Unravelling the pathophysiology of complex regional pain syndrome: focus on sympathetically maintained pain

Peripheral mechanisms of chronic pain

Acutely, pain serves to protect us from potentially harmful stimuli, however damage to the somatosensory system can cause maladaptive changes in neurons leading to chronic pain. Although acute pain is fairly well controlled, chronic pain remains difficult to treat. Chronic pain is primarily a neuropathic condition, but studies examining the mechanisms underlying chronic pain are now looking beyond afferent nerve lesions and exploring new receptor targets, immune cells, and the role of the autonomic nervous system in contributing chronic pain conditions. The studies outlined in this review reveal how chronic pain is not only confined to alterations in the nervous system and presents findings on new treatment targets and for this debilitating disease.

The neuronal tyrosine kinase receptor ligand ALKAL2 mediates persistent pain

The anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase known for its oncogenic potential that is involved in the development of the peripheral and central nervous system. ALK receptor ligands ALKAL1 and ALKAL2 were recently found to promote neuronal differentiation and survival. Here, we show that inflammation or injury enhanced ALKAL2 expression in a subset of TRPV1⁺ sensory neurons. Notably, ALKAL2 was particularly enriched in both mouse and human peptidergic nociceptors, yet weakly expressed in nonpeptidergic, large-diameter myelinated neurons or in the brain. Using a coculture expression system, we found that nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn of the spinal cord. Finally, depletion of ALKAL2 in dorsal root ganglia or blocking ALK with clinically available compounds crizotinib or lorlatinib reversed thermal hyperalgesia and mechanical allodynia induced by inflammation or nerve injury, respectively. Overall, our work uncovers the ALKAL2/ALK signaling axis as a central regulator of nociceptor-induced sensitization. We propose that clinically approved ALK inhibitors used for non–small cell lung cancer and neuroblastomas could be repurposed to treat persistent pain conditions.

Botulinum Toxin Type A for Lumbar Sympathetic Ganglion Block in Complex Regional Pain Syndrome: A Randomized Trial

BACKGROUND

The present study was designed to test the hypothesis that botulinum toxin would prolong the duration of a lumbar sympathetic block measured through a sustained increase in skin temperature. The authors performed a randomized, double-blind, controlled trial to investigate the clinical outcome of botulinum toxin type A for lumbar sympathetic ganglion block in patients with complex regional pain syndrome.

METHODS

Lumbar sympathetic ganglion block was conducted in patients with lower-extremity complex regional pain syndrome using 75 IU of botulinum toxin type A (botulinum toxin group) and local anesthetic (control group). The primary outcome was the change in the relative temperature difference on the blocked sole compared with the contralateral sole at 1 postoperative month. The secondary outcomes were the 3-month changes in relative temperature differences, as well as the pain intensity changes.

RESULTS

A total of 48 participants (N = 24/group) were randomly assigned. The change in relative temperature increase was higher in the botulinum toxin group than in the control group (1.0°C ± 1.3 vs. 0.1°C ± 0.8, respectively; difference: 0.9°C [95% CI, 0.3 to 1.5]; P = 0.006), which was maintained at 3 months (1.1°C ± 0.8 vs. -0.2°C ± 1.2, respectively; P = 0.009). Moreover, pain intensity was greatly reduced in the botulinum toxin group compared with the control group at 1 month (-2.2 ± 1.0 vs. -1.0 ± 1.6, respectively; P = 0.003) and 3 months (-2.0 ± 1.0 vs. -0.6 ± 1.6, respectively; P = 0.003). There were no severe adverse events pertinent to botulinum toxin injection.

CONCLUSIONS

In patients with complex regional pain syndrome, lumbar sympathetic ganglion block using botulinum toxin type A increased the temperature of the affected foot for 3 months and also reduced the pain.

EDITOR’S PERSPECTIVE

Protein kinase G signaling pathway is involved in sympathetically maintained pain by modulating ATP-sensitive potassium channels

BACKGROUND

Sympathetically maintained pain (SMP) involves an increased excitability of dorsal root ganglion (DRG) neurons to sympathetic nerve stimulation and circulating norepinephrine. The current treatment of SMP has limited efficacy, and hence more mechanistic insights into this intractable pain condition are urgently needed.

METHODS

A caudal trunk transection (CTT) model of neuropathic pain was established in mice.Immunofluorescence staining, small interfering RNA, pharmacological and electrophysiological studies were conducted to test the hypothesis that norepinephrine increases the excitability of small-diameter DRG neurons from CTT mice through the activation of cyclic guanosine monophosphate-protein kinase G (cGMP-PKG) signaling pathway.

RESULTS

Behavior study showed that CTT mice developed mechanical and heat hypersensitivities, which were attenuated by intraperitoneal injection of guanethidine. CTT mice also showed an abnormal sprouting of tyrosine hydroxylase-positive nerve fibers in DRG, and an increased excitability of small-diameter DRG neurons to norepinephrine, suggesting that CTT is a useful model to study SMP. Importantly, inhibiting cGMP-PKG pathway with small interfering RNA and KT5823 attenuated the increased sympathetic sensitivity in CTT mice. In contrast, cGMP activators (Sp-cGMP, 8-Br-cGMP) further increased sympathetic sensitivity. Furthermore, phosphorylation of ATP-sensitive potassium channel, which is a downstream target of PKG, may contribute to the adrenergic modulation of DRG neuron excitability.

CONCLUSIONS

Our findings suggest an important role of cGMP-PKG signaling pathway in the increased excitability of small-diameter DRG neurons to norepinephrine after CTT, which involves an inhibition of the ATP-sensitive potassium currents through PKG-induced phosphorylation. Accordingly, drugs targeting this pathway may help to treat SMP.

