The Enigma of the Motor Nerve Conduction Study

The insignificant change in the CMAP in spite of axon AP dispersion is an enigma. We hypothesize that the terminal conduction time (TCT) (i.e., conduction in terminal axon branches, neuromuscular transmission, etc.) is independent of axon CV, represents a significant portion of the latency, masks AP dispersion, and reduces CMAP dispersion. This yields similar CMAPs with distal and proximal stimulation. The onset latency at the distal stimulation site does not depend on CV. Thus, onset latency and CV may not reflect the conduction properties of the fastest conducting axons.