Complex regional pain syndrome type I: incidence and prevalence in Olmsted county, a population-based study

Lived experience perspectives of persons with complex regional pain syndrome: a survey study of the history of their condition, treatments and functional outcomes

Background

Complex Regional Pain Syndrome (CRPS) is a rare, chronic pain disorder that can have a devastating impact. Its cause remains unclear and debate over treatment strategies continues. The aim of the study was to utilise patient-reported outcomes to aid in the further evaluation of treatment options.

Method

An online survey was distributed with ethical approval to members of a CRPS charity. The Checklist for Reporting Results of Internet E-Surveys was implemented. Adults who met the patient-reported aspect of the Budapest Criteria were included (non-validated). Functional scores were reported using the shortened Disabilities of the Arm, Shoulder and Hand outcome measurement tool (QuickDASH) and Lower Extremity Functional Scale (LEFS). Participants completed a pre-injury score, a score related to injury and a score related specifically to CRPS symptoms. Respondents were also asked to rate a number of pharmacological and non-pharmacological treatments for CRPS.

Results

Respondents were mostly female (87%, 447/514) with a mean age of 49 years (SD 13). 69% (354/514) reported trauma as the inciting event. Anxiety (55%, 283/514) was the most commonly reported co-morbidity. Opioids (72%, 258/358) and Physical Therapy/Rehabilitation (63%, 281/444) were reported as the most beneficial (used by >10% of respondents) pharmacological and non-pharmacological therapies respectively. Median CRPS functional scores were significantly worse than scores relating to the injury alone, for both QuickDASH (56 (IQR 36-77) versus 77 (IQR 61-91), p < .001) and LEFS (20 (IQR 8-40) versus 7 (IQR 3-17), p < .001).

Conclusion

We present the first study using validated patient-reported outcome measures of limb-specific function in a solely CRPS population. These data quantify the devastating impact of CRPS and help make its prevention and treatment a priority amongst those who encounter it. The treatment data should inform future research, especially in successful therapies that were less commonly utilised.

Associated factors, triggers and long-term outcome in Complex Regional Pain Syndrome (CRPS) in the upper limb - A descriptive cross-sectional study

The pathophysiology behind Complex Regional Pain Syndrome (CRPS) is not fully understood and associated factors and triggers for developing the condition are debated. We aimed to study such factors and long-term outcome in a descriptive cross-sectional study with a well-defined population with CRPS in the upper limb and related to sex and CRPS type. In retrospectively collected data from medical records, 149 subjects [women n = 104 (70%); type 1 CRPS, n = 108 (72%); type 2 CRPS, n = 41 (28%); follow-up time 21 [8-43] months] were identified and analysed (Chi-squared test, Mann-Whitney U-test, and multiple linear regression). A majority were manual workers, and a larger proportion of subjects were smokers and had less post-secondary education than a reference population (p < 0.001 and p < 0.008). Men were younger, more frequently smoked, had higher BMI, and had lower education levels than women (p = 0.044, p = 0.007, p < 0.001, and p = 0.016, respectively). Subjects with CRPS type 2 were younger and had a longer time from symptoms until diagnosis, longer follow-up time, and more follow-up visits, indicating worse outcome (p = 0.016, p = 0.0012, p = 0.003, and p = 0.004, respectively). Among CRPS, 32% had a prior pain disorder and 7% had previously visited a pain management clinic. While there was no significant difference in mental illness occurrence before CRPS diagnosis compared to a reference population, mental illness increased by 76% after diagnosis. Factors such as CRPS type 2, older age, and delayed diagnosis were associated with longer follow-up periods. Additionally, 45% were on sick leave for over 12 months, and 20% were permanently unable to work. Socioeconomic deprivation is an associated factor in developing CRPS, in which a variety of triggers exist. Subjects with CRPS, particularly type 2, are at high risk of severe remaining symptoms, including mental illness and risk of never returning to work.

Comparative Analysis of Temperature Variations Following Sympathetic Blocks in Warm and Cold Subtypes of Complex Regional Pain Syndrome (CRPS): A Retrospective Cohort Study

Background/Objectives: The pathophysiological mechanisms of temperature asymmetry differ between patients with warm and cold subtypes of Complex Regional Pain Syndrome (CRPS). Consequently, the response to lumbar sympathetic blocks (LSBs) and the resulting temperature improvement may vary between these two subtypes. We aimed to evaluate whether there was a significant difference in temperature elevation following sympathetic blocks in warm versus cold subtypes of CRPS. Methods: We calculated the temperature difference by analyzing forward-looking infrared (FLIR) thermal camera images of the affected extremity at pre-block and 5-min post-block time points. The primary outcome measure was that the mean temperature increase following LSB would be higher in the cold CRPS group than in the warm CRPS group. The secondary outcome measure was that the mean temperature elevation following the sympathetic block in the cold CRPS subtype would be at least 50% higher than in the warm CRPS subtype. Results: The study assessed warm and cold CRPS subtypes by analyzing temperature profiles from 90 lumbar sympathetic blocks performed on 34 patients. The temperature change in the affected extremity following LSB varied widely, with the highest increase observed in one patient at 10.99 °C. The cold CRPS patients demonstrated a higher mean temperature increase at the 5 min time point following LSB, averaging 3.37 °C in initial cases and 2.67 °C across all cases. In comparison, warm CRPS patients had lower mean increases of 0.58 °C in initial cases and 1.23 °C across all cases. Notably, the mean temperature rise in the cold CRPS group exceeded that of the warm CRPS group by more than 50%, meeting the secondary outcome goal. Conclusions: Our results indicated that patients with the cold subtype of CRPS tend to experience greater temperature improvements compared to those with the warm subtype after undergoing a sympathetic block. Therefore, our findings suggest that the criteria for determining the success of a sympathetic block should be revised to account for the cold and warm subtypes of CRPS.

Retrospective Analysis of 28 Cases of Complex Regional Pain Syndrome

Background

Complex Regional Pain Syndrome (CRPS) is a chronic condition characterized by persistent pain and local autonomic dysfunction. Its exact cause remains unclear, making diagnosis and treatment challenging.

Objective

The objective was to investigate the clinical characteristics of CRPS patients and identify risk factors influencing its onset.

Design

Retrospective analysis of medical records from 28 CRPS patients, examining variables such as demographics, comorbidities, triggering events, pain duration and location, previous examinations and treatments, clinical findings, auxiliary tests, initial and follow-up treatment outcomes, symptom relief time, and degree.

Methods

Statistical methods were used to analyze the clinical data of 28 CRPS patients, assessing general characteristics and risk factors associated with the disease.

Results

Females accounted for 57.14% of the cases, with an average patient age of 57.89 years. About 82.14% of patients experienced a triggering event prior to the onset of pain. The median time to diagnosis was 4.5 months, with a maximum duration of up to 7 years. Misdiagnosis occurred in 46.43% of patients. Laboratory tests showed that 77.78% (7 of 9) had abnormal bone metabolism; among those who underwent bone density scans, 66.67% (6 of 9) had osteoporosis, whereas 11.11% (1 of 9) had reduced bone mass. X-rays of 25 patients revealed that 44% (11 of 25) had either reduced bone mass or osteoporosis, with 2 showing more severe osteoporosis on the affected side compared with the healthy side. Rheumatoid arthritis was observed in 7.14% of patients. Post-treatment, significant pain relief was noted in 26 patients.

Conclusion

This study helps clinicians more accurately identify and manage CRPS, reducing misdiagnosis and delayed diagnosis. In addition, the data suggest that osteoporosis and rheumatoid arthritis may be potential risk factors for CRPS.

Global Burden of Complex Regional Pain Syndrome in At-Risk Populations: Estimates of Prevalence From 35 Countries Between 1993 and 2023

BACKGROUND

Complex regional pain syndrome (CRPS) is a debilitating and painful condition accompanied by sensory, autonomic, trophic, and/or motor abnormalities. Although CRPS is rare in the general population, the prevalence among individuals at higher risk, particularly posttraumatic and postsurgical patients, remains unknown. This study aims to provide a benchmark that quantifies CRPS prevalence in high-risk groups, and offers insights on potential predictors of developing CRPS.

METHODS

We conducted a systematic review and meta-analysis to identify studies reporting prevalence of CRPS after an inciting event (eg, fracture, surgery), specifically 12-month and 24-month prevalence (primary outcomes), as well as 3-month and 6-month prevalence (secondary outcomes). Estimates from individual studies were transformed using double-arcsine transformation, and the resulting estimates with 95% confidence interval (CI) were pooled in a meta-analysis using a random-effects model.

RESULTS

We included 214 articles with data from 2491,378 participants worldwide (35 countries), of which 16,873 had CRPS. The pooled 12-month and 24-month global prevalence was 3.04% (95% CI, 2.64-3.48) and 6.46% (95% CI, 5.46-7.53), respectively. Subgroup analysis and meta-regression were performed to understand the impact of population-dependent (mechanism of injury, type of CRPS), contextual-dependent (socioeconomic status), and methodological-dependent (study design, publication year) factors. The 12-month prevalence was higher in countries with a high human development index (HDI) compared to those with a medium or very high HDI, was higher in participants with a traumatic inciting injury only versus those with surgical injury only or traumatic/surgical injury, and was higher in prospective versus retrospective studies. Meta-regression analysis showed that publication year was a significant moderator, with more recent articles reporting lower 12-month prevalence.

