The association between conditioned pain modulation and psychological factors in people with chronic spinal pain: A systematic review

A Systematic Review and Meta-Analysis of Conditioned Pain Modulation in Children and Young People with Chronic Pain

BACKGROUND/OBJECTIVES

Conditioned pain modulation (CPM) is a psychophysical experimental measure of the endogenous pain inhibitory pathway in humans, wherein one pain stimulus (the conditioning stimulus) is used to inhibit an individual's perception of a second painful (test) stimulus. Research provides evidence of impaired endogenous inhibitory pain responses in adults with chronic pain. CPM is now increasingly applied in paediatric research and clinical practice. The primary aim of this systematic review was to examine the efficacy of CPM in paediatric chronic pain populations (6-24-year-olds) compared to pain-free children and young people (CYP).

METHODS

The protocol was registered on PROSPERO (CRD42020221927). A systematic search of seven databases was conducted from database inception to 20th June 2024. Study inclusion criteria were as follows: (i) recruited a sample of CYP aged 6 to 24 (inclusive) with chronic pain or who were pain-free; and (ii) applied a CPM paradigm comprising both a painful test and conditioning stimuli that were sufficiently detailed to allow for replication,(iii) adhered to a study design of randomised control trial, case control or cohort study, including cross-sectional or longitudinal; (iv) available in the English language. Study exclusion criteria were: (i) The CPM paradigm used a non-painful test or conditioning stimulus only; and (ii) was only available as an abstract, letter, poster, editorial, case report, or review with or without meta-analyses. Risk of bias was assessed using the Appraisal Tool for Cross Sectional Studies (AXIS). Meta-analyses were conducted in Comprehensive Meta Analysis 3.0 using random effects models to compare the overall CPM responses in CYP with chronic pain conditions to healthy control CYP.

RESULTS

Thirty-two studies were eligible for inclusion, six of which were included in one or more meta-analysis (n = 407 chronic pain, n = 205 control). Meta-analysis revealed significantly weaker CPM responses in CYP with a variety of chronic pain conditions compared to healthy controls (standardized mean difference (SMD) = 0.352), and significantly weaker CPM responses in CYP with abdominal pain conditions compared to healthy controls (SMD = 0.685). No significant difference in CPM response was found between CYP with migraine and healthy controls (SMD = -0.201).

CONCLUSIONS

Variable results were found across individual studies, and the meta-analysis of the small number of eligible studies provides tentative evidence for impaired CPM in CYP with chronic pain compared to healthy controls. Further research is clearly needed. In particular, studies should present CPM results separately for different age groups, ethnic groups, and sexes, as these variables shape clinical pain responses.

Effects of Executive Functions and Cognitive Variables in Experimentally Induced Acute Pain Perception during a Distraction Task: A Study on Asymptomatic Pain-Free Individuals

The aim of this study was to investigate the influence of executive functioning and cognitive performance on individual experimentally induced pain perception during distractor tasks in an asymptomatic pain-free population. A total of 59 healthy pain-free subjects (59.3% women, mean age: 46.5 ± 24.7 years) completed a battery test that assessed execution functions (cognitive flexibility, working memory, mental inhibition), attention level, and psychological aspects (anxiety/depressive levels-HADS, pain catastrophizing-PCS, pain anxiety symptoms-PASS 20, sleep quality-PSQI) before conducting two n-back distraction tasks. Pain was experimentally induced with a thermal stimulus that was able to induce moderate pain (70/100 points) and applied to the non-dominant forearm. The thermal stimulus was applied before and during both (one-back and two-back) distraction tasks. The analyses consisted of separated repeated-measures ANOVA that considered the functioning on each test (cognitive flexibility, working memory, mental inhibition, selective attention) and controlled for sociodemographic and psychological aspects by comparing the pain intensity at the baseline and during the one-back and two-back distractor tasks. All ANOVAs found a significant effect of the distraction task, which indicates that the perceived pain intensity scores were lower during the one-back and two-back tasks (p < 0.001) as compared with the baseline. No interaction effect between the distractor tasks and working memory (p = 0.546), mental inhibition (p = 0.16), cognitive flexibility (p = 0.069), or selective attention (p = 0.105) was identified. The current study found that a distraction task decreased the perceived intensity of experimentally induced pain in asymptomatic pain-free individuals and that this effect was not related to executive function or attention levels.