Sympathectomy attenuates excitability of dorsal root ganglion neurons and pain behaviour in a lumbar radiculopathy model

Lumbar Sympathetic Block Leading to Increased Arterial Diameter and Blood Flow: A Mechanism of Therapeutic Benefit

Lumbar sympathetic blocks (LSBs) have long been used for the treatment of chronic lower extremity pain and for conditions such as complex regional pain syndrome (CRPS). With a better understanding of the autonomic nervous system and its function, these blocks have grown in their utility. Through this growth, however, our understanding of sympathetic-mediated pain is still vaguely understood. Here, we present a case of a patient who underwent a point-of-care ultrasound (POCUS) before and after an LSB, and we were able to show significant dilation of the posterior tibial artery (PTA) following the block. We propose that this arterial dilation plays a mechanistic role in providing pain relief to patients who undergo LSB. This increased blood flow can not only enhance healing properties to surrounding tissues but also allow for nitric oxide to play potential regulatory roles in pain pathways. Here, we also review potential mechanisms of the amelioration of sympathetic-mediated pain as well as the potential utilization of LSBs and neuromodulation in treating visceral pathologies through a better understanding of visceral somatic relationships.

Effectiveness of combined dorsal root ganglion and spinal cord stimulation: a retrospective, single-centre case series for chronic focal neuropathic pain

OBJECTIVE

This case series retrospectively reviewed the outcomes in patients implanted with combined, synchronous dorsal root ganglion stimulation (DRGS) and spinal cord stimulation (SCS) connected to a single implantable pulse generator (IPG) in a tertiary referral neuromodulation centre in the United Kingdom.

METHODS

Twenty-six patients underwent a trial of DRGS+SCS for treating focal neuropathic pain between January 2016 and December 2019, with a follow-up in February 2022. A Transgrade approach was employed for DRGS. Patients were provided with 3 possible stimulation programs: DRGS-only, SCS-only, or DRGS+SCS. Patients were assessed for pain intensity, patients' global impression of change (PGIC), preferred lead(s) and complications.

RESULTS

Twenty patients were successful and went on for full implantation. The most common diagnosis was Complex Regional Pain Syndrome. After an average of 3.1 years follow-up, 1 patient was lost to follow-up, and 2 were non-responders. Of the remaining 17 patients, 16 (94%) continued to report a PGIC of 7. The average pain intensity at Baseline was 8.5 on an NRS scale of 0-10. At the last follow-up, the average NRS reduction overall was 78.9% with no statistical difference between those preferring DRGS+SCS (n = 9), SCS-only (n = 3) and DRGS-only (n = 5). The combination of DRGS+SCS was preferred by 53% at the last follow-up. There were no serious neurological complications.

CONCLUSIONS

This retrospective case series demonstrates the potential effectiveness of combined DRGS+SCS with sustained analgesia observed at an average follow-up of over 3 years. Implanting combined DRGS+SCS may provide programming flexibility and therapeutic alternatives.

Efficacy of the lumbar sympathetic ganglion block in lower limb pain and its application prospects during the perioperative period

The sympathetic nervous system is involved in the physiological pathogenesis of many different types of chronic pain. Sympathetic blocks can interrupt the reflex control system by intercepting the noxious afferent fibers accompanying autonomic nerves, resulting in changes in peripheral or central sensory processing. A lumbar sympathetic ganglion block (LSGB), as a treatment method, refers to the injection of nerve blockers into the corresponding lumbar sympathetic nerve segments, usually requiring imaging assistance (CT, X-ray, ultrasound) to guide. At present, LSGB has been widely used in the clinical treatment of lower limb pain, such as neuropathic pain, lower limb ischemic pain, and so on. Its mechanism of action may be through inhibiting sympathetic nerve activity and dilating blood vessels, thereby alleviating pain and inhibiting stress response. However, there are few reports of LSGB during the perioperative period, especially in postoperative pain and gastrointestinal function. Therefore, by studying the literature about LSGB-related studies, this article reviews the anatomy of the lumbar sympathetic nerve (LSN), with its clinical application and possible mechanism. We reviewed the analgesic effect of LSGB in patients with lower limb pain and postoperative pain and the potential application prospects in the recovery of gastrointestinal function, finally providing a reference for its clinical application.

Effects of the Ultrasound-Guided Stellate Ganglion Block on Hemodynamics, Stress Response, and Gastrointestinal Function in Postoperative Patients with Colorectal Cancer

Objective

The aim of the study was to study the effects of the ultrasound-guided stellate ganglion block on hemodynamics, stressful response, and postoperative gastrointestinal functions in patients with colorectal cancer.

