NMDA-receptor antagonist and morphine decrease CRPS-pain and cerebral pain representation

Pharmacologic Treatments in Upper Extremity Complex Regional Pain Syndrome: A Review and Analysis of Quality of Evidence

BACKGROUND

The purpose of this study was to assess the quality of evidence informing on common pharmacologic modalities used in upper extremity complex regional pain syndrome (CRPS).

METHODS

A literature search was performed for primary prospective trials that reported on the pharmacologic treatment of CRPS type I and II specific to the upper extremity. Thirty-one trials were included and evaluated by 2 independent reviewers according to the Oxford Levels of Evidence (LOE), modified Coleman Methodology Score, and the revised Consolidated Standards of Reporting Trials (CONSORT) score. Cohen's kappa coefficient was calculated to measure interrater reliability.

RESULTS

Twenty-two Oxford LOE I and 9 level II trials met the inclusion criteria. Overall, there was high interrater reliability in the Oxford LOE (100% agreement), modified Coleman Methodology Score (87% agreement), and CONSORT score (94% agreement). The pharmacologic interventions with the highest quality of evidence supporting use in treatment of upper extremity CRPS were bisphosphonates and ketamine. Interventions that lack high-quality evidence are tricyclic antidepressants (TCAs) and topical dimethyl sulfoxide (DMSO). Pharmacologic agents that remain inconclusive are calcitonin, gabapentin, mycophenolate, probiotics, steroids, nonsteroidal anti-inflammatory drugs, vitamin C, and N-acetylcysteine. Agents with limited benefit are mannitol, isosorbide dinitrate, guanethidine, and morphine.

CONCLUSIONS

Based on the evidence evaluated in this study, bisphosphonates should be considered as a first-line medication in the treatment of CRPS. In patients presenting with chronic or refractory CRPS, strong consideration should be given for the use of ketamine. Adjunct treatment in the acute setting should include TCAs and/or topical DMSO.

An update on the pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a rare and painful condition that has a wide range of triggering factors, often traumatic, and can present various clinical manifestations. The lack of knowledge about the underlying mechanisms has led to numerous treatment approaches, both conservative and surgical, which work through different mechanisms of action.

AREAS COVERED

In this review, the authors explore the key aspects of CRPS, including definition, diagnostic criteria, pitfalls, pathogenic hypotheses, and treatment strategies with a focus on pharmacotherapy. The review was based on a comprehensive search of the literature using PubMed, while also considering international guidelines for managing CRPS.

EXPERT OPINION

Based on the available evidence, pharmacological interventions appear to be effective in treating CRPS, especially when they target peripheral mechanisms, specifically nociceptive inflammatory pain, and when administered early in the course of the disease. However, there is still a lack of reliable evidence regarding the effects of drugs on central mechanisms of chronic pain in CRPS. In our expert opinion, drug therapy should be initiated as soon as possible, particularly in warm CRPS patient clusters, to prevent significant functional limitations, psychological distress, and negative impacts on individuals' social and economic well-being.

Algorithm for multimodal medication therapy in patients with complex regional pain syndrome

Complex regional pain syndrome (CRPS), previously known as reflex sympathetic dystrophy and causalgia, is a clinical entity characterized by classic neuropathic pain, autonomic involvement, motor symptoms, and trophic changes in the skin, nails, and hair. Although various therapeutic modalities are used to control CRPS-related pain, severe pain due to CRPS often persists and progresses to the chronic phase. In this study, we constructed an algorithm for multimodal medication therapy for CRPS based on the established pathology of CRPS. Oral steroid pulse therapy is recommended for initial pain management in patients with CRPS. Oral steroid therapy can reduce peripheral and central neuroinflammation, contributing to the development of neuropathic pain during the acute and chronic phases. If steroid pulse therapy offers poor relief or is ineffective, treatment to control central sensitization in the chronic phase should be initiated. If pain persists despite all drug adjustments, ketamine with midazolam 2 mg before and after ketamine injection can be administered intravenously to inhibit the N-methyl D-aspartate receptor. If this treatment fails to achieve sufficient efficacy, intravenous lidocaine can be administered for 2 weeks. We hope that our proposed drug treatment algorithm to control CRPS pain will help clinicians appropriately treat patients with CRPS. Further clinical studies assessing patients with CRPS are warranted to establish this treatment algorithm in clinical practice.

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.

Modern Principles of Diagnosis and Treatment in Complex Regional Pain Syndrome

BACKGROUND

Background: Complex regional pain syndrome (CRPS) is a relatively common complication, occurring in 5% of cases after injury or surgery, particularly in the limbs. The incidence of CPRS is around 5-26/100 000. The latest revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) now categorizes CRPS as a primary pain condition of multifactorial origin, rather than a disease of the skeletal system or the autonomic nervous system.

METHODS

Method: Based on a selective search of the literature, we summarize current principles for the diagnosis and treatment of CRPS.

RESULTS

Results: Regional findings in CRPS are accompanied by systemic symptoms, especially by neurocognitive disorders of body perception and of symptom processing. The therapeutic focus is shifting from predominantly passive peripheral measures to early active treatments acting both centrally and peripherally. The treatment is centered on physiotherapy and occupational therapy to improve sensory perception, strength, (fine) motor skills, and sensorimotor integration/ body perception. This is supported by stepped psychological interventions to reduce anxiety and avoidance behavior, medication to decrease inflammation and pain, passive physical measures for reduction of edema and of pain, and medical aids to improve functioning in daily life. Interventional procedures should be limited to exceptional cases and only be performed in specialized centers. Spinal cord and dorsal root ganglion stimulation, respectively, are the interventions with the best evidence.

CONCLUSION

Conclusion: The modern principles for the diagnosis and treatment of CRPS consider both, physiological and psychological mechanisms, with the primary goal of restoring function and participation. More research is needed to strengthen the evidence base in this field.

The missing mechanistic link: Improving behavioral treatment efficacy for pediatric chronic pain

Pediatric chronic pain is a significant global issue, with biopsychosocial factors contributing to the complexity of the condition. Studies have explored behavioral treatments for pediatric chronic pain, but these treatments have mixed efficacy for improving functional and psychological outcomes. Furthermore, the literature lacks an understanding of the biobehavioral mechanisms contributing to pediatric chronic pain treatment response. In this mini review, we focus on how neuroimaging has been used to identify biobehavioral mechanisms of different conditions and how this modality can be used in mechanistic clinical trials to identify markers of treatment response for pediatric chronic pain. We propose that mechanistic clinical trials, utilizing neuroimaging, are warranted to investigate how to optimize the efficacy of behavioral treatments for pediatric chronic pain patients across pain types and ages.

