Comparison of Thermal and Electrical Modalities in the Assessment of Temporal Summation of Pain and Conditioned Pain Modulation.

Monica Sean,Martine Bordeleau,Serge Marchand,Louis Gendron,Guillaume Léonard,Matthieu Vincenot,Alexia Coulombe-Lévêque

doi:10.3389/fpain.2021.659563

Monica Sean, Martine Bordeleau + Show 5 more

Open Access

https://doi.org/10.3389/fpain.2021.659563

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Abstract

Temporal summation of pain (TSP) and conditioned pain modulation (CPM) can be measured using a thermode and a cold pressor test (CPT). Unfortunately, these tools are complex, expensive, and are ill-suited for routine clinical assessments. Building on the results from an exploratory study that attempted to use transcutaneous electrical nerve stimulation (TENS) to measure CPM and TSP, the present study assesses whether a “new” TENS protocol can be used instead of the thermode and CPT to measure CPM and TSP. The objective of this study was to compare the thermode/CPT protocol with the new TENS protocol, by (1) measuring the association between the TSP evoked by the two protocols; (2) measuring the association between the CPM evoked by the two protocols; and by (3) assessing whether the two protocols successfully trigger TSP and CPM in a similar number of participants. We assessed TSP and CPM in 50 healthy participants, using our new TENS protocol and a thermode/CPT protocol (repeated measures and randomized order). In the TENS protocol, both the test stimulus (TS) and the conditioning stimulus (CS) were delivered using TENS; in the thermode/CPT protocol, the TS was delivered using a thermode and the CS consisted of a CPT. There was no association between the response evoked by the two protocols, neither for TSP nor for CPM. The number of participants showing TSP [49 with TENS and 29 with thermode (p < 0.001)] and CPM [16 with TENS and 30 with thermode (p = 0.01)] was different in both protocols. Our results suggest that response to one modality does not predict response to the other; as such, TENS cannot be used instead of a thermode/CPT protocol to assess TSP and CPM without significantly affecting the results. Moreover, while at first glance it appears that TENS is more effective than the thermode/CPT protocol to induce TSP, but less so to induce CPM, these results should be interpreted carefully. Indeed, TSP and CPM response appear to be modality-dependent as opposed to an absolute phenomenon, and the two protocols may tap into entirely different mechanisms, especially in the case of TSP.

Highlights

Chronic pain affects approximately one-quarter of Canadians and remains a challenging condition for healthcare professionals [1]
Different protocols can be used to assess temporal summation of pain (TSP) and conditioned pain modulation (CPM) using various types of modalities [16,17,18,19]. One such protocol, which has been developed by our team [20], allows for the measurement of both TSP and CPM, by administering a test stimulus (TS) before and after a conditioning stimulus (CS): TSP is assessed by measuring the fluctuations in pain scores throughout the first instance of the TS, and CPM is assessed by calculating the difference in pain levels evoked by the TS before and after the CS
The average pain intensity induced by the CS was different between the two protocols (62 ± 22/100 with the cold pressor test (CPT) and 78 ± 15/100 with transcutaneous electrical nerve stimulation (TENS); p < 0.001), as was the average unpleasantness of pain evoked by the CS (66 ± 26 /100 with the CPT and 83 ± 16/100 with the TENS; p < 0.001; Figure 3)

Summary

Introduction

Chronic pain affects approximately one-quarter of Canadians and remains a challenging condition for healthcare professionals [1]. One such protocol, which has been developed by our team [20], allows for the measurement of both TSP and CPM, by administering a test stimulus (TS) before and after a conditioning stimulus (CS): TSP is assessed by measuring the fluctuations in pain scores throughout the first instance of the TS, and CPM is assessed by calculating the difference in pain levels evoked by the TS before and after the CS This protocol originally used thermal stimulation, with the TS consisting of a moderately painful tonic heat stimulation delivered for 120 s using a thermode, and the CS consisting of a cold pressor test (CPT), wherein the subjects immerse their dominant forearm in a cold-water bath (10◦C) for 120 s. This protocol, like most other TSP and CPM protocols, requires complex, costly, and time-consuming apparatus and procedures; as such, it is not a realistic option for routine clinical assessment [21]

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