the PNS and the musculature it innervates
- Performed by MD, PT, and other members of healthcare profession
What are the major purposes of nerve conduction velocity tests?
NCV – nerve conduction velocity
- Helps diagnose nerve damage or disease
- Measurement of how well electrical signals (Aps) travel up/down peripheral nerves
- Evaluates the peripheral nerve in its entirety
What are the major purposes of electromyography?
EMG – electromyography
- Determines myopathic involvement
- Measurement of how muscles respond to electrical signals (Aps) both during rest and with activity
- Looks at the muscle belly and neuromuscular junction
What information does NCV/EMG provide?
- Time course of disease
- Anatomic location of pathology
- Nature of pathology
- Distribution of pathology
- Physiological status of lesion
- Data for clinical/lab use
What nerves do we test? Why?
Large diameter myelinated nerves
Easier to zap and easier to measure due to myelin
In the motor nerve conduction testing portion of NCVs, what are CMAPs?
- Compound Motor AP – measures amplitude of AP
o Test is grabbing the last AP at the neuromuscular junction before it hits the muscle belly
In the sensory nerve conduction testing portion of NCVs, what are SNAPs?
- Sensory nerve AP
In the motor and sensory conduction tests, what is latency?
- Time in which AP travels from stimulator to electrode
In the motor and sensory conduction tests, what is conduction velocity and how is it determined?
- Speed of AP
- Length/(proximal latency – distal latency)
o Proximal latency – elbow or knee
o Distal latency – wrist or ankle
What is the difference between orthodromic and antidromic testing?
- Orthodromic – stim distal and record proximal
o Natural direction of sensory APs - Antidromic – stim in middle and have bidirectional AP
o Opposite direction of sensory APs
When are F wave tests performed? How do they work?
F-wave
- Retrograde “rebound” motor impulse – travels full length of motor axon and back (rebounds at anterior horn)
- Used to evaluate proximal damage and demyelination (GBS, radiculopathy, peripheral neuropathies)
When are H-reflex tests performed? How do they work?
H-wave
- Used to evaluate radiculopathy
- Follows muscle stretch reflex arc – goes all the way to spinal cord
- Can help in evaluation of nerve root lesions and UPPER motor neuro lesions (spinal cord)
What are some of the basic interpretations that can be made within a NCV study? (3 definitions)
- Amplitude – related to # of axons in nerve
- Latency – marker in time, therefore most affected by demyelinating processes
- Conduction velocity – speed, can be affected by both axonal loss and demyelination
What is the conduction velocity when large, fast-conducting fibers are lost?
moderate slowing
What is the conduction velocity during demyelination?
marked slowing
What types of pathology are EMGs most helpful in diagnosing?
Conditions that interfere with MUSCULAR CONTRACTION
- Diseases that affect the muscle (muscular dystrophies)
- Diseases that affect the neuromuscular junction (myasthenia gravis)
- Diffuse nerve disorders that cause peripheral neuropathies
- Disorders that affect the motor neurons (anterior horn cells) in the spinal cord (ALS, ruptured spinal disc)
Explain what a motor unit action potential is, and how its relevant to EMGs.
- MUP – summed electrical activity of all muscle fibers activated within the motor unit
- What is measured during an EMG
What is considered normal muscle activity surrounding insertional activity?
- Normal – slight movement but then there should be silence while muscle is at rest
What does a decrease in normal insertional activity mean?
associated with loss of muscle fibers or metabolic disease
What does an increase in normal insertional activity mean?
associated with neuropathic or myopathic disorders
What does a prolonged insertional activity mean?
post-acute denervation, inflammatory muscle disorders, muscular dystrophy
What is considered normal versus abnormal muscle activity at rest?
- Normal – silence at rest with the occasional movement as things fire
- Abnormal – nothing moves at rest
What 3 things determine speed of AP?
- diameter of axon
- presence of myelin
- amount of myelin
What are limitations to electrodiagnostic testing?
- easily affected by: age, temp, obesity, edema
- must be diligent about electrode placement
What is fibrillation associated with?
single muscle fiber that is degenerating
- suggests there is a LMN problem
- look like a mini EKG
When are fibrillations seen?
