Reflex sympathetic dystrophy of the hand: an excessive inflammatory response?

Complex regional pain syndrome type I in children

BACKGROUND

Complex Regional Pain Syndrome type I (CRPS I) is a potentially incapacitating syndrome which can occur after a minor injury or operation to a limb. It is a disorder characterized by pain, sensory and motor disturbances. CRPS I is well known in adults, but a relatively new diagnostic entity in children. The clinical presentation of CRPS I in children is, to some extent, different from adults and therefore sometimes not recognized early. The aim of this study was to search for differences in patient characteristics between children and adults with CRPS I.

METHODS

We have performed a retrospective chart review of 78 children (age </=16 year) with CRPS I and compared the data with those of 951 adults with CRPS I.

RESULTS

The child population consisted predominantly of girls and older children (median age 13 years). The child population differed from adults in that the skin temperature of the involved extremity at onset was more often cooler, the lower extremity was involved more frequently and neurological and sympathetic symptoms were less pronounced.

CONCLUSIONS

In several aspects, CRPS I in children has a different presentation than in adults.

Pentoxifylline attenuates nociceptive sensitization and cytokine expression in a tibia fracture rat model of complex regional pain syndrome

BACKGROUND

Tibia fracture in rats evokes chronic hindpaw warmth, edema, allodynia, and regional osteopenia, a syndrome resembling complex regional pain syndrome (CRPS). Previous studies suggest that the pathogenesis of some of these changes involves an exaggerated regional inflammatory response to injury and we postulated that inflammatory cytokines contribute to the development of CRPS-like changes after fracture.

METHODS

The distal tibia was fractured and the hindlimb casted for 4 weeks. The rats were given drinking water with or without the cytokine inhibitor pentoxifylline (PTX) starting the day before fracture and continuing for 4 weeks, after which time the cast was removed and multiple assays were performed in the hindpaw. PCR and immunoassays were used to evaluate changes in cytokine expression. Bilateral hindpaw thickness, temperature, and nociceptive thresholds were determined, and bone microarchitecture was measured by microcomputed tomography (microCT).

RESULTS

Tibia fracture chronically up-regulated TNFalpha, IL-1beta and IL-6 mRNA and protein levels in hindpaw skin and PTX treatment significantly reduced the mRNA expression and cytokine protein levels for all these cytokines. PTX inhibited the nociceptive sensitization and some vascular changes, but had insignificant effects on most of the bone-related parameters measured in these studies. Immunostaining of hindpaw skin was negative for immunocyte infiltration at 4 weeks post-fracture.

CONCLUSIONS

These results suggest that pro-inflammatory cytokines contribute to the nociceptive and vascular sequelae of fracture and that PTX treatment can reverse these CRPS-like changes.

Serum and salivary oxidative analysis in Complex Regional Pain Syndrome

Although both inflammatory and neural mechanisms have been suggested as potential contributors to Complex Regional Pain Syndrome type I (CRPS-I), the pathogenesis of the syndrome is still unclear. Clinical trials have shown that free radical scavengers can reduce signs and symptoms of CRPS-I, indirectly suggesting that free radicals and increased oxidative stress are involved in the pathogenesis of CRPS-I. This study investigated this premise by determining the levels of antioxidants in the serum and saliva of 31 patients with CRPS-I and in a control group of 21 healthy volunteers. Serum lipid peroxidation products (MDA) and all antioxidative parameters analyzed were significantly elevated in CRPS-I patients: median salivary peroxidase and superoxide dismutase (SOD) activity values, uric acid (UA) concentration and total antioxidant status (TAS) values were higher in CRPS-I patients by 150% (p=0.01), 280% (p=0.04), 60% (p=0.0001), and 200% (p=0.0003), respectively, as compared with controls. Similar although not as extensive pattern of oxidative changes were found in the serum: mean serum UA and MDA concentrations and TAS value in the CRPS-I patients were higher by 16% (p=0.04), 25% (p=0.02), and 22% (p=0.05), respectively, than in the controls. Additionally, median salivary albumin concentration and median salivary LDH activities in the patients were 2.5 times (p=0.001) and 3.1 (p=0.004) times higher than in the controls. The accumulated data show that free radicals are involved in the pathophysiology of CRPS-I, which is reflected both in serum and salivary analyses. These data could be used for both diagnostic and therapeutic purposes in CRPS-I patients.

Treatment of early complex regional pain syndrome type 1 by a combination of mannitol and dexamethasone

A total of 75 patients, 68 women (91%) and seven men (9%), with a mean age of 58 (range 38-82) years with early Complex Regional Pain Syndrome Type 1 (CRPS Type 1), present for less than 4 months, were given in-patient treatment with 10% mannitol 2 x 250 ml per day and 8 mg dexamethasone per day for 1 week. Measurements assessed included the pain, the range of finger movements, grip strength and our own clinical severity scoring system for CRPS Type 1 (CRPS score). The results were assessed at 1 week and, finally, at a mean of 9 (range 8-12) months. At 1-week assessment, all variables decreased significantly: pain from a mean Visual Analogue Scale (VAS) of 6.7 to 2.3, loss of finger flexion (6-0.3 cm) and the CRPS score (7.6-2.2 points). Total grip strength did not improve. At the final assessment of 70 patients, the VAS score was a mean of 1.8, loss of finger flexion a mean of 0.1 cm, the CRPS score was a mean of 1.6 and grip strength a mean of 34% of the strength of the unaffected hand. All these variables showed statistically significant improvement.

