Bone loss in the contralateral asymptomatic hand in patients with complex regional pain syndrome type 1

Exploring neuronal mechanisms of osteosarcopenia in older adults

Until recently, research on the pathogenesis and treatment of osteoporosis and sarcopenia has primarily focused on local and systemic humoral mechanisms, often overlooking neuronal mechanisms. However, there is a growing body of literature on the neuronal regulation of bone and skeletal muscle structure and function, which may provide insights into the pathogenesis of osteosarcopenia. This review aims to integrate these neuronal regulatory mechanisms to form a comprehensive understanding and inspire future research that could uncover novel strategies for preventing and treating osteosarcopenia. Specifically, the review explores the functional adaptation of weight-bearing bone to mechanical loading throughout evolutionary development, from Wolff's law and Frost's mechanostat theory to the mosaic hypothesis, which emphasizes neuronal regulation. The recently introduced bone osteoregulation reflex points to the importance of the osteocytic mechanoreceptive network as a receptor in this neuronal regulation mechanism. Finally, the review focuses on the bone myoregulation reflex, which is known as a mechanism by which bone loading regulates muscle functions neuronally. Considering the ageing-related regressive changes in the nerve fibres that provide both structural and functional regulation in bone and skeletal muscle tissue and the bone and muscle tissues they innervate, it is suggested that neuronal mechanisms might play a central role in explaining osteosarcopenia in older adults.

Exploring the Differences Between Dominant and Nondominant Feet and Hands Bone Mineral Density

The assessment of regional bone mineral density (BMD) has proved to be useful for illustrating the impact of focal bone demineralization diseases on bone mass. In these scenario, a common practice is to compare the affected limb with the contralateral limb. However, there are no studies comparing BMD differences between dominant vs nondominant limbs at these sites. In addition, most studies have assessed BMD in specific ROIs (regions of interests) instead of in the whole limb. The purpose of our study was to compare the BMD of dominant vs nondominant hands and feet in healthy individuals, using both the whole limb software and specific ROIs. We performed a cross-sectional analysis on untrained women and men over 18 years of age who volunteered to participate. BMD (g/cm²), bone area (cm²) and BMC (bone mineral content) (g) were measured by Lunar Prodigy DXA (GE Healthcare, Madison, WI, USA), using 2 different approaches: whole limb/region software and specific ROIs. A total of 42 subjects (11 men and 31 women) were included. Mean age was 44.19 ± 10.49 years. BMD was greater in the dominant in comparison with the nondominant hand. The difference was 0.014 (95% CI, 0.009-0.018) for the whole hand BMD, 0.023 (95% CI, 0.003-0.044) for ROI 1, and 0.016 (95% CI, 0.003-0.029) for ROI 2. No significant differences were found between dominant and nondominant foot BMD, using the whole limb software and specific ROIs. To our knowledge, this is the first study to explore the differences in BMD, bone area and BMC in terms of limb dominance, supporting the usefulness of DXA as an accurate and objective complementary diagnostic or follow-up tool in focal bone demineralization diseases.

Prognostic Value of Pain Sensitization During Early Recovery After Distal Radius Fracture in Complex Regional Pain Syndrome

OBJECTIVE

To evaluate the influence of pain sensitization in the early recovery of distal radius fractures (DRFs) on the occurrence and prognosis of complex regional pain syndrome (CRPS) type I.

METHODS

We enrolled 58 patients who were diagnosed with CRPS I based on Budapest criteria within six months after sustaining DRF; they were age- and gender-matched with 58 patients with DRF who did not have CRPS I. We commonly measured patients' pressure pain thresholds (PPTs) in the forearm and administered a Pain Sensitivity Questionnaire (PSQ) when patients complained of pain with numeric rating scale ≥4 at three-month follow-up. Participants were followed up three, six, and 12 months after injury, and the symptoms and sign of CRPS were evaluated at each follow-up.

RESULTS

Patients with CRPS I were more likely to have sustained high-energy injuries, had severe fractures, and had significantly higher PSQ scores and lower PPTs than the age- and gender-matched controls. At 12 months after injury, CRPS symptoms improved in 52% (30/58) of patients who had been diagnosed with CRPS I at three months after injury. The initial degree of pain sensitization and high-energy injury were associated with persistence of CRPS symptoms up to 12 months after initial injury.

