Pulsed Radiofrequency Applied to the Sciatic Nerve Improves Neuropathic Pain by Down-regulating The Expression of Calcitonin Gene-related Peptide in the Dorsal Root Ganglion

The histomorphological and stereological assessment of rat dorsal root ganglion tissues after various types of sciatic nerve injury

Peripheral nerve injuries lead to significant changes in the dorsal root ganglia, where the cell bodies of the damaged axons are located. The sensory neurons and the surrounding satellite cells rearrange the composition of the intracellular organelles to enhance their plasticity for adaptation to changing conditions and response to injury. Meanwhile, satellite cells acquire phagocytic properties and work with macrophages to eliminate degenerated neurons. These structural and functional changes are not identical in all injury types. Understanding the cellular response, which varies according to the type of injury involved, is essential in determining the optimal method of treatment. In this research, we investigated the numerical and morphological changes in primary sensory neurons and satellite cells in the dorsal root ganglion 30 days following chronic compression, crush, and transection injuries using stereology, high-resolution light microscopy, immunohistochemistry, and behavioral analysis techniques. Electron microscopic methods were employed to evaluate fine structural alterations in cells. Stereological evaluations revealed no statistically significant difference in terms of mean sensory neuron numbers (p > 0.05), although a significant decrease was observed in sensory neuron volumes in the transection and crush injury groups (p < 0.05). Active caspase-3 immunopositivity increased in the injury groups compared to the sham group (p < 0.05). While crush injury led to desensitization, chronic compression injury caused thermal hyperalgesia. Macrophage infiltrations were observed in all injury types. Electron microscopic results revealed that the chromatolysis response was triggered in the sensory neuron bodies from the transection injury group. An increase in organelle density was observed in the perikaryon of sensory neurons after crush-type injury. This indicates the presence of a more active regeneration process in crush-type injury than in other types. The effect of chronic compression injury is more devastating than that of crush-type injury, and the edema caused by compression significantly inhibits the regeneration process.

Comparisons of the analgesic effect of different pulsed radiofrequency targets in SNI-induced neuropathic pain

An injury of the peripheral nerve may lead to neuropathic pain, which could be treated with pulsed radiofrequency to the dorsal root ganglion (DRG) or peripheral nerve [the nerve trunk (NT) or proximal to the injury site (NI)]. However, it is not clear whether there is any difference in analgesic effect or maintenance among the three targets. PRF was applied to the ipsilateral L5 DRG, peripheral nerve (NT or NI) 5 days after spared nerve injury (SNI). Triptolide (10 µg/kg) or vehicle was intrathecally administered 5 days after SNI for 3 days. Mechanical withdrawal thresholds were tested after treatment at different time points. Furthermore, microglia and the P2X7 receptor (P2X7R) in the ipsilateral spinal cord were measured with immunofluorescence and western blotting, respectively. PRF + NI exerted a more remarkable analgesic effect than PRF + DRG and PRF + NT at the early stage, but PRF + DRG had a stronger analgesic effect than PRF + NI and PRF + NT at the end of our study. In addition, PRF + DRG showed no significant difference from intrathecal administration of triptolide. Moreover, SNI-induced microglia activation and upregulation of P2X7R in spinal dorsal horn could be markedly inhibited by PRF + DRG. The results suggest that the analgesic effect of PRF + DRG increased with time whereas the other two not and microglia and P2X7R in the ipsilateral spinal dorsal horn may be involved in the process.

Neurostimulation for Chronic Pain: A Systematic Review of High-Quality Randomized Controlled Trials With Long-Term Follow-Up

OBJECTIVE

This study aimed to review the best evidence on the long-term efficacy of neurostimulation for chronic pain.

MATERIALS AND METHODS

We systematically reviewed PubMed, CENTRAL, and WikiStim for studies published between the inception of the data bases and July 21, 2022. Randomized controlled trials (RCTs) with a minimum of one-year follow-up that were of high methodologic quality as ascertained using the Delphi list criteria were included in the evidence synthesis. The primary outcome was long-term reduction in pain intensity, and the secondary outcomes were all other reported outcomes. Level of recommendation was graded from I to III, with level I being the highest level of recommendation.

