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We compared itch sensations and axon reflex flare induced by transcutaneous electrical (0.08–8ms, 2–200Hz) and chemical (histamine iontophoresis; 100μC) stimulation. Stimuli were applied to non-lesional volar wrist skin in 20 healthy human subjects and 10 patients with atopic dermatitis. Intensity of evoked itch and pain sensations were rated on a numerical rating scale (NRS) of 0 (no sensation) to 10 (the maximum sensation imaginable). The axon reflex erythema was measured by laser Doppler imager and areas of alloknesis (itch evoked by light brushing) and hyperknesis (itch evoked by pricking) were assessed psychophysically. Electrical stimulation was most effective for stimulus durations ≥2ms and frequencies ≥50Hz. It evoked pure itch as threshold sensation in 80% of the subjects that was perceived with a delay of approximately 1s. Itch intensities of up to 7/10 were not accompanied by an axon reflex flare. In contrast, histamine provoked a massive increase of axon reflex erythema and maximum itch ratings of 3.1±0.2. The extention of alloknesis areas (2.3±0.5cm) evoked by electrical stimulation clearly exceeded those induced by histamine (0.7±0.3cm). Healthy subjects and patients with atopic dermatitis did not differ significantly in their response to either stimulation. We conclude that C-fiber activation underlies the electrically evoked itch sensation. The low electrical thresholds and the absence of an axon reflex flare suggest that these fibers are not identical with the previously described mechano-insensitive histamine responsive C fibers, but represent a separate peripheral neuronal system for the induction of itch.
Now I'm not going to protend to understand all that, but what it looks like to me is that there is a way to induce itching or more specifically the sensation of itch with a TENS unit, by direct nerve induction.
If that is the case I have an idea.