Clinical evaluation of excitability measures in sensory nerve

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.