Incidence of inadvertent intercostal or epidural spread during thoracic sympathetic ganglion block

Background

Sympathetic blocks (SBs) have been used widely to relieve the symptoms of sympathetically maintained pain (SMP). The thoracic sympathetic ganglion is not separated from somatic nerves by muscles and connective tissue. The upper thoracic ganglion runs along the posterior surface of the vertebral column in close proximity to the adjacent epidural region. This anatomical difference leads to frequent epidural and intercostal spread in cases of thoracic SBs. The purpose of this study was to investigate the incidence of inadvertent intercostal and epidural injections during thoracic SBs.

Methods

Twenty-two patients who were suffering from complex regional pain syndrome or lymphedema after breast cancer surgery were managed with two or three times of thoracic SBs. Therefore, injections of 63 thoracic SBs from 22 patients were enrolled in this study. An investigator who did not attend the procedure evaluated the occurrence of intercostal or epidural spread using anteroposterior fluoroscopic images.

Results

The overall incidence of inadvertent intercostal or epidural spread of contrast was 47.5%. Among the inadvertent injections, intercostal spread (34.9%) was more frequent than epidural spread (12.6%). Only 52.5% of the thoracic SBs demonstrated successful contrast spread without any inadvertent spread. The mean difference in skin temperature between the blocked and unblocked sides was 2.5 ± 1.8ºC. Fifty-nine (93.6%) injections demonstrated more than 1.5ºC difference.

Conclusions

Thoracic SBs showed a high incidence (47.5%) of inadvertent epidural or intercostal injection. Thus, special attention is required for the diagnosis of SMP or the injection of any neurolytic agent around sympathetic ganglion.

Human Dorsal Root Ganglion Stimulation Reduces Sympathetic Outflow and Long-Term Blood Pressure

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DRGS at upper lumbar levels significantly reduces sympathetic nerve firing

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Reduction in sympathetic activity appears to be independent to pain relief

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DRGS significantly reduced BP at 6 months and 2 years

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BP reduction was lateralized to DRGS on the left side

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Three refractory hypertensives became normotensive after chronic stimulation.

This study hypothesized that dorsal root ganglion (DRG) stimulation would reduce sympathetic nerve activity and would alter hemodynamic variables. This study directly recorded muscle sympathetic nerve activity during ON and OFF stimulation of the DRG while measuring hemodynamic parameters. DRG stimulation significantly reduced the firing frequency of sympathetic nerves, as well as significantly reducing blood pressure, with greater reductions evident when stimulation was left-sided. Left-sided DRG stimulation lowers sympathetic nerve activity, leading to long-term phenotypic changes. This raises the potential of DRG stimulation being used to treat de novo autonomic disorders such as hypertension or heart failure.

Decreased neural expression of the noradrenaline transporter in the papillary dermis after partial sciatic nerve lesion

After peripheral nerve injury, regeneration or collateral sprouting of noradrenergic nerve fibres in the papillary dermis of the injured limb may contribute to sympathetically-maintained pain. The aim of this study was to determine whether noradrenergic nerve fibre regeneration after partial sciatic nerve ligation (PSL) in Wistar rats was accompanied by parallel shifts in expression of the noradrenaline transporter (NAT). Four or 28 days after PSL surgery, immunohistochemistry was used to examine NAT expression in plantar hind paw skin in relation to pan-neuronal markers (class III beta-tubulin and protein gene product 9.5), peptidergic afferents containing calcitonin gene-related peptide (CGRP), nonpeptidergic afferents labelled by isolectin B₄ (IB₄), and tyrosine hydroxylase (TH), a marker for cutaneous noradrenergic nerve fibres. Most dermal nerve fibre populations decreased shortly after PSL. However, four weeks after PSL, an increase in staining intensity of CGRP and novel expression of TH were observed in the papillary dermis on the injured side. In contrast, neural expression of NAT was reduced in this region. Loss of NAT might have implications for sympathetically-maintained pain, as failure to rapidly clear noradrenaline could exacerbate aberrant sympathetic-sensory signalling between closely apposed noradrenergic and peptidergic nerve fibres.

Hazard of complex regional pain syndrome following human papillomavirus vaccination among adolescent girls in the United States: a case-cohort analysis of insurance claims data

Objectives: Complex regional pain syndrome (CRPS) cases have followed human papillomavirus (HPV) vaccination, but no causal link has been established.Methods: Using insurance claims, the authors observed unvaccinated 11-year-old girls for CRPS diagnoses. The authors used time-dependent Cox regression to identify health-related CRPS predictors using diagnosis codes. Next, the authors identified HPV vaccinations using procedural codes. HPV vaccination and CRPS predictors were considered time-dependent covariates to estimated adjusted hazard ratios (HR) and 95% confidence intervals (CI) for CRPS, 30, 90, and 180-days post-vaccination.Results: 1,232,572 girls received 563 unique CRPS diagnoses. In a 10% sub-cohort of 123,981 girls accounting for potential confounders and predisposing risk factors (i.e. injury, infection, mental illness, primary care use), CRPS hazard was not significantly elevated 30 days (HR: 0.90, 95% CI: 0.46, 1.73), 90 days (HR: 1.17, 95% CI: 0.83, 1.65), or 180-days post-vaccination (HR: 1.11, 95% CI: 0.83, 1.47).Conclusion: The results support the safety and continued administration of HPV vaccines to adolescents.

