Remission of hypersensitivity by simple weight load stimuli in a complex regional pain syndrome mouse model

Painful sensitivity of the hand or foot are the most common and debilitating symptoms of complex regional pain syndrome (CRPS). Physical therapy is standard treatment for CRPS, but evidence supporting its efficacy is minimal and it can be essentially impossible for CRPS patients to actively exercise the painful limb. Using the well-characterized distal tibial fracture CRPS mouse model, we compared the therapeutic effects of several weeks of daily hindlimb loading versus rotarod walking exercise. The effects of loading and exercise were evaluated by weekly testing of hind-paw withdrawal thresholds to von Frey fibers and radiant heat, as well as measurements of paw and ankle edema. At 6 weeks after fracture, the mice were killed and the ipsilateral femur, spinal cord and L4/5 dorsal root ganglia, and hind-paw skin collected for PCR assays and paw skin Immunohistochemistry evaluation. Hindlimb loading reduced hind-paw von Frey allodynia and heat hyperalgesia and edema within a week and these effects persisted for at least a week after discontinuing treatment. These therapeutic effects of loading exceeded the beneficial effects observed with rotarod walking exercise in fracture mice. Levels of nerve growth factor and transient receptor potential vanilloid 1 (TRPV1) immunostaining in the hind-paw skin were increased at 6 weeks after fracture, and both loading and exercise treatment reduced increases. Collectively, these results suggest that loading may be an effective and possibly curative treatment in CRPS patients with sensitivity in the affected limb.

Pronociceptive autoantibodies in the spinal cord mediate nociceptive sensitization, loss of function, and spontaneous pain in the lumbar disk puncture model of chronic back pain

ABSTRACT

Previously, we observed that B cells and autoantibodies mediated chronic nociceptive sensitization in the mouse tibia fracture model of complex regional pain syndrome and that complex regional pain syndrome patient antibodies were pronociceptive in fracture mice lacking mature B cells and antibodies (muMT). The current study used a lumbar spinal disk puncture (DP) model of low back pain in wild-type (WT) and muMT mice to evaluate pronociceptive adaptive immune responses. Spinal disks and cords were collected 3 weeks after DP for polymerase chain reaction and immunohistochemistry analyses. Wild-type DP mice developed 24 weeks of hindpaw mechanical allodynia and hyperalgesia, grip weakness, and a conditioned place preference response indicative of spontaneous pain, but pain responses were attenuated or absent in muMT DP mice. Spinal cord expression of inflammatory cytokines, immune cell markers, and complement components were increased in WT DP mice and in muMT DP mice. Dorsal horn immunostaining in WT DP mice demonstrated glial activation and increased complement 5a receptor expressionin spinal neurons. Serum collected from WT DP mice and injected into muMT DP mice caused nociceptive sensitization, as did intrathecal injection of IgM collected from WT DP mice, and IgM immune complexes were observed in lumbar spinal disks and cord of WT DP mice. Serum from WT tibia fracture mice was not pronociceptive in muMT DP mice and vice versa, evidence that each type of tissue trauma chronically generates its own unique antibodies and targeted antigens. These data further support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain state.

Microvascular Barrier Protection by microRNA-183 via FoxO1 Repression: A Pathway Disturbed in Neuropathy and Complex Regional Pain Syndrome

Blood nerve barrier disruption and edema are common in neuropathic pain as well as in complex regional pain syndrome (CRPS). MicroRNAs (miRNA) are epigenetic multitarget switches controlling neuronal and non-neuronal cells in pain. The miR-183 complex attenuates hyperexcitability in nociceptors, but additional non-neuronal effects via transcription factors could contribute as well. This study explored exosomal miR-183 in CRPS and murine neuropathy, its effect on the microvascular barrier via transcription factor FoxO1 and tight junction protein claudin-5, and its antihyperalgesic potential. Sciatic miR-183 decreased after CCI. Substitution with perineural miR-183 mimic attenuated mechanical hypersensitivity and restored blood nerve barrier function. In vitro, serum from CCI mice und CRPS patients weakened the microvascular barrier of murine cerebellar endothelial cells, increased active FoxO1 and reduced claudin-5, concomitant with a lack of exosomal miR-183 in CRPS patients. Cellular stress also compromised the microvascular barrier which was rescued either by miR-183 mimic via FoxO1 repression or by prior silencing of Foxo1. PERSPECTIVE: Low miR-183 leading to barrier impairment via FoxO1 and subsequent claudin-5 suppression is a new aspect in the pathophysiology of CRPS and neuropathic pain. This pathway might help untangle the wide symptomatic range of CRPS and nurture further research into miRNA mimics or FoxO1 inhibitors.

