Sympathetic dysfunction in long-term complex regional pain syndrome. Clin J Pain. 2010;26:128-131. [PMID: 20090439 DOI: 10.1097/ajp.0b013e3181b5effc]

Denying the Truth Does Not Change the Facts: A Systematic Analysis of Pseudoscientific Denial of Complex Regional Pain Syndrome

Purpose

Several articles have claimed that complex regional pain syndrome (CRPS) does not exist. Although a minority view, it is important to understand the arguments presented in these articles. We conducted a systematic literature search to evaluate the methodological quality of articles that claim CRPS does not exist. We then examined and refuted the arguments supporting this claim using up-to-date scientific literature on CRPS.

Methods

A systematic search was conducted in MEDLINE, EMBASE and Cochrane CENTRAL databases. Inclusion criteria for articles were (a) a claim made that CRPS does not exist or that CRPS is not a distinct diagnostic entity and (b) support of these claims with subsequent argument(s). The methodological quality of articles was assessed if possible.

Results

Nine articles were included for analysis: 4 narrative reviews, 2 personal views, 1 letter, 1 editorial and 1 case report. Seven points of controversy were used in these articles to argue that CRPS does not exist: 1) disagreement with the label “CRPS”; 2) the “unclear” pathophysiology; 3) the validity of the diagnostic criteria; 4) CRPS as a normal consequence of immobilization; 5) the role of psychological factors; 6) other identifiable causes for CRPS symptoms; and 7) the methodological quality of CRPS research.

Conclusion

The level of evidence for the claim that CRPS does not exist is very weak. Published accounts concluding that CRPS does not exist, in the absence of primary evidence to underpin them, can harm patients by encouraging dismissal of patients’ signs and symptoms.

Autonomic dysfunction in a group of lower extremities arterial disease outpatients

BACKGROUND

The understanding of the specific role of sympathetic neural control and dysregulation in lower extremities arterial disease (LEAD) is still very limited. Aim of our study was to investigate the autonomic profile in LEAD patients and to evaluate if the eventual autonomic alterations were more severe in patients with advanced disease.

METHODS

We enrolled all consecutive outpatients with LEAD referred to our Departments between July 2012 and September 2014. They were compared to a group of matched outpatients without LEAD. All patients underwent Holter ECG monitoring. Time-domain analysis of heart rate variability (HRV) was evaluated.

RESULTS

Compared to controls, patients with LEAD had a lower SDNN (P=0.007) and SDANN (P=0.003). Patients with clinically advanced LEAD had a lower SDNN (P=0.006) and SDANN (P=0.004) compared to LEAD patients with less severe disease and to those without disease.

CONCLUSIONS

LEAD patients had a reduced SDNN and SDANN than patients without LEAD. Autonomic dysfunction was more significant in clinically advanced stages of disease. This association did not relate to ABI value but to clinical stage of disease.

Changes in cardiovascular parameters in rats exposed to chronic widespread mechanical allodynia induced by hind limb cast immobilization

To elucidate the relationship between chronic pain conditions with cast immobilization and autonomic function, we investigated the functional changes of the autonomic nervous system in conscious rats with chronic post-cast pain (CPCP) induced by a two-week cast immobilization of one hind limb. We telemetrically examined the time courses of systolic arterial blood pressure (SBP), heart rate (HR), and the middle-frequency (MF) component obtained from the power spectral analysis of SBP variability as a vasomotor sympathetic index. We also investigated the baroreflex sensitivity to phentolamine, an α-adrenoceptor antagonist, and the SBP and HR responses to a low ambient temperature (LT; 9.0 ± 0.2°C) exposure, a sympathetic stimulant. Rats exposed to cast immobilization exhibited mechanical allodynia lasting for at least 10 weeks after cast removal in the calf area (skin and muscle) of the bilateral hind limbs. Under resting conditions, the SBP, HR, and MF components were significantly increased during cast immobilization (all p < 0.001). Following cast removal, these parameters gradually decreased and within 1 week reached lower than baseline levels, lasting for over 10 weeks. Phentolamine administration (10 mg/kg, intraperitoneally) significantly decreased the SBP before and during cast immobilization (before, p < 0.001; during, p = 0.001) but did not lower the SBP after cast removal. The baroreflex gain after phentolamine administration, calculated as the HR increase divided by the SBP reduction, was significantly increased after cast removal (p = 0.002). The SBP increase on LT exposure was significantly greater after cast removal than that before cast immobilization, suggesting hypersensitivity to sympathetic neurotransmitters. These results revealed that, in the CPCP model, sympathetic activation was augmented during cast immobilization, which then decreased after cast removal and remained below normal levels with persisting pain behaviors. Additionally, the responsiveness of the autonomic nervous system was impaired in the CPCP model.

