Chapter 3: Basic NCS Flashcards
Advantages of sensory peak latencies vs. onset latencies? Disadvantages?
Advantages: 1. Can ascertain in straightforward manner 2. Can easily mark the point of deflection;
Disadvantages: 1. Cannot calculate CV 2. Normal values for peak latencies depend on using standard distances
Advantage of performing antidromic sensory conduction study? Disadvantage?
Advantage: 1. Higher SNAP amplitude;
Disadvantage: 2. Likely going to have volume-conducted motor potential following the SNAP
What phenomenon is seen with sensory nerve conduction studies more so than motor conduction studies when stimulating proximally? Why?
Temporal dispersion and phase cancellation (Overlap of the trailing positive phase of the fastest potential overlapping with the leading negative phase of the slower fibers)
Characteristics of axonal loss lesions with regards to amplitude, CV, and distal latency?
Amplitude: decreased;
CV: normal or slightly decreased, but not below 75% of LLN;
Distal latency: normal or slightly prolonged, but not greater than 130% of ULN
What can happen if stimulation is performed in an acute axonal loss lesion during the first 3 days after nerve insult with respect to the amplitude proximally and distally? When could this be seen?
Larger amplitude distally, reduced proximally;
Pseudo-conduction block seen with acute trauma/transection of the nerve, or nerve infarction as seen in vasculitic neuropathy
Which nerve conduction study amplitudes are typically low or absent in demyelinating lesions? Why?
Sensory;
More temporal dispersion –> more phase cancellation
Why would CMAP amplitudes and distal latencies in myopathy still be normal usually?
Most myopathies affect proximal muscles
Examples of hereditary demyelinating neuropathies?
CMT I, IV, X-linked; Dejerine-Sottas, Refsum, HNPP;
Metachromatic leukodystrophy, Krabbe, Adrenoleukodystrophy;
Niemann-Pick Disease
Examples of acquired demyelinating neuropathies?
AIDP and CIDP;
Associated with HIV, MGUS, anti-MAG, Waldenstrom;
MMN; diphtheria
