Itch induction by audiovisual stimuli and histamine iontophoresis: a randomized, controlled noninferiority study

Abstract

Summary Background Previous research has mainly used skin‐manipulating methods to induce itch. In comparison, itch induced by audiovisual stimuli lacks direct skin manipulation. Objectives The aim of this double blind, noninferiority study was to test the experimental hypothesis that itch induced by audiovisual stimuli is noninferior to itch induced by histamine iontophoresis in case of priming and without priming. Methods In 80 of 160 healthy volunteers itch was induced by histamine iontophoresis, while in the other 80 itch was induced by audiovisual stimulation. Forty people in each group experienced either an initial resting phase or dermal priming. Itch intensity was measured by visual analogue scales, while scratch duration and frequency were video‐recorded and evaluated by two independent raters. In addition, itch quality and location were measured by self‐report. Results Itch induced by audiovisual stimuli was inferior to itch induced by histamine iontophoresis in the absence of dermal priming. However, in the case of priming, maximal itch induced by audiovisual stimuli was not inferior to maximal itch induced by histamine iontophoresis. Additionally, differences in itch quality and location were observed. Conclusions The finding that maximal audiovisually‐induced itch was comparable with maximal histamine itch only after priming emphasizes that attention plays a dominant role in mentally‐induced itch. The comparability of maximal histamine and audiovisually‐induced itch in the case of priming opens up new research opportunities. What's already known about this topic? Itch is a multidimensional sensation that is altered by, among other things, attention. To induce itch in basic research, different methods are used, which are partially invasive or cause skin manipulation. Noninvasive audiovisual stimuli can be used to induce itch. What does this study add? This study investigated whether itch induced by audiovisual stimuli is noninferior to itch induced by histamine iontophoresis. Itch induced by audiovisual stimuli is noninferior with regard to maximal intensity in the case of priming. Noninferiority was not shown in the case of no priming, emphasizing the role of attention in itch induction. Histamine and audiovisually‐induced itch differ in terms of quality and location, but not in affective reaction.

Optimizing audiovisual itch induction: the role of attention and expectancy

“…In the present study, it is not unlikely that placebo iontophoresis induced nocebo effects on itch, amplifying the itch‐inducing effects of the audiovisual itch induction. Marzell and colleagues’ statement that somatosensory provocations induce anxiety – which plays a key role in nocebo effects – is consistent with this hypothesis.…”

“…In this issue of the BJD , Marzell and colleagues show for the first time that the level of itch induced by audiovisual itch stimuli is not inferior to histaminergic itch after dermal priming. New insights into the underlying mechanisms of audiovisual itch induction can further optimize its effectiveness.…”

“…Itch contagion may serve a nocifensive function (i.e. signalling potential bodily threat), and it probably involves activation of an affective mirror neuron system . Audiovisual itch contagion has been described for both humans and nonhuman primates, but it does not seem effective in rodents .…”

“…showing a nonitch‐inducing skin‐related video). They plausibly state that dermal priming would lead to attention being shifted in a way that it ‘potentiates mental processes’ . Priming prioritizes subsequent stimuli presented within the same modality, arguably resulting in facilitation of the audiovisual material (whether somatosensory priming would result in prioritization of somatosensory input remains to be investigated).…”

“…To conclude, advantages of audiovisual itch induction over histamine iontophoresis are noninvasiveness, more widespread distribution of audiovisual itch (representative of patients’ symptoms) and less contamination by painful sensations . Limitations of audiovisual itch include its inability to target specific body locations, and less control over induced scratching and the onset and duration of induced itch.…”