Commonalities and differences in abnormal peripheral metabolites between patients with fibromyalgia and complex regional pain syndrome

Background: Fibromyalgia (FM) and complex regional pain syndrome (CRPS) share many pathological mechanisms related to chronic pain that could contribute to multifactorial pathological mechanisms.Methods: We investigated peripheral metabolites in FM and CRPS patients compared to healthy controls based on cross-sectional study.Results: Mean corpuscular hemoglobin (p < 0.001), mean corpuscular volume (p = 0.014), and total bilirubin levels (p = 0.017) were lower in FM patients than in healthy controls. On the other hand, CRPS patients showed lower levels of total bilirubin than healthy controls (p = 0.037). Creatinine level was lower in FM patients (p = 0.057) compared to healthy controls, particularly when comparing the low-hemoglobin subgroup among FM patients (p = 0.035) with the low-hemoglobin subgroup among healthy controls. Red blood cell count (r = -0.620, p = 0.031), hematocrit (r = -0.593, p = 0.042), and creatinine level (r = -0.598, p = 0.040) showed negative correlations with McGill Pain Questionnaire-Affective (MPQ-A) scores in FM patients. A negative correlation was observed between MCV and McGill Pain Questionnaire-Sensory scores (r = -0.680, p = 0.015) in CRPS patients.Conclusion: We found specific peripheral metabolites that may exhibit different tendency between FM and CRPS patients as well as some common metabolites, which may be associated with peripheral pathology in the patients. Considering this study had a few limitations such as a small sample sizes and using a liberal threshold of significance in the correlation analysis, future studies with larger sample sizes may be needed to generalize these findings.

Clinical Course and Impact of Complex Regional Pain Syndrome Confined to the Knee

OBJECTIVE

Although complex regional pain syndrome (CRPS) of the knee is comparable to CRPS of the ankle/foot at time of diagnosis, no reports are available concerning the course of knee CRPS. Therefore, this study investigated the clinical course in terms of the symptoms and signs, health-related quality of life (HR-QoL), and work status of patients diagnosed with CRPS of the knee.

DESIGN

Observational, descriptive study.

SETTING

Single-center study.

SUBJECTS

Patients with CRPS of the knee.

METHODS

Patients self-reported their past and current CRPS symptoms, HR-QoL, and work status; all underwent a physical examination. A comparison was made of changes in symptoms over time between patients with CRPS of the knee and those with CRPS of more distal locations.

RESULTS

In total, 32 patients were enrolled. The follow-up time was 11.5 ± 6.29 years since diagnosis, and symptoms and signs showed a significant decrease over time. Twelve patients (37.5%) rated their health as (generally) positive. Patients who were still able to work (31.3%) stated that their physical health gave them at least some problems in the performance of their job. A change in symptoms occurred significantly less often in CRPS of the knee.

CONCLUSIONS

CRPS of the knee changes in terms of symptoms over time, but significantly less than CRPS of other locations. A change in work status was reported in 82% of the patients due to their CRPS, and in 91%, the pain interfered with their daily life. CRPS of the knee is a painful condition with persistent symptoms causing a diminished HR-QoL.

Complex regional pain syndrome: a focus on the autonomic nervous system

PURPOSE

Although autonomic features are part of the diagnostic criteria for complex regional pain syndrome (CRPS), the role of the autonomic nervous system in CRPS pathophysiology has been downplayed in recent years. The purpose of this review is to redress this imbalance.

METHODS

We focus in this review on the contribution of the autonomic nervous system to CRPS pathophysiology. In particular, we discuss regional sympathetic and systemic autonomic disturbances in CRPS and the mechanisms which may underlie them, and consider links between these mechanisms, immune disturbances and pain.