Atypical dermatologic manifestations in complex regional pain syndrome: a case report

BACKGROUND

Complex regional pain syndrome is a chronic pain condition characterized by autonomic dysfunction, changes in sympathetic and vasomotor activity, and sensory and motor changes. Complex regional pain syndrome is a clinical diagnosis and may occur after trauma or surgery. Complex regional pain syndrome-related pain may occur spontaneously and is out of proportion with the inciting event. We report herein the rare case of a man who developed concomitant painful generalized ulcerations after diagnosis of complex regional pain syndrome.

CASE PRESENTATION

A 43-year-old Caucasian male with history of four-extremity complex regional pain syndrome type 2 secondary to right rotator cuff surgery performed at an outside hospital presented to a tertiary care center for treatment of generalized ulcerations on all extremities of unknown etiology. Dermatology performed an extensive work-up including laboratory evaluations and biopsies, which were relatively unremarkable. His ulcers were treated with vinegar-based dressings, hydrotherapy, and irrigation and debridements. He was started on methadone (replacing a home fentanyl patch), ketamine infusion, and amitriptyline in addition to his home adjuncts. He obtained good symptom control, improved sleep, and diminished cognitive slowing, compared with his fentanyl patches.

CONCLUSION

This case report emphasizes an atypical case of generalized ulceration formation in the setting of complex regional pain syndrome. This case highlights the challenging nature of treating complex regional pain syndrome and using multimodal analgesia to target various nociceptive receptors to successfully reduce symptoms.

Clinical and Neurophysiological Effects of Progressive Movement Imagery Training for Pathological Pain

Movement limitation is a common characteristic of chronic pain such that pain prevents the very movement and activity that is most likely to promote recovery. This is particularly the case for pathological pain states such as complex regional pain syndrome (CRPS). One clinical approach to CRPS that has growing evidence of efficacy involves progressive movement imagery training. Graded Motor Imagery (GMI) targets clinical and neurophysiological effects through a stepwise progression through implicit and explicit movement imagery training, mirror therapy and then functional tasks. Here we review experiences from over 20 years of clinical and research experience with GMI. We situate GMI in terms of its historical underpinnings, the benefits and outstanding challenges of its implementation, its potential application beyond CRPS. We then review the neuropathological targets of GMI and current thought on its effects on neurophysiological biomarkers. Perspective This article provides an overview of our experiences with graded motor imagery training over the last 20 years focussing on the treatment of CRPS. It does both cover the theoretical underpinnings for this treatment approach, biomarkers which indicate potential changes driven by GMI, and experiences for achieving optimal treatment results.

OUP accepted manuscript

There have been some modest recent advancements in the research of Complex Regional Pain Syndrome, yet the amount and quality of the work in this complicated multifactorial disease remains low (with some notable exceptions; e.g., the recent work on the dorsal root ganglion stimulation). The semi-systematic (though in some cases narrative) approach to review is necessary so that we might treat our patients while waiting for “better research.” This semi-systematic review was conducted by experts in the field, (deliberately) some of whom are promising young researchers supplemented by the experience of “elder statesman” researchers, who all mention the system they have used to examine the literature. What we found is generally low- to medium-quality research with small numbers of subjects; however, there are some recent exceptions to this. The primary reason for this paucity of research is the fact that this is a rare disease, and it is very difficult to acquire a sufficient sample size for statistical significance using traditional statistical approaches. Several larger trials have failed, probably due to using the broad general diagnostic criteria (the “Budapest” criteria) in a multifactorial/multi-mechanism disease. Responsive subsets can often be identified in these larger trials, but not sufficient to achieve statistically significant results in the general diagnostic grouping. This being the case the authors have necessarily included data from less compelling protocols, including trials such as case series and even in some instances case reports/empirical information. In the humanitarian spirit of treating our often desperate patients with this rare syndrome, without great evidence, we must take what data we can find (as in this work) and tailor a treatment regime for each patient.

Graded motor imagery modifies movement pain, cortical excitability and sensorimotor function in complex regional pain syndrome

Patients with complex regional pain syndrome suffer from chronic neuropathic pain and also show a decrease in sensorimotor performance associated with characteristic central and peripheral neural system parameters. In the brain imaging domain, these comprise altered functional sensorimotor representation for the affected hand side. With regard to neurophysiology, a decrease in intracortical inhibition for the sensorimotor cortex contralateral to the affected hand has been repetitively verified, which might be related to increased primary somatosensory cortex functional activation for the affected limb. Rare longitudinal intervention studies in randomized controlled trials have demonstrated that a decrease in primary somatosensory cortex functional MRI activation coincided with pain relief and recovery in sensorimotor performance. By applying a randomized wait-list control crossover study design, we tested possible associations of clinical, imaging and neurophysiology parameters in 21 patients with complex regional pain syndrome in the chronic stage (>6 months). In more detail, we applied graded motor imagery over 6 weeks to relieve movement pain of the affected upper limb. First, baseline parameters were tested between the affected and the non-affected upper limb side and age-matched healthy controls. Second, longitudinal changes in clinical and testing parameters were associated with neurophysiological and imaging parameters. During baseline short intracortical inhibition, as assessed with transcranial magnetic stimulation, was decreased only for hand muscles of the affected hand side. During movement of the affected limb, primary somatosensory cortex functional MRI activation was increased. Hand representation area size for somatosensory stimulation in functional MRI was smaller on the affected side with longer disease duration. Graded motor imagery intervention but not waiting, resulted in a decrease of movement pain. An increase of somatosensory hand representation size over graded motor imagery intervention was related to movement pain relief. Over graded motor imagery intervention, pathological parameters like the increased primary somatosensory cortex activation during fist movement or decreased short intracortical inhibition were modified in the same way as movement pain and hand performance improved. No such changes were observed during the waiting period. Overall, we demonstrated characteristic changes in clinical, behaviour and neuropathology parameters applying graded motor imagery in patients with upper limb complex regional pain syndrome, which casts light on the effects of graded motor imagery intervention on biomarkers for chronic neuropathic pain.