Effect of anti-NGF antibodies in a rat tibia fracture model of complex regional pain syndrome type I

Tibia fracture in rats evokes chronic hindpaw warmth, edema, allodynia, and regional osteopenia resembling the clinical characteristics of patients with complex regional pain syndrome type I (CRPS I). Nerve growth factor (NGF) has been shown to support nociceptive and other types of changes found in neuropathic pain models. We hypothesized that anti-NGF antibodies might reduce one or more of the CRPS I-like features of the rat fracture model. For our studies one distal tibia of each experimental rat was fractured and casted for 4 weeks. The rats were injected with anti-NGF or vehicle at days 17 and 24 post-fracture. Nociceptive testing as well as assessment of edema and hindpaw warmth were followed during this period. Molecular and biochemical techniques were used to follow cytokine, NGF and neuropeptide levels in hindpaw skin and sciatic nerves. Lumbar spinal cord Fos immunostaining was performed. Bone microarchitecture was measured using microcomputed tomography (microCT). We found that tibia fracture upregulated NGF expression in hindpaw skin and tibia bone along with sciatic nerve neuropeptide content. We also found nociceptive sensitization, enhanced spinal cord Fos expression, osteopenia and enhanced cytokine content of hindpaw skin on the side of the fracture. Anti-NGF treatment reduced neuropeptide levels in sciatic nerve and reduced nociceptive sensitization. There was less spinal cord Fos expression and bone loss in the anti-NGF treated animals. Conversely, anti-NGF did not decrease hindpaw edema, warmth or cytokine production. Collectively, anti-NGF reduced some but not all signs characteristic of CRPS illustrating the complexity of CRPS pathogenesis and NGF signaling.

Tumor necrosis factor-alpha and interleukin-6 are not correlated with the characteristics of Complex Regional Pain Syndrome type 1 in 66 patients

It was previously shown in a group of 9 patients with complex regional pain syndrome type 1 (CRPS1) that levels of the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) are higher in blister fluid from the involved side. We hypothesize that local inflammation is responsible for the characteristics of CRPS1. The aim of this study was to confirm the previous observation in a large group of CRPS1 patients, repeating the measurement of TNF-alpha and IL-6 in blister fluid. Furthermore, we sought to determine whether these cytokines are responsible for the characteristics of CRPS1 and characterize the relationship between cytokine levels and duration of the disease. Sixty-six patients with CRPS1 participated. Skin blisters were artificially induced for measurement of cytokines in both extremities. The following disease characteristics were assessed: pain and differences in temperature, volume, and mobility between the extremities. TNF-alpha and IL-6 levels were significantly higher in blister fluid from the involved side. However, cytokine levels did not correlate with the characteristics or duration of the disease. Our findings confirm the presence of local inflammation in a population of 66 patients in the first 2 years of CRPS1. Proinflammatory cytokines seem to be only partly involved in the pathophysiology of CRPS1, as indicated by the lack of coherence between TNF-alpha and IL-6 levels and the signs and symptoms of inflammation and disease duration. Other inflammatory mediators and mechanisms, such as central sensitization, are probably involved in the early stages of CRPS1.

TNF signaling contributes to the development of nociceptive sensitization in a tibia fracture model of complex regional pain syndrome type I

Tibia fracture in rats initiates a cascade of nociceptive, vascular, and bone changes resembling complex regional pain syndrome type I (CRPS I). Previous studies suggest that the pathogenesis of these changes is attributable to an exaggerated regional inflammatory response to injury. We postulated that the pro-inflammatory cytokine tumor necrosis factor alpha (TNF) might mediate the development of CRPS-like changes after fracture. RT-PCR and EIA assays were used to evaluate changes in TNF expression and content in skin, nerve, and bone after fracture. Bilateral hindpaw thickness, temperature, and nociceptive thresholds were determined, and bone microarchitecture was measured using microcomputed tomography. Lumbar spinal cord Fos immunostaining was performed for quantification of Fos positive neurons. After baseline testing, the distal tibia was fractured and the hindlimb casted for 4 weeks. The rats were subcutaneously injected either with a soluble TNF receptor type 1 (sTNF-R1, 5mg/kg/d) or saline every 3 days over 28 days and then were retested at 4 weeks post-fracture. Tibia fracture chronically upregulated TNF expression and protein levels in the hindpaw skin and sciatic nerve. After fracture the rats developed hindpaw mechanical allodynia and unweighting, which were reversed by sTNF-R1 treatment. Consistent with the behavioral data, spinal Fos increased after fracture and this effect was inhibited by sTNF-R1 treatment. Collectively, these data suggest that facilitated TNF signaling in the hindlimb is an important mediator of chronic regional nociceptive sensitization after fracture, but does not contribute to the hindlimb warmth, edema, and bone loss observed in this CRPS I model.

Quantitative evaluation of very acute stage of complex regional pain syndrome after stroke using three-phase bone scintigraphy

PURPOSE

Three-phase bone scintigraphy (TPBS) is an objective diagnostic test for complex regional pain syndrome (CRPS). The diagnostic importance of an increased uptake on the delayed phase has been proven in early CRPS, but that of the vascular and blood pool phases has not. The purpose of this study is to improve the diagnostic strength of the very acute stage of CRPS after stroke through a combined quantitative evaluation of each TPBS phase.

METHODS

Quantitative TPBS analysis was performed in 26 post-stroke hemiplegic patients with very acute stage of CRPS and in 12 controls with no CRPS after brain lesion. Regions of interest (hands without fingers--carpal bones, metacarpal bones and metacarpopharyngeal joints) were selected and the count ratios of the affected to unaffected sides were calculated.

RESULTS

The maximum values of control in each phase were used as the criteria of positive findings of each TPBS phase. Eleven patients in the vascular phase, 13 in the blood pool phase and 17 in the delayed phase had a higher assumption than the maximum values and a sensitivity of 42.3%, 50% and 65.4%, respectively. Twenty-one of 26 patients were interpreted as abnormal when at least one phase showed a positive finding. As a result, increased sensitivity of 80.8% and identical specificity of 100% were achieved.

CONCLUSION

These findings suggest that the combination of quantitative evaluation of each TPBS phase can improve the diagnostic strength of the very acute stage of CRPS after stroke.

Assessment of endothelial function in complex regional pain syndrome type I

The objective of this study is to investigate the endothelial function in complex regional pain syndrome. A total of 21 patients with CRPS and 15 healthy controls were enrolled. The mean age of patients was 22 +/- 4.9 years and the mean duration of the disease was 5.9 +/- 2.5 months. Flow-mediated vasodilatation (FMD) technique was performed for evaluating the endothelial function. Parameters were the waveforms obtained and the increase in diameter and blood flow of the brachial artery, which were expressed as the percent change from baseline. The differences of the waveforms obtained in the affected limbs in comparison to non-affected limbs and to controls were statistically significant. We observed a trend of greater percent dilating responses in the affected limbs; however, the differences showed no statistical significance. In macrovascular evaluation, the endothelial function seems to be impaired in the earlier stage of the disease.