CONCLUSIONS

This study provides a benchmark of the global prevalence of CRPS, which anesthesiologists and pain specialists can use to prioritize early diagnosis and identify those at the highest risk for CRPS.

How can Blood Flow Restriction Exercise be Utilised for the Management of Persistent Pain Following Complex Injuries in Military Personnel? A Narrative Review

BACKGROUND

Persistent pain is a complicated phenomenon associated with a wide array of complex pathologies and conditions (e.g., complex regional pain syndrome, non-freezing cold injury), leading to extensive disability and reduced physical function. Conventional resistance training is commonly contraindicated in load compromised and/or persistent pain populations, compromising rehabilitation progression and potentially leading to extensive pharmacological intervention, invasive procedures, and reduced occupational status. The management of persistent pain and utility of adjunct therapies has become a clinical and research priority within numerous healthcare settings, including defence medical services.

MAIN BODY

Blood flow restriction (BFR) exercise has demonstrated beneficial morphological and physiological adaptions in load-compromised populations, as well as being able to elicit acute hypoalgesia. The aims of this narrative review are to: (1) explore the use of BFR exercise to elicit hypoalgesia; (2) briefly review the mechanisms of BFR-induced hypoalgesia; (3) discuss potential implications and applications of BFR during the rehabilitation of complex conditions where persistent pain is the primary limiting factor to progress, within defence rehabilitation healthcare settings. The review found BFR application is a feasible intervention across numerous load-compromised clinical populations (e.g., post-surgical, post-traumatic osteoarthritis), and there is mechanistic rationale for use in persistent pain pathologies. Utilisation may also be pleiotropic in nature by ameliorating pathological changes while also modulating pain response. Numerous application methods (e.g., with aerobic exercise, passive application, or resistance training) allow practitioners to cater for specific limitations (e.g., passive, or contralateral application with kinesiophobia) in clinical populations. Additionally, the low-mechanical load nature of BFR exercise may allow for high-frequency use within residential military rehabilitation, providing a platform for conventional resistance training thereafter.

CONCLUSION

Future research needs to examine the differences in pain modulation between persistent pain and pain-free populations with BFR application, supporting the investigation of mechanisms for BFR-induced hypoalgesia, the dose-response relationship between BFR-exercise and pain modulation, and the efficacy and effectiveness of BFR application in complex musculoskeletal and persistent pain populations.

Early CRPS Is a Heterogeneous Condition: Results From a Latent Class Analysis

BACKGROUND

Complex regional pain syndrome (CRPS) is a debilitating condition characterised by significant heterogeneity. Early diagnosis is critical, but limited data exists on the condition's early stages. This study aimed to characterise (very) early CRPS patients and explore potential subgroups to enhance understanding of its mechanisms.

METHODS

A total of 113 early CRPS patients were recruited, with 89 undergoing physical assessments. Data included demographic information, work-related factors, CRPS history and clinical features, body perception disturbances, quantitative sensory testing (QST), and a visuospatial attention task.

RESULTS

QST identified deficits in detecting thermal and mechanical stimuli, alongside increased sensitivity to thermal and blunt pressure painful stimuli. Participants reported body perception disturbances similar to those of persistent CRPS. Visuospatial biases were observed in two subgroups of patients. Latent class analysis (LCA) of 85 participants, based on five clinical parameters, identified four profiles: Mild, Moderate, Body Representation Disturbance (BRD), and Pressure Allodynia CRPS. The Mild and Moderate profiles were associated with higher-intensity trauma, with the latter showing worse outcomes. BRD and Pressure Allodynia CRPS followed mild trauma but exhibited the poorest outcomes. BRD CRPS displayed significant body perception disturbances, while Pressure Allodynia CRPS presented the highest sensitivity to pressure and psychosocial risk of chronification. Neither condition duration nor skin temperature effectively distinguished subgroups.

CONCLUSIONS

These findings emphasise the heterogeneity within (very) early CRPS patients and support the absence of a minimum required duration prior to the CRPS diagnosis. Central/systemic mechanisms may play critical roles in severe cases.

SIGNIFICANCE

This study identifies distinct (very) early CRPS profiles, suggesting different pathophysiological mechanisms and challenging traditional classifications. It paves the way for improved diagnosis and tailored treatments.

[Cognitive behavioral therapy for complex regional pain syndrome]

Complex regional pain syndrome (CRPS) is often associated with severe mental impairments. Initial pain-related fears in particular appear to be negative predictors for long-term therapy results. Procedures for cognitive behavioral therapy are an important component of treatment. The psychotherapy of CRPS consists of various elements that are implemented in the different phases of treatment. In the beginning the focus is on targeted psychoeducation. In the following activation phase body awareness exercises are accompanied by occupational and physiotherapeutic treatment in order to improve the perception of individual maximum loads. Behavioral analyses are used to uncover dysfunctional coping patterns, such as a fear avoidance coping strategy. In this case the use of graded activity treatment approach is indicated, in which the activity level is gradually increased. In the transfer phase psychotherapy supports affected patients in (re)designing their professional and private environments.

Positive and negative emotions in patients with Sudeck's syndrome according to religiosity before and after the disease

BACKGROUND

Sudeck's syndrome is a chronic and painful disease that affects a significant number of people. Despite this, it is a disease little researched in general and even less in the field of the psychology of religion. The aim of this study was to analyze the relationship between religiosity and emotions in patients with Sudeck's syndrome.

PARTICIPANTS AND PROCEDURE

The sample consisted of 80 people with Sudeck's syndrome, 92.5% of whom were women. The average age of the participants was 41.8 years, with a range of 23 to 60 years. Participants came from fourteen different countries in the Americas and Europe, including Spain (36.3%), Argentina (20%) and Peru (15%). A clinical and sociodemographic data sheet was used, as well as questions aimed at assessing the emotional state of the participants.

RESULTS

The results indicate that patients experienced a significant increase in anxiety and sadness after the diagnosis of the disease, while optimism and energy decreased significantly. On the other hand, no differences were found in positive or negative emotions in believing or non-believing patients.

CONCLUSIONS

The data suggest that the diagnosis of Sudeck's syndrome has a negative impact on the emotional health of individuals and that this is independent of whether the patient is a believer or non-believer. However, further research is needed to confirm these findings and to explore the underlying mechanisms of this relationship.

Ketamine Infusion for Complex Regional Pain Syndrome Treatment: A Narrative Review

PURPOSE OF REVIEW

Complex Regional Pain Syndrome (CRPS) is a neuropathic pain disorder characterized by pain disproportionate to the inciting event that is constant for an extended duration. Numerous treatment options for this condition have been explored with unsatisfactory results in many cases. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist typically used as an anesthetic and analgesic, presents a promising potential treatment for CRPS in patients who fail to respond to traditional therapies.

RECENT FINDINGS

Numerous studies report significant improvement in the degree of pain, mobility of extremities, and other parameters after ketamine infusion in patients with CRPS. Although adverse effects were not reported often, some subjects experienced nausea, vomiting, headache or psychotropic or psychomimetic symptoms which could be mitigated with cessation of the drug. Although more research is needed to determine optimal dosing and duration, ketamine seems to be a safe and effective treatment for refractory cases of CRPS.

CONCLUSION

The present investigation summarizes existing knowledge and research surrounding ketamine infusions for CRPS to provide a well-rounded depiction of advantages and disadvantages for physicians who may be considering it for patients with this challenging and complex condition.

Examining the effects of race/ethnicity and other factors on outcomes of care for complex regional pain syndrome type 1 in the United States

Complex regional pain syndrome is a chronic pain disorder marked by symptoms such as swelling, impaired motor function, and sympathetic dysfunction. Our primary objective was to determine the total number of complex regional pain syndrome type 1 (CRPS-1) emergency department (ED) visits and hospitalizations by race/ethnicity, as well as to assess sex and age distributions by race/ethnicity. Secondary objectives were to examine whether race/ethnicity, as well as select characteristics, are associated with hospitalization and longer length of stay. We completed a cross-sectional study of adults (19+ years) using acute and inpatient care data from the 2020 Nationwide Emergency Department Sample and the National Inpatient Sample. The overall rate of CRPS-1 diagnosis among ED visits and hospitalizations was 0.02% and 0.04%, respectively. Most CRPS-1 care was provided to White (ED: 83.1%; inpatient: 82.8%) patients. Within race/ethnicity groups, CRPS-1 ED visits and hospitalizations generally increased with age. Secondary findings included: 1) ED visits by Black individuals (compared with White) were significantly negatively associated with immediate hospitalization (adjusted odds ratio (AOR) 0.74, 95% CI 0.55 to 0.99); 2) hospitalizations by Black patients (compared with White) were independently associated with increased length of stay (odds ratio (OR) 1.45, 95% CI 1.07 to 1.96), though the association diminished with adjustment; and 3) drug abuse was significantly associated with hospitalization (AOR 4.67, 95% CI 3.53 to 6.18) and longer length of stay (AOR 1.81, 95% CI 1.34 to 2.46). Race/ethnicity was minimally associated with studied CRPS-1 outcomes. Additional studies are required to determine the impact of race/ethnicity on seeking care for CRPS-1.

10. Complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a clinical disorder that can develop following surgery or trauma. Based on the most prominent underlying pathophysiological mechanisms, CRPS can be classified into different subtypes, namely inflammatory, nociplastic/neuropathic, vasomotor, and motor. Depending on the subtype, personalized treatment can be applied. If conservative treatments are insufficient or ineffective, more invasive treatments may be recommended. This article provides an overview of the most recent insights into CRPS and discusses the most common invasive treatments.

METHODS

The literature regarding interventional treatments for CRPS has been systematically reviewed and summarized.

RESULTS

Bisphosphonates are effective in treating the inflammatory subtype, while ketamine can provide pain relief for the nociplastic/neuropathic subtype. Sympathetic blocks are effective in addressing vasomotor disturbances. For patients with refractory symptoms, neurostimulation is a viable option due to its multimechanistic properties for all subtypes. End-of-line motor disturbances may benefit from intrathecal baclofen.

CONCLUSIONS

CRPS is a debilitating condition with an unpredictable course. The effectiveness of treatment varies from patient to patient. When conservative approaches prove insufficient, gradual progression to invasive treatments based on the underlying subtype is recommended.

Effect of Prednisolone on Clinical and Cytokine mRNA Profiling in Complex Regional Pain Syndrome

The cardinal clinical features of complex regional pain syndrome type I (CRPS-I) are pain, edema, autonomic changes, and limitation of motoric movement, which may indicate the role of inflammation and cytokines. We report the effect of prednisolone on the clinical severity and mRNA profiling of proinflammatory (tumor necrosis factor (TNF)-α and interleukin (IL)-2) and anti-inflammatory cytokines (IL-10 and transforming growth factor (TGF)-β) in the patient with CRPS-I. Thirty-nine patients with CRPS-I of shoulder joint were enrolled. Their CRPS, Visual Analog Scale (VAS) and Daily Sleep Interference Scale (DSIS) scores were recorded. TNF-α, IL-2, IL-10, and TGF-β gene expressions at mRNA of whole blood were measured by reverse transcriptase polymerase chain reaction. Patients were randomized to prednisolone 20 mg or 40 mg using 1: 1 randomization. The primary outcome was change in VAS score, and secondary outcomes were change in CRPS and DSIS scores at 1 month. Side effects were noted. The patients had increased expressions of TNF-α (p < 0.001) and IL-2 (p < 0.001) and reduced IL-10 (p < 0.01) mRNA compared to the healthy controls. The baseline characteristics were matched between the two treatment arms. At 1 month, CRPS, VAS, and DSIS scores improved significantly compared to baseline, which paralleled with improvement in IL-10 (p < 0.032) and reduction in TNF-α (p = 0.046). The improvement in clinical and biomarkers was similar in prednisolone 20 mg and 40 mg arms. None had to be withdrawn due to severe side effects. Future study in larger cohort may validate these findings.

Dorsal Root Ganglion Size in Patients With Complex Regional Pain Syndrome of the Lower Extremity: A Retrospective Pilot Study

OBJECTIVE

Complex regional pain syndrome (CRPS) is a debilitating chronic condition characterized by severe, nociplastic pain along with various other symptoms. Neuromodulation, particularly electrical stimulation of the dorsal root ganglion (DRG), has emerged as a promising intervention for patients with CRPS unresponsive to conventional treatments. However, little is known about the anatomical characteristics of DRGs in patients with CRPS. This study aimed to assess DRG size in patients with CRPS compared with healthy controls.

MATERIALS AND METHODS

A retrospective pilot study was conducted in 12 patients with unilateral lower extremity CRPS who have a history of lumbar magnetic resonance imaging, and evaluated DRG sizes bilaterally. Patients were age-, race-, and sex-matched to patients in the control group who were asymptomatic at matched spinal level. DRG sizes were evaluated by a neuroradiologist. Statistical analyses including paired t-tests were performed to compare the difference in DRG size in contralateral sides in patients with CRPS and their matched controls.

RESULTS

Patients with CRPS exhibited a statistically significant reduction in DRG size on the affected side compared with the unaffected side (4.4 mm-4.8 mm, respectively). This difference was significant when compared with the difference observed in healthy controls (4.9 mm-5.0 mm, respectively). In addition, the mean DRG size difference between the affected and unaffected side showed a greater difference in DRG size in patients with CRPS (0.6 mm difference) than in control patients (0.2 mm difference).

CONCLUSIONS

The findings suggest that CRPS is associated with a smaller DRG size in affected dermatomes, potentially indicating neuronal atrophy. Importantly, the study offers insights for DRG stimulation therapy especially among concerns for DRG compression after placement. This pilot study reveals a significant size difference in DRGs between affected and unaffected sides in patients with CRPS compared with controls, highlighting potential implications for treating CRPS. Further research is warranted to validate these findings and explore implications for clinical practice, including optimized neuromodulation strategies.

Spinal cord stimulation as a treatment option for complex regional pain syndrome: a narrative review

Objectives: This review aims to analyze the last years' experience of applying spinal cord stimulation (SCS) in complex regional pain syndrome (CRPS) patients with persistent or refractory chronic pain. Methods: This is a narrative review which was executed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and was carried out through the following databases: PUBMED and Cochrane Library. Also, a search for trials in the metaRegister of controlled trials (www.clinicaltrials.gov) was performed. Results: SCS provides pain reduction and improves sensory, vasomotor and sudomotor symptoms. It can reduce opioid using, offering better life quality for the patients. Conclusions: SCS found to be an excellent therapeutic alternative for patients with CRPS. It offers immediate pain relief and allows patients to regain functionality and have a better quality of life.

Analysis of Analgesics and Adjuvant Medications on Psychiatric Comorbidities in Patients With Complex Regional Pain Syndrome 1

Complex regional pain syndrome (CRPS) is a chronic pain disorder characterized by severe, disproportionate pain relative to an inciting event. The disorder's pathophysiology is complex, involving both central and peripheral nervous system alterations, alongside genetic, inflammatory, and psychological factors. Using data from TriNetX, this study investigated the impact of analgesic and adjuvant therapies on psychiatric outcomes in CRPS patients. The analysis included 1,029 patients treated with non-opioid versus opioid analgesics and those using antidepressants versus anticonvulsants. Results revealed no significant differences in major depressive disorder (MDD), anxiety, suicidal ideation, or post-traumatic stress disorder (PTSD) between opioid and non-opioid analgesic groups. However, opioid analgesic was associated with a lower risk of behavioral disorders due to psychoactive substance use disorder (0.732; 95% confidence interval [CI] 0.555-0.899). Anticonvulsants, compared to antidepressants, were linked to significantly higher odds and hazards of psychiatric comorbidities: depression (odds ratio [OR] 5.475), anxiety (OR 1.87), PTSD (OR 1.551), and suicidal ideation (OR 2.718). Hazard ratios also showed higher risks for antidepressants in depression, anxiety, and PTSD. These findings highlight the risks and benefits associated with opioid analgesics and the potential therapeutic effects of antidepressants in patients with CRPS. Treatment should consider physiological and psychiatric symptoms, as both are impactful on pain management.

Psychology of nerve injury, repair, and recovery: a systematic review

Background

Peripheral nerve injuries (PNIs) are associated with significant physical and psychological challenges, impacting both functional recovery and quality of life. Despite the physical focus of traditional treatments, psychological factors play a crucial role in the outcomes of PNI repair and recovery.

Objectives

This systematic review aims to evaluate the impact of psychological and social factors on the repair and recovery of peripheral nerve injuries.

Methods

A comprehensive literature search was conducted in PubMed/Medline, EMBASE, and Cochrane databases, covering studies from January 1985 to December 2022. A total of 36,190 records were identified, and after screening with Rayyan AI and applying inclusion criteria, 111 articles were selected for review.

Results

The review highlights that pre-existing psychological conditions, as well as psychological responses to the injury and treatment, significantly influence recovery outcomes in PNI patients. Psychological interventions, when integrated into standard care, may improve functional recovery and quality of life.

Conclusions

Psychosocial factors are critical in the management of PNIs and should be incorporated into treatment algorithms to enhance patient outcomes. Future research should focus on developing and integrating psychological support strategies in PNI treatment protocols.

The Efficacy of Neuromodulation, Interventional Treatment and Unconventional Therapies in the Treatment of Complex Regional Pain Syndrome: A Systematic Review

Complex regional pain syndrome (CRPS) is a chronic debilitating multisystem neuropathic pain disorder. It is characterized by continuous pain, usually out of proportion to any known tissue injury, vasomotor changes, sudomotor or edema, and motor or trophic changes. The objective of this study is to assess the efficacy of neuromodulation, interventional, and unconventional treatments for CRPS. The primary focus is pain reduction, assessed through various scales, with secondary outcomes examining effects on autonomic, sensory, motor, and psychological aspects, and quality of life. PubMed, Cochrane Library, MDPI, and ScienceDirect databases were thoroughly searched using our detailed search strategy and relevant literature compiled. Articles were assessed using our eligibility criteria and quality appraisal tools. All types of study designs were considered. Initially, 463 articles were identified; after a thorough assessment, 23 articles comprising 2307 patients were shortlisted. Neuromodulation interventions, specifically Dorsal Root Ganglion (DRG) and Spinal Cord Stimulation (SCS) demonstrated statistically significant pain reduction (43-82% and up to 70%, respectively). Both modalities demonstrate improvement in secondary outcomes and quality of life. Interventional interventions, specifically nerve blockade ranging from sympathetic, stellate ganglion, and regional nerve blocks, all demonstrate varying levels of efficacy on measured pain and secondary outcomes. Unconventional: Botulinum toxin injections through multiple delivery systems demonstrated varying levels of efficacy in treating pain and improving secondary outcomes. In conclusion, DRG stimulation and SCS, nerve blockade, and botulinum toxin all display promise in alleviating symptoms of CRPS. Definite conclusions were not made due to a lack of clinical trial data, and longer multi-year follow-up is recommended.

