Changes resembling complex regional pain syndrome following surgery and immobilization

Clinical outcomes following tibiotalocalcaneal arthrodesis with intramedullary nailing combined with partial fibulectomy and onlay bone graft

INTRODUCTION

Although intramedullary nailing is a popular method for tibiotalocalcaneal arthrodesis, nonunion is one of the most commonly reported complications. This study aimed to evaluate the fusion rate, improvement in functional outcomes, and occurrence of complications in tibiotalocalcaneal arthrodesis using retrograde intramedullary nailing with partial fibulectomy and onlay bone graft technique.

MATERIALS AND METHODS

Twenty-six consecutive patients using the proposed technique were retrospectively reviewed. For radiographic outcomes, the union rate, alignment, and any related complications were assessed. Functional outcomes were evaluated using the American Orthopedic Foot and Ankle Society hindfoot scale, Foot and Ankle Outcome Score, and visual analog scale, preoperatively and at the final follow-up.

RESULTS

The mean follow-up period was 38.2 months. The tibiotalar joint achieved complete union in 80.8% at six months postoperatively, while all the cases achieved complete union at 12 months postoperatively. However, the subtalar joint achieved complete union in 26.9% at six months postoperatively, which gradually increased to 73.1% at 12 months postoperatively, and 80.8% at the final follow-up without revision surgery. A subgroup analysis showed there was a trend of higher subtalar fusion rate when an additional screw for the subtalar joint fixation was placed (86.7% vs. 54.5%). The functional outcomes significantly improved at the final follow-up. A few minor complications occurred, including surgical site infection, irritational symptoms, and metal failure; however, they eventually resolved.

CONCLUSIONS

Our technique of tibiotalocalcaneal arthrodesis with partial fibulectomy and onlay bone grafting could be a good option where both the tibiotalar and subtalar joints need to be fused.

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

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

A systematic review of the psychometric properties of pressure pain detection threshold in evaluating mechanical pain threshold in people with hand or wrist injuries

PURPOSE

The aim of this study was to conduct a systematic review of the psychometric properties of Pressure Pain Detection Threshold (PPDT) measures in people with hand or wrist injuries.

STUDY DESIGN AND METHODS

MEDLINE, Embase, and CINAHL databases were searched to identify eligible studies evaluating psychometric properties of PPDT in samples composed of at least 50% of people with hand or wrist injury. The Consensus-based Standards for the Measurement of Health Instruments' risk of bias checklist was used to critically appraise the included studies, and qualitative synthesis was performed by pooling the results of all studies that presented the same measurement property using Grading of Recommendations, Assessment, Development, and Evaluation.

RESULTS

From 415 studies, 11 relevant studies were identified. Of the 11 studies, four hand or wrist injuries were represented; carpal tunnel syndrome, distal radius fractures, osteoarthritis, and complex regional pain syndrome. Intra-rater reliability was considered sufficient (intraclass correlation coefficient 0.64-0.94), with small reported standard error of the mean values (5.3-39.2 kPa). Results of validity and responsiveness could not be synthesized due to heterogeneity. Risk of bias for reliability and measurement error was assessed as very good or adequate, whereas validity and responsiveness were doubtful or inadequate. Overall quality of evidence was low or very low for all measurement properties.

CONCLUSIONS

Inconsistent results and low quality evidence provide little confidence in the overall measurement properties of PPDT in a hand or wrist injury population. No criterion standard for pain further highlights complexities around pain measurement such that the results obtained from PPDT measures in clinical practice cannot be compared to a gold standard measure.

Diagnosis and Outcomes of 225 Consecutive Cases of Complex Regional Pain Syndrome of the Hand

BACKGROUND

The lack of specific tests and potential diagnostic inaccuracy may be behind the stunning figures of complex regional pain syndrome (CRPS) cases. The author tested the hypothesis that patients diagnosed with CRPS at referral could be assigned to recognized conditions and treated accordingly.

METHODS

From January of 2018 to April of 2021, 225 consecutive patients attended the author's office having been diagnosed with and treated for CRPS for an average of 16 ± 26 months. There were 180 women and 45 men; no patient was excluded.

RESULTS

All patients could be allocated in named conditions: 79 had a wrong diagnosis; seven had a true causalgia; 16 were dystonic-psychogenic hands; 20 presented a flare reaction; and 90 had an "irritative" carpal tunnel syndrome. The remaining 13 patients had a miscellany of symptoms within a substandard management setting. Surgery was offered to 175 with a correctable cause; 50 (20 of whom had a tangible cause responsible for their pain) declined, and their outcome is unknown. The remaining 125 were operated on and tracked for an average of 20 ± 9 months. In the operated group, pain dropped 7.5 ± 2.2 points ( P < 0.0001) on a numerical rating scale of 0 to 10. Disabilities of the Arm, Shoulder, and Hand questionnaire scores fell from 80 to 16 ( P < 0.0001). Patients who were operated on rated their satisfaction on a scale of 0 to 10 as 8.9 ± 1.9.

CONCLUSIONS

Unlike with CRPS, all patients in this series had a true, diagnosable condition explaining their clinical picture. Most patients who agreed to be operated on had a favorable outcome.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

[Complex Regional Pain Syndrome (CRPS) - State of the Art in Diagnostics and Therapy]

The complex regional pain syndrome (CRPS) usually occurs within a few weeks in 2-5% of all patients after trauma or surgery or subsequent measures of the distal extremities. There are certain risk factors for its occurrence but no "CRPS personality", instead there are factors that negatively influence the course. The prognosis is generally good ("rule of thirds"), but remaining limitations are common. The diagnosis is clinically possible according to the "Budapest criteria". Additional examinations are possible in case of doubt but are neither conclusive nor exclusive. Corticoids and bisphosphonates are used alongside drugs that have an effect on neuropathic pain. Invasive therapies do not have good evidence and have therefore lost their importance. The rehabilitative therapy is carried out actively and with a lot of self-exercises at an early stage. Invasive anesthetic, passive therapies are obsolete. Special forms of treatment are "graded exposure" (GEXP) in the case of dominant anxiety and, e.g., "graded motor imagery" (GMI) in case of neglect-like symptoms. In addition to educational and behavioral therapy elements, psychotherapy for CRPS also includes participation as part of graded exposure.

