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Fuentes J.1,2, Guajardo E.1, Lizana M.1, Rodriguez M.1
1Catholic University of Maule, Physical Therapy, Talca, Chile, 2University of Alberta, Physical Therapy, Edmonton, Canada
Background: Current conceptualization for the placebo phenomenon includes the psychosocial context surrounding the patient. For example, recent evidence has confirmed the positive effect of the interaction patient-clinician and patients' expectations on the placebo analgesia. However, other aspects of the therapeutic encounter, such as the appearance of the therapeutic equipment and its impact on the placebo effect in experimental pain has not been fully explored.
Purpose: The objective of this study was to evaluate the effect of the appearance of the therapeutic equipment in the placebo effect of the transcutaneous electrical nerve stimulation using an experimentally-induced ischemic pain.
Methods: This was a randomized parallel placebo controlled study. Seventy five (45 men, 30 women), healthy university students (mean age 21.29 ± 0.64 years) with no previous experience in electrotherapy treatments. Participants were allocated into three groups: control (no intervention n=25), portable placebo group (n=25), and cabinet placebo group (n=25). All participants underwent an experimentally induced ischemic pain (SETT). Placebo groups did not receive an electrical stimuli during the experimental protocol. The informational context during the application of placebo interventions included positive verbal suggestions of treatment effectiveness. Outcome measures included pain threshold (PT), tolerance (Ptol), and pain perception (PI-NRS).
Results: The test of multivariate analysis of variance (MANOVA) with repeated measures showed significant differences among groups (p=0.007). PTol was statistically different (p = 0.003). Compared to Control group PTol was delayed 22 % and 20.5% for the portable placebo TENS and cabinet placebo TENS respectively. PT did not show differences among groups (p=0.76). Changes in PI-NRS were significant different between the control group and portable placebo TENS group (p = 0.05). No other comparisons for PI-NRS were significant. Effect size (ES) calculated for PI-NRS changes between control and portable placebo TENS group was large (d= 1.09). Moderate ES were calculated for the differences between control and cabinet placebo TENS (d= 0.52), and between portable placebo TENS and cabinet placebo TENS group (d= 0.57).
Conclusion(s): The results of this study show that pain is a context dependent variable being influenced by the appearance of the therapeutic equipment and therapists positive verbal suggestions. An enhanced placebo effect was obtained during the portable placebo TENS intervention for the participants of this study. Therefore, it is possible that in young people with clinical pain, its application may be associated with a better treatment responsiveness. However, these results need to be confirmed in a clinical setting.
Implications: This research thesis provides some insight into how the placebo phenomenon operates in healthy subjects under experimentally-induced pain when receiving a sham physiotherapy treatment. The therapeutic context including the appearance of the therapeutic equipment and therapists positive verbal suggestions seem to play a relevant role in the placebo response. These factors should be considered when implementing interventions in physical therapy for a better response to treatments. The findings of this study have implications for future research in physiotherapy helping to characterize placebo responders.
Funding acknowledgements: No funding declared.
Topic: Pain & pain management
Ethics approval: Scientific Ethics Committee Catholic University of Maule.
All authors, affiliations and abstracts have been published as submitted.
