Abstract
Objectives
Assessment of pain inhibitory mechanisms using conditioned pain modulation (CPM) is relevant clinically in prediction of pain and analgesic efficacy. Our objective is to provide necessary estimates of intersession CPM reliability, to enable transformation of the CPM paradigm into a clinical tool.
Design
Two cohorts of young healthy subjects (N = 65) participated in two dual-session studies. In Study I, a Bath-Thermode CPM protocol was used, with hot water immersion and contact heat as conditioning- and test-stimuli, respectively, in a classical parallel CPM design introducing test-stimulus first, and then the conditioning- and repeated test-stimuli in parallel. Study II consisted of two CPM protocols: 1) Two-Thermodes, one for each of the stimuli, in the same parallel design as above, and 2) single test-stimulus (STS) protocol with a single administration of a contact heat test-stimulus, partially overlapped in time by a remote shorter contact heat as conditioning stimulus. Test–retest reliability was assessed within 3–7 days.
Results
The STS-CPM had superior reliability intraclass correlation (ICC2,1 = 0.59) over Bath-Thermode (ICC2,1 = 0.34) or Two-Thermodes (ICC2,1 = 0.21) protocols. The hand immersion conditioning pain had higher reliability than thermode pain (ICC2,1 = 0.76 vs ICC2,1 = 0.16). Conditioned test-stimulus pain scores were of good (ICC2,1 = 0.62) or fair (ICC2,1 = 0.43) reliability for the Bath-Thermode and the STS, respectively, but not for the Two-Thermodes protocol (ICC2,1 = 0.20).
Conclusions
The newly developed STS-CPM paradigm was more reliable than other CPM protocols tested here, and should be further investigated for its clinical relevance. It appears that large contact size of the conditioning-stimulus and use of single rather than dual test-stimulus pain contribute to augmentation of CPM reliability.
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