Complex Regional Pain Syndrome. A Comprehensive Review on Neuroplastic Changes Supporting the Use of Non-invasive Neurostimulation in Clinical Settings

Background: Complex regional pain syndrome (CRPS) is a rare debilitating disorder characterized by severe pain affecting one or more limbs. CRPS presents a complex multifactorial physiopathology. The peripheral and sensorimotor abnormalities reflect maladaptive changes of the central nervous system. These changes of volume, connectivity, activation, metabolism, etc., could be the keys to understand chronicization, refractoriness to conventional treatment, and developing more efficient treatments. Objective: This review discusses the use of non-pharmacological, non-invasive neurostimulation techniques in CRPS, with regard to the CRPS physiopathology, brain changes underlying chronicization, conventional approaches to treat CRPS, current evidence, and mechanisms of action of peripheral and brain stimulation. Conclusion: Future work is warranted to foster the evidence of the efficacy of non-invasive neurostimulation in CRPS. It seems that the approach has to be individualized owing to the integrity of the brain and corticospinal function. Non-invasive neurostimulation of the brain or of nerve/muscles/spinal roots, alone or in combination with conventional therapy, represents a fertile ground to develop more efficient approaches for pain management in CRPS.

Alcohol amplifies cingulate cortex signaling and facilitates immobilization-induced hyperalgesia in female rats

Complex Regional Pain Syndrome (CRPS) is a musculoskeletal pain condition that often develops after limb injury and/or immobilization. Although the exact mechanisms underlying CRPS are unknown, the syndrome is associated with central and autonomic nervous system dysregulation and peripheral hyperalgesia symptoms. These symptoms also manifest in alcoholic neuropathy, suggesting that the two conditions may be pathophysiologically accretive. Interestingly, people assigned female at birth (AFAB) appear to be more sensitive to both CRPS and alcoholic neuropathy. To better understand the biobehavioral mechanisms underlying these conditions, we investigated a model of combined CRPS and alcoholic neuropathy in female rats. Animals were pair-fed either a Lieber-DeCarli alcohol liquid diet or a control diet for ten weeks. CRPS was modeled via unilateral hind limb cast immobilization for seven days, allowing for the other limb to serve as a within-subject control for hyperalgesia measures. To investigate the role of circulating ovarian hormones on pain-related behaviors, half of the animals underwent ovariectomy (OVX). Using the von Frey procedure to record mechanical paw withdrawal thresholds, we found that cast immobilization and chronic alcohol drinking separately and additively produced mechanical hyperalgesia observed 3 days after cast removal. We then examined neuroadaptations in AMPA GluR1 and NMDA NR1 glutamate channel subunits, extracellular signal-regulated kinase (ERK), and cAMP response element-binding protein (CREB) in bilateral motor and cingulate cortex across all groups. Consistent with increased pain-related behavior, chronic alcohol drinking increased GluR1, NR1, ERK, and CREB phosphorylation in the cingulate cortex. OVX did not alter any of the observed effects. Our results suggest accretive relationships between CRPS and alcoholic neuropathy symptoms and point to novel therapeutic targets for these conditions.

Effects of Chronic Pain Treatment on Altered Functional and Metabolic Activities in the Brain: A Systematic Review and Meta-Analysis of Functional Neuroimaging Studies

Previous studies have identified altered brain changes in chronic pain patients, however, it remains unclear whether these changes are reversible. We summarized the neural and molecular changes in patients with chronic pain and employed a meta-analysis approach to quantify the changes. We included 75 studies and 11 of these 75 studies were included in the activation likelihood estimation (ALE) analysis. In the 62 functional magnetic resonance imaging (fMRI) studies, the primary somatosensory and motor cortex (SI and MI), thalamus, insula, and anterior cingulate cortex (ACC) showed significantly decreased activity after the treatments compared to baseline. In the 13 positron emission tomography (PET) studies, the SI, MI, thalamus, and insula showed significantly increased glucose uptake, blood flow, and opioid-receptor binding potentials after the treatments compared to baseline. A meta-analysis of fMRI studies in patients with chronic pain, during pain-related tasks, showed a significant deactivation likelihood cluster in the left medial posterior thalamus. Further studies are warranted to understand brain reorganization in patients with chronic pain compared to the normal state, in terms of its relationship with symptom reduction and baseline conditions.

Contribution of the μ opioid receptor and enkephalin to the antinociceptive actions of endomorphin-1 analogs with unnatural amino acid modifications in the spinal cord

Endomorphin analogs containing unnatural amino acids have demonstrated potent analgesic effects in our previous studies. In the present study, the differences in antinociception and the mechanisms thereof for analogs 1-3 administered intracerebroventricularly and intrathecally were explored. All analogs at different routes of administration produced potent analgesia compared to the parent peptide endomorphin-1. Multiple antagonists and antibodies were used to explore the mechanisms of action of these analogs, and it was inferred that analogs 1-3 stimulated the μ opioid receptor to induce antinociception. Moreover, the antibody data suggested that analog 2 may induce the release of immunoreactive [Leu⁵]-enkephaline and [Met⁵]-enkephaline to produce a secondary component of antinociception at the spinal level and analog 3 may stimulate the the release of immunoreactive [Met⁵]-enkephaline at the spinal level. Finally, analogs 2 and 3 produced no acute tolerance in the spinal cord. We hypothesize that the unique characteristics of the endomorphin analogs result from their capacities to stimulate the release of endogenous antinociceptive substances.

Modifications in fMRI Representation of Mental Rotation Following a 6 Week Graded Motor Imagery Training in Chronic CRPS Patients

Complex regional pain syndrome (CRPS) is a neuropathic pain condition that is difficult to treat. For behavioral interventions, graded motor imagery (GMI) showed relevant effects, but underlying neural substrates in patient groups have not been investigated yet. A previous study investigating differences in the representation of a left/right hand judgment task demonstrated less recruitment of subcortical structures, such as the putamen, in CRPS patients than in healthy controls. In healthy volunteers, the putamen activity increased after a hand judgment task training. In order to test for longitudinal effects of GMI training, we investigated 20 CRPS patients in a wait-list crossover design with 3 evaluation time points. Patients underwent a 6 week GMI treatment and a 6 week waiting period in a randomized group assignment and treatment groups were evaluated by a blinded rater. When compared to healthy matched controls at baseline, CRPS patients showed less functional activation in areas processing visual input, left sensorimotor cortex, and right putamen. Only GMI treatment, but not the waiting period showed an effect on movement pain and hand judgment task performance. Regression analyses revealed positive associations of movement pain with left anterior insula activation at baseline. Right intraparietal sulcus activation change during GMI was associated with a gain in performance of the hand judgment task. The design used here is reliable for investigating the functional representation of the hand judgment task in an intervention study. PERSPECTIVE: Twenty chronic CRPS patients underwent a 6 week GMI intervention in a randomized wait-list crossover design. functional MRI was tested pre and post for the hand lateralization task which improved over GMI but not over WAITING. Performance gain was positively related to right parietal functional MRI activation.