RESULTS

Of the 7119 records screened, 24 RCTs were included in the evidence synthesis. Therapies with recommendations for their usage include pulsed radiofrequency (PRF) for postherpetic neuralgia, transcutaneous electrical nerve stimulation for trigeminal neuralgia, motor cortex stimulation for neuropathic pain and poststroke pain, deep brain stimulation for cluster headache, sphenopalatine ganglion stimulation for cluster headache, occipital nerve stimulation for migraine, peripheral nerve field stimulation for back pain, and spinal cord stimulation (SCS) for back and leg pain, nonsurgical back pain, persistent spinal pain syndrome, and painful diabetic neuropathy. Closed-loop SCS is recommended over open-loop SCS for back and leg pain. SCS is recommended over PRF for postherpetic neuralgia. Dorsal root ganglion stimulation is recommended over SCS for complex regional pain syndrome.

CONCLUSIONS

Neurostimulation is generally effective in the long term as an adjunctive treatment for chronic pain. Future studies should evaluate whether the multidisciplinary management of the physical perception of pain, affect, and social stressors is superior to their management alone.

Elucidating the Mechanisms of Pulsed Radiofrequency for Pain Treatment

Pulsed radiofrequency is a well-documented treatment option for multiple painful conditions where pulses of energy are delivered close to neural elements. Since its earliest adoption, this technique has gained increasing acceptance as a minimally invasive procedure, and new applications are evolving. Studies have shown microscopic and biochemical changes that reflect beneficial effects; however, the exact mechanism of action is not yet completely understood. To redress this paucity, 11,476 articles of scientific relevance published between 1980 and November 2022 were mined through a search of the PubMed database, arriving at 49 studies both in animals and humans. In general, the experimental studies examined have shown that pulsed radiofrequency induces multiple changes with antinociceptive and neuromodulatory effects. These modifications include changes in neural and glial cells, synaptic transmission, and perineural space. Studies also reveal that pulsed radiofrequency regulates inflammatory responses, cellular signaling proteins, and the expression of genes related to pain transmission, acting in biological processes in structures such as myelin, mitochondria, axons, glial cells, connective tissue, regulation of proteins, ion channels, and neurotransmitters.

High-frequency electrical stimulation attenuates neuronal release of inflammatory mediators and ameliorates neuropathic pain

BACKGROUND

Neuroinflammation is an important driver of acute and chronic pain states. Therefore, targeting molecular mediators of neuroinflammation may present an opportunity for developing novel pain therapies. In preclinical models of neuroinflammatory pain, calcitonin gene-related peptide (CGRP), substance P and high mobility group box 1 protein (HMGB1) are molecules synthesized and released by sensory neurons which activate inflammation and pain. High-frequency electrical nerve stimulation (HFES) has achieved clinical success as an analgesic modality, but the underlying mechanism is unknown. Here, we reasoned that HFES inhibits neuroinflammatory mediator release by sensory neurons to reduce pain.

METHODS

Utilizing in vitro and in vivo assays, we assessed the modulating effects of HFES on neuroinflammatory mediator release by activated sensory neurons. Dorsal root ganglia (DRG) neurons harvested from wildtype or transgenic mice expressing channelrhodopsin-2 (ChR2) were cultured on micro-electrode arrays, and effect of HFES on optogenetic- or capsaicin-induced neuroinflammatory mediator release was determined. Additionally, the effects of HFES on local neuroinflammatory mediator release and hyperalgesia was assessed in vivo using optogenetic paw stimulation and the neuropathic pain model of chronic constriction injury (CCI) of the sciatic nerve.

RESULTS

Light- or capsaicin-evoked neuroinflammatory mediator release from cultured transgenic DRG sensory neurons was significantly reduced by concurrent HFES (10 kHz). In agreement with these findings, elevated levels of neuroinflammatory mediators were detected in the affected paw following optogenetic stimulation or CCI and were significantly attenuated using HFES (20.6 kHz for 10 min) delivered once daily for 3 days.

CONCLUSION

These studies reveal a previously unidentified mechanism for the pain-modulating effect of HFES in the setting of acute and chronic nerve injury. The results support the mechanistic insight that HFES may reset sensory neurons into a less pro-inflammatory state via inhibiting the release of neuroinflammatory mediators resulting in reduced inflammation and pain.

