Central Sensitization and Psychological State Distinguishing Complex Regional Pain Syndrome from Other Chronic Limb Pain Conditions: A Cluster Analysis Model

Explicit Motor Imaging Abilities Are Similar in Complex Regional Pain Syndrome, Chronic Limb Pain and Healthy Individuals: A Cross-Sectional Study

Background

Complex regional pain syndrome (CRPS) is a chronic pain condition characterized by peripheral, central sensory and motor dysfunction. Implicit motor imagery is known to be impaired in CRPS patients, but evidence for explicit motor imagery is still lacking. Using a self-rated questionnaire, this study aims to compare explicit motor imagery abilities between individuals with CRPS, with chronic limb pain (CLP), and healthy controls, and to also examine differences between affected and unaffected limbs. We hypothesize that both CRPS and CLP patients will show a decrease in motor imagery abilities compared to healthy controls and in their affected limb compared to their own contralateral, unaffected side.

Patients and Methods

In this single-center observational study, 123 participants were recruited (CRPS = 40, chronic limb pain, CLP = 40, and healthy individuals = 43). Participants completed the Movement Imagery Questionnaire-Revised Second (MIQ-RS) once for each side of the body. The total MIQ-RS score, and the kinesthetic and visual subscores were compared between groups and between the affected and unaffected sides.

Results

A high degree of heterogeneity was observed in the explicit motor imagery scores and subscores, regardless of whether the participants were healthy or individuals with chronic pain. The MIQ-RS did not reveal any significant differences in explicit motor imagery abilities, neither between groups nor between the affected and unaffected side. Bayesian testing of the null hypothesis for kinesthetic motor imagery abilities indicated a sevenfold likelihood of no differences between groups and a more than a fivefold likelihood of no differences between sides.

Conclusion

Individuals with CRPS and chronic limb pain displayed preserved explicit motor imagery abilities, notably on the pain side. The preservation of these abilities supports the recommendation of mental imagery therapy to improve motor function and relieve pain in chronic pain patients.

Clinical and Molecular Barriers to Understanding the Pathogenesis, Diagnosis, and Treatment of Complex Regional Pain Syndrome (CRPS)

Complex regional pain syndrome (CRPS) is an idiopathic, highly debilitating chronic disorder with persistent regional pain accompanied by a combination of sensory, motor, and autonomic abnormalities. It is not only difficult to treat but also difficult to study. This scoping review aimed to identify the key clinical and molecular challenges encountered in CRPS research and to examine the assessment tools currently employed. A comprehensive search was conducted across PubMed/Medline, Science Direct, Scopus, Wiley Online Library, and Google Scholar using a combination of free text and MeSH terms related to CRPS, clinical and molecular aspects, neuroinflammation, biomarkers, and research challenges. We analyzed 55 original clinical research papers on CRPS and 17 studies of immunological/biochemical/molecular aspects of CRPS. A significant degree of heterogeneity was observed in the methodologies employed across the reviewed studies. The most frequently reported challenges included difficulties in participant recruitment and controlling confounding factors (reported in 62% of studies), such as the heterogeneity of the patient population, the influence of pain coping strategies and psychological factors, and the impact of sociocultural factors (reported in 62% of studies). Research into diagnostic and prognostic markers for CRPS also faces numerous challenges. Recruiting participants is difficult due to the rarity of the condition, resulting in small sample sizes for studies. In vitro models often fail to replicate the complexity of in vivo inflammation, limiting their applicability. Findings from early CRPS stages may not generalize to chronic CRPS because of differing pathophysiological mechanisms and symptom profiles. Additional obstacles include the disorder's heterogeneity, difficulties in controlling confounding factors, variability in treatment approaches, and the lack of standardized tools and baseline comparisons. These issues hinder the development of reliable biomarkers and evidence-based treatments. Due to these difficulties, the exact cause of CRPS is still not fully understood, making it difficult to develop effective, specific treatments and conduct targeted research.

Contact-Heat Evoked Potentials: Insights into Pain Processing in CRPS Type I

Purpose

The pathophysiological mechanisms underlying the development of chronic pain in complex regional pain syndrome (CRPS) are diverse and involve both peripheral and central changes in pain processing, such as sensitization of the nociceptive system. The aim of this study was to objectively distinguish the specific changes occurring at both peripheral and central levels in nociceptive processing in individuals with chronic CRPS type I.

Patients and Methods

Nineteen individuals with chronic CRPS type I and 16 age- and sex-matched healthy controls (HC) were recruited. All individuals underwent a clinical examination and pain assessment in the most painful limb, the contralateral limb, and a pain-free control area to distinguish between peripheral and central mechanisms. Contact-heat evoked potentials (CHEPs) were recorded after heat stimulation of the three different areas and amplitudes and latencies were analyzed. Additionally, quantitative sensory testing (QST) was performed in all three areas.

Results

Compared to HC, CHEP amplitudes in CRPS were only increased after stimulation of the painful area (p=0.025), while no increases were observed for the pain-free control area (p=0.14). None of the CHEP latencies were different between the two cohorts (all p>0.23). Furthermore, individuals with CRPS showed higher pain ratings after stimulation of the painful limb compared to their contralateral limb (p=0.013). Lastly, compared to HC, mechanical (p=0.012) and thermal (p=0.046) sensitivity was higher in the painful area of the CRPS cohort.

Conclusion

This study provides neurophysiological evidence supporting an intact thermo-nociceptive pathway with signs of peripheral sensitization, such as hyperexcitable primary afferent nociceptors, in individuals with CRPS type I. This is further supported by the observation of mechanical and thermal gain of sensation only in the painful limb. Additionally, the increased CHEP amplitudes might be related to fear-induced alterations of nociceptive processing.