New Developments in Non-invasive Brain Stimulation in Chronic Pain

Purpose of Review

The goal of this review is to present a summary of the recent literature of a non-invasive brain stimulation (NIBS) to alleviate pain in people with chronic pain syndromes. This article reviews the current evidence for the use of transcranial direct current (tDCS) and repetitive transcranial magnetic stimulation (rTMS) to improve outcomes in chronic pain. Finally, we introduce the reader to novel stimulation methods that may improve therapeutic outcomes in chronic pain.

Recent Findings

While tDCS is approved for treatment of fibromyalgia in Canada and the European Union, no NIBS method is currently approved for chronic pain in the United States. Increasing sample sizes in randomized clinical trials (RCTs) seems the most efficient way to increase confidence in initial promising results. Trends at funding agencies reveal increased interest and support for NIBS such as recent Requests for Application from the National Institutes of Health. NIBS in conjunction with cognitive behavioral therapy and physical therapy may enhance outcomes in chronic pain. Novel stimulation methods, such as transcranial ultrasound stimulation, await rigorous study in chronic pain.

Symptom reduction and improved function in chronic CRPS type 1 after 12-week integrated, interdisciplinary therapy

Background and aims Complex Regional Pain Syndrome (CRPS) often recovers spontaneously within the first year, but when it becomes chronic, available rehabilitative therapies (pharmacological management, physiotherapy, and psychological intervention) have limited effectiveness. This study examined the effect of a 12-week intensive outpatient rehabilitation on pain relief and function in chronic CRPS patients. Rehabilitation program included memantine and morphine treatment (added to patient's prior pain medication) and concurrent psychological and physiotherapeutic intervention. Primary outcome measure was a change in CRPS symptom count and secondary outcomes were motor performance, psychological factors, pain intensity, and quality of life. Methods Ten patients with chronic upper limb CRPS I (median 2.9 years, range 8 months to 12 years) were recruited to the study and were assessed before and after the intervention. Hand motor function of the patients was evaluated by an independent physiotherapist. There were standardized questionnaires for depression, pain anxiety, pain acceptance, quality of life, and CRPS symptom count. In addition, psychological factors were evaluated by a semi-structured interview. Severity of experienced pain was rated at movement and at rest. In addition, a video experiment of a hand action observation was conducted pre- and post-intervention to study possible change in neuronal maladaptation. Intervention consisted of pharmacological, psychological and physiotherapeutic treatment. First, 10 mg daily morphine was started and increased gradually to 30 mg daily, if tolerated. After 30 mg/day or tolerated dose of morphine was achieved, 5 mg daily memantine was started and increased gradually to 40 mg, if tolerated. Psychological intervention consisted of weekly group sessions, using cognitive and behavioral methods (relaxation, behavioral activation, and exposure) and acceptance and commitment therapy (ACT) and daily home practice. Physiotherapeutic intervention consisted of graded motor imagery and physiotherapy exercises with weekly group sessions and/or individual guidance by the physiotherapist, and individual exercise of the affected upper limb. Results Multimodal intensive intervention resulted in significant decrease in CRPS symptom count. The effect was strongest in motor and trophic symptoms (19% decrease after intervention) and in sensory symptoms (18% decrease). Additionally, improvement was seen in some, but not all, secondary outcomes (movement pain, motor symptoms, change in perceptions during video experiment of hand actions, and summary index with motor functioning, pain, and psychological factors). There were no dropouts. Conclusions Intensive 12-week multimodal intervention reduced some CRPS symptoms but was not sufficient to alter patients' rest pain, distress, or quality of life. Implications These results support the efficacy of an interdisciplinary rehabilitation program for pain and function in chronic CRPS patients. After intervention, some CRPS symptoms reduced and function improved, but distress and quality of life were unchanged. This may be due to the relatively short duration of this program; to delayed effects; to particular cognitive problems of CPRS patients; and/or to low distress levels at baseline that make statistically significant reduction less likely.

New analgesic: Focus on botulinum toxin

In 2010, Kissin concluded pessimistically that of the 59 new drugs introduced in the fifty-year period between 1960 and 2009 and still in use, only seven had new molecular targets. Of these, only one, sumatriptan, was effective enough to lead to the introduction of multiple drugs targeting the same target molecules (triptans) (Kissin, 2010). Morphine and acetylsalicylic acid (aspirin), introduced for the treatment of pain more than a century ago, continue to dominate biomedical publications despite their limited effectiveness in many areas (e.g., neuropathic pain) and serious adverse effects. Today, are we really closer to ideal analgesics that would work hard enough, long enough, and did not have unwanted side effects? The purpose of the present article is to analyze where we are now. Several drugs, like long-acting opioids or botulinum toxins open some hope. Advantage of botulinum toxin A is unique duration of action (months). New discoveries showed that after peripheral application botulinum toxin by axonal transport reaches the CNS. Major analgesic mechanism of action seems to be of central origin. Will botulinum toxin in the CNS bring new indications and or/adverse effects? Much more basic and clinical research should be in front of us. Although relatively safe as a drug, botulinum toxin is not without adverse effect. Policy makers, clinicians and all those applying botulinum toxin should be aware of that. Unfortunately the life without the pain is still not possible.

Pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndromes (CRPS) are rare painful conditions characterized by considerable variability in possible triggering factors, usually traumatic, and in the clinical scenario. The limited knowledge of the pathophysiological mechanisms has led to countless treatment attempts with multiple conservative and surgical options that act by different mechanisms of action.

AREAS COVERED

In this narrative review, the authors discuss key points about CRPS definitions, diagnostic criteria and pitfalls, pathophysiological hypotheses, and treatment strategies with particular reference to pharmacotherapy. The article was based on a literature search using PubMed while the available guidelines for the management of CRPS were also examined.

EXPERT OPINION

According to the quality of evidence, pharmacological interventions for CRPS seem to be more effective all the more so when they act on peripheral mechanisms, particularly on nociceptive pain, and when applied early in the disease, while reliable evidence about central mechanisms of chronic pain in CRPS is lacking. In our opinion, drug therapy should be preferred as early as possible, particularly in warm forms of CRPS to prevent significant functional limitation, psychological distress, and social and economic fallout.

A systematic review and meta-analysis of memantine for the prevention or treatment of chronic pain

BACKGROUND AND OBJECTIVE

N-methyl-D-aspartate (NMDA) receptors are involved in pain signalling and neuroplasticity. Memantine has been shown to have analgesic properties in pre-clinical and small clinical studies. We conducted a systematic review and meta-analysis to assess the efficacy of memantine to prevent or reduce chronic pain.