Ameliorative Potential of Hot Compress on Sciatic Nerve Pain in Chronic Constriction Injury-Induced Rat Model

Hot compress modalities are used to ameliorate pain despite prevalent confusion about which modality should be used and when. Most recommendations for hot compresses are based on empirical experience, with limited evidence to support its efficacy. To obtain insight into the nerve transmission mechanism of hot compresses and to identify the nerve injury marker proteins specifically associated with sciatic nerve pain, we established a rat model of chronic constriction injury (CCI) and performed mechanical allodynia, electrophysiology, and histopathological analysis. All CCI rats exhibited geometric representation of the affected hind paw, which indicated a hyper-impact on both mechanical gait and asymmetry of gait on day 28. The CCI model after 28 days of surgery significantly reduced compound muscle action potential (CMAP) amplitude, but also significantly reduced latency. Administration of hot compress for 3 weeks (heated at 40–42°C, cycle of 40 min, and rest for 20 min, three cycles each time, three times per week) significantly increased the paw withdrawal thresholds in response to stimulation by Von Frey fibers and reversed the CCI-induced reduced sciatic functional index (SFI) scores. Hot compress treatment in the CCI model improved CMAP amplitude and latency. The S100 protein expression level in the CCI+Hot compression group was 1.5-fold higher than in the CCI group; it dramatically reduced inflammation, such as tumor necrosis factor alpha and CD68 expression in nerve injury sites. Synaptophysin (Syn) expression in the CCI+Hot compression group was less than threefold in the CCI group at both nerve injury sites and brain (somatosensory cortex and hippocampus). This finding indicates that local nerve damage and inflammation cause significant alterations in the sensorimotor strip, and hot compress treatment could significantly ameliorate sciatic nerve pain by attenuating Syn and inflammatory factors from local pathological nerves to the brain. This study determines the potential efficacy and safety of hot compress, and may have important implications for its widespread use in sciatic nerve pain treatment.

Correct Sciatic Nerve Management to Apply Ultrasound-Guided Percutaneous Neuromodulation in Patients With Chronic Low Back Pain: A Pilot Study

BACKGROUND

The objectives of this study were to evaluate the effects of an ultrasound (US)-guided percutaneous neuromodulation (PNM) intervention on the sciatic nerve, regarding pain, hip range of motion (ROM), balance, and functionality in patients with chronic low back pain (LBP); and to determine the optimal anatomical location of sciatic nerve stimulation to obtain therapeutic benefits in such patients.

MATERIALS AND METHODS

Thirty patients with chronic LBP were recruited and divided randomly into three groups. All patients received a single percutaneous electrical stimulation intervention on the sciatic nerve, with a different anatomical application location for each group (proximal, middle, and distal). Level of pain, hip passive ROM, dynamic balance, and Oswestry disability index were analyzed. All variables were calculated before the intervention, immediately postintervention, 48 hours and one week after the intervention, except the LBP questionnaire (before, and 48 hours and one week after the intervention).

RESULTS

All interventions decreased the level of pain and increased the ROM, balance, and functionality. Besides, these therapeutic effects were maintained during one week, regardless of the anatomical location of application.

CONCLUSIONS

The choice of an anatomical location of application of the US-guided PNM on the sciatic nerve by the physiotherapist does not influence the improvement of pain, ROM, balance, and function in patients with chronic LBP.

CT-Guided Pulsed Radiofrequency at Different Voltages in the Treatment of Postherpetic Neuralgia

Background

Postherpetic neuralgia (PHN) is a form of long-lasting neuropathic pain that can severely affect patients’ quality of life. Pulsed radiofrequency (PRF) has been proven to be effective in treating PHN, but the optimal radiofrequency parameters are still not well defined. This retrospective study aimed to compare the efficacy and safety of CT-guided PRF at three different voltages for the treatment of PHN patients.

Methods

This study included 109 patients with PHN involving the thoracic dermatome who were treated in the Department of Pain Management of Shengjing Hospital, China Medical University, from January 2017 to May 2019. They were divided into three groups based on the PRF voltage used: group A (45 V), group B (55 V), and group C (65 V). The PRF therapy (voltage 45, 55, and 65 V) was performed in all patients by targeting the thoracic dorsal root ganglion. After surgery, patients were followed at 3 days, 1 month, 3 months, 6 months, and 12 months. Observation at each follow-up included basic patient characteristics, visual analog scale (VAS), 36-Item Short Form Health Survey (SF-36) scores, patient satisfaction, complications, and side effects.