Effects of Mecobalamin on the Functional Outcomes of Complex Regional Pain Syndrome Type 1 of the Foot and Ankle

BACKGROUND

Because of the unclear pathophysiology and the lack of consensus on the gold standard treatment of complex regional pain syndrome (CRPS), management requires a multidisciplinary approach, with the use of various treatment modalities. Nonetheless, no studies have ever been conducted to uncover the potential of mecobalamin as a treatment for CRPS type 1. Hence, the aim of this clinical trial was to evaluate the effects of mecobalamin on the functional outcomes of patients with CRPS type 1 of the foot and ankle, the total amount of pregabalin ingested, and the duration of pregabalin use in each patient.

METHODS

Forty-seven patients diagnosed with acute CRPS type 1 of the foot and ankle were recruited. Patients were randomly allocated into a control group (23 patients) and a mecobalamin group (24 patients), both receiving similar pain control medications and rehabilitation programs. Three divided doses of mecobalamin 1.5 mg/d were provided to the mecobalamin group for the first 3 months, whereas a placebo was administered to the control group. Data were collected from the pretreatment period, and from 1, 3, 6, and 12 months following the treatment.

RESULTS

Both groups had similar demographics. The mean Foot and Ankle Ability Measure (FAAM) activities of daily living (ADL) and FAAM-sport scores in the mecobalamin group at 3 months were 74.5 ± 17.9 and 56.3 ± 22.9, whereas the mean FAAM-ADL and FAAM-sport scores in the placebo group at 3 months were 62.2.5 ± 15.2 and 43.4 ± 14.9, respectively (P < .05). The 36-Item Short Form Health Survey (SF-36) mental health subscale after 3 months were 83.3 ± 9.5 points and 75.8 ± 12.6 points in the mecobalamin and placebo group, respectively (P < .05). However, at other time points of assessment (1, 6, and 12 months), the improvement in symptoms was not distinguishable between the 2 groups. Both the amount and duration of total pregabalin required to achieve similar improvements in pain scores were significantly lower in the mecobalamin group than the control group.

CONCLUSION

This small study revealed an improvement of the functional outcomes in patients with CRPS type 1 of the foot and ankle who received mecobalamin instead of a placebo at 3 months that was not sustained at 6 and 12 months. We identified an average 39% total reduction in the amount of total pregabalin used in the mecobalamin group in the first 12 months.

Complex regional pain syndrome type II localized to the index finger. A case report translating scientific evidence into clinical practice

BACKGROUND

Complex regional pain syndrome type II (CRPS-II) is a rare condition associated with peripheral nervous system lesions. Its localized distribution in the fingers is unique, and its treatment is unclear.

CASE DESCRIPTION

A 56-year-old male presented to the emergency department with a saw-cut index finger injury with associated tendon and nerve injuries. After surgery, he was admitted to physical therapy (PT) with persistent pain, joint stiffness, allodynia, and trophic changes compatible with CRPS-II localized in the index finger. The diagnosis was confirmed after applying the Budapest Criteria, and PT was progressive and individualized according to the patient's needs, including graded motor imagery, mobilizations, exercises, and education.

OUTCOMES

After 12 weeks of PT, a clinically significant decrease in pain intensity and improvements in mobility and index finger and upper limb functionality was observed, reducing CRPS symptomatology.

DISCUSSION

This report provides information about a unique case of a localized form of CRPS-II. After reviewing the literature on clinical cases of both CRPS-II and localized forms of CRPS, we highlight that the clinical features of this patient and his positive therapeutic response support the importance of translating the scientific evidence on CRPS into clinical practice.

[Prospective, multicenter study of the outcome of complex regional pain syndrome after 12 months]

BACKGROUND AND OBJECTIVES

Complex regional pain syndrome (CRPS) can lead to severe pain and limited functionality in the long term. Guidelines should help to optimize treatment procedures. It should be investigated which outcome is achieved after 1 year with guideline-based therapy.

MATERIALS AND METHODS

In a prospective multicenter study, 40 patients with newly diagnosed CRPS were examined to determine how their pain and functional limitations changed within 1 year. In addition, it was investigated whether the time of diagnosis and invasive measures influence these outcome parameters.

RESULTS

All patients received physiotherapy and/or ergotherapy, treatment with glucocorticoids and/or bisphosphonates 29 (72.5%); various invasive measures were carried out in 13 (32.5%). After 1 year, both pain and functionality were significantly improved; two-thirds reported a tolerable average pain intensity. Severe functional impairment according to von Korff disability points was found after 1 year in 9 (22.5%), and a moderate or severe impairment according to medical evaluation in 6 (15%) and 3 (7.5%) patients, respectively. Earlier diagnosis and corresponding earlier start of treatment correlated with better outcome in terms of pain and functionality according to von Korff, but not according to medical evaluation. The influence of invasive procedures on the outcome parameters tended to be low.

CONCLUSION

Guideline-based treatment led to a good outcome in terms of pain and functionality in the majority of patients. Early diagnosis correlated with better outcome, so suspected cases should be referred quickly to a medical facility with appropriate expertise.

Refractory CRPS pain treated with psilocybin: A case report

Psilocybin shows promise as a treatment for CRPS, offering significant pain relief and functional improvement in a patient with refractory symptoms. This case highlights the need for further research into psilocybin's efficacy and optimal dosing for chronic pain management.

Nitrous oxide for the treatment of complex regional pain syndrome: a randomized blinded trial

INTRODUCTION

Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS.

METHODS

Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption.

RESULTS

44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46).

CONCLUSIONS

Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS.

Temperature difference between the affected and unaffected limbs in complex regional pain syndrome

Background: Complex regional pain syndrome (CRPS) is classified into two subtypes based on clinical presentation: warm or cold.Methods: We examined the distribution of warm and cold subtypes in CRPS patients before they received lumbar sympathetic block. We retrospectively analyzed 81 prelumbar sympathetic block Forward Looking InfraRed images obtained from 30 patients to study temperature asymmetry between affected and unaffected limbs.Results: In 23 of the 30 patients (77%), the temperature difference between the affected and affected limbs was within the normal range (<0.6°C difference). Of the remaining seven cases, six (20%) were diagnosed with cold-CRPS and one (3%) with warm-CRPS. During subsequent interventions, 74% of the patients maintained a temperature difference within the normal range (<0.6°C difference).Conclusion: Retrospective analysis of Forward Looking InfraRed thermal camera images in CRPS patients showed that 77% of patients did not exhibit significant temperature asymmetry (<0.6°C difference) between affected and unaffected limbs.

Complex Regional Pain Syndrome in Cancer Cases: Current Knowledge and Perspectives

Background

Complex regional pain syndrome (CRPS) is a disabling painful disorder caused by many different and poorly understood mechanisms. It often affects the distal limbs and usually happens as consequence of a trauma. Its severity can remarkably affect patients' quality of life. When this painful complication happens in a cancer patient, the impact may be exponential. To date, there is limited knowledge of the surrounding circumstances of CRPS cases in this population.

Methods

We present two clinical cases of patients diagnosed with cancer-related pain presenting with symptoms and signs compatible with CRPS. In one case, CRPS was attributed to direct tumor nerve compression, and it responded successfully to an interventional pain procedure. The second case was associated with a Zoster infection in an immunocompromised cancer patient. Patient responded to multidisciplinary pain management strategies. Additionally, we conducted a literature review to investigate the coexistence of cancer pain and CRPS and suggest some pathophysiology mechanisms of action.

Results and Discussion

Literature reviewed and potential pathophysiology mechanisms are simultaneously explored in terms of classification, etiopathology, evidence, challenges, and future scientific directions.

Conclusion

Comorbid CRPS can impact negatively in cases of cancer pain by affecting their diagnosis and treatment. Further studies are necessary to elucidate how these two conditions present together and how they can be better addressed.

Integrative approaches in spinal cord stimulation: Neuropathic pain management and motor recovery in spinal cord injury. A narrative review

Introduction

Spinal cord stimulation is a widespread treatment of chronic neuropathic pain from different conditions. Several novel and improving technologies have been recently developed to increase the effect of neuromodulation in patients refractory to pharmacological therapy.

Research question

To explore spinal cord stimulation's mechanisms of action, indications, and management.

Material and methods

The paper initially explores the mechanism of action of this procedure based on the generation of an electric field between electrodes placed on the posterior dural surface of the spinal cord probably interfering with the transmission of pain stimuli to the brain. Subsequently, the most consolidated criteria for selecting patients for surgery, which constitute a major issue of debate, were defined. Thereafter, the fundamental patterns of stimulation were summarized by exploring the advantages and side effects. Lastly, the most common side effects and the related management were discussed.