Local and Systemic Expression Pattern of MMP-2 and MMP-9 in Complex Regional Pain Syndrome

Matrix metalloproteinases (MMP)-2 and MMP-9 play important roles in inflammation as well as in pain processes. For this reason, we compared the concentrations of these enzymes in skin and serum of patients with complex regional pain syndrome (CRPS), other pain diseases and healthy subjects. We analyzed ipsi- and contralateral skin biopsies of 18 CRPS patients, as well as in 10 pain controls and 9 healthy subjects. Serum samples were analyzed from 20 CRPS, 17 pain controls and 17 healthy subjects. All samples were analyzed with ELISA. Concentrations were then compared to clinical data as well as to quantitative sensory testing data.MMP-2 was increased in both ipsi- and contralateral skin biopsies of CRPS patients compared to healthy subjects. While low ipsilateral MMP-2 was associated with trophic changes, contralateral MMP-2 inversely correlated with the CRPS severity. MMP-9 was also locally increased in ipsilateral CRPS skin, and higher ipsi- and contralateral MMP-9 levels correlated with CRPS severity. We conclude that MMP-2 and MMP-9 are differently expressed depending on the clinical phenotype in CRPS. PERSPECTIVE: This article describes an upregulation of MMPs in CRPS and pain controls and shows different expression of MMP-2 and -9 depending on clinical phenotype in CRPS. These results provide evidence that MMP-2 and -9 play a key role in CRPS pathophysiology.

Dimethyl Fumarate Reduces Oxidative Stress and Pronociceptive Immune Responses in a Murine Model of Complex Regional Pain Syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a highly disabling cause of pain often precipitated by surgery or trauma to a limb. Both innate and adaptive immunological changes contribute to this syndrome. Dimethyl fumarate (DMF) works through the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor and other targets to activate antioxidant systems and to suppress immune system activation. We hypothesized that DMF would reduce nociceptive, functional, and immunological changes measured in a model of CRPS.

METHODS

Male C57BL/6 mice were used in the well-characterized tibial fracture model of CRPS. Some groups of mice received DMF 25 mg/kg/d orally, per os for 3 weeks after fracture versus vehicle alone. Homozygous Nrf2 null mutant mice were used as test subjects to address the need for this transcription factor for DMF activity. Allodynia was assessed using von Frey filaments and hindlimb weight-bearing data were collected. The markers of oxidative stress malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were quantified in the skin of the fractured mice using immunoassays along with the innate immune system cytokines IL-1β and IL-6. The accumulation of IgM in the fractured limbs and lymph node hypertrophy were used as indexes of adaptive immune system activation, and the passive transfer of serum from wildtype fractured mice to B cell-deficient fractured muMT mice (mice lacking B cells and immunoglobulin) helped to assess the pronociceptive activity of humoral factors.

RESULTS

We observed that oral DMF administration strongly prevented nociceptive sensitization and reduced uneven hindlimb weight bearing after fracture. DMF was also very effective in reducing the accumulation of markers of oxidative stress, activation of innate immune mediator production, lymph node hypertrophy, and the accumulation of IgM in fractured limbs. The sera of fractured vehicle-treated but not DMF-treated mice conferred pronociceptive activity to recipient mice. Unexpectedly, the effects of DMF were largely unchanged in the Nrf2 null mutant mice.

