Complex regional pain syndrome: mystery explained?

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.

Acute posttraumatic ischemia of the limbs: algodystrophy or related syndrome? A prospective study on a series of 25 patients

The aim of this study was to present clinical and paraclinical features of a rarely studied vascular syndrome that usually occurs after a minor traumatic injury. The prospective study of 25 patients identified a group of young subjects, mainly women, generally with history of vascular hyperactivity to cold, showing disseminated pain in a limb always combined with vasospasm, consecutive to a minor traumatic injury in general, and simulating acute ischemia of a limb. The patients' arterial and microcirculatory flows were restored after warming, which proved that they were suffering from intense, reversible but pathological vasospasm, because of its duration, diffusion, intensity, and disproportion as to the triggering event. The symptoms may recur, but they respond to physiotherapy. Patients' follow-up showed that microcirculatory function remains abnormal sometime after the initial episode with, in particular, an exacerbation of the venoarteriolar reflex.

Vasodilative effect of isosorbide dinitrate ointment in complex regional pain syndrome type 1

BACKGROUND

In complex regional pain syndrome type 1 (CRPS1) vascular changes occur from the initial, inflammatory event onto the trophic signs during chronicity of the disease, resulting in blood flow disturbances and marked temperature changes. Pharmacotherapeutic treatment is generally inadequate.

AIM

To determine whether local application of the nitric oxide donor isosorbide dinitrate (ISDN) could cause vasodilation and thereby improve tissue blood distribution in the affected extremity.

METHODS

In a pilot study, 5 female patients with CRPS1 in one hand were treated with ISDN ointment 4 times daily during 10 weeks. As a primary objective videothermography was used to monitor changes in blood distribution in both the involved and contralateral extremities.

RESULTS

Patients treated with ISDN showed an increase of 4 degrees C to 6 degrees C in mean skin temperature of the cold CRPS1 hands, reaching values similar to that of the contralateral extremities within 2 to 4 weeks time, suggesting normalization of blood distribution. This was confirmed by an improvement in skin color. In 3 patients the Visual Analog Scale pain declined, whereas in the other 2 patients the Visual Analog Scale pain was unchanged over time.

CONCLUSIONS

In this pilot study, topical application of ISDN seems to be beneficial to improve symptoms for patients with cold type CRPS1, but further study is needed.

Sympathetic vasoconstrictor antagonism and vasodilatation relieve mechanical allodynia in rats with chronic postischemia pain

Chronic pain that responds to antisympathetic treatments and alpha-adrenergic antagonists is clinically referred to as sympathetically maintained pain. Animal models of neuropathic pain have shown mixed results in terms of antinociceptive effectiveness of antisympathetic agents. The effectiveness of these agents have not been yet investigated in animal models of complex regional pain syndrome-type 1 (CRPS-I). In this study, we examined the effectiveness of antisympathetic agents and sympathetic vasoconstrictor antagonists, as well as agents that are vasodilators, in relieving mechanical allodynia in a recently developed animal model of CRPS-I (chronic postischemia pain or CPIP) produced by 3 hours of hind paw ischemia-reperfusion injury. Systemic guanethidine, phentolamine, clonidine, and prazosin are effective in reducing mechanical allodynia particularly at 2 days after reperfusion, and less so at 7 days after reperfusion. A nitric oxide donor vasodilator, SIN-1, also reduces mechanical allodynia more effectively at 2 days after reperfusion, but not at 7 days after reperfusion. These results suggest that the pain of CPIP, and possibly also CRPS-I, is relieved by reducing sympathetically mediated vasoconstriction, or enhancing vasodilatation.

PERSPECTIVE

The results of this study indicate that sympathetic block, or administration of alpha(1)-adrenergic antagonists, clonidine, or a nitric oxide donor, relieve allodynia in an animal model of CRPS-I. Thus, the pain of CRPS-I may depend on enhanced vasoconstrictor responsiveness, which may be relieved by blocking sympathetic efferent-dependent vasoconstriction, or by enhancing nitric oxide-dependent vasodilatation.

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.