2-3 weeks after an injury
What is associated with fibrillations and are they always seen together?
positive sharp waves
- not always seen with fibrillation but often seen together
What is a fasciculation? Normal or abnormal?
- spontaneous, repetitive, twitch-like contraction of the examined muscle at rest
- normal and abnormal
- occurs at LMN
What are complex repetitive discharge? What is a specific component that they have?
- polyphasic high frequency waveforms that are fixed in amplitude and consistent with discharge rate
- have an audio component
When do we see complex repetitive discharge?
chronic pathologies
- chronic nerve entrapment
- Marie Charcot tooth
What does myokymic muscle activity look like?
waves of contractions in groups
What does myotonic muscle activity look like? What disorders are these present with?
all over the place contractions
- indicative of myotonic disease (rare genetic diseases characterized by muscle weakness and wasting)
After an injury to MUP and the nerve has recovered, what will be seen on an EMG?
AP amplitudes are bigger and the waveforms are stretched out because 1 nerve has twice as many terminal axons as before
nerve conduction velocity results with neuropraxia (ie: carpal tunnel)
- increase latency and decreased conduction velocity
- decreased amplitude of SNAP & CMAP if prolonged compression
EMG results of neuropraxia (ie: carpal tunnel)
normal or show signs of denervation if prolonged
nerve conduction velocity results of incomplete disruption axonotmesis
- decreased amplitude of SNAP & CMAP
- increased in distal segment latency with decreased conduction velocity
nerve conduction velocity results of complete disruption axonotmesis
- complete loss of motor and sensory response when proximal segment is stimulated
- absence of CMAP & SNAP in distal segment
EMG results of axonotmesis
- prolonged insertional activity
- fibrillation and positive sharp waves
- polyphasic MUAPs, initially reduced recruitment that increases with time
nerve conduction velocity results of neurotmesis
- decreased amplitude of SNAP & CMAP
- increased in distal segment latency with decreased conduction velocity
(same as axonotmesis)
EMG of neurotmesis
- prolonged insertional activity
- abnormal activity at rest (fibrillation, + sharp waves, fasiculations)
- polyphasic MUAPs, initially reduced recruitment that increases with time
- no voluntary activity
carpal tunnel amplitude during nerve conduction
normal for CMAP and SNAP
carpal tunnel latency during nerve conduction
goes up (increase time) no matter where you zap them
- should be really obvious when you zap them at the wrist
carpal tunnel conduction velocity during nerve conduction
- goes down because of the increase in latency
What would you expect to see with EMG findings for carpal tunnel?
normal
What is the expected result of a CMAP w/ diabetic neuropathy?
- leads to decreased amplitude due to axon degeneration
What is the expected result of a orthodromic SNAP w/ diabetic neuropathy?
- see a decreased amplitude when the stem is placed in an area of sensory loss
- will see normal conduction when the stem is placed above the area of sensory loss
What will you see in the NCV study if the patient has lost 50% integrity of its nerve fibers?
the amplitude would decrease and increase in latency
- decrease in conduction velocity
Why are EMGs less helpful in adding diagnostic value to diabetic neuropathies until later in the disease progression?
muscles aren’t affected until later on in the progression of the injury
EMG results of diabetic neuropathy
- fibrillation potentials
- sharp waves
- LE > UE
- increased amplitude and duration of MUAP
Nerve conduction velocity results of charcot marie tooth disease
- uniform slowing of latency and reduction of conduction velocity
- chronic - reduced amplitude
When is an EMG helpful with charcot marie?
during the chronic stages
EMG results of charcot marie
- fibrillation
- sharp waves
- increased amplitude and duration of MUAP
Nerve conduction results of guillan-barre
- increased latency due to loss of myeline at points along axon
- decreased amplitude b/c myeline insulates axon and when its gone the AP starts leaking out
T/F: EMGs are not helpful in ruling in demyelinating disorders if in the acute phase
true
nerve conduction test results of myopathies like muscular dystrophy
typically normal
EMG results of myopathies like muscular dystrophy
- early maximum recruitment
- fibrilation, + sharp waves
- decreased amplitude, duration MUAP; polyphasic
