Pathophysiology of complex regional pain syndrome

Mechanisms of complex regional pain syndrome

Complex Regional Pain Syndrome (CRPS) is a chronic pain disorder characterized by a diverse array of symptoms, including pain that is disproportionate to the initial triggering event, accompanied by autonomic, sensory, motor, and sudomotor disturbances. The primary pathology of both types of CRPS (Type I, also known as reflex sympathetic dystrophy, RSD; Type II, also known as causalgia) is featured by allodynia, edema, changes in skin color and temperature, and dystrophy, predominantly affecting extremities. Recent studies started to unravel the complex pathogenic mechanisms of CRPS, particularly from an autoimmune and neuroimmune interaction perspective. CRPS is now recognized as a systemic disease that stems from a complex interplay of inflammatory, immunologic, neurogenic, genetic, and psychologic factors. The relative contributions of these factors may vary among patients and even within a single patient over time. Key mechanisms underlying clinical manifestations include peripheral and central sensitization, sympathetic dysregulation, and alterations in somatosensory processing. Enhanced understanding of the mechanisms of CRPS is crucial for the development of effective therapeutic interventions. While our mechanistic understanding of CRPS remains incomplete, this article updates recent research advancements and sheds light on the etiology, pathogenesis, and molecular underpinnings of CRPS.

Complex regional pain syndrome: diagnostic challenges and favorable response to prednisolone

Complex regional pain syndrome (CRPS), characterized by severe and disproportionate pain, is a rare and debilitating condition. Due to its rarity, evidence-based treatment guidelines remain limited, creating a challenge for clinicians. We present the case of a 20-year-old female with CRPS type 1 of the right hand. Her pain, initially triggered by a minor trauma, had persisted for three months. The patient demonstrated severe pain, swelling, hyperesthesia, and restricted range of motion. Despite multiple hospital visits, her symptoms did not improve until she was diagnosed with CRPS and treated with oral prednisolone. A dosage of 40 mg daily led to a dramatic response within 10 days. Our report emphasizes the importance of recognizing CRPS and highlights the potential of prednisolone as a treatment option, particularly in resource-limited settings, where more specialized interventions may be unavailable. Further research is essential to establish a stronger evidence base for the use of steroids in CRPS management.

Clinical results of lumbar sympathetic blocks in lower limb complex regional pain syndrome using infrared thermography as a support tool

AIM

To describe the clinical outcomes for a group of complex regional pain syndrome patients using infrared thermography as an intraprocedural support tool when undertaking fluoroscopy-guided lumbar sympathetic blocks.

SUBJECTS

27 patients with lower limb complex regional pain syndrome accompanied by severe pain and persistent functional impairment.

METHODS

A series of three fluoroscopic-guided lumbar sympathetic blocks with local anesthetic and corticoids using infrared thermography as an intraprocedural support tool were performed. Clinical variables were collected at baseline, prior to each block, and one, three, and six months after blocks in a standardized checklist assessing each of the clinical categories of complex regional pain syndrome stipulated in the Budapest criteria.

RESULTS

23.75% of the blocks required more than one chance to achieve the desired thermal pattern and therefore to be considered as successful. A decrease in pain measured on a visual analogic scale was observed at all time points compared to pre-blockade data, but only 37% of the cases were categorized as responders, representing a ≥ 30% decrease in VAS, with the disappearance of pain at rest. An improvement of most of the clinical variables recorded was observed, such as tingling, edema, perception of thermal asymmetry, difference in coloring and sweating. There was a significant decrease of neuropathic pain and improvement of functional limitation. Logistic regression analysis showed the main variable to explain the probability of being a responder was immobilization time (odds ratio of 0.89).

CONCLUSION

A series of fluoroscopy-guided lumbar sympathetic blocks controlled by infrared thermography in the treatment of lower limb CRPS showed a responder rate of 37%.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Prescription Trends in Complex Regional Pain Syndrome: A Retrospective Case-Control Study

OBJECTIVE

The objective of this study was to evaluate discrepancies in prescription trends for analgesic medications in complex regional pain syndrome (CRPS) patients based on recommendations in the literature.

DESIGN

We conducted a retrospective case-control study.

SUBJECTS

A total of 2510 CRPS patients and 2510 demographic-matched controls participated in this study.

METHODS

The SlicerDicer feature in Epic was used to find patients diagnosed with CRPS I or II between January 2010 and November 2022. An equal number of age-, gender-, and race-matched controls without a CRPS diagnosis were retracted from Epic. General and CRPS-associated prescription frequencies for the following classes were retrieved for both cases and controls: benzodiazepines, bisphosphonates, calcitonin, capsaicin, neuropathic pain medications, NSAIDs, opioids, and steroids.

RESULTS

A total of 740 (29%) CRPS patients and 425 (17%) controls were prescribed benzodiazepines (95% CI 0.1-0.15), 154 (6.1%) CRPS patients and 52 (2.1%) controls were prescribed capsaicin (95% CI 0.03-0.05), 1837 (73%) CRPS patients and 927 (37%) controls were prescribed neuropathic pain medications (95% CI 0.05-0.34), 1769 (70%) CRPS patients and 1217 (48%) controls were prescribed opioids (95% CI 0.19-0.25), 1095 (44%) CRPS patients and 1217 (48%) controls were prescribed steroids (95% CI 0.08-0.14), and 1638 (65%) CRPS patients and 1765 (70%) controls were prescribed NSAIDs (95% CI -0.08-0.02), p < 0.001 for all classes. With CRPS-associated prescriptions, (95% CI 0.05-0.16, p < 0.001) more CRPS patients were prescribed opioids (N = 398, 59%) than controls (N = 327, 49%).

CONCLUSIONS

CRPS is difficult to treat with significant variance in suggested treatment modalities. Based on the results of our study, there is a divergence between some published recommendations and actual practice.

