Mechanism-based treatment in complex regional pain syndromes

A surgical approach to complex regional pain syndrome with neurogenic thoracic outlet syndrome in a reoperation patient

Thoracic outlet syndrome (TOS) and complex regional pain syndrome (CRPS) are two etiologies of chronic pain. TOS is a group of conditions that occur due to compression of the neurovascular structures of the upper extremity while CRPS is a disorder characterized by chronic and unremitting pain. This case highlights the experience of a 22-year-old female who presented following a traumatic injury to her left arm and was initially diagnosed with neurogenic TOS and later CRPS. Over a 10-year-period, she underwent a total of four operations to try and address her debilitating pain. In our third-time reoperation, symptoms of both pathologies nearly completely resolved with extensive neurolysis of the left brachial plexus and application of a scar tissue barrier.

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.

Effectiveness of motor imagery in complex regional pain syndrome: A systematic review with meta-analysis

OBJECTIVE

The purpose of this study was to determine the effects of motor imagery (MI) on pain intensity and disability in individuals with complex regional pain syndrome (CRPS).

METHODS

A systematic search was conducted in various electronic databases to identify all relevant studies: PubMed, CINAHL, WOS, PEDro, CENTRAL, and Scopus. Randomized controlled trials assessing the effects of MI in individuals with CRPS were included. The risk of bias was assessed with the Cochrane Risk of Bias tool, the methodological quality was evaluated using PEDro scale, and the level of evidence was reported according to the GRADE. Between-groups standardized mean differences (SMD) were calculated.

RESULTS

Six studies were included. The meta-analysis found moderate-quality evidence that MI improves pain intensity and related disability as immediate (pain: SMD -1.07, 95% CI: -1.53 to -0.60; disability: SMD 1.05, 95% CI: 0.59 to 1.51), short-term (pain: SMD -1.28, 95% CI: -2.14 to -0.42; disability: SMD 1.37; 95% CI: 0.16 to 2.58), and long-term effects (pain: SMD -1.18; 95% CI: -1.89 to -0.46; disability: SMD 1.18; 95% CI: 0.46 to 1.89), as compared with a comparison group. The risk of bias of the trials was relatively low, but the imprecision of the results downgraded the level of evidence.

CONCLUSIONS

Moderate-quality evidence suggests a positive effect of MI for improving pain intensity and disability immediately after and at short-term in individuals with CRPS.

Repetitive Transcranial Magnetic Stimulation with Sensorimotor Training for the Treatment of Complex Regional Pain Syndrome Type 2 of the Upper Limb Case Report

This case report describes the use of repetitive transcranial magnetic stimulation (rTMS) combined with sensorimotor training (SMT) to treat an individual with complex regional pain syndrome (CRPS) type 2 with allodynia of the right hand/wrist. After the 9-week intervention, there was a clinically meaningful reduction in pain intensity which continued to 3 months after intervention. Further, clinically meaningful improvements in wrist and hand function and allodynia were observed. Although the use of rTMS for CRPS has been reported, this unique report provides valuable insight into the clinical utility of rTMS plus SMT for the treatment of CRPS and related symptoms.

Different Types of Pain in Complex Regional Pain Syndrome Require a Personalized Treatment Strategy

Complex regional pain syndrome (CRPS) is a debilitating painful state of an extremity that can develop after trauma. CRPS is diagnosed by the new International Association for the Study of Pain (IASP) diagnostic criteria for CRPS. The syndrome is characterized by continuing regional pain with abnormal sensory, motor, sudomotor, vasomotor, edema, and/or trophic signs. The clinical presentation of CRPS can be very heterogeneous because CRPS is a multi-mechanism syndrome. Therefore, mechanism-based subgroups have been suggested to personalize treatment for CRPS. Additionally, the presentation of symptom pain may also be able to identify different subgroups of CRPS. In this review, the types of pain recognized by the IASP-nociceptive, neuropathic, and nociplastic pain-will be discussed as possible subgroups for CRPS. Each pain type should be identified in CRPS patients, with a thorough history taking, physical examination, and diagnostic tests or (novel) biomarkers to optimize treatment effectiveness. Over the course of the syndrome, patients with CRPS probably experience more than one distinct pain type. Therefore, pain specialists should be alert to not only adjust their treatment if underlying pathophysiologic mechanisms tend to change but also to personalize the treatment of the associated type of pain in the CRPS patient.

Peripheral BDNF Regulates Somatosensory-Sympathetic Coupling in Brachial Plexus Avulsion-Induced Neuropathic Pain

Brachial plexus avulsion (BPA) is a combined injury involving the central and peripheral nervous systems. Patients with BPA often experience severe neuropathic pain (NP) in the affected limb. NP is insensitive to the existing treatments, which makes it a challenge to researchers and clinicians. Accumulated evidence shows that a BPA-induced pain state is often accompanied by sympathetic nervous dysfunction, which suggests that the excitation state of the sympathetic nervous system is correlated with the existence of NP. However, the mechanism of how somatosensory neural crosstalk with the sympathetic nerve at the peripheral level remains unclear. In this study, through using a novel BPA C7 root avulsion mouse model, we found that the expression of BDNF and its receptor TrκB in the DRGs of the BPA mice increased, and the markers of sympathetic nervous system activity including α1 and α2 adrenergic receptors (α1-AR and α2-AR) also increased after BPA. The phenomenon of superexcitation of the sympathetic nervous system, including hypothermia and edema of the affected extremity, was also observed in BPA mice by using CatWalk gait analysis, an infrared thermometer, and an edema evaluation. Genetic knockdown of BDNF in DRGs not only reversed the mechanical allodynia but also alleviated the hypothermia and edema of the affected extremity in BPA mice. Further, intraperitoneal injection of adrenergic receptor inhibitors decreased neuronal excitability in patch clamp recording and reversed the mechanical allodynia of BPA mice. In another branch experiment, we also found the elevated expression of BDNF, TrκB, TH, α1-AR, and α2-AR in DRG tissues from BPA patients compared with normal human DRGs through western blot and immunohistochemistry. Our results revealed that peripheral BDNF is a key molecule in the regulation of somatosensory-sympathetic coupling in BPA-induced NP. This study also opens a novel analgesic target (BDNF) in the treatment of this pain with fewer complications, which has great potential for clinical transformation.

Rehabilitation Interventions for Complex Regional Pain Syndrome: An Overview of Systematic Reviews

OBJECTIVES

An increasing number of systematic reviews have been conducted on various conservative management of complex regional pain syndrome (CRPS) targeting different rehabilitation interventions and objectives. The intent of this article was to summarize and critically appraise the body of evidence on conservative management of the CRPS and to provide an overall picture of the current state of the literature.

METHODS

This study was an overview of systematic reviews on conservative treatments for CRPS. We conducted a literature search from inception to January 2023 in the following databases: Embase, Medline, CINAHL, Google Scholar, Cochrane Library, and Physiotherapy Evidence Database (PEDro). Two independent reviewers conducted study screening, data extraction, and methodological quality assessment (using AMSTAR-2). Qualitative synthesis was the preferred method for reporting the findings of our review. We calculated the corrected covered area index to account for the proportion of overlapping primary studies that were included in multiple reviews.

