Lecture 6 Flashcards
What is electrodiagnostic testing?
Used to assess function and integrity of the PNS and the musculature it innervates
What are the 2 most common electrodiagnostic tests?
- Electromyography (EMG)
- Nerve Conduction Velocity Studies (NCV)
Are EMG and NCV tests usually done together?
Normally yes, but they do provide different information
A NCV helps diagnose _____ damage or disease and is a measurement of how well electrical signals (APs) travel up/down _________ nerves.
- nerve
- peripheral
A EMG determines __________ involvement, and is a measurement of how ________ responds to electrical signals (APs) both during rest and with activity.
- myopathic
- muscle
Overall, what is the difference between an EMG and a NCV test?
NCV detects a problem with the nerve, whereas an EMG detects whether the muscle is working properly in response to the nerve’s stimulus.
The electrodiagnostic tests are in correlation and done after a ___________ and _____
- physical exam
- PMHx (past medical history)
What can these electrodiagnostic tests help with in regards to neuropathic or neuromuscular disease?
- time course of disease (acute vs chronic)
- anatomical location of pathology
- nature of pathology (axonal damage vs myelination, entrapment like carpal tunnel)
- distribution (widespread or local)
- physiological status of lesion (is PNS regenerating)
- data for clinical/ lab research
What can NCV/EMG diagnose?
- Motor Neuron Disease
- Radiculopathy
- Plexopathy
- Neuromuscular Junction Disease
- Muscle Disease
- Ocular and Pharyngeal weakness
- Neuropathy
- Weakness in ICU
NERVE CONDUCTION VELOCITY STUDIES
NERVE CONDUCTION VELOCITY STUDIES
Strong AP have _______ messages, weak AP have ______ messages.
- strong
- weak
What types of nerves does NCV tests look at?
- look at large diameter, highly myelinated nerves
- median n., radial n., ulnar n., peroneal n., posterior tib n., sural n.
What are the two primary components of NCV tests?
- motor NCV testing
- sensory NCV testing
Where is the recording electrode placed?
Over the muscle belly that is innervated by that nerve.
Where is the stimulator placed?
multiple places where nerve conduction would occur (armpit, elbow, wrist)
Do we care about a muscle twitch in NCV testing? Why?
No, nerve conduction tests are only looking at the peripheral nerve up until right before it innervates the muscle.
What do we care about in NCV testing instead of the muscle twitch?
Compound Motor Action Potential (CMAP)
-AP right before the muscle twitch occurs
What is the Compound Motor Action Potential a measure of?
the amplitude of the last AP (indicator of strength)
Why do we measure the amplitude of the AP at multiple sites (for example armpit, elbow, and wrist)?
- The AP should generally be the same at all points, may see a little decrease.
- We are concerned if we see the AP decreasing as it moves down.
What are two additional measurements we may look at when performing a NCV test other than amplitude?
- latency (proximal and distal)
- conduction velocity (length/(proximal lat.-distal lat.))
What is latency?
What is it measured in?
- Time it takes for the AP to travel from the point of stimulation to the recording electrodes
- ms
What is conduction velocity?
What is it measured in?
How is it measured?
- Also a reflection of the speed of AP
- m/s
- tape measure distance between point of stimulation and electrode and / by proximal latency-distal latency
What are the 2 things that impact latency and conduction velocity?
- diameter of nerve
- myelin sheath
- When conducting NCV tests, we want to aim for SUPRA-MAXIMAL stimulation, why is this?
- How do we reach this point?
- If we only provide a small electrical stimulation, we may be only recruiting half of the nerves and this could look like there is a reduction in the tests but we just didn’t wake the nerve up enough.
- Gradually increasing stimulation until we see a peak of the amplitude (CMAP)
As we increase electrical stimulation, we will see an increase in the ______. Eventually we will see a leveling off of the amplitude of the CMAP, this will be the amount of electricity we use for the test.
-CMAP (compound motor AP)
When we are performing sensory NCV tests, what are we measuring instead of CMAP?
Sensory Nerve Action Potential (SNAP)
Are SNAPs or CMAPs larger in amplitude in general?
CMAP
What is the fallback of SNAP testing?
- they tend to be more sensitive and liable to artifact
- artifact is a random recording you may see but isn’t indicative of anything
What is the positive of SNAP testing?
they are much more sensitive to mild or smaller lesions
What is an important concept with Sensory NCV testing?
concept of Orthodromically vs Antidromically
What is an orthodromic test?
testing the natural direction of sensory APs
What is an antidromic test?
testing the opposite direction of sensory APs
Which test is more common when testing sensory NCV, orthodromic or antidromic tests and why?
Antidromic
- Examiner preference
- Easier
- Slight Higher Amplitude Responses
F wave and H-Reflex tests are both used to answer very _________ clinical questions.
specific
The F waves are ________ “rebound” motor impulses that travel the full length of the motor axon and back.
The F wave tests are primarily used to evaluate _________ damage and demyelination.
- retrograde
- proximal
The H-Reflex is used to evaluate __________ and follows the muscle stretch reflex arc. This test can help in evaluating nerve ____ lesions and _______ motor neuron lesions. It is most common at the __ nerve root.
- radiculopathy
- root
- UPPER
- S1
Basic Interpretations with NCV Studies
- If we see changes in amplitude, that is related to the number of ________ in nerve.
- If we see changes in latency (a marker of time), this is most affected by _____________ processes
- If we see changes in conduction velocity (speed), this is affected by both ______ loss and ________.
- axons
- demyelinating
- axon loss and demyelination
If we are just seeing axonal loss, we will see a ________ loss in conduction velocity, when we have demyelination we will see a ___________ loss in conduction velocity.
- moderate
- significant
General Principles
- Test both ________ and _______ nerve conduction
- Test several __________ of the nerve
- Test the ____________ side
- Test __________ nerves
- Interpret the results in context with the _____________ of the suspected disorder
- sensory and motor
- segments (motor)
- contralateral for baseline
- multiple
- time course
What are limitations of NCV testing?
- easily affected by age, temp (cold = slower), obesity, edema
- must be diligent about electrode placement
ELECTROMYOGRAPHY (EMG)
ELECTROMYOGRAPHY (EMG)
What does EMG test?
electrical activity of muscles
EMG assists in diagnosis of conditions that interfere with muscular ___________.
contraction
- diseases that affect the muscle (dystrophies)
- diseases that affect the NM junction (myasthenia gravis)
- diffuse nerve disorders that cause peripheral neuropathies
- disorders that affect the motor neurons (anterior horn cells) in the spinal cord
Where is EMG helpful?
gives additional diagnostic and prognostic info about the neuropathic conditions
Is EMG an invasive test?
Yes, causes mild discomfort from needle inserted into muscle belly
The display screen of an EMG has both __________ and _________ displays.
- visual
- auditory
What is the EMG procedure?
- small wire like needle inserted into muscle belly
- look at insertional activity
- look at muscles at rest (fasciculations and fibrillations)
- look at muscles when activated
What is a motor unit?
cell body, dendrites of a motor neuron, the multiple axons, and the muscle fibers that it innervates
What is a motor unit action potential (MUAP)?
Are all MUAPs alike?
- summed electrical activity of all muscle fibers activated within a motor unit
- No, can see variations in amplitude, duration, configuration. This is due to muscle fiber sizes and number of fibers.
As the needle is inserted into the muscle belly, we have ________ activity, which is a burst of positive and negative spikes.
- insertional (50-200ms)
- sounds like static
_______ is golden when performing an EMG at rest
silence
Healthy muscle at rest is generally electrically silent when the needle electrode is not moving. However there is normal ___________ activity that can be represented by what 3 terms?
-spontaneous
- Motor End Plate Potential (MEPP)
- End Plate Potential (EPP)
- End Plate Spike (EPS)
- Is it a good thing when you see MEPP, EPP, and EPS?
- Where can this be important?
- Yes, shows there is a portion of muscle that is innervated
- things such as hysterical paralysis where there is nothing wrong neurologically to see there is some innervation occuring
Abnormal Muscle Activity At Rest
- Decrease in normal insertional activity is associated with loss of ____________ and has also been noted in ____________ disorders.
- Increase in normal insertional activity is associated with ________ or ____________ disorders
- Prolonged insertional activity can mean there is post acute ___________, __________ muscle disorders, or muscular ____________
- muscle fibers, metabolic
- neuropathic or myopathic
- denervation, inflammatory, dystrophy
Electrical activity other than MEPPs and EPPs in muscle at rest is indicative of what?
neuropathy or myopathy
The most common abnormal electrical activity that is seen at rest is what?
fibrillation
Fibrillation are __________ discharges that are usually ____ muscle fiber that can arise for several reasons.
- spontaneous
- one
Fibrillations are thought to be caused by an unstable muscle fiber ___________.
membrane
Fibrillations are usually seen - weeks after an injury
Fibrillations can be due to both ________ and ___________ conditions.
- 2 to 3 weeks
- myopathic and neuropathic
What types of waves are closely associated with fibrillation?
positive sharp waves
What are fasciculations?
spontaneous, repetitive, twitchlike contractions of the examined muscle at rest
Are fasciculations indicative of pathologies?
What is a fasciculation akin to?
- No, not necessarily
- twitch
As opposed to fibrillations, fasciculations are more often than not associated with ___________ fibers.
Fasciculations occur - days after denervation.
- multiple
- 2 to 3 days
What is a very common time we see fasciculations?
- disease involving alpha motor neurons
- also seen with chronic demyelnation
What are 3 other uncommon abnormal activities we may see at rest?
- complex repetitive discharge
- myokymic
- myotonic
What is complex repetitive discharge?
- spontaneous discharges of several different muscle fibers firing asynchronously but doing it at the same sequence every time
- this results in a “machine gun” like sound on EMG
Complex repititive discharge is generally seen with ________ conditions.
chronic
What is myokymic?
- groups of recurring spontaneous motor APs that fire in a repetitive burst pattern
- results in a “marching soldier” like sound on EMG
What is myotonic?
- rhythmic discharges arising from spontaneous muscle fibers
- amplitude and frequency constantly rise and fall
- specifically related to myotonic diseases (rare)
You can characterize the origin of EMG potentials as firing _____ or firing _________.
- alone
- in groups
Which of the EMG potentials are “firing alone”? (one motor unit)
- end plate spikes
- fibrillation
- myotonic discharges
Which of the EMG potentials are “firing in groups”? (multiple motor units)
Adjacent muscle fibers -complex repetitive discharge -insertional activity Motor Unit Potentials -fasciculation potentials -myokymic discharges -neurotonic discharges
If you need to produce a bigger muscle contraction you need to fire ____ muscle fibers and ________ APs.
- more
- stronger
Normally, our motor unit APs will be _________ or ___________.
- biphasic or triphasic (moreso triphasic)
- biphasic and triphasic is how many turns in the EMG
If we ever see more than 3 phases to an AP propogation, that is indicative to ________.
pathology
The motor unit AP is a sum of ________ smaller APs because a motor unit innervates multiple __________, each has its own AP.
- multiple
- muscle fibers
The muscle fibers in a healthy muscle belly will contract ______, so the APs are happening at the _______.
- in sync
- same time
Temporal Course of MUAP Changes - Neurogenic
- If 2 nerves are innervating a muscle belly and 1 of them stops, we will see ________ recruitment resulting in a worse contraction, but we will see an ________ in firing rate from the still intact nerve.
- The intact nerve will start to _______ sprout to help the denervated muscle fibers 1 month after. These contractions may be _______ however, resulting in a _________ AP.
- 2 months after we see that is is still ________ and longer spread out durations of the ____.
- 6 months after we see that it goes back to normal __________ setup. The main difference is that the amplitude and duration are ________ than where we started, why?
- reduced, increased
- collaterally, out of sync, polyphasic
- polyphasic, APs
- triphasic, larger, because we have 1 nerve with 2x as many muscle fibers it has to innervate
Polyphasic MUAP are indicative of ________ occuring.
neurogenesis
Myopathic conditions occur when you see a ________ in the number of viable muscle fibers.
decrease
Lower muscle fibers results in a lower _____.
MUAP
The remaining available muscle fibers will _______ due to the myopathic conditon.
shrink
MUAP is dependent on _____ and ____ of muscle fibers.
number and size
MUAP amplitude and duration will _______ in response to decrease in number and size of muscle fibers. We will also see an _______ in the number of phases seen from the triphasic wave.
- decrease
- increase