Methods

A total of 100 patients with colorectal cancer hospitalized from January 2021 to December 2021 were selected. After anesthesia induction, the right stellate ganglion block was performed under ultrasound guidance in the research group and the general anesthesia was performed in the control group. The heart rate (HR), mean arterial pressure (MAP), epinephrine, cortisol, self-rating anxiety scale (SAS), Ramsay sedation score (RSS), postoperative bowel sound recovery time, anal exhaust time, and the incidence of gastrointestinal adverse reactions 24 hours after operation were studied pre-and post-24-hour anesthesia induction.

Results

Following 24-hour operation, the HR and MAP values were largely reduced (p < 0.05). Following 24-hour operation, epinephrine and cortisol became obviously higher (p < 0.05). After 24-hour operation, the levels of epinephrine and cortisol in the research group were greatly lower. The score of the SAS in the study cohort was less than that of the controls (p < 0.05). The RSS of the research group was obviously increased (p < 0.05). The recovery time of intestinal sound and the anal exhaust time of the study cohort became remarkably shorter (p < 0.05). The incidence of gastrointestinal adverse reactions 24 hours after operation of the study cohort was much less common (p < 0.05).

Conclusion

The ultrasound-guided stellate ganglion block can reduce the fluctuation of blood circulation during radical resection of colorectal cancer, reduce postoperative gastrointestinal dysfunction and stress reaction, relieve patients' anxiety, and contribute to the recovery of gastrointestinal function.

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 Effect of a Combined Modified Pectoral and Stellate Ganglion Block on Stress and Inflammatory Response in Patients Undergoing Modified Radical Mastectomy

Background and Aims

Regional anaesthesia reports to attenuate stress and inflammatory responses associated with surgical resection; however, the effectiveness of combined nerve blocks is less often investigated. We evaluated whether a combination of a pectoral nerve block (PNB) and stellate ganglion block (SGB) is more effective than a PNB alone in reducing these responses in women undergoing modified radical mastectomy (MRM).

Methods

This is a prospective randomized controlled trial. Fifty patients with breast cancer were randomly allocated to receive an ultrasound-guided PNB (n = 25, PNB only group) or ultrasound-guided PNB combined with SGB (n = 25, combined blockade group). The primary outcome was perioperative plasma level of interleukin- (IL-) 6. Secondary outcomes included perioperative plasma levels of cortisol, glucose, IL-8, and tumour necrosis factor- (TNF-) α, pain scores, haemodynamic variables, sleep quality, and complications postsurgery.

Results

The combined blockade group exhibited significantly lower IL-6 and TNF-α levels 24 h postsurgery. Cortisol levels were significantly lower in the combined blockade group at the end of the surgery. Glucose levels at the time of incision were lower in the combined blockade group. Pain scores up to 12 h postsurgery were significantly lower in the combined blockade group, which also exhibited better perioperative haemodynamic stability. Patients in the combined blockade group reported better sleep quality on the night of surgery.

Conclusion

In patients undergoing MRM, PNB combined with SGB block effectively blunted perioperative inflammatory response than PNB alone. A combined block approach can also alleviate stress response and postoperative acute pain with stable perioperative haemodynamics and better postoperative sleep quality.

Ultrasound-guided stellate ganglion block alleviates stress responses and promotes recovery of gastrointestinal function in patients

BACKGROUND

This study aimed to investigate the effect of preoperative ultrasound-guided stellate ganglion block (SGB) on the perioperative stress responses and gastrointestinal functions of patients undergoing laparoscopic colorectal cancer surgery.

METHODS

A total of 60 colorectal cancer patients were enrolled in study and were randomized to be treated with or without SGB therapy. In the SGB group, patients were injected with 7 mL 0.5% ropivacaine in stellate ganglion under ultrasound guidance before anesthesia. Mean artery pressure (MAP), heart rate (HR), recovery of bowel sound and first exhaust, as well as levels of motilin, gastrin, norepinephrine, cortisol, interleukin-6 (IL-6) and C-reactive protein (CRP) were recorded at various time points.

RESULTS

26 patients in the SGB group and 27 patients in the control group were analyzed. No significant differences in MAP or HR were observed between the two groups before, during and after the surgery. SGB promoted recovery of gastrointestinal functions, as evidenced by earlier recovery of bowel sound and first exhaust, as well as increased motilin and gastrin levels. SGB also attenuated stress responses, as shown in reduced norepinephrine, cortisol, IL-6 and CRP levels.

CONCLUSIONS

SGB promotes the recovery of gastrointestinal functions and reduces stress responses of colorectal patients undergoing laparoscopic colorectal cancer surgery.

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.