RESULT

We identified 214 articles, and a total of 9 systematic reviews of randomized controlled trials were eligible for inclusion. Pain and disability were the most common outcomes evaluated in the reviews. There were 6 (6/9; 66%) high-quality, 2 (2/9; 22%) moderate-quality, and 1 critically low-quality systematic review (1/9;11%), with the quality of the included trials ranging from very low to high. There was a large overlap across primary studies that were included in the systematic reviews (corrected covered area=23%). The findings of high-quality reviews support the effectiveness of mirror therapy (MT) and graded motor imagery (GMI) programs on pain and disability improvement in CRPS patients. The large effect size was reported for the effectiveness of MT on pain and disability (SMD:1.88 (95% CI: 0.73-3.02) and 1.30 (95% CI: 0.11-2.49), respectively) and the effectiveness of GMI program (GMIP) on pain and disability improvement (SMD: 1.36 (95% CI: 0.75-1.96) and 1.64 (95% CI: 0.53-2.74), respectively).

DISCUSSION

The evidence is in favor of adopting movement representation techniques, such as MT and GMI programs, for the treatment of pain and disability in patients with CRPS. However, this is based on a small body of primary evidence, and more research is required to generate conclusions. Overall, the evidence is not comprehensive or of sufficient quality to make definitive recommendations about the effectiveness of other rehabilitation interventions in improving pain and disability.

The association of self-reported symptoms of central sensitization and sleep disturbances in neuropathic pain

Introduction

Patients with neuropathic pain (NP) report a higher impairment of quality of life and sleep than patients with chronic pain without neuropathic characteristics. These include somatosensory peculiarities like allodynia, a surrogate marker for central sensitization.

Objectives

This study aimed to investigate the relation between symptoms of central sensitization and sleep disturbances in patients with NP.

Methods

Within this cross-sectional study, data sets of 3339 patients with chronic NP syndromes (painful diabetic polyneuropathy, n = 543; postherpetic neuralgia, n = 1480) or complex regional pain syndromes (CRPS, n = 1316) were analyzed. Neuropathic pain symptoms were assessed with the painDETECT questionnaire (PD-Q), depression with the Patient Health Questionnaire-9, and sleep impairment with items of the Medical Outcomes Study Sleep Scale in 4 subscales. The association of demographic/clinical data, somatosensory phenotype, depression, and pain intensity with sleep impairment was assessed by unadjusted Spearman correlation analyses and multivariable regression analyses.

Results

Sleep impairment was observed in all pain aetiologies although with some significant differences in the single sleep items. The intensity of the individual PD-Q items differed to some extent between the 3 pain entities, whereas the PD-Q sum score was similar. Thermal hyperalgesia and burning assessed by the PD-Q were significantly associated with sleep disturbance, adequacy, and quantity but not with sleep somnolence. Only depression and self-reported allodynia had a significant relation to all 4 sleep elements.

Conclusion

Beside depression, allodynia as a surrogate marker hints to a possible impact of central sensitization on the sleep disruption of patients with NP.

Central sensitization in CRPS patients with widespread pain: a cross-sectional study

OBJECTIVE

Widespread pain hypersensitivity and enhanced temporal summation of pain (TSP) are commonly reported in patients with complex regional pain syndrome (CRPS) and discussed as proxies for central sensitization. This study aimed to directly relate such signs of neuronal hyperexcitability to the pain phenotype of CRPS patients.

METHODS

Twenty-one CRPS patients and 20 healthy controls (HC) were recruited. The pain phenotype including spatial pain extent (assessed in % body surface) and intensity were assessed and related to widespread pain hypersensitivity, TSP, and psychological factors. Quantitative sensory testing (QST) was performed in the affected, the contralateral and a remote (control) area.

RESULTS

CRPS patients showed decreased pressure pain thresholds in all tested areas (affected: t(34)  = 4.98, P < .001, contralateral: t(35) = 3.19, P = .005, control: t(31) = 2.65, P = .012). Additionally, patients showed increased TSP in the affected area (F(3,111) = 4.57, P = .009) compared to HC. TSP was even more enhanced in patients with a high compared to a low spatial pain extent (F(3,51) = 5.67, P = .008), suggesting pronounced spinal sensitization in patients with extended pain patterns. Furthermore, the spatial pain extent positively correlated with the Bath Body Perception Disturbance Scale (ρ = 0.491; P = .048).

CONCLUSIONS

Overall, we provide evidence that the pain phenotype in CRPS, that is, spatial pain extent, might be related to sensitization mechanism within the central nociceptive system. This study points towards central neuronal excitability as a potential therapeutic target in patients with more widespread CRPS.

Person-centred management of upper limb complex regional pain syndrome: an integrative review of non-pharmacological treatment

Introduction

Complex Regional Pain Syndrome (CRPS) is most common in the upper limb and associated with high disability. The purpose of this review was to critically appraise and synthesise literature exploring non-pharmacological treatment for upper limb CRPS, to guide upper-limb-specific management.

Methods

Using an integrative review methodology, 13 databases were searched to identify all published studies on non-pharmacological management of upper limb CRPS. The Crowe Critical Appraisal Tool was used to provide quality ratings for included studies, and analysis employed a qualitative descriptive approach.

Results

From 236 abstracts reviewed, 113 full texts were read, and 38 articles selected for data extraction. Designs included single case (n = 14), randomised controlled trial (n = 8), prospective cohort (n = 8), case series (n = 4), retrospective (n = 3), and mixed methods (n = 1). Interventions were categorised as sensory retraining (n = 13), kinesiotherapy (n = 7), manual therapies (n = 7), physical modalities (n = 6), and interdisciplinary treatment programmes (n = 5). All studies measured pain intensity, and most (n = 24) measured physical parameters such as strength, movement, or perceptual abilities. Few measured patient-rated function (n = 13) or psychological factors (n = 4). Quality ratings ranged from 30% to 93%, with a median of 60%.

Conclusion

Methodological quality of non-pharmacological treatment approaches for upper limb CRPS is overall poor. Movement, desensitisation, and graded functional activity remain the mainstays of intervention. However, despite the impact of CRPS on wellbeing and function, psychological factors and functional outcomes are infrequently addressed. Further robust research is required to determine which aspects of treatment have the greatest influence on which symptoms, and when and how these should be introduced and progressed.

From a Symptom-Based to a Mechanism-Based Pharmacotherapeutic Treatment in Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is a debilitating painful condition of a distal extremity that can develop after tissue damage. CRPS is thought to be a multimechanism syndrome and ideally the most prominent mechanism(s) should be targeted by drugs in an individually tailored manner. This review gives an overview of the action and evidence of current and future pharmacotherapeutic options for CRPS. The available options are grouped in four categories by their therapeutic actions on the CRPS mechanisms, i.e. inflammation, central sensitisation, vasomotor disturbances and motor disturbances. More knowledge about the underlying mechanisms of CRPS helps to specifically target important CRPS mechanisms. In the future, objective biomarkers could potentially aid in selecting appropriate mechanism-based drugs in order to increase the effectiveness of CRPS treatment. Using this approach, current and future pharmacotherapeutic options for CRPS should be studied in multicentre trials to prove their efficacy. The ultimate goal is to shift the symptom-based selection of therapy into a mechanism-based selection of therapy in CRPS.