Pharmacotherapy options for complex regional pain syndrome

Complex regional pain syndrome is a painful disorder of unclear etiology, typically involving the distal part of one limb, represented by spontaneous and evoked pain as well as autonomic, motor and trophic abnormalities. It can be incapacitating and severely affect function and quality of life. Although full-blown complex regional pain syndrome can be diagnosed easily, less fulminate forms of the syndrome often remain undiagnosed. Controlled trials have demonstrated that a short course of oral corticosteroids, intranasal or intramuscular calcitonin, intravenous bisphosphonates, free-radical scavengers, gabapentin, regional intravenous sympathetic blocks with bretylium and spinal cord stimulation or physical therapy and occupational therapy can be efficacious for complex regional pain syndrome. Nonetheless, the management of this syndrome is difficult because currently available drugs and technologies do not provide adequate pain relief for a considerable percentage of sufferers. The present review focuses primarily on the pharmacotherapy of complex regional pain syndrome and describes briefly the epidemiology, pathogenesis and clinical manifestations of the syndrome.

Pharmacologic therapies for complex regional pain syndrome

Complex regional pain syndrome (CRPS) remains a challenging condition to diagnose and treat. There are few large-scale, randomized trials of pharmacologic agents, and most published studies are small, uncontrolled, or presented only in abstract form at meetings. The most commonly used agents, such as anticonvulsants, antidepressants, and opiates, have been found to be useful for other neuropathic pain conditions in large-scale trials but have not been adequately studied in CRPS. Systemic steroids delivered by multiple routes continue to be used, with some good evidence for short-term administration. N-methyl-D-aspartate antagonists have recently gained in popularity, without evidence from well-controlled trials. Bisphosphonates have been well studied and offer promise. In addition, there has been interest in thalidomide; however, we are still awaiting well-controlled trials. This article presents an overview of the available data regarding pharmacologic therapies for CRPS. These agents should be used in conjunction with a comprehensive interdisciplinary approach aimed at functional restoration and improved quality of life.

Leukocytes in Complex Regional Pain Syndrome Type I

OBJECTIVE

The pathophysiology of Complex Regional Pain Syndrome type I (CRPS I) is unclear. An inflammatory reaction may cause the syndrome in which leukocytes may play an important role.

MATERIALS AND METHODS

In this pilot study of six patients with acute warm CRPS I, we performed radiolabeled autologous leukocyte scans of both hands, in order to assess leukocyte accumulation. Comparison was made with the unaffected limb, and with three control patients with a Colles fracture without CRPS I.

RESULTS

Images of the CRPS I patients obtained 4 h after leukocyte injection provided the clearest results. At 4 h post-injection, there was clear, asymmetrical leukocyte accumulation in the affected extremity with a mean ratio of 1.49+/-0.19. In control patients, no asymmetry was observed between hands (mean ratio 1.09+/-0.06), indicating the absence of specific leukocyte accumulation. There was a statistically significant difference between CRPS I and control subjects 4 h post injection (p=0.012).

CONCLUSION

We found a significantly increased accumulation of leukocytes in patients with CRPS I. This is the first study to show a possible role for leukocytes in the pathophysiology of acute CRPS I.

Inflammatory mediators are altered in the acute phase of posttraumatic complex regional pain syndrome

OBJECTIVES

Complex regional pain syndrome type 1 (CRPS 1) is a disorder that can affect an extremity after minor trauma or surgery. The pathogenesis of this syndrome is unclear. It has clinical signs of severe local inflammation as a result of an exaggerated inflammatory response, but neurogenic dysregulation also may contribute to it.

METHODS

For further insights into the pathogenesis of CRPS 1, the authors investigated inflammatory and neurogenic mediators-C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-8 (IL-8), soluble tumor necrosis factor receptor I/II (sTNFR I/II), sE-selectin, sL-selectin, sP-selectin, substance P, neuropeptide Y, and calcitonin gene-related peptide-in venous blood from both the healthy arm and the arm with acute CRPS I from 25 patients and from 30 healthy volunteers.

RESULTS

Levels of IL-8 and sTNFR I/II were significantly elevated in patients, whereas all soluble forms of selectins were significantly suppressed. There was no significant difference in white blood cell count (WBC), CRP, and IL-6. Substance P was significantly elevated in patients. The other two neuropeptides were unchanged. None of the parameters studied showed any differences between the CRPS I-affected arm and the normal arm.

CONCLUSIONS

Elevated IL-8 and sTNFR I/II levels indicate an association between CRPS I and an inflammatory process. Normal WBC, CRP, and IL-6 give evidence for localized inflammation. The hypothesis of neurogenic-induced inflammation mediated by neuropeptides is supported by elevated substance P levels.

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.

Impairments as measured by ISS do not greatly change between one and eight years after CRPS 1 diagnosis

BACKGROUND

Complex Regional Pain Syndrome type 1 (CRPS 1) is a potentially incapacitating complication in which pain seems to be the most disabling factor. We performed a late follow up study of a well-defined CRPS 1 population more than eight years after diagnosis. The relationships between early and late impairments were studied with a view to outcome prediction and to investigate possible differences in long-term impairments according to initial CRPS 1 subdiagnosis (i.e. "warm" or "cold", diagnosed according to skin temperature measured via infrared thermometer).

METHODS

We again measured patients using the Impairment Level SumScore (ISS) (T8). These data were compared with earlier ISS measurements at CRPS diagnosis (T0) and after one year's treatment (T1). Correlations were determined between these measures.

RESULTS

Forty-five patients participated in the present study. Total median ISS improved by 55% (statistically/clinically significant) after one year's treatment (T1), and worsened (non-significantly) by 14% from T1 to T8 - without differences according to original subdiagnosis. ISS correlations were stronger for T1 vs. T8 than for T0 vs. T1 or T0 vs. T8, being strongest for the ISS factors related to pain.

