The Role of the Dorsal Root Ganglion in Cervical Radicular Pain: Diagnosis, Pathophysiology, and Rationale for Treatment

Dorsal root ganglion-pulsed neuromodulation radiofrequency treatment has significant clinical efficacy in chronic spinal-origin pain, bringing noticeable improvement in symptoms and sleep quality for patients

BACKGROUND

Chronic spinal-origin pain poses a substantial clinical challenge, prompting the investigation of novel treatment modalities. This study aims to evaluate the potential application of spinal nerve dorsal root ganglion (DRG) radiofrequency treatment in addressing chronic spinal-origin pain.

METHODS

The study encompassed patients undergoing treatment for chronic spinal-origin pain, with a particular focus on those experiencing pain localized in specific regions. Inclusion criteria comprised patients with conditions such as a herniated intervertebral disc or foraminal stenosis leading to compression of descending or exiting nerve roots, accompanied by reported radicular pain in the lower limb.

RESULTS

There was no significant difference in comparability between the two groups (p > 0.05). The clinical effective rate in the study group was significantly higher than that in the control group (p < 0.05). The VAS scores of the study group at 2 weeks and 1 month after treatment were significantly lower than those of the control group (p < 0.05). The PSQI index of the study group after treatment was significantly lower than that of the control group (p < 0.05). There was no significant difference in the incidence of complications between the two groups (p > 0.05).

CONCLUSION

Spinal nerve DRG radiofrequency treatment has significant clinical efficacy in chronic spinal-origin pain, bringing noticeable improvement in symptoms and sleep quality for patients. The occurrence of complications is relatively low, and it can be reduced through strict operational standards and preoperative and postoperative management. However, caution should be exercised in its widespread application, but it is worthy of broad clinical use.

2. Cervical radicular pain

INTRODUCTION

Cervical radicular pain is pain perceived in the upper limb, caused by irritation or compression of a cervical spine nerve, the roots of the nerve, or both.

METHODS

The literature on the diagnosis and treatment of cervical radicular pain was retrieved and summarized.

RESULTS

The diagnosis is made by combining elements from the patient's history, physical examination, and supplementary tests. The Spurling and shoulder abduction tests are the two most common examinations used to identify cervical radicular pain. MRI without contrast, CT scanning, and in some cases plain radiography can all be appropriate imaging techniques for nontraumatic cervical radiculopathy. MRI is recommended prior to interventional treatments. Exercise with or without other treatments can be beneficial. There is scant evidence for the use of paracetamol, nonsteroidal anti-inflammatory drugs, and neuropathic pain medications such as gabapentin, pregabalin, tricyclic antidepressants, and anticonvulsants for the treatment of radicular pain. Acute and subacute cervical radicular pain may respond well to epidural corticosteroid administration, preferentially using an interlaminar approach. By contrast, for chronic cervical radicular pain, the efficacy of epidural corticosteroid administration is limited. In these patients, pulsed radiofrequency treatment adjacent to the dorsal root ganglion may be considered.

CONCLUSIONS

There is currently no gold standard for the diagnosis of cervical radicular pain. There is scant evidence for the use of medication. Epidural corticosteroid injection and pulsed radiofrequency adjacent to the dorsal root ganglion may be considered. [Correction added on 12 June 2023, after first online publication: The preceding sentence was corrected.].

The involvement of immune system in intervertebral disc herniation and degeneration