Effect of sympathetic sprouting on the excitability of dorsal root ganglion neurons and afferents in a rat model of neuropathic pain

Increased sympathetic nerve excitability has been reported to aggravate a variety of chronic pain conditions, and an increase in the number of sympathetic nerve fibers in the dorsal root ganglion (DRG) has been found in neuropathic pain (NP) models. However, the mechanism of the neurotransmitter norepinephrine (NE) released by sympathetic nerve fiber endings on the excitability of DRG neurons is still controversial, and the adrenergic receptor subtypes involved in this biological process are also controversial. In our study, we have two objectives: (1) To determine the effect of the neurotransmitter NE on the excitability of different neurons in DRG; (2) To determine which adrenergic receptors are involved in the excitability of DRG neurons by NE released by sprouting sympathetic fibers. In this experiment, a unique field potential recording method of spinal cord dorsal horn was innovatively adopted, which can be used for electrophysiological study in vivo. The results showed that： Forty days after SNI, patch clamp and field potential recording methods confirmed that NE enhanced the excitability of ipsilateral DRG large neurons, and then our in vivo electrophysiological results showed that the α₂ receptor blocker Yohimbine could block the excitatory effect of NE on A-fiber and the inhibitory effect on C-fiber, while the α_2A-adrenergic receptor agonist guanfacine (100 μM) had the same biological effect as NE. Finally, we concluded that NE from sympathetic fiber endings is involved in the regulation of pain signaling by acting on α_2A-adrenergic receptors in DRG.

Complex Regional Pain Syndrome in Athletes: Scoping Review

Background and Objectives: Complex regional pain syndrome (CRPS) is a chronic condition characterized by disproportionate regional pain, usually affecting distal limbs, that follows trauma or surgery. Athletes may develop CRPS because of exposure to traumatic or overuse injuries. The aim of the present study is to review the available literature about CRPS type 1 in athletes. Materials and Methods: We searched two online databases (PubMed and Web of Science), selecting papers aiming at investigating CRPS type 1 (algodystrophy) in athletes. The analysis of databases was made considering original articles published until 30 June 2021, written in English. Results: Fifteen papers (12 case reports, 3 case series) were selected for a total of 20 clinical cases (15 females, 5 males), aged between 10 and 46 years (mean age 18.4 ± 9.8 standard deviation years). Patients included practiced different types of sport (soccer, athletics, gymnastics, basketball). The most involved anatomical sites were lower limbs, and time to diagnosis ranged from 2 days to 4 years. The most used treatments were pharmacological and physical therapies, but sometimes invasive approaches, as regional nerve, or lumbar sympathetic blocks, were provided. The main assessed outcomes were return to activity and pain. Conclusions: Our review suggests a higher prevalence of CRPS type 1 in younger people and in lower limbs than in general population but confirms the higher prevalence in females. However, the number of studies addressing CRPS in athletes is limited, as well as the number of involved patients, considering that only few and heterogeneous case reports were published about this topic. Moreover, the high prevalence of old studies (only 5 available studies in the last 10 years) might have influenced the choice of both assessment tools and management strategies. Despite these limitations, athletes showing disproportionate pain after sport-related injury should be promptly evaluated and treated through a multidimensional approach to avoid long-term consequences of algodystrophy.

Denying the Truth Does Not Change the Facts: A Systematic Analysis of Pseudoscientific Denial of Complex Regional Pain Syndrome

Purpose

Several articles have claimed that complex regional pain syndrome (CRPS) does not exist. Although a minority view, it is important to understand the arguments presented in these articles. We conducted a systematic literature search to evaluate the methodological quality of articles that claim CRPS does not exist. We then examined and refuted the arguments supporting this claim using up-to-date scientific literature on CRPS.

Methods

A systematic search was conducted in MEDLINE, EMBASE and Cochrane CENTRAL databases. Inclusion criteria for articles were (a) a claim made that CRPS does not exist or that CRPS is not a distinct diagnostic entity and (b) support of these claims with subsequent argument(s). The methodological quality of articles was assessed if possible.

Results

Nine articles were included for analysis: 4 narrative reviews, 2 personal views, 1 letter, 1 editorial and 1 case report. Seven points of controversy were used in these articles to argue that CRPS does not exist: 1) disagreement with the label “CRPS”; 2) the “unclear” pathophysiology; 3) the validity of the diagnostic criteria; 4) CRPS as a normal consequence of immobilization; 5) the role of psychological factors; 6) other identifiable causes for CRPS symptoms; and 7) the methodological quality of CRPS research.

Conclusion

The level of evidence for the claim that CRPS does not exist is very weak. Published accounts concluding that CRPS does not exist, in the absence of primary evidence to underpin them, can harm patients by encouraging dismissal of patients’ signs and symptoms.

Complex Regional Pain Syndrome with Aortic Distress after Thoracic Endovascular Aortic Repair and False Lumen Exclusion with "Candy Plug" Technique

A 41-year-old male presented for pain treated with oxycodone. A zone-2 thoracic endovascular aortic repair with distal PETTICOAT (provisional extension to induce complete attachment) for complicated Type-IIIB aortic dissection was performed 18 months before. Repeated hospitalizations did not show any issues to justify the recurrent pain. The aortic nature of the pain was suspected considering the plug as a pain trigger. Through a left thoracoabdominal incision in the eighth intercostal space, the candy plug was removed. Pain diminished after thoracoabdominal surgery steadily.

Effect of intravenous low-dose S-ketamine on pain in patients with Complex Regional Pain Syndrome: A retrospective cohort study

Objective

The objective of this study was to assess the effectiveness of a low‐dose intravenous S‐ketamine treatment on refractory pain in patients with Complex Regional Pain Syndrome (CRPS).

Methods

In this retrospective study, patients with CRPS who received intravenous S‐ketamine from March 2010 to April 2019 were included. According to our inpatient protocol, S‐ketamine dose was increased until pain reduction was achieved or side effects were observed. Maximum dose was 14 mg/h and treatment duration was 7 days. Primary outcome parameters were pain scores (Numeric Rating Scale) at baseline (T0), end of infusion (T1), and approximately 4 weeks postinfusion (T2). Patients were categorized as responder/nonresponder at T1 and T2. Patients were considered a responder in case there was pain score reduction of greater than or equal to 2 points or if treatment was reported as successful.

Results

Forty‐eight patients were included. Mean disease duration was 5 years (interquartile range [IQR] = 6 years). Median pain score significantly decreased from 8 (IQR = 2) at T0 to 6 (IQR = 4) at T1 (p < 0.001). At T1, 62% of the patients were responders. At T2, 48% of the patients remained a responder. A significant proportion of the responders at T1 turned into nonresponders at T2 (p = 0.03).

Conclusion

In a group of patients with CRPS with refractory pain, low‐dose intravenous S‐ketamine treatment resulted in effective pain relief during infusion. Although a significant proportion of initial responders became nonresponders at follow‐up, half of the patients were still a responder at ~ 4 weeks postinfusion. Further research is needed to investigate mechanisms responsible for pain relief by S‐ketamine infusions and to ascertain possible predictors of response to the treatment.