Results

Visual analog scale scores decreased and SF-36 scores increased for all patients in the three groups at each post-operative time point (1, 3, 6, and 12 months; all P < 0.01). Pain relief, improvement in quality of life, and overall satisfaction were more significant for patients in group C than for those in groups A and B at the 3-, 6-, and 12-month follow-ups (all P < 0.05). Patients in group B had lower VAS scores and higher overall satisfaction levels than those in group A (both P < 0.01). A small number of patients from each group (n ≤ 3) experienced mild intraoperative and post-operative complications, which bore no relationship with group assignment (all P > 0.05). At post-operative day 3, patients in group C had skin numbness affecting a larger area than patients in the other two groups (both P < 0.05), but the differences were no longer statistically significant at day 30 after the operation. All patients experienced a drop in numbness area of more than 30% after surgery.

Conclusion

Compared with PFR at 45 and 55 V, PFR at 65 V had superior efficacy in treating PNH, with a favorable safety profile.

Excessive walking exercise precipitates diabetic neuropathic foot pain: hind paw suspension treadmill exercise experiment in a rat model

The harmful effects of excessive mechanical loading on diabetic neuropathy and the reason diabetic neuropathic symptoms are common in feet are unclear. In this study, the hind paw suspension treadmill exercise model was used in rats to investigate whether mechanical loading applied to the front paws precipitates neuropathic pain, especially in diabetic conditions. Thirty-two rats were divided into six groups according to the presence of diabetes (DM) and the intensity of mechanical loading applied to the front paws: DM-Hi (high-intensity); DM-Lo (low-intensity); DM-No (non-mechanical loading); Sham-Hi; Sham-Lo; and Sham-No. DM was induced by streptozotocin injection. For high-intensity or low-intensity mechanical loading, treadmill walking exercise was conducted with or without hind paw suspension, respectively. The mechanical withdrawal threshold of the front paw decreased significantly after 8 weeks only in the DM mechanical loading groups (DM-Hi and DM-Lo), and high-intensity loading more significantly decreased the front-paw withdrawal threshold than low-intensity loading. In the DM-Hi group only, macrophage migration inhibitory factor (MIF) increased significantly, and intra-epidermal nerve fibers (IENF) in the front paws decreased significantly. In diabetic conditions, mechanical overloading such as excessive walking is likely to precipitate mechanical allodynia and damage IENF¸ which could explain why diabetic neuropathic symptoms are common in feet. This finding might be related to up-regulation of intracellular signaling cascades such as MIF, rather than inflammatory processes.

The Application of Radiofrequency Waves in Supportive Treatment of Temporomandibular Disorders

In recent years, the number of patients applying for prosthetic treatment due to temporomandibular joint disorders (TMD) has been increasing. The main methods for treating disorders are the use of occlusal splints and physiotherapeutic rehabilitation as supportive treatment. Radio waves are electromagnetic waves with radiation frequency between 3 Hz and 3 THz, used for physiotherapeutic treatment of skeletal muscle relaxation in the range of 3 to 6 MHz. The rehabilitation effect of these waves is based on diathermy by means of high-voltage quick alternating current. Aim. The aim of the study was to evaluate the influence of radiofrequency waves on the pain of the masticatory muscles in the course of TMD and the usefulness of these procedures in the supporting treatment of these disorders. Materials and Methods. Patients aged 19 to 45 years, of both sexes, reported to the Consulting Room of TMD at the Institute of Dentistry in Krakow to undertake prosthetic treatment of TMD (I a—according to RDC/TMD). Study group (SG) consists of 20 patients who had 10 supportive treatments with radiofrequency currents. In the case of application of radiation to the muscle area, the energy was 20 J to the area of the masticatory muscles, the frequency was 3 MHz, bipolar technique, the duration of the procedure was 10 minutes, and the coupling substance was a gel for ultrasound examinations. The control group (CG) consisted of 20 patients who had 10 supportive treatments with sonophoresis procedures. For the area of masticatory muscles, 0.9 W/cm² treatments were applied, the duty factor was 80%, the treatment time was 10 minutes, and the medical substance was 25% Voltaren gel. Results. Analysis of the results of the first clinical examinations (axis I) conducted in both groups shows a homogeneous clinical material and similar results. The second clinical examination revealed improved clinical parameters, but it showed a greater improvement in the SG. In the SG, the mean level of VAS was 6.25, and the extreme values were 5.9–0.14, the median was 2.15, and the standard deviation was 1.54. In the CG, the average value of VAS was 6.20 (peak of 5.2–0.7), the median was 2.4, and the standard deviation was 1.87. Summary. The search for new methods of supportive treatment of TMD is an important research direction due to the complex etiology of this disease and the lack of an explicit treatment algorithm. Conclusion. The results of our own research clearly indicate that the use of the radiofrequency waves brings pain relief and improvement of clinical parameters to a greater extent than in sonophoresis. It can be a very important new method in supportive treatment of TMD. Research needs to be continued.