CONCLUSIONS

Oxidative stress and immune system activation are robust after hindlimb fracture in mice. DMF strongly reduces activation of those systems, and the Nrf2 transcription factor is not required. DMF or drugs working through similar mechanisms might provide effective therapy for CRPS or other conditions where oxidative stress causes immune system activation.

Disruption of Homeostasis Based on the Right and Left Hemisphere in Patients with Complex Regional Pain Syndrome

OBJECTIVE

Although the clinical features and pathophysiology of complex regional pain syndrome (CRPS) have been studied in the peripheral and central nervous systems, few plausible pathological interactions are known among the metabolites in these systems. Thus, the purpose of this study was to investigate abnormal relationships and interactions between peripheral metabolites and central neurometabolites in patients with CRPS.

METHODS

Various metabolites and molecules were measured in the peripheral blood, and central neurometabolites in the right and left thalamus using proton magnetic resonance spectroscopy in 12 patients with CRPS and 11 healthy controls. Interactions between peripheral metabolites in blood and central neurometabolites in the right and left thalamus were also investigated.

RESULTS

The interactions between peripheral and central metabolites were different in the right and left hemispheres of healthy subjects, suggesting the presence of right hemisphere-dependent energy homeostasis and left hemisphere-dependent acid-base homeostasis that enables effective functioning. The interactions between central and peripheral metabolites in CRPS patients were distinct from those in healthy individuals, supporting the possibility of abnormal interactions and disrupted homeostasis between peripheral and central metabolites, which may result from neuroinflammation and immune system dysfunction.

CONCLUSION

To the authors' knowledge, this is the first report describing abnormal metabolic dysfunction and disrupted homeostasis in interactions between metabolites of the peripheral and central nervous systems in CRPS. The approach used to uncover hidden pathophysiologies will improve understanding of how chronic pain can disrupt homeostasis in interactions between two systems and how alternative metabolites can be activated to recover and compensate for pathological dysfunctions in patients with CRPS.

Complex Regional Pain Syndrome Type I, a Debilitating and Poorly Understood Syndrome. Possible Role for Pulsed Electromagnetic Fields: A Narrative Review

BACKGROUND

Complex regional pain syndrome type I (CRPS-I), also called algodystrophy, is a complex syndrome characterized by limb pain, edema, allodynia, hyperalgesia and functional impairment of bone with a similar clinical picture of osteoporosis, including an increased release of various pro-inflammatory neuropeptides and cytokines. Several treatments have been proposed for CRPS-I, but due to the poor outcome of conventional drugs and the invasiveness of some techniques, expectations are now directed towards new resources that could be more effective and less invasive.

OBJECTIVE

In the light of preclinical evidence, which underlined pulsed electromagnetic fields' (PEMFs) properties on osteoblasts (OBs), osteoclasts (OCs), and pathologies with an inflammatory profile, the present review aims to investigate whether there is a rationale for the use of PEMFs, as a combined approach, in CRPS-I.

STUDY DESIGN

This review analyzed the 44 in vitro and in vivo studies published in the last decade that focused on 2 main aspects of CRPS-I: local osteoporosis (OP) and inflammation.

SETTING

Not applicable.

METHODS

This review includes in vitro and in vivo studies found with a PubMed and Web of Knowledge database search by 2 independent authors. The limits of the search were the publication date between January 1, 2006, and January 1, 2016, and English language. In detail, the search strategy was based on: 1) CRPS-I or algodystrophy; 2) OP, OCs, and OBs; and 3) inflammatory aspects.

RESULTS

The included studies looked at the relationship between PEMFs and OCs (2 in vitro studies), osteoporotic animal models (8 in vivo studies), OBs (20 in vitro studies), inflammatory cytokines, and reactive oxygen species. They also tried to define the molecular cell pathways involved (5 in vivo and 9 in vitro studies on inflammatory models). It was observed that PEMFs increased OC apoptosis, OB viability, bone protein and matrix calcification, antioxidant protein, and the levels of adenosine receptors, while it decreased the levels of pro-inflammatory cytokines.