Local Sympathectomy Promotes Anti-inflammatory Responses and Relief of Paclitaxel-induced Mechanical and Cold Allodynia in Mice

BACKGROUND

Patients undergoing cancer treatment often experience chemotherapy-induced neuropathic pain at their extremities, for which there is no U.S. Food and Drug Administration-approved drug. The authors hypothesized that local sympathetic blockade, which is used in the clinic to treat various pain conditions, can also be effective to treat chemotherapy-induced neuropathic pain.

METHODS

A local sympathectomy (i.e., cutting the ipsilateral gray rami entering the spinal nerves near the L3 and L4 dorsal root ganglia) was performed in mice receiving intraperitoneal injections every other day of the chemotherapeutic drug paclitaxel. Sympathectomy effects were then assessed in chemotherapy-induced pain-like behaviors (i.e., mechanical and cold allodynia) and neuroimmune and electrophysiologic responses.

RESULTS

Local microsympathectomy produced a fast recovery from mechanical allodynia (mean ± SD: sympathectomy vs. sham at day 5, 1.07 ± 0.34 g vs. 0.51 ± 0.17g, n = 5, P = 0.030 in male mice, and 1.08 ± 0.28 g vs. 0.62 ± 0.16 g, n = 5, P = 0.036 in female mice) and prevented the development of cold allodynia in both male and female mice after paclitaxel. Mechanistically, microsympathectomy induced transcriptional increases in dorsal root ganglia of macrophage markers and anti-inflammatory cytokines, such as the transforming growth factor-β. Accordingly, depletion of monocytes/macrophages and blockade of transforming growth factor-β signaling reversed the relief of mechanical allodynia by microsympathectomy. In particular, exogenous transforming growth factor-β was sufficient to relieve mechanical allodynia after paclitaxel (transforming growth factor-β 100 ng/site vs. vehicle at 3 h, 1.21 ± 0.34g vs. 0.53 ± 0.14 g, n = 5, P = 0.001 in male mice), and transforming growth factor-β signaling regulated neuronal activity in dorsal root ganglia.

CONCLUSIONS

Local sympathetic nerves control the progression of immune responses in dorsal root ganglia and pain-like behaviors in mice after paclitaxel, raising the possibility that clinical strategies already in use for local sympathetic blockade may also offer an effective treatment for patients experiencing chemotherapy-induced neuropathic pain.

Utilization of Concurrent Dorsal Root Ganglion Stimulation and Dorsal Column Spinal Cord Stimulation in Complex Regional Pain Syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) can be effectively treated with spinal cord stimulation (t-SCS). There is also evidence that dorsal root ganglion (DRG) stimulation may be superior to t-SCS in CRPS. However, there has been no published data, to our knowledge, that looked at the concurrent use of t-SCS and DRG stimulation for treatment of CRPS.

METHODS

Our study includes four patients with severe CRPS who had all been implanted with a t-SCS. While all these patients had positive results from their t-SCS, they all had areas which lacked coverage, giving them incomplete pain relief. These patients also underwent successful trial and implantation of DRG-S. All four patients reported further improvement in their residual pain and function with DRG-S (>60%), and even superior pain relief (>80%) with concurrent use of t-SCS and t-SCS.

RESULTS

All patients had a diagnosis of lower extremity CRPS-1. After DRG-S implantation, multiple attempts were made in each patient to use DRG-S alone by temporarily turning the t-SCS off. However, in each attempt, all patients consistently reported superior pain relief and improvement in function with the concurrent use of t-SCS and DRG, as compared to DRG alone. The average numeric rating scale pain score decreased from approximately 7 in the regions not covered by t-SCS to 3 after DRG-S implantation, and to 1.25 with concurrent use t-SCS and DRG-S.

CONCLUSION

Both t-SCS and DRG-S have been shown to be effective in treatment of patients with CRPS. In our study, concurrent use of t-SCS and DRG-S provided significant improvement in pain and function as compared to using either device alone. This suggests the potential that combination therapy with t-SCS and DRG-S may be beneficial in patients with CRPS. Further prospective studies are required to evaluate this concept.

T Cells as an Emerging Target for Chronic Pain Therapy

The immune system is critically involved in the development and maintenance of chronic pain. However, T cells, one of the main regulators of the immune response, have only recently become a focus of investigations on chronic pain pathophysiology. Emerging clinical data suggest that patients with chronic pain have a different phenotypic profile of circulating T cells compared to controls. At the preclinical level, findings on the function of T cells are mixed and differ between nerve injury, chemotherapy, and inflammatory models of persistent pain. Depending on the type of injury, the subset of T cells and the sex of the animal, T cells may contribute to the onset and/or the resolution of pain, underlining T cells as a major player in the transition from acute to chronic pain. Specific T cell subsets release mediators such as cytokines and endogenous opioid peptides that can promote, suppress, or even resolve pain. Inhibiting the pain-promoting functions of T cells and/or enhancing the beneficial effects of pro-resolution T cells may offer new disease-modifying strategies for the treatment of chronic pain, a critical need in view of the current opioid crisis.