Chronic Pain after Bone Fracture: Current Insights into Molecular Mechanisms and Therapeutic Strategies

Bone fracture following traumatic injury or due to osteoporosis is characterized by severe pain and motor impairment and is a major cause of global mortality and disability. Fracture pain often originates from mechanical distortion of somatosensory nerve terminals innervating bones and muscles and is maintained by central sensitization. Chronic fracture pain (CFP) after orthopedic repairs is considered one of the most critical contributors to interference with the physical rehabilitation and musculoskeletal functional recovery. Analgesics available for CFP in clinics not only have poor curative potency but also have considerable side effects; therefore, it is important to further explore the pathogenesis of CFP and identify safe and effective therapies. The typical physiopathological characteristics of CFP are a neuroinflammatory response and excitatory synaptic plasticity, but the specific molecular mechanisms involved remain poorly elucidated. Recent progress has deepened our understanding of the emerging properties of chemokine production, proinflammatory mediator secretion, caspase activation, neurotransmitter release, and neuron-glia interaction in initiating and sustaining synaptogenesis, synaptic strength, and signal transduction in central pain sensitization, indicating the possibility of targeting neuroinflammation to prevent and treat CFP. This review summarizes current literature on the excitatory synaptic plasticity, microgliosis, and microglial activation-associated signaling molecules and discusses the unconventional modulation of caspases and stimulator of interferon genes (STING) in the pathophysiology of CFP. We also review the mechanisms of action of analgesics in the clinic and their side effects as well as promising therapeutic candidates (e.g., specialized pro-resolving mediators, a caspase-6 inhibitor, and a STING agonist) for pain relief by the attenuation of neuroinflammation with the aim of better managing patients undergoing CFP in the clinical setting.

Substance P Serum Degradation in Complex Regional Pain Syndrome - Another Piece of the Puzzle?

In a previous study, we demonstrated that the serum peptidase system might be less efficient in complex regional pain syndrome (CRPS). Since the neuropeptide substanc P (SP) contributes to inflammation in CRPS, we now investigated the metabolism of SP in CRPS specifically. An SP metabolism assay was performed in 24 CRPS patients, which constitute a subgroup of our previous investigation on BK degradation. In addition, we included 26 healthy controls (24 newly recruited plus 2 from our previous investigation), and 13 patients after limb trauma, who did not fulfil the CRPS diagnostic criteria (trauma controls, TC) were included. We adapted a thin layer chromatography assay (TLC) to quantify SP disappearance after incubation with 7.5 µL of serum. These results were compared with bradykinin (BK) metabolization to BK1-8 and BK1-5 fragments from our previous study. In addition, TC were clinically and quantitative sensory testing (QST) phenotyped; the phenotyping of CRPS patients was retrieved from our existing database. SP metabolism was less efficient in CRPS and TC patient serum vs human control (HC) serum (P < .03) suggesting reduced activity of the neutral endopeptidase (NEP) and/or the angiotensin converting enzyme (ACE). Together with the decreased occurrence of BK1-5 fragment in CRPS and TC, this suggests a reduced activation of the angiotensin converting enzyme (ACE). There was no clear clinical phenotype related to impaired SP degradation; duration of disease and gender were also not associated. Most importantly, results in TC did not differ from CRPS. Collectively, our current and previous experimental results suggest that limb trauma reduces serum peptidase metabolism of SP ex vivo, specifically serum ACE activity. However, this finding is not CRPS-specific and seems to be rather a long-term consequence of the trauma itself. PERSPECTIVE: The experimental data from this study further support the hypothesis that impaired metabolism of inflammatory peptides potentially contribute to the development of posttraumatic pain in CRPS or limb trauma patients.

Decreasing incidence of complex regional pain syndrome in the Netherlands: a retrospective multicenter study

Background:

Complex regional pain syndrome type I (CRPS) is a symptom-based diagnosis of which the reported incidence varies widely. In daily practice, there appears to be a decrease in incidence of CRPS after a distal radius fracture and in general.

Questions/purposes:

The aim of this study was to assess the trend in the incidence of CRPS after a distal radius fracture and in general in the Netherlands from 2014 to 2018.

Methods:

The incidence of CRPS after a distal radius fracture was calculated by dividing the number of confirmed cases of CRPS after distal radius fracture by the total number of patients diagnosed with a distal radius fracture. Medical records of these patients were reviewed. Hospital-based data were used to establish a trend in incidence of CRPS in general. A Dutch national database was used to measure the trend in the incidence of CRPS in the Netherlands by calculating annual incidence rates: the number of new CRPS cases, collected from the national database, divided by the Dutch mid-year population.

Results:

The incidence of CRPS after distal radius fracture over the whole study period was 0.36%. Hospital data showed an absolute decrease in CRPS cases from 520 in 2014 to 223 in 2018. National data confirmed this with a decrease in annual incidence from 23.2 (95% CI: 22.5–23.9) per 100,000 person years in 2014 to 16.1 (95% CI: 15.5–16.7) per 100,000 person years in 2018.

Conclusion:

A decreasing trend of CRPS is shown in this study. We hypothesize this to be the result of the changing approach towards CRPS and fracture management, with more focus on prevention and the psychological aspects of disproportionate posttraumatic pain.

Level of Evidence:

level 3 (retrospective cohort study).

Complex Regional Pain Syndrome: The Importance of Early Diagnosis

Complex regional pain syndrome (CRPS) is a potentially life-altering, neuropathic pain condition that often affects an extremity in response to surgery or even minor trauma. The pain is often disproportionate to the injury sustained or the surgical procedure performed-and it has been described as excruciating and unbearable. CRPS can result in irreversible, disabling changes in the affected limb. In some cases it has resulted in amputation or severe psychological issues. However, CRPS outcomes are generally more successful with early detection and treatment. This article presents an overview of CRPS and discusses the critical role nurses can play in recognizing the condition early, assisting with treatment, and providing psychological support.

Involvement of Mast Cells in the Pathophysiology of Pain

Mast cells (MCs) are immune cells and are widely distributed throughout the body. MCs are not only classically viewed as effector cells of some allergic diseases but also participate in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. Mounting evidence indicates that activation of MCs releasing numerous vasoactive and inflammatory mediators has effects on the nervous system and has been involved in different pain conditions. Here, we review the latest advances made about the implication of MCs in pain. Possible cellular and molecular mechanisms regarding the crosstalk between MC and the nervous system in the initiation and maintenance of pain are also discussed.