Outcomes of Sympathetic Blocks in the Management of Complex Regional Pain Syndrome

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Sympathetic dysfunction may be present in complex regional pain syndrome, and sympathetic blocks are routinely performed in practice. To investigate the therapeutic and predictive values of sympathetic blocks, the authors test the hypotheses that sympathetic blocks provide analgesic effects that may be associated with the temperature differences between the two extremities before and after the blocks and that the effects of sympathetic blocks may predict the success (defined as achieving more than 50% pain reduction) of spinal cord stimulation trials.

Methods

The authors performed a retrospective study of 318 patients who underwent sympathetic blocks in a major academic center (2009 to 2016) to assess the association between pain reduction and preprocedure temperature difference between the involved and contralateral limbs. The primary outcome was pain improvement by more than 50%, and the secondary outcome was duration of more than 50% pain reduction per patient report. The authors assessed the association between pain reduction and the success rate of spinal cord stimulation trials.

Results

Among the 318 patients, 255 were diagnosed with complex regional pain syndrome and others with various sympathetically related disorders. Successful pain reduction (more than 50%) was observed in 155 patients with complex regional pain syndrome (155 of 255, 61%). The majority of patients (132 of 155, 85%) experienced more than 50% pain relief for 1 to 4 weeks or longer. The degree and duration of pain relief were not associated with preprocedure temperature parameters with estimated odds ratio of 1.03 (97.5% CI, 0.95–1.11) or 1.01 (97.5% CI, 0.96–1.06) for one degree decrease (P = 0.459 or 0.809). There was no difference in the success rate of spinal cord stimulation trials between patients with or without more than 50% pain relief after sympathetic blocks (35 of 40, 88% vs. 26 of 29, 90%, P > 0.990).

Conclusions

The authors conclude that sympathetic blocks may be therapeutic in patients with complex regional pain syndrome regardless of preprocedure limb temperatures. The effects of sympathetic blocks do not predict the success of spinal cord stimulation.

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.

Pain descriptors of taxane acute pain syndrome (TAPS) in breast cancer patients-a prospective clinical study

BACKGROUND

Taxane acute pain syndrome (TAPS) is a clinically significant side-effect of taxane chemotherapy, often described as arthralgia and myalgia that occurs 2-3 days after infusion. The aim of this study was to assess pain descriptors used by patients during their experience of TAPS.

METHODS

A clinical prospective cohort study was conducted on breast cancer patients who had not received prior chemotherapy and were asked to complete diaries on three consecutive docetaxel treatment cycles on days 1-7, 14, and 21 (acute phase). Questionnaires to assess pain severity, descriptors of pain, and the interference in activities due to pain were adapted from the Brief Pain Inventory and the McGill Pain Questionnaire. Telephone questionnaire follow-up was done at 1, 3, 6, 9, and 12 months following docetaxel (delayed phase).

RESULTS

The most commonly used descriptor for acute and chronic pain was "aching" (90-96%). However, in the delayed phase of the study, "burning" (32-50%), "radiating" (39-48%), and "sharp" (40-69%) were used more often. In both acute and chronic pain phases, most patients experienced moderate/severe pain regardless of the location. Pain in cycle 1 was predictive of pain in subsequent taxane cycles (p < 0.0001). Pain in cycle 3 was predictive of chronic pain (p < 0.002).

CONCLUSIONS

The descriptors used by patients experiencing chemotherapy-induced pain (ChIP) may be reflective of the underlying mechanisms. It is suspected that TAPS initiates as an acute inflammatory pain, which over time develops into neuropathic pain, known as chemotherapy-induced peripheral neuropathy (CIPN). However, the subjective pain experience varies from patient to patient.

Complex regional pain syndrome: intradermal injection of phenylephrine evokes pain and hyperalgesia in a subgroup of patients with upregulated α1-adrenoceptors on dermal nerves

The aim of this study was to determine whether upregulated cutaneous expression of α1-adrenoceptors (α1-AR) is a source of pain in patients with complex regional pain syndrome (CRPS). Immunohistochemistry was used to identify α1-AR on nerve fibres and other targets in the affected and contralateral skin of 90 patients, and in skin samples from 38 pain-free controls. The distribution of α1-AR was compared between patients and controls, and among subgroups of patients defined by CRPS duration, limb temperature asymmetry, and diagnostic subtype (CRPS I vs CRPS II). In addition, α1-AR expression was investigated in relation to pain and pinprick hyperalgesia evoked by intradermal injection of the α1-AR agonist phenylephrine. Expression of α1-AR on nerve bundles in the CRPS-affected limb was greater in patients who reported prolonged pain and pinprick hyperalgesia around the phenylephrine injection site than in patients with transient pain after the injection. In addition, α1-AR expression in nerve bundles was greater in patients with CRPS II than CRPS I, and was greater in acute than more long-standing CRPS. Although less clearly associated with the nociceptive effects of phenylephrine, α1-AR expression was greater on dermal nerve fibres in the painful than contralateral limb. Together, these findings are consistent with nociceptive involvement of cutaneous α1-AR in CRPS. This involvement may be greater in acute than chronic CRPS, and in CRPS II than CRPS I.

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.

Mental load during cognitive performance in complex regional pain syndrome I

BACKGROUND

Complex regional pain syndrome (CRPS) is associated with deficits in limb recognition. The purpose of our study was to determine whether mental load during this task affected performance, sympathetic nervous system activity or pain in CRPS patients.

METHODS

We investigated twenty CRPS-I patients with pain in the upper extremity and twenty age- and sex-matched healthy controls. Each participant completed a limb recognition task. To experimentally manipulate mental load, the presentation time for each picture varied from 2 s (greatest mental load), 4, 6 to 10 s (least mental load). Before and after each run, pain intensity was assessed. Skin conductance was recorded continuously.