Short-term results of bilateral S2-S4 sacral neuromodulation for the treatment of refractory interstitial cystitis, painful bladder syndrome, and chronic pelvic pain

We evaluated the efficacy of bilateral caudal epidural sacral neuromodulation for the treatment of refractory chronic pelvic pain (CPP), painful bladder syndrome, and interstitial cystitis (IC). Thirty consecutive patients (21 female, 9 male) with severe refractory symptoms underwent bilateral S2-S4 sacral neuromodulation for CPP/IC. Patients were evaluated with the O'Leary IC symptom and problem index (ICSI, ICPI), the short form of the Urogenital Distress Inventory (UDI-6), and the RAND 36-item health survey (SF-36) preoperatively and 6 months postoperatively. The mean and minimum follow-up were 15 and 6 months, respectively. Of the 30 patients, 23 (77%) had a successful trial stimulation and were permanently implanted. Among these patients, the ICSI and ICPI scores improved by 35 (p = 0.005) and 38% (p = 0.007), respectively. The pain score improved by 40% (p = 0.04) and the UDI-6 score by 26% (p = 0.05). On average, patients reported a 42% improvement in their symptoms. SF-36 scores did not improve significantly. In refractory patients, bilateral caudal epidural sacral neuromodulation is another possible mode of treatment, which appears to improve both pelvic pain and voiding symptoms.

Proprioceptive feedback enhancement induced by vibratory stimulation in complex regional pain syndrome type I: An open comparative pilot study in 11 patients

OBJECTIVE

Complex regional pain syndrome type I (CRPS-I) is now considered as a central nervous system disease with peripheral manifestations. CRPS-I may result from a mismatch between sensory input and motor output leading to a disorganization of motor programming in cortical structures. According to previous studies in the field of motor control, one efficient way to correct this mismatch could be a proprioceptive feedback enhancement. The goal of the present study was to determine whether vibratory stimulation by improving proprioceptive feedback may increase range of motion and minimize pain in patients with CRPS-I.

METHODS

An open non-randomized study was conducted in 11 patients with CRPS-I of the hand and wrist. Conventional rehabilitation sessions were given for 10 weeks. During each session, patients in the intervention group (n=7) received vibratory stimulation of the affected region; the remaining 4 patients served as the controls.

RESULTS

After 10 weeks, range-of-motion gains were about 30% larger and pain severity was about 50% lower in the intervention group than in the control group. A significant decrease in analgesic use occurred in the intervention group.

DISCUSSION

Vibratory stimulation may significantly improve range of motion and pain in patients with CRPS-I, probably by reestablishing consonance between sensory input and motor output at cortical level. Prospective randomized studies in larger numbers of patients are needed. Cross-over designs or simulated vibratory stimulation should be used to minimize bias.

Psychoneuroendocrine stress response may impair neutrophil function in complex regional pain syndrome

In order to elucidate the interaction between pain, stress and innate immunity in complex regional pain syndrome (CRPS), we assessed pain and stress levels in CRPS patients and compared ex vivo functions of neutrophils between patients with CRPS and healthy volunteers. As compared with healthy volunteers, the following major alterations in CRPS patients were found: (I) elevated stress score (PTSS-10) and stress hormone concentrations, (II) decreased expression of the CD62L and CD11b/CD18 on neutrophils, (III) impaired ability of autologous plasma to enhance the capability of neutrophils to phagocytose zymosan particles, and (IV) a negative correlation between PTSS-10 values and autologous plasma enhanced phagocytosis. In vitro incubation of neutrophils with catecholamines decreased phagocytosis of zymosan. In conclusion, CRPS patients exhibit signs of impaired innate immunity which might reflect the immunological consequence of an immunosuppressive neuroendocrine stress response.

Complex regional pain syndrome with special emphasis on the knee

Complex regional pain syndrome is characterised by an exaggerated response to injury in a limb with intense prolonged pain, vasomotor disturbance, delayed functional recovery and trophic changes. This review describes the current knowledge of the condition and outlines the methods of treatment available with particular emphasis on the knee.

Pediatric complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a relatively new diagnostic entity in pediatrics. There is debate as to what constitutes the most effective treatment for pediatric CRPS. This study presents the patient characteristics, clinical course, and treatment outcome of 20 children diagnosed with CRPS at a major children's hospital during a 4-year period. The results showed that pediatric CRPS occurs predominantly in girls (90%) in later childhood and adolescence (mean age, 11.8 [range, 8-16 years]). It affects mainly the lower limbs (85%), with a predilection for the foot (75% of all cases), and was frequently initiated by minor trauma (80%). In many cases, there was a lengthy time to diagnosis (mean, 13.6 weeks) that delayed the institution of treatment, which consisted of intensive physiotherapy and psychological therapy. Most children (70%) required adjuvant medications (amitriptyline and/or gabapentin) for analgesia and to enable them to participate in physiotherapy. A high percentage of children had complete resolution of symptoms using this treatment regime (mean, 15.4 weeks [range, 3 days to 64 weeks]), but 40% required treatment as a hospital inpatient and 20% had a relapse episode. In conclusion, pediatric CRPS is under-recognized by clinicians, resulting in diagnostic delays, but has a favorable outcome to noninvasive treatment in that complete resolution of symptoms and signs occur in most patients. However, the lengthy period to achieve symptom resolution in some children and a high relapse rate support the need for further research into other treatment modalities.