Ultrasound-guided pulsed radiofrequency of the saphenous nerve in a complex regional pain syndrome patient with lower limb pain

Complex regional pain syndrome is a painful and debilitating syndrome in which the patient presents with disabling pain, edema, and/or vasomotor or sudomotor abnormalities. The mechanism is complex and not well understood. There is no definitive treatment for the condition yet. Pulsed radiofrequency is a minimally invasive, minimal destructive, and safe intervention. It can be used for neuropathic pain. A 40-year-old man with complex regional pain syndrome complained of intractable pain of the lower limb secondary to injury to the saphenous nerve due to a third-degree burn. Conventional medications, epidural block, and sympathetic nerve block provided temporary relief. We performed pulsed radiofrequency of the saphenous nerve for the management of lower limb pain, and the symptoms remained under control at 3 months. To the best of our knowledge, this is the first application of ultrasound-guided pulsed radiofrequency of the saphenous nerve for the management of complex regional pain syndrome.

The challenge of recognizing severe pain and autonomic abnormalities for early diagnosis of CRPS

OBJECTIVES

Complex regional pain syndrome (CRPS) is a disabling usually post-traumatic pain condition. International guidelines emphasize early diagnosis for treatment and improved outcome. Early intense and persistent pain along with features of autonomic dysfunction in the first week's post-injury are early warning signs for development of CRPS. We have previously reported a delayed diagnosis of CRPS. The main purpose of the present study was to investigate possible causes of a delayed diagnosis, with a special focus of recognition of risk factors.

METHODS

A total of 52 CRPS 1 (without detectable nerve damage) and CRPS 2 (with evidence of nerve lesion) patients were included in the study. When examined at OUS-Rikshospitalet, we retrospectively asked the patients on the development of pain and autonomic abnormalities from the time of the eliciting injury, performed a thorough clinical investigation with an emphasis on signs of autonomic failure and compared symptoms and clinical findings with such information in previous medical records. We also evaluated symptoms and signs according to the type of injury they had suffered.

RESULTS

Of a total of 52 patients (30 women and 22 men, mean age 39.0 years at the time of injury), 34 patients had CRPS type 1 (65.4%) and 18 CRPS type 2 (34.6%), 25 patients with pain in the upper and 27 in the lower extremity. A total of 35 patients (67.3%) were diagnosed with CRPS (following mean 2.1 years) prior to the investigation at OUS-Rikshospitalet (mean 4.86 years following injury). Mean time from injury to diagnosis was 33.5 months (SD 30.6) (2.8 years) for all patients. In retrospect, all 17 patients first diagnosed at OUS met the CRPS diagnosis at an earlier stage. All patients retrospectively reported intense pain (numeric rating scale > 7) from the time of injury with a large discrepancy to previous medical records which only stated intense pain in 29.4% of patients with CRPS type 1 and 44.4% of patients with CRPS type 2 within the first four months. While the patients reported an early onset of autonomic dysfunction, present in 67.3 and 94.2% of the patients within one week and one month, respectively, reports of autonomic abnormalities within the first four months was far less (maximum in 51.7% of patients with CRPS type 1 and in 60% in CRPS 2). In 10 patients with CRPS type 1, no symptom nor sign of autonomic abnormalities was reported.

CONCLUSIONS

We still find a significant delay in the diagnosis of CRPS. There is a large discrepancy between both self-reporting of intense, disproportionate pain, as well as symptoms of autonomic abnormalities from the time of injury, and documentation in previous medical records. Our findings suggest a lack of awareness of risk factors for the development of CRPS, such as early intense pain and autonomic abnormalities without recovery, contributing to delayed diagnosis. The present results suggest causes of delayed CRPS-diagnosis. An increased attention to early warning signs/risk factors may improve diagnosis of CRPS.

Autoimmune regulation of chronic pain

Chronic pain is an unpleasant and debilitating condition that is often poorly managed by existing therapeutics. Reciprocal interactions between the nervous system and the immune system have been recognized as playing an essential role in the initiation and maintenance of pain. In this review, we discuss how neuroimmune signaling can contribute to peripheral and central sensitization and promote chronic pain through various autoimmune mechanisms. These pathogenic autoimmune mechanisms involve the production and release of autoreactive antibodies from B cells. Autoantibodies-ie, antibodies that recognize self-antigens-have been identified as potential molecules that can modulate the function of nociceptive neurons and thereby induce persistent pain. Autoantibodies can influence neuronal excitability by activating the complement pathway; by directly signaling at sensory neurons expressing Fc gamma receptors, the receptors for the Fc fragment of immunoglobulin G immune complexes; or by binding and disrupting ion channels expressed by nociceptors. Using examples primarily from rheumatoid arthritis, complex regional pain syndrome, and channelopathies from potassium channel complex autoimmunity, we suggest that autoantibody signaling at the central nervous system has therapeutic implications for designing novel disease-modifying treatments for chronic pain.

The serotonin receptor 2A (HTR2A) rs6313 variant is associated with higher ongoing pain and signs of central sensitization in neuropathic pain patients

BACKGROUND

The serotonin receptor 2A (HTR2A) has been described as an important facilitation mediator of spinal nociceptive processing leading to central sensitization (CS) in animal models of chronic pain. However, whether HTR2A single nucleotide variants (SNVs) modulate neuropathic pain states in patients has not been investigated so far. The aim of this study was to elucidate the potential association of HTR2A variants with sensory abnormalities or ongoing pain in neuropathic pain patients.

METHODS

At total of 240 neuropathic pain patients and 253 healthy volunteers were included. Patients were phenotypically characterized using standardized quantitative sensory testing (QST). Patients and controls were genotyped for HTR2A g.-1438G > A (rs6311) and c.102C > T (rs6313). Genotype-related differences in QST parameters were assessed considering QST profile clusters, principal somatosensory components and sex.

RESULTS

There was an equal distribution of rs6313 and linked rs6311 between patients and controls. However, the rs6313 variant was significantly associated with a principal component of pinprick hyperalgesia and dynamic mechanical allodynia, indicating enhanced CS in patients with sensory loss (-0.34 ± 0.15 vs. +0.31 ± 0.11 vs., p < .001). In this cluster, the variant allele was also associated with single QST parameters of pinprick hyperalgesia (MPT, +0.64 ± 0.18 vs. -0.34 ± 0.23 p = .002; MPS, +0.66 ± 0.17 vs. -0.09 ± 0.23, p = .009) and ongoing pain was increased by 30%.

CONCLUSIONS

The specific association of the rs6313 variant with pinprick hyperalgesia and increased levels of ongoing pain suggests that the HTR2A receptor might be an important modulator in the development of CS in neuropathic pain.

SIGNIFICANCE

This article presents new insights into serotonin receptor 2A-mediating mechanisms of central sensitization in neuropathic pain patients. The rs6313 variant allele was associated with increased mechanical pinprick sensitivity and increased levels of ongoing pain supporting a contribution of central sensitization in the genesis of ongoing pain providing a possible route for mechanism-based therapies.