DATABASES AND DATA TREATMENT

MEDLINE, EMBASE and CENTRAL databases were searched for comparative trials using memantine, either against placebo or active medications, for chronic pain in adults. Pain relief was considered our primary outcome. Meta-analyses were conducted if outcomes were reported in two or more studies. Outcomes were reported as mean differences (MD) or risk ratios (RR) with 95% confidence intervals (CI). Quality was assessed using the GRADE approach.

RESULTS

Among 454 citations, 15 studies were included with populations predominantly consisting of neuropathic conditions and fibromyalgia. Overall, we observed unclear reporting of randomization and allocation methods, apart from potential for publication bias. Among the 11 studies looking at chronic pain treatment, the difference in end pain score with memantine was not significant: MD = -0.58 units (95% CI -1.31, 0.14); I²  = 82% (low quality). In two surgical studies using memantine for pain prevention, memantine decreased pain intensity: MD = -1.02 units (95% CI -1.38, -0.66); I²  = 0%. Dizziness was significantly more common with memantine: RR = 4.90 (95% CI 1.26, 18.99); I²  = 52% (moderate quality).

CONCLUSION

The current evidence regarding the use of memantine for chronic pain is limited and uncertain. Despite its potential, pain relief achieved in clinical studies is small and is associated with an increase in dizziness.

SIGNIFICANCE

Despite a sound rationale, the benefit of using memantine for chronic pain is unclear. Our systematic review and meta-analysis show that memantine may have the potential to decrease pain. However, it can also increase common adverse effects. Considering the small number of studies with potential for bias and inconclusive evidence, there was low to very low certainty. Hence, no clear recommendations can be made about its routine clinical use until larger and more definitive studies are conducted.

Differences in Neuronal Representation of Mental Rotation in Patients With Complex Regional Pain Syndrome and Healthy Controls

Spatial integration of parts of the body is impaired in patients with complex regional pain syndrome (CRPS). Because the training of mental rotation (MR) has been shown to be among the effective therapy strategies for CRPS, impairment of MR is also important for the pathophysiological understanding of CRPS. The aim of this study was to evaluate whether differences in the neural representation of MR occur between patients with CRPS and healthy controls (HC). Therefore, we included 15 patients with chronic CRPS and 15 age- and gender-matched HC. We assessed behavioral (accuracy and reaction time for MR of both hands), clinical (Disabilities of Arm, Shoulder and Hand questionnaire) and magnetic resonance imaging (T1-weighted, function magnetic resonance imaging during MR) data. Reaction times in the patient group were delayed compared with HC without a lateralization effect for the affected hand side. Although both groups showed an activation pattern typical for MR, only HC showed a highly significant contrast for the rotated versus unrotated hands in the right intraparietal sulcus. Patients with CRPS showed a reduction of functional magnetic resonance imaging activation in areas including the subthalamic nucleus, nucleus accumbens, and putamen. Regression analysis for the CRPS group emphasized the importance of putamen and nucleus accumbens activation for MR performance. This study highlights the reduced access of patients with CRPS for mental resources modulating arousal, emotional response, and subcortical sensorimotor integration. PERSPECTIVE: This study localized the underlying neural responses for impaired mental rotation in patients with complex regional pain syndrome as a decrease in basal ganglia (putamen) and nucleus accumbens activation.

Altered tactile localization and spatiotemporal integration in complex regional pain syndrome patients

BACKGROUND

In complex regional pain syndrome (CRPS), altered perception of the affected hand and neglect-like symptoms of the affected body side are common features. In this study, we presented tactile stimuli to the affected hands in CRPS patients and matched healthy controls.

METHODS

The participants' task was to point at the perceived positions of the stimuli using a tracking device. The spatial coordinates of the perceived positions were analysed for accuracy and consistency. We also presented patterns consisting of two stimuli at distinct positions with a delay of 100 ms. These patterns are known to induce spatiotemporal integration ("sensory saltation").

RESULTS

CRPS patients were less accurate and less consistent in the spatial perception of tactile stimuli on their hands. Furthermore, they showed increased spatiotemporal integration, although these effects were smaller than expected. These deficiencies were related to the clinically assessed intensity of recurrent pain episodes. Surprisingly, the intensity of clinically assessed ongoing pain was associated with increased precision.

CONCLUSIONS

In line with earlier reports, our findings indicate that the representation of the affected hands in CRPS patients is less accurate than in healthy people, probably reflecting reorganization in somatosensory cortices. The exact relationships between these findings and other aspects of CRPS remain to be elucidated.

SIGNIFICANCE

CRPS patients performed poorly in localizing positions on their affected hands via pointing and exhibited increased spatiotemporal integration. The presented method may prove useful in diagnostics as well as psychophysical and neurofunctional research on CRPS and other chronic pain disorders.

Altered cerebral blood flow in the anterior cingulate cortex is associated with neuropathic pain

OBJECTIVE

To assess the cerebral blood flow (CBF) in patients with diabetic neuropathic pain, and its changes after duloxetine therapy.

METHODS

Using iodine-123-N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (IMP-SPECT), we performed a cross-sectional study of 44 patients with diabetes, and compared CBF in those with (n = 24) and without neuropathic pain (n = 20). In patients with neuropathic pain, we also longitudinally assessed changes in CBF 3 months after treatment with duloxetine.

RESULTS

IMP-SPECT with voxel-based analyses showed a significant increase in cerebral blood flow in the right anterior cingulate cortex and a decrease in the left ventral striatum in patients with neuropathic pain, compared with those without pain. After duloxetine treatment, volume of interest analyses revealed a decrease in cerebral blood flow in the anterior cingulate cortex in patients with significant pain relief but not in non-responders. Furthermore, voxel-based whole brain correlation analyses demonstrated that greater baseline CBF in the anterior cingulate cortex was associated with better pain relief on the numerical rating scale.

CONCLUSIONS

Our results suggest that the development of neuropathic pain is associated with increased activity in the anterior cingulate cortex, and greater baseline activation of this region may predict treatment responsiveness to pharmacological intervention.

TRIAL REGISTRATION NUMBER

UMIN000017130;Results.

Treatment of complex regional pain syndrome: an updated systematic review and narrative synthesis

PURPOSE

Although multiple treatments have been advocated for complex regional pain syndrome (CRPS), the levels of supportive evidence are variable and sometimes limited. The purpose of this updated review is to provide a critical analysis of the evidence pertaining to the treatment of CRPS derived from recent randomized-controlled trials (RCTs).