Complete recovery from intractable complex regional pain syndrome, CRPS-type I, following anesthetic ketamine and midazolam

OBJECTIVE

To describe the treatment of an intractable complex regional pain syndrome I (CRPS-I) patient with anesthetic doses of ketamine supplemented with midazolam.

METHODS

A patient presented with a rapidly progressing contiguous spread of CRPS from a severe ligamentous wrist injury. Standard pharmacological and interventional therapy successively failed to halt the spread of CRPS from the wrist to the entire right arm. Her pain was unmanageable with all standard therapy. As a last treatment option, the patient was transferred to the intensive care unit and treated on a compassionate care basis with anesthetic doses of ketamine in gradually increasing (3-5 mg/kg/h) doses in conjunction with midazolam over a period of 5 days.

RESULTS

On the second day of the ketamine and midazolam infusion, edema, and discoloration began to resolve and increased spontaneous movement was noted. On day 6, symptoms completely resolved and infusions were tapered. The patient emerged from anesthesia completely free of pain and associated CRPS signs and symptoms. The patient has maintained this complete remission from CRPS for 8 years now.

CONCLUSIONS

In a patient with severe spreading and refractory CRPS, a complete and long-term remission from CRPS has been obtained utilizing ketamine and midazolam in anesthetic doses. This intensive care procedure has very serious risks but no severe complications occurred. The psychiatric side effects of ketamine were successfully managed with the concomitant use of midazolam and resolved within 1 month of treatment. This case report illustrates the effectiveness and safety of high-dose ketamine in a patient with generalized, refractory CRPS.

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.

Complex regional pain syndrome with special emphasis on trauma

Complex regional pain syndrome (CRPS) is a condition characterised by a disproportionate regional response to a stimulus leading to disproportionate pain and sensory changes with signs of sympathetic autonomic over-activity. This article summarises the literature on CRPS, particularly the diagnosis and treatment with special emphasis on trauma.

Neurogenic painful inflammation

PURPOSE OF REVIEW

Neurogenic inflammation results from the release of neuropeptides from peripheral nerve terminals. This secretion can be induced by two mechanisms: activation of afferent sensory nerves (e.g. by disease processes or experimentally by electrical stimulation) or activation of receptors expressed on peripheral nerve terminals. While the role of these mechanisms in the regulation of inflammation is well described, its significance for the generation of pain is much less clear and will be examined in this review.

RECENT FINDINGS

Activation of two receptors on peripheral sensory neurons (i.e. transient receptor potential vanilloid-1 channel and proteinase activated receptor-2) has been shown to induce neurogenic inflammation. Interference with this activation can ameliorate pain, but it remains uncertain whether this effect is indeed mediated by blockage of neurogenic inflammation. Two human diseases (complex regional pain syndrome and migraine) are believed to result from aberrant neuronal activation. In complex regional pain syndrome, studies in human patients and in a recently established animal model do not support a role for neurogenic inflammation in pain. In migraine, antagonists to the receptor for calcitonin gene related peptide ameliorated headache and could be the first conclusive evidence for the role of neurogenic inflammation in the generation of pain. Lastly, spinal mechanisms also appear to regulate immune cell recruitment to a peripheral site and seem to interfere with antinociception.

SUMMARY

While considerable experimental and clinical evidence supports the existence of neurogenic inflammation, it is less clear whether this process plays an important role in the generation of pain.

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.

Imaging in Early Posttraumatic Complex Regional Pain Syndrome

OBJECTIVES

The complex regional pain syndrome type I (CRPS I) still is difficult to diagnose in posttraumatic patients. As CRPS I is a clinical diagnosis the characteristic symptoms have to be differentiated from normal posttraumatic states. Several diagnostic procedures are applied to facilitate an early diagnosis, although their value for diagnosing posttraumatic CRPS I is unclear.

METHODS

One hundred fifty-eight consecutive patients with distal radial fracture were followed up for 16 weeks after trauma. To assess the diagnostic value of the commonly applied methods a detailed clinical examination was carried out 2, 8, and 16 weeks after trauma in conjunction with bilateral thermography, plain radiographs of the hand skeleton, three phase bone scans (TPBSs), and contrast-enhanced magnetic resonance imaging (MRI). All imaging procedures were assessed blinded.

RESULTS

At the end of the observation period 18 patients (11%) were clinically identified as having CRPS I and 13 patients (8%) revealed an incomplete clinical picture which were defined as CRPS borderline cases. The sensitivity of all diagnostic procedures used was poor and decreased between the first and the last examinations (thermography: 45% to 29%; TPBS: 19% to 14%; MRI: 43% to 13%; bilateral radiographs: 36%). In contrast a high specificity was observed in the TPBS and MRI at the eighth and sixteenth-week examinations (TPBS: 96%, 100%; MRI: 78%, 98%) and for bilateral radiographs 8 weeks after trauma (94%). The thermography presented a fair specificity that improved from the second to the sixteenth week (50% to 89%).