RESULTS

The focused literature research revealed that immune reactions, alterations in receptor populations (e.g., upregulation of adrenoceptors and reduced cutaneous nerve fiber density) and central changes in autonomic drive seem to contribute to regional and systemic disturbances in sympathetic activity and to sympathetically maintained pain in CRPS.

CONCLUSIONS

We conclude that alterations in the sympathetic nervous system contribute to CRPS pathology. Understanding these alterations may be an important step towards providing appropriate treatments for CRPS.

CRPS: what’s in a name? Taxonomy, epidemiology, neurologic, immune and autoimmune considerations

This account of the condition now termed complex regional pain syndrome (CRPS) spans approximately 462 years since a description embodying similar clinical features was described by Ambroise Paré in 1557. While reviewing its historical origins, the text describes why it became necessary to change the taxonomies of two clinical syndromes with similar pathophysiologies to one which acknowledges this aspect but does not introduce any mechanistic overtones. Discussed at length is the role of the sympathetic component of the autonomic nervous system (ANS) and why its dysfunction has both directly and indirectly influenced our understanding of the inflammatory aspects of CRPS. As the following article will show, our knowledge has expanded in an exponential fashion to include musculoskeletal, immune, autoimmune, central and peripheral nervous system and ANS dysfunction, all of which increase the complexity of its clinical management. A burgeoning literature is beginning to shed light on the mechanistic aspects of these syndromes and the increasing evidence of a genetic influence on such factors as autoimmunity, and its importance is also discussed at length. An important aspect that has been missing from the diagnostic criteria is a measure of disease severity. The recent validation of a CRPS Severity Score is also included.

Bladder pain induced by prolonged peripheral alpha 1A adrenoceptor stimulation involves the enhancement of transient receptor potential vanilloid 1 activity and an increase of urothelial adenosine triphosphate release

AIM

Pathophysiological mechanisms of chronic visceral pain (CVP) are unknown. This study explores the association between the sympathetic system and bladder nociceptors activity by testing the effect of a prolonged adrenergic stimulation on transient receptor potential vanilloid 1 (TRPV1) activity and on urothelial adenosine triphosphate (ATP) release.

METHODS

Female Wistar rats received saline, phenylephrine (PHE), PHE + silodosin, PHE + naftopidil or PHE + prazosin. TRPV1 knockout and wild-type mice received saline or PHE. Visceral pain behaviour tests were performed before and after treatment. Cystometry was performed, during saline and capsaicin infusion. Fos immunoreactivity was assessed in L6 spinal cord segment. Human urothelial ATP release induced by mechanical and thermal stimulation was evaluated.

RESULTS

Subcutaneous, but not intrathecal, PHE administration induced pain, which was reversed by silodosin, a selective alpha 1A adrenoceptor antagonist, but not by naftopidil, a relatively selective antagonist for alpha 1D adrenoceptor. Silodosin also reversed PHE-induced bladder hyperactivity and L6 spinal cord Fos expression. Thus, in subsequent experiments, only silodosin was used. Wild-type, but not TRPV1 knockout, mice exhibited phenylephrine-induced pain. Capsaicin induced a greater increase in voiding contractions in PHE-treated rats than in control animals, and silodosin reversed this effect. When treated with PHE, ATP release from human urothelial cells was enhanced either by mechanical stimulation or by lowering the thermal threshold of urothelial TRPV1, which becomes abnormally responsive at body temperature.

CONCLUSION

This study suggests that the activation of peripheral alpha 1A adrenoceptors induces CVP, probably through its interaction with TRPV1 and ATP release.