Suppression of Sympathetic Nerve Sprouting by Local Administration of an α-antagonist Around the Dorsal Root Ganglion in a Lumbar Radiculopathy Model

STUDY DESIGN

Animal experimental study with intervention.

OBJECTIVE

The purpose of this study was to elucidate whether local administration of an α-antagonist around the dorsal root ganglion (DRG) suppressed sympathetic nerve sprouting, from the acute to the chronic pain development phase, in a lumbar radiculopathy model using immunohistochemical methods.

SUMMARY OF BACKGROUND DATA

The abnormal sympathetic-somatosensory interaction may underlie some forms of neuropathic pain. There were several reports suggesting α-antagonists are effective to treat neuropathic pain. However, its pathophysiological mechanisms remain obscure.

METHODS

We used 70 male Sprague-Dawley rats. After root constriction (RC), rats received a series of three local injections of the nonselective α-antagonist phentolamine around the DRG for 3 days. There were three groups of rats: those that were injected from the day of surgery and those injected from day 4 and third group injected from day 11. The control rats were subjected to RC but equal-volume normal saline injections, and the naïve rats were not subjected to any surgical procedures. At the 14th postoperative day, the left L5 DRG was removed, embedded in paraffin, and sectioned. Sections were then immunostained with antibodies to tyrosine hydroxylase (TH). To quantify the extent of the presence of sympathetic nerve fibers, we counted TH-immunoreactive fibers in the DRG using a light microscope equipped with a micrometer graticule. We counted the squares of the graticule, which contained TH-immunoreactive fibers for each of five randomly selected sections of the DRG.

RESULTS

In the naïve group, TH-immunoreactive fibers were scarce in the DRG. α-antagonist injections from postoperative day 0 and 4 suppressed sympathetic nerve sprouting compared with the control group. α-antagonist injections from postoperative day 11 had no suppressant effect compared with the control group.

CONCLUSION

The α-antagonist administered around the DRG could suppress neural plastic changes in the early phase after nerve injury.

LEVEL OF EVIDENCE

N/A.

Localized Sympathectomy Reduces Mechanical Hypersensitivity by Restoring Normal Immune Homeostasis in Rat Models of Inflammatory Pain

Some forms of chronic pain are maintained or enhanced by activity in the sympathetic nervous system (SNS), but attempts to model this have yielded conflicting findings. The SNS has both pro- and anti-inflammatory effects on immunity, confounding the interpretation of experiments using global sympathectomy methods. We performed a "microsympathectomy" by cutting the ipsilateral gray rami where they entered the spinal nerves near the L4 and L5 DRG. This led to profound sustained reductions in pain behaviors induced by local DRG inflammation (a rat model of low back pain) and by a peripheral paw inflammation model. Effects of microsympathectomy were evident within one day, making it unlikely that blocking sympathetic sprouting in the local DRGs or hindpaw was the sole mechanism. Prior microsympathectomy greatly reduced hyperexcitability of sensory neurons induced by local DRG inflammation observed 4 d later. Microsympathectomy reduced local inflammation and macrophage density in the affected tissues (as indicated by paw swelling and histochemical staining). Cytokine profiling in locally inflamed DRG showed increases in pro-inflammatory Type 1 cytokines and decreases in the Type 2 cytokines present at baseline, changes that were mitigated by microsympathectomy. Microsympathectomy was also effective in reducing established pain behaviors in the local DRG inflammation model. We conclude that the effect of sympathetic fibers in the L4/L5 gray rami in these models is pro-inflammatory. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some chronic inflammatory pain conditions.

SIGNIFICANCE STATEMENT

Sympathetic blockade is used for many pain conditions, but preclinical studies show both pro- and anti-nociceptive effects. The sympathetic nervous system also has both pro- and anti-inflammatory effects on immune tissues and cells. We examined effects of a very localized sympathectomy. By cutting the gray rami to the spinal nerves near the lumbar sensory ganglia, we avoided widespread sympathetic denervation. This procedure profoundly reduced mechanical pain behaviors induced by a back pain model and a model of peripheral inflammatory pain. One possible mechanism was reduction of inflammation in the sympathetically denervated regions. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some inflammatory conditions.

