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

Previous research has mainly used skin-manipulating methods to induce itch. In comparison, itch induced by audiovisual stimuli lacks direct skin manipulation.

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.

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.

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.

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.