CONCLUSIONS

Considerable impairments, as measured by ISS, are still present over eight years after first CRPS 1 diagnosis. These do not greatly change between one and eight years post-diagnosis. ISS outcomes are similar for "cold" and "warm" CRPS 1 diagnostic subgroups. Component ISS scores associated with pain appear to possess greatest predictive power.

Changes in cerebrospinal fluid levels of pro-inflammatory cytokines in CRPS

Complex Regional Pain Syndrome (CRPS) Types I and II are characterized by various combinations of sensory, autonomic and motor abnormalities. Pain disproportionate to the severity and duration of the inciting event is the most devastating symptom. In animal studies, conditions resulting in exaggerated pain states demonstrate elevated pro-inflammatory cytokines. In addition, pro-inflammatory cytokines have been shown to induce or increase neuropathic and inflammatory pain. Utilizing high sensitivity enzyme linked immunosorbent assay (ELISA), we compared the levels of the pro-inflammatory cytokines interleukin-1beta (IL-1beta), interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-alpha) in the cerebrospinal fluid (CSF) of patients afflicted with CRPS to CSF levels found in other patients with and without painful conditions. The results from this study demonstrated significant increases in IL-1beta and IL-6, but not TNF-alpha in the CSF of individuals afflicted with CRPS as compared to controls. CSF cytokine levels in controls with painful conditions did not differ from levels in controls without pain. These increases showed no correlation with the patient's gender or weight. These results are consistent with studies that suggest that the pathogenesis of CRPS is due in part to central neuroimmune activation.

Determination of inflammation of reflex sympathetic dystrophy at early stages with Tc-99m HIG scintigraphy: preliminary results

The pathogenesis of reflex sympathetic dystrophy (RSD) is not completely understood. However, an excessive regional inflammation, sensitization of primary somatosensory afferents, and sensitization of spinal neurons are considered to have a role in the pathogenesis of RSD. The underlying pathophysiology relating the clinical picture may help to determine the pharmacotherapeutic approach for an individual patient. Scintigraphy using radiolabelled human polyclonal non-specific immunoglobulin (HIG) has been recognized as a useful tool for the localization of inflammatory disorders. Thirty-six consecutive RSD patients associated with hemiplegia were included in this study. All the patients in this study had three phases bone scan and Tc-99m HIG scintigraphy. On admission, of 36 patients with positive bone scan, 30 had positive Tc-99m HIG scan. All the patients were symptomatic at the time of bone scanning. On the contrary, 24 out of 36 patients subsequently became asymptomatic at an 8-month re-evaluation period. Tc-99m HIG scintigraphy is a non-invasive complementary method for the determination of ongoing inflammatory reactions which also aids the clinicians to predict the response to anti-inflammatory therapy at the very early phase of RSD associated with hemiplegia. This preliminary study may be a source of inspiration for further studies with larger series and longer follow-up .

Patients initially diagnosed as 'warm' or 'cold' CRPS 1 show differences in central sensory processing some eight years after diagnosis: a quantitative sensory testing study

We used quantitative sensory testing (QST) to gain further insight into mechanisms underlying pain in CRPS 1. Specific goals were: (1) to identify altered patterns of sensory processing some 8 years after diagnosis, (2) to document differences in sensory processing between 'warm' and 'cold' diagnostic subgroups, (3) to determine relationships between changed sensory processing and disease progression regarding pain. The study was performed on a cohort of patients (n=47) clinically diagnosed with CRPS 1 of one upper extremity approximately 8 years previously. Pain was quantified by VAS and MacGill Pain Questionnaire (MPQ), and all subjects underwent electrical and mechanical QST. Cold patients (n=13) had poorer MPQ scores than warm ones (n=34), and more pain on electrical stimulation. Their evoked pain increased with disease progression and correlated with clinical pain measures. For both diagnostic subgroups, thresholds to pressure pain were lower on the affected extremity and with disease progression. Eight years after original diagnosis, cold CRPS 1 patients have poorer clinical pain outcomes and show persistent signs of central sensitisation correlating with disease progression. The latter is not the case for warm CRPS 1 patients. Both diagnostic subgroups show greater pressure hyperalgesia on the affected limb and with disease progression. QST may prove useful in the subdiagnosis of CRPS 1 and in quantifying its progression, with both applications warranting further investigation for clinical and research use.

In vivo evidence for apoptosis, but not inflammation in the hindlimb muscle of neuropathic rats

Loose ligation of the rat sciatic nerve (chronic constriction injury (CCI) model) provokes signs and symptoms like those observed in complex regional pain syndrome (CRPS) patients. Neurogenic inflammation is a purported cause of neuropathic pain despite inconsistent evidence to support this hypothesis. To clarify this issue, we examined effects of CCI on microcirculation, inflammatory cell-cell interaction and cell integrity in muscle tissue using intravital fluorescence microscopic, molecular and immunohistochemical techniques. CCI-rats, but not sham-operated animals developed symptoms of neuropathic pain and oedema on the ipsilateral hindpaw. Despite signs of neuropathic pain, high resolution in vivo multifluorescence microscopy revealed physiological values for functional capillary density, leukocyte-endothelial cell interaction and microvascular permeability in muscle tissue of CCI-animals, similarly as found in controls, indicating absence of perfusion failure and inflammatory cell reaction. However, CCI-animals represented with marked apoptosis of bisbenzimide-stained muscle tissue cells, as given by in vivo fluorescence microscopic assessment of cell death-associated condensation, fragmentation and/or crescent-shaped formation of their nuclear chromatin. Apoptosis was further confirmed by increased caspase 3 protein levels and positive terminal deoxyuridine nick end labeling histochemistry. The present study demonstrates that sciatic nerve ligation-induced neuropathy causes cell apoptosis without concomitant inflammation-associated microcirculatory dysfunction in muscle tissue. Beside the well-known pattern of neuropathic pain, the CCI-model has now additionally been shown to reflect the response of muscle tissue to impaired innervation, i.e. prompting muscle cells to undergo non-inflammatory apoptotic cell death. This finding deserves further investigation in that apoptosis may contribute to neuropathic pain conditions like CRPS.