Intervertebral disc (IVD) herniation and degeneration contributes significantly to low back pain (LBP), of which the molecular pathogenesis is not fully understood. Disc herniation may cause LBP and radicular pain, but not all LBP patients have disc herniation. Degenerated discs could be the source of pain, but not all degenerated discs are symptomatic. We previously found that disc degeneration and herniation accompanied by inflammation. We further found that anti-inflammatory molecules blocked immune responses, alleviated IVD degeneration and pain. Based on our recent findings and the work of others, we hypothesize that immune system may play a prominent role in the production of disc herniation or disc degeneration associated pain. While the nucleus pulposus (NP) is an immune-privileged organ, the damage of the physical barrier between NP and systemic circulation, or the innervation and vascularization of the degenerated NP, on one hand exposes NP as a foreign antigen to immune system, and on the other hand presents compression on the nerve root or dorsal root ganglion (DRG), which both elicit immune responses induced by immune cells and their mediators. The inflammation can remain for a long time at remote distance, with various types of cytokines and immune cells involved in this pain-inducing process. In this review, we aim to revisit the autoimmunity of the NP, immune cell infiltration after break of physical barrier, the inflammatory activities in the DRG and the generation of pain. We also summarize the involvement of immune system, including immune cells and cytokines, in degenerated or herniated IVDs and affected DRG.

Full Endoscopic Key Hole Technique for Cervical Foraminal Stenosis: Is Mere Dorsal Decompression Enough?

OBJECTIVE

To study whether and when mere dorsal decompression is enough in the full endoscopic key hole technique for foraminal stenosis.

METHODS

We retrospectively reviewed a total of 22 patients with cervical foraminal stenosis who underwent full endoscopic key hole mere dorsal decompression in our institute from October 2016 to October 2017.

RESULTS

Preoperative neck disability index, neck visual analog scale score, and arm visual analog scale score were 25.8 ± 0.8, 4.9 ± 0.6, and 7.5 ± 0.5 in the group. Immediate postoperative scores were 6.9 ± 0.9, 1.3 ± 0.9, and 1.4 ± 0.5. Follow-up scores at 3 months (7.0 ± 0.9, 1.9 ± 0.6, and 2.7 ± 0.9), 6 months (7.3 ± 0.9, 2.1 ± 0.9, and 1.9 ± 0.5), and 12 months (7.6 ± 0.5, 2.5 ± 0.8, and 2.1 ± 0.7). The symptoms had improved significantly (P < 0.05). According to the Macnab criteria, 15 patients reported excellent results, 2 reported good results, and 2 reported fair results at the 12-month follow-up.

CONCLUSIONS

Stenosis is mainly caused by dorsal structures; mere dorsal decompression is enough. In both cases, the ventral and dorsal structures contributed to the stenosis. When there is no herniated soft fragment contributing to the stenosis, ventral decompression is not always necessary. If intraoperative exploration detects less tension formed by the ventral abnormal structures, mere dorsal decompression is enough to settle the symptoms.

Evaluation of Clinical and Histologic Effects of High-Dose Radiosurgery on Rat Dorsal Root Ganglion

BACKGROUND

Stereotactic radiosurgery (SRS) is an effective technique to create lesions of the trigeminal nerve to treat refractory trigeminal neuralgia. In the lumbar spine, the dorsal root ganglion (DRG) contains the body of the sensory neurons responsible for pain sensitivity. Neuromodulation of the DRG might therefore improve chronic peripheral pain. This study was performed to determine the feasibility, clinical, and histologic effects of delivering high-dose SRS targeted to the lumbar DRG in a rat model.

METHODS

Four Sprague Dawley male rats underwent 80 Gy maximum-dose single-fraction SRS to the left L5 and L6 DRG using the Leksell Gamma Knife Icon (Elekta, Atlanta, Georgia, USA). The right L5 and L6 DRGs served as controls. The animals were evaluated for motor and sensory deficits every 2 weeks and were sacrificed at 3 and 6 months after SRS. Common histologic techniques were used to assess for fibrosis and demyelination at the target levels.

RESULTS

No detectable motor or sensory deficits were seen in any animal. Histologic changes including fibrosis and loss of myelin were noted to the left L5 and L6 DRGs, but not the right side control DRGs. Fibrotic changes within the vertebral body were also evident on the treated sides of the vertebral bodies.

CONCLUSIONS

We were able to detect a demyelinating response from SRS delivered to the DRG in rats. Because such changes mimic those seen after trigeminal SRS in experimental animals, we hypothesize that radiosurgery may be a potential option in chronic spinal radicular pain amenable to neuromodulation.