CONCLUSIONS

Patients with CRPS I after DRF exhibited significantly higher pain sensitization in the early post-trauma period, and the degree of initial pain sensitization and high-energy injuries were associated with prolonged CRPS I signs and symptoms up to one year after initial injury.

The Rodent Tibia Fracture Model: A Critical Review and Comparison With the Complex Regional Pain Syndrome Literature

Distal limb fracture is the most common cause of complex regional pain syndrome (CRPS), thus the rodent tibia fracture model (TFM) was developed to study CRPS pathogenesis. This comprehensive review summarizes the published TFM research and compares these experimental results with the CRPS literature. The TFM generated spontaneous and evoked pain behaviors, inflammatory symptoms (edema, warmth), and trophic changes (skin thickening, osteoporosis) resembling symptoms in early CRPS. Neuropeptides, inflammatory cytokines, and nerve growth factor (NGF) have been linked to pain behaviors, inflammation, and trophic changes in the TFM model and proliferating keratinocytes were identified as the primary source of cutaneous cytokines and NGF. Tibia fracture also activated spinal glia and upregulated spinal neuropeptide, cytokine, and NGF expression, and in the brain it changed dendritic architecture. B cell-expressed immunoglobulin M antibodies also contributed to pain behavior, indicating a role for adaptive immunity. These results modeled many findings in early CRPS, but significant differences were also noted.

PERSPECTIVE

Multiple neuroimmune signaling mechanisms contribute to the pain, inflammation, and trophic changes observed in the injured limb of the rodent TFM. This model replicates many of the symptoms, signs, and pathophysiology of early CRPS, but most post-fracture changes resolve within 5 months and may not contribute to perpetuating chronic CRPS.

The effect of a previous created distal arteriovenous-fistula on radial bone DXA measurements in prevalent renal transplant recipients

Background

Accelerated bone loss occurs rapidly following renal transplantation due to intensive immunosuppression and persistent hyperparathyroidism. In renal transplant recipients (RTRs) due to the hyperparathyroidism the non-dominant forearm is often utilized as a peripheral measurement site for dual-energy x-ray absorptiometry (DXA) measurements. The forearm is also the site of previous created distal arteriovenous fistulas (AVF). Although AVF remain patent long after successful transplantation, there are no data available concerning their impact on radial bone DXA measurements.

Methods

In this cross-sectional study we performed DXA in 40 RTRs with preexisting distal AVF (RTRs-AVF) to assess areal bone mineral density (aBMD) differences between both forearms (three areas) and compared our findings to patients with chronic kidney disease (CKD, n = 40), pre-emptive RTRs (RTRs-pre, n = 15) and healthy volunteers (n = 20). In addition, we assessed relevant demographic, biochemical and clinical aspects.

Results

We found a marked radial asymmetry between the forearms in RTRs with preexisting AVF. The radial aBMD at the distal AVF forearm was lower compared to the contralateral forearm, resulting in significant differences for all three areas analyzed: the Rad-1/3: median (interquartile range) in g/cm², Rad-1/3: 0.760 (0.641–0.804) vs. 0.742 (0.642, 0.794), p = 0.016; ultradistal radius, Rad-UD: 0.433 (0.392–0.507) vs. 0.420 (0.356, 0.475), p = 0.004; and total radius, Rad-total: 0.603 (0.518, 0.655) vs. 0.599 (0.504, 0.642), p = 0.001). No such asymmetries were observed in any other groups. Lower aBMD in AVF forearm subregions resulted in misclassification of osteoporosis.

Conclusions

In renal transplant recipients, a previously created distal fistula may exert a negative impact on the radial bone leading to significant site-to-site aBMD differences, which can result in diagnostic misclassifications.

Bisphosphonates Inhibit Pain, Bone Loss, and Inflammation in a Rat Tibia Fracture Model of Complex Regional Pain Syndrome

BACKGROUND

Bisphosphonates are used to prevent the bone loss and fractures associated with osteoporosis, bone metastases, multiple myeloma, and osteogenesis deformans. Distal limb fractures cause regional bone loss with cutaneous inflammation and pain in the injured limb that can develop into complex regional pain syndrome (CRPS). Clinical trials have reported that antiresorptive bisphosphonates can prevent fracture-induced bone loss, inhibit serum inflammatory cytokine levels, and alleviate CRPS pain. Previously, we observed that the inhibition of inflammatory cytokines or adaptive immune responses attenuated the development of pain behavior in a rat fracture model of CRPS, and we hypothesized that bisphosphonates could prevent pain behavior, trabecular bone loss, postfracture cutaneous cytokine upregulation, and adaptive immune responses in this CRPS model.

METHODS

Rats underwent tibia fracture and cast immobilization for 4 weeks and were chronically administered either subcutaneously perfused alendronate or oral zoledronate. Behavioral measurements included hindpaw von Frey allodynia, unweighting, warmth, and edema. Bone microarchitecture was measured by microcomputed tomography, and bone cellular activity was evaluated by static and dynamic histomorphometry. Spinal cord Fos immunostaining was performed, and skin cytokine (tumor necrosis factor, interleukin [IL]-1, IL-6) and nerve growth factor (NGF) levels were determined by enzyme immunoassay. Skin and sciatic nerve immunoglobulin levels were determined by enzyme immunoassay.

RESULTS

Rats with tibia fractures developed hindpaw allodynia, unweighting, warmth, and edema, increased spinal Fos expression and trabecular bone loss in the lumbar vertebra and bilateral distal femurs as measured by microcomputed tomography, increased trabecular bone resorption and osteoclast surface with decreased bone formation rates, increased cutaneous inflammatory cytokine and NGF expression, and elevated immunocomplex deposition in skin and nerve. Alendronate (60 μg/kg/d subcutaneously [s.c.]) or zoledronate (3 mg/kg/d orally) treatment for 28 days, started at the time of fracture, completely inhibited the development of hindpaw allodynia and reduced hindpaw unweighting by 44% ± 13% and 58% ± 5%, respectively. Orally administered zoledronate (3 mg/kg/d for 21 days) treatment also completely reversed established allodynia and unweighting when started at 4 weeks postfracture. Histomorphometric and microcomputed tomography analysis demonstrated that both the 3 and 60 μg/kg/d alendronate treatments reversed trabecular bone loss (an 88% ± 25% and 188% ± 39% increase in the ipsilateral distal femur BV/TV, respectively) and blocked the increase in osteoclast numbers and erosion surface observed in bilateral distal femurs and in L5 vertebra of the fracture rats. Alendronate treatment inhibited fracture-induced increases in hindpaw inflammatory mediators, reducing postfracture levels of tumor necrosis factor by 43% ± 9%, IL-1 by 60% ± 9%, IL-6 by 56% ± 14%, and NGF by 37% ± 14%, but had no effect on increased spinal cord Fos expression, or skin and sciatic nerve immunocomplex deposition.

CONCLUSIONS

Collectively, these results indicate that bisphosphonate therapy inhibits pain, osteoclast activation, trabecular bone loss, and cutaneous inflammation in the rat fracture model of CRPS, data supporting the hypothesis that bisphosphonate therapy can provide effective multimodal treatment for CRPS.

Effect of arteriovenous fistula and usage of arm with fistula on bone mineral density in hemodialysis patients

We aimed to determine the incidence of osteoporosis in hemodialysis patients, to evaluate the differences due to arteriovenous fistula on bone mineral density (BMD) and to investigate whether usage of arm with fistula has an effect on BMD. In this cross-sectional study, 96 patients with chronic renal disease undergone to dialysis were included. Place of fistula (radial and brachial) and dominant hand were recorded. All patients were asked to complete Likert's scale in order to determine the frequency of their usage of arm with fistula. Patients were assigned in two groups: age >51 and < 50 years. Age-matched control group included 60 subjects. BMD measurements were done on lumbar vertebra, femur and both forearms. BMD measurement of proximal femur and total radius were significantly lower in patients >50 years compared to healthy controls and bone density measurement of lumbar vertebra, proximal femur, 1/3 distal and total radius were significantly lower in patients < 50 years compared to healthy controls (p < 0.05). BMD measurement was significantly lower in arms with fistula, especially with radial fistula, compared to both arms without fistula and healthy controls (p < 0.05). When all patients were evaluated, BMD scores were lowering by increasing age, duration of dialysis and fistula and decreasing usage of arm with fistula. BMD in hemodialysis patients is lower than normal population. BMD of arm with fistula is lower than arm without fistula and healthy controls. Both radial and brachial fistula affect negatively ipsilateral BMD. Movement of arm with fistula has positive effects on BMD.