Exploring the impact of pain management programme attendance on complex regional pain syndrome (CRPS) patients' decision making regarding immunosuppressant treatment to manage their chronic pain condition

Objectives Complex regional pain syndrome (CRPS) is a rare chronic pain condition for which no curative treatment exists. Patients in tertiary centres are often required to make decisions about treatment options. This study was conducted to explore how prior attendance of a pain management program might alter patients' decision making processes. Methods This qualitative study uses focus groups to gather patient views on an immunosuppressant drug treatment (mycophenolate) for the management of CRPS. Participants were allocated to one of three focus groups based on their treatment journey; Group 1 (n=3) were involved in a recent mycophenolate drug trial; Group 2 (n=5) were neither involved in the trial nor attended a Pain Management Programme (PMP); Group 3 (n=6) were not involved in the trial but had attended a PMP. Outcomes were considered within the framework of Leventhal's Common Sense Model (CSM) in relation to the decision making process. Results Thematic analysis identified differing themes for each group. Group 1: (1) Medication as a positive form of treatment, (2) The trial/drug and (3) Pacing. Group 2: (1) Medication as form of treatment, (2) Other forms of support/treatment and (3) Side effects of mycophenolate. Group 3: (1) Varied view of medication, (2) Consideration of other forms of support and (3) Side effects. Conclusions Attendance on a PMP might provide patients with skills to better manage uncertainty when faced with various treatment options. Leventhal's model goes some way to explaining this. The specific importance of, and benefit from understanding pacing when commencing an effective drug treatment for chronic pain became apparent.

Patient tolerability of suprascapular and median nerve blocks for the management of pain in post-stroke shoulder-hand syndrome

BACKGROUND

Current management options for pain in stroke patients with the shoulder-hand syndrome (SHS) are limited and often ineffective. The use of peripheral nerve blocking in SHS has been limited due to concerns of hyperalgesia and allodynia in these patients. This study assessed the tolerability of suprascapular nerve (SSN) and median nerve blocks for acute control of pain in patients with post-stroke SHS.

METHODS

All SHS patients fulfilled diagnosis using the Budapest criteria. Patient tolerability was defined by a composite score that included a change on the visual analog scale (VAS) from baseline for shoulder and hand pain, presence of adverse events, and a self-reported patient satisfaction score. Pain assessment was performed 1 h before (baseline), and 1 h and 2 weeks after the procedure.

RESULTS

Five patients (68.5 ± 9.5 years) with post-stroke SHS underwent SSN and median nerve blocks. Participant assessment 1 h after the procedure indicated that the 2 blocking procedures were well tolerated and that VAS scores for shoulder and hand pain decreased by 79% (- 62.6 mm ± 25.6; p = 0.043) and 48% (- 33 mm ± 40.2; p = 0.080), respectively from baseline. After 2 weeks, average VAS scores remained 56% and 37% below baseline, respectively. There were no adverse events and all patients were satisfied after the procedure.

CONCLUSIONS

Suprascapular and median nerve blocks are safe and well-tolerated procedures for acute pain control in post-stroke SHS. Further studies should address the benefit of these procedures on overall pain reduction, functional recovery, and quality of life in SHS patients.

Macrophages and Schwann cell TRPA1 mediate chronic allodynia in a mouse model of complex regional pain syndrome type I

Complex regional pain syndrome type I (CRPS-I) is characterized by intractable chronic pain. Poor understanding of the underlying mechanisms of CRPS-I accounts for the current unsatisfactory treatment. Antioxidants and antagonists of the oxidative stress-sensitive channel, the transient receptor potential ankyrin 1 (TRPA1), have been found to attenuate acute nociception and delayed allodynia in models of CRPS-I, evoked by ischemia and reperfusion (I/R) of rodent hind limb (chronic post ischemia pain, CPIP). However, it is unknown how I/R may lead to chronic pain mediated by TRPA1. Here, we report that the prolonged (day 1-15) mechanical and cold allodynia in the hind limb of CPIP mice was attenuated permanently in Trpa1^-/- mice and transiently after administration of TRPA1 antagonists (A-967079 and HC-030031) or an antioxidant (α-lipoic acid). Indomethacin treatment was, however, ineffective. We also found that I/R increased macrophage (F4/80⁺ cell) number and oxidative stress markers, including 4-hydroxynonenal (4-HNE), in the injured tibial nerve. Macrophage-deleted MaFIA (Macrophage Fas-Induced Apoptosis) mice did not show I/R-evoked endoneurial cell infiltration, increased 4-HNE and mechanical and cold allodynia. Furthermore, Trpa1^-/- mice did not show any increase in macrophage number and 4-HNE in the injured nerve trunk. Notably, in mice with selective deletion of Schwann cell TRPA1 (Plp1-Cre^ERT;Trpa1^fl/fl mice), increases in macrophage infiltration, 4-HNE and mechanical and cold allodynia were attenuated. In the present mouse model of CRPS-I, we propose that the initial oxidative stress burst that follows reperfusion activates a feed forward mechanism that entails resident macrophages and Schwann cell TRPA1 of the injured tibial nerve to sustain chronic neuroinflammation and allodynia. Repeated treatment one hour before and for 3 days after I/R with a TRPA1 antagonist permanently protected CPIP mice against neuroinflammation and allodynia, indicating possible novel therapeutic strategies for CRPS-I.

Can self-reported pain characteristics and bedside test be used for the assessment of pain mechanisms? An analysis of results of neuropathic pain questionnaires and quantitative sensory testing

Hyperalgesia and allodynia are frequent in neuropathic pain. Some pain questionnaires such as the Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) and the Neuropathic Pain Scale (NPS) include self-assessment or bedside testing of hyperalgesia/allodynia. The aim of this study was to determine to what extent LANSS and NPS data are congruent with findings on quantitative sensory testing (QST). Self-reported presence of dynamic mechanical allodynia (DMA) and descriptors of hot, cold, or deep ongoing pain (the NPS and LANSS) as well as bedside findings of mechanical allodynia (LANSS) were compared with signs of DMA and thermal hyperalgesia on QST in 617 patients with neuropathic pain. Self-reported abnormal skin sensitivity (LANSS) showed a moderate concordance with DMA during bedside test (67.9%, κ = 0.391) or QST (52.8%, κ = 0.165). Receiver operating curve analysis for self-reported DMA yielded similar area-under-the-curve values for the LANSS (0.65, confidence interval: 0.59%-0.97%) and NPS (0.71, confidence interval: 0.66%-0.75%) with high sensitivity but low specificity. Self-reported deep pain intensity was higher in patients with blunt pressure hyperalgesia, but not in patients with DMA or thermal hyperalgesia. No correlations were observed between self-reported hot or cold pain quality and thermal hyperalgesia on QST. Self-reported abnormal skin sensitivity has a high sensitivity to identify patients with DMA, but its low specificity indicates that many patients mean something other than DMA when reporting this symptom. Self-reported deep pain is related to deep-tissue hypersensitivity, but thermal qualities of ongoing pain are not related to thermal hyperalgesia. Questionnaires mostly evaluate the ongoing pain experience, whereas QST mirrors sensory functions. Therefore, both methods are complementary for pain assessment.

Understanding the Rehabilitation Needs of Korean Patients With Complex Regional Pain Syndrome

OBJECTIVE

To evaluate the current status of pain severity and quality of life (QoL) in patients with complex regional pain syndrome (CRPS), and to assess both their perceived needs and any unmet needs of current rehabilitation services.

