Deep Brain Stimulation Improves the Symptoms and Sensory Signs of Persistent Central Neuropathic Pain from Spinal Cord Injury: A Case Report

Comparative outcomes of microsurgical dorsal root entry zone lesioning (DREZotomy) for intractable neuropathic pain in spinal cord and cauda equina injuries

Treatment of neuropathic pain in patients with spinal cord injury (SCI) and cauda equina injury (CEI) remains challenging. Dorsal root entry zone lesioning (DREZL) or DREZotomy is a viable surgical option for refractory cases. This study aimed to compare DREZL surgical outcomes between patients with SCI and those with CEI and to identify predictors of postoperative pain relief. We retrospectively analyzed 12 patients (6 with SCI and 6 with CEI) with intractable neuropathic pain who underwent DREZL. The data collected were demographic characteristics, pain distribution, and outcomes assessed by numeric pain rating scores. Variables and percentages of pain improvement at 1 year and long-term were statistically compared between the SCI and CEI groups. The demographic characteristics and percentage of patients who experienced pain improvement at 1 year postoperatively did not differ between the groups. Compared with the SCI group, the CEI group presented significantly better long-term pain reduction (p = 0.020) and favorable operative outcomes (p = 0.015). Patients with border zone pain had significantly better long-term pain relief and outcomes than did those with diffuse pain (p = 0.008 and p = 0.010, respectively). Recurrent pain after DREZL occurred in the SCI group but not in the CEI group. DREZL provided superior pain relief in patients with CEI. The presence of border zone pain predicted favorable outcomes. CEI patients or SCI patients with border zone pain are good surgical candidates for DREZL, whereas SCI patients with below-injury diffuse pain are poor candidates.

The mechanisms of electrical neuromodulation

The central and peripheral nervous systems are specialized to conduct electrical currents that underlie behaviour. When this multidimensional electrical system is disrupted by degeneration, damage, or disuse, externally applied electrical currents may act to modulate neural structures and provide therapeutic benefit. The administration of electrical stimulation can exert precise and multi-faceted effects at cellular, circuit and systems levels to restore or enhance the functionality of the central nervous system by providing an access route to target specific cells, fibres of passage, neurotransmitter systems, and/or afferent/efferent communication to enable positive changes in behaviour. Here we examine the neural mechanisms that are thought to underlie the therapeutic effects seen with current neuromodulation technologies. To gain further insights into the mechanisms associated with electrical stimulation, we summarize recent findings from genetic dissection studies conducted in animal models. KEY POINTS: Electricity is everywhere around us and is essential for how our nerves communicate within our bodies. When nerves are damaged or not working properly, using exogenous electricity can help improve their function at distinct levels - inside individual cells, within neural circuits, and across entire systems. This method can be tailored to target specific types of cells, nerve fibres, neurotransmitters and communication pathways, offering significant therapeutic potential. This overview explains how exogenous electricity affects nerve function and its potential benefits, based on research in animal studies. Understanding these effects is important because electrical neuromodulation plays a key role in medical treatments for neurological conditions.

Periaqueductal gray connectivity in spinal cord injury-induced neuropathic pain

BACKGROUND AND PURPOSE

Neuropathic pain (NP) is a debilitating condition following spinal cord injury (SCI). The role of periaqueductal gray (PAG) in NP development following SCI remains underexplored. Using resting-state functional MRI (rsfMRI), our study aimed to demonstrate the alterations in functional connectivity (FC) of PAG in NP following SCI.

METHODS

Ten SCI patients (SCI + NP, n = 7, and SCI - NP, n = 3), alongside 10 healthy controls (HCs), were enrolled. rsfMRI was conducted followed by seed-to-voxel analysis using PAG as the seed region and then group-based analysis comprising three groups (SCI + NP, SCI - NP, and HC). Age and gender were considered as confounding variables.

RESULTS

Compared to HCs, SCI + NP demonstrated decreased FC between PAG and right insula, right frontal orbital cortex, right pallidum, dorsal raphe nucleus (DRN), red nuclei (RN), substantia nigra (SN), and ventral posterolateral (VPL) thalamic nuclei. Compared to SCI - NP, SCI + NP demonstrated increased FC between PAG and posterior cingulate cortex (PCC), hippocampus, cerebellar vermis lobules IV and V, and thalamic structures (posterior and lateral pulvinar, the mediodorsal nuclei, and the ventral lateral nuclei). Additionally, decreased FC between the PAG and VPL, geniculate bodies, intralaminar nuclei of thalamus, DRN, RN, SN, and prefrontal cortex was observed in this comparison.