Antihyperalgesic effects of Meteorin in the rat chronic constriction injury model: a replication study

Careful attention to study design, bioactive material, and drug exposure was used in replication of a single study supporting efficacy of Meteorin in experimental neuropathic pain.

Data from preclinical research have been suggested to suffer from a lack of inherent reproducibility across laboratories. The goal of our study was to replicate findings from a previous report that demonstrated positive effects of Meteorin, a novel neurotrophic factor, in a rat model of neuropathic pain induced by chronic constriction injury (CCI). Notably, 5 to 6 intermittent subcutaneous (s.c.) injections of Meteorin had been reported to produce reversal of mechanical allodynia/thermal hyperalgesia after injury, wherein maximum efficacy of Meteorin was reached slowly and outlasted the elimination of the compound from the blood by several weeks. Here, we evaluated the efficacy of Meteorin in reversing hindpaw mechanical hyperalgesia and cold allodynia in male, Sprague-Dawley rats with CCI. Nociceptive behavior was monitored before and after CCI, and after drug treatment until day 42 after injury. Systemic administration of recombinant mouse Meteorin (0.5 and 1.8 mg/kg, s.c.) at days 10, 12, 14, 17, and 19 after CCI produced a prolonged reversal of neuropathic hypersensitivity with efficacy comparable with that obtained with gabapentin (100 mg/kg, orally). Despite some protocol deviations (eg, nociceptive endpoint, animal vendor, testing laboratory, investigator, etc.) being incurred, these did not affect study outcome. By paying careful attention to key facets of study design, using bioactive material, and confirming drug exposure, the current data have replicated the salient findings of the previous study, promoting confidence in further advancement of this novel molecule as a potential therapy for neuropathic pain.

An Analysis of the Anti-Neuropathic Effects of Qi She Pill Based on Network Pharmacology

Background

Qi She Pill (QSP) is a traditional prescription for the treatment of neuropathic pain (NP) that is widely used in China. However, no network pharmacology studies of QSP in the treatment of NP have been conducted to date.

Objective

To verify the potential pharmacological effects of QSP on NP, its components were analyzed via target docking and network analysis, and network pharmacology methods were used to study the interactions of its components.

Materials and Methods

Information on pharmaceutically active compounds in QSP and gene information related to NP were obtained from public databases, and a compound-target network and protein-protein interaction network were constructed to study the mechanism of action of QSP in the treatment of NP. The mechanism of action of QSP in the treatment of NP was analyzed via Gene Ontology (GO) biological process annotation and Kyoto Gene and Genomics Encyclopedia (KEGG) pathway enrichment, and the drug-like component-target-pathway network was constructed.

Results

The compound-target network contained 60 compounds and 444 corresponding targets. The key active compounds included quercetin and beta-sitosterol. Key targets included PTGS2 and PTGS1. The protein-protein interaction network of the active ingredients of QSP in the treatment of NP featured 48 proteins, including DRD2, CHRM, β2-adrenergic receptor, HTR2A, and calcitonin gene-related peptide. In total, 53 GO entries, including 35 biological process items, 7 molecular function items, and 11 cell related items, were identified. In addition, eight relevant (KEGG) pathways were identified, including calcium, neuroactive ligand-receptor interaction, and cAMP signaling pathways.

Conclusion

Network pharmacology can help clarify the role and mechanism of QSP in the treatment of NP and provide a foundation for further research.

