• Tatum M Cummins, Stephen B McMahon, and Kirsty Bannister.
• Central Modulation of Pain, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK.
• Eur J Pain. 2021 Feb 1; 25 (2): 415-429.

BackgroundReporting in conditioned pain modulation (CPM) studies is not standardised. Here, two CPM protocols were performed in populations of healthy human subjects in order to investigate the influence of the CPM paradigm and stringent analyses parameters on the identification of a net CPM effect.MethodsA standard thermal or mechanical CPM protocol was carried out on 25 and 17 subjects, respectively. The standard error of measurement (SEM) of the CPM effect was calculated in order to determine a change in pain thresholds greater than that due to measurement error or 'real' change in test scores. In addition, each individual underwent a minimum of two control CPM sessions, which were paired with the CPM test sessions. To quantify a net CPM effect, the intrasession difference between baseline and conditioning was subtracted from the difference calculated at the same time points during the control session.ResultsFor both protocols, excellent reliability for intrasession repeats of the test stimulus at baseline was demonstrated for thermal and mechanical stimulation (ICC > 0.9). Test-retest subject responses (in terms of experimental Session 1 versus. Session 2) showed excellent reliability for mechanical (ICC > 0.8), compared to thermal stimulation, which ranged from poor to moderate (ICC < 0.4->0.75). However, calculating the net CPM effect using control session data demonstrated poor-fair reliability for both protocols (ICC < 0.4-0.59).ConclusionCalculating the net CPM effect should be optimised and standardised for comparison of CPM data collected from global research groups. Recommendation is made for the performance of a multicentre, test-retest study.© 2020 European Pain Federation - EFIC®.

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