Repetitive nerve stimulation: effects of recording site and the nature of 'pseudofacilitation'.
OBJECTIVE
To describe changes in the waveform of the compound muscle action potential (CMAP) during repetitive nerve stimulation for various recording sites.


METHODS
Responses to trains of 10 stimuli given at 0.1, 1, 3, 5, 10 and 30 Hz to the ulnar nerve were recorded simultaneously from 8 hand sites in 15 healthy subjects. Percentile changes of amplitude, duration and area of both negative and positive phases were analyzed.


RESULTS
Duration consistently decreased during the trains. At 30 Hz, the mean amplitude of the negative phase increased on 5 sites but decreased on 3. Area consistently decreased, but least for hypothenar sites. Repeated stimulation causes an alteration in the waveform of the CMAP that consists of 4 elements: (1) shorter duration; (2) changed amplitude of the negative phase (up or down); (3) merging of bifid peaks; (4) changes were more pronounced for positive than negative phases.


CONCLUSIONS
As the term 'pseudofacilitation' implies an increase in amplitude, it is often not appropriate. Increased muscle fiber conduction velocity can explain most of the waveform alterations. Movement and shortening of muscles may play additional roles. Consequences for diagnostic yield await a comparison with disease groups.
van Dijk
J G
JG
Department of Neurology and Clinical Neurophysiology, Leiden University Medical Centre, The, Leiden, Netherlands. vandijk@knf.azl.nl
van der Hoeven
B J
BJ
van der Hoeven
H
H
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction / Q000502:physiology*; D013997:Time Factors; D014459:Ulnar Nerve / Q000502:physiology*