Mast cell stabilizer ketotifen fumarate reverses inflammatory but not neuropathic-induced mechanical pain in mice

Supplemental Digital Content is Available in the Text.

Our preclinical findings indicate that ketotifen fumarate's analgesic effects are MC-dependent, and the case series report presented supports its use for the treatment of chronic pain.

Introduction:

Mast cell (MC) activation could establish a positive feedback loop that perpetuates inflammation and maintains pain. Stabilizing MCs with ketotifen fumarate (KF) may disrupt this loop and relieve pain.

Objective:

We aimed to test the effect of treatment with KF in pain assays in mice and in a case series of patients with chronic widespread pain.

Methods:

The analgesic effect of KF was tested in CD-1 mice injected with formalin, complete Freund's adjuvant, or subjected to spared nerve injury. In addition, wild-type (C57BL/6) and MC-deficient (C57BL/6-Kit^W-sh/W-sh) mice were injected with formalin or complete Freund's adjuvant and treated with KF. Patients with chronic widespread pain (n = 5; age: 13–16 years) who failed to respond to standard of care participated in a 16-week treatment trial with KF (6 mg/d). Ketotifen fumarate's therapeutic effect was evaluated using the patient global impression of change.

Results:

In the mouse experiments, KF produced dose- and MC-dependent analgesic effects against mechanical allodynia in the acute and chronic inflammatory pain but not neuropathic pain assays. In the patient case series, 4 patients reported that activity limitations, symptoms, emotions, and overall quality of life related to their pain condition were “better” or “a great deal better” since beginning treatment with KF. This was accompanied by improvements in pain comorbid symptoms.

Conclusion:

Treatment with KF is capable of reducing established inflammatory-induced mechanical nociception in an MC-dependent manner in mice, and it may be beneficial for the treatment of chronic pain conditions.

IL-6 signaling mediates the germinal center response, IgM production and nociceptive sensitization in male mice after tibia fracture

BACKGROUND

Up-regulated interleukin 6 (IL-6) signaling, immune system activation, and pronociceptive autoantibodies are characteristic of complex regional pain syndrome (CRPS). IL-6 is known to promote B cell differentiation, thus we hypothesized that IL-6 signaling plays a crucial role in the development of adaptive immune responses and nociceptive sensitization in a murine tibia fracture model of CRPS.

METHODS

Mice deficient in IL-6 expression (IL-6^-/-) or B cell deficient (muMT) underwent tibia fracture and 3 weeks of cast immobilization or sham injury. The deposition of IgM in fractured limbs was followed using Western blotting, and passive serum transfer to muMT fracture mice was used to detect nociception-supporting autoantibodies. Lymph nodes were assessed for hypertrophy, IL-6 expression was measured using qPCR and ELISA, and germinal center formation was evaluated using FACS and immunohistochemistry. The therapeutic effects of exogenous neutralizing anti-IL-6 antibodies were also evaluated in the CRPS fracture model.

RESULTS

Functional IL-6 signaling was required for the post fracture development of nociceptive sensitization, vascular changes, and IgM immune complex deposition in the skin of injured limbs. Passive transfer of sera from wild-type, but not IL-6^-/- fracture mice into muMT fracture mice caused enhanced allodynia and postural unweighting. IL-6^-/- fracture mice displayed reduced popliteal lymphadenopathy after fracture. Germinal center responses were detected in the popliteal lymph nodes of wild-type, but not in IL-6^-/- fracture mice. We observed that IL-6 expression was dramatically enhanced in popliteal lymph node tissue after fracture. Conversely, administration of anti-IL-6 antibodies reduced nociceptive and vascular changes after fracture and inhibited lymphadenopathy.

CONCLUSIONS

Collectively, these data support the hypothesis that IL-6 signaling in the fracture limb of mice is required for germinal center formation, IgM autoantibody production and nociceptive sensitization. Anti-IL-6 therapies might, therefore, reduce pain after limb fracture or in the setting of CRPS.

Pathophysiology of musculoskeletal pain: a narrative review

Musculoskeletal pain (excluding bone cancer pain) affects more than 30% of the global population and imposes an enormous burden on patients, families, and caregivers related to functional limitation, emotional distress, effects on mood, loss of independence, and reduced quality of life. The pathogenic mechanisms of musculoskeletal pain relate to the differential sensory innervation of bones, joints, and muscles as opposed to skin and involve a number of peripheral and central nervous system cells and mediators. The interplay of neurons and non-neural cells (e.g. glial, mesenchymal, and immune cells) amplifies and sensitizes pain signals in a manner that leads to cortical remodeling. Moreover, sex, age, mood, and social factors, together with beliefs, thoughts, and pain behaviors influence the way in which musculoskeletal pain manifests and is understood and assessed. The aim of this narrative review is to summarize the different pathogenic mechanisms underlying musculoskeletal pain and how these mechanisms interact to promote the transition from acute to chronic pain.

Cross Cultural Adaptation and Validation of Italian Version of the Leeds Assessment of Neuropathic Symptoms and Signs Scale and Pain DETECT Questionnaire for the Distinction between Nociceptive and Neuropathic Pain

OBJECTIVE

This study aimed to validate Italian versions of Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) scale and Pain DETECT questionnaire (PD-Q) and evaluate the ability of these questionnaires to discriminate between nociceptive and neuropathic pain.

DESIGN

Multicenter prospective validation cohort study. Subjects and Setting. One hundred patients were included with a diagnosis formulated by a specialist in outpatient settings (50 affected by knee osteoarthritis as nociceptive pain and 50 affected by trigeminal or postherpetic neuralgia as neuropathic pain).

METHODS

The Italian versions of both questionnaires according to Italian cultural characteristics were performed according to the following steps: (1) translation of the questionnaires from English into Italian; (2) review by a bilingual individual for consistency; (3) proposed version after a mail round between experts; (4) backward translation; (5) comparison with the original English version by the experts; (6) approved version of the questionnaires. One hundred patients were enrolled and completed the two questionnaires administered by a specialist or blinded nursing staff, at the baseline and after 24/48 hours. Internal consistency, stability, validity, and discriminative power were analyzed.