Managing Chronic Regional Pain Syndrome: The Potential Impact of the Food and Drug Omnibus Reform Act

Complex regional pain syndrome (CRPS) is a neurological disorder characterized by persistent limb symptoms. With there being no definitive tests, diagnosis can be challenging. The Budapest criteria are the standard for diagnosis. The underlying mechanisms of CRPS involve changes in skin innervation, sensitization of the nervous system, inflammatory cytokines, and genetic and psychological factors. Treatment typically involves a multidisciplinary approach. We present a case of a 71-year-old male with CRPS involving the right upper extremity and a complex history of management including physical therapy, oxycodone, muscle relaxers, non-steroidal anti-inflammatory drugs, and multiple stellate ganglion blocks. The patient manages his pain with off-label medications, including methadone, duloxetine, and pregabalin. In the United States, the management of chronic pain may be affected by potential usage restrictions imposed by the Food and Drug Omnibus Reform Act (FDORA). Under this new act, physicians may face limitations in prescribing off-label medications for specific diagnoses. We aim to highlight the need for prioritizing patient care and individualized treatment in healthcare policy decision-making.

Pain mechanisms in complex regional pain syndrome: a systematic review and meta-analysis of quantitative sensory testing outcomes

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic condition following inciting events such as fractures or surgeries with sensorimotor and autonomic manifestations and poor prognosis. This review aimed to provide conclusive evidence about the sensory phenotype of CRPS based on quantitative sensory testing (QST) to understand the underlying pain mechanisms and guide treatment strategies.

DATABASES

Eight databases were searched based on a previously published protocol. Forty studies comparing QST outcomes (thermal, mechanical, vibration, and electric detection thresholds, thermal, mechanical, pressure, and electric pain thresholds, wind-up ratio, mechanical pain sensitivity, allodynia, flare area, area after pinprick hyperalgesia, pleasantness after C-tactile stimulation, and pain ratings) in chronic CRPS (adults and children) versus healthy controls were included.

RESULTS

From 37 studies (14 of low quality, 22 of fair quality, and 1 of good quality), adults with CRPS showed: (i) significant loss of thermal, mechanical, and vibration sensations, significant gain of thermal and mechanical pain thresholds, significant elevation of pain ratings, and no difference in wind-up ratio; (ii) significant reduction of pleasantness levels and increased area of pinprick hyperalgesia, in the affected limb. From three fair-quality studies, adolescents and children with CRPS showed loss of cold detection with cold hyperalgesia in the affected limb. There was moderate to substantial overall heterogeneity.

CONCLUSION

Diffuse thermal and mechanical hypoesthesia with primary and secondary hyperalgesia, enhanced pain facilitation evidenced by increased area of pinprick hyperalgesia, and elevated pain ratings are dominant in adults with CRPS. Adolescents and children with CRPS showed less severe sensory abnormalities.

Possible complex regional pain syndrome following SARS-CoV-2 infection: Case report

SARS-CoV-2 infection has various manifestations including neurological and musculoskeletal system involvement. COVID-19 infection causes peripheral nerve lesions including small fibre neuropathy. Complex regional pain syndrome is a debilitating neurological condition manifested by predominantly pain associated with other sensory, motor, autonomic and tropic involvement. Identification and early treatment of CRPS has better prognosis. Here, we report a 21-year-old woman presented with pain, hyperalgesia, and swelling of left upper and lower limb following SARS-CoV-2 infection managed as possible complex regional pain syndrome.

Improved symptoms of complex regional pain syndrome after novel lymphatic treatment and interdisciplinary pain management

INTRODUCTION

Complex regional pain syndrome (CRPS) is a pain syndrome with no singular mechanism and no specific cure. The aim of this case report is to study the impact of Lymphatic Enhancement Technology (LET) treatment on CRPS-related symptoms.

METHODS

A 51 year-old female presented with a chief complaint of severe, refractory ankle pain and CRPS related to a tibial and fibular fracture sustained three years earlier. The patient completed twelve cognitive behavioral therapy sessions over a 4-week period, and eleven physical therapy sessions over a four-month period, six of which utilized LET.

RESULTS

Pain and swelling were largely unchanged with interdisciplinary treatment before the introduction of LET. A within-session change of 37.5% in pain intensity and 87.5% in ankle girth was observed immediately after the first application of LET. Three months after beginning LET treatment, the patient maintained a 43.8% improvement in pain intensity and 100% improvement in measurements of lower extremity girth and ankle range of motion. No side effects or adverse events were associated with the LET treatment.

CONCLUSION

Swelling, pain, and mobility loss are common symptoms and features of CRPS. LET is a novel, non-invasive treatment that appears to be quite safe and effective for improving pain, swelling, and mobility loss related to CRPS.

Direct Sciatic Nerve Electrical Stimulation for Complex Regional Pain Syndrome Type 1

OBJECTIVE

Foot and leg pain in complex regional pain syndrome (CRPS) presents a challenge even with neuromodulation techniques such as spinal cord stimulation (SCS). We report our experience with a novo technique of direct sciatic nerve electrical stimulation (DISNES) for intractable foot and leg pain in CRPS I.

MATERIALS AND METHODS

Following Research Ethics Board (REB) approval, data were gathered for 16 patients (10 women and 6 men, age 26-61 years) who had been subjected to ipsilateral DISNES. All 16 patients had failed conventional medical management. As well, seven subjects were previously treated with SCS for CRPS I pain. These subjects reported pain relief in the thigh and leg, however the SCS was unable to alleviate the disabling foot pain despite varied and multiple programming techniques. The remaining nine subjects were treated primarily with DISNES. Evaluation was done using visual analog scale (VAS), Oswestry Disability Index version 2 (ODI), and quality of life (EQ-5D and SF-36) scores done both pre-DISNES and at two follow-ups.