DISCUSSION

The poor sensitivity of all tested procedures combined with a reasonable specificity produced a low positive predictive value (17% to 60%) and a moderate negative predictive value (79% to 86%). These results suggest, that those procedures cannot be used as screening tests. Imaging methods are not able to reliably differentiate between normal posttraumatic changes and changes due to CRPS I. Clinical findings remain the gold standard for the diagnosis of CRPS I and the procedures described above may serve as additional tools to establish the diagnosis in doubtful cases.

Applied information retrieval and multidisciplinary research: new mechanistic hypotheses in complex regional pain syndrome

Background

Collaborative efforts of physicians and basic scientists are often necessary in the investigation of complex disorders. Difficulties can arise, however, when large amounts of information need to reviewed. Advanced information retrieval can be beneficial in combining and reviewing data obtained from the various scientific fields. In this paper, a team of investigators with varying backgrounds has applied advanced information retrieval methods, in the form of text mining and entity relationship tools, to review the current literature, with the intention to generate new insights into the molecular mechanisms underlying a complex disorder. As an example of such a disorder the Complex Regional Pain Syndrome (CRPS) was chosen. CRPS is a painful and debilitating syndrome with a complex etiology that is still unraveled for a considerable part, resulting in suboptimal diagnosis and treatment.

Results

A text mining based approach combined with a simple network analysis identified Nuclear Factor kappa B (NFκB) as a possible central mediator in both the initiation and progression of CRPS.

Conclusion

The result shows the added value of a multidisciplinary approach combined with information retrieval in hypothesis discovery in biomedical research. The new hypothesis, which was derived in silico, provides a framework for further mechanistic studies into the underlying molecular mechanisms of CRPS and requires evaluation in clinical and epidemiological studies.

Laser-evoked Potentials Correlate With Clinical Evolution in a Case of Spontaneous and Recurrent Complex Regional Pain Syndrome Type I

We describe a case of spontaneous complex regional pain syndrome developing first in the left arm and 2 years later in the right foot of a 14-year-old girl. Physical examination showed abnormalities in tactile and thermal sensitivity. Laser-evoked potentials (LEPs) after stimulation of the affected right foot were absent in the acute phase and then progressively recovered over a period of 5 months, in correlation with clinical changes. To our knowledge, no systematic analysis of LEPs in complex regional pain syndrome has been published. We suggest that the observed electrophysiologic alterations could result from a temporary dysfunction of attentional systems, which are assumed to contribute greatly to the LEPs vertex complex. Further studies are needed to test this hypothesis.

Dysynchiria is not a common feature of neuropathic pain

Patients with chronic neuropathic pain (non-CRPS) and brush-evoked allodynia watched a reflected image of their corresponding but opposite skin region being brushed in a mirror. Unlike complex regional pain syndrome Type 1, this process did not evoke any sensation at the affected area ('dysynchiria'). We conclude that central nociceptive sensitisation alone is not sufficient to cause dysynchiria in neuropathic pain. The results imply a difference in cortical pain processing between complex regional pain syndrome and other chronic neuropathic pain.

Brain imaging of neuropathic pain

Many studies have focused on defining the network of brain structures involved in normal physiological pain. The different dimensions of pain perception (i.e., sensory discriminative, affective/emotional, cognitive/evaluative) have been shown to depend on different areas of the brain. In contrast, much less is known about the neural basis of pathological chronic pain. In particular, it is unclear whether such pain results from changes to the physiological "pain matrix". We review here studies on changes in brain activity associated with neuropathic pain syndromes-a specific category of chronic pain associated with peripheral or central neurological lesions. Patients may report combinations of spontaneous pain and allodynia/hyperalgesia-abnormal pain evoked by stimuli that normally induce no/little sensation of pain. Modern neuroimaging methods (positron emission tomography (PET) and functional MRI (fMRI)) have been used to determine whether different neuropathic pain symptoms involve similar brain structures and whether these structures are related to the physiological "pain matrix". PET studies have suggested that spontaneous neuropathic pain is associated principally with changes in thalamic activity and the medial pain system, which is preferentially involved in the emotional dimension of pain. Both PET and fMRI have been used to investigate the basis of allodynia. The results obtained have been very variable, probably reflecting the heterogeneity of patients in terms of etiology, lesion topography, symptoms and stimulation procedures. Overall, these studies indicated that acute physiological pain and neuropathic pain have distinct although overlapping brain activation pattern, but that there is no unique "pain matrix" or "allodynia network".