Chronic post-ischemia pain (CPIP): a novel animal model of complex regional pain syndrome-type I (CRPS-I; reflex sympathetic dystrophy) produced by prolonged hindpaw ischemia and reperfusion in the rat

A neuropathic-like pain syndrome was produced in rats following prolonged hindpaw ischemia and reperfusion, creating an animal model of complex regional pain syndrome-Type I (CRPS-I; reflex sympathetic dystrophy) that we call chronic post-ischemia pain (CPIP). The method involves placing a tourniquet (a tight fitting O-ring) on one hindlimb of an anesthetized rat just proximal to the ankle joint for 3 h, and removing it to allow reperfusion prior to termination of the anesthesia. Rats exhibit hyperemia and edema/plasma extravasation of the ischemic hindpaw for a period of 2-4 h after reperfusion. Hyperalgesia to noxious mechanical stimulation (pin prick) and cold (acetone exposure), as well as mechanical allodynia to innocuous mechanical stimulation (von Frey hairs), are evident in the affected hindpaw as early as 8 h after reperfusion, and extend for at least 4 weeks in approximately 70% of the rats. The rats also exhibit spontaneous pain behaviors (hindpaw shaking, licking and favoring), and spread of hyperalgesia/allodynia to the uninjured contralateral hindpaw. Light-microscopic examination of the tibial nerve taken from the region just proximal to the tourniquet reveals no signs of nerve damage. Consistent with the hypothesis that the generation of free radicals may be partly responsible for CRPS-I and CPIP, two free radical scavengers, N-acetyl-L-cysteine (NAC) and 4-hydroxy-2,2,6,6-tetramethylpiperydine-1-oxyl (Tempol), were able to reduce signs of mechanical allodynia in this model.

Intrathecal edaravone, a free radical scavenger, is effective on inflammatory-induced pain in rats

BACKGROUND

Free radicals have some roles in inflammation and systemic and local tissue injuries. (Free radical scavengers are neuroprotective against excitotoxic insults.) Therefore, we hypothesized that free radical scavenger would be analgesic on pain induced by excitotoxicity or inflammation. The purpose of this study was to investigate analgesic effects of intrathecally administered edaravone, a free radical scavenger, on thermal and inflammatory pain.

METHODS

Sprague-Dawley rats were implanted with lumbar intrathecal catheters. Edaravone 0.05, 0.1, 0.5, and 1 mg per 20 microl or saline 20 microl (control) were administered intrathecally, and the withdrawal response to thermal stimulation to the tail (tail-flick test) or flinch responses to subcutaneous formalin injection into the hind paw (formalin test) were tested. General behaviour and motor function were also examined. In each dose group, eight rats were used.

RESULTS

No dose-dependent analgesic effects were observed in the tail-flick test. However, dose-dependent analgesia was obtained in both phase 1 and 2 of the formalin test. The 50% effective dose values were 0.25 mg (95% confidence interval, 0.11-0.56 mg) in phase 1 and 0.25 mg (95% confidence interval, 0.061-1.05 mg) in phase 2. No behavioural side-effects nor motor dysfunction was observed, even with the maximum soluble dose (1 mg/20 microl).

CONCLUSION

Intrathecally administered edaravone, a free radical scavenger, had analgesic effects on inflammatory-induced acute and facilitated pain but not on acute thermal pain, without any behavioural side-effects.

Mast cells are involved in inflammatory reactions during Complex Regional Pain Syndrome type 1

BACKGROUND

The Complex Regional Pain Syndrome type 1 (CRPS1) is a complication of surgery or trauma but spontaneous development is also described. Although the pathogenesis remains debatable, afferent, efferent and central nervous system mechanisms are proposed. Recently we showed involvement of the proinflammatory cytokines IL-6 and TNFalpha which is direct evidence for an inflammatory process. Many types of cells, such as activated T lymphocytes, monocytes, macrophages and skin resident cells like mast cells, could contribute to the production of cytokines. Involvement of mast cells is relatively easy to detect by measurement of tryptase.

AIM

To establish whether mast cells are involved in the inflammatory reactions during CRPS1.

METHODS

Twenty patients fulfilling the Bruehl criteria with CRPS1 in one extremity were studied. Impairment was assessed by registration of pain and measurement of differences in temperature, volume and mobility between the involved and uninvolved extremity. Blisters were made with a suction method in order to determine cytokines and mast cell derived tryptase in the involved and uninvolved extremity.

RESULTS

In the blister fluid a significant difference (median +/- interquartile range, Wilcoxon signed-ranks test P < 0.05) was found between the involved and uninvolved extremity in IL-6 [53.5 (17.3-225) versus 6.2 (2-20.3) pg/ml], TNFalpha [31 (15.5-131.5) versus 8 (4-39) pg/ml], and tryptase [37 (20.5-62.3) versus 12.5 (6.7-23.5) ng/ml]. There was a significant correlation (0.455) between the intensity of pain and tryptase levels in the involved extremity (Spearman's test, P < 0.05).

CONCLUSION

Mast cells are involved in inflammatory reactions during the CRPS1. Mast cells could play a role in the production of cytokines such as TNFalpha.