Efficacy of Pulsed Radiofrequency to Cervical Nerve Root for Postherpetic Neuralgia in Upper Extremity

Background

Postherpetic neuralgia (PHN) seriously affects a patient’s quality of life, and it is urgent to find a method that can effectively alleviate the PHN of the upper extremity.

Objective

To observe the Efficacy of pulsed radiofrequency (PRF) to cervical nerve root for PHN in upper extremity under CT guidance.

Study Design

Retrospective comparative study.

Setting

Shengjing Hospital of China Medical University.

Methods

Fifty patients with PHN in upper extremity were enrolled in Pain Management. Patients were randomized into two groups: cervical nerve root block (A group, n = 25) and cervical nerve root PRF (B group, n = 25). At each observation time, the general characteristics, visual analog scale (VAS), quality of life scores assessment (SF-36), the total efficacy rate, dosage of antiepileptic and narcotic analgesics, and the incidence of complications were followed up.

Results

Compared with the preoperative, the postoperative VAS decreased, the physical component summary (PCS) and the mental component summary (MCS) increased in both groups (P < 0.05). The differences between group B and group A were statistically significant after 1 month, which could be maintained for 1 year (P < 0.05). The total efficacy rate of group A and group B was 52.0% and 80.0% at 1 Year, respectively. The total efficacy rate of group B was higher than that of group A (P < 0.05). The dosage of antiepileptic and narcotic analgesics in group B decreased significantly, and the decline was significant compared with group A (P < 0.05). The incidence of complications between the two groups were similar (P > 0.05).

Conclusion

CT-guided PRF to cervical nerve root for the treatment of PHN in the upper extremity is safe and effective. PRF can replicate the location of pain, precise positioning, reduce trauma, and increased pain relief rate.

Pulsed radiofrequency inhibits expression of P2X3 receptors and alleviates neuropathic pain induced by chronic constriction injury in rats

Background:

Pulsed radiofrequency (PRF) is a minimally invasive interventional technique that provides a novel and effective treatment strategy for neuropathic pain (NP). PRF is advantageous because it does not damage nerves and avoids sensory loss after treatment. At present, animal studies have demonstrated that PRF is safe and effective for relieving the NP associated with sciatic nerve damage in rats with chronic constriction injury (CCI). However, the mechanism through which this effect occurs is unknown. An increasing body of evidence shows that the expression of the P2X ligand-gated ion channel 3 (P2X₃) receptor is closely related to NP; this study was to investigate whether the expression of this receptor is involved in NP relief due to PRF.

Methods:

A total of 36 healthy adult male Sprague-Dawley (SD) rats were randomly divided into three groups: Sham group, CCI group, and PRF group. The right sciatic nerve was ligated in CCI group and PRF group to establish a CCI model; the right sciatic nerve was separated but not ligated in Sham group. On day 14 after the operation, PRF was administered to the ligated sciatic nerve in PRF group (42°C, 45 V, 2 min). A non-live electrode was placed at the exposed sciatic nerve for the rats in Sham and CCI groups. The hindpaw withdrawal threshold (HWT) and thermal withdrawal latency (TWL) were measured at the right hindpaw at different time points before and after PRF or sham therapy. On day 28 after treatment, the dorsal root ganglion (DRG) and spinal dorsal horn of the right L4–6 were harvested from each group to determine the mRNA and protein levels of the P2X₃ receptor.

Results:

On day 28 after PRF treatment, the HWT (8.33 ± 0.67 g vs. 3.62 ± 0.48 g) and TWL (25.42 ± 1.90 s vs. 15.10 ± 1.71 s) were significantly higher in PRF group as compared to CCI group (P < 0.05). The mRNA expression of the P2X₃ receptor in the DRG in PRF group was 23.7% lower than that in CCI group (P < 0.05), in the spinal dorsal horns in PRF group was 22.7% lower than that in CCI group (P < 0.05). The protein expression of the P2X₃ receptor in the DRG in PRF group was 27.8% lower than that in CCI group (P < 0.05), in the spinal dorsal horns in PRF group was 35.6% lower than that in CCI group (P < 0.05).

Conclusion:

PRF possibly reduces NP in CCI rats by inhibiting the expression of the P2X₃ receptor in the L4–6 DRG and spinal dorsal horns.