LIMITATIONS

Data from clinical trials are scarce; moreover, experimental conditions and PEMF parameters are not standardized.

CONCLUSIONS

The present review underlined the rationale for the use of PEMFs in the complex contest of CRPS-I syndrome, in combination with conventional drugs. Key words: Complex regional pain syndrome type I, algodystrophy, pulsed electromagnetic field stimulation, osteoporosis, inflammation, osteoclasts, osteoblasts, pain.

[11C]-(R)-PK11195 positron emission tomography in patients with complex regional pain syndrome: A pilot study

Complex regional pain syndrome (CRPS) is characterized by severe and chronic pain, but the pathophysiology of this disease are not clearly understood. The primary aim of our case-control study was to explore neuroinflammation in patients with CRPS using positron emission tomography (PET), with an 18-kDa translocator protein specific radioligand [C]-(R)-PK11195. [C]-(R)-PK11195 PET scans were acquired for 11 patients with CRPS (30-55 years) and 12 control subjects (30-52 years). Parametric image of distribution volume ratio (DVR) for each participant was generated by applying a relative equilibrium-based graphical analysis. The DVR of [C]-(R)-PK11195 in the caudate nucleus (t(21) = -3.209, P = 0.004), putamen (t(21) = -2.492, P = 0.022), nucleus accumbens (t(21) = -2.218, P = 0.040), and thalamus (t(21) = -2.395, P = 0.026) were significantly higher in CRPS patients than in healthy controls. Those of globus pallidus (t(21) = -2.045, P = 0.054) tended to be higher in CRPS patients than in healthy controls. In patients with CRPS, there was a positive correlation between the DVR of [C]-(R)-PK11195 in the caudate nucleus and the pain score, the visual analog scale (r = 0.661, P = 0.026, R = 0.408) and affective subscales of McGill Pain Questionnaire (r = 0.604, P = 0.049, R = 0.364). We demonstrated that neuroinflammation of CRPS patients in basal ganglia. Our results suggest that microglial pathology can be an important pathophysiology of CRPS. Association between the level of caudate nucleus and pain severity indicated that neuroinflammation in this region might play a key role. These results may be essential for developing effective medical treatments.

Advances in translational neuropathic research: example of enantioselective pharmacokinetic-pharmacodynamic modeling of ketamine-induced pain relief in complex regional pain syndrome

Historically, complex regional pain syndrome (CRPS) was poorly defined, which meant that scientists and clinicians faced much uncertainty in the study, diagnosis, and treatment of the syndrome. The problem could be attributed to a nonspecific diagnostic criteria, unknown pathophysiologic causes, and limited treatment options. The two forms of CRPS still are painful, debilitating disorders whose sufferers carry heavy emotional burdens. Current research has shown that CRPS I and CRPS II are distinctive processes, and the presence or absence of a partial nerve lesion distinguishes them apart. Ketamine has been the focus of various studies involving the treatment of CRPS; however, currently, there is incomplete data from evidence-based studies. The question as to why ketamine is effective in controlling the symptoms of a subset of patients with CRPS and not others remains to be answered. A possible explanation to this phenomenon is pharmacogenetic differences that may exist in different patient populations. This review summarizes important translational work recently published on the treatment of CRPS using ketamine.

The role of genomic oxidative-reductive balance as predictor of complex regional pain syndrome development: a novel theory