SOURCE

The MEDLINE, EMBASE, Psychinfo, and CINAHL databases were searched to identify relevant RCTs conducted on human subjects and published in English between 1 May 2009 and 24 August 2017.

PRINCIPAL FINDINGS

The search yielded 35 RCTs of variable quality pertaining to the treatment of CRPS. Published trials continue to support the use of bisphosphonates and short courses of oral steroids in the setting of CRPS. Although emerging evidence suggests a therapeutic role for ketamine, memantine, intravenous immunoglobulin, epidural clonidine, intrathecal clonidine/baclofen/adenosine, aerobic exercise, mirror therapy, virtual body swapping, and dorsal root ganglion stimulation, further confirmatory RCTs are warranted. Similarly, trials also suggest an expanding role for peripheral sympathetic blockade (i.e., lumbar/thoracic sympathetic, stellate ganglion, and brachial plexus blocks).

CONCLUSIONS

Since our prior systematic review article (published in 2010), 35 RCTs related to CRPS have been reported. Nevertheless, the quality of trials remains variable. Therefore, further research is required to continue investigating possible treatments for CRPS.

Complex regional pain syndrome-up-to-date

Complex regional pain syndrome (CRPS) was described for the first time in the 19th century by Silas Weir Mitchell. After the exclusion of other causes, CRPS is characterised by a typical clinical constellation of pain, sensory, autonomic, motor, or trophic symptoms which can no longer be explained by the initial trauma. These symptoms spread distally and are not limited to innervation territories. If CRPS is not improved in the acute phase and becomes chronic, the visible symptoms change throughout because of the changing pathophysiology; the pain, however, remains. The diagnosis is primarily clinical, although in complex cases further technical examination mainly for exclusion of alternative diagnoses is warranted. In the initial phase, the pathophysiology is dominated by a posttraumatic inflammatory reaction by the activation of the innate and adaptive immune system. In particular, without adequate treatment, central nociceptive sensitization, reorganisation, and implicit learning processes develop, whereas the inflammation moderates. The main symptoms then include movement disorders, alternating skin temperature, sensory loss, hyperalgesia, and body perception disturbances. Psychological factors such as posttraumatic stress or pain-related fear may impact the course and the treatability of CRPS. The treatment should be ideally adjusted to the pathophysiology. Pharmacological treatment maybe particularly effective in acute stages and includes steroids, bisphosphonates, and dimethylsulfoxide cream. Common anti-neuropathic pain drugs can be recommended empirically. Intravenous long-term ketamine administration has shown efficacy in randomised controlled trials, but its repeated application is demanding and has side effects. Important components of the treatment include physio- and occupational therapy including behavioural therapy (eg, graded exposure in vivo and graded motor imaging). If psychosocial comorbidities exist, patients should be appropriately treated and supported. Invasive methods should only be used in specialised centres and in carefully evaluated cases. Considering these fundamentals, CRPS often remains a chronic pain disorder but the devastating cases should become rare.

Alternatives to Opioids in the Pharmacologic Management of Chronic Pain Syndromes: A Narrative Review of Randomized, Controlled, and Blinded Clinical Trials

Chronic pain exerts a tremendous burden on individuals and societies. If one views chronic pain as a single disease entity, then it is the most common and costly medical condition. At present, medical professionals who treat patients in chronic pain are recommended to provide comprehensive and multidisciplinary treatments, which may include pharmacotherapy. Many providers use nonopioid medications to treat chronic pain; however, for some patients, opioid analgesics are the exclusive treatment of chronic pain. However, there is currently an epidemic of opioid use in the United States, and recent guidelines from the Centers for Disease Control (CDC) have recommended that the use of opioids for nonmalignant chronic pain be used only in certain circumstances. The goal of this review was to report the current body of evidence-based medicine gained from prospective, randomized-controlled, blinded studies on the use of nonopioid analgesics for the most common noncancer chronic pain conditions. A total of 9566 studies were obtained during literature searches, and 271 of these met inclusion for this review. Overall, while many nonopioid analgesics have been found to be effective in reducing pain for many chronic pain conditions, it is evident that the number of high-quality studies is lacking, and the effect sizes noted in many studies are not considered to be clinically significant despite statistical significance. More research is needed to determine effective and mechanism-based treatments for the chronic pain syndromes discussed in this review. Utilization of rigorous and homogeneous research methodology would likely allow for better consistency and reproducibility, which is of utmost importance in guiding evidence-based care.

A critical evaluation of validity and utility of translational imaging in pain and analgesia: Utilizing functional imaging to enhance the process

Assessing clinical pain and metrics related to function or quality of life predominantly relies on patient reported subjective measures. These outcome measures are generally not applicable to the preclinical setting where early signs pointing to analgesic value of a therapy are sought, thus introducing difficulties in animal to human translation in pain research. Evaluating brain function in patients and respective animal model(s) has the potential to characterize mechanisms associated with pain or pain-related phenotypes and thereby provide a means of laboratory to clinic translation. This review summarizes the progress made towards understanding of brain function in clinical and preclinical pain states elucidated using an imaging approach as well as the current level of validity of translational pain imaging. We hypothesize that neuroimaging can describe the central representation of pain or pain phenotypes and yields a basis for the development and selection of clinically relevant animal assays. This approach may increase the probability of finding meaningful new analgesics that can help satisfy the significant unmet medical needs of patients.

A Comparative Study on the Efficacy of Oral Memantine and Placebo for Acute Postoperative Pain in Patients Undergoing Dacryocystorhinostomy (DCR)

Background

Memantine is an N-methyl-D-Aspartate (NMDA) antagonist. By transferring acute postoperative pain, the NMDA channels may lead to active excess and neuropathic pain. Objectives: This study attempted to investigate the effect of preoperative use of single oral dose of memantine in controlling Dacryocystorhinostomy (DCR) postoperative pain.

Methods

A double-blind clinical trial was conducted on 60 patients undergoing DCR. On arrival at the operating room, the memantine group received 20 mg of oral memantine and the control group received placebo. The severities of pain by visual analogue scale (VAS) and sedation by Ramsy Scale were measured immediately 1, 2, and 6 hours after the operation. The drug’s side effects were recorded.

Results

The pain scores of patients in the recovery in 1, 2, and 6 hours after operation were significantly lower in the memantine group than the placebo group (P < 0.001). The sedation score, 1 hour after the operation, was significantly greater in the memantine group than the placebo (P < 0.001). The sedation scores did not have any statistically significant difference in recovery and 2 hours after surgery between the two groups. Moreover, the sedation scores in 6 hours after the surgery were identical in the two groups.

Conclusions

The oral single-dose 20 mg of memantine administered before DCR can reduce postoperative pain compared with placebo.