The "kick-off" position: a new sign for early diagnosis of complex regional pain syndrome in the leg

BACKGROUND

Complex regional pain syndrome (CRPS) is a clinical entity that develops after a precipitating injury. It involves dysfunction of the sensory, autonomic, and motor systems and frequently is missed on initial presentation. The purpose of this report was to describe a simple clinical sign that can aid in its diagnosis.

METHODS

A retrospective review was conducted of 39 consecutive patients with CRPS type I or II seen in a foot and ankle clinic between October, 2001, and May, 2005. The diagnosis was based on clinical findings.

RESULTS

Twenty-six patients had type I (67%) and 13 patients had type II (33%) CRPS. The most common nerve involved in type II was the superficial peroneal nerve. Each patient, while sitting on the exam table, held the affected extremity with the knee extended against gravity. When the leg was pushed back to a relaxed and suspended position, the patient eventually involuntarily resumed the extended position. This position in which the patients held their legs was termed the "kick-off" position sign. Nine patients were seen at the foot and ankle clinic within 6 weeks of the initial inciting event and had an established "kick-off" position sign within 3 months from the time of injury. The disappearance of this sign correlated with the subsidence of pain.

CONCLUSIONS

Patients with CRPS have variable clinical presentations. The awareness of this simple observation in the right clinical setting should raise the index of suspicion of CRPS in the differential diagnosis. Early treatment of this syndrome is associated with better outcome.

Increased endothelin-1 and diminished nitric oxide levels in blister fluids of patients with intermediate cold type complex regional pain syndrome type 1

Background

In complex regional pain syndrome type 1 (CRPS1) pro-inflammatory mediators and vascular changes play an important role in the sustained development and outcome of the disease. The aim of this study was to determine the involvement of vasoactive substances endothelin-1 (ET-1) and nitric oxide (NO) during early chronic CRPS1.

Methods

Included were 29 patients with CRPS 1 who were diagnosed during the acute stage of their disease and observed during follow-up visits. Disease activity and impairment were determined and artificial suction blisters were made on the CRPS1 and the contralateral extremities for measurements of IL-6, TNF-α, ET-1 and nitrate/nitrite (NOx).

Results

The levels of IL-6, TNF-α and ET-1 in blister fluid in the CRPS1 extremity versus the contralateral extremity were significantly increased and correlated with each other, whereas NOx levels were decreased.

Conclusion

The NOx/ET-1 ratio appears to be disturbed in the intermediate stage of CRPS, resulting in vasoconstriction and consequently in a diminished tissue blood distribution.

Sensorimotor integration in Complex Regional Pain Syndrome: a transcranial magnetic stimulation study

There is evidence that patients with Complex Regional Pain Syndrome (CRPS) have altered central sensorimotor processing. Sensory input can influence motor output either through indirect pathways or through direct connections from the sensory to motor cortex. The purpose of this study was to investigate sensorimotor interaction via direct connections in patients with CRPS and to compare the results with normal subjects'. Direct short-latency sensory-motor interaction was evaluated in eight patients with CRPS1 affecting a hand. Modulation of EMG responses to transcranial magnetic stimulation (TMS) induced by concomitant median nerve stimulation was measured, the so-called, short-latency afferent inhibition (SAI). Results were compared with eight normal subjects who were age and sex matched with the patients. As expected, all the normal subjects' EMG responses to TMS with median nerve stimulation were smaller than responses to TMS alone. In seven of the eight CRPS patients EMG responses to TMS were suppressed when paired with median nerve stimulation. Only one CRPS patient's results showed no suppression of EMG responses. These results suggest that the disease mechanisms of CRPS1 do not typically affect the direct neural circuit between sensory and motor cortex and that normal sensorimotor interaction is occurring via this route.

Advances in treatment of complex regional pain syndrome: recent insights on a perplexing disease

PURPOSE OF REVIEW

The paper is a critical appraisal of recent advances in the treatment of complex regional pain syndrome. Rapidly changing concepts related to the pathophysiology of this disease has transformed its current management and necessitates an updated review of the literature.

RECENT FINDINGS

Chronic regional pain syndrome is a perplexing disease that continues to challenge researchers with respect to its cause and treatment. Recent modification to diagnostic criteria has enabled clinicians to diagnose this disease in a more consistent fashion. Emerging data indicate a possible role of inflammation in the overall pathophysiology and have led to treatment trials with newer anti-inflammatory medications. Certain 'conventional' interventional techniques have been recently scrutinized. A few novel therapeutic options like graded imagery are also outlined.

