Background & Aims
The conditioned pain modulation (CPM) test can be influenced by supraspinal mechanisms, such as expectation. In addition, examining such impact in individuals with distinct profiles of CPM efficiency could enhance our understanding of the mechanisms underlying endogenous pain modulation and its clinical implications. Therefore, this study assessed the effect of expectation of analgesia on CPM in healthy participants with inhibitory and non-inhibitory modulation.
Methods
The CPM was assessed on 21 women and 22 men, with a mean age of 26 ± 4.3 years, in two sessions with a 7-day interval: baseline and expectation of analgesia session, which was induced by audiovisual suggestion. Two different test stimuli (TS) were applied: mechanically controlled palpation (Palpeter® 4 Kg) and the pressure pain threshold (PPT), and two different areas were assessed: anterior temporalis muscle and thenar eminence of the hand. The conditioning stimulus (CS) involved immersing the non-dominant forearm in an ice water, and a parallel paradigm was applied. This CPM protocol was iterated three times with a 1-minute interval between the sequences of TS and areas across two blocks with a 20-min interval. The standard error of measurement was computed to identity inhibitors and non-inhibitors. Cochran’s Q, mixed ANOVA and ANCOVA were applied to the data (p<0.05).
Results
There was a significant decrease in the proportion of non-inhibitors during the expectation of analgesia session (32.6–44.2%) when compared with the baseline session (51.2–72.1%). The magnitude of CPM was lower in non-inhibitors in block 1 of baseline session for both techniques in both the trigeminal region (PPT: p = 0.001; Palpeter® 4 Kg: p = 0.000) and the spinal region (PPT: p = 0.001; Palpeter® 4 Kg: p = 0.003) compared to inhibitors. However, at other evaluation times, there was no difference between inhibitors and non-inhibitors (p>0.050). Additionally, there was a difference in the magnitude of CPM for the non-inhibitor group, being higher in block 1 of expectation of analgesia session when compared to block 1 of baseline session for PPT in the trigeminal region (p = 0.032), Palpeter® 4 Kg in the trigeminal region (Bonferroni p = 0.000), and PPT in the spinal region (p = 0.001). However, there were no differences between the sessions for the inhibitor group (p>0.050).
Conclusions
Placebo analgesia emerges as a clinically relevant pathway for activating the descending pain inhibitory system. Consequently, the clinical impact of tests assessing CPM is not solely reflective of inhibition within the spinal cord – brainstem – spinal cord circuit. Instead, it is shaped by the interplay of psychological and cognitive factors. Moreover, the absence of an additional effect in inhibitors hints at saturation or a potential “ceiling effect” in this analgesic response. As such, it becomes imperative to consider the influence of these cortical mechanisms for an accurate and pertinent profiling of pain modulation.
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Presenting Author
Allen Matheus da Silva Nascimento
Poster Authors
Allen Matheus Nascimento
PhD Student
Piracicaba Dental School, University of Campinas
Lead Author
Soraya Ardestani
University of Campinas/Piracicaba Dental School
Lead Author
Isabela Coelho Novaes
DDS
Piracicaba Dental School, University of Campinas
Lead Author
Leonardo Rigoldi Bonjardim
Bauru School of Dentistry, University of São Paulo
Lead Author
Fernando Exposto
Section of Orofacial Pain and Jaw Function, Aarhus University
Lead Author
Peter Svensson
DDS
Department of Dentistry and Oral Health, Aarhus University
Lead Author
Yuri Martins Costa
DDS, PhD
Department of Biosciences, Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil
Lead Author
Topics
- Placebo