RESULTS

Patients with CRPS did not differ from controls in terms of limb recognition and skin conductance reactivity. However, patients with CRPS reported an increase in pain during the task, particularly during high mental load and during the latter stages of the task. Interestingly, state anxiety and depressive symptoms were also associated with increases in pain intensity during high mental load.

CONCLUSIONS

These findings indicate that high mental load intensifies pain in CRPS. The increase of pain in association with anxiety and depression indicates a detrimental effect of negative affective states in situations of high stress and mental load in CRPS.

SIGNIFICANCE

The effects of mental load need to be considered when patients with CRPS-I are investigated for diagnostic or therapeutic reasons.

Evidence already exists for motor system reorganization in CRPS

Complex regional pain syndrome (CRPS) is a disabling condition that is usually preceded by trauma or surgical procedure. Involvement of the motor system is a well-known phenomenon in CRPS, though the pathophysiologic mechanisms of motor system affliction in CRPS are poorly understood. Graded motor imagery (GMI) has been proposed to be one of the therapeutic interventions to help improve pain and other disabling symptoms associated with CRPS, though the benefits noted are modest and inconsistent. The neurophysiological mechanisms implicated in motor imagery are intended to target the aberrant prefrontal and sensorimotor integration areas, which may potentially help restore the aberrant cortical plasticity in CRPS. Detailed well-controlled experiments using insights from the existing body of literature on motor system reorganization in CRPS are required to better understand this complicated disorder. Attempts to gain pathophysiologic insights about complicated disorders like CRPS based on case reports with poorly performed and uncontrolled interventions are misguided.

Does Temperature Increase by Sympathetic Neurolysis Improve Pain in Complex Regional Pain Syndrome? A Retrospective Cohort Study

BACKGROUND

Lumbar sympathetic neurolysis (LSN) is a treatment option for complex regional pain syndrome (CRPS). We examined whether LSN-related temperature changes are associated with clinical outcome and investigated relationships between the outcome of LSN and clinical variables in patients with CRPS-I.

METHODS

We included 95 patients with CRPS-I affecting a single lower extremity, by the Budapest criteria, and who underwent LSN after successful lumbar sympathetic blocks, in this retrospective study. Fluoroscopy-guided LSN was conducted with 1.5 mL of 99% alcohol at L2 and L3 vertebral levels. Positive outcome was defined as a reduction of ≥50% on a numeric rating scale pain score at 6 months after LSN. The relationship between successful outcome and clinical variables was analyzed.

RESULTS

Positive LSN outcome occurred in 49.5% of patients, and it was suggested that Sympathetically maintained pain may accompany CRPS-I in 28% of patients. The overall temperature in the affected limb was increased after LSN, without contralateral limb temperature changes, but did not differ significantly between the positive and negative outcome groups (P = 0.590). Temperature after LSN in warm-type CRPS was reduced in the affected limb, without contralateral limb temperature changes. The absolute temperature change was significantly greater in cold-type than in warm-type CRPS (P = 0.026). In multivariate analysis, a short duration of pain and concurrent cold intolerance were significant factors predicting a positive outcome after LSN.

CONCLUSIONS

LSN may be effective in some patients with CRPS, irrespective of temperature changes and temperature asymmetry pattern. A short duration of pain and concurrent cold intolerance significantly predict successful LSN.

Effects of Linearly Polarized Near-Infrared Irradiation Near the Stellate Ganglion Region on Pain and Heart Rate Variability in Patients with Neuropathic Pain

Background

Neuropathic pain associated with sympathetic overactivity can be effectively relieved by light irradiating the region near stellate ganglion (SGI), applied as an alternative to a conventional sympathetic blockade. The clinical effect of SGI on heart rate variability (HRV) and its association with pain outcomes require investigation.

Objective

This study attempted to identify the effects of SGI on pain outcomes and HRV indices and to determine the association between pain and HRV outcomes.

Design

A prospective double-blind, randomized study.

Setting

An outpatient pain medicine clinic.

Subjects and Methods

A total of 44 patients were enrolled and randomized into the experimental group ( n = 22) and control group ( n = 22). The experimental group received 12 sessions (twice weekly) of standard SGI, whereas the control group received the same protocol with sham irradiation. Pain and HRV were measured before and after each irradiation session. All outcome measures used in the first- and second-half treatment courses were analyzed.

Results

Pain and HRV outcome measures of the experimental group significantly improved after SGI when compared with the control group in both courses. Considering time and frequency domains, the changes in HRV in the second-half treatment course exceeded those in the first-half treatment course. Pain was significantly associated with postirradiated HRV indices ( P < 0.001).

Conclusions

Twelve sessions of SGI exerted time-dependent positive effects on pain and sympathovagal imbalance. HRV outcomes, including time and frequency domains, were an independent indicator of the clinical efficiency of SGI for treating pain in patients with neuropathic pain.

Adult Complex Regional Pain Syndrome Type I: A Narrative Review

Complex regional pain syndrome type I (CRPS I) is a multifactorial painful disorder with a complex pathogenesis. Both peripheral and central mechanisms are involved. Acute CRPS I is considered to be an exaggerated inflammatory disorder; however, over time, because of altered function of the sympathetic nervous system and maladaptive neuroplasticity, CRPS I evolves into a neurological disorder. This review thoroughly describes the pathophysiological aspects of CRPS I and summarizes the potential therapeutic options. The mechanisms and targets of the treatment are different in the early and late stages of the disease. This current review builds on a previous review by this author group by deepening the role of the peripheral classic and neuronal inflammatory component in the acute stage of this painful disorder.

