Intact endogenous pain inhibition in complex regional pain syndrome type 1

Introduction: Impaired endogenous pain modulation is a common characteristic of various chronic pain conditions and may be a key mechanism underlying the development of chronic pain in complex regional pain syndrome (CRPS). One way to assess endogenous pain modulation in humans is through conditioned pain modulation (CPM) paradigms. Objectives: This study aimed to assess CPM capacity in chronic CRPS type 1 and its potential association with the individual pain phenotype. Methods: Sixteen individuals with chronic CRPS type 1 and 15 age- and sex-matched healthy controls (HC) were enrolled. Parallel and sequential CPM paradigms were performed at 2 testing sites: the most painful area and a remote, pain-free area using pressure pain thresholds as a test stimulus and a cold water bath as a conditioning stimulus. Individuals with CRPS underwent pain phenotyping to assess the characteristics of CRPS-related pain. Conclusion: Our results indicate that in individuals with chronic CRPS type 1, endogenous pain inhibition is intact and comparable with healthy individuals. Therefore, pathomechanisms underlying chronic CRPS are likely related to increased pain facilitatory rather than impaired inhibitory processes.