Detailed Characterization of Sympathetic Chain Ganglia (SChG) Neurons Supplying the Skin of the Porcine Hindlimb

It is generally known that in the skin sympathetic fibers innervate various dermal structures, including sweat glands, blood vessels, arrectores pilorum muscles and hair follicles. However, there is a lack of data about the distribution and chemical phenotyping of the sympathetic chain ganglia (SChG) neurons projecting to the skin of the pig, a model that is physiologically and anatomically very representative for humans. Thus, the present study was designed to establish the origin of the sympathetic fibers supplying the porcine skin of the hind leg, and the pattern(s) of putative co-incidence of dopamine-β-hydroxylase (DβH) with pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin (SOM), neuronal nitric oxide synthase, substance P, vasoactive intestinal peptide, neuropeptide Y (NPY), leu5-enkephalin and galanin (GAL) using combined retrograde tracing and double-labeling immunohistochemistry. The Fast Blue-positive neurons were found in the L₂-S₂ ganglia. Most of them were small-sized and contained DβH with PACAP, SOM, NPY or GAL. The findings of the present study provide a detailed description of the distribution and chemical coding of the SChG neurons projecting to the skin of the porcine hind leg. Such data may be the basis for further studies concerning the plasticity of these ganglia under experimental or pathological conditions.

Sympathectomy and Sympathetic Blockade Reduce Pain Behavior Via Alpha-2 Adrenoceptor of the Dorsal Root Ganglion Neurons in a Lumbar Radiculopathy Model

STUDY DESIGN

Animal experimental study with intervention.

OBJECTIVE

We investigated whether sympathectomy and pharmacological sympathetic blockade reduced pain behavior and reversed adrenoceptor mRNA expression of the dorsal root ganglion (DRG) in a lumbar radiculopathy model.

SUMMARY OF BACKGROUND DATA

The abnormal sympathetic-somatosensory interaction may underlie some forms of neuropathic pain. There are several reports that sympathectomy and pharmacological sympathetic blockades are often effective to treat neuropathic pain. However, its pathophysiological mechanisms remain obscure.

METHODS

We used 91 male Sprague-Dawley rats. Just after root constriction (RC), the rats underwent sympathectomy or received 3 local injections of subtype-specific α-adrenergic receptor antagonists around the DRG. We evaluated the analgesic effects of sympathectomy and sympathetic blockade using behaviors indicative mechanical allodynia and thermal hyperalgesia. We estimated the mRNA expression levels of the DRG adrenoceptor subtypes using real time reverse transcription polymerase chain reaction.

RESULTS

Sympathectomy and α2-antagonist significantly reduced the mechanical allodynia and thermal hyperalgesia after RC. Real time reverse transcription polymerase chain reaction analysis indicated that sympathectomy possibly reversed α2A- and α2B-adrenoceptors mRNA overexpression in the DRG after RC.

CONCLUSION

We considered that pain behaviors of neuropathic pain are due, at least in part, to enhanced sympathetic noradrenergic transmission within the DRG. Suppression of sympathetic activity by reducing adrenergic release, α2-adrenoceptor stimulation, and/or α2-adrenoceptor upregulation in the DRG may relieve neuropathic pain.

LEVEL OF EVIDENCE

3.

Progress in Sympathetically Mediated Pathological Pain

Aim of review

Many chronic pain conditions remain difficult to treat, presenting a high burden to society. Conditions such as complex regional pain syndrome may be maintained or exacerbated by sympathetic activity. Understanding the interactions between sympathetic nervous system and sensory system will help to improve the effective management of pathological pain including intractable neuropathic pain and persistent inflammatory pain.

Method

We first described the discovery of abnormal connections between sympathetic and sensory neurons. Subsequently, the functional roles of sympathetic sprouting in altered neuronal excitability and increased pain sensitivity were discussed. The mechanisms of the sympathetic sprouting were focusing on its relationship with neurotrophins, local inflammation, and abnormal spontaneous activity. Finally, we discussed clinical implications and conflicting findings in the laboratory and clinical research with respect to the interaction between sympathetic system and sensory system.

Recent findings

The findings that sprouting of sympathetic fibers into the sensory ganglia (dorsal root ganglion) after peripheral nerve injury, offers a possible explanation of the sympathetic involvement in pain. It is also suggested that releases of adenosine triphosphate (ATP), in addition to norepinephrine, from sympathetic nerve endings play important roles in sympathetic-mediated pain. New evidence indicates the importance of sympathetic innervation in local inflammatory responses.

Summary

Hopefully, this review will reinvigorate the study of sympathetic-sensory interactions in chronic pain conditions, and help to better understand how sympathetic system contributes to this serious clinical problem.