Placebo effects on cutaneous pain and itch

Placebo effects on cutaneous pain and itch: a systematic review and meta-analysis of experimental results and methodology

Blythe, Joseph S. (Universiteit Leiden)
Thomaidou, Mia A. (Universiteit Leiden)
Peerdeman, Kaya J. (Universiteit Leiden)
van Laarhoven, Antoinette I.M. (Universiteit Leiden; Leiden University Medical Center)
van Schothorst, Myrthe M.E. (Universiteit Leiden)
Veldhuijzen, Dieuwke S. (Universiteit Leiden; Leiden University Medical Center)
Evers, A.W.M. (TU Delft Applied Ergonomics and Design)

2022

Placebo effects, positive treatment outcomes that go beyond treatment processes, can alter sensations through learning mechanisms. Understanding how methodological factors contribute to the magnitude of placebo effects will help define the mechanisms by which these effects occur. We conducted a systematic review and meta-analysis of experimental placebo studies in cutaneous pain and itch in healthy samples, focused on how differences in methodology contribute to the resulting placebo effect magnitude. We conducted meta-analyses by learning mechanism and sensation, namely, for classical conditioning with verbal suggestion, verbal suggestion alone, and observational learning, separately for pain and itch. We conducted subgroup analyses and meta-regression on the type of sensory stimuli, placebo treatment, number of acquisition and evocation trials, differences in calibrated intensities for placebo and control stimuli during acquisition, age, and sex. We replicated findings showing that a combination of classical conditioning with verbal suggestion induced larger placebo effects on pain (k = 68, g = 0.59) than verbal suggestion alone (k = 39, g = 0.38) and found a smaller effect for itch with verbal suggestion alone (k = 7, g = 0.14). Using sham electrodes as placebo treatments corresponded with larger placebo effects on pain than when topical gels were used. Other methodological and demographic factors did not significantly affect placebo magnitudes. Placebo effects on pain and itch reliably occur in experimental settings with varied methods, and conditioning with verbal suggestion produced the strongest effects. Although methods may shape the placebo effect to some extent, these effects appear robust overall, and their underlying learning mechanisms may be harnessed for applications outside the laboratory.

Placebo effects
Pain
Itch
Conditioning
Verbal suggestion
Observational learning

http://resolver.tudelft.nl/uuid:6f263c82-868a-46f7-a08e-815985bad561

10.1097/j.pain0000000000002820

0304-3959

Pain

Institutional Repository

journal article

© 2022 Joseph S. Blythe, Mia A. Thomaidou, Kaya J. Peerdeman, Antoinette I.M. van Laarhoven, Myrthe M.E. van Schothorst, Dieuwke S. Veldhuijzen, A.W.M. Evers