Psychophysical or spinal reflex measures when assessing conditioned pain modulation?

Abstract

Background Assessing conditioning pain modulation (CPM) with spinal reflex measures may produce more objective and stable CPM effects than using psychophysical measures. The aim of the study was to compare the CPM effect and test–retest reliability between a psychophysical protocol with thermal test‐stimulus and a spinal reflex protocol with electrical test‐stimulus. Methods Twenty‐five healthy volunteers participated in two identical experiments separated by minimum 1 week. The thermal test‐stimulus was a constant heat stimulation of 120 s on the subjects’ forearm with continuous ratings of pain intensity on a 10 cm visual analogue scale. The electrical test‐stimulus was repeated electrical stimulation on the arch of the foot for 120 s, which elicited a nociceptive withdrawal reflex recorded from the anterior tibial muscle. Conditioning stimulus was a 7°C water bath. Differences in the magnitude and test–retest reliability were investigated with repeated‐measures analysis of variance and by relative and absolute reliability indices. Results The CPM effect was −46% and 4.5% during the thermal and electrical test‐stimulus (p < 0.001) respectively. Intraclass correlation coefficient of 0.5 and 0.4 was found with the electrical and thermal test‐stimulus respectively. Wide limits of agreement were found for both the electrical (−3.4 to 3.8 mA) and the thermal test‐stimulus (−3.2 to 3.6 cm). Conclusions More pronounced CPM effect was demonstrated when using a psychophysical protocol with thermal test‐stimulus compared to a spinal reflex protocol with electrical test‐stimulus. Fair relative reliability and poor absolute reliability (due to high intraindividual variability) was found in both protocols. Significance The large difference in CPM effect between the two protocols suggests that the CPM effect relates to pain perception rather than nociception on the spinal level. Due to poor absolute intrarater reliability, we recommend caution and further research before using any of the investigated CPM protocols in clinical decision making on an individual level.

The impact of paradigm and stringent analysis parameters on measuring a net conditioned pain modulation effect: A test, retest, control study

“…There was considerable variation in the time between experimental sessions for a proportion of subjects, which might explain some of the variability in CPM effect sizes reported across time. However, the results of our reliability analysis do not deviate from what has been reported previously, even when taking into account the variability in the ICC model used across different studies (Gehling et al., 2016; Imai et al., 2016; Lie et al., 2019). An important consideration when interpreting CPM data is that it represents a gross, top‐down output.…”

“…Further, inter‐session CPM responses (i.e. effect sizes) are variable in healthy subjects (Gehling et al., 2016; Granovsky, 2013; Imai et al., 2016; Kennedy et al., 2016; Larsen et al., 2019; Lie et al., 2019; Vaegter et al., 2018). Despite best recommendations (Kennedy et al., 2019; Vaegter & Graven‐Nielsen, 2016; Yarnitsky et al., 2015) a gold standard CPM protocol, or the most effective modality for reliably evoking a stable CPM response, has not been determined.…”

Factors Associated with Low Inter-Session Reliability of Conditioned Pain Modulation in Older People with or Without Chronic Musculoskeletal Pain

“…Long intervals (eg, two or four month) decreased the test-retest reliability for CPM. 67 As such diversity of protocols leads to differences in the reliability for CPM, [68][69][70] further investigation is necessary for other protocols of CPM.…”

Inhibition of current perception thresholds in A-delta and C fibers through somatosensory stimulation of the body surface

“…All stroking stimuli were delivered manually by an experimenter trained to apply the strokes with constant force and velocity. In the noxious condition, participants immersed their non-dominant hands into a circulating water bath maintained at a temperature of 6 − 8 °C 22 – 24 . In reference to a previous study 25 , an interval of 20 min was allowed between stimuli.…”