RESULTS

VAS scores decreased by 59% at follow-up (F/U) 1 (P = 0.00001) and 46% F/U 2. ODI improving by 40% F/U 1 (P = 0.0038) and 37% F/U 2. SF-36 scores improved by 69% F/U 1 (P = 0.015) and 80% F/U 2. EQ-5D scores improved significantly by F/U 1 (P = 0.00030) but insignificantly at F/U 2 (P = 0.81). There was also a rapid resolution of autonomic features such as edema, hyperemia, and allodynia (within 7-10 days). Three subjects returned to work post-DISNES.

CONCLUSION

Our study shows that DISNES helps to control the disabling foot pain in CRPS I, thus improving the quality of life, improving ambulation and decreasing disability. DISNES also alleviates autonomic features and dystonia in CRPS I. Further studies are needed to determine long-term efficacy as this study pool is limited in size and follow-up period.

The use of bisphosphonates to meet orthopaedic challenges

The anti-resorptive properties of bisphosphonates have been explored to manage several conditions that traditionally have required a surgical solution. In osteonecrosis, their use is predicated on the principle that bone collapse occurs during the revascularisation phase of the disease. If the associated resorptive activity were modulated, the resultant preserved joint architecture may improve clinical outcome and reduce the need for joint replacement. Pre-clinical and small-scale clinical studies have given non-conclusive support for this principle. Adequately powered clinical trials with relevant long-term endpoints are still required to firmly clarify the clinical efficacy of this treatment. Several clinical studies have shown that bisphosphonates can reduce periprosthetic bone loss and, in some situations, enhance implant fixation in the early period after joint replacement. This may be advantageous in settings where osseointegration is problematic. However, the ultimate goals of their use in joint replacement has been to reduce the incidence of late periprosthetic inflammatory osteolysis, the main cause of prosthesis failure. Population-based observational studies have associated bisphosphonate use with a lower incidence of revision surgery, supported by pre-clinical data. However, clinical trials have, to date, failed to demonstrate any efficacy for the human disease. The timing of bisphosphonate administration for secondary prevention after acute osteoporotic fracture has been subject to extensive investigation, with pre-clinical studies showing increased callus formation but decreased remodelling and no effect on the restoration of mechanical integrity of bone. Meta-analysis of clinical trial data indicates that early administration of bisphosphonate after acute fracture does not adversely affect fracture union, pain or functional outcomes. Finally, bisphosphonates have also been explored as a treatment for complex regional pain syndrome type-I. A recent meta-analysis has shown a beneficial effect on visual analogue scale pain scores, but an increase in mild adverse events.

Successful Treatment of Long Standing Complex Regional Pain Syndrome with Hyperbaric Oxygen Therapy

Complex regional pain syndrome (CRPS) is a devastating posttraumatic neuroinflammatory condition with both autoinflammatory and autoimmune features, characterized by unrelenting severe pain and disability, with the majority of affected patients being unable to function socially or vocationally. Remission is more likely in children than adults, and if treatment is started early. Once established, there are no universally effective treatments, and these are desperately needed. A single limb is often involved, but there can be multi-limb spread, and systemic autonomic manifestations. We describe a case of long-standing CRPS with multi-limb spread and systemic autonomic features, controlled only with very high dose oral corticosteroids, which led to several complications. Multiple other treatment modalities failed or were insufficient to control the CRPS and allow tapering of the corticosteroids, but the patient had a dramatic response to hyperbaric oxygen therapy (HBOT), allowing a reduction in prednisone dose to just over the physiologic range. When symptoms started to increase several months later, a second course of HBOT treatments allowed reduction in prednisone dose into the physiologic range while still controlling CRPS symptoms. This case is unique in that it shows that HBOT can be effective in long-standing CRPS, both initially, and for subsequent flares, and adds to the evidence supporting HBOT as a potential treatment for this condition. Graphical Abstract HBOT effect on prednisone dose for symptom control.

Complex regional pain syndrome: a narrative review for the practising clinician

Complex regional pain syndrome (CRPS) is a life-altering condition that usually affects the extremities after a trauma or nerve injury. The physiologic changes that occur as a result of the inciting injury are complex, as the name of the syndrome implies. The pain and disability associated with CRPS often lead to psychological co-morbidities that create a vicious cycle of pain, isolation, and depression. We review recent developments in the understanding of CRPS and advancements in management of this syndrome. Further research in targeting specific mechanisms involved in the pathophysiology of CRPS should lead to prevention of this condition.

Anti-tumor activity of phenoxybenzamine and its inhibition of histone deacetylases

The principal finding from this study was the recognition that the α-adrenergic antagonist, phenoxybenzamine, possesses histone deacetylase inhibitory activity. Phenoxybenzamine is approved by the United States Food and Drug Administration for the treatment of hypertensive crises associated with tumors of the adrenal medulla, pheochromocytomas. It has several "off label" indications relative to its capacity to relax vascular smooth muscle and smooth muscle of the urogenital tract. The drug also has a long history of apparent efficacy in ameliorating, and perhaps reversing, the severe symptoms of neuropathic pain syndromes. Our interest in this feature of the drug relates to the fact that certain types of neuropathic pain, in particular complex regional pain syndrome, demonstrate a proliferative nature, with the capacity to spread from an injured limb, for example, to a non-injured limb and perhaps to essentially the entire body. Sensory neuronal sprouting in the spinal cord has been observed under conditions where there is a high sensory input from painful stimuli. Searches of gene expression signatures in the BroadBuild02 Molecular Signature Database using their connectivity map software suggested that phenoxybenzamine may have histone deacetylase inhibitory activity. Studies by others have reported inhibitory effects of phenoxybenzamine on growth, invasion and migration of human tumor cell cultures and, in one study, inhibition of tumor expansion in animal experiments. Inhibitory effects on human tumor cell cultures are also reported in the present study. Phenoxybenzamine was also found to have histone deacetylase inhibitory activity; histone deacetylase isoforms 5, 6, and 9 were the most sensitive to inhibition by phenoxybenzamine. The importance of elevated levels of these isoforms as biomarkers of poor prognosis in human malignant disease, and the recognized suppression of tumor growth that may accrue from their inhibition, opens consideration of possible translation of phenoxybenzamine to new clinical applications. This might be facilitated by the fact that phenoxybenzamine is already an approved drug entity. There appears to be no previous report of the activity of phenoxybenzamine as a histone deacetylase inhibitor.