Histological, electrophysiological and clinical effects of thermal radiofrequency therapy of the saphenous nerve and pulsed radiofrequency therapy of the sciatic nerve in dogs

OBJECTIVE

Thermal radiofrequency (TRF) of the saphenous nerve (a sensory nerve) combined with pulsed radiofrequency (PRF) of the sciatic nerve (a sensory and motor nerve) might relieve intractable stifle osteoarthritis (OA) pain in dogs. The objective was to determine if saphenous nerve TRF induces Wallerian degeneration and if sciatic nerve PRF induces degeneration or dysfunction.

STUDY DESIGN

Blinded, controlled, randomized, preclinical study.

ANIMALS

A group of six intact, female Beagle dogs aged 14-16 months.

METHODS

In each dog, one pelvic limb was assigned randomly to the control group and the other to the treatment group. Dogs were anesthetized and, using ultrasonography, radiofrequency electrodes were positioned adjacent to saphenous and sciatic nerves bilaterally; TRF and PRF were performed only in the treatment limb. Motor nerve conduction velocity (MNCV) was measured in both sciatic nerves 2 weeks later, and the dogs were euthanized. Hematoxylin and eosin-stained sections of saphenous and sciatic nerves were examined using light microscopy. Degeneration and inflammation were scored 0 (none) to 3 (severe). A one-tailed, paired Wilcoxon signed-rank test was used to test for differences in scores and MNCV between control and treatment nerves.

RESULTS

Degeneration and inflammation scores were higher in treatment saphenous nerves in 5/6 dogs [83%; 95% confidence interval (CI), 36%, 99%]; however, after Bonferroni correction only degeneration score was higher (p = 0.0313). Degeneration, inflammation or decreased MNCV were not observed in sciatic nerves (each outcome: 0/6 nerves, 0%; 95% CI, 0%, 48%). No dogs experienced postprocedural pain or neurological deficits.

CONCLUSIONS AND CLINICAL RELEVANCE

The degeneration in TRF-treated saphenous nerves appears sufficient to impair transmission. Sciatic nerve PRF did not cause degeneration with attendant motor deficits, consistent with a proposed neuromodulatory mechanism. A clinical trial is needed to confirm the combined techniques produce analgesia without motor deficits in dogs with stifle OA.

Impaired AMPK‑CGRP signaling in the central nervous system contributes to enhanced neuropathic pain in high‑fat diet‑induced obese rats, with or without nerve injury

Obesity is associated with increased sensitivity to pain, including neuropathic pain, but the precise mechanisms are not fully understood. Recent evidence has revealed that AMP-activated protein kinase (AMPK) in the central nervous system (CNS) regulates the neuropeptide calcitonin gene-related peptide (CGRP), a principal neurotransmitter of the class C nerve fiber, which serves an important role in initiating and maintaining neuropathic pain. AMPK has been demonstrated to be downregulated in the CNS in obesity. The present study hypothesized that obesity may lead to increased sensitivity to neuropathic pain by downregulating AMPK and upregulating CGRP expression levels in the CNS. Sprague-Dawley rats consuming a high-fat diet (HF) for 12 weeks developed obesity; they exhibited significantly decreased levels of phospho (p)-AMPK and increased CGRP expression levels in the spinal cord (SC) and dorsal root ganglion (DRG), respectively, compared with rats consuming a low-fat (LF) diet. HF-fed rats that underwent spared nerve injury (SNI) also exhibited lower p-AMPK and higher CGRP expression levels in the SC and DRG, compared with the corresponding LF-diet rats. The 50% paw withdrawal threshold (PWT; as measured by Von Frey testing) was significantly lower in HF-fed compared with LF-fed rats, with or without SNI. Through intrathecal treatment, the AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR) or the CGRP antagonist CGRP8-37 decreased CGRP expression levels and increased the 50% PWT; however, the AMPK inhibitor dorsomorphin augmented CGRP expression levels and further reduced the 50% PWT in HF-fed rats, but not LF-fed rats, with or without SNI. The results indicated that blocking the AMPK-CGRP pathway may enhance neuropathic pain in HF-induced obesity, with or without nerve injury. Targeting AMPK in the CNS may be a novel strategy for the prevention and treatment of obesity-associated neuropathic pain.