Results

Proper selection of the patient is of paramount importance to achieve the best results from this specific neuromodulation treatment. Regarding the different types of stimulation patterns, no definite evidence-based guidelines exist on the most appropriate approach in relation to the specific type of neuropathic pain. Both burst stimulation and high-frequency stimulation are innovative techniques that reduce the risk of paresthesias compared with conventional stimulation.

Discussion and conclusion

Novel protocols of stimulation (burst stimulation and high frequency stimulation) may improve the trade-off between therapeutic benefits and potential side effects. Likewise, decreasing the rates of hardware-related complications will be also useful to increase the application of neuromodulation in clinical settings.

Painful Raynaud's mimics

Raynaud's syndrome is a common finding in many autoimmune conditions. Accurately diagnosing Raynaud's, and differentiating it from mimicking conditions, is imperative in rheumatologic diseases. Raynaud's syndrome and Raynaud's mimickers, especially painful Raynaud's mimickers, can prove a diagnostic challenge for the practicing rheumatologist. Painful Raynaud's mimickers can lead to increased patient stress and unnecessary medical work up; Healthcare providers need to be aware of Raynaud's mimickers when evaluating patient concerns of skin color changes and pain. The present narrative review aims to highlight Raynaud's syndrome, important painful mimickers that may be seen, diagnosis, and updated management recommendations.

The efficacy of oral corticoids in treating complex regional pain syndrome: A retrospective cohort study

OBJECTIVES

There is growing evidence supporting the role of inflammatory mechanisms in complex regional pain syndrome (CRPS). Corticoids, as most effective anti-inflammatory drugs, are widely used in treating inflammation. The aim of this study was to retrospectively assess the efficacy of oral corticoid treatment in CRPS patients.

METHODS

Patients treated at the center of pain medicine in the Erasmus University Medical Centre between January 2015 and January 2020 were approached to partake in this study. Medical records were screened for age, gender, medical history, duration of CRPS, and CRPS severity score. Also, treatment effect, dose and duration, pain scores (NRS), and side effects were extracted from medical records. In addition, global perceived effect was completed in patients treated with corticoids.

RESULTS

Between January 2015 and January 2020, twenty-nine CRPS patients received corticoids and met the inclusion criteria. One extreme outlier was excluded and treatment effect was unknown for one patient. Average daily dose was 28.9 mg (range 10-30 mg) and the mean treatment duration was 10.5 days (7-21 days). Fourteen patients (51.9%) responded positively to treatment and thirteen (48.1%) did not respond. Side effects were reported in five patients (17.9%).

CONCLUSIONS

Corticoid treatment was effective in more than half of the patients. With only mild side effects reported the treatment also appears to be relatively safe. Further research is needed to investigate the efficacy of corticoids in treating (early) CRPS, preferably in an intervention study.

A case of truncal complex regional pain syndrome: literature review

Introduction and importance

Complex regional pain syndrome is a rare and chronic pain disorder characterized by an abnormal level of pain disproportionate to the initiating cause, often manifesting well after the triggering event.

Case presentation

The authors present a free past medical history 33-year-old female, employed as a nurse in an intensive care unit, presented with a 9-year history of diffuse back pain. Her symptoms initially emerged at the neck with muscle spasms and restricted neck mobility, eventually progressing along the spine. Notably, the pain became episodic and intensified over time, significantly impeding her daily activities. Analgesic (non-steroidal anti-inflammatory drugs) treatments proved ineffective, and a distinct feature emerged-a change in skin colour to dark purple spots on her back, accompanied by hyperhidrosis and extreme tenderness. Despite an exhaustive evaluation involving bloodwork, inflammatory markers, serological tests, and radiographic imaging, a definitive diagnosis remained elusive until she responded positively to Pregabilin.

Clinical discussion

Although typically associated with extremities, this case challenges the conventional understanding of complex regional pain syndrome by showcasing its manifestation in the truncal region. The patient's clinical history, examination findings, and diagnostic journey are detailed herein, shedding light on the complexity and diagnostic considerations associated with this condition.

Conclusion

The case underscores the importance of a comprehensive approach and prompts a reevaluation of the existing guidelines to encompass such atypical presentations.

Economic evaluation of management strategies for complex regional pain syndrome (CRPS)

Background: The economic impact of Complex Regional Pain Syndrome (CRPS) on both patients and the global healthcare system continues to escalate. However, the economic implications associated with management interventions for CRPS have received limited attention. Therefore, our objective is to perform a thorough examination of published economic assessments of the various management strategies utilized for CRPS. Methods: A thorough search spanning four general medical databases and three health economic databases to identify full economic evaluations on CRPS management strategies from January 1994 to June 2023 were conducted. The quality of these studies were evaluated by employing the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) statement. To enable cross-study comparisons conducted in different countries, we adjusted the costs reported in the selected studies for inflation and converted them into 2023 US dollars. Results: A total of nine economic evaluations, consisting of eight high-quality and one medium-quality, were identified across five nations during a span of 29 years. The findings suggest that the most economically efficient intervention for CRPS are interventional approaches of Spinal Cord Stimulation (SCS) in comparison to conventional management for long periods of time. Furthermore, in situations where there is a limited time period of less than 1 year, rehabilitation therapies, particularly physical therapy, have been demonstrated to be more effective in terms of both cost and clinical outcomes. Conclusion: The interventional management strategies, particularly for severe and persistent CRPS over long periods, may offer the greatest cost efficiency. In conditions with limited timelines, rehabilitation measures, such as rehabilitation therapies, can be cost-effective. However, insufficient data for other common interventions prevents the formation of a definitive conclusion. Similarly, it is crucial to recognize that the results of these interventions might be affected by the selection of comparator and the threshold for willingness to pay.

Evidence of a genetic background predisposing to complex regional pain syndrome type 1

BACKGROUND

Complex regional pain syndrome type 1 (CRPS-1) is a rare, disabling and sometimes chronic disorder usually arising after a trauma. This exploratory study examined whether patients with chronic CRPS-1 have a different genetic profile compared with those who do not have the condition.

METHODS

Exome sequencing was performed to seek altered non-synonymous SNP allele frequencies in a discovery cohort of well-characterised patients with chronic CRPS-1 (n=34) compared with population databases. Identified SNP alleles were confirmed by Sanger sequencing and sought in a replication cohort (n=50). Gene expression of peripheral blood macrophages was assessed.

RESULTS

In the discovery cohort, the rare allele frequencies of four non-synonymous SNPs were statistically increased. The replication cohort confirmed this finding. In a chronic pain cohort, these alleles were not overexpressed. In total, 25 out of 84 (29.8%) patients with CRPS-1 expressed a rare allele. The SNPs were rs41289586 in ANO10, rs28360457 in P2RX7, rs1126930 in PRKAG1 and rs80308281 in SLC12A9. Males were more likely than females to have a rare SNP allele, 8 out of 14 (57.1%) vs 17 out of 70 (24.3%) (Fisher's p=0.023). ANO10, P2RX7, PRKAG1 and SLC12A9 were all expressed in macrophages from healthy human controls.

CONCLUSION

A single SNP in each of the genes ANO10, P2RX7, PRKAG1 and SLC12A9 was associated with developing chronic CRPS-1, with more males than females expressing these rare alleles. Our work suggests the possibility that a permissive genetic background is an important factor in the development of CRPS-1.

Subtypes of complex regional pain syndrome-a systematic review of the literature

To systematically identify and summarize possible subtypes of complex regional pain syndrome (CRPS), we searched MEDLINE, Embase, Cochrane, Scopus, and Web of Science for original studies reporting or investigating at least one subtype within a group of patients with CRPS. The search retrieved 4239 potentially relevant references. Twenty-five studies met our inclusion criteria and were included in the analysis. Complex regional pain syndrome phenotypes were investigated based on the following variables: clinical presentation/sensory disturbances, dystonia, skin temperature, disease duration, onset type, CRPS outcome, and neuropsychological test performance. Support was found for the following CRPS subtypes: CRPS type I, CRPS type II, acute CRPS, chronic CRPS, centralized CRPS, cold CRPS, warm CRPS, inflammatory CRPS, dystonic CRPS, nondystonic CRPS, familial CRPS, and nonfamilial CRPS. It is unclear whether these are distinct or overlapping subtypes. The results of this comprehensive review can facilitate the formulation of well-defined CRPS subtypes based on presumed underlying mechanisms. Our findings provide a foundation for establishing and defining clinically meaningful CRPS subtypes, with the ultimate goal of developing targeted and enhanced treatments for CRPS.