Evidence already exists for motor system reorganization in CRPS

Complex regional pain syndrome (CRPS) is a disabling condition that is usually preceded by trauma or surgical procedure. Involvement of the motor system is a well-known phenomenon in CRPS, though the pathophysiologic mechanisms of motor system affliction in CRPS are poorly understood. Graded motor imagery (GMI) has been proposed to be one of the therapeutic interventions to help improve pain and other disabling symptoms associated with CRPS, though the benefits noted are modest and inconsistent. The neurophysiological mechanisms implicated in motor imagery are intended to target the aberrant prefrontal and sensorimotor integration areas, which may potentially help restore the aberrant cortical plasticity in CRPS. Detailed well-controlled experiments using insights from the existing body of literature on motor system reorganization in CRPS are required to better understand this complicated disorder. Attempts to gain pathophysiologic insights about complicated disorders like CRPS based on case reports with poorly performed and uncontrolled interventions are misguided.

A Comprehensive Outcome-Specific Review of the Use of Spinal Cord Stimulation for Complex Regional Pain Syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful, debilitating affliction that is often difficult to treat. It has become common international practice to use spinal cord stimulation (SCS) for the treatment of CRPS as other therapies fail to provide adequate relief, quality of life, or improvement in function. This comprehensive outcome-specific systematic review of the use of SCS for CRPS was performed to elucidate the available evidence with focus on clinically relevant patient-specific outcomes.

METHODS

A systematic review of the literature was conducted to evaluate the effects of SCS on patients with CRPS for the following outcomes and provide summary levels of evidence in regard to each outcome: perceived pain relief, pain score, resolution of CRPS signs, functional status, quality of life, psychological impact, sleep hygiene, analgesic medication utilization, and patient satisfaction with SCS therapy. Search terms included "complex regional pain syndrome," "spinal cord stimulation," and "reflex sympathetic dystrophy," without restriction of language, date, or type of publication, albeit only original data were included in analyses. Of 30 studies selected, seven systematic reviews were excluded, as were four studies reporting combination therapy that included SCS and other therapies (ie, concurrent peripheral nerve stimulation, intrathecal therapy) without clear delineation to the effect of SCS alone on outcomes. A total of 19 manuscripts were evaluated.

RESULTS

Perceived pain relief, pain score improvement, quality of life, and satisfaction with SCS were all rated 1B+, reflecting positive high-level (randomized controlled trial) evidence favoring SCS use for the treatment of CRPS. Evidence for functional status improvements and psychological effects of SCS was inconclusive, albeit emanating from a randomized controlled trial (evidence level 2B±), and outcomes evidence for both sleep hygiene and resolution of CRPS signs was either nonexistent or of too low quality from which to draw conclusions (evidence level 0). An analgesic sparing effect was observed in nonrandomized reports, reflecting an evidence level of 2C+.

CONCLUSIONS

Spinal cord stimulation remains a favorable and effective modality for treating CRPS with high-level evidence (1B+) supporting its role in improving CRPS patients' perceived pain relief, pain score, and quality of life. A paucity of evidence for functional improvements, resolution of CRPS signs, sleep hygiene, psychological impact, and analgesic sparing effects mandate further investigation before conclusions can be drawn for these specific outcomes.

The Use of Transdermal Buprenorphine in Complex Regional Pain Syndrome: A Report of Two Cases

Management of complex regional pain syndrome (CRPS) can be challenging. Various pharmacological approaches have produced mixed results. Buprenorphine activates mu-opioid receptors and antagonizes kappa and delta receptors, acts at N-methyl-d-aspartate (NMDA) receptor, and is an orphan-related ligand-1 receptor agonist. It is available in transdermal patches that last for up to 7 days. This report describes two patients with refractory CRPS who were treated with transdermal buprenorphine. The patients experienced approximately 50% reduction in pain intensity scores. Application site rash that occurred was managed with topical steroid spray used before applying the patch.

Microcirculatory changes identified by photoacoustic microscopy in patients with complex regional pain syndrome type I after stellate ganglion blocks

Complex regional pain syndrome (CRPS) is a chronic pain syndrome that causes intractable pain, disability, and poor quality of life for patients. The etiology and pathophysiology of CRPS are still poorly understood. Due to a lack of proper diagnostic tools, the prognosis of CRPS is primarily based on clinical observation. The objective of this work is to evaluate a new imaging modality, photoacoustic microscopy (PAM), for assisting diagnoses and monitoring the progress and treatment outcome of CRPS. Blood vasculature and oxygen saturation (sO₂) were imaged by PAM from eight adult patients with CRPS-1. Patients' hands and cuticles were imaged both before and after stellate ganglion block (SGB) for comparison. For all patients, both vascular structure and sO₂ could be assessed by PAM. In addition, more vessels and stronger signals were observed after SGB. The results show that PAM can help diagnose and monitor CRPS.