Substance P signaling contributes to the vascular and nociceptive abnormalities observed in a tibial fracture rat model of complex regional pain syndrome type I

Wrist and ankle fractures are the most frequent causes of complex regional pain syndrome (CRPS type I). The current study examined the temporal development of vascular, nociceptive and bony changes after distal tibial fracture in rats and compared these changes to those observed after cast immobilization in intact normal rats. After baseline testing the right distal tibial was fractured and the hindlimb casted. A control group was simply casted without fracturing the tibia. After 4 weeks the casts were removed and the rats retested. Subsequent testing was performed at 6, 8, 10, 16, and 20 weeks after onset of treatment. Distal tibial fracture or cast immobilization alone generated chronic hindlimb warmth, edema, spontaneous protein extravasation, allodynia, and periarticular osteoporosis, changes resembling those observed in CRPS. Hindlimb warmth and allodynia resolved much more quickly after cast immobilization than after fracture. Previously we observed that the substance P receptor (NK(1)) antagonist LY303870 reversed vascular and nociceptive changes in a sciatic section rat model of CRPS type II. Postulating that facilitated substance P signaling may also contribute to the vascular and nociceptive abnormalities observed after tibial fracture or cast immobilization, we attempted to reverse these changes with LY303870. Hindpaw warmth, spontaneous extravasation, edema, and allodynia were inhibited by LY303870. Collectively, these data support the hypotheses that the distal tibial fracture model simulates CRPS, immobilization alone can generate a syndrome resembling CRPS, and substance P signaling contributes to the vascular and nociceptive changes observed in these models.

Complex regional pain syndrome: mystery explained?

Complex regional pain syndrome (CRPS) is the result of changes to the somatosensory systems that process noxious, tactile, and thermal information; to the sympathetic systems that innervate skin (blood vessels, sweat glands); and to the somatomotor systems. The changes suggest that the CNS representations of the systems have been altered. Patients with CRPS also have peripheral changes (eg, oedema, signs of inflammation, sympathetic-afferent coupling [the basis for sympathetically maintained pain], and trophic changes) that cannot be explained by central changes. On the basis of clinical observation and research in human beings and animals, we hypothesise that CRPS is a systemic disease involving the CNS and peripheral nervous system. The most important question for future research is what causes CRPS? In this article, we suggest a change to the focus of research efforts and treatment. We also suggest there be diagnostic reclassification and redefinition of CRPS.

A substance P receptor (NK1) antagonist can reverse vascular and nociceptive abnormalities in a rat model of complex regional pain syndrome type II

Sciatic nerve section in rats evokes chronic hindlimb edema, pain behavior, and hyperalgesia, a syndrome resembling complex regional pain syndrome (CRPS II) in man. Furthermore, there is an increase in spontaneous protein extravasation in the hindpaw skin of rats after sciatic transection, similar to the increased protein extravasation observed in the edematous limbs of CRPS patients. Now we demonstrate that sciatic nerve section also generates chronic hindlimb warmth, distal articular tenderness, allodynia, and periarticular osteoporosis, sequelae of nerve injury resembling those observed in CRPS. We postulated that facilitated substance P signaling may contribute to these vascular and nociceptive abnormalities and attempted to reverse these changes with the long acting substance P receptor (NK(1)) antagonist LY303870. Hindpaw spontaneous extravasation was inhibited by LY303870. Systemic administration of LY303870 also reversed hindpaw edema and cutaneous warmth. Intrathecal, but not systemic administration of LY303870 reversed soft tissue and articular mechanical hyperalgesia in the hindpaw. Collectively, these data further support the hypothesis that the sciatic nerve transection model closely resembles CRPS and that substance P contributes to the spontaneous extravasation, edema, warmth, and mechanical hyperalgesia observed in this model.

Doppler sonographic assessment of posttraumatic reflex sympathetic dystrophy

OBJECTIVE

To reveal the arterial Doppler sonographic findings in cases of posttraumatic reflex sympathetic dystrophy

METHODS

Eleven patients had hand reflex sympathetic dystrophy, and 9 had foot reflex sympathetic dystrophy. The duration of symptoms ranged from 1 to 28 weeks, and the history of fracture ranged from 6 to 48 weeks. Bilateral brachial or popliteal arteries proximal to injuries were evaluated by Doppler sonography with a 7.5-MHz linear transducer. All patients also had triphasic bone scintigraphy and extremity thermography

RESULTS

Two patients had monophasic waveforms and 4 had low-pulsatility triphasic waveforms on the affected limbs when compared with the asymptomatic limbs. All opposite asymptomatic limbs had normal triphasic waveforms in these 6 cases. Spectral analysis revealed a loss or decrease of a normal reversed flow component with a reduced pulsatility index on the affected limb. Fourteen other patients had symmetric triphasic waveforms. We observed that the patients who had stage 1 reflex sympathetic dystrophy and warm limbs with durations of symptoms of more than 2 weeks had positive Doppler sonographic findings, whereas all patients with stage 2 reflex sympathetic dystrophy and all with normal skin temperature, regardless of stage, had normal waveforms.

CONCLUSIONS

Doppler sonography revealed loss of normal triphasic arterial waveforms in some of the cases of stage 1 disease, whereas many cases of stage 1 disease and all cases of stage 2 disease had normal findings. Therefore, we think that Doppler sonography cannot be used for the diagnosis of reflex sympathetic dystrophy but may help in assessing hemodynamic stages of the disease.

The treatment of complex regional pain syndrome type I with free radical scavengers: a randomized controlled study

To compare the effects of two free radical scavengers, dimethylsulfoxide 50% (DMSO) and N-acetylcysteine (NAC), for treatment of complex regional pain syndrome I (CRPS I), a randomized, double-dummy controlled, double-blind trial was conducted. Two outpatient clinics of two university hospitals in The Netherlands participated in the study and 146 patients, were included over a period of 24 months. Patients were randomized into two treatment groups, one was instructed to apply DMSO 50% five times daily to the affected extremity, the second was treated with NAC 600mg effervescent tablets three times daily, both combined with placebo. Interventions were accompanied by pain medication, occupational therapy for upper extremity CRPS I and physical therapy for lower extremity CRPS I in specific circumstances. Treatment was given for 17 weeks, with a possibility to continue or switch medication after this period, up to 1 year following the onset of treatment. An impairment level sum score was the primary outcome measure. Upper and lower extremity skills and functions, and general health status were also evaluated. Overall, no significant differences were found between NAC and DMSO after 17 and 52 weeks on impairment level and general health status. Significant differences were found for subscores of lower extremity function, in favor of DMSO-treatment. Subgroup analysis showed more favorable results for DMSO for warm CRPS I and significantly better performance of NAC for patients with a cold CRPS I. Results tended to be negatively influenced if the duration of the complaint was longer. Treatment with DMSO and NAC are generally equally effective in treatment of CRPS I. Strong indications exist for differences in effects for subgroups of patients with warm or cold CRPS I: for warm CRPS I, DMSO-treatment appears more favorable, while for cold CRPS I, NAC-treatment appears to be more effective.