RESULTS

Statistically significant differences were reported about the ability of both questionnaires to discriminate between patients affected by neuropathic or nociceptive pain. Internal consistency for the Italian version of the LANSS was 0.76, and for PD-Q, it was 0.80, assessed by Cronbach's α; LANSS showed a good test-retest reliability with an ICC of 0.76, and PD-Q showed a high test-retest reliability with an ICC of 0.96. For interrater reliability, there was a concordance rate of 83.3% between reference diagnosis and LANSS (Cohen's kappa = 0.67, CI 95% 0.52-0.75).

CONCLUSIONS

This study validated the Italian versions of LANSS and PD-Q as reliable instruments with good psychometric characteristics, for pain evaluation, discriminating between nociceptive and neuropathic pain. Our findings were similar to those observed in the original study. Furthermore, we have reported the test-retest reliability for both questionnaires, not addressed in original validation studies.

Complex regional pain syndrome - Autoimmune or functional neurologic syndrome

Complex regional pain syndrome (CRPS) purports to explain extremity pain accompanied by a variety of subjective complaints, including sensitivity to touch, fatigue, burning sensations, allodynia and signs consistent with voluntary immobilization, including skin changes, edema and trophic changes. By its own definition, CRPS pain is disproportionate to any inciting event or underlying pathology, which means that the syndrome describes non-anatomic and exaggerated symptoms. Although CRPS was coined in the early 1990s, physicians have described unexplained exaggerated pain for centuries. Before a small group of researchers assigned this historical phenomenon with the name CRPS, other physicians in various subspecialties investigated the existence of a common pathophysiologic mechanism but found none. The literature was searched for evidence of a reproducible pathologic mechanism for CRPS. Although some have suggested that CRPS is an autoimmune disease, there is a paucity of evidence to support this. While cytokines such as IL-1β, IL-6 and TNF-α have been detected during the early phases of CRPS, this cannot lead to the conclusion that CRPS is an autoimmune disease, nor that it is an autoinflammatory disorder. Moreover, intravenous immunoglobulin has showed inconsistent results in the treatment of CRPS. On the other hand, CRPS has been found to meet at least three out of four criteria of malingering, which was previously a DSM-IV diagnosis; and its diagnostic criteria are virtually identical to current DSM-5 Functional Neurological Disorder ("FND"), and proposed ICD-11 classification, which includes FND as a distinct neurological diagnosis apart from any psychiatric condition. Unfortunately, the creation of CPRS is not merely misguided brand marketing. It has serious social and health issues. At least in part, the existence of CRPS has led to the labeling of many patients with a diagnosis that allows the inappropriate use of invasive surgery, addictive opioids, and ketamine. The CRPS hypothesis also ignores the nature and purpose of pain, as a symptom of some organic or psychological process. Physicians have long encountered patients who voice symptoms that cannot be biologically explained. Terminology historically used to describe this phenomenon have been medically unexplained symptoms ("MUS"), hysterical, somatic, non-organic, psychogenic, conversion disorder, or dissociative symptoms. The more recent trend describes disorders where there is a functional, rather than structural cause of the symptoms, as "functional disorders." Physicians report high success treating functional neurological symptoms with reassurance, physiotherapy, and cognitive behavior therapy measured in terms of functional improvement. The CRPS label, however, neither leads to functional improvement in these patients nor resolution of symptoms. Under principles of evidence-based medicine, the CRPS label should be abandoned and the syndrome should simply be considered a subset of FNDs, specifically Functional Pain Disorder; and treated appropriately.

A randomized controlled trial on Aspirin and complex regional pain syndrome after radius fractures

Complex regional pain syndrome (CRPS) is often diagnosed in patients who are recovered with surgery or injury. CRPS is usually diagnosed in patients recovering from distal radius fractures. The aim of study was the effects of aspirin in prevention of the complex regional pain syndrome (CRPS) following a fracture of distal radius. In a double-blind, randomized controlled trial, 91 patients with unilateral extra-articular distal radius fractures were randomly allocated to receive either placebo (PLA) or 500 mg of aspirin (ASA) daily for 7 days. The effect of aspirin on the occurrence of CRPS was evaluated. The patients were assessed clinically and radiographically in the second, fourth and twelfth weeks by a physician who was unaware of the treatment allocation. Ninety-one patients (ASA, n=44; PLA, n=47) were enrolled in the study. The prevalence of CRPS in all patients was 16.5%. The prevalence of CRPS in the aspirin group was lower (13.6%) than the placebo group (19.1%), but this difference was not statistically significant. The only significant difference was the lower rate of regional osteoporosis seen in the radiographs of aspirin group. Mean age was significantly higher in the patients with CRPS. Also, comminuted distal radius fractures (A3-type) were significantly more common in the patients with CRPS. Administration of aspirin in patients with a distal radius fracture was associated with a lower incidence of CRPS, but, not statistically significant. Further investigations needs to be done with a larger sample size, longer follow-up period and multi-center design.

Visuo-tactile stimulation, but not type of movement, modulates pain during the vision of a moving virtual limb

Aim: Evidence has revealed a relationship between pain and the observation of limb movement, but it is unknown whether different types of movements have diverse modulating effects. In this immersive virtual reality study, we explored the effect of the vision of different virtual arm movements (arm vs wrist) on heat pain threshold of healthy participants. Patients & methods: 40 healthy participants underwent four conditions in virtual reality, while heat pain thresholds were measured. Visuo-tactile stimulation was used to attempt to modulate the feeling of virtual limb ownership while the participants kept their arms still. Results: Effects on pain threshold were present for type of stimulation but not type of movement. Conclusion: The type of observed movement does not appear to influence pain modulation, at least not during acute pain states.

Sympathetic dysfunction dermatitis in a revascularised upper extremity after near-total amputation - A case report and review of literature

Commonly reported complications after revascularisation or replantation of extremity are vascular thrombosis leading to complete or partial failure, bony non-union or malunion, joint stiffness and incomplete or abnormal sensory recovery. Sympathetic dysfunction dermatitis is an unreported complication after revascularisation or replantation surgery which results due to denervation of the extremity. We report a case of a young adult who developed eczematous dermatitis over the revascularised upper limb and discuss the role of sympathetic dysfunction in the development of these skin lesions. The patient was successfully treated with a short course of oral and topical steroids. Sympathetic dysfunction dermatitis is a rare form of skin eruptions occurring in the revascularised or replanted part of an extremity due to abnormal sympathetic function in the affected part.