Advances in Pain Management: Palliative Care Applications

One of the most important goals of palliative medicine and hospice care is pain relief. Although great strides have been made in veterinary analgesia, severe pain, especially at home, is still difficult to control. Pain control in the context of palliative medicine and hospice care is far more advanced in human medicine. Many modalities used in chronically or terminally ill humans might be adapted to animals to better manage severe pain. This article discusses drugs and procedures used to control pain in humans that are relatively nascent or unavailable in veterinary medicine and deserve further attention.

CT-Guided Stellate Ganglion Pulsed Radiofrequency Stimulation for Facial and Upper Limb Postherpetic Neuralgia

Objective: Postherpetic neuralgia (PHN) is the most common complication of herpes zoster, manifesting as a persistent, spontaneous, knife-like pain or paroxysmal burning that seriously affects a patient’s quality of life. An effective treatment of PHN is lacking. This retrospective study examined the efficacy and safety of stellate ganglion (SG) pulsed radiofrequency (PRF) on facial and upper limb PHN.

Methods: Eighty-four patients with PHN on the face or upper limbs were enrolled for the study. Patients were randomly divided into two surgical groups according to the order of enrollment; one group underwent SG block (SG-B group, n = 42) and the other underwent SG pulsed radiofrequency (SG-P group, n = 42). After surgery, patients were followed at 1 week, 2 weeks, 1 month, 3 months, and 6 months. Observation at each follow-up included basic patient characteristics, visual analog scale (VAS), quality of life (QOL) using Physical Component Summary (PCS), and Mental Component Summary (MCS) to assess, total effective rate, complications and side effects.

Results: Compared with preoperative values, VAS decreased in both groups after surgery (P < 0.05). In the SG-B group, VAS increased after 1 month, while in the SG-P group, VAS gradually decreased at later follow-up time points. VAS decreased more significantly in the SG-P group after 1 month (P < 0.05). PCS and MCS increased in both groups after the operation, and the difference was significant compared with preoperative values (P < 0.05). The total effective rates of the SG-B and SG-P groups were 64.3 and 83.3%, respectively. The total effective rate of the SG-P group was higher than that of the SG-B group (P < 0.05). The incidence of complications and side effects in the SG-B group was higher than that in the SG-P group (P < 0.05).

Conclusion: SG pulsed radiofrequency treatment of facial and upper limb PHN is safe and effective. It is a treatment method worth promoting.

Efficacy and Safety of Computed Tomography-Guided Pulsed Radiofrequency Modulation of Thoracic Dorsal Root Ganglion on Herpes Zoster Neuralgia

OBJECTIVE

Pulsed radiofrequency (PRF) can relieve postherpetic neuralgia (PHN) caused by herpes zoster (HZ) infection. Nevertheless, its curative effect can vary and may be related to the duration of treatment period. The following study investigates the efficacy and safety of CT-guided PRF modulation on HZ neuralgia over different periods and different time points.

MATERIALS AND METHODS

A total of 150 patients with HZ/PHN were enrolled at the Pain Department, Shengjing Hospital of China Medical University between January 2013 and December 2016. According to the course of disease, the patients were randomly divided into group A, which included patients with acute stage (n = 50; course <1 m); group B, which included patients with subacute stage (n = 50; 1 m <course <3 m); and group C, which included patients with chronic stage (n = 50; course >3 m). The PRF therapy was performed in all patients by targeting thoracic dorsal root ganglion (DRG). The visual analogue scale (VAS), SF-36, total effective rate of treatment, and dosage of antiepileptic analgesic drugs were observed at different time points, before and after the surgery.

RESULTS

Compared to preoperative time, decreased VAS, improved SF-36, and the decreased dosage of antiepileptic analgesic drugs were observed at all time points, and in all groups after surgery (p < 0.05). In group A, pain relief lasted longer, and it further decreased over time. In addition, significantly lower VAS, higher SF-36, and lower dosage of antiepileptic analgesic drugs were found in group A compared to group B, and in group B compared to group C (all p < 0.05). Furthermore, the total effective rates in groups A, B, and C were 88, 72, and 52%, respectively.

CONCLUSIONS

CT-guided PRF targeting thoracic DRG for modulation of HZ neuralgia in different periods is safe and effective. It is recommended to perform early intervention therapy at the acute phase of HZ.