LEVEL OF EVIDENCE

Not applicable.

Hypertension: a problem of organ blood flow supply-demand mismatch

This review introduces a new hypothesis that sympathetically mediated hypertensive diseases are caused, in the most part, by the activation of visceral afferent systems that are connected to neural circuits generating sympathetic activity. We consider how organ hypoperfusion and blood flow supply–demand mismatch might lead to both sensory hyper-reflexia and aberrant afferent tonicity. We discuss how this may drive sympatho-excitatory-positive feedback and extend across multiple organs initiating, or at least amplifying, sympathetic hyperactivity. The latter, in turn, compounds the challenge to sufficient organ blood flow through heightened vasoconstriction that both maintains and exacerbates hypertension.

Pulsed Radiofrequency of Dorsal Root Ganglia for the Treatment of Complex Regional Pain Syndrome in an Adolescent with Poliomyelitis Sequel: A Case Report

OBJECTIVE

Complex regional pain syndrome (CRPS) is a painful and disabling syndrome in which the patient presents with neuropathic pain, edema, or vasomotor or pseudomotor abnormalities that are often refractory to treatment. Polio paralysis is caused by the damage or destruction of motor neurons in the spine, which lead to corresponding muscle paralysis. This report is a case report on the application of a pulsed radiofrequency (PRF) current to dorsal root ganglia (DRG) for the treatment of CRPS type 1 in an adolescent patient.

DESIGN

Single case report.

SETTING

Selcuk University Hospital.

PATIENT

A 16-year-old girl who suffered from CRPS type 1 secondary to surgeries for the sequelae of poliomyelitis.

INTERVENTIONS

PRF current application to the lumbar 4 and lumbar 5 DRG.

OUTCOME MEASURES

Pain reduction.

RESULTS

The patient had complete resolution of her symptoms, which was maintained at a 6-month follow-up.

CONCLUSIONS

This case illustrates that PRF applied to lumbar 4 and lumbar 5 DRG may play a significant role in CRPS type 1 management after the surgical treatment of poliomyelitis sequelae in adolescent patients. Further randomized, controlled studies are needed to support this argument.

How big of a threat is needlestick-injury-induced complex regional pain syndrome? A "scientific" perspective

Complex regional pain syndrome (CRPS), previously known as reflex sympathetic dystrophy, is attracting more public attention in Japan which is likely a result of the recent upsurge in lawsuits filed against medical institutes. A recent court ruling over a case of injection-needlestick-injury induced CRPS has touched off serious debates among both medical practitioners and legal professionals. Although the court rejected the plaintiff's claims, the high court admitted them in view of the evidence and the entire pleadings and ordered the defendant to pay compensation. As venipuncture is the most frequently conducted and minimally invasive procedure in daily clinical practice, this court decision has attracted tremendous interest throughout the nation, alarming medical practitioners, and encouraging attorneys. The purpose of this article is twofold: to highlight the patient's clinical course in summary based on an unofficial case law report and to provide a scientific perspective on this issue based on recent relevant articles.

Increased bilateral expression of α1-adrenoceptors on peripheral nerves, blood vessels and keratinocytes does not account for pain or neuroinflammatory changes after distal tibia fracture in rats

In certain forms of nerve injury and inflammation, noradrenaline augments pain via actions on up-regulated α1-adrenoceptors (α1-ARs). The aim of this study was to use immunohistochemistry to examine α1-AR expression on peripheral neurons, cutaneous blood vessels and keratinocytes after distal tibia fracture and cast immobilization, a model of complex regional pain syndrome type 1. We hypothesized that there would be increased α1-AR expression on neurons and keratinocytes in the injured limb in comparison to the contralateral unaffected limb after distal tibia fracture, in association with inflammatory changes and pain. α1-AR expression was increased on plantar keratinocytes, dermal blood vessels and peripheral nerve fibers at 16weeks after injury both in the fractured and contralateral uninjured limb. Similar changes were seen in controls whose limb had been immobilized in a cast for 4weeks but not fractured. Neurofilament 200 (NF200), a marker of myelinated neurons, and calcitonin gene-related peptide (CGRP), a neuropeptide involved in neuro-inflammatory signaling, decreased 4weeks after fracture and casting but then increased at the 16-week time point. As some of these changes were also detected in the contralateral hind limb, they probably were triggered by a systemic response to fracture and casting. Soon after the cast was removed, intraplantar injections of the α1-AR antagonist prazosin released local vasoconstrictor tone but had no effect on pain behaviors. However, systemic injection of prazosin inhibited behavioral signs of pain, suggesting that fracture and/or casting triggered an up-regulation of α1-ARs in central nociceptive pathways that augmented pain. Together, these findings indicate that α1-AR expression increases in the hind limbs after distal tibia fracture and cast immobilization. However, these peripheral increases do not contribute directly to residual pain.

Up-regulation of cutaneous α1 -adrenoceptors in complex regional pain syndrome type I

BACKGROUND

In a small radioligand-binding study of cutaneous α1 -adrenoceptors in complex regional pain syndrome (CRPS), signal intensity was greater in the CRPS-affected limb than in controls. However, it was not possible to localize heightened expression of α1 -adrenoceptors to nerves, sweat glands, blood vessels, or keratinocytes using this technique.

METHODS

To explore this in the present study, skin biopsies were obtained from 31 patients with CRPS type I and 23 healthy controls of similar age and sex distribution. Expression of α1 -adrenoceptors on keratinocytes and on dermal blood vessels, sweat glands, and nerves was assessed using immunohistochemistry.

