Effect of interelectrode distance on sural nerve action potential parameters.
OBJECTIVE
To assess differences in amplitude, latency, and duration, using a 3-cm vs. 4-cm distance between the active and reference electrodes when performing sural nerve conduction studies (NCS). Current normative data in lower-limb studies are generally based on 3-cm interelectrode differences, although 4-cm differences have been reported to be optimal in the upper limb.


METHODS
Prospective study comparing the onset latency, peak latency, duration, and amplitude for the sural sensory nerve action potential (SNAP) recording at two interelectrode distances in adult volunteers.


RESULTS
Forty-three sural nerves were studied in 22 normal subjects. Peak latencies recorded with a 4-cm interelectrode distance were significantly longer than those recorded with a 3-cm distance (mean difference = 0.06 msecs [SD = 0.09, P = 0.0073]). Duration was significantly longer (mean difference = 0.03 msecs [SD = 0.07, P = 0.0270]), conduction velocities were significantly slower (mean difference = -0.7 msecs [SD 1.0, P = 0.0012]), and onset latency and amplitude were not found to differ significantly. Average differences in peak latencies, duration, velocity, onset latency, and amplitude were not correlated with gender, age, or BMI.


CONCLUSIONS
In contrast to studies of upper-limb sensory NCS, sural SNAP parameters obtained with 3- and 4-cm interelectrode distances did not differ for onset latencies and amplitude. Peak latencies, duration, and conduction velocity differences, though statistically significant, were of insufficient magnitude to be clinically meaningful. By using a 4-cm instead of a 3-cm interelectrode difference for sural nerve studies, the small prolongation of 0.06 msecs in peak latency and tiny increment of 0.27 muV observed in our investigation is unlikely to influence the electrodiagnostician's interpretation of the study.
Plastaras
Christopher T
CT
Rehabilitation Institute of Chicago and Northwestern Feinberg School of Medicine, Chicago, Illinois, USA
Marciniak
Christina M
CM
Sipple
Daniel P
DP
D'Amore
Kirsten Gross
KG
Garvan
Cynthia
C
Zaman
Shehzaad M
SM
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004566:Electrodes; D004576:Electromyography / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D009431:Neural Conduction / Q000502:physiology*; D012016:Reference Values; D013497:Sural Nerve / Q000502:physiology*