Anxiety, Disability, and Pain Predict Outcomes of Complex Regional Pain Syndrome: An 8-year Follow-up of a Prospective Cohort

Factors contributing to the varied outcomes of complex regional pain syndrome (CRPS) are not well known. This study aimed to determine whether baseline psychological factors, pain, and disability influence long-term CRPS outcomes. We conducted an 8-year follow-up from a previous prospective study of CRPS outcomes. Sixty-six people diagnosed with acute CRPS were previously assessed at baseline, 6 months, and 12 months and in the current study, 45 were followed up after 8 years. At each timepoint, we measured signs and symptoms of CRPS, pain, disability, and psychological factors. Mixed-model repeated measures were used to identify baseline predictors of CRPS severity, pain, and disability at 8 years. Predictors of greater CRPS severity at 8 years were female sex, greater baseline disability, and greater baseline pain. Predictors of greater pain at 8 years were greater baseline anxiety and disability. The only predictor of greater disability at 8 years was greater baseline pain. Findings suggest CRPS is best understood from a biopsychosocial perspective, and baseline anxiety, pain, and disability may influence the trajectory of CRPS outcomes as far as 8 years later. These variables could be used to identify those at risk of poor outcomes or form targets for early interventions. PERSPECTIVE: This paper presents the findings of the first study to prospectively investigate predictors of CRPS outcomes over 8 years. Baseline anxiety, pain, and disability predicted greater CRPS severity, pain, and disability over 8 years. These factors could identify those at risk of poor outcomes or form targets for early interventions.

Virtual reality in managing Complex Regional Pain Syndrome (CRPS): a scoping review

Background

Complex Regional Pain Syndrome (CRPS) is a severe pain disorder that does not yet have a specific treatment. Patients with CRPS not only suffer from a wide range of symptoms that affect their quality of life but also present psychological affections to the way they see their body and specifically their affected limb. Virtual Reality (VR) modalities have become a targeted treatment for chronic pain and in the case of CRPS, may be a valuable approach to the mechanisms that affect these patients.

Objectives

Using the PRISMA Scoping Review guidelines, we intend to uncover the key information from the studies available about VR modalities in the treatment of CRPS. We focus on the improvement of pain levels, body perception disturbances (BPD), and limb movement/daily function.

Results

Our search strategy resulted in 217 articles from PubMed. Twenty were assessed for eligibility and seven were included in the final qualitative synthesis. Of these seven articles, we included a clinical trial, three pilot studies, a blinded randomized controlled trial, a crossover double-blind trial, and a randomized controlled trial. These studies provide important subjective patient findings, along with some statistically significant results in the experiences of VR therapies modulating pain, BPD, and improving limb movement/daily function. However, not all the studies included statistical analysis, and there are contradicting data found from some patients that did not perceive any improvement from VR therapies.

Conclusions

We describe the results found in 7 articles that focus on the treatment of CRPS with VR modalities. Overall, the articles have various limitations, but the strategies related to immersive virtual reality, cardiac signaling, body switching and limb modulation have shown the most promising results for pain reduction and BPD improvement. These strategies reflect on pathophysiological mechanisms that are hypothesized to be affected in CRPS patients leading to the chronic pain and BPD that they experience. Not much evidence was found for improvement in limb movement and daily function. This review is a pathway for future studies on this topic and a more extensive data synthesis when more information is available.

Complex Regional Pain Syndrome (CRPS) and the Value of Early Detection

PURPOSE OF REVIEW

The goal of this narrative review is to describe the current understanding of the pathology of Complex Regional Pain Syndrome (CRPS), as well as diagnostic standards and therapeutic options. We will then make the case for early recognition and management.

RECENT FINDINGS

CRPS remains an enigmatic pain syndrome, comprising several subtypes. Recent recommendations clarify diagnostic ambiguities and emphasize the importance of standardized assessment and therapy. Awareness of CRPS should be raised to promote prevention, early detection, and rapid escalation of therapy in refractory cases. Comorbidities and health costs (i.e., the socioeconomic impact) must also be addressed early to prevent negative consequences for patients.

Complex Regional Pain Syndrome: Evidence-Based Advances in Concepts and Treatments

PURPOSE OF REVIEW

This review presents the most current information about the epidemiology of complex regional pain syndrome (CRPS), classification and diagnostic criteria, childhood CRPS, subtypes, pathophysiology, conventional and less conventional treatments, and preventive strategies.

RECENT FINDINGS

CRPS is a painful disorder with multifactorial pathophysiology. The data describe sensitization of the central and peripheral nervous systems, inflammation, possible genetic factors, sympatho-afferent coupling, autoimmunity, and mental health factors as contributors to the syndrome. In addition to conventional subtypes (type I and type II), cluster analyses have uncovered other proposed subtypes. Prevalence of CRPS is approximately 1.2%, female gender is consistently associated with a higher risk of development, and substantial physical, emotional, and financial costs can result from the syndrome. Children with CRPS seem to benefit from multifaceted physical therapy leading to a high percentage of symptom-free patients. The best available evidence along with standard clinical practice supports pharmacological agents, physical and occupational therapy, sympathetic blocks for engaging physical restoration, steroids for acute CRPS, neuromodulation, ketamine, and intrathecal baclofen as therapeutic approaches. There are many emerging treatments that can be considered as a part of individualized, patient-centered care. Vitamin C may be preventive. CRPS can lead to progressively painful sensory and vascular changes, edema, limb weakness, and trophic disturbances, all of which substantially erode healthy living. Despite some progress in research, more comprehensive basic science investigation is needed to clarify the molecular mechanisms of the disease so that targeted treatments can be developed for better outcomes. Incorporating a variety of standard therapies with different modes of action may offer the most effective analgesia. Introducing less conventional approaches may also be helpful when traditional treatments fail to provide sufficient improvement.

Animal models of complex regional pain syndrome: A scoping review

BACKGROUND

complex regional pain syndrome (CRPS) leads to a debilitating chronic pain condition. The lack of cause, etiology, and treatment for CRPS has been widely explored in animal models.

OBJECTIVE

Provide a comprehensive framework of the animal models used for investigating CRPS.

ELIGIBILITY CRITERIA

Preclinical studies to induce the characteristics of CRPS, with a control group, in any language or publication date.

SOURCES OF EVIDENCE

The search was performed in the Medline (PubMed) and ScienceDirect databases.

RESULTS

93 studies are included. The main objective of the included studies was to understand the CRPS model. Rats, males and adults, exposed to ischemia/reperfusion of the paw or fracture of the tibia were the most common characteristics. Nociceptive evaluation using von Frey monofilaments was the most widely adopted in the studies.

CONCLUSIONS

For the best translational science between the animal models and individuals with CRPS, future studies should include more heterogeneous animals, and multiple assessment tools, in addition to improving the description and performance of measures that reduce the risk of bias.

A retrospective review of the management and outcomes of patients diagnosed with complex regional pain syndrome type II using electrodiagnostic findings

Objectives

The objective of this study was to assess the outcomes of the use of electrodiagnosis in the diagnosis and management of discrete nerve injuries in patients with complex regional pain syndrome (CRPS).

Design

This study is a secondary retrospective cohort analysis of patients diagnosed with CRPS from a single outpatient physical medicine and rehabilitation clinic and included all patients who had abnormal electrodiagnostic findings, in addition to CRPS.

Results

Sixty patients of 248 diagnosed with CRPS underwent electrodiagnosis, 41 of whom had abnormal electrodiagnostic findings indicating a discrete nerve injury. Only 51% of the 41 referrals had indicated the suspicion of a nerve injury. Nearly all patients had undergone physiotherapy. Forty-one percent responded to treatment with oral prednisone alone, 54% had a functional improvement after a combination of treatments including corticosteroids, and 5% improved with treatments that did not involve corticosteroids. Surgical interventions for nerve injuries were required for 34% of patients in the cohort. All surgeries involved the median or ulnar nerve, with the exception of one fibular nerve. After treatment, 39 of 41 patients had functional recoveries or better.

Conclusions

Electrodiagnosis can inform diagnosis of nerve injury and direct intervention including the need for surgical intervention. Electrodiagnosis should be considered for patients with initial signs of concomitant discrete nerve injury or with CRPS who are not responding to treatments because a nerve injury may be underlying.

What is Known Complex Regional Pain Syndrome (CRPS) is a poorly understood pain condition. CRPS has been divided into two subtypes, the second subtype involves a discrete nerve injury with pain that extends beyond the territory of the nerve injury.

What is New We observed that nerve injuries that may require surgical intervention are diagnosed just over half of the time upon initial assessment in patients with suspected CRPS. We observed that nerve injuries frequently required specifically directed interventions in place of or in conjunction with CRPS treatments. We suggest that electrodiagnosis is an important part of the triage protocol for CRPS II to reveal discrete nerve injuries that may be hidden. We recommend that electrodiagnosis be considered for patients with initial signs of concomitant discrete nerve injury or for CRPS patients who do not improve with medical therapies.

Interventions for treating pain and disability in adults with complex regional pain syndrome- an overview of systematic reviews

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually occurs in a limb following trauma or surgery. It is characterised by persisting pain that is disproportionate in magnitude or duration to the typical course of pain after similar injury. There is currently no consensus regarding the optimal management of CRPS, although a broad range of interventions have been described and are commonly used. This is the first update of the original Cochrane review published in Issue 4, 2013.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the efficacy, effectiveness, and safety of any intervention used to reduce pain, disability, or both, in adults with CRPS.