Complex regional pain syndrome - False hopes and miscommunications

Complex regional pain syndrome (CRPS) has been considered to be an autoimmune disease and there have been clinical trials with intravenous immunoglobulin. Often the etiology of the so-called CRPS diagnosis cannot be discerned and there are no validated instruments that provide functional metrics. The term complex regional pain syndrome (CRPS), coined in 1994 to describe patients in whom the pain is out of proportion to the injury, was actually a diagnosis proposed during the American Civil War, but was originally known as causalgia. Physicians have long observed similar sensitivity and inflammatory symptoms following periods of immobilization and disuse, which generally resolve within a few months of remobilization. Following the original description, persistent disproportionate pain would come to be known under many other names until researchers theorized that it was related to dysfunction in the sympathetic nervous system, after which it acquired the moniker, Reflex Sympathetic Dystrophy ("RSD"). In the latter quarter of the twentieth century, after researchers failed to prove the connection between the pain and the sympathetic nervous system, a small cadre of physicians-without rigorous science-invented CRPS. This new descriptor, CRPS, has become not only a diagnosis without objective data but with proposed criteria involving ambiguous signs and symptoms with low specificity. It has led to patients being treated erroneously with sympatholytic drugs, with or without pharmaceutical or surgical blockade of the sympathetic nervous system, unwarranted use of ketamine infusions, inappropriate use of narcotics and nerve stimulation. Intravenous immunoglobulin infusions have not been effective in the treatment of chronic pain. The indiscriminate use of pain medications to treat subjective symptoms of unclear diagnoses can be a risk factor for opioid and analgesic misuse or abuse.

Effects of Stellate Ganglion Block on Analgesia Produced by Cervical Paravertebral Block as Established by Quantitative Sensory Testing: A Randomized Controlled Trial

Objective

To use quantitative sensory testing (QST) to assess whether a stellate ganglion block (SGB) modulates the analgesia induced by cervical paravertebral block (CPVB).

Design

A prospective double-blind randomized controlled trial.

Setting

Department of Anesthesia, Antwerp University Hospital, October 2011 to December 2015.

Subjects

Twenty-eight adults scheduled for arthroscopy of a nonfractured shoulder were enrolled.

Methods

Participants were randomly assigned to receive either single CPVB (5 mL of levobupivacaine 0.5%) or combined CPVB + SGB (5 mL and 3 mL of levobubivacaine 0.5%, respectively). The detection thresholds for cold/warm sensations and cold/heat pain were established using thermal QST on the C4-C7 dermatomes before local anesthetic infiltration and at 0.5, 6, 10, and 24 hours thereafter. Our primary outcome was the time course of QST thresholds for the different neurosensitive/nociceptive modalities. As secondary and tertiary outcomes, we evaluated the degree of motor block and the time to first administration of rescue analgesics.

Results

We randomized 20 patients. There were no significant differences in the detection thresholds for the neurosensitive/nociceptive modalities, motor block, or timing for rescue analgesics between the groups (P = 0.15-0.94). All patients with CPVB + SGB exhibited Horner's signs, whereas patients in the CPVB group did not exhibit these signs; however, this does not exclude sympathetic block.

Conclusions

We were unable to demonstrate any analgesic benefit of CPVB + SGB in arthroscopic shoulder surgery. It is therefore not unreasonable to suppose that pain from soft tissue injuries without bony lesions is transmitted mainly by somatic nerves with no or only minimal involvement of the sympathetic nervous system.

Autoinflammatory and autoimmune contributions to complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a highly enigmatic syndrome typically developing after injury or surgery to a limb. Severe pain and disability are common among those with chronic forms of this condition. Accumulating evidence suggests that CRPS may involve both autoinflammatory and autoimmune components. In this review article, evidence for dysfunction of both the innate and adaptive immune systems in CRPS is presented. Findings from human studies in which cytokines and other inflammatory mediators were measured in the skin of affected limbs are discussed. Additional results from studies of mediator levels in animal models are evaluated in this context. Similarly, the evidence from human, animal, and translational studies of the production of autoantibodies and the potential targets of those antibodies is reviewed. Compelling evidence of autoinflammation in skin and muscle of the affected limb has been collected from CRPS patients and laboratory animals. Cytokines including IL-1β, IL-6, TNFα, and others are reliably identified during the acute phases of the syndrome. More recently, autoimmune contributions have been suggested by the discovery of self-directed pain-promoting IgG and IgM antibodies in CRPS patients and model animals. Both the autoimmune and the autoinflammatory components of CRPS appear to be regulated by neuropeptide-containing peripheral nerve fibers and the sympathetic nervous system. While CRPS displays a complex neuroimmunological pathogenesis, therapeutic interventions could be designed targeting autoinflammation, autoimmunity, or the neural support for these phenomena.

Selective Fiber Degeneration in the Peripheral Nerve of a Patient With Severe Complex Regional Pain Syndrome

Aims: Complex regional pain syndrome (CRPS) is characterized by chronic debilitating pain disproportional to the inciting event and accompanied by motor, sensory, and autonomic disturbances. The pathophysiology of CRPS remains elusive. An exceptional case of severe CRPS leading to forearm amputation provided the opportunity to examine nerve histopathological features of the peripheral nerves.

Methods: A 35-year-old female developed CRPS secondary to low voltage electrical injury. The CRPS was refractory to medical therapy and led to functional loss of the forelimb, repeated cutaneous wound infections leading to hospitalization. Specifically, the patient had exhausted a targeted conservative pain management programme prior to forearm amputation. Radial, median, and ulnar nerve specimens were obtained from the amputated limb and analyzed by light and transmission electron microscopy (TEM).

Results: All samples showed features of selective myelinated nerve fiber degeneration (47–58% of fibers) on electron microscopy. Degenerating myelinated fibers were significantly larger than healthy fibers (p < 0.05), and corresponded to the larger Aα fibers (motor/proprioception) whilst smaller Aδ (pain/temperature) fibers were spared. Groups of small unmyelinated C fibers (Remak bundles) also showed evidence of degeneration in all samples.