High field structural MRI in the management of degenerative cervical myelopathy

Introduction: This is a narrative overview of the pathophysiology, investigation and management of Degenerative Cervical Myelopathy (DCM). This review article also takes a look ahead to the impact high resolution MRI may have on treatment.Background: DCM is the most common cause of spinal dysfunction and yet it remains poorly understood. It is becoming increasingly common in our ageing population. Disc and facet joint abnormalities, osteophytes, spondylothisthesis and ligamentous hypertrophy all act together to produce spinal canal and neuronal foramina stenosis which in turn causes neural compromise. Its impact on the quality of life of this patient group and the wider economy is vast. Some patients with overt cord compression and MRI signal change in their cervical cord may only have subtle clinical signs whilst others with less striking imaging may be profoundly myelopathic. Who to operate on and when remains a neurosurgical dilemma in this group of patients.Methods: A number of articles with a broad variation in methodology were reviewed and referenced during the production of this paper.Results: This paper is a narrative review. The results presented in all the referenced articles were considered.Conclusion: The process of developing new imaging techniques will give a greater understanding of the causes of the symptoms of DCM and in a wider context facilitate further surgical and medical strategies that are more cost effective and beneficial to patients. The advent of 7T MRI or further optimisation of safer 3T MRI sequences may soon provide this opportunity and the diagnostic gap in spinal cord imaging can begin to close.

A Randomized Comparative Study of Pulsed Radiofrequency Treatment With or Without Selective Nerve Root Block for Chronic Cervical Radicular Pain

BACKGROUND

We demonstrated a combination of pulsed radiofrequency (PRF) and cervical nerve root block (CNRB) via a posterior approach was superior to a transforaminal epidural steroid injection through the anterolateral approach for cervical radicular pain in a previous study. This randomized trial was conducted to determine the comparative efficacy between CNRB, PRF, and CNRB + PRF for cervical radicular pain.

METHODS

A prospective and randomized design was used in this study. Sixty-two patients were randomized into three parallel groups: CNRB, PRF, or CNRB + PRF. Numeric Rating Scale (NRS) was used to measure pain intensity, and global perceived effect (GPE) was scored by the patient on a 7-point scale, ranging from much worse (-3), no change (0), to total improvement (+3). The outcomes were evaluated at 1 week, 1 month, 3 months, and 6 months. Side effects and complications were noted.

RESULTS

The NRS was significantly reduced in all three groups 1 week after the treatments (P < 0.001), and the rates of positive GPE (+2 or +3) were not significantly different between the three groups. At 1, 3, and 6 months of follow-ups, the combined therapy achieved significantly lower NRS and higher GPE compared to CNRB or PRF alone group (P < 0.001). There were no significant differences between the CNRB and PRF groups (P > 0.05). No serious complications were observed in any of the patients.

CONCLUSIONS

Combining CNRB and PRF appeared to be a safe and efficacious technique for cervical radicular pain. The combination therapy yielded better outcomes than either CNRB or PRF alone.

Upregulation of Ih expressed in IB4-negative Aδ nociceptive DRG neurons contributes to mechanical hypersensitivity associated with cervical radiculopathic pain

Cervical radiculopathy represents aberrant mechanical hypersensitivity. Primary sensory neuron’s ability to sense mechanical force forms mechanotransduction. However, whether this property undergoes activity-dependent plastic changes and underlies mechanical hypersensitivity associated with cervical radiculopathic pain (CRP) is not clear. Here we show a new CRP model producing stable mechanical compression of dorsal root ganglion (DRG), which induces dramatic behavioral mechanical hypersensitivity. Amongst nociceptive DRG neurons, a mechanically sensitive neuron, isolectin B4 negative Aδ-type (IB4⁻ Aδ) DRG neuron displays spontaneous activity with hyperexcitability after chronic compression of cervical DRGs. Focal mechanical stimulation on somata of IB4^- Aδ neuron induces abnormal hypersensitivity. Upregulated HCN1 and HCN3 channels and increased I_h current on this subset of primary nociceptors underlies the spontaneous activity together with neuronal mechanical hypersensitivity, which further contributes to the behavioral mechanical hypersensitivity associated with CRP. This study sheds new light on the functional plasticity of a specific subset of nociceptive DRG neurons to mechanical stimulation and reveals a novel mechanism that could underlie the mechanical hypersensitivity associated with cervical radiculopathy.

