A New Diagnostic Method to Assess Small Fiber Neuropathies at Early Stages – An Experimental study investigating perception threshold stability

Background: Previous research has proven that epidermal- and transcutaneous stimulation can investigate the function of large and small nerve fibers individually using different electrodes. This study aimed to determine the stability of the perception thresholds when using such electrodes. This assessment is valuable for future research investigating small and large nerve fiber function separately using the technique over an extended period.

Methods: Twenty healthy volunteers participated in the study. The perception threshold of large nerve fibers, using a patch and small nerve fibers using a pin electrode was estimated 30 times during a period of 60 minutes. A threshold was established every other minute, alternating between the two electrodes. The stimulus duration was 1 ms and the interstimulus interval was 1.5-2.5 seconds. Linear regressions of the perception threshold as a function of time were performed. The slopes were used as an estimate of habituation and were compared between the electrodes.

Results: There was a significant difference in slope between the pin electrode (Mean: 0.023 [0.014; 0.031] mA/trial) and patch electrode (Mean: 0.011 [0.003; 0.020] mA/trial) (p=0.027, paired t-test), representing small and large fiber respectivly.

Conclusion: Both small and large fibers showed significant perception threshold increases over an hour. The higher slope of the pin electrode indicated that the small sensory nerve fibers are more prone to habituation than the large sensory nerve fibers.