Pain reduction due to novel sensory-motor training in Complex Regional Pain Syndrome I – A pilot study

Background and aims

Patients suffering from Complex Regional Pain Syndrome (CRPS) of the upper limb show a changed cortical representation of the affected hand. The lip area invades the former hand area contralateral to the affected hand. This change in cortical representation is correlated to the intensity of ongoing pain in patients with CRPS. Further studies revealed that restoration of the original representation coincides with a decrease of pain. Sensory-motor training protocols can increase and/or relocate cortical somatosensory and motor representation areas of the fingers, as shown, for example, in Braille reading individuals and professional violin players. Further, there is evidence that sensory-motor discrimination training has a beneficial effect on both the intensity of pain and the mislocalization of sensory-motor cortical areas in CRPS patients. Based on these propositions, we developed a novel sensory-motor self-training paradigm for CRPS patients to use in a home-based manner.

Methods

Ten CRPS patients performed the sensory-motor training for 2 weeks. The training consists of a braille-like haptic task with different training modes (bi-manual, speed and memory training). During the training, as well as 1 week before and after, patients were asked to fill out pain diaries. Furthermore, measures of impairment were acquired at baseline and post training.

Results

Patients showed significant pain reduction after the 2 week training period. The overall disability as well as the depression scores showed a trend to improve after the 2 week training. The reduction in pain was correlated with the total amount of training performed.

Conclusions

This is a first proof of principle study of a novel sensory-motor self-training protocol to reduce pain in CRPS patients. The more consistent the patients trained the larger the pain reduction. Sensory-motor training, which can be performed on a regular basis at home might provide a novel interventional strategy to improve symptoms of CRPS.

Implications

Although a larger study needs to be conducted to confirm our findings, including long-term follow-up, the results show, that a sensory-motor home-based training is a strategy worth exploring further for the reduction of pain as well as high frequency training for patients with CRPS.

The clinical relevance of complex regional pain syndrome type I: The Emperor's New Clothes

The management of patients with chronic pain is a nearly daily challenge to rheumatologists, neurologists, orthopedic surgeons, pain specialists and indeed a issue in nearly every clinical practice. Among the myriad of causes of pain are often included a unique syndrome, generally referred to as complex regional pain syndrome type I (CRPS). Unfortunately CRPS I has become a catch all phase and there are serious questions on whether it exists at all; this has led to an extraordinary number of poorly defined diagnostic criteria. It has also led to an etiologic quagmire that includes features as diverse as autoimmunity to simple trauma. These, in turn, have led to overdiagnosis and often overzealous use of pain medications, including narcotics. In a previous paper, we raised the issue of whether CRPS type I reflected a valid diagnosis. Indeed, the diagnostic criteria for CRPS I, and therefore the diagnosis itself, is unreliable for a number of reasons: 1) the underlying pathophysiology of the signs and symptoms of CPRS I are not biologically plausible; 2) there are no consistent laboratory or imaging testing available; 3) the signs and symptoms fluctuate over time without a medical explanation; 4) the definitions of most studies are derived from statistical analysis with little consideration to required sample size, i.e. power calculations; 5) interobserver reliability in the assessment of the signs and symptoms are often only fair to moderate, and agreement on the diagnosis of "CRPS I" is poor. Even physicians who still believe in the concept of "CRPS I" admit that it is vastly overdiagnosed and has become a diagnosis of last resort, often without a complete differential diagnosis and an alternative explanation. Finally, one of the most convincing arguments that there is no clinical entity as "CRPS I" comes from the enormous heterogeneity in sign and symptom profiles and the heterogeneity of pathophysiological mechanisms postulated. This observation is underscored by the diversity of responses among "CRPS I" patients to essentially all treatment modalities. It has even led to the concept that the signs and symptoms of CRPS can spread throughout the body, as if it is an infectious disease, without any medical plausible explanation. If true progress is to be made in helping patients with pain, it will require entirely new and different concepts and abandoning CRPS I as a legitimate diagnosis.

Hsa-miR-34a mediated repression of corticotrophin releasing hormone receptor 1 regulates pro-opiomelanocortin expression in patients with complex regional pain syndrome

Background

Ketamine provides relief for a subset of patients with complex regional pain syndrome (CRPS). The poor responders had a lower body mass index (BMI) relative to responders. Regulation of proopiomelanocortin (POMC) expression is crucial in normal body weight homeostasis. The main objectives of this study were to investigate the mechanisms underlying lower BMI characterizing CRPS patients responding poorly to intravenous ketamine therapy and identify potential biomarkers for predicting response.

Methods

We investigated POMC transcript levels in blood from CRPS patients grouped as responders and poor responders to ketamine therapy. Plasma levels of β-endorphin, ACTH and α-MSH were measured by ELISA. We previously identified differential expression of small noncoding microRNA hsa-miR-34a in blood between responders and poor responders. We investigated whether a 11-fold downregulation of hsa-miR-34a in poor responders relative to responders is contributing to the differences in POMC levels by targeting POMC regulator CRHR1. Binding of miR-34a to CRHR1 was assessed using reporter assay; changes in mRNA and protein levels of CRHR1 were used to determine the regulation of CRHR1 by miR-34a. RNA from blood of CRPS and control subjects were used for quantitative PCR for CRHR1.

Results

Though ketamine treatment did not alter POMC expression, poor responders had higher levels of POMC mRNA than responders, both before and after treatment. Corticotropin-releasing hormone (CRH) is a key regulator of POMC expression and the biological effects are mediated through its receptor corticotrophin releasing hormone receptor 1 (CRHR1). We show that hsa-miR-34a is a negative regulator of CRHR1; overexpression of hsa-miR-34a in Jurkat cells resulted in reduction of CRH-mediated POMC expression. Poor responders had higher expression of CRHR1 transcripts than responders, indicating a regulatory role for miR-34a. In addition, we found positive correlations between the pretreatment levels of miR-34a to BMI and response to ketamine therapy.

Conclusions

Our findings indicate a mechanism by which hsa-miR-34a can regulate the CRH/CRHR1/POMC axis and may influence BMI. Studies in larger patient cohorts are required to confirm the biomarker utility of circulating hsa-miR-34a levels in predicting treatment response to ketamine therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0820-1) contains supplementary material, which is available to authorized users.