A posterior approach to cervical nerve root block and pulsed radiofrequency treatment for cervical radicular pain: a retrospective study

BACKGROUND

Catastrophic complications have been reported for selective cervical nerve root block (SCNRB) or pulsed radiofrequency (PRF) via an anterolateral transforaminal approach. A posterior approach to these procedures under computed tomography guidance has been reported. Here, we report the clinical outcomes of 42 patients with chronic cervical radicular pain (CCRP) treated with a combination of SCNRB and PRF through a posterior approach under fluoroscopy guidance.

METHODS

We retrospectively reviewed the clinical outcomes of 42 consecutive patients with CCRP who received a combination of SCNRB and PRF through a posterior approach under fluoroscopy guidance. The thresholds of electrical stimulation and imaging of the nerve roots after contrast injection were used to evaluate the accuracy of needle placement. The numeric rating scale was used to measure the pain and numbness levels as primary clinical outcomes, which were evaluate in scheduled follow-up visits of up to 3 months.

RESULTS

A total of 53 procedures were performed on 42 patients at the levels of C5-C8. All patients reported concordant paresthesia in response to electrical stimulation. The average sensory and motor thresholds of stimulation were 0.28 ± 0.14 and 0.36 ± 0.14 V, respectively. Injection of nonionic contrast resulted in excellent spread along the target nerve root in large majority of the procedures. The numeric rating scale scores for both pain and numbness improved significantly at 1 day, 1 week, and 1 and 3 months after the treatment. No serious adverse effects were observed in any of the patients.

CONCLUSIONS

The posterior approach to combined SCNRB and PRF under fluoroscopy guidance appears to be safe and efficacious in the management of CCRP.

Delayed Pneumocephalus Following Fluoroscopy Guided Cervical Interlaminar Epidural Steroid Injection: A Rare Complication and Anatomical Considerations

Cervical epidural steroid injection is indicated for radicular symptoms with or without axial neck pain. Complications are rare but can be serious. Here, we report the case of a 54-year-old man with cervical radicular pain who was treated with cervical epidural steroid injection. Injection was administered twice under fluoroscopic guidance with the loss-of-resistance technique using air to confirm the epidural space. After the second procedure, the patient complained of severe persistent headache and was diagnosed with pneumocephalus on brain computed tomography. The patient returned home without any neurological complication, after a few days of conservative treatment. Though, a fluoroscopic guidance cervical epidural injection is also known to diminish the risk of complications. Physicians should always keep in mind that it does not guarantee safety, particularly in the cervical region, related to its anatomical considerations.

Cervical foraminal steroid injections under CT guidance: retrospective study of in situ contrast aspects in a serial of 248 cases

OBJECTIVES

To describe all the CT findings after in situ contrast injection just before steroid injection and to recognize the abnormal aspects associated with intravascular contamination.

MATERIAL AND METHODS

We retrospectively evaluated 248 cervical transforaminal steroid injections done at the university hospital in Dijon, France, in 2008-2012, to treat cervicobrachial neuralgia inadequately improved by optimal medical treatment for at least 3 weeks. Features describing the opacification patterns were recorded.

RESULTS

Five main nonvascular opacification patterns were identified: clumps of contrast agent outside the foramen (16 %), a crab claw pattern surrounding the ganglion (13 %), a "French" circumflex accent pattern (15 %), reflux along the needle (7 %), and facet joint capsule opacification (22 %). Concerning the situations requiring a change in needle position, intravenous injection occurred in 26 % of the patients, with a crab claw pattern in half the cases and a clump pattern in half the cases. Intraarteriolar injection was noted in two patients.