The aftermath of sequencing the human genome has birthed many efforts to utilize an individual's genetic information in order to tailor optimal treatment strategies - so-called personalized medicine. An individual's genetic information may eventually help diagnosis and treatment, as well selecting optimal pharmacologic agents based partly on how well they reach their target, how well they will bind to and produce an effect at their targets, how well they will be metabolized, and the profile of their adverse effects. It also appears that clinicians may be able to utilize an individual's genetic information to ascertain a subject's risk or susceptibility of developing a particular medical condition. Although, this has not been widely utilized in pain medicine at this point, the future may revolutionize the role of genetic information in the evaluation and management of various pain conditions. One reason for variations in therapeutic outcomes from different pharmacologic pain treatments is the different genetic disposition of patient to develop pain or to respond to analgesics. The patient's phenotype may represent a conglomerate of several different genetic variants concomitantly present in an individual. Genetic variants may modulate the risk of developing a painful condition, or may modulate the perception of pain (e.g. OPRM1 or GCH1 variants conferring modest "protection" from pain by increasing the tone of the endogenous opioid system or decreasing nitric oxide formation). Other genetic polymorphisms may alter pharmacokinetic mechanisms (e.g. CYP2D6 related prodrug activation of codeine to morphine), alter pharmacodynamic mechanisms (e.g. opioid receptor mutations), or alter other analgesic effects (e.g. diminished euphoric effects from opioids potentially due to DRD2 polymorphisms decreasing the functioning of the dopaminergic reward system). This article theorizes that genetic alterations including functional polymorphisms of Nrf2 (a master regulator of the transcription of multiple antioxidants) may render certain subjects more or less susceptible to developing complex regional pain syndrome after surgery or trauma. If this hypothesis is correct, knowing this information may translate into significant and "far-reaching" effects on clinical decision-making surrounding the management of pain in patients who may be more susceptible to develop complex regional pain syndrome. Furthermore, it could lead to the development of novel prevention or intervention strategies, in efforts to prevent, abort, or ameliorate the development of and/or effectively treat complex regional pain syndrome.

Successful intravenous regional block with low-dose tumor necrosis factor-alpha antibody infliximab for treatment of complex regional pain syndrome 1

Cytokines, particularly tumor necrosis factor-alpha, may play an important role in the mediation of mechanical hyperalgesia and autonomic signs in complex regional pain syndrome 1. We performed an IV regional block with low-dose administration of the tumor necrosis factor-alpha antibody, infliximab, in a patient with typical clinical signs of complex regional pain syndrome 1 (moderate pain, edema, hyperhidrosis, elevated skin temperature compared with the contralateral side). A significant improvement of clinical variables was observed 24 h after infliximab treatment. Almost complete remission was reached within 8 wk, but sensory signs improved only after 6 mo. No adverse events were observed.

Continuous intra-arterial application of substance P induces signs and symptoms of experimental complex regional pain syndrome (CRPS) such as edema, inflammation and mechanical pain but no thermal pain

Substance P is involved in nociception in both the peripheral nervous system and the CNS and has been documented to play a crucial role in the complex regional pain syndrome (CRPS). So far, however, most experimental animal models are restricted to the effect of neurokinin-1 receptor blockers to inhibit substance P and do not directly evaluate its action. Thus, this study was conducted to test the hypothesis that local application of substance P causes signs and symptoms of CRPS. For this purpose rats received a continuous infusion of either substance P or saline over 24 h delivered by a mini-osmotic pump connected to an intrafemoral catheter. Animals were analyzed at either day 1 (n=6, each group) or day 4 (n=5, each group) after start of infusion. Substance P application caused a significant and long-lasting decrease in paw withdrawal thresholds upon mechanical stimulation, while animals did not present with thermal allodynia at days 1 and 4 after onset of infusion. In addition, severe s.c. edema was observed in all animals receiving substance P. In vivo fluorescence microscopy of the extensor digitorum longus muscle of the affected hind paw revealed enhanced leukocyte-endothelial cell interaction with a significant rise in the number of leukocytes both rolling along and firmly adhering to the wall of postcapillary venules, while saline-exposed animals were free of this local inflammatory response. Muscle cell apoptosis, as assessed by in vivo bisbenzimide staining, terminal deoxynucleotidyl transferase nick end labeling analysis and caspase 3-cleavage, could not be observed in either of the animals. In summary, the present study indicates that substance P is responsible for neurogenic inflammation, including local cell response, edema formation and mechanical pain, while it seems not to contribute to the generation of thermal allodynia.