[Maladaptive plasticity in chronic and neuropathic pain]

Chronic pain results in structural and functional changes of the brain. However, most of the neurophysiologic and imaging studies have been conducted with small sample sizes, some have been reproduced, but studies on larger populations are lacking. Larger epidemiologic studies are currently being performed to show specific structural changes due to chronic pain. Longitudinal studies using neurophysiologic or imaging methods are very rare and often not feasible. Most methods are very complex, which hampers their application in daily practice. But it is not only the complexity of methods, but also a lack of interaction between researchers and practitioners to formulate joint research topics and targets. This article tries to fill the gap between the practicing pain therapist and the researcher in summarizing neurophysiological and imaging results on neuropathic and chronic pain in a clear and simple manner.

The complex regional pain syndrome

Complex regional pain syndrome (CRPS) is the current consensus-derived name for a syndrome usually triggered by limb trauma. Required elements include prolonged, disproportionate distal-limb pain and microvascular dysregulation (e.g., edema or color changes) or altered sweating. CRPS-II (formerly "causalgia") describes patients with identified nerve injuries. CRPS-I (formerly "reflex sympathetic dystrophy") describes most patients who lack evidence of specific nerve injuries. Diagnosis is clinical and the pathophysiology involves combinations of small-fiber axonopathy, microvasculopathy, inflammation, and brain plasticity/sensitization. Females have much higher risk and workplace accidents are a well-recognized cause. Inflammation and dysimmunity, perhaps facilitated by injury to the blood-nerve barrier, may contribute. Most patients, particularly the young, recover gradually, but treatment can speed healing. Evidence of efficacy is strongest for rehabilitation therapies (e.g., graded-motor imagery), neuropathic pain medications, and electric stimulation of the spinal cord, injured nerve, or motor cortex. Investigational treatments include ketamine, botulinum toxin, immunoglobulins, and transcranial neuromodulation. Nonrecovering patients should be re-evaluated for neurosurgically treatable causal lesions (nerve entrapment, impingement, infections, or tumors) and treatable potentiating medical conditions, including polyneuropathy and circulatory insufficiency. Earlier impressions that CRPS represents malingering or psychosomatic illness have been replaced by evidence that CRPS is a rare complication of limb injury in biologically susceptible individuals.

Reporting of sample size calculations in analgesic clinical trials: ACTTION systematic review

Sample size calculations determine the number of participants required to have sufficiently high power to detect a given treatment effect. In this review, we examined the reporting quality of sample size calculations in 172 publications of double-blind randomized controlled trials of noninvasive pharmacologic or interventional (ie, invasive) pain treatments published in European Journal of Pain, Journal of Pain, and Pain from January 2006 through June 2013. Sixty-five percent of publications reported a sample size calculation but only 38% provided all elements required to replicate the calculated sample size. In publications reporting at least 1 element, 54% provided a justification for the treatment effect used to calculate sample size, and 24% of studies with continuous outcome variables justified the variability estimate. Publications of clinical pain condition trials reported a sample size calculation more frequently than experimental pain model trials (77% vs 33%, P < .001) but did not differ in the frequency of reporting all required elements. No significant differences in reporting of any or all elements were detected between publications of trials with industry and nonindustry sponsorship. Twenty-eight percent included a discrepancy between the reported number of planned and randomized participants. This study suggests that sample size calculation reporting in analgesic trial publications is usually incomplete. Investigators should provide detailed accounts of sample size calculations in publications of clinical trials of pain treatments, which is necessary for reporting transparency and communication of pre-trial design decisions.

PERSPECTIVE

In this systematic review of analgesic clinical trials, sample size calculations and the required elements (eg, treatment effect to be detected; power level) were incompletely reported. A lack of transparency regarding sample size calculations may raise questions about the appropriateness of the calculated sample size.

Primary somatosensory cortex function in complex regional pain syndrome: a systematic review and meta-analysis

That complex regional pain syndrome (CRPS) is associated with functional reorganization in the primary somatosensory cortex (S1) is widely accepted and seldom questioned. Despite more than a decade of research, there has been no systematic review of the CRPS literature concerning the changes in S1 function, and therefore the extent of these changes is unclear. Here we conduct a systematic review and meta-analysis to quantify the spatial and temporal aspects of S1 function in CRPS. A comprehensive search strategy identified functional neuroimaging studies of S1 in CRPS. We adhered to a rigorous systematic review protocol when extracting data and appraising risk of bias. Outcomes were grouped into spatial representation; activation levels, including disinhibition; peak latency of activation; and glucose metabolism. Meta-analysis was conducted where possible. Fifteen studies were included, all investigating upper-extremity CRPS. In patients with CRPS, the S1 spatial representation of the affected hand is smaller than that of the unaffected hand and that of non-CRPS controls; however, this evidence comes from only a few studies. There is no difference in activation, disinhibition, or latency of peripherally evoked S1 responses in CRPS. The risk of bias was high across studies, mainly from unclear sampling methods and unblinded analysis of outcomes.

PERSPECTIVE

The evidence for a difference in function of the primary somatosensory cortex in CRPS compared with controls is clouded by high risk of bias and conflicting results, but reduced representation size seems consistent.

Interventions for treating pain and disability in adults with complex regional pain syndrome

BACKGROUND

There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome (CRPS).

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of the following databases: Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE, Ovid EMBASE, CINAHL, LILACS and PEDro. We included non-Cochrane systematic reviews where they contained evidence not covered by identified Cochrane reviews. The methodological quality of reviews was assessed using the AMSTAR tool.We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes of quality of life, emotional well being and participants' ratings of satisfaction or improvement. Only evidence arising from randomised controlled trials was considered. We used the GRADE system to assess the quality of evidence.

MAIN RESULTS

We included six Cochrane reviews and 13 non-Cochrane systematic reviews. Cochrane reviews demonstrated better methodological quality than non-Cochrane reviews. Trials were typically small and the quality variable.There is moderate quality evidence that intravenous regional blockade with guanethidine is not effective in CRPS and that the procedure appears to be associated with the risk of significant adverse events.There is low quality evidence that bisphosphonates, calcitonin or a daily course of intravenous ketamine may be effective for pain when compared with placebo; graded motor imagery may be effective for pain and function when compared with usual care; and that mirror therapy may be effective for pain in post-stroke CRPS compared with a 'covered mirror' control. This evidence should be interpreted with caution. There is low quality evidence that local anaesthetic sympathetic blockade is not effective. Low quality evidence suggests that physiotherapy or occupational therapy are associated with small positive effects that are unlikely to be clinically important at one year follow up when compared with a social work passive attention control.For a wide range of other interventions, there is either no evidence or very low quality evidence available from which no conclusions should be drawn.

AUTHORS' CONCLUSIONS

There is a critical lack of high quality evidence for the effectiveness of most therapies for CRPS. Until further larger trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult.