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30 Cards in this Set

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What voltage range are motor studies in? Sensory?
millivolts. Microvolts.
What part of the stimulator is placed closest to the active electrode?
The cathode.
What is the compound muscle action potential?
The summation of all underlying muscle fiber action potentials.
How much supramaximal stimulation should you go?
20%
What three processes does CMAP latency represent?
conduction velocity along the nerve, NMJ transmission, muscle depolarization.
When is CMAP duration usually present (pathologically)?
In demyelinating lesions, due to loss of synchony.
What is the typical amplitude range of sensory studies (SNAPs)?
1-50 microA
What are some of the advantages of measuring a SNAP peak latency? What's the deal with this and CV?
It's less affected by artifact and noise. It doesn't represent the fastest fibers thus cannot be used to find CV.
What are the typical durations of CMAPs and SNAPs?
1.5 ms, 5-6 ms
What is the main advantage of antidromic NCS?
Usually, when done, the antidromic recording electrodes are closer to the nerve.
What is the main disadvantage with antidromic SNAPs?
Sometimes the CMAP is volume conducted along with it, causing a larger negative deflection to follow (and sometimes overlap).
If you are unsure if you're looking at a CMAP or SNAP, what is the best way to differentiate?
Look at the duration (SNAP 1.5 ms, CMAP 6 ms).
Re: CMAPs, SNAPs, and MUAPs (EMG), what will a lesion proximal to the DRG frequently show?
Decreased amplitude on CMAPs, signs of denervation on EMG, normal SNAPs.
Describe the differing effects of phase cancellation and temporal dispersion with sensory and motor NCS.
Little effect on motor b/t distal and proximal stim. With sensory, increased duration, decreased area and amplitude.
Describe temporal dispersion and phase cancellation
Basically the same thing: change in the summated waveform over distance when there is a variability in conduction velocity among the components of the SNAP. Phase cancellation occurs with temporal dispersion when the positive deflection of a wave subtracts from the total area of the waveform.
Why is there not much temporal dispersion with motor NCS?
Pretty much all MUAPs conduct at the same speed, with the same duration.
What are the three most common mixed nerve conduction studies?
Median nerve at the wrist, ulnar at the elbow, tibial at the tarsal tunnel.
What types of nerves are recorded with mixed nerve action potentials?
type Ia.
What is the typical NCS pattern seen with axon loss?
Decreased amplitude with preserved CV and DL.
When does mild slowing occur with pure axonal loss? Major slowing?
with axonal loss of the fastest axons. Significant slowing should not occur.
What's the cutoff of CV and DL drop for purely axonal lesions with NCS?
never less than 75% of the lower limit of normal for CV and never more than 130% of the upper limit of normal for DL.
Timewise, how is Wallerian degeneration different for motor versus sensory nerves?
motor degrades faster (3-5 days) than sensory (6-10)
What conduction velocities denote unequivocal demyelination?
Less than 35 m/s in the UEs or 30 m/s in the LEs.
What is the rare exception when markedly slow CVs don't denote demyelination?
Nerve regrowth/resprouting following transection.
What class of pathology does conduction block most typically occur?
With acquired demyelination.
What is the CMAP amplitude drop cutoff usually used to denote conduction block?
20% drop (especially when associated with slowing)
Why is the presence of demyelination with polyneuropathy a significant finding?
Because few PNs are demyelinating.
With demyelinating polyneuropathies, when would you see a diffuse pattern versus a focal pattern?
Diffuse pattern typically seen more with inherited pathologies (e.g. CMT type 1), focal pattern seen with acquired (AIDP, CIDP).
What do CMAPs look like with myopathies?
Typically normal, but sometimes distal CMAP amplitudes may be low (rare myopathies and critical illness myopathy).
How does the CMAP differ in presynaptic and postsynaptic NMJ disorders?
Normal in postsynaptic. In presynaptic, amplitude is low at rest and is improved with RNS.