Complex regional pain syndrome in a competitive athlete and regional osteoporosis assessed by dual-energy X-ray absorptiometry: a case report

Introduction

Dual-energy X-ray absorptiometry is rarely utilized in the clinical care of patients with complex regional pain syndrome, but may be useful for the non-invasive determination of regional bone fragility and fracture risk, as well as muscular atrophy and regional body composition. This is the first report in the literature of complex regional pain syndrome and musculoskeletal co-morbidities in an athlete, and is the first to focus on dual-energy X-ray absorptiometry for the clinical assessment of complex regional pain syndrome.

Case presentation

In this report, we describe the case of a 29-year-old Caucasian man with type 1 complex regional pain syndrome. His body mass index was 29.4kg/m² at the time of presentation. Despite severe complex regional pain syndrome in the left limb and long term use of a wheelchair, the patient participated in high-performance powerlifting. Dual-energy X-ray absorptiometry revealed marked unilateral differences in bone strength and lean mass between the affected regions and the contralateral regions. Low bone mineral density for age was found in the left hip, with Z-scores ranging from −2.2 to −3.0, and the patient had previously suffered two fractures. Bone density Z-scores in the right hip and legs were normal.

Conclusions

Dual-energy X-ray absorptiometry is a valuable tool for the clinical investigation of musculoskeletal health in patients with complex regional pain syndrome. Regional osteoporosis in complex regional pain syndrome patients is complicated and should be investigated and monitored. Physical activity is possible for some complex regional pain syndrome patients, depending on the type of exercise and the region affected, and it may protect bone density and strength at non affected skeletal sites.

Complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a challenging pain condition for doctors and patients, with a natural history characterized by chronicity and relapses that can result in significant disability. CRPS is difficult to diagnose and treat, and requires close follow-up to ensure that progress is being made. Early diagnosis and treatment are required to prevent a long-standing or permanent disability. Clinical features such as spontaneous pain, edema, hyperalgesia, temperature or sudomotor changes, motor function abnormality, and autonomic changes are the hallmark of this disease. The treatment of CRPS remains controversial, and includes medications, physical therapy, regional anesthesia, and neuromodulation.

A hypothesis for the cause of complex regional pain syndrome-type I (reflex sympathetic dystrophy): pain due to deep-tissue microvascular pathology

Complex regional pain syndrome-type I (CRPS-I; reflex sympathetic dystrophy) is a chronic pain condition that usually follows a deep-tissue injury such as fracture or sprain. The cause of the pain is unknown. We have developed an animal model (chronic post-ischemia pain) that creates CRPS-I-like symptomatology. The model is produced by occluding the blood flow to one hind paw for 3 hours under general anesthesia. Following reperfusion, the treated hind paw exhibits an initial phase of hyperemia and edema. This is followed by mechano-hyperalgesia, mechano-allodynia, and cold-allodynia that lasted for at least 1 month. Light microscopic analyses and electron microscopic analyses of the nerves at the site of the tourniquet show that the majority of these animals have no sign of injury to myelinated or unmyelinated axons. However, electron microscopy shows that the ischemia-reperfusion injury produces a microvascular injury, slow-flow/no-reflow, in the capillaries of the hind paw muscle and digital nerves. We propose that the slow-flow/no-reflow phenomenon initiates and maintains deep-tissue ischemia and inflammation, leading to the activation of muscle nociceptors, and the ectopic activation of sensory afferent axons due to endoneurial ischemia and inflammation. These data, and a large body of clinical evidence, suggest that in at least a subset of CRPS-I patients, the fundamental cause of the abnormal pain sensations is ischemia and inflammation due to microvascular pathology in deep tissues, leading to a combination of inflammatory and neuropathic pain processes. Moreover, we suggest a unifying idea that relates the pathogenesis of CRPS-I to that of CRPS-II. Lastly, our hypothesis suggests that the role of the sympathetic nervous system in CRPS-I is a factor that is not fundamentally causative, but may have an important contributory role in early-stage disease.

Arteriovenous fistula affects bone mineral density measurements in end-stage renal failure patients

BACKGROUND AND OBJECTIVES

Hemodialysis needs an arteriovenous fistula (AVF) that may influence the structure and growth of nearby bone and affect bone mass measurement. The study analyzed the effect of AVF in the assessment of forearm bone mineral density (BMD) measured by dual energy x-ray absorptiometry (DXA) and examined its influence on the final diagnosis of osteoporosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Forty patients (52 +/- 18 yr) in hemodialysis program (12 +/- 8 yr) with permeable AVF in forearm were included. Patients were divided in two groups (over and under 50 yr). BMD of both forearms(three areas), lumbar spine, and femur was measured by DXA. Forearm measurements in each arm were compared. Patients were diagnosed as normal only if all territories were considered nonpathologic and osteoporosis/osteopenia was determined by the lowest score found.