CONCLUSION

CT after in situ contrast injection ensures proper needle positioning outside the blood vessels before steroid injection. Penetration of the needle tip into a vein is very common, whereas arteriolar puncture is extremely rare.

Computed tomography-guided cervical selective transforaminal epidural block for a patient with bilateral anatomical variations of vertebral artery -a case report-

A 56-year-old woman complained of radiating pain to the left arm. She was diagnosed with left-sided foraminal stenosis at the C5-6 level. The neurosurgeon requested a left C6 cervical selective transforaminal epidural block (CSTE). Cervical MRI showed a left-sided large tortuous vertebral artery (VA) at the C5-6 level. Before performing CSTE, a CT angiogram was carried out and showed bilateral tortuous VAs. To minimize adverse events, CSTE was performed with non-particulated steroids and under CT guidance. Following the procedure, the patient's symptoms were relieved completely. Although complication rates of CSTE are generally low, if it occurs, disastrous situation could be. Additionally, if the patient has anatomical variations, the possibility of a complication occurring is greatly increased. It is therefore important to determine whether the patient has any anatomical variations of the VA before performing procedures such as CSTE, and to ensure that needle placement is correct during the procedure and an appropriate drug, such as a non-particulated steroid, is selected.

Pulsed radiofrequency treatment adjacent to the lumbar dorsal root ganglion for the management of lumbosacral radicular syndrome: a clinical audit

INTRODUCTION

Lumbosacral radicular syndrome (LRS) is probably the most frequent neuropathic pain syndrome. Three months to 1 year after onset, 30% of the patients still experience ongoing pain. The management of those patients is complex, and treatment success rates are rather low. The beneficial effect of pulsed radiofrequency (PRF) therapy has been described for the treatment of LRS in case reports and in retrospective and prospective studies. Up until now, no neurological complications have been reported after PRF treatment. The current clinical audit has been performed to assess the amount of pain relief after a single PRF treatment.

METHODS

Sixty consecutive patients who received a PRF treatment adjacent to the lumbar dorsal root ganglion for the management of LRS in the period 2007-2009 were included. The main study objective was to measure the reduction of pain after the pulsed radiofrequency treatment by using the global perceived effect. The primary end point was defined as at least 50% pain relief for a period of 2 months or longer.

RESULTS

The primary end point was achieved in 29.5% of all the PRF interventions. After 6 months, 50% pain relief was still present in 22.9% of the cases and after 12 months in 13.1% of the cases. The need for pain medication was significantly lower after pulsed radiofrequency treatment in the success group compared with the nonsuccess group.

CONCLUSIONS

PRF treatment can be considered for the management of LRS patients. These results need to be confirmed in a randomized clinical trial.

Application of pulsed radiofrequency currents to rat dorsal root ganglia modulates nerve injury-induced tactile allodynia

BACKGROUND

Application of pulsed radiofrequency (PRF) currents to the dorsal root ganglia (DRG) has been reported to produce relief from certain pain states without causing thermal ablation. In this study, we examined the direct correlation between PRF application to DRG associated with spinal nerve injury and reversal of injury-induced behavioral hypersensitivity in a rat neuropathic pain model.

METHODS

Neuropathic lesioning was performed via left L5 spinal nerve ligation on male adult Sprague-Dawley rats. Once the injured rats had developed tactile allodynia, one group was then assigned to PRF treatment of the L5 DRG and another group was assigned to the sham treatment to the DRG. Behavioral testing was performed on both the control and treated paws using the von Frey filament test before the surgery and at indicated days. The resulting data were analyzed using a linear mixed model to assess the overall difference between the treatment groups and the overall difference among the study days. Cohen's d statistic was computed from paired difference-from-baseline scores for each of the 14 study days after treatment and these measures of effect size were then used to descriptively compare the recovery patterns over time for each study group.