Changes in immune and glial markers in the CSF of patients with Complex Regional Pain Syndrome

Complex Regional Pain Syndrome is a severe chronic pain condition characterized by sensory, autonomic, motor and dystrophic signs and symptoms. The pain in CRPS is continuous, it worsens over time, and it is usually disproportionate to the severity and duration of the inciting event. This study compares cerebrospinal fluid (CSF) levels of pro- and anti-inflammatory cytokines, chemokines and several biochemical factors (glial fibrillary acidic protein (GFAP), the nitric oxide metabolites (nitrate plus nitrite), the excitatory amino acid neurotransmitter glutamate, calcium, total protein and glucose) in patients afflicted with CRPS to levels found in patients suffering with other non-painful or painful conditions. The aim of the study is to determine the degree of involvement of glial cells and immune system mediators in the pathophysiology of CRPS. There was no elevation or reduction of a CSF marker that was specific for CRPS patients. However, there were several patterns of markers that could be helpful in both elucidating the mechanisms involved in the disease process and supporting the diagnosis of CRPS. The most common pattern was found in 50% (11 out of 22) of the CRPS patients and consisted of; elevated IL-6, low levels of IL-4 or IL-10, increased GFAP or MCP1 and increases in at least two of the following markers NO metabolites, calcium or glutamate. The results from this and other similar studies may aid in elucidating the mechanisms involved in the pathophysiology of CRPS. A better understanding of these mechanisms may lead to novel treatments for this very severe, life-altering illness.

The Challenge to Manage Reflex Sympathetic Dystrophy/Complex Regional Pain Syndrome

The challenge to understand reflex sympathetic dystrophy/complex regional pain syndrome may require a better understanding of the complex relationship between the central and peripheral nervous systems. There is no comprehensive hypothesis that clearly explains the etiology and no uniformly successful treatment method. This brief summary of the challenge reviews some of what is known, hypothesizes a possible etiologic mechanism, and proposes 10 common-sense principles for management that recognizes the handicap of limited knowledge.

Brain processing during mechanical hyperalgesia in complex regional pain syndrome: a functional MRI study

Complex Regional Pain Syndromes (CRPS) are characterized by a triad of sensory, motor and autonomic dysfunctions of still unknown origin. Pain and mechanical hyperalgesia are hallmarks of CRPS. There are several lines of evidence that central nervous system (CNS) changes are crucial for the development and maintenance of mechanical hyperalgesia. However, little is known about the cortical structures associated with the processing of hyperalgesia in pain patients. This study describes the use of functional magnetic resonance imaging (fMRI) to delineate brain activations during pin-prick hyperalgesia in CRPS. Twelve patients, in whom previous quantitative sensory testing revealed the presence of hyperalgesia to punctuate mechanical stimuli (i.e. pin-prick hyperalgesia), were included in the study. Pin-prick-hyperalgesia was elicited by von-Frey filaments at the affected limb. For control, the identical stimulation was performed on the unaffected limb. fMRI was used to explore the corresponding cortical activations. Mechanical stimulation at the unaffected limb was non-painful and mainly led to an activation of the contralateral primary somatosensory cortex (S1), insula and bilateral secondary somatosensory cortices (S2). The stimulation of the affected limb was painful (mechanical hyperalgesia) and led to a significantly increased activation of the S1 cortex (contralateral), S2 (bilateral), insula (bilateral), associative-somatosensory cortices (contralateral), frontal cortices and parts of the anterior cingulate cortex. The results of our study indicate a complex cortical network activated during pin-prick hyperalgesia in CRPS. The underlying neuronal matrix comprises areas not only involved in nociceptive, but also in cognitive and motor processing.

