A recently described method for recording multiple excitability parameters
of human motor nerves has been adapted to the study of sensory nerves. The
protocol measures stimulus-response behavior using two stimulus durations (
from which the distribution of strength-duration time constants is estimate
d), threshold electrotonus to 100 ms polarizing currents, a current-thresho
ld relationship (indicating inward and outward rectification), and the reco
very of excitability following supramaximal activation. The method was test
ed on 50 healthy volunteers, stimulating the median nerve at the wrist and
recording the antidromic compound sensory nerve action potential (SNAP) fro
m digit 2. The excitability measurements were similar, where comparisons we
re possible, with published sensory nerve data, and confirmed differences f
rom motor nerves, particularly in strength-duration behavior and recovery c
ycle, likely to reflect functional differences between sensory and motor ne
rves. Although slower than for motor nerves, the sensory nerve recordings w
ere sufficiently quick (16 to 18 min) to allow them to be included in routi
ne clinical studies. We propose that this method, which provides quite diff
erent and complementary information about nerve function to conventional co
nduction studies, provides a useful new approach for exploring the pathophy
siology of sensory neuropathies. (C) 2001 John Wiley & Sons, Inc.