gms | German Medical Science

Objective: Electrical peripheral nerve stimulation (PNS) primarily bases upon the gate-control-theory that was suggested by Melzack and Wall in 1965 [1]. Preclinical data indicate that PNS reduces release of excitatory amino acids, increases release of GABA and serotonin, inhibits sympathetic activity, and activates descending inhibitory pathways from the brainstem [2], [3], [4], [5], [6]. PNS is reported to be an effective pain treatment [7], [8]. However, randomized clinical trials have not been performed so far. Furthermore, an objective proof of antinociceptive effects is lacking. The human experimental study addressed PNS effects on nociception and pain by clinical neurophysiology and psychophysics.

Method: The randomized controlled cross-over trial was conducted in healthy volunteers. Each volunteer participated in three experimental sessions in randomized order on different days. In all sessions painful laser test stimuli were applied to the left hand dorsum and cortical potentials were recorded by EEG. Conditioning stimulation included electrical PNS of the left (PNS ipsilateral) or the right superficial radial nerve trunk (PNS contralateral). PNS consisted of rectangular electrical pulses (200 µs) with a frequency of 100 Hz. PNS intensity was adjusted to evoke tingling sensations on hand dorsum without any painful or unpleasant perception. Local cutaneous anesthesia at PNS site provided for preferential nerve trunk stimulation. In the control session no active PNS was applied. Cortical potentials (LEP) evoked by painful laser stimulation and mechanical and thermal perception thresholds were recorded at the same site before, during, and after PNS or a no stimulation period (Control).

Results: Mechanical and thermal perception decreased in the anesthetized area above the superficial radial nerve. LEP amplitude decreased independently of PNS site. Exclusively under ipsilateral, left PNS, LEP latency increased and laser pain ratings decreased. Mechanical detection threshold transiently increased during ipsilateral PNS at hand dorsum.

Conclusions: PNS induced reduction of mechanical perception due to peripheral collision of orthodromic (test stimulus) and antidromic (PNS) selective Aβ fiber excitation. Delay of LEP and reduction of laser pain were specific to ipsilateral PNS. Divergent and common effects of ipsilateral and contralateral PNS suggest a combination of peripheral and central antinociceptive mechanisms. The study in man documents inhibition of nociception and pain by PNS and provides with an experimental model for future objectives in neuromodulation.