Complex regional pain syndrome--diagnostic, mechanisms, CNS involvement and therapy

Complex regional pain syndromes (CRPS, formerly reflex sympathetic dystrophy and causalgia) are neuropathic pain conditions of one extremity developing inadequately after a trauma. The initiating trauma affects primarily the extremity, but can also be a central lesion (e.g., spinal cord injury, stroke). CRPS is clinically characterized by sensory, autonomic and motor disturbances. Pathophysiologically there is evidence for functional changes within the central nervous system and for involvement of peripheral inflammatory processes. The sympathetic nervous system plays a key role in maintaining pain and autonomic dysfunction in the affected extremity. After a primary central lesion, secondary peripheral changes in the paretic extremity are suggested to be important in initiating a CRPS. Though there is no diagnostic gold standard, careful clinical evaluation and additional test procedures should lead to an adequate diagnosis. An early diagnosis and an interdisciplinary approach are important for optimal and successful treatment.

Beyond neurons: evidence that immune and glial cells contribute to pathological pain states

Chronic pain can occur after peripheral nerve injury, infection, or inflammation. Under such neuropathic pain conditions, sensory processing in the affected body region becomes grossly abnormal. Despite decades of research, currently available drugs largely fail to control such pain. This review explores the possibility that the reason for this failure lies in the fact that such drugs were designed to target neurons rather than immune or glial cells. It describes how immune cells are a natural and inextricable part of skin, peripheral nerves, dorsal root ganglia, and spinal cord. It then examines how immune and glial activation may participate in the etiology and symptomatology of diverse pathological pain states in both humans and laboratory animals. Of the variety of substances released by activated immune and glial cells, proinflammatory cytokines (tumor necrosis factor, interleukin-1, interleukin-6) appear to be of special importance in the creation of peripheral nerve and neuronal hyperexcitability. Although this review focuses on immune modulation of pain, the implications are pervasive. Indeed, all nerves and neurons regardless of modality or function are likely affected by immune and glial activation in the ways described for pain.

Defining the therapeutic role of local anesthetic sympathetic blockade in complex regional pain syndrome: a narrative and systematic review

OBJECTIVE

There is growing controversy on the value of blocking the sympathetic nervous system for the treatment of complex regional pain syndromes (CRPS). The authors sought to evaluate the efficacy of sympathetic blockade with local anesthetic in these syndromes. In addition, they performed a comprehensive review of the pathophysiology and other treatments for CRPS.

DESIGN

Systematic review of the literature was performed. MEDLINE was searched from 1966 through 1999. The authors identified only three randomized controlled trials (RCTs) that evaluated sympathetic blockade with local anesthetic, but because of differences in study design they were unable to pool the study data. The authors therefore included nonrandomized studies and case series.

INTERVENTIONS

Studies were included if local anesthetic sympathetic blockade was used in at least 10 patients. Studies were excluded if continuous infusion techniques, somatic nerve blocks, or combined sympatholytic therapies were evaluated.

OUTCOME MEASURES

Pain relief was classified as full, partial, or absent. The lack of a comparison group in the studies allowed only the calculation of distribution of the response categories, and the sum of the pooled rates does not equal 100%.

RESULTS

Twenty-nine studies were included that evaluated 1,144 patients. Nineteen studies were retrospective, 5 prospective case series, 3 RCTs, and 2 nonrandomized controlled studies. The quality of the publications was generally poor. Twenty-nine percent of patients had full response, 41% had partial response, and 32% had absent response. It was not possible to estimate the duration of pain relief.

CONCLUSIONS

This review raises questions as to the efficacy of local anesthetic sympathetic blockade as treatment of CRPS. Its efficacy is based mainly on case series. Less than one third of patients obtained full pain relief. The absence of control groups in case series leads to an overestimation of the treatment response that can explain the findings.

Evidence for local inflammation in complex regional pain syndrome type 1

BACKGROUND

The pathophysiology of complex regional pain syndrome type 1 (CRPS 1) is still a matter of debate. Peripheral afferent, efferent and central mechanisms are supposed. Based on clinical signs and symptoms (e.g. oedema, local temperature changes and chronic pain) local inflammation is suspected.

AIM

To determine the involvement of neuropetides, cytokines and eicosanoids as locally formed mediators of inflammation.

METHODS

In this study, nine patients with proven CRPS 1 were included. Disease activity and impairment was determined by means of a Visual Analogue Scale, the McGill Pain Questionnaire, the difference in volume and temperature between involved and uninvolved extremities, and the reduction in active range of motion of the involved extremity. Venous blood was sampled from and suction blisters made on the involved and uninvolved extremities for measurement of cytokines interleukin (IL)-6, II-1beta and tumour necrosis factor-alpha (TNF-alpha), the neuropetides NPY and CRGP, and prostaglandin E2

RESULTS

The patients included in this study did have a moderate to serious disease activity and impairment. In plasma, no changes of mediators of inflammation were observed. In blister fluid, however, significantly higher levels of IL-6 and TNF-alpha in the involved extremity were observed in comparison with the uninvolved extremity.

CONCLUSIONS

This is the first time that involvement of mediators of inflammation in CRPS 1 has been so clearly and directly demonstrated. This observation opens new approaches for the succesful use and development of immunosuppressives in CRPS 1.

Neuroimmune alterations in the complex regional pain syndrome

This review focuses on some clinical aspects of the complex regional pain syndrome, such as oedema, local temperature changes and chronic pain, as a result of supposed neurogenic inflammation. Involvement of the immune system could imply the subsequent release of neuropeptides, pro-inflammatory cytokines and eicosanoids, which in turn leads to a complex cross-talk of primary and secondary generated mediators of inflammation. The development and application of drugs that act through selective receptor antagonism or enzymatic synthesis inhibition to prevent further stimulation of this cascade that could inevitably lead to chronicity of this disease are extensively discussed.