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of Ovid MEDLINE, Ovid Embase, Cochrane Database of Systematic Reviews, CINAHL, PEDro, LILACS and Epistemonikos from inception to October 2022, with no language restrictions. We included systematic reviews of randomised controlled trials that included adults (≥18 years) diagnosed with CRPS, using any diagnostic criteria.  Two overview authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools respectively. We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes quality of life, emotional well-being, and participants' ratings of satisfaction or improvement with treatment.  MAIN RESULTS: We included six Cochrane and 13 non-Cochrane systematic reviews in the previous version of this overview and five Cochrane and 12 non-Cochrane reviews in the current version. Using the AMSTAR 2 tool, we judged Cochrane reviews to have higher methodological quality than non-Cochrane reviews. The studies in the included reviews were typically small and mostly at high risk of bias or of low methodological quality. We found no high-certainty evidence for any comparison.  There was low-certainty evidence that bisphosphonates may reduce pain intensity post-intervention (standardised mean difference (SMD) -2.6, 95% confidence interval (CI) -1.8 to -3.4, P = 0.001; I2 = 81%; 4 trials, n = 181) and moderate-certainty evidence that they are probably associated with increased adverse events of any nature (risk ratio (RR) 2.10, 95% CI 1.27 to 3.47; number needed to treat for an additional harmful outcome (NNTH) 4.6, 95% CI 2.4 to 168.0; 4 trials, n = 181).  There was moderate-certainty evidence that lidocaine local anaesthetic sympathetic blockade probably does not reduce pain intensity compared with placebo, and low-certainty evidence that it may not reduce pain intensity compared with ultrasound of the stellate ganglion. No effect size was reported for either comparison. There was low-certainty evidence that topical dimethyl sulfoxide may not reduce pain intensity compared with oral N-acetylcysteine, but no effect size was reported. There was low-certainty evidence that continuous bupivacaine brachial plexus block may reduce pain intensity compared with continuous bupivacaine stellate ganglion block, but no effect size was reported. For a wide range of other commonly used interventions, the certainty in the evidence was very low and provides insufficient evidence to either support or refute their use. Comparisons with low- and very low-certainty evidence should be treated with substantial caution. We did not identify any RCT evidence for routinely used pharmacological interventions for CRPS such as tricyclic antidepressants or opioids.

AUTHORS' CONCLUSIONS

Despite a considerable increase in included evidence compared with the previous version of this overview, we identified no high-certainty evidence for the effectiveness of any therapy for CRPS. Until larger, high-quality trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult. Current non-Cochrane systematic reviews of interventions for CRPS are of low methodological quality and should not be relied upon to provide an accurate and comprehensive summary of the evidence.

Effectiveness of Infliximab in Patients with Complex Regional Pain Syndrome: A Case Series

Purpose

Complex regional pain syndrome (CRPS) is a multi-mechanism disease, with an exaggerated inflammatory response as an important underlying mechanism. Auto-inflammation can theoretically be combated by anti-inflammatories, such as TNF-α inhibitors. This study's aim was to assess the effectiveness of intravenous infliximab, a TNF-α inhibitor, in patients with CRPS.

Patients and Methods

CRPS patients treated with infliximab between January 2015 and January 2022 were approached to participate in this retrospective study. Medical records were screened for age, gender, medical history, CRPS duration, and CRPS severity score. Additionally, treatment effect, dose and duration, and side effects were extracted from medical records. Patients who still receive infliximab completed a short global perceived effect survey.

Results

Eighteen patients received infliximab, and all but two gave consent. Trial treatment with three sessions of 5 mg/kg intravenous infliximab was completed in 15 patients (93.7%). Eleven patients (73.3%) were categorized as responders with a positive treatment effect. Treatment was continued in nine patients, and seven patients are currently treated. Infliximab dose is 5 mg/kg, and frequency is every four to six weeks. Seven patients completed a global perceived effect survey. All patients reported improvement (median 2, IQR 1-2) and treatment satisfaction (median 1, IQR 1-2). One patient described side effects such as itching and rash.

Conclusion

Infliximab proved effective in 11 out of 15 CRPS patients. Seven patients are still being treated. Further research is needed on the role of infliximab in the treatment of CRPS and possible predictors of response to treatment.

Ketamine for Complex Regional Pain Syndrome: A Narrative Review Highlighting Dosing Practices and Treatment Response

This is a narrative review of intravenous ketamine infusions for the treatment of complex regional pain syndrome (CRPS). It briefly covers the definition of CRPS, its epidemiology, and other treatments before introducing ketamine as the article's focus. A summary of ketamine's evidence base and its mechanisms of action is provided. The authors then review ketamine dosages reported in peer-reviewed literature for the treatment of CRPS, and their associated duration of pain relief. The observed response rates to ketamine and predictors of treatment response are also discussed.

A predictive model based on random forest for shoulder-hand syndrome

Objectives

The shoulder-hand syndrome (SHS) severely impedes the function recovery process of patients after stroke. It is incapable to identify the factors at high risk for its occurrence, and there is no effective treatment. This study intends to apply the random forest (RF) algorithm in ensemble learning to establish a predictive model for the occurrence of SHS after stroke, aiming to identify high-risk SHS in the first-stroke onset population and discuss possible therapeutic methods.

Methods

We retrospectively studied all the first-onset stroke patients with one-side hemiplegia, then 36 patients that met the criteria were included. The patients’ data concerning a wide spectrum of demographic, clinical, and laboratory data were analyzed. RF algorithms were built to predict the SHS occurrence, and the model’s reliability was measured with a confusion matrix and the area under the receiver operating curves (ROC).

Results

A binary classification model was trained based on 25 handpicked features. The area under the ROC curve of the prediction model was 0.8 and the out-of-bag accuracy rate was 72.73%. The confusion matrix indicated a sensitivity of 0.8 and a specificity of 0.5, respectively. And the feature importance scored the weights (top 3 from large to small) in the classification were D-dimer, C-reactive protein, and hemoglobin.

Conclusion

A reliable predictive model can be established based on post-stroke patients’ demographic, clinical, and laboratory data. Combining the results of RF and traditional statistical methods, our model found that D-dimer, CRP, and hemoglobin affected the occurrence of the SHS after stroke in a relatively small sample of data with tightly controlled inclusion criteria.

Morphological and electrophysiological evaluation of median and ulnar nerve in complex regional pain syndrome type 1

OBJECTIVE

Complex regional pain syndrome (CRPS) can be distinguished as type I without and type II with electrophysiological evidence of major nerve lesion. The pathophysiology of both subgroups is still under investigation. The aim of this research is to demonstrate the nerve morphology and electrophysiology in CRPS type I patients.

MATERIALS AND METHODS

Bilateral median and ulnar nerve cross-sectional areas were evaluated with ultrasound and also median and ulnar nerve conduction studies of both hands were performed. Cross-sectional areas of median and ulnar nerves and nerve conduction studies in healthy controls were also obtained and compared with the patients.

RESULTS

Twenty-five male patients and 11 healthy male controls were enrolled in the study. The mean age of the patients was 24.08 ± 5.50 years and controls was 23.18 ± 5.09 (p > 0.05). Compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes of the diseased side were found significantly lower than the healthy side (p < 0.05). Both median and ulnar nerve distal motor latency values were significantly higher in the patient group (p < 0.05). There was no significant difference in the median and ulnar nerve cross-sectional area when compared with the opposite extremity and healthy volunteers.

CONCLUSION

The lower SNAP and CMAP amplitudes of the median and ulnar nerves compared to the healthy side and the prolongation of the affected side median and ulnar nerve distal motor latencies of the affected individuals may indicate axonal involvement in patients with CRPS type 1. Decreased CMAP amplitudes may also indicate muscle atrophy due to a decrease in the number of functional motor units.

Dorsal root ganglion stimulation for treatment of chronic postsurgical pain secondary to triple neurectomy

Triple neurectomy (resection of Ilioinguinal, Iliohypogastric, and Genitofemoral nerves) is performed in cases of inguinal neuralgia, refractory to conservative management. However, this procedure comes with several adverse effects, including but not limited to ectopic afferent firing and tactile allodynia. In such a scenario, the inguinal pain can become chronic and debilitating and can be classified as chronic post-surgical pain. Spinal neuromodulation techniques have been employed for treating such refractory, intractable chronic groin, pelvic and abdominal pain. One such technique is dorsal root ganglion stimulation which is designed to manage difficult-to-treat chronic pain in specific areas of the lower body, such as the foot, knee, hip, or groin. The authors present a case in which the patient underwent a laparoscopic neurectomy of ilioinguinal, Iliohypogastric, and genitofemoral nerves that failed to resolve her pain-related symptoms. The patient presented to the authors' pain clinic with severe inguinal pain and allodynia, refractory to multiple analgesic agents. The patient underwent a successful trial and subsequent implant with ipsilateral dorsal root ganglion stimulation at L1& L2. At six months post-implant, the patient continues to report 80-90% improvement in her pain and physical function.

Biological and psychological early prognostic factors in complex regional pain syndrome: A systematic review

BACKGROUND AND OBJECTIVE

Several risk factors for the onset of CRPS have been found, but evidence for prognostic factors associated with the progression of this condition remains sparse. However, the detection and management of these factors are necessary to design secondary prevention strategies. The objective of this systematic review was to identify prognostic factors in adult individuals with early CRPS.

DATABASE AND DATA TREATMENT

PubMed, Embase, PsycINFO, Cochrane Library and Scopus, were published between January 1990 and November 2021. Two independent investigators selected cross-sectional and longitudinal studies looking at early (<12 weeks from onset) prognostic factors for pain, CRPS severity score, disability, return to work, or quality of life. The quality in prognostic studies (QUIPS) tool was used to assess the risk of bias. A qualitative meta-synthesis was performed.