METHODS

A single-center questionnaire-based survey was conducted on 47 patients with CRPS who were diagnosed based on Budapest's criteria. It collected demographic and clinical data, and the structured questionnaire included the Brief Pain Inventory (BPI), the Korean version of the World Health Organization Disability Assessment Schedule II (WHODAS-K II), as well as the 5-Level EuroQol-5D (EQ-5D-5L) for measuring the QoL.

RESULTS

The average value of BPI and WHODAS-K II were 7.69%±2.26% and 70.49%±19.22%, respectively. In the evaluation of their perceived needs and unmet needs for rehabilitation, patients had the highest rehabilitation needs in terms of pain (95.74%), followed by bodyaches (80.85%). Regarding their unmet needs, patients had the highest unmet needs in terms of memory impairment (83.33%), followed by weight management (72.00%). According to the regression analysis, only the overall BPI was significantly associated with QoL (p=0.01), and a higher BPI value led to poorer results for QoL.

CONCLUSION

In Korea, patients with CRPS do not receive adequate rehabilitation, and they are not satisfied with current received treatments. A more structured and individualized rehabilitation treatment plan is required to manage every aspect related to chronic pain, and provision should be made for improved care guidelines for future CRPS management.

Highlighting the Role of Biomarkers of Inflammation in the Diagnosis and Management of Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is characterized by continuous pain that is often accompanied by sensory, motor, vasomotor, sudomotor, and trophic disturbances. If left untreated, it can have a significant impact on the quality of life of patients. The diagnosis of CRPS is currently based on a set of relatively subjective clinical criteria: the New International Association for the Study of Pain clinical diagnostic criteria for CRPS. There are still no objective laboratory tests to diagnose CRPS and there is a great need for simple, objective, and easily measurable biomarkers in the diagnosis and management of this disease. In this review, we discuss the role of inflammation in the multi-mechanism pathophysiology of CRPS and highlight the application of potential biomarkers of inflammation in the diagnosis and management of this disease.

Bradykinin Receptors Play a Critical Role in the Chronic Post-ischaemia Pain Model

Complex regional pain syndrome type-I (CRPS-I) is a chronic painful condition resulting from trauma. Bradykinin (BK) is an important inflammatory mediator required in acute and chronic pain response. The objective of this study was to evaluate the association between BK receptors (B₁ and B₂) and chronic post-ischaemia pain (CPIP) development in mice, a widely accepted CRPS-I model. We assessed mechanical and cold allodynia, and paw oedema in male and female Swiss mice exposed to the CPIP model. Upon induction, the animals were treated with BKR antagonists (HOE-140 and DALBK); BKR agonists (Tyr-BK and DABK); antisense oligonucleotides targeting B₁ and B₂ and captopril by different routes in the model (7, 14 and 21 days post-induction). Here, we demonstrated that treatment with BKR antagonists, by intraperitoneal (i.p.), intraplantar (i.pl.), and intrathecal (i.t.) routes, mitigated CPIP-induced mechanical allodynia and oedematogenic response, but not cold allodynia. On the other hand, i.pl. administration of BKR agonists exacerbated pain response. Moreover, a single treatment with captopril significantly reversed the anti-allodynic effect of BKR antagonists. In turn, the inhibition of BKRs gene expression in the spinal cord inhibited the nociceptive behaviour in the 14th post-induction. The results of the present study suggest the participation of BKRs in the development and maintenance of chronic pain associated with the CPIP model, possibly linking them to CRPS-I pathogenesis.

Mechanism-specific rehabilitation management of complex regional pain syndrome: Proposed recommendations from evidence synthesis

STUDY DESIGN

Narrative review.

INTRODUCTION

There are a variety of treatments with demonstrated effectiveness for the management of complex regional pain syndrome (CRPS). However given the variability in symptom presentation in this population, therapists may be unsure what treatments would be most effective for individual clients.

PURPOSE OF THE STUDY

To present a brief synthesis of the literature and propose a rehabilitation version of a mechanism-specific management algorithm to guide personalized treatment of CRPS.

METHODS

A systematic search of the literature was conducted to identify all randomized controlled trials, systematic reviews, and clinical practice guidelines addressing rehabilitation of CRPS. Results were reviewed independently by 2 reviewers and final selection of articles was reached by consensus, Data was extracted using standardized forms, and a single rater gave quality ratings. Both reviewers then used the extracted data to present a synthesis of the evidence categorized by the proposed mechanisms of effect.

RESULTS

A total of 111 articles were retrieved and reviewed for inclusion; 49 were selected for data extraction. A synthesis of the key recommendations was compiled into a rehabilitation-specific version of the mechanism-based management algorithm proposed by Gierthmühlen et al (2014).

CONCLUSIONS

Consideration of mechanism-appropriate rehabilitation interventions may assist therapists to select the most appropriate and effective treatments from the body of evidence supporting rehabilitation of CRPS.

Somatosensory rehabilitation for allodynia in complex regional pain syndrome of the upper limb: A retrospective cohort study

STUDY DESIGN

Retrospective cohort study.

INTRODUCTION

Somatosensory rehabilitation is a standardized method of evaluation and conservative treatment of painful disorders of vibrotactile sensation, including the mechanical allodynia and burning pain of complex regional pain syndrome (CRPS).

PURPOSE OF THE STUDY

The purpose of this study was to examine the effectiveness of somatosensory rehabilitation for reducing allodynia in persons with CRPS of 1 upper limb in a retrospective consecutive cohort of patients.

METHODS

An independent chart review of all client records (May 2004-August 2015) in the Somatosensory Rehabilitation Centre (Fribourg, Switzerland) identified 48 persons meeting the Budapest criteria for CRPS of 1 limb who had undergone assessment and treatment. Outcomes of interest were the French version of the McGill Pain Questionnaire (Questionnaire de la Douleur St-Antoine [QDSA]), total area of allodynia as recorded by mapping the area of skin where a 15-g monofilament was perceived as painful, and the allodynia threshold (minimum pressure required to elicit pain within the allodynic territory).

RESULTS

This cohort was primarily women (70%), with a mean age of 45 years (range: 18-74). Mean duration of burning pain was 31 months (range: 1 week-27.5 years), and baseline QDSA core was 48. The average primary area of allodynia was 66 cm² (range: 2.6-320), and the most common allodynia threshold was 4.0 g. The average duration of treatment was 81 days. At cessation of treatment, the average QDSA score was 20 (effect size Cohen's d = 1.64). Allodynia completely resolved in 27 persons (56% of the total sample where only 58% completed treatment).

DISCUSSION

This uncontrolled retrospective study suggests that somatosensory rehabilitation may be an effective treatment with a large effect size for reducing the allodynia and painful sensations associated with CRPS of the upper limb. More work is in progress to provide estimates of reliability and validity for the measurement tools for allodynia employed by this method.

LEVEL OF EVIDENCE

2c.

Analysis of quantitative sudomotor axon reflex test patterns in patients with complex regional pain syndrome diagnosed using the Budapest criteria

BACKGROUND

Although the quantitative sensory axon reflex test (QSART) is used to evaluate sudomotor dysfunction in the diagnosis of complex regional pain syndrome (CRPS), its validity remains controversial. This study investigated the diagnostic performance of the QSART for CRPS and assessed associations between results of the QSART and other clinical variables.