RESULTS

Ten patients were excluded and 30 patients were analyzed. BMD in the forearm with AVF was significantly lower than that observed in the contralateral forearm in both groups of patients and in all forearm areas analyzed. When only lumbar spine and femur measurements were considered, 70% of patients were nonpathologic and 30% were osteoporotic. However, inclusion of AVF forearm classified 63% as osteoporotic and a further 27% as osteopenic, leaving only 10% as nonpathologic.

CONCLUSIONS

Forearm AVF affects BMD measurements by decreasing their values in patients with end-stage renal failure. This may produce an overdiagnosis of osteoporosis, which should be taken into account when evaluating patients of this type.

Clinical expression profiles of complex regional pain syndrome, fibromyalgia and a-specific repetitive strain injury: More common denominators than pain?

PURPOSE

To systematically evaluate and compare the clinical manifestations, disease course, risk factors and demographic characteristics of Complex Regional Pain Syndrome type 1 (CRPS), fibromyalgia (FM) and a-specific Repetitive Strain Injury (RSI).

METHOD

A literature search was performed using terms related to the aforementioned topics and diseases. Only original clinical studies that included at least 20 subjects were eligible.

RESULTS

Fifty-nine studies on CRPS, 73 on FM and 7 on a-specific RSI were identified. The diseases show similarities in age distribution, male-female ratio, pain characteristics and sensory signs and symptoms. Motor, autonomic and trophic changes are frequently reported in CRPS, but only occasionally in FM and RSI. Systemic symptoms are found in patients with CRPS and FM, and in a subgroup of patients with RSI. In all three disorders, symptoms usually start locally, but may spread to other body regions later, which, in the case of FM, is a prerequisite for diagnosis. Disease onset is always, usually, or occasionally of traumatic origin in RSI, CRPS and FM, respectively. Anxiety and depression are more frequent in patients compared to controls, but probably not very different from patients with other pain conditions or chronic diseases.

CONCLUSIONS

Apart from some obvious differences between CRPS, FM and RSI, the similarities are conspicuous. The common features of CRPS, FM and a-specific RSI may suggest that a common pathway is involved, but until patients with these type of symptoms are assessed with a uniform assessment procedure, a thorough comparison cannot be made. A systematic evaluation of patients with a suspected diagnosis of CRPS, FM or RSI, may lead to a better appreciation of the differences and similarities in these diseases and help to unravel the underlying mechanisms.

Bone health and back pain: what do we know and where should we go?

Bone health is generally not considered in patients who present with chronic back pain. Nonetheless, bone health and back pain share common genetic and environmental correlates suggesting a co-dependence. Evidence exists for a relationship between back pain and impaired bone health. Here we present the evidence, theoretic framework and clinical relevance. Bone health and back pain are important determinants of musculoskeletal health. Back pain experienced in youth is a risk factor for future back pain, while suboptimal bone health during development increases the risk of skeletal fragility in later life. Generally, bone health is not considered in patients with chronic back pain who do not demonstrate other well-recognised bone health risk factors or associated conditions. Nonetheless, evidence suggests that back pain and impaired bone health share common environmental and genetic correlates, indicating that bone health ought to be considered in the context of back pain in otherwise healthy individuals. This review describes the likely mechanisms explaining the relationship between back pain and impaired bone health, evidence concerning the relationship and suggestions for future research. A narrative literature search was conducted using CINAHL, Medline, PubMed and Web of Science electronic databases. A history of back pain is associated with decreased bone mineral density in adults, yet this tends to be site-specific. No studies were identified examining this association in youth, yet the negative effects of childhood skeletal trauma and obesity on bone and spinal health provide indirect evidence for an association. Further research is required to clarify the impact of back pain on bone health at different lifespan stages using prospective cohort designs.