SUMMARY

Enhanced insight into the pathophysiology of chronic regional pain syndrome has modified current clinical practice and the focus of research. Certain 'standard' therapeutic options for chronic regional pain syndrome have failed the test of time while others have prevailed. New options have recently been evaluated and have shown promising early results. Knowledge of recent advances in chronic regional pain syndrome will help pain physicians provide optimal care to these patients.

Mechanisms of disease: neuropathic pain--a clinical perspective

Neuropathic pain syndromes-pain after a lesion or disease of the peripheral or central nervous system-are clinically characterized by spontaneous and evoked types of pain, which are underpinned by various distinct pathophysiological mechanisms in the peripheral and central nervous systems. In some patients, the nerve lesion triggers molecular changes in nociceptive neurons, which become abnormally sensitive and develop pathological spontaneous activity. Inflammatory reactions of the damaged nerve trunk can induce ectopic nociceptor activity, causing spontaneous pain. The hyperactivity in nociceptors induces secondary changes in processing neurons in the spinal cord and brain, so that input from mechanoreceptive A-fibers is perceived as pain. Neuroplastic changes in the central pain modulatory systems can lead to further hyperexcitability. The treatment of neuropathic pain is still unsatisfactory, and a new hypothetical concept has been proposed, in which pain is analyzed on the basis of underlying mechanisms. The increased knowledge of pain-generating mechanisms and their translation into symptoms and signs might eventually allow a dissection of the mechanisms that operate in each patient. If a precise clinical phenotypic characterization of the neuropathic pain is combined with a selection of drugs that act on those mechanisms, it should ultimately be possible to design optimal treatments for individuals. This review discusses the conceptual framework of the novel mechanism-based classification, encouraging the reader to see neuropathic pain as a clinical entity rather than a compilation of single disease states.

Many cold sensitive peripheral neurons of the mouse do not express TRPM8 or TRPA1

Neurons of the peripheral nervous system detect changes in temperature through activation of specialised ion channels. Members of the transient receptor potential family TRPM8 and TRPA1 are candidates for the principal transducers of cold stimuli. Using ratiometric calcium imaging we now show that 19% of acutely dissociated mouse dorsal root (DRG) and 45% of superior cervical ganglia (SCG) neurons responded to a brief cold stimulus. Amongst cold-responsive DRG neurons 34+/-2% responded to the TRPM8 agonist menthol, 18+/-3% to the TRPA1 agonist mustard oil and 5% to both stimuli. A third of the cold-sensitive neurons did not respond to any TRP channel agonist. Cold-sensitive neurons of the SCG did not respond to menthol and only 3% responded to mustard oil. The threshold of SCG neurons was at significantly cooler temperatures than that of DRG neurons. Using real-time PCR, TRPA1 was expressed over 100-fold more in DRG than SCG, while TRPM8 was present in DRG only. The relatively small amount of TRPA1 transcript present in SCG did not correlate with the high level of cold sensitivity. We conclude that cold sensitivity in sympathetic neurons and in a significant proportion of sensory neurons is generated in the absence of TRPM8 and TRPA1.

Severity and specificity of neglect-like symptoms in patients with complex regional pain syndrome (CRPS) compared to chronic limb pain of other origins

In the literature, the neglect-like syndrome is described as an additional phenomenon of CRPS. The perception of the affected limb as strange, disordered and not belonging to the body is typical of and characterises this syndrome. Since this phenomenon has never been studied in other pain conditions, we assessed occurrence and extent of neglect-like symptoms in patients with CRPS of the upper and lower limb (n = 123) and in a control group with chronic limb pain of other origins (n = 117). Our questionnaire for describing the neglect-like syndrome encompassed five items following Galer and Jensen [Galer BS, Jensen M. Neglect-like symptoms in complex regional pain syndrome: results of a self-administered survey. Journal of Pain and Symptom Management 1999;18:213-6], with a six-point response scale inquiring the extent of respective symptoms. Results show that CRPS-patients as well as patients with non-CRPS limb pain exhibit the so-called neglect-like syndrome. However, the number of patients confirming such symptoms was significantly higher (OR = 2.87) in the CRPS group, moreover, these patients reported more severe symptoms (F = 17.74; p = 0.001). If the neglect-like total score is > or = 5, the diagnostic sensitivity is low (21.1%), but the specificity for the diagnosis of CRPS reaches 90.6%. In this study, patients with CRPS of the upper and lower limb were included. The only difference between these two localisations concerning the neglect-like syndrome was the symptom of 'involuntary movements', which occurs significantly more often in affected legs. In conclusion, we recommend to evaluate neglect-like symptoms and to use them as an additional criterion in the diagnosis of CRPS. High scores of > or = 5 confirm the diagnosis of CRPS, whereas lower scores must not be used for disease classification.