RESULTS

α1 -Adrenoceptors were expressed more strongly in dermal nerve bundles and the epidermis both on the affected and contralateral unaffected side in patients than in controls (P<0.05). However, expression of α1 -adrenoceptors in sweat glands and blood vessels was similar in patients and controls. α1 -Adrenoceptor staining intensity in the CRPS-affected epidermis was associated with pain intensity (P < 0.05), but a similar trend for nerve bundles did not achieve statistical significance.

DISCUSSION

Epidermal cells influence nociception by releasing ligands that act on sensory nerve fibers. Moreover, an increased expression of α1 -adrenoceptors on nociceptive afferents has been shown to aggravate neuropathic pain. Thus, the heightened expression of α1 -adrenoceptors in dermal nerves and epidermal cells might augment pain and neuroinflammatory disturbances after tissue injury in patients with CRPS type I.

Radiofrequency ablation of stellate ganglion in a patient with complex regional pain syndrome

Complex regional pain syndrome (CRPS) is characterized by a combination of sensory, motor, vasomotor, pseudomotor dysfunctions and trophic signs. We describe the use of radiofrequency (RF) ablation of Stellate ganglion (SG) under fluoroscopy, for long-term suppression of sympathetic nervous system, in a patient having CRPS-not otherwise specified. Although the effects of thermal RF neurolysis may be partial or temporary, they may promote better conditions toward rehabilitation. The beneficial effect obtained by the RF neurolysis of SG in this particular patient strongly advocates the use of this mode of therapy in patients with CRPS.

High-resolution ultrasound visualization of the subcutaneous nerves of the forearm: a feasibility study in anatomic specimens

INTRODUCTION

The aim of this ultrasound-anatomical study was to evaluate the ability of high-resolution ultrasound (HRUS) to visualize and infiltrate small subcutaneous nerves of the forearm in anatomic specimens.

METHODS

Seven nonembalmed human bodies (4 men, 3 women; mean age at death, 60 years) were included in the study. Two investigators scanned the anatomic specimens using 15-MHz and 18-MHz HRUS transducers. The lateral, medial, and posterior antebrachial cutaneous nerves were scanned and interventionally marked with ink using HRUS-guidance. Subsequently, dissections were performed to assess the anatomical correlation of HRUS findings.

RESULTS

All 3 nerves were identified consistently using HRUS. The precision of the ink-markings was excellent, with good correlation with the small peripheral branches of all 3 nerves.

CONCLUSIONS

HRUS can identify precisely the small subcutaneous nerves of the forearm and may aid in both diagnosis and therapy in cases of neuropathy.

Treatment of patients with painful blind eye using stellate ganglion block

BACKGROUND AND OBJECTIVES

management of pain in painful blind eyes is still a challenge. Corticosteroids and hypotensive agents, as well as evisceration and enucleation, are some of the strategies employed so far that are not always effective and, depending on the strategy, cause a deep emotional shock to the patient. Given these issues, the aim of this case report is to demonstrate a new and viable option for the management of such pain by treating the painful blind eye with the stellate ganglion block technique, a procedure that has never been described in the literature for this purpose.

CASE REPORT

six patients with painful blind eye, all caused by glaucoma, were treated; in these patients, VAS (visual analogue scale for pain assessment, in which 0 is the absence of pain and 10 is the worst pain ever experienced) ranged from 7 to 10. We opted for weekly sessions of stellate ganglion block with 4 mL of bupivacaine (0.5%) without vasoconstrictor and clonidine 1 mcg/kg. Four patients had excellent results at VAS, ranging between 0 and 3, and two remained asymptomatic (VAS=0), without the need for additional medication. The other two used gabapentin 300 mg every 12h.

CONCLUSION

currently, there are several therapeutic options for the treatment of painful blind eye, among which stand out the retrobulbar blocks with chlorpromazine, alcohol and phenol. However, an effective strategy with low rate of serious complications, which is non-mutilating and improves the quality of life of the patient, is essential. Then, stellate ganglion block arises as a demonstrably viable and promising option to meet this demand.

Inflammation in CRPS: role of the sympathetic supply

Acute Complex Regional Pain Syndrome (CRPS) is associated with signs of inflammation such as increased skin temperature, oedema, skin colour changes and pain. Pro-inflammatory cytokines (tumour necrosis factor-α (TNF-α), interleukin-2 (IL-2), IL-1beta, IL-6) are up-regulated, whereas anti-inflammatory cytokines (IL-4, IL-10) are diminished. Adaptive immunity seems to be involved in CRPS pathophysiology as many patients have autoantibodies directed against β2 adrenergic and muscarinic-2 receptors. In an animal tibial fracture model changes in the innate immune response such as up-regulation of keratinocytes are also found. Additionally, CRPS is accompanied by increased neurogenic inflammation which depends mainly on neuropeptides such as CGRP and Substance P. Besides inflammatory signs, sympathetic nervous system involvement in CRPS results in cool skin, increased sweating and sympathetically-maintained pain. The norepinephrine level is lower in the CRPS-affected than contralateral limb, but sympathetic sprouting and up-regulation of alpha-adrenoceptors may result in an adrenergic supersensitivity. The sympathetic nervous system and inflammation interact: norepinephrine influences the immune system and the production of cytokines. There is substantial evidence that this interaction contributes to the pathophysiology and clinical presentation of CRPS, but this interaction is not straightforward. How inflammation in CRPS might be exaggerated by sympathetic transmitters requires further elucidation.