Functional significance of macrophage-derived exosomes in inflammation and pain

Exosomes, secreted microvesicles transporting microRNAs (miRNAs), mRNAs, and proteins through bodily fluids, facilitate intercellular communication and elicit immune responses. Exosomal contents vary, depending on the source and the physiological conditions of cells, and can provide insights into how cells and systems cope with physiological perturbations. Previous analysis of circulating miRNAs in patients with complex regional pain syndrome (CRPS), a debilitating chronic pain disorder, revealed a subset of miRNAs in whole blood that are altered in the disease. To determine functional consequences of alterations in exosomal biomolecules in inflammation and pain, we investigated exosome-mediated information transfer in vitro, in a rodent model of inflammatory pain, and in exosomes from patients with CRPS. Mouse macrophage cells stimulated with lipopolysaccharides secrete exosomes containing elevated levels of cytokines and miRNAs that mediate inflammation. Transcriptome sequencing of exosomal RNA revealed global alterations in both innate and adaptive immune pathways. Exosomes from lipopolysaccharide-stimulated cells were sufficient to cause nuclear factor-κB activation in naive cells, indicating functionality in recipient cells. A single injection of exosomes attenuated thermal hyperalgesia in a murine model of inflammatory pain, suggesting an immunoprotective role for macrophage-derived exosomes. Macrophage-derived exosomes carry a protective signature that is altered when secreting cells are exposed to an inflammatory stimulus. We also show that circulating miRNAs altered in patients with complex regional pain syndrome are trafficked by exosomes. With their systemic signaling capabilities, exosomes can induce pleiotropic effects potentially mediating the multifactorial pathology underlying chronic pain, and should be explored for their therapeutic utility.

Stimulation of dorsal root ganglia for the management of complex regional pain syndrome: a prospective case series

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic and progressive pain condition usually involving the extremities and characterized by sensorimotor, vascular, and trophic changes. Spinal cord stimulation (SCS) is an effective intervention for this condition, but is hampered by the technical challenges associated with precisely directing stimulation to distal extremities. Dorsal root ganglia (DRG) may be more effective as a physiological target for electrical modulation due to recruitment of the primary sensory neurons that innervate the painful distal anatomical regions.

METHODS

Eleven subjects diagnosed with uni- or bilateral lower-extremity CRPS were recruited as part of a larger study involving chronic pain of heterogeneous etiologies. Quadripolar epidural leads of a newly developed neurostimulation system were placed near lumbar DRGs using conventional percutaneous techniques. The neurostimulators were trialed; 8 were successful and permanently implanted and programed to achieve optimal pain-paresthesia overlap.

RESULTS

All 8 subjects experienced some degree of pain relief and subjective improvement in function, as measured by multiple metrics. One month after implantation of the neurostimulator, there was significant reduction in average self-reported pain to 62% relative to baseline values. Pain relief persisted through 12 months in most subjects. In some subjects, edema and trophic skin changes associated with CRPS were also mitigated and function improved. Neuromodulation of the DRG was able to provide excellent pain-paresthesia concordance in locations that are typically hard to target with traditional SCS, and the stimulation reduced the area of pain distributions.

CONCLUSIONS

Neuromodulation of the DRG appears to be a promising option for relieving chronic pain and other symptoms associated with CRPS. The capture of discrete painful areas such as the feet, combined with stable paresthesia intensities independent of body position, suggests this stimulation modality may allow more selective and consistent targeting of painful areas than traditional SCS.

Phenoxybenzamine in complex regional pain syndrome: potential role and novel mechanisms

There is a relatively long history of the use of the α-adrenergic antagonist, phenoxybenzamine, for the treatment of complex regional pain syndrome (CRPS). One form of this syndrome, CRPS I, was originally termed reflex sympathetic dystrophy (RSD) because of an apparent dysregulation of the sympathetic nervous system in the region of an extremity that had been subjected to an injury or surgical procedure. The syndrome develops in the absence of any apparent continuation of the inciting trauma. Hallmarks of the condition are allodynia (pain perceived from a nonpainful stimulus) and hyperalgesia (exaggerated pain response to a painful stimulus). In addition to severe, unremitting burning pain, the affected limb is typically warm and edematous in the early weeks after trauma but then progresses to a primarily cold, dry limb in later weeks and months. The later stages are frequently characterized by changes to skin texture and nail deformities, hypertrichosis, muscle atrophy, and bone demineralization. Earlier treatments of CRPS syndromes were primarily focused on blocking sympathetic outflow to an affected extremity. The use of an α-adrenergic antagonist such as phenoxybenzamine followed from this perspective. However, the current consensus on the etiology of CRPS favors an interpretation of the symptomatology as an evidence of decreased sympathetic activity to the injured limb and a resulting upregulation of adrenergic sensitivity. The clinical use of phenoxybenzamine for the treatment of CRPS is reviewed, and mechanisms of action that include potential immunomodulatory/anti-inflammatory effects are presented. Also, a recent study identified phenoxybenzamine as a potential intervention for pain mediation from its effects on gene expression in human cell lines; on this basis, it was tested and found to be capable of reducing pain behavior in a classical animal model of chronic pain.

Plasma amino acids changes in complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a severe chronic pain condition that most often develops following trauma. Blood samples were collected from 220 individuals, 160 CRPS subjects, and 60 healthy pain-free controls. Plasma amino acid levels were compared and contrasted between groups. L-Aspartate, L-glutamate, and L-ornithine were significantly increased, whereas L-tryptophan and L-arginine were significantly decreased in CRPS subjects as compared to controls. In addition, the L-kynurenine to L-tryptophan ratio demonstrated a significant increase, whereas the global arginine bioavailability ratio (GABR) was significantly decreased in the CRPS subjects. The CRPS subjects demonstrated a significant correlation between overall pain and the plasma levels of L-glutamate and the L-kynurenine to L-tryptophan ratio. CRPS subjects also showed a correlation between the decrease in plasma L-tryptophan and disease duration. This study shows that CRPS subjects exhibit significant changes in plasma levels of amino acids involved in glutamate receptor activation and in amino acids associated with immune function as compared to healthy pain-free controls. A better understanding of the role plasma amino acids play in the pathophysiology of CRPS may lead to novel treatments for this crippling condition.

Pentoxifylline reduces chronic post-ischaemia pain by alleviating microvascular dysfunction

BACKGROUND

Microvascular dysfunction and ischaemia in muscle play a role in the development of cutaneous tactile allodynia in chronic post-ischaemia pain (CPIP). Hence, studies were designed to assess whether pentoxifylline (PTX), a vasodilator and haemorrheologic agent, relieves allodynia in CPIP rats by alleviating microvascular dysfunction.