RESULTS

Spinal nerve injury resulted in the development of behavioral hypersensitivity to von Frey filament stimulation (allodynia) in the hindpaw of the left (injury) side. Mixed linear modeling showed a significant difference between the treatment groups (P = 0.0079) and a significant change of paw withdrawal threshold means over time (P = 0.0006) for all 12 animals. Evaluation of Cohen's d (effect size) revealed that the PRF-treated animals exhibited better recovery and recorded larger effect sizes than the sham-treated animals on 10 of the 14 post-PRF treatment days and exhibited moderate-to-strong effects posttreatment at days 8 to 10 and at and beyond day 32.

CONCLUSIONS

Findings from this study support that PRF of the DRG causes reversal of nerve injury (spinal nerve ligation)-induced tactile allodynia in rats. This allodynia reversal indicates that nonablative PRF acting via modulation of the DRG can speed recovery in nerve injury-induced pain.

Axonal thermosensitivity and mechanosensitivity of cutaneous afferent neurons

We hypothesized that cutaneous afferent myelinated fibers (A-fibers) and afferent unmyelinated fibers (C-fibers) respond to the same natural stimuli applied to their axons as to their terminals in the skin. In anesthetized rats, activity was recorded from afferent axons in strands isolated proximally from the sural nerve. Mechanical, cold or heat stimuli were applied to the skin or along a 15-mm length of the distal sural nerve. One-hundred and eighteen A-fibers and 109 C-fibers were characterized by their conduction velocity and/or shape of their action potentials, and by their responses to natural stimulation of the skin. Then, these fibers were tested for their responses to the same stimuli applied to the nerve. In some cases, the nerve was crushed distally after the nerve fibers had been characterized by their responses to physiological stimulation of the skin, and the responses to stimuli applied to the nerve proximal to the lesion were tested again. Almost all non-nociceptive cold-sensitive (type 1) C-fibers (97%) could be activated by cold stimuli applied to the nerve. Of nociceptive cold-sensitive (type 2) C-fibers, 39% were activated by cold stimuli applied to the nerve. Furthermore, 34% of heat-sensitive C-fibers could be activated by heating the nerve. In contrast, only 2-4% of mechanosensitive A-fibers and C-fibers responded to mechanical stimuli applied to the nerve. In conclusion, cold and heat sensitivity of cutaneous afferent neurons is not restricted to their terminals in the skin, but often extends along the axons in the nerve. Mechanosensitivity is restricted to the afferent endings in the skin.

4. Cervical radicular pain

Cervical radicular pain is defined as pain perceived as arising in the arm caused by irritation of a cervical spinal nerve or its roots. Approximately 1 person in 1,000 suffers from cervical radicular pain. In the absence of a gold standard, the diagnosis is based on a combination of history, clinical examination, and (potentially) complementary examination. Medical imaging may show abnormalities, but those findings may not correlate with the patient's pain. Electrophysiologic testing may be requested when nerve damage is suspected but will not provide quantitative/qualitative information about the pain. The presumed causative level may be confirmed by means of selective diagnostic blocks. Conservative treatment typically consists of medication and physical therapy. There are no studies assessing the effectiveness of different types of medication specifically in patients suffering cervical radicular pain. Cochrane reviews did not find sufficient proof of efficacy for either education or cervical traction. When conservative treatment fails, interventional treatment may be considered. For subacute cervical radicular pain, the available evidence on efficacy and safety supports a recommendation (2B+) of interlaminar cervical epidural corticosteroid administration. A recent negative randomized controlled trial of transforaminal cervical epidural corticosteroid administration, coupled with an increasing number of reports of serious adverse events, warrants a negative recommendation (2B-). Pulsed radiofrequency treatment adjacent to the cervical dorsal root ganglion is a recommended treatment for chronic cervical radicular pain (1B+). When its effect is insufficient or of short duration, conventional radiofrequency treatment is recommended (2B+). In selected patients with cervical radicular pain, refractory to other treatment options, spinal cord stimulation may be considered. This treatment should be performed in specialized centers, preferentially study related.