VGLUTs in Peripheral Neurons and the Spinal Cord: Time for a Review

Vesicular glutamate transporters (VGLUTs) are key molecules for the incorporation of glutamate in synaptic vesicles across the nervous system, and since their discovery in the early 1990s, research on these transporters has been intense and productive. This review will focus on several aspects of VGLUTs research on neurons in the periphery and the spinal cord. Firstly, it will begin with a historical account on the evolution of the morphological analysis of glutamatergic systems and the pivotal role played by the discovery of VGLUTs. Secondly, and in order to provide an appropriate framework, there will be a synthetic description of the neuroanatomy and neurochemistry of peripheral neurons and the spinal cord. This will be followed by a succinct description of the current knowledge on the expression of VGLUTs in peripheral sensory and autonomic neurons and neurons in the spinal cord. Finally, this review will address the modulation of VGLUTs expression after nerve and tissue insult, their physiological relevance in relation to sensation, pain, and neuroprotection, and their potential pharmacological usefulness.

Effects of inflammation on the innervation of the colon

Inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease lead to altered gastrointestinal (GI) function as a consequence of the effects of inflammation on the tissues that comprise the GI tract. Among these tissues are several types of neurons that detect the state of the GI tract, transmit pain, and regulate functions such as motility, secretion, and blood flow. This review article describes the structure and function of the enteric nervous system, which is embedded within the gut wall, the sympathetic motor innervation of the colon and the extrinsic afferent innervation of the colon, and considers the evidence that colitis alters these important sensory and motor systems. These alterations may contribute to the pain and altered bowel habits that accompany IBD.

Painful effects of auditory startle, forehead cooling and psychological stress in patients with fibromyalgia or rheumatoid arthritis

OBJECTIVE

The aim of this study was to determine whether the clinical pain associated with rheumatoid arthritis or fibromyalgia would increase during standard laboratory tasks and, if so, whether these increases were linked with individual differences in psychological distress.

METHODS

Twenty-three patients with fibromyalgia and 16 patients with rheumatoid arthritis rated changes in clinical pain after an acoustic startle stimulus, during painful forehead cooling, and during stressful mental arithmetic. In addition, pain tolerance was assessed during a submaximal effort tourniquet test, and patients provided ratings of distress on a standard Depression, Anxiety and Stress Inventory.

RESULTS

Pain at rest was associated with depression scores in patients with rheumatoid arthritis, and was associated with stress scores in the fibromyalgia group. However, pain tolerance was unrelated to individual differences in psychological distress in either group. In patients with fibromyalgia, clinical pain increased after the acoustic startle stimulus and painful forehead cooling, and increased during stressful mental arithmetic. Arthritic pain also increased during forehead cooling and mental arithmetic in association with indices of psychological distress.

CONCLUSIONS

These findings suggest that processes linked with individual differences in distress aggravate pain in rheumatoid arthritis, whereas some other mechanism (e.g., failure of stress-related pain modulation processes or an aberrant interaction between nociceptive afferent and sympathetic efferent fibers) triggers stress-induced pain in fibromyalgia.

A possible role of the locus coeruleus in complex regional pain syndrome

Heightened sensitivity to painful stimulation commonly spreads from the affected limb to the ipsilateral forehead in patients with complex regional pain syndrome (CRPS). In addition, acoustic startle evokes greater auditory discomfort and increases in limb pain when presented on the affected than unaffected side. In contrast, limb pain ordinarily evokes analgesia in the ipsilateral forehead of healthy participants, and acoustic startle suppresses limb pain. Together, these findings suggest that hemilateral and generalized pain control mechanisms are disrupted in CRPS, and that multisensory integrative processes are compromised. Failure to inhibit nociceptive input from the CRPS-affected limb could sensitize spinal and supraspinal neurons that receive convergent nociceptive and auditory information from hemilateral body sites. Somatosensory, auditory, and emotional inputs may then aggravate pain by feeding into this sensitized nociceptive network. In particular, a disturbance in hemilateral pain processing that involves the locus coeruleus could exacerbate the symptoms of CRPS in some patients.

Interleukin-17A increases neurite outgrowth from adult postganglionic sympathetic neurons

Inflammation can profoundly alter the structure and function of the nervous system. Interleukin (IL)-17 has been implicated in the pathogenesis of several inflammatory diseases associated with nervous system plasticity. However, the effects of IL-17 on the nervous system remain unexplored. Cell and explant culture techniques, immunohistochemistry, electrophysiology, and Ca2+ imaging were used to examine the impact of IL-17 on adult mouse sympathetic neurons. Receptors for IL-17 were present on postganglionic neurons from superior mesenteric ganglia (SMG). Supernatant from activated splenic T lymphocytes, which was abundant in IL-17, dramatically enhanced axonal length of SMG neurons. Importantly, IL-17-neutralizing antiserum abrogated the neurotrophic effect of splenocyte supernatant, and incubation of SMG neurons in IL-17 (1 ng/ml) significantly potentiated neurite outgrowth. The neurotrophic effect of IL-17 was accompanied by inhibition of voltage-dependent Ca2+ influx and was recapitulated by incubation of neurons in a blocker of N-type Ca2+ channels (ω-conotoxin GVIA; 30 nM). IL-17-induced neurite outgrowth in vitro appeared to be independent of glia, as treatment with a glial toxin (AraC; 5 μM) did not affect the outgrowth response to IL-17. Moreover, application of the cytokine to distal axons devoid of glial processes enhanced neurite extension. An inhibitor of the NF-κB pathway (SC-514; 20 μM) blocked the effects of IL-17. These data represent the first evidence that IL-17 can act on sympathetic somata and distal neurites to enhance neurite outgrowth, and identify a novel potential role for IL-17 in the neuroanatomical plasticity that accompanies inflammation.