METHODS

Laser Doppler flowmetry of plantar blood flow was used to examine the effects of PTX on CPIP-induced alterations in post-occlusive reactive hyperaemia (reflecting microvascular dysfunction), and von Frey testing was used to examine its effects on CPIP-induced allodynia. Time-course effects of PTX on allodynia and microvascular dysfunction were assessed early (2-8 days) and late (18-25 days) post-ischaemia/reperfusion (I/R) injury, and its effects on allodynia were also tested at 30 days post-I/R injury.

RESULTS

PTX (25 mg/kg) produced significant anti-allodynic effects throughout the 21-day time course, but was not effective 30 days post-I/R injury. In laser Doppler studies, the reduced reactive hyperaemia in early CPIP rats was significantly improved by PTX (25 mg/kg). Conversely, treatment with PTX at the same dose did not affect reactive hyperaemia in late CPIP rats, likely since reactive hyperaemia was not significantly reduced pre-drug in these animals.

CONCLUSION

Since poor tissue perfusion underlies early stages of CPIP pain, the ameliorative effect of PTX on microvascular dysfunction might account for its anti-allodynic effect in our experimental model of complex regional pain syndrome type I.

Gardner-Diamond syndrome associated with complex regional pain syndrome

BACKGROUND

Gardner-Diamond syndrome (GDS) is also known as psychogenic purpura, autoerythrocyte sensitization syndrome and painful bruising syndrome.

MAIN OBSERVATION

This is a case report of 27-year-old woman who presented with unexplained bruising and intramuscular hematomas after a seven year history of complex regional pain syndrome. Her evaluation consisted of hematological studies, skin and muscle biopsy; it failed to reveal an underlying coagulopathy, vasculitis or other demonstrable cause. In the absence of any other etiology, she was diagnosed as Gardner-Diamond syndrome.

CONCLUSIONS

This patient is unique because of intramuscular hematomas and the association of Complex regional pain syndrome with Gardner-Diamond syndrome.

SBOTE study: extracorporeal shock wave therapy versus electrical stimulation after botulinum toxin type a injection for post-stroke spasticity-a prospective randomized trial

Research is on-going to identify new methods of biostimulation to increase the effect of botulinum toxin type A (BTX-A) in the treatment of spasticity. The Spasticity treated by Botulinum Toxin and ESWT (SBOTE) study is a prospective, randomized controlled trial assessing the effectiveness of extracorporeal shock wave therapy (ESWT) given immediately after BTX-A injections compared with electrical stimulation (ES) given immediately after BTX-A therapy for the management of focal upper limb spasticity in stroke patients. ES was given for 30 min twice a day for 5 days starting at 5 Hz; ESWT was given once a day for 5 days. At study follow-up, patients treated with BTX-A injections and ESWT showed a statistically greater significance and continuous decrease of spasticity measure (modified Ashworth scale [MAS]: 1.37, 1.75 and 1.58 at 15, 30 and 90 days post-treatment, respectively), of spasms (spasm frequency scale [SFS]: 0.8 and 0.25 at 30 and 90 days post-treatment, respectively) and of pain (visual analogue scale [VAS]: 1.94 and 1.87 at 30 and 90 days, respectively) compared with patients treated with BTX-A injections and ES (MAS: 2.37, 2.18 and 2.18, respectively) (p < 0.05) (SFS: 1.5 and 1.06, respectively) (p < 0.05) (VAS: 2.44 and 2.69 respectively) (p < 0.05). ESWT enhances the effect of BTX-A to a greater extent than ES, probably by modulating rheology of the muscle and neurotransmission at the neuromuscular junction.

The association of greater dispositional optimism with less endogenous pain facilitation is indirectly transmitted through lower levels of pain catastrophizing

Dispositional optimism has been shown to beneficially influence various experimental and clinical pain experiences. One possibility that may account for decreased pain sensitivity among individuals who report greater dispositional optimism is less use of maladaptive coping strategies such as pain catastrophizing, a negative cognitive/affective response to pain. An association between dispositional optimism and conditioned pain modulation, a measure of endogenous pain inhibition, has previously been reported. However, it remains to be determined whether dispositional optimism is also associated with temporal summation (TS), a measure of endogenous pain facilitation. The current study examined whether pain catastrophizing mediated the association between dispositional optimism and TS among 140 older, community-dwelling adults with symptomatic knee osteoarthritis. Individuals completed measures of dispositional optimism and pain catastrophizing. TS was then assessed using a tailored heat pain stimulus on the forearm. Greater dispositional optimism was significantly related to lower levels of pain catastrophizing and TS. Bootstrapped confidence intervals revealed that less pain catastrophizing was a significant mediator of the relation between greater dispositional optimism and diminished TS. These findings support the primary role of personality characteristics such as dispositional optimism in the modulation of pain outcomes by abatement of endogenous pain facilitation and less use of catastrophizing.

PERSPECTIVE

Results from this study further support the body of evidence that attests to the beneficial effects of positive personality traits on pain sensitivity and pain processing. Further, this study identified diminished pain catastrophizing as an important mechanism explaining the inverse relation between dispositional optimism and endogenous pain facilitation.

Immediate effects of a thoracic spine thrust manipulation on the autonomic nervous system: a randomized clinical trial

Thoracic spine manipulation has been shown to be effective for the management of neck pain. The purpose of this study was to investigate the immediate effect of a T3-T4 spinal thrust manipulation on autonomic nervous system activity in subjects with chronic cervical pain. An additional aim was to determine if the manipulation resulted in an immediate pain relief in patients with chronic neck pain when compared to a placebo intervention. One hundred subjects with chronic neck pain were randomly assigned to receive either a thoracic thrust manipulation or a placebo intervention. The Friedman's test was used to evaluate the change in pupil diameter within both groups. The Wilcoxen signed-ranks test was used to explore pupil changes over time and to make paired comparisons of the pupil change between the groups. The Mann-Whitney U test was used to compare the change in pain perception for the chronic cervical pain group subjects receiving either the thrust manipulation or the placebo intervention. The results demonstrated that manipulation did not result in a change in sympathetic activity. Additionally, there was no significant difference in the subject's pain perception (P = 0.961) when comparing the effects of the thrust manipulation to the placebo intervention within this group of subjects with chronic neck pain. The clinical impression of this study is that manipulation of the thoracic spine may not be effective in immediately reducing pain in patients with chronic neck pain.

Pain acceptance-based coping in complex regional pain syndrome Type I: daily relations with pain intensity, activity, and mood

This study aimed to examine the temporal patterning of pain acceptance-based coping, activity, and mood in patients with complex regional pain syndrome Type I (CRPS-I), by using a daily diary method. A total of 30 patients with CRPS-I seeking treatment in a tertiary pain management center located in Seoul, Korea participated in the study. Multilevel random effects analyses indicated that (a) engagement in pain acceptance-based coping was significantly associated with lower same-day pain and negative mood and greater same-day activity and positive mood; (b) pain acceptance-based coping predicted increases in activity on the following day; (c) greater pain intensity was significantly associated with lower same-day pain acceptance-based coping and activity and greater same-day negative mood; and (d) pain intensity did not predict pain acceptance-based coping, activity, or mood on the following day. These findings suggest that patients with CRPS-I may benefit from responding to pain with acceptance. Further study and eventual application of this process in CRPS-I may improve upon the success of current approaches to this problem.

Changes in plasma cytokines and their soluble receptors in complex regional pain syndrome

Complex Regional Pain Syndrome (CRPS) is a chronic and often disabling pain disorder. There is evidence demonstrating that neurogenic inflammation and activation of the immune system play a significant role in the pathophysiology of CRPS. This study evaluated the plasma levels of cytokines, chemokines, and their soluble receptors in 148 subjects afflicted with CRPS and in 60 gender- and age-matched healthy controls. Significant changes in plasma cytokines, chemokines, and their soluble receptors were found in subjects with CRPS as compared with healthy controls. For most analytes, these changes resulted from a distinct subset of the CRPS subjects. When the plasma data from the CRPS subjects was subjected to cluster analysis, it revealed 2 clusters within the CRPS population. The category identified as most important for cluster separation by the clustering algorithm was TNFα. Cluster 1 consisted of 64% of CRPS subjects and demonstrated analyte values similar to the healthy control individuals. Cluster 2 consisted of 36% of the CRPS subjects and demonstrated significantly elevated levels of most analytes and in addition, it showed that the increased plasma analyte levels in this cluster were correlated with disease duration and severity.

PERSPECTIVE

The identification of biomarkers that define disease subgroups can be of great value in the design of specific therapies and of great benefit to the design of clinical trials. It may also aid in advancing our understanding of the mechanisms involved in the pathophysiology of CRPS, which may lead to novel treatments for this very severe condition.

Gabapentin for complex regional pain syndrome in Machado-Joseph disease: a case report

Introduction

Case presentation

Conclusions

MicroRNA modulation in complex regional pain syndrome

Background

Aberrant expression of small noncoding RNAs called microRNAs (miRNAs) is a common feature of several human diseases. The objective of the study was to identify miRNA modulation in patients with complex regional pain syndrome (CRPS) a chronic pain condition resulting from dysfunction in the central and/or peripheral nervous systems. Due to a multitude of inciting pathologies, symptoms and treatment conditions, the CRPS patient population is very heterogeneous. Our goal was to identify differentially expressed miRNAs in blood and explore their utility in patient stratification.

Methods

We profiled miRNAs in whole blood from 41 patients with CRPS and 20 controls using TaqMan low density array cards. Since neurogenic inflammation is known to play a significant role in CRPS we measured inflammatory markers including chemokines, cytokines, and their soluble receptors in blood from the same individuals. Correlation analyses were performed for miRNAs, inflammatory markers and other parameters including disease symptoms, medication, and comorbid conditions.

Results

Three different groups emerged from miRNA profiling. One group was comprised of 60% of CRPS patients and contained no control subjects. miRNA profiles from the remaining patients were interspersed among control samples in the other two groups. We identified differential expression of 18 miRNAs in CRPS patients. Analysis of inflammatory markers showed that vascular endothelial growth factor (VEGF), interleukin1 receptor antagonist (IL1Ra) and monocyte chemotactic protein-1 (MCP1) were significantly elevated in CRPS patients. VEGF and IL1Ra showed significant correlation with the patients reported pain levels. Analysis of the patients who were clustered according to their miRNA profile revealed correlations that were not significant in the total patient population. Correlation analysis of miRNAs detected in blood with additional parameters identified miRNAs associated with comorbidities such as headache, thyroid disorder and use of narcotics and antiepileptic drugs.

Conclusions

miRNA profiles can be useful in patient stratification and have utility as potential biomarkers for pain. Differentially expressed miRNAs can provide molecular insights into gene regulation and could lead to new therapeutic intervention strategies for CRPS.

Syncope in complex regional pain syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a debilitating pain syndrome characterized clinically by severe pain along with signs and symptoms of autonomic dysfunction. Presyncope and syncope are common in these patients. The purpose of this study was to investigate the cause of these symptoms in these patients.

HYPOTHESIS

Patients with CRPS are more prone to presyncope and syncope as evidenced by head-up tilt table testing (HUTT).

METHODS

Patients with CRPS underwent a complete cardiac evaluation that included a 12-lead electrocardiogram, 2-dimensional echocardiography, 24-hour Holter monitoring, and HUTT.

RESULTS

Seventy-four patients with CRPS were evaluated. Eight CRPS patients (10%) could not complete a HUTT due to pain. Of the 66 CRPS patients who completed a HUTT, 15 (37.9%) reported pretest symptoms of presyncope or syncope. Twenty-eight CRPS patients (42.4%) had a positive HUTT. CRPS patients with lower limb involvement were more likely to have vasovagal syncope or orthostasis on HUTT than those with upper extremity or total body involvement (12 of 18 [67%] vs 16 of 48 [33%]; P = 0.015).