METHODS

We examined the electronic medical records of 196 consecutive patients who underwent the QSART with a suspected diagnosis of CRPS, during the period from January 2013 to December 2015. To assess the diagnostic performance of the QSART for CRPS based on the Budapest research criteria, we calculated sensitivity, specificity, positive likelihood ratio and negative likelihood ratio. Furthermore, we performed binary logistic regression analyses to investigate the relationships between QSART results and other clinical variables.

RESULTS

The sensitivity and specificity of the QSART for diagnosing CRPS were 67.6% and 40.6%, respectively. The OR for diagnosing CRPS using the QSART was not statistically significant (1.43; 95% CI 0.65 to 3.14; p=0.376), whereas it was for distinguishing CRPS types I and II (4.11; 95% CI 1.34 to 12.57; p=0.013). In multivariable analysis, there were no correlations between the results of the QSART and other variables, except hypertension (OR=0.34; 95% CI 0.13 to 0.91; p=0.032).

CONCLUSION

The QSART showed low diagnostic value as a screening or a confirmatory test for CRPS according to the Budapest research criteria. CRPS type II was more likely than CRPS type I to result in abnormal QSART results.

Nociceptive mechanisms involved in the acute and chronic phases of a complex regional pain syndrome type 1 model in mice

Complex regional pain syndrome I (CRPS-I) is a chronic painful pathology still undertreated. CTK 01512-2 is a recombinant version of the spider peptide Phα1β, and it functions as a voltage-gated calcium channel blocker and a transient receptor potential ankyrin 1 (TRPA1) antagonist with antinociceptive effect in different pain models. Here, we investigate the mechanisms involved in the acute and chronic nociceptive phases of a model of CPRS-I in mice and assess the antinociceptive effect of CTK 01512-2 using this model. Adult male and female mice C57BL/6 (20-30 g) were used to determine mechanical (von Frey test) or cold (acetone test) allodynia induction. Inflammatory parameters (serum and tibial nerve lactate levels, hind paw temperature and edema, or tissue cell infiltration) were evaluated after chronic post-ischemia pain (CPIP, a model of CPRS-I) induction. Anti-inflammatory and anti-neuropathic drugs or CTK 01512-2 were tested. First, we detected that CPIP-induced mechanical and cold allodynia in male and female mice in a similar way. In the acute phase (1 day after CPIP), an increase in inflammatory parameters were observed, as well as the anti-allodynic effect of anti-inflammatory compounds. In the chronic phase (17 days after CPIP), mice exhibited mechanical and cold allodynia, and anti-neuropathic drugs induced antinociception, while no inflammatory alterations were found. CTK 01512-2 reversed the CPIP allodynic effect in both nociceptive phases. Thus, this CPRS-I model can be used to understand the mechanisms involved in CPRS-I induced pain and inflammation. Besides, we observed that CTK 01512-2 has a valuable antinociceptive effect in this pain model.

Early Treatment With Metformin in a Mice Model of Complex Regional Pain Syndrome Reduces Pain and Edema

BACKGROUND

Metformin, an adenosine monophosphate (AMP)-activated protein kinase activator, as well as a common drug for type 2 diabetes, has previously been shown to decrease mechanical allodynia in mice with neuropathic pain. The objective of this study is to determine if treatment with metformin during the first 3 weeks after fracture would produce a long-term decrease in mechanical allodynia and improve a complex behavioral task (burrowing) in a mouse tibia fracture model with signs of complex regional pain syndrome.

METHODS

Mice were allocated into distal tibia fracture or nonfracture groups (n = 12 per group). The fracture was stabilized with intramedullary pinning and external casting for 21 days. Animals were then randomized into 4 groups (n = 6 per group): (1) fracture, metformin treated, (2) fracture, saline treated, (3) nonfracture, metformin treated, and (4) nonfracture, saline treated. Mice received daily intraperitoneal injections of metformin 200 mg/kg or saline between days 14 and 21. After cast removal, von Frey force withdrawal (every 3 days) and burrowing (every 7 days) were tested between 25 and 56 days. Paw width was measured for 14 days after cast removal. AMP-activated protein kinase downregulation at 4 weeks after tibia fracture in the dorsal root ganglia was examined by immunohistochemistry for changes in the AMP-activated protein kinase pathway.

RESULTS

Metformin injections elevated von Frey thresholds (reduced mechanical allodynia) in complex regional pain syndrome mice versus saline-treated fracture mice between days 25 and 56 (difference of mean area under the curve, 42.5 g·d; 95% CI of the difference, 21.0-63.9; P < .001). Metformin also reversed burrowing deficits compared to saline-treated tibial fracture mice (difference of mean area under the curve, 546 g·d; 95% CI of the difference, 68-1024; P < .022). Paw width (edema) was reduced in metformin-treated fracture mice. After tibia fracture, AMP-activated protein kinase was downregulated in dorsal root ganglia neurons, and mechanistic target of rapamycin, ribosomal S6 protein, and eukaryotic initiation factor 2α were upregulated.

CONCLUSIONS

The important finding of this study was that early treatment with metformin reduces mechanical allodynia in a complex regional pain syndrome model in mice. Our findings suggest that AMP-activated protein kinase activators may be a viable therapeutic target for the treatment of pain associated with complex regional pain syndrome.

CRPS: what’s in a name? Taxonomy, epidemiology, neurologic, immune and autoimmune considerations

This account of the condition now termed complex regional pain syndrome (CRPS) spans approximately 462 years since a description embodying similar clinical features was described by Ambroise Paré in 1557. While reviewing its historical origins, the text describes why it became necessary to change the taxonomies of two clinical syndromes with similar pathophysiologies to one which acknowledges this aspect but does not introduce any mechanistic overtones. Discussed at length is the role of the sympathetic component of the autonomic nervous system (ANS) and why its dysfunction has both directly and indirectly influenced our understanding of the inflammatory aspects of CRPS. As the following article will show, our knowledge has expanded in an exponential fashion to include musculoskeletal, immune, autoimmune, central and peripheral nervous system and ANS dysfunction, all of which increase the complexity of its clinical management. A burgeoning literature is beginning to shed light on the mechanistic aspects of these syndromes and the increasing evidence of a genetic influence on such factors as autoimmunity, and its importance is also discussed at length. An important aspect that has been missing from the diagnostic criteria is a measure of disease severity. The recent validation of a CRPS Severity Score is also included.

Dynamic of the somatosensory system in postherpetic neuralgia

Introduction:

In postherpetic neuralgia (PHN) different types of patients can be distinguished regarding their predominant peripheral nociceptor function.

Objective:

The aim was to examine somatosensory profiles in the course of disease with special regard to the different subtypes existing in PHN.

Methods:

Twenty patients with PHN (7 men and 13 women, age 67 ± 9.6 years) were examined at baseline (disease duration 18.1 ± 26 months) and follow-up (31.6 ± 23.8 months later) with quantitative sensory testing (protocol of the German Research Network on Neuropathic Pain).