Cerebral glucose metabolism change in patients with complex regional pain syndrome: a PET study

PURPOSE

The aim of this study was to examine abnormalities of the central nervous system in patients with chronic pain who were diagnosed with complex regional pain syndrome (CRPS).

MATERIALS AND METHODS

Brain activity was assessed using (18)F-fluorodeoxyglucose positron emission tomography. The data collected from 18 patients were compared with data obtained from 13 normal age-matched controls.

RESULTS

Our results showed that glucose metabolism was bilaterally increased in the secondary somatosensory cortex, mid-anterior cingulated cortex (ACC) or posterior cingulated cortex (PCC) (or both), parietal cortex, posterior parietal cortex (PPC), and cerebellum as well as in the right posterior insula and right thalamus in our patients. In contrast, glucose metabolism was reduced contralaterally in the dorsal prefrontal cortex and primary motor cortex. Glucose metabolism was bilaterally elevated in the mid-ACC/PCC and the PPC, which correlated with pain duration.

CONCLUSION

These data suggested that glucose metabolism in the brains of patients with CRPS changes dramatically at each location. In particular, glucose metabolism was increased in the areas concerned with somatosensory perception, possibly due to continuous painful stimulation.

The clinical challenge of chronic neuropathic pain

BACKGROUND

The clinician often faces the problem that certain types of chronic pains remain refractory to the commonly used analgesic treatment options. Neuropathic pain, which is defined as pain caused by direct nerve lesions, may have different causes and a variety of clinical presentations. A correct management of chronic neuropathic pain requires a thorough understanding of the potential causes, the diagnosis and the pathophysiological mechanisms.

OBJECTIVES

The purpose of this review article is to provide the reader with the latest insights in the diagnostic work-out and the clinical presentation of neuropathic pain. Additionally, the possible pathophysiological changes induced by nerve lesions are explained.

METHODS

An extensive literature review was performed using Pubmed citations.

RESULTS AND CONCLUSIONS

This article, which is based on extensive literature review, aims at providing a concise review of the current knowledge regarding aetiology, diagnosis and pathophysiology of neuropathic pain.

Pathophysiology of complex regional pain syndrome

Complex regional pain syndrome (CRPS) most often follows injury to peripheral nerves or their endings in soft tissue. A combination of prostanoids, kinins and cytokines cause peripheral nociceptive sensitization. In time, the Mg(2+) block of the N-methyl-D-aspartate receptor is removed, pain transmission neurons (PTN) are altered by an influx of Ca(2+) that activates kinases for excitation and phosphatases for depression, activity-dependent plasticity that alters the firing of PTN. In time, these neurons undergo central sensitization that lead to a major physiological change of the autonomic, pain and motor systems. The role of the immune system and the sickness response is becoming clearer as microglia are activated following injury and can induce central sensitization while astrocytes may maintain the process.

Current diagnosis and therapy of complex regional pain syndrome: refining diagnostic criteria and therapeutic options

Complex regional pain syndrome is a clinically challenging entity both in terms of accurate diagnosis and effective treatment. Complex regional pain syndrome is a post-traumatic painful neurologic syndrome involving the somatosensory, sympathetic and often the somatomotor systems. This complex condition consists of local neurogenic inflammation out of proportion to injury; severe pain in the skin, subcutaneous tissues and joints; and a central hyperexcitability that is often compounded with a sympathetic component. The syndrome is multifaceted manifesting both central and peripheral neurologic pathophysiology, frequently including a prominent psychosocial component. The wide array of possible patient presentations and antecedent pathologies also complicate successful treatment. To further add to the clinical challenges of complex regional pain syndrome, the epidemiology and natural history of complex regional pain syndrome are only partially known; evidence concerning complex regional pain syndrome treatment has grown slowly, due in large part to the vagaries of diagnosis; and research data--when they are available--are difficult to interpret. Thus, in spite of our evolving understanding of this neurologic disorder, in many cases complex regional pain syndrome remains difficult to diagnose and treat successfully.

Pathologic alterations of cutaneous innervation and vasculature in affected limbs from patients with complex regional pain syndrome

Complex regional pain syndromes (CRPS, type I and type II) are devastating conditions that can occur following soft tissue (CRPS type I) or nerve (CRPS type II) injury. CRPS type I, also known as reflex sympathetic dystrophy, presents in patients lacking a well-defined nerve lesion, and has been questioned as to whether or not it is a true neuropathic condition with an organic basis. As described here, glabrous and hairy skin samples from the amputated upper and lower extremity from two CRPS type I diagnosed patients were processed for double-label immunofluorescence using a battery of antibodies directed against neural-related proteins and mediators of nociceptive sensory function. In CRPS affected skin, several neuropathologic alterations were detected, including: (1) the presence of numerous abnormal thin caliber NF-positive/MBP-negative axons innervating hair follicles; (2) a decrease in epidermal, sweat gland, and vascular innervation; (3) a loss of CGRP expression on remaining innervation to vasculature and sweat glands; (4) an inappropriate expression of NPY on innervation to superficial arterioles and sweat glands; and (5) a loss of vascular endothelial integrity and extraordinary vascular hypertrophy. The results are evidence of widespread cutaneous neuropathologic changes. Importantly, in these CRPS type I patients, the myriad of clinical symptoms observed had detectable neuropathologic correlates.

