Abstract
BackgroundConditioned Pain Modulation (CPM) is often used to assess human descending pain inhibition. Nine different studies on the test-retest-reliability of different CPM paradigms have been published, but none of them has investigated the commonly used heat-cold-pain method. The results vary widely and therefore, reliability measures cannot be extrapolated from one CPM paradigm to another. Aim of the present study was to analyse the test-retest-reliability of the common heat-cold-pain method and its correlation to pain thresholds.MethodsWe tested the short-term test-retest-reliability within 40 ± 19.9 h using a cold-water immersion (10 °C, left hand) as conditioning stimulus (CS) and heat pain (43-49 °C, pain intensity 60 ± 5 on the 101-point numeric rating scale, right forearm) as test stimulus (TS) in 25 healthy right-handed subjects (12females, 31.6 ± 14.1 years). The TS was applied 30s before (TSbefore), during (TSduring) and after (TSafter) the 60s CS. The difference between the pain ratings for TSbefore and TSduring represents the early CPM-effect, between TSbefore and TSafter the late CPM-effect. Quantitative sensory testing (QST, DFNS protocol) was performed on both sessions before the CPM assessment. Statistics: paired t-tests, Intraclass correlation coefficient (ICC), standard error of measurement (SEM), smallest real difference (SRD), Pearson’s correlation, Bland-Altman analysis, significance level p < 0.05 with Bonferroni correction for multiple comparisons, when necessary.ResultsPain ratings during CPM correlated significantly (ICC: 0.411…0.962) between both days, though ratings for TSafter were lower on day 2 (p < 0.005). The early (day 1: 16.7 ± 11.7; day 2: 19.5 ± 11.9; ICC: 0.618, SRD: 20.2) and late (day 1: 1.7 ± 9.2; day 2: 7.6 ± 11.5; ICC: 0.178, SRD: 27.0) CPM effect did not differ significantly between both days. Both early and late CPM-effects did not correlate with the pain thresholds.ConclusionsThe short-term test-retest-reliability of the early CPM-effect using the heat-cold-pain method in healthy subjects achieved satisfying results in terms of the ICC. The SRD of the early CPM effect showed that an individual change of > 20 NRS can be attributed to a real change rather than chance. The late CPM-effect was weaker and not reliable.
Highlights
Conditioned Pain Modulation (CPM) is often used to assess human descending pain inhibition
In all subjects a TSinitial with a pain rating of 60 ± 5 on the NRS (0–100) could be determined at both days with a temperature between 45 and 49 °C. 6 subjects had a difference of 1 °C in their TSinitial between both days
Mild erythema was detected in all subjects in the application area of the thermode, disappearing within 30 min after testing
Summary
Conditioned Pain Modulation (CPM) is often used to assess human descending pain inhibition. Nine different studies on the test-retest-reliability of different CPM paradigms have been published, but none of them has investigated the commonly used heat-cold-pain method. Aim of the present study was to analyse the test-retest-reliability of the common heat-cold-pain method and its correlation to pain thresholds. The descending inhibitory pathways can be assessed using two noxious stimuli [6]. Plenty of paradigms assessing the conditioned pain modulation (CPM) have been described, using thermal, mechanical, electrical or pressure stimuli as test stimulus (TS) and/ or conditioning stimulus (CS) in different combinations. The so-called CPM-effect is typically calculated as the difference between pain ratings of the TS before and the TS during or - to analyse its persistence - after application of the CS [7, 8]. There is no consensus whether a certain CPM protocol is preferable over the others [9]
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