RESULTS

Out of 4652 different articles, six studies met the inclusion criteria. We identified 21 early factors associated with a poorer prognosis in type I CRPS. We found moderate evidence to support six of them: higher pain intensity, self-rated disability, anxiety, pain-related fear, being a female and high-energy triggering event. Only two studies had an overall low risk of bias.

CONCLUSIONS

This study showed an important lack of information on early prognostic factors in CRPS. Only one article investigated the link with psychological characteristics. There is a crucial need for larger studies, with a well-defined population using validated measures.

SIGNIFICANCE

This systematic review highlights the lack of knowledge about early prognostic factors in CRPS. A few putative prognostic factors were identified. Most of the moderate evidence is related to a single cohort. Future research is required to find out which patients are vulnerable to chronification.

Delphi study to define core clinical outcomes for inclusion in a complex regional pain syndrome international research registry and data bank

ABSTRACT

Complex regional pain syndrome (CRPS) clinical trials have historically captured a diverse range of outcomes. A minimum set of CRPS patient-reported outcomes has been agreed for inclusion in a future CRPS international clinical research registry and data bank. This study aimed to identify a complementary set of core clinical outcomes. Clinicians and researchers from the international CRPS community informed the content of a 2-round electronic Delphi study. Participation was invited from members of the International Association for the Study of Pain CRPS Special Interest Group and the International Research Consortium for CRPS. In round 1, participants rated the relevance of 59 clinical outcomes in relation to the question "What is the clinical presentation and course of CRPS, and what factors influence it?" (1 = not relevant and 9 = highly relevant). In round 2, participants rerated each outcome in the light of the round 1 median scores. The criterion for consensus was median score ≥7, agreed by 75% of respondents. The core study team considered the feasibility of data collection of each identified outcome in agreeing final selections. Sixty respondents completed both survey rounds, with responses broadly consistent across professions. Nine outcomes met the consensus criterion. Final outcomes recommended for inclusion in the core clinical set were record of medications, presence of posttraumatic stress disorder, extent of allodynia, and skin temperature difference between limbs. Study findings provide robust recommendations for core clinical outcome data fields in the future CPRS international clinical research registry. Alongside patient-reported outcomes, these data will enable a better understanding of CRPS.

Signs and symptoms of pediatric complex regional pain syndrome -type 1: A retrospective cohort study

Background

Complex regional pain syndrome (CRPS) presents with an array of symptoms that can vary from child to child, making it difficult to diagnose and differentiate from other pain conditions such as chronic musculoskeletal (MSK) pain. Thirteen symptoms and signs are outlined in the Budapest criteria for CRPS (developed and validated for adults) but have not been well described in pediatrics.

Aims

The aim of this study was to describe the signs and symptoms of pediatric CRPS type 1 (CRPS 1) and determine whether a cluster of symptoms can differentiate CRPS 1 from chronic MSK pain.

Methods

A retrospective cohort study of pediatric patients with CRPS 1 and MSK pain in a pediatric pain program was conducted. Descriptive statistics were used to report demographics and pain characteristics. The chi-square test was used to evaluate differences in signs and symptoms between patients with CRPS and MSK pain. A logistic regression model was used to evaluate whether a cluster of symptoms could predict a diagnosis of CRPS 1.

Results

The sample included 187 patients (99 with CRPS 1 and 88 with MSK pain); 81% were female with a mean age 14.1 years. The most prevalent CRPS symptoms were hyperalgesia (54%) and allodynia (52%). A cluster of symptoms (hyperalgesia, color changes, and range of motion) predicted the probability of a diagnosis of CRPS 1.

Conclusions

A cluster of symptoms may be critical in differentiating pediatric CRPS 1 and MSK pain. Future research is needed to determine if this model is valid in external populations and to explore whether a similar model can differentiate CRPS 1 from other pain conditions (e.g., neuropathic pain).

Gonadal hormone-dependent nociceptor sensitization maintains nociplastic pain state in female mice

ABSTRACT

Nociplastic pain conditions develop predominantly in women. We recently established a murine nociplastic pain model by applying postinjury thermal (40°C) stimulation to an injured (capsaicin-injected) area, triggering a transition to a nociplastic pain state manifesting as persistent mechanical hypersensitivity outside of the previously injured area. The nociplastic pain state was centrally maintained by spinal microglia in males but peripherally by ongoing afferent activity at the previously injured area in females. Here, we investigated whether gonadal hormones are critical for the development of this peripherally maintained nociplastic pain state in females. Although the transition to a nociplastic pain state still occurred in ovariectomized females, the pain state was maintained neither by ongoing afferent activity at the previously injured area nor by spinal microglia. Estradiol reconstitution a week before the injury plus postinjury stimulation, but not after the transition had already occurred, restored the development of peripherally maintained nociplastic mechanical hypersensitivity in ovariectomized females. G protein-coupled estrogen receptor antagonism during the transition phase mimicked ovariectomy in gonad-intact females, whereas the receptor antagonism after the transition gradually alleviated the nociplastic mechanical hypersensitivity. At the previously injured area, afferents responsive to allyl isothiocyanate (AITC), a TRPA1 agonist, contributed to the maintenance of nociplastic mechanical hypersensitivity in gonad-intact females. In ex vivo skin-nerve preparations, only AITC-responsive afferents from the nociplastic pain model in gonad-intact females showed ongoing activities greater than control. These results suggest that gonadal hormones are critical for peripherally maintained nociplastic pain state in females by sensitizing AITC-responsive afferents to be persistently active.

Differences in incidence rate and onset timing of undiagnosed finger symptom among shoulder surgeries related to complex regional pain syndrome

The purpose of this study was to clarify the difference in onset timing and incidence of undiagnosed finger symptom (UDFS) between various shoulder surgical procedures. In this study, UDFS symptoms included the following four symptoms in the fingers;edema, limited range-of-motion, skin color changes, and abnormal sensations. UDFS cases were defined as those presenting with at least one UDFS. In result, the incidence rate of UDFS cases was 7.1% overall (58/816 shoulders), 7.4% (32/432) in arthroscopic rotator cuff repair (ARCR), 9.0% (11/122) in open rotator cuff repair (ORCR), 1.4% (2/145) in arthroscopic subacromial decompression (ASD), 13.2% (5/38) in open reduction and internal fixation (ORIF), 11.1% (3/27) in humeral head replacement, 4.8% (1/21) in anatomical total shoulder arthroplasty, and 12.9% (4/31) in reverse total shoulder arthroplasty cases. The Rate was significantly higher with ARCR compared to ASD (p<.01). About onset timing in weeks postoperatively, the ORIF group had a statistically earlier symptom onset than the Rotator cuff repair (ARCR + ORCR) group (2.4 weeks vs. 6.0 weeks, p<.01). When classifying the onset timing into before and after the removal of the abduction pillow, the ORIF group showed a statistically higher rate of onset before brace removal than the Rotator cuff repair groups (p<.01). Differences in UDFS among shoulder surgeries were demonstrated in this study. J. Med. Invest. 70 : 415-422, August, 2023.

Pain-autonomic measures reveal nociceptive sensitization in complex regional pain syndrome

BACKGROUND

Allodynia and hyperalgesia are common signs in individuals with complex regional pain syndrome (CRPS), mainly attributed to sensitization of the nociceptive system. Appropriate diagnostic tools for the objective assessment of such hypersensitivities are still lacking, which are essential for the development of mechanism-based treatment strategies.

OBJECTIVES

This study investigated the use of pain-autonomic readouts to objectively detect sensitization processes in CRPS.

METHODS

Twenty individuals with chronic CRPS were recruited for the study alongside 16 age- and sex-matched healthy controls (HC). All individuals underwent quantitative sensory testing and neurophysiological assessments. Sympathetic skin responses (SSRs) were recorded in response to 15 pinprick and 15 noxious heat stimuli of the affected (CRPS hand/foot) and a control area (contralateral shoulder/hand).

RESULTS

Individuals with CRPS showed increased mechanical pain sensitivity and increased SSR amplitudes compared with HC in response to pinprick and heat stimulation of the affected (p < 0.001), but not in the control area (p > 0.05). Habituation of pinprick-induced SSRs was reduced in CRPS compared to HC in both the affected (p = 0.018) and slightly in the control area (p = 0.048). Habituation of heat-induced SSR was reduced in CRPS in the affected (p = 0.008), but not the control area (p = 0.053).

CONCLUSIONS

This is the first study demonstrating clinical evidence that pain-related autonomic responses may represent objective tools to quantify sensitization processes along the nociceptive neuraxis in CRPS (e.g. widespread hyperexcitability). Pain-autonomic readouts could help scrutinize mechanisms underlying the development and maintenance of chronic pain in CRPS and provide valuable metrics to detect mechanism-based treatment responses in clinical trials.

SIGNIFICANCE

This study provides clinical evidence that autonomic measures to noxious stimuli can objectively detect sensitization processes along the nociceptive neuraxis in complex regional pain syndrome (CRPS) (e.g. widespread hyperexcitability). Pain-autonomic readouts may represent valuable tools to explore pathophysiological mechanisms in a variety of pain patients and offer novel avenues to help guide mechanism-based therapeutic strategies.