Tissue hypoxia in complex regional pain syndrome

Untreated complex regional pain syndrome (CRPS) may progress from acute stages with increased hair and nail growth in the affected limb to chronic stages with atrophy of the skin, muscles and bones. The aim of this study was to investigate whether tissue hypoxia could be one mechanism responsible for this late CRPS symptoms. Nineteen patients with CRPS and two control groups (healthy control subjects, surgery patients with edema) participated in this study. Skin capillary hemoglobin oxygenation (HbO(2)) was measured non-invasively employing micro-lightguide spectrophotometry (EMPHO). The EMPHO probe was mounted force-controlled onto the skin of the affected and unaffected hand. HbO(2) was measured at rest and during postischemic reactive hyperemia. HbO(2) did not differ between the right (58.20%+/-1.12) and left (57.79%+/-1.31, ns) hand in control subjects. However, in patients, HbO(2) of the affected side (36.63%+/-2.16) was significantly decreased as compared to the clinically unaffected side (46.35%+/-2.97, P<0.01). As compared to controls, HbO(2) in CRPS was reduced on both sides (P<0.001). Postischemic hyperoxygenation was impaired on the affected side in CRPS (60.81%+/-2.90)--as compared to the unaffected side (67.73%+/-1.50, P<0.04) and to controls (68.63%+/-0.87, P<0.005). The unaffected limb in CRPS did not differ from controls. Despite skin edema, pre- (49.06%+/-2.02) and postsurgery HbO(2) (53.15%+/-4.44, ns) were not different in the second control group. Our results indicate skin hypoxia in CRPS. Impairment of nutritive blood flow in the affected limb may be one factor contributing to atrophy and ulceration in chronic CRPS. The investigation of patients after surgery revealed that edema could not be the only reason for hypoxia.

Increased production of nitric oxide stimulated by interferon-gamma from peripheral blood monocytes in patients with complex regional pain syndrome

This study examines immediate nitric oxide (NO) release from monocytes following interleukin-1beta (IL-1beta), interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) challenge in patients with complex regional pain syndrome (CRPS). Study patients exhibited the following: (1), mechanical allodynia; (2), evidence of either vasomotor or sudomotor disturbance; and (3), concordant painful allodynia documented with quantitative sensory testing that was temporarily abolished with sympathetic block. Ten subjects (CRPS, N=5; control, N=5) were enrolled. Peripheral blood monocytes were challenged with 100 microl of IL-1beta (1 ng), IFN-gamma (1 ng), TNF-alpha (0.01 ng), and normal saline (NS) and the resultant immediate NO release measured. Subjects with CRPS exhibited a statistically significant increase in NO release in response to IFN-gamma (P<0.012) compared with controls. The NO responses to IFN-gamma in excess of NS (P<0.025) and as the ratio IFN-gamma/NS (P<0.022) were also significantly increased.

Facilitated neurogenic inflammation in complex regional pain syndrome

Complex regional pain syndrome (CRPS) is characterized by a variety of clinical features including spontaneous pain and hyperalgesia. Increased neuropeptide release from peripheral nociceptors has been suggested as a possible pathophysiologic mechanism triggering the combination of trophic changes, edema, vasodilatation and pain. In order to verify the increased neuropeptide release in CRPS, electrically induced neurogenic vasodilatation and protein extravasation were evaluated in patients and controls. We performed a prospective study on 10 patients with acute and untreated CRPS and 10 matched healthy controls. Neurogenic inflammation was elicited by strong transcutaneous electrical stimulation via intradermal microdialysis capillaries which simultaneously enabled measurement of protein extravasation. Laser-Doppler scanning was used to assess axon reflex vasodilatation. Axon reflex vasodilatation was significantly increased in CRPS patients (438 +/- 68% of baseline vs. 306 +/- 52%; P < 0.05) and transcutaneous electrical stimulation provoked protein extravasation only in the patients (before, 0.28 +/- 0.03 mg/ml; during stimulation, 0.34 +/- 0.04 mg/ml), whereas protein concentration steadily declined during stimulation in the healthy controls (before, 0.23 +/- 0.04 mg/ml; during stimulation, 0.18 +/- 0.04; P < 0.001). The time course of electrically induced protein extravasation in the patients resembled the one observed following application of exogenous substance P (SP). We conclude that neurogenic inflammation is facilitated in CRPS. Our results suggest an increased releasability of neuropeptides in CRPS.