Glucocorticoid inhibition of neuropathic limb edema and cutaneous neurogenic extravasation

Sciatic nerve section in rats evokes chronic limb edema, pain behavior, and hindpaw hyperalgesia, a syndrome resembling the complex regional pain syndrome type II (CRPS II or causalgia) in man. Glucocorticoids such as methylprednisolone (MP) have been used as analgesic and anti-edematous agents in patients suffering from CRPS, and interestingly these therapeutic effects appear to persist in some patients after stopping the medication. Similar to the CRPS clinical response to glucocorticoids, we now demonstrate that chronic hindpaw edema in the sciatic transection CRPS model is reversed by a continuous infusion of MP (3 mg/kg/day over 21 days), and this anti-edematous effect persists for at least 1 week after discontinuing MP. Furthermore, there is a chronic increase in spontaneous protein extravasation in the hindpaw skin of rats after sciatic transection, similar to the increased protein extravasation observed in the edematous hands of CRPS patients. A 2-week infusion of MP (3 mg/kg/day) reduced spontaneous protein extravasation in the hindpaw skin by 80%. We postulated that increased spontaneous neurogenic extravasation resulted in development of limb edema in both the animal model and the CRPS patient, and that the anti-edematous effects of MP are due to an inhibition of spontaneous extravasation. Additional experiments examined the inhibitory effects of MP infusion on electrically-evoked neurogenic extravasation in the hindpaw skin of normal rats. MP inhibition was dose- and time-dependent, with an ED(50) of 1.2 mg/kg/day for a 14-day continuous infusion of MP, and a maximum inhibitory effect requiring 17 days of MP infusion (3 mg/kg/day). MP (3 mg/kg/day for 14 days) also blocked both capsaicin- and SP-evoked neurogenic extravasation, indicating a post-junctional inhibitory effect. Our interpretation is that increased spontaneous neurogenic extravasation in this CRPS model contributed to the development and maintenance of hindpaw edema, and that chronic MP administration dose- and time-dependently blocked neurogenic extravasation at a post-junctional level, thus reversing spontaneous extravasation and limb edema in this model.

Assessment of the peripheral microcirculation using computer-assisted venous congestion plethysmography in post-traumatic complex regional pain syndrome type I

In complex regional pain syndrome type I (CRPS-I), edema of the affected limb is a common finding. Therefore, the changes in macro- and microcirculatory parameters were investigated to elucidate the underlying pathophysiology. Twenty-four patients with post-traumatic CRPS-I and 25 gender- and age-matched healthy subjects were examined by means of an advanced computer-assisted venous congestion strain-gauge plethysmograph. The recording of the volume response of the forearm to a stepwise inflation of an occlusion cuff placed at the upper arm enabled the calculation of the arterial blood flow into the arm (Q(a)), the vascular compliance (C), the peripheral venous pressure (P(v)), the isovolumetric venous pressure (P(vi); = hydrostatic pressure needed to achieve net fluid filtration) and the capillary filtration capacity (CFC)--an index of microvascular permeability. The study revealed no difference in any of the parameters between the right and left hand of healthy subjects. In CRPS-I patients, however Q(a), P(v), P(vi) and CFC were significantly (p < 0.01/0.001) elevated in the affected arm (Q(a) 11.2 +/- 7.0 ml x min(-1) x 100 ml(-1), P(v) 20.2 +/- 8.1 mm Hg, P(vi) 24.7 +/- 4.2 mm Hg, CFC 0.0058 +/- 0.0015 ml x min(-1) x 100 ml(-1) x mm Hg(-1)) compared to the unaffected arm (Q(a) 4.2 +/- 2.4 ml x min(-1) x 100 ml(-1), P(v) 10.0 +/- 5.1 mm Hg, P(vi) 13.2 +/- 3.7 mm Hg, CFC 0.0038 +/- 0.0005 ml x min(-1) x 100 ml(-1) x mm Hg(-1)) and the values obtained in healthy controls (Q(a) 5.1 +/- 1.3 ml x min(-1) x 100 ml(-1), P(v) 10.4 +/- 4.3 mm Hg, P(vi) 15.7 +/- 3.3 mm Hg, CFC 0.0048 +/- 0.0012 ml x min(-1) x 100 ml(-1) x mm Hg(-1)). Whereas the values in the unaffected arm of CRPS-I patients revealed no difference in Q(a), P(v) and P(vi) but a lower CFC (p < 0.01) compared to those from healthy controls. These results suggest profound changes in both macro- and microvascular perfusion in the affected arm of CRPS-I patients. The high CFC contributes to the edema formation, and combined with the elevated P(vi), they are in agreement with the hypothesis of an inflammatory origin of CRPS.

Influence of painful chronic neuropathy on neurogenic inflammation

The effect of topical application of capsaicin cream on neurogenic inflammation was investigated in a neuropathic pain model in rat. The neuropathic state was induced by loose ligation of the sciatic nerve with a chromic gut suture. A marked thermal hyperalgesia was observed in response to heat stimulation applied to the operated side from 3 days through 2 weeks, followed by a gradual return to the control level 35 days after surgery. In sham-operated animals, topical application of capsaicin cream to both sides of the hind paw, the instep and sole, as well as antidromic stimulation of the sciatic nerve led to a significant increase in the amounts of Evans blue and substance P (SP) released into the perfusates. This stimulus-induced extravasation was significantly suppressed by pretreatment with RP67580, an NK1 antagonist. On day 7 after ligation, capsaicin- and antidromic stimulation-induced extravasation were significantly reduced. At this time, both amount of SP released immediately after application of capsaicin and during antidromic stimulation were almost similar to that in sham-operated rats, whereas the basal amount of SP release significantly increased in ligated animals. In particular a major release of SP was detected immediately after the start of the perfusion compared with that in sham-operated rats. Plasma extravasation evoked by SP (10(-4) M) applied to the subcutaneous perfusate was significantly less in ligated than in sham-operated rats. These results suggest that nerve injury with chronic pain may produce increase in basal SP release into the peripheral tissues, and then such enhanced SP release cause reduction of SP-induced extravasation.