Conclusions: We are the first to show large fiber degeneration in CRPS using TEM. Degeneration of Aα fibers may lead to an imbalance in nerve signaling, inappropriately triggering the smaller healthy Aδ fibers, which transmit pain and temperature. These findings suggest peripheral nerve degeneration may play a key role in CRPS. Improved knowledge of pathogenesis will help develop more targeted treatments.

Complex Regional Pain Syndrome Type 1: Diagnosis and Management

Diagnosis of Complex regional pain syndrome (CRPS) is made primarily on a clinical basis, and no specific test is known to confirm or exclude CRPS diagnosis. That is, there aren’t specific diagnostic tools and instrumental tests are made only for identifying an etiology at the basis of the CRPS. Numerous therapeutic methods have been introduced, but none have shown definitive results. When symptoms persist, patients experience permanent impairment and disability. Therefore, early recognition of CRPS, along with proper treatment, is important for minimizing permanent loss of function. As there is no gold standard test for CRPS, several clinical diagnostic criteria have been introduced and applied in various studies. However, to date, no formal or standardized diagnostic criteria for CRPS have been widely accepted. However, the Budapest diagnostic criteria have recently increased in popularity and are frequently used in scientific studies. The goal for management of CRPS is the return of normal limb function. No specific technique has been shown to prevent CRPS following surgery, but avoidance of prolonged immobilization may be important. Therefore, initiating early post-surgical rehabilitation, where possible, is important. A multidisciplinary approach would seem to be optimal, above all things objectives of physical and occupational therapy are fulfilled with combination pharmacotherapy due to provide pain relief to facilitate physical rehabilitation. Future research using large randomized controlled trials should focus on collecting strong evidence for the etiology of CRPS, testing pharmacological effects, and determining appropriate combination treatment strategies.

Complex Regional Pain Syndrome following an Episode of Herpes Zoster: A Case Report

INTRODUCTION

Complex regional pain syndrome (CRPS) is characterized by searing pain, hyperalgesia, edema, allodynia, and skin changes. CRPS may be difficult to diagnose and to treat given poorly understood mechanisms as well as its presentation of symptoms that may mimic common conditions such as joint stiffness in this condition as well as rheumatoid arthritis.

CASE REPORT

A 71-year-old female presented to our clinic post shingles of the right upper extremity. We diagnosed her with CRPS based on the Budapest diagnostic criteria and the clinical findings of pain and decreased the range of motion along with edema, hypersensitivity, discoloration and allodynia of the right thumb and index finger. She was treated with vitamin C as well as gabapentin and physical therapy. The patient was unable to go consistently to physical therapy due to insurance limitations, and we found no clinical benefit of vitamin C in reducing her symptoms. She was lost to follow-up during her treatment but re-emerged at 21 months. At that time she reported, she was largely unchanged in regards to her right-hand symptoms but did believe the gabapentin was helpful and still continued to take 300 mg daily.

CONCLUSION

This case report highlights the usefulness of the Budapest diagnostic criteria to make the diagnosis of CRPS when associated with shingles, which can cause long-term pain and mimic some findings. Prompt diagnosis is important, as recovery typically extends beyond 6 months; our patient still reported continued symptoms at 21 months post initial presentation. Our primary treatment plan was physical therapy, which she discontinued due to insurance limitations. We recommend that patients, physicians, and third-party payers work together to extend access to physical therapy. More investigation is warranted regarding symptomatic treatment, as we found limited clinical benefit of gabapentin and vitamin C.

Bone pain mechanism in osteoporosis: a narrative review

Bone pain in elderly people dramatically affects their quality of life, with osteoporosis being the leading cause of skeletal related events. Peripheral and central mechanisms are involved in the pathogenesis of the nervous system sensitization. Osteoporosis in the elderly has been associated with increased density of bone sensory nerve fibers and their pathological modifications, together with an over-expression of nociceptors sensitized by the lowering pH due to the osteoclastic activity. The activation of N-methyl-D-aspartate (NMDA) receptors and the microglia, as a response to a range of pathological conditions, represent the leading cause of central sensitization. Unfortunately, osteoporosis is named the "silent thief" because it manifests with painful manifestation only when a fracture occurs. In the management of patients suffering from bone pain, both the nociceptive and the neuropathic component of chronic pain should be considered in the selection of the analgesic treatment.

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.

Sensorimotor dysfunction after limb fracture - An exploratory study

BACKGROUND

Chronic pain is often associated with sensorimotor dysfunction but little is known about the early impact of limb fracture on sensory and motor performance. This exploratory study sought to assess these changes in patients with recent wrist and ankle fractures. A secondary aim was to determine the incidence of Complex Regional Pain Syndrome (CRPS) and its clinical features.

METHODS

Fifty-three patients at a UK fracture centre underwent Quantitative Sensory Testing (QST), Motor Imagery (MI) and Body Perception Disturbance (BPD) assessments ≤5 weeks post-fracture (Time 1). Subjective evaluation of recovery and clinical examination for CRPS was conducted 5 weeks later (Time 2, 50 patients). Patient-reported outcomes of pain, psychological distress and limb function were collected at Times 1 and 2, and 6 months after T1 (Time 3, 36 patients, postal questionnaire).

RESULTS

Quantitative sensory testing at Time 1 demonstrated cold and pressure-pain hyperalgesia in the fractured limb compared to the non-fractured side (p < 0.05). Imagined movements were reported as significantly more difficult to perform on the fractured side (p < 0.001). There was evidence of BPD in the fractured limb, similar to that found in CRPS. The incidence of CRPS was 9.4%; however, individual signs and symptoms of the condition were commonly present (70% reported ≥ one symptom). Only 33% of patients reported to being 'back to normal' 6 months after fracture with 34% reporting ongoing pain.

CONCLUSIONS

Limb fracture is associated with changes in pain perceptions, motor planning, and disruption to body perception. Signs and symptoms of CRPS, ongoing pain and delayed recovery post-fracture are common. WHAT DOES THIS STUDY ADD?: In the immediate post-fracture period: Body perception disturbance is reported in the fractured limb. Imagined movements of the fractured limb are less vivid and associated with pain This study contributes to the incidence literature on CRPS.