Pressure and stretch mechanosensitivity of peripheral nerve fibres following local inflammation of the nerve trunk

Patients with non-specific limb pain often show signs of nerve mechanosensitivity, i.e. local tenderness over nerve trunks and pain in response to limb movements that cause nerve stretch. In such patients a nerve lesion is not apparent, and it has been suggested that local neural inflammation may be a key factor. The present study examines the extent to which nerve fibres in regions of local inflammation respond to small stretches, and whether functional changes occur throughout the primary afferent neurone. A local neuritis was induced in adult rats by wrapping oxidised cellulose saturated in complete Freund's adjuvant (CFA) around the peroneal or sciatic nerves. A small cut was made in the perineurium of some of the peroneal lesioned animals. A- and C-fibre recordings were made 2-10 days post-surgery from filaments dissected proximal to the lesion. Local mechanosensitivity was assessed using a glass probe and by small stretches. Responses to stretch and local pressure were recorded in 7% of C- and 8% of A-fibres from the peroneal nerve following CFA treatment with the sheath opened. A smaller proportion of stretch sensitive fibres were seen in sciatic and peroneal nerves after CFA treatment alone (2% of C- and 3% of A-fibres), but such fibres were not seen in control preparations. The most responsive fibres fired to 3% stretch, which is within the range of nerve stretch seen during normal limb movements. Less than 1% of stretch sensitive fibres had peripheral fields, indicating that most had probably degenerated distally.

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.

Hyperexcitable polymodal and insensitive nociceptors in painful human neuropathy

Six patients with chronic pain, mechanical and thermal hyperalgesia/allodynia, and cutaneous vasodilatation starting distally in their extremities, were evaluated using clinical and neurophysiological methods and microneurography. Evidence of small-fiber polyneuropathy was documented in all, but the etiology remained cryptogenic in several. Different forms of hyperexcitability were detected by microneurography in both common polymodal and mechanically insensitive C nociceptors, which explain all the somatosensory abnormalities. Signs of hyperexcitability included reduced receptor threshold (accounting for mechanical and heat allodynias), spontaneous C nociceptor discharge (explaining spontaneous "burning" pain and antidromic vasodilatation), and multiplied nociceptor responses to stimulation (accounting for hyperalgesia). The clinical and electrophysiological profiles of these patients resemble the experimental syndrome evoked by application of capsaicin to the skin. This similarity, and the striking heat dependence of the spontaneous pain, suggest that a common feature may be altered expression or modulation of vanilloid 1 receptor, provoking abnormal nociceptor discharges.

Reduction of pain-related fear in complex regional pain syndrome type I: the application of graded exposure in vivo

Fear of (re)injury/movement has been identified as a potential predictor of chronic disability in complex regional pain syndrome type I (CRPS-I). In order to reduce pain-related fears and pain disability, graded exposure in vivo (GEXP) is likely to be an appropriate treatment. Indeed, there is evidence that in chronic pain patients reporting substantial fear of (re)injury/movement, GEXP is successful in reducing pain disability. However, the efficacy of exposure-based protocols in the treatment of CRPS-I patients for reducing pain disability has not been tested. The main research question of this study was whether the reduction of pain-related fear through GEXP also resulted in a decrease of disability in a subgroup of patients with CRPS-I who report substantial pain-related fear. A single-case experimental ABCD-design was used with random determination of the start of the intervention. Eight patients with CRPS-I were included in the study. To assess daily changes in pain intensity, pain-related fear, pain catastrophizing, and activity goal achievement, a diary was used. Standardized questionnaires of pain-related fear, pain disability, and self-reported signs and symptoms of CRPS-I were administered before and after each intervention, and at 6-month follow-up. The current study supports a GEXP approach to chronic CRPS-I. The GEXP was successful in decreasing levels of self-reported pain-related fear, pain intensity, disability, and physiological signs and symptoms. These results support the hypothesis that the meaning people attach to a noxious stimulus influences its experienced painfulness, and that GEXP activates cortical networks and reconciles motor output and sensory feedback.

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.