New Concepts in Complex Regional Pain Syndrome

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

Altered Autonomic Nervous System Reactivity to Pain in Trigeminal Neuralgia

Background: In the past two decades, there has been increasing evidence to suggest that trigeminal neuralgia (TN) may be linked to a dysfunction of the autonomic nervous system (ANS). The aim of the present study was to formally test this hypothesis by comparing the reactivity of the ANS to experimental pain in a population of TN patients and healthy controls. Methods: Twelve patients diagnosed with classical TN and 12 healthy controls participated in the study. Cardiac activity was assessed while participants were instructed to rest and again during a cold pressor test (CPT). Heart rate variability analyses were performed off-line to obtain parasympathetic (high-frequency) and sympathetic (low-frequency) indices. Results: At baseline, ANS measures did not differ between healthy controls and TN patients, and both groups showed a similar increase in heart rate during the CPT (all p values >0.05). However, TN patients showed a greater increase in cardiac sympathetic activity and a greater decrease in cardiac parasympathetic activity during CPT compared with healthy controls (all p values <0.05). Importantly, changes in sympathetic reactivity, from baseline to CPT, were negatively associated with the number of pain paroxysms experienced each day by TN patients in the preceding week (r=−.58, p<0.05). Conclusions: These results suggest that TN, like many other short-lasting, unilateral facial pain conditions, is linked to ANS alterations. Future studies are required to determine if the altered ANS response observed in TN patients is a cause or a consequence of TN pain

Complex regional pain syndrome: From diagnosis to rehabilitation

Complex regional pain syndrome (CRPS) is a debilitating pathology characterised by intense chronic pain associated with vasomotor, sensory and motor dysfunction of the affected limb. Although the pathophysiology of CRPS is not fully understood, it is recognised that inflammatory processes and autonomic dysfunction are involved. These processes are associated with peripheral and central sensitisation as well as changes in brain structure and function, and are reflected in the clinical presentation of CRPS. CRPS management requires an interdisciplinary team and requires the therapeutic approach to be individualised. With regard to pharmacological treatment, bisphosphonates, corticosteroids, ketamine and anticonvulsants have been demonstrated to be effective for CRPS management. Psychotherapy, including cognitive-behavioural therapy, has produced promising results but more studies are needed to confirm its efficacy. Among rehabilitation interventions, there is evidence of the efficacy of physiotherapy and occupational therapy in diminishing CRPS symptoms and achieving a higher level of functioning. In this regard, the rehabilitation modality that seems the most promising according to the actual literature is graded motor imagery, which can help to reverse the maladaptive neuroplasticity occurring in CRPS.

Transforming pain medicine: adapting to science and society

The field of chronic pain medicine is currently facing enormous challenges. The incidence of chronic pain is increasing worldwide, particularly in the developed world. As a result, chronic pain is imposing a growing burden on Western societies in terms of cost of medical care and lost productivity. This burden is exacerbated by the fact that despite research efforts and a huge expenditure on treatment for chronic pain, clinicians have no highly effective treatments or definitive diagnostic measures for patients. The lack of an objective measure for pain impedes basic research into the biological and psychological mechanisms of chronic pain and clinical research into treatment efficacy. The development of objective measurements of pain and ability to predict treatment responses in the individual patient is critical to improving pain management. Finally, pain medicine must embrace the development of a new evidence-based therapeutic model that recognizes the highly individual nature of responsiveness to pain treatments, integrates bio-psycho-behavioural approaches, and requires proof of clinical effectiveness for the various treatments we offer our patients. In the long-term these approaches will contribute to providing better diagnoses and more effective treatments to lessen the current challenges in pain medicine.

Efficacy and safety of high-dose vitamin C on complex regional pain syndrome in extremity trauma and surgery--systematic review and meta-analysis

Complex regional pain syndrome (CRPS) is a devastating condition often seen after foot and ankle injury and surgery. Prevention of this pathology is attractive not only to patients but also to surgeons, because the treatment of this condition can be difficult. We evaluated the effectiveness of vitamin C in preventing occurrence of CRPS in extremity trauma and surgery by systematically reviewing relevant studies. The databases used for this review included: Ovid EMBASE, Ovid MEDLINE, CINAHL, and the Cochrane Database. We searched for comparative studies that evaluated the efficacy of more than 500 mg of daily vitamin C. After screening for inclusion and exclusion criteria, we identified 4 studies that were relevant to our study question. Only 1 of these 4 studies was on foot and ankle surgery; the rest concerned the upper extremities. All 4 studies were in favor of this intervention with minimal heterogeneity (Tau(2) = 0.00). Our quantitative synthesis showed a relative risk of 0.22 (95% confidence interval = 0.12, 0.39) when daily vitamin C of at least 500 mg was initiated immediately after the extremity surgery or injury and continued for 45 to 50 days. A routine, daily administration of vitamin C may be beneficial in foot and ankle surgery or injury to avoid CRPS. Further foot and ankle specific and dose-response studies are warranted.