New Concepts in Complex Regional Pain Syndrome

Despite the severe pain and disability associated with complex regional pain syndrome (CRPS), the lack of understanding of the pathophysiological mechanisms supporting this enigmatic condition prevents the rational design of new therapies, a situation that is frustrating to both the physician and the patient. The review highlights some of the mechanisms thought to be involved in the pathophysiology of CRPS in preclinical models and CRPS patients, with the ultimate goal that understanding these mechanisms will lead to the design of efficacious, mechanism-based treatments available to the clinic.

Acute versus chronic phase mechanisms in a rat model of CRPS

Background

Tibia fracture followed by cast immobilization in rats evokes nociceptive, vascular, epidermal, and bone changes resembling complex regional pain syndrome (CRPS). In most cases, CRPS has three stages. Over time, this acute picture, allodynia, warmth, and edema observed at 4 weeks, gives way to a cold, dystrophic but still painful limb. In the acute phase (at 4 weeks post fracture), cutaneous immunological and NK1-receptor signaling mechanisms underlying CRPS have been discovered; however, the mechanisms responsible for the chronic phase are still unknown. The purpose of this study is to understand the mechanisms responsible for the chronic phases of CRPS (at 16 weeks post fracture) at both the peripheral and central levels.

Methods

We used rat tibial fracture/cast immobilization model of CRPS to study molecular, vascular, and nociceptive changes at 4 and 16 weeks post fracture. Immunoassays and Western blotting were carried out to monitor changes in inflammatory response and NK1-receptor signaling in the skin and spinal cord. Skin temperature and thickness were measured to elucidate vascular changes, whereas von Frey testing and unweighting were carried out to study nociceptive changes. All data were analyzed by one-way analysis of variance (ANOVA) followed by Neuman-Keuls multiple comparison test to compare among all cohorts.

Results

In the acute phase (at 4 weeks post fracture), hindpaw allodynia, unweighting, warmth, edema, and/or epidermal thickening were observed among 90 % fracture rats, though by 16 weeks (chronic phase), only the nociceptive changes persisted. The expression of the neuropeptide signaling molecule substance P (SP), NK1 receptor, inflammatory mediators TNFα, IL-1β, and IL-6 and nerve growth factor (NGF) were elevated at 4 weeks in sciatic nerve and/or skin, returning to normal levels by 16 weeks post fracture. The systemic administration of a peripherally restricted IL-1 receptor antagonist (anakinra) or of anti-NGF inhibited nociceptive behaviors at 4 weeks but not 16 weeks. However, spinal levels of NK1 receptor, TNFα, IL-1β, and NGF were elevated at 4 and 16 weeks, and intrathecal injection of an NK1-receptor antagonist (LY303870), anakinra, or anti-NGF each reduced nociceptive behaviors at both 4 and 16 weeks.

Conclusions

These results demonstrate that tibia fracture and immobilization cause peripheral changes in neuropeptide signaling and inflammatory mediator production acutely, but central spinal changes may be more important for the persistent nociceptive changes in this CRPS model.

Terminology, criteria, and definitions in complex regional pain syndrome: challenges and solutions

Complex regional pain syndrome has long been recognized as a severe and high impact chronic pain disorder. However, the condition has historically been difficult to define and classify and little attention has been given to where complex regional pain syndrome sits within other apparently similar chronic pain disorders, such as fibromyalgia and regional pain syndrome. In this review challenges in regard to nomenclature, definitions, and classification of complex regional pain syndrome are reviewed and suggestions are provided about future directions.

Complex regional pain syndrome-significant progress in understanding

Research into complex regional pain syndrome (CRPS) has made significant progress. First, there was the implementation of the official IASP "Budapest" diagnostic criteria. It would be desirable to also define exclusion and outcome criteria that should be reported in studies. The next step was to recognize the complex pathophysiology. After trauma, some inflammation is physiological; in acute CRPS, this inflammation persists for months. There is an abundance of inflammatory and a lack of anti-inflammatory mediators. This proinflammatory network (cytokines and probably also other mediators) sensitizes the peripheral and spinal nociceptive system, it facilitates the release of neuropeptides from nociceptors inducing the visible signs of inflammation, and it stimulates bone cell or fibroblast proliferation, and endothelial dysfunction leading to vascular changes. Trauma may also expose nervous system structures to the immune system and triggers autoantibodies binding to adreno- and acetylcholine receptors. In an individual time frame, the pain in this inflammatory phase pushes the transition into "centralized" CRPS, which is dominated by neuronal plasticity and reorganization. Sensory-motor integration becomes disturbed, leading to a loss of motor function; the body representation is distorted leading to numbness and autonomic disturbances. In an attempt to avoid pain, patients neglect their limb and learn maladaptive nonuse. The final step will be to assess large cohorts and to analyze these data together with data from public resources using a bioinformatics approach. We could then develop diagnostic toolboxes for individual pathophysiology and select focused treatments or develop new ones.

Algodystrophy (CRPS) in minor orthopedic surgery

Algodystrophy or Chronic Regional Pain Syndrome (CRPS) is a painful disorder that develops especially at upper or lower extremities of the limbs after a fracture. This syndrome is probably due to bone microvascular changes with subsequent sympathetic nervous system involvement. The pain that characterizes CRPS is spontaneous, disproportionate to the traumatic event and is associated with hyperalgesia, and a variety of autonomic and trophic disorders. This condition has a variable incidence up to 37% of the cases, increasing along with the severity of the fracture. CRPS has a higher chance of developing in women, in older individuals, in smokers, and in patients with reduced bone strength. Early diagnosis is associated with remission in 80-90% of cases. Since the typical onset of the disease is insidious over 2 weeks after surgery, a diagnostic and therapeutic delay may occur. These are the major causes of a high percentage of chronic and disabling complications leading to impaired functional outcomes. In the acute or subacute phase, infusion of bisphosphonates has proven to be the first-choice of treatment with a high percentage of remissions. Moreover, it has been suggested the utility of vitamin C in prevention of CRPS. Furthermore, in the chronic phase electroanalgesia seems to provide promising results.

