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Fibular motor nerve conduction studies: Investigating the mechanism for compound muscle action potential amplitude drop with proximal stimulation
Author(s) -
Kamel Jordan T.,
KnightSadler Rory J.,
Roberts Leslie J.
Publication year - 2015
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.24671
Subject(s) - compound muscle action potential , stimulation , amplitude , electrophysiology , chemistry , anatomy , medicine , physics , quantum mechanics
The compound muscle action potential (CMAP) amplitude of extensor digitorum brevis can show a drop with proximal stimulation in normal fibular nerves. Methods : We assessed the contribution of the far‐field potential recorded by the reference electrode (R‐CMAP) to the fibular CMAP. Negative R‐CMAP amplitude, peak‐to‐peak amplitude, and negative area were measured and correlated with the amplitude decrease. Fibular motor nerves from 14 healthy participants were studied. Results : The mean CMAP amplitude drop with proximal stimulation was 14.0 ± 9.3%, including a >30% reduction in 1 study. All measured R‐CMAP parameters correlated with the degree of amplitude drop. Conclusions : A greater R‐CMAP contribution to the fibular CMAP leads to greater phase cancellation and temporal dispersion. The resulting amplitude drop seen in the proximal CMAP can be large enough to be classified incorrectly as “probable conduction block” by several different diagnostic criteria. Muscle Nerve 52 : 993–996, 2015