Clinical features and pathophysiology of complex regional pain syndrome

A complex regional pain syndrome (CRPS)--multiple system dysfunction, severe and often chronic pain, and disability--can be triggered by a minor injury, a fact that has fascinated scientists and perplexed clinicians for decades. However, substantial advances across several medical disciplines have recently improved our understanding of CRPS. Compelling evidence implicates biological pathways that underlie aberrant inflammation, vasomotor dysfunction, and maladaptive neuroplasticity in the clinical features of CRPS. Collectively, the evidence points to CRPS being a multifactorial disorder that is associated with an aberrant host response to tissue injury. Variation in susceptibility to perturbed regulation of any of the underlying biological pathways probably accounts for the clinical heterogeneity of CRPS.

Some lumbar sympathetic neurons develop a glutamatergic phenotype after peripheral axotomy with a note on VGLUT₂-positive perineuronal baskets

Glutamate is the main excitatory neurotransmitter in the nervous system, including in primary afferent neurons. However, to date a glutamatergic phenotype of autonomic neurons has not been described. Therefore, we explored the expression of vesicular glutamate transporter (VGLUT) types 1, 2 and 3 in lumbar sympathetic chain (LSC) and major pelvic ganglion (MPG) of naïve BALB/C mice, as well as after pelvic nerve axotomy (PNA), using immunohistochemistry and in situ hybridization. Colocalization with activating transcription factor-3 (ATF-3), tyrosine hydroxylase (TH), vesicular acetylcholine transporter (VAChT) and calcitonin gene-related peptide was also examined. Sham-PNA, sciatic nerve axotomy (SNA) or naïve mice were included. In naïve mice, VGLUT(2)-like immunoreactivity (LI) was only detected in fibers and varicosities in LSC and MPG; no ATF-3-immunoreactive (IR) neurons were visible. In contrast, PNA induced upregulation of VGLUT(2) protein and transcript, as well as of ATF-3-LI in subpopulations of LSC neurons. Interestingly, VGLUT(2)-IR LSC neurons coexpressed ATF-3, and often lacked the noradrenergic marker TH. SNA only increased VGLUT(2) protein and transcript in scattered LSC neurons. Neither PNA nor SNA upregulated VGLUT(2) in MPG neurons. We also found perineuronal baskets immunoreactive either for VGLUT(2) or the acetylcholinergic marker VAChT in non-PNA MPGs, usually around TH-IR neurons. VGLUT(1)-LI was restricted to some varicosities in MPGs, was absent in LSCs, and remained largely unaffected by PNA or SNA. This was confirmed by the lack of expression of VGLUT(1) or VGLUT(3) mRNAs in LSCs, even after PNA or SNA. Taken together, axotomy of visceral and non-visceral nerves results in a glutamatergic phenotype of some LSC neurons. In addition, we show previously non-described MPG perineuronal glutamatergic baskets.

Sensory disturbances in complex regional pain syndrome: clinical observations, autonomic interactions, and possible mechanisms

OBJECTIVE

To review mechanisms that might contribute to sensory disturbances and sympathetically-maintained pain in complex regional pain syndrome (CRPS).

BACKGROUND

CRPS is associated with a range of sensory and autonomic abnormalities. In a subpopulation of patients, sympathetic nervous system arousal and intradermal injection of adrenergic agonists intensify pain.

RESULTS

Mechanisms responsible for sensory abnormalities in CRPS include sensitization of primary afferent nociceptors and spinothalamic tract neurons, disinhibition of central nociceptive neurons, and reorganization of thalamo-cortical somatosensory maps. Proposed mechanisms of sympathetically-maintained pain include adrenergic excitation of sensitized nociceptors in the CRPS-affected limb, and interaction between processes within the central nervous system that modulate nociception and emotional responses. Central mechanisms could involve adrenergic facilitation of nociceptive transmission in the dorsal horn or thalamus, and/or depletion of bulbo-spinal opioids or tolerance to their effects.

CONCLUSIONS

Sympathetic neural activity might contribute to pain and sensory disturbances in CRPS by feeding into nociceptive circuits at the site of injury or elsewhere in the CRPS-affected limb, within the dorsal horn, or via thalamo-cortical projections.

Expression of α1-adrenoceptors on peripheral nociceptive neurons

The purpose of this study was to determine whether α(1)-adrenoceptors are expressed on primary nociceptive afferents that innervate healthy skin. Skin and dorsal root ganglia were collected from adult male Wistar rats and assessed using fluorescence immunohistochemistry with antibodies directed against α(1)-adrenoceptors alone or in combination with specific labels including myelin basic protein and neurofilament 200 (markers of myelinated nerve fibres), protein gene product 9.5 (a pan-neuronal marker), tyrosine hydroxylase (sympathetic neurons), isolectin B(4) (IB(4): non-peptidergic sensory neurons), calcitonin gene related peptide (CGRP) and transient receptor potential vanilloid receptor 1 (TRPV1) (peptidergic sensory neurons). Double labelling in dorsal root ganglia confirmed the expression of α(1)-adrenoceptors within sub-populations of CGRP, IB(4) and TRPV1 immunoreactive neurons. Myelinated and unmyelinated sensory nerve fibres in the skin expressed α(1)-adrenoceptors whereas sympathetic nerve fibres did not. The expression of α(1)-adrenoceptors on C- and A-delta nociceptive afferent fibres provides a histochemical substrate for direct excitation of these fibres by adrenergic agonists. This may help to explain the mechanism of sensory-sympathetic coupling that sometimes develops on surviving primary nociceptive afferents in neuropathic pain states.