CONCLUSIONS

Syncope is common in patients with CRPS, especially with lower limb involvement. Autonomic dysregulation of the lower extremities leads to impaired sympathetic vasoconstriction and venous pooling, which can predispose these patients to syncope. Physician awareness of this syndrome will lead to improved recognition and treatment of their symptoms of presyncope or syncope.

Elevated blood levels of inflammatory monocytes (CD14+ CD16+ ) in patients with complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a chronic pain disorder. Although its pathophysiology is not completely understood, neurogenic inflammation is thought to play a significant role. Microglia and astrocytes are activated following tissue injury or inflammation and have been reported to be both necessary and sufficient for enhanced nociception. Blood-borne monocytes/macrophages can infiltrate the central nervous system (CNS) and differentiate into microglia resulting in hypersensitivity and chronic pain. The primary aim of this study was to evaluate the proportion of the proinflammatory CD14(+) CD16(+) monocytes as well as plasma cytokine levels in blood from CRPS patients compared to age- and gender-matched healthy control individuals. Forty-six subjects (25 CRPS, 21 controls) were recruited for this study. The percentage of monocytes, T, B or natural killer (NK) cells did not differ between CRPS and controls. However, the percentage of the CD14(+) CD16(+) monocyte/macrophage subgroup was elevated significantly (P<0·01) in CRPS compared to controls. Individuals with high percentage of CD14(+) CD16(+) demonstrated significantly lower (P<0·05) plasma levels on the anti-inflammatory cytokine interleukin (IL)-10. Our data cannot determine whether CD14(+) CD16(+) monocytes became elevated prior to or after developing CRPS. In either case, the elevation of blood proinflammatoty monocytes prior to the initiating event may predispose individuals for developing the syndrome whereas the elevation of blood proinflammatory monocytes following the development of CRPS may be relevant for its maintenance. Further evaluation of the role the immune system plays in the pathogenesis of CRPS may aid in elucidating disease mechanisms as well as the development of novel therapies for its treatment.

Fibromyalgia and the complex regional pain syndrome: similarities in pathophysiology and treatment

Although the pain of fibromyalgia usually is not preceded by an injury to the involved tissue, whereas that of the complex regional pain syndrome usually starts at a site of prior trauma or surgery, both disorders may share a common mechanism-pathologic sensitization of brain mechanisms that integrate nociceptive signals-and both apparently respond to treatment with ketamine, an anesthetic-analgesic agent whose actions include blockade of N-methyl-D-aspartate receptors. Ketamine's widespread illegal use as a recreational agent probably precludes developing it as a general treatment of centrally mediated pain disorders; however, its efficacy suggests that related, to-be-discovered agents could be useful.

Enantioselective pharmacokinetics of (R)- and (S)-ketamine after a 5-day infusion in patients with complex regional pain syndrome

INTRODUCTION

This study determined the pharmacokinetics and pharmacodynamics of (R)- and (S)-ketamine and (R)- and (S)-norketamine following a 5-day moderate dose, as a continuous (R,S)-ketamine infusion in complex regional pain syndrome (CRPS) patients.

MATERIALS AND METHODS

Ketamine was titrated to 10-40 mg/h and maintained for 5 days. (R)- and (S)-Ketamine and (R)- and (S)-norketamine pharmacokinetic and pharmacodynamic studies were performed. Blood samples were obtained on Day 1 preinfusion, and at 60-90, 120-150, 180-210, and 240-300 min after the start of the infusion, on Days 2, 3, 4, 5, and on Day 5 at 60 min after the end of infusion. The plasma concentrations of (R)- and (S)-ketamine and (R)- and (S)-norketamine were determined using enantioselective liquid chromatography-mass spectrometry.

RESULTS

Ketamine and norketamine levels stabilized 5 h after the start of the infusion. (R)-Ketamine clearance was significantly lower resulting in higher steady-state plasma concentrations than (S)-ketamine. The first-order elimination for (S)-norketamine was significantly greater than that of (R)-enantiomer. When comparing the pharmacokinetic parameters of the patients who responded to ketamine treatment with those who did not, no differences were observed in ketamine clearance and the first-order elimination of norketamine.

CONCLUSION

The results indicate that (R)- and (S)-ketamine and (R)- and (S)-norketamine plasma concentrations do not explain the antinociceptive activity of the drug in patients suffering from CRPS.

Skin incision induces expression of axonal regeneration-related genes in adult rat spinal sensory neurons

Skin incision and nerve injury both induce painful conditions. Incisional and postsurgical pain is believed to arise primarily from inflammation of tissue and the subsequent sensitization of peripheral and central neurons. The role of axonal regeneration-related processes in development of pain has only been considered when there has been injury to the peripheral nerve itself, even though tissue damage likely induces injury of resident axons. We sought to determine if skin incision would affect expression of regeneration-related genes such as activating transcription factor 3 (ATF3) in dorsal root ganglion (DRG) neurons. ATF3 is absent from DRG neurons of the normal adult rodent, but is induced by injury of peripheral nerves and modulates the regenerative capacity of axons. Image analysis of immunolabeled DRG sections revealed that skin incision led to an increase in the number of DRG neurons expressing ATF3. RT-PCR indicated that other regeneration-associated genes (galanin, GAP-43, Gadd45a) were also increased, further suggesting an injury-like response in DRG neurons. Our finding that injury of skin can induce expression of neuronal injury/regeneration-associated genes may impact how clinical postsurgical pain is investigated and treated.

PERSPECTIVE

Tissue injury, even without direct nerve injury, may induce a state of enhanced growth capacity in sensory neurons. Axonal regeneration-associated processes should be considered alongside nerve signal conduction and inflammatory/sensitization processes as possible mechanisms contributing to pain, particularly the transition from acute to chronic pain.