Results:

Fourteen (70%) PHN patients presented with impaired (iPHN) and 6 (30%) with preserved (pPHN) C-fiber function. Groups did not differ regarding age, disease duration, or pain intensity at baseline. Both groups did not differ regarding change in pain intensity (−0.5 ± 2.3 vs −1.7 ± 2.6 numerical rating scale, P = n.s.) at follow-up. Impaired PHN improved in thermal and mechanical detection thresholds as well as allodynia independent from change in pain intensity. By contrast, pPHN showed an increase in mechanical pain sensitivity (1.4 ± 2.5 vs −0.4 ± 2.2, P < 0.05) and a trend towards a stronger loss of detection (66% vs 33%, P = n.s.) on follow-up.

Conclusion:

Results demonstrate that patients with preserved C-fiber function are more predisposed to develop signs of central sensitization as demonstrated by an increased mechanical pain sensitivity. Impaired C-fiber function is able to improve even in chronic cases, but a functional loss is unlikely to play a role here. The knowledge of development of somatosensory profiles in the course of the disease offers possibilities to optimize a mechanism-based treatment.

Biochemical and Pharmacological Characterization of a Mice Model of Complex Regional Pain Syndrome

BACKGROUND AND OBJECTIVES

Complex regional pain syndrome is a challenging disease to treat. Recently, a mouse fracture model of complex regional pain syndrome has been developed that has many signs of the clinical syndrome. However, many aspects of the sensory neuron biochemistry and behavioral and pharmacological characterization of this model remain to be clarified.

METHODS

Mice were randomly assigned to fracture/cast or control (naive) groups. Fracture/cast mice underwent a closed distal tibia facture, with hindlimb wrapped in casting tape for 3 weeks. After cast removal, mice were tested for mechanical allodynia, burrowing behavior, and motor ability over a 12-week period. Protein immunohistochemistry was performed for substance P, calcitonin gene-related peptide, tropomyosin receptor kinase A, nerve growth factor, Nav1.7, and transient receptor potential cation-channel V1, colocalized in neurons, in the ipsilateral lumbar dorsal root ganglia (DRGs). Analgesic drugs were tested for pain-relieving efficacy.

RESULTS

Mechanical allodynia was greater in the ipsilateral hindpaw (P = 0.0002) in the fracture/cast group versus the control group, over the 3- to 12-week period. The amount of burrowing material removed was decreased (P = 0.0026), and there were deficits in spontaneous motor-rearing behavior (P = 0.018). Immunostaining of substance P, calcitonin gene-related peptide, Trk A receptor, nerve growth factor, Nav1.7, and transient receptor potential cation-channel V1 all demonstrated up-regulation in the DRGs of fracture mice versus controls (all P < 0.05). Morphine, pregabalin, ketamine, acetaminophen, and dexamethasone transiently increased force withdrawal thresholds on the ipsilateral (fracture) side and improved burrowing activity after injection (all P < 0.05). Ketorolac improved only burrowing.

CONCLUSIONS

Persistent pain-related behavior was demonstrated in this mouse fracture/cast model with wide-scale DRG up-regulation of pain mediators. Antihyperalgesic drugs reduced mechanical allodynia and improved burrowing.

Pain management in patients with vascular disease

Vascular disease covers a wide range of conditions, including arterial, venous, and lymphatic disorders, with many of these being more common in the elderly. As the population ages, the incidence of vascular disease will increase, with a consequent increase in the requirement to manage both acute and chronic pain in this patient population. Pain management can be complex, as there are often multiple co-morbidities to be considered. An understanding of the underlying pain mechanisms is helpful in the logical direction of treatment, particularly in chronic pain states, such as phantom limb pain or complex regional pain syndrome. Acute pain management for vascular surgery presents a number of challenges, including coexisting anticoagulant medication, that may preclude the use of regional techniques. Within the limited evidence base, there is a suggestion that epidural analgesia provides better pain relief and reduced respiratory complications after major vascular surgery. For carotid endarterectomy, there is again some evidence supporting the use of local anaesthetic analgesia, either by infiltration or by superficial cervical plexus block. Chronic pain in vascular disease includes post-amputation pain, for which well-known risk factors include high pain levels before amputation and in the immediate postoperative period, emphasizing the importance of good pain control in the perioperative period. Complex regional pain syndrome is another challenging chronic pain syndrome with a wide variety of treatment options available, with the strongest evidence being for physical therapies. Further research is required to gain a better understanding of the underlying pathophysiological mechanisms in pain associated with vascular disease and the best analgesic approaches to manage it.

miR-34a-mediated regulation of XIST in female cells under inflammation

Background

Evidence is overwhelming for sex differences in pain, with women representing the majority of the chronic pain patient population. There is a need to explore novel avenues to elucidate this sex bias in the development of chronic inflammatory pain conditions. Complex regional pain syndrome (CRPS) is a chronic neuropathic pain disorder, and the incidence of CRPS is greater in women than in men by ~4:1. Since neurogenic inflammation is a key feature of CRPS, dysregulation of inflammatory responses can be a factor in predisposing women to chronic pain.

Methods

Our studies investigating alterations in circulating microRNAs (miRNAs) in whole blood from female CRPS patients showed significant differential expression of miRNAs between responders and poor responders to ketamine treatment. Several of these miRNAs are predicted to target the long noncoding RNA, X-inactive-specific transcript (XIST). XIST mediates X-chromosome inactivation and is essential for equalizing the expression of X-linked genes between females and males. Based on the well-established role in inflammatory process, we focused on miR-34a, one of the miRNAs predicted to target XIST, and downregulated in CRPS patients responding poorly to ketamine.

Results

Our in vitro and in vivo models of acute inflammation and data from patients with CRPS showed that miR-34a can regulate XIST under inflammation directly, and through pro-inflammatory transcription factor Yin-Yang 1 (YY1). XIST was significantly upregulated in a subset of CRPS patients responding poorly to ketamine.

Conclusion

Since dysregulation of XIST can result in genes escaping inactivation or reactivation in female cells, further investigations on the role of XIST in the predominance of chronic inflammatory and pain disorders in women is warranted.

Sensory symptoms in low back pain-how do they matter?

OBJECTIVE

Successful treatment of chronic low back pain (LBP) is difficult in clinical practice and hard to measure in trials. One reason might be the use of insufficient outcome parameters. The aim was to investigate the importance of typical clinical characteristics of chronic LBP on QoL and functionality.

METHODS

A total of 51 patients with chronic LBP (19 with, 32 without radiculopathy) were investigated with different questionnaires.

RESULTS

Burdening symptoms differed in frequency, intensity and impairment of QoL and functionality between patients with and without radiculopathy and between the area of pain within the same patient, i.e. between back and leg. Symptoms of nerve affection such as prickling pain and numbness were rated higher in the area of radiating pain than on the back in radiculopathy, and typical neuropathic pain symptoms such as burning pain, prickling, spontaneous pain, and feeling of deep pressure and pain at the beginning of movement were rated with a higher impairment of QoL and functionality in patients with compared to those without radiculopathy. Furthermore, intensity, impairment of QoL, and functionality were not necessarily reported in association with one another: some patients were highly impaired in QoL or functionality, despite a moderate-to-low pain intensity, whereas others suffered from severe pain, but were less impaired in QoL or functionality.

CONCLUSION

Results suggest the consideration of impairment of QoL and functionality in addition to symptom intensity for treatment evaluation of chronic LBP. This can help to improve overall well-being of the patients and enhance efficacy in clinical pain trials and patient-centered treatment.