Clinical evaluation of excitability measures in sensory nerve

Abstract

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 estimated), threshold electrotonus to 100 ms polarizing currents, a current-threshold relationship (indicating inward and outward rectification), and the recovery of excitability following supramaximal activation. The method was tested on 50 healthy volunteers, stimulating the median nerve at the wrist and recording the antidromic compound sensory nerve action potential (SNAP) from digit 2. The excitability measurements were similar, where comparisons were possible, with published sensory nerve data, and confirmed differences from motor nerves, particularly in strength-duration behavior and recovery cycle, likely to reflect functional differences between sensory and motor nerves. Although slower than for motor nerves, the sensory nerve recordings were sufficiently quick (16 to 18 min) to allow them to be included in routine clinical studies. We propose that this method, which provides quite different and complementary information about nerve function to conventional conduction studies, provides a useful new approach for exploring the pathophysiology of sensory neuropathies.

Long-Term Neuropathy After Oxaliplatin Treatment: Challenging the Dictum of Reversibility

“…Neurophysiological assessment of nerve function was undertaken using conventional nerve conduction studies [14,26] and axonal excitability studies [12,27]. A Medelec Synergy system (Oxford Instruments, Oxfordshire, U.K.) was used for nerve conduction studies of upper and lower limb nerves.…”

“…The median nerve was stimulated at the wrist with a reference electrode placed 10 cm distal over bone and compound sensory action potentials (CSAPs) were recorded from the second digit. Using established protocols [12,27], multiple excitability parameters were recorded, as in prior studies of oxaliplatin-induced neurotoxicity [8,15], as indirect measures of resting axonal membrane potential. The recovery of excitability following impulse conduction, marking the function of voltage-gated Na ϩ channels, was assessed with the parameters refractoriness and superexcitability, calculated as the percent change in threshold 2.5 msec and 7 msec after supramaximal stimulation [12,29,30].…”

Normal data on axonal excitability in Koreans

“…17 Our study has reaffirmed that the tendency of excitability differences between motor and sensory axons within the human distal median nerve. 18 It is known that large myelinated sensory axons have a greater persistent sodium current than alpha motor axons, and also exhibit inward rectification. 17 This difference in excitability can explain why paresthesia develops in sensory nerves more often than does fasciculation or cramp in motor nerves in PNs.…”

Reproducibility of current perception threshold with the Neurometer® vs the Stimpod NMS450 peripheral nerve stimulator in healthy volunteers: an observational study

“…It has been suggested that the pulse duration used in direct current peripheral nerve stimulators has some bearing on whether motor or sensory nerves are stimulated. In particular, a pulse duration of B 0.1 msec is suggested to stimulate motor neurons more selectively without undue sensory discomfort, 24 whereas a pulse duration of C 0.3 msec is considered to be more selective for sensory nerves, 12 although this distinction remains unclear in clinical practice. 25 The ICCs of the Stimpod at a frequency of 2 Hz and a pulse width of 0.3 msec fell within the ''good'' and ''excellent'' ranges of reproducibility for the second and fifth digits, respectively, potentially making this a useful combination of settings for CPT testing.…”