Functional adaptation to loading of a single bone is neuronally regulated and involves multiple bones

Regulation of load-induced bone formation is considered a local phenomenon controlled by osteocytes, although it has also been hypothesized that functional adaptation may be neuronally regulated. The aim of this study was to examine bone formation in multiple bones, in response to loading of a single bone, and to determine whether adaptation may be neuronally regulated. Load-induced responses in the left and right ulnas and humeri were determined after loading of the right ulna in male Sprague-Dawley rats (69 +/- 16 days of age). After a single period of loading at -760-, -2000-, or -3750-microepsilon initial peak strain, rats were given calcein to label new bone formation. Bone formation and bone neuropeptide concentrations were determined at 10 days. In one group, temporary neuronal blocking was achieved by perineural anesthesia of the brachial plexus with bupivicaine during loading. We found right ulna loading induces adaptive responses in other bones in both thoracic limbs compared with Sham controls and that neuronal blocking during loading abrogated bone formation in the loaded ulna and other thoracic limb bones. Skeletal adaptation was more evident in distal long bones compared with proximal long bones. We also found that the single period of loading modulated bone neuropeptide concentrations persistently for 10 days. We conclude that functional adaptation to loading of a single bone in young rapidly growing rats is neuronally regulated and involves multiple bones. Persistent changes in bone neuropeptide concentrations after a single loading period suggest that plasticity exists in the innervation of bone.

Medical history and the onset of complex regional pain syndrome (CRPS)

Knowledge concerning the medical history prior to the onset of complex regional pain syndrome (CRPS) might provide insight into its risk factors and potential underlying disease mechanisms. To evaluate prior to CRPS medical conditions, a case-control study was conducted in the Integrated Primary Care Information (IPCI) project, a general practice (GP) database in the Netherlands. CRPS patients were identified from the records and validated through examination by the investigator (IASP criteria) or through specialist confirmation. Cases were matched to controls on age, gender and injury type. All diagnoses prior to the index date were assessed by manual review of the medical records. Some pre-specified medical conditions were studied for their association with CRPS, whereas all other diagnoses, grouped by pathogenesis, were tested in a hypothesis-generating approach. Of the identified 259 CRPS patients, 186 cases (697 controls) were included, based on validation by the investigator during a visit (102 of 134 visited patients) or on specialist confirmation (84 of 125 unvisited patients). A medical history of migraine (OR: 2.43, 95% CI: 1.18-5.02) and osteoporosis (OR: 2.44, 95% CI: 1.17-5.14) was associated with CRPS. In a recent history (1-year before CRPS), cases had more menstrual cycle-related problems (OR: 2.60, 95% CI: 1.16-5.83) and neuropathies (OR: 5.7; 95% CI: 1.8-18.7). In a sensitivity analysis, including only visited cases, asthma (OR: 3.0; 95% CI: 1.3-6.9) and CRPS were related. Psychological factors were not associated with CRPS onset. Because of the hypothesis-generating character of this study, the findings should be confirmed by other studies.

Glucocorticoid inhibition of vascular abnormalities in a tibia fracture rat model of complex regional pain syndrome type I

Tibia fracture in rats evokes chronic hindpaw warmth, spontaneous extravasation, edema, allodynia, and periarticular bone loss, a syndrome resembling complex regional pain syndrome type I (CRPS I). Glucocorticoids such as methylprednisolone (MP) are probably effective analgesic and anti-edematous agents in patients suffering from CRPS and this study examined the effects of chronic MP treatment in the rat CRPS I model. Bilateral hindpaw thickness, temperature, and nociceptive thresholds were determined, and the hindlimb bone density was measured using dual-energy X-ray absorptiometry (DXA). Spontaneous cutaneous extravasation and substance P infusion evoked extravasation were determined using an Evans blue vascular permeability assay. After baseline testing, the distal tibia was fractured and the hindlimb casted for 4 weeks. At 2 weeks post-fracture MP infusion was started (1 mg/kg/day for 28 days). The rats were retested at 4, 6, and 8 weeks post-fracture. Hindpaw edema and warmth after fracture were reversed by MP infusion and these effects persisted after discontinuing treatment. Furthermore, there was an increase in spontaneous protein extravasation and an enhanced substance P evoked extravasation and edema response in the hindpaw at 4 weeks that was inhibited by MP infusion. Glucocorticoid treatment had no effect on the allodynia, hindpaw unweighting, or the periarticular bone loss observed after tibia fracture. We postulate that post-junctional facilitation of substance P signaling contributes to the hindpaw warmth, edema, and the enhanced spontaneous protein extravasation observed in this CRPS I model, and that the anti-edematous effects of glucocorticoid treatment are due to inhibition of post-junctional neuropeptide signaling.