Exuberant sprouting of sensory and sympathetic nerve fibers in nonhealed bone fractures and the generation and maintenance of chronic skeletal pain

Skeletal injury is a leading cause of chronic pain and long-term disability worldwide. While most acute skeletal pain can be effectively managed with nonsteroidal anti-inflammatory drugs and opiates, chronic skeletal pain is more difficult to control using these same therapy regimens. One possibility as to why chronic skeletal pain is more difficult to manage over time is that there may be nerve sprouting in nonhealed areas of the skeleton that normally receive little (mineralized bone) to no (articular cartilage) innervation. If such ectopic sprouting did occur, it could result in normally nonnoxious loading of the skeleton being perceived as noxious and/or the generation of a neuropathic pain state. To explore this possibility, a mouse model of skeletal pain was generated by inducing a closed fracture of the femur. Examined animals had comminuted fractures and did not fully heal even at 90+days post fracture. In all mice with nonhealed fractures, exuberant sensory and sympathetic nerve sprouting, an increase in the density of nerve fibers, and the formation of neuroma-like structures near the fracture site were observed. Additionally, all of these animals exhibited significant pain behaviors upon palpation of the nonhealed fracture site. In contrast, sprouting of sensory and sympathetic nerve fibers or significant palpation-induced pain behaviors was never observed in naïve animals. Understanding what drives this ectopic nerve sprouting and the role it plays in skeletal pain may allow a better understanding and treatment of this currently difficult-to-control pain state.

Pathological mechanism of musculoskeletal manifestations associated with CRPS type II: an animal study

Patients with complex regional pain syndrome (CRPS) often complain of abnormal sensations beyond the affected body part, but causes of this spread of musculoskeletal manifestations into contiguous areas remain unclear. In addition, immobilization can predispose to the development of CRPS. We examined functional, biochemical, and histological alterations in affected parts, including contiguous zones, using an animal model. Ten-week-old male Wistar rats were assigned to 5 groups: a normal group receiving no treatment, a sham operation group with surgical exploration, an immobilization group with surgical exploration plus internal knee joint immobilization, a surgical neuropathy group prepared by spinal nerve ligation (SNL) of the left L5 nerve root, and a surgical neuropathy+immobilization group with simultaneous SNL and knee joint immobilization. Mechanical allodynia and knee contracture were compared between groups, and tissues were harvested for histological assessments and gene and protein expression analyses. Neither surgical procedures nor immobilization induced detectable mechanical sensitivity. However, the addition of nerve injury resulted in detectable mechanical allodynia, and immobilization not only accelerated hyperalgesia, but also resulted in muscle fibrosis. Nerve growth factor (NGF) and other mediators of neurogenic inflammation were highly expressed not only in denervated muscles, but also in innervated muscles in contiguous areas, suggesting the spread of NGF production beyond the myotome of the injured nerve. Transforming growth factor β was involved in the development of contracture in CRPS. These findings imply that neuroinflammatory components play major roles in the progression and dispersion of both sensory pathologies and pathologies that are exacerbated by immobilization.

Mast cells: versatile gatekeepers of pain

Mast cells are important first responders in protective pain responses that provoke withdrawal from intense, noxious environmental stimuli, in part because of their sentinel location in tissue-environment interfaces. In chronic pain disorders, the proximity of mast cells to nerves potentiates critical molecular cross-talk between these two cell types that results in their synergistic contribution to the initiation and propagation of long-term changes in pain responses via intricate signal networks of neurotransmitters, cytokines and adhesion molecules. Both in rodent models of inflammatory pain and chronic pain disorders, as well as in increasing evidence from the clinic, it is abundantly clear that understanding the mast cell-mediated mechanisms underlying protective and maladaptive pain cascades will lead to improved understanding of mast cell biology as well as the development of novel, targeted therapies for the treatment and management of debilitating pain conditions.

The neurobiology of skeletal pain

Disorders of the skeleton are one of the most common causes of chronic pain and long-term physical disability in the world. Chronic skeletal pain is caused by a remarkably diverse group of conditions including trauma-induced fracture, osteoarthritis, osteoporosis, low back pain, orthopedic procedures, celiac disease, sickle cell disease and bone cancer. While these disorders are diverse, what they share in common is that when chronic skeletal pain occurs in these disorders, there are currently few therapies that can fully control the pain without significant unwanted side effects. In this review we focus on recent advances in our knowledge concerning the unique population of primary afferent sensory nerve fibers that innervate the skeleton, the nociceptive and neuropathic mechanisms that are involved in driving skeletal pain, and the neurochemical and structural changes that can occur in sensory and sympathetic nerve fibers and the CNS in chronic skeletal pain. We also discuss therapies targeting nerve growth factor or sclerostin for treating skeletal pain. These therapies have provided unique insight into the factors that drive skeletal pain and the structural decline that occurs in the aging skeleton. We conclude by discussing how these advances have changed our understanding and potentially the therapeutic options for treating and/or preventing chronic pain in the injured, diseased and aged skeleton.

Acute and chronic phases of complex regional pain syndrome in mice are accompanied by distinct transcriptional changes in the spinal cord

BACKGROUND

CRPS is a painful, debilitating, and often-chronic condition characterized by various sensory, motor, and vascular disturbances. Despite many years of study, current treatments are limited by our understanding of the underlying mechanisms. Little is known on the molecular level concerning changes in gene expression supporting the nociceptive sensitization commonly observed in CRPS limbs, or how those changes might evolve over time.

RESULTS

We used a well-characterized mouse tibial fracture/cast immobilization model of CRPS to study molecular, vascular and nociceptive changes. We observed that the acute (3 weeks after fracture) and chronic (7 weeks after fracture) phases of CRPS-like changes in our model were accompanied by unique alterations in spinal gene expression corresponding to distinct canonical pathways. For the acute phase, top regulated pathways were: chemokine signaling, glycogen degradation, and cAMP-mediated signaling; while for the chronic phase, the associated pathways were: coagulation system, granzyme A signaling, and aryl hydrocarbon receptor signaling. We then focused on the role of CcL2, a chemokine that we showed to be upregulated at the mRNA and protein levels in spinal cord tissue in our model. We confirmed its association with the nociceptive sensitization displayed in this model by demonstrating that the spinal but not peripheral administration of a CCR2 antagonist (RS504393) in CRPS animals could decrease mechanical allodynia. The spinal administration of CcL2 itself resulted in mechanical allodynia in control mice.

CONCLUSIONS

Our data provide a global look at the transcriptional changes in the spinal cord that accompany the acute and chronic phases of CRPS as modeled in mice. Furthermore, it follows up on one of the top-regulated genes coding for CcL2 and validates its role in regulating nociception in the fracture/cast model of CRPS.