CONCLUSIONS

Altered FC between PAG and right anterior insula, VPL, DRN, RN, SN, cerebellar vermis lobules IV and V, frontal cortex, and PCC was associated with NP sequelae of SCI. Additionally, SCI was independently associated with decreased FC between PAG and right posterior insula, cerebellar lobules IV and V, and cerebellar vermis lobules III, IV, and V.

Brain region changes following a spinal cord injury

Brain-related complications are common in clinical practice after spinal cord injury (SCI); however, the molecular mechanisms of these complications are still unclear. Here, we reviewed the changes in the brain regions caused by SCI from three perspectives: imaging, molecular analysis, and electrophysiology. Imaging studies revealed abnormal functional connectivity, gray matter volume atrophy, and metabolic abnormalities in brain regions after SCI, leading to changes in the structure and function of brain regions. At the molecular level, chemokines, inflammatory factors, and damage-associated molecular patterns produced in the injured area were retrogradely transmitted through the corticospinal tract, cerebrospinal fluid, or blood circulation to the specific brain area to cause pathologic changes. Electrophysiologic recordings also suggested abnormal changes in brain electrical activity after SCI. Transcranial magnetic stimulation, transcranial direct current stimulation, and deep brain stimulation alleviated pain and improved motor function in patients with SCI; therefore, transcranial therapy may be a new strategy for the treatment of patients with SCI.

Application of Vagus Nerve Stimulation in Spinal Cord Injury Rehabilitation

Spinal cord injury (SCI) is a prevalent devastating condition causing significant morbidity and mortality, especially in developing countries. The pathophysiology of SCI involves ischemia, neuroinflammation, cell death, and scar formation. Due to the lack of definitive therapy for SCI, interventions mainly focus on rehabilitation to reduce deterioration and improve the patient's quality of life. Currently, rehabilitative exercises and neuromodulation methods such as functional electrical stimulation, epidural electrical stimulation, and transcutaneous electrical nerve stimulation are being tested in patients with SCI. Other spinal stimulation techniques are being developed and tested in animal models. However, often these methods require complex surgical procedures and solely focus on motor function. Vagus nerve stimulation (VNS) is currently used in patients with epilepsy, depression, and migraine and is being investigated for its application in other disorders. In animal models of SCI, VNS significantly improved locomotor function by ameliorating inflammation and improving plasticity, suggesting its use in human subjects. SCI patients also suffer from nonmotor complications, including pain, gastrointestinal dysfunction, cardiovascular disorders, and chronic conditions such as obesity and diabetes. VNS has shown promising results in alleviating these conditions in non-SCI patients, which makes it a possible therapeutic option in SCI patients.

Identification of Deep Brain Stimulation Targets for Neuropathic Pain After Spinal Cord Injury Using Localized Increases in White Matter Fiber Cross Section

OBJECTIVES

The spinal cord injury (SCI) patient population is overwhelmingly affected by neuropathic pain (NP), a secondary condition for which therapeutic options are limited and have a low degree of efficacy. The objective of this study was to identify novel deep brain stimulation (DBS) targets that may theoretically benefit those with NP in the SCI patient population. We hypothesize that localized changes in white matter identified in SCI subjects with NP compared to those without NP could be used to develop an evidence-based approach to DBS target identification.

MATERIALS AND METHODS

To classify localized neurostructural changes associated with NP in the SCI population, we compared white matter fiber density (FD) and cross section (FC) between SCI subjects with NP (n = 17) and SCI subjects without NP (n = 15) using diffusion-weighted magnetic resonance imaging (MRI). We then identified theoretical target locations for DBS using fiber bundles connected to significantly altered regions of white matter. Finally, we used computational models of DBS to determine if our theoretical target locations could be used to feasibly activate our fiber bundles of interest.

RESULTS

We identified significant increases in FC in the splenium of the corpus callosum in pain subjects when compared to controls. We then isolated five fiber bundles that were directly connected to the affected region of white matter. Our models were able to predict that our fiber bundles of interest can be feasibly activated with DBS at reasonable stimulation amplitudes and with clinically relevant implantation approaches.

CONCLUSIONS

Altogether, we identified neuroarchitectural changes associated with NP in the SCI cohort and implemented a novel evidence-driven target selection approach for DBS to guide future research in neuromodulation treatment of NP after SCI.

The role of endogenous opioid neuropeptides in neurostimulation-driven analgesia

Due to the prevalence of chronic pain worldwide, there is an urgent need to improve pain management strategies. While opioid drugs have long been used to treat chronic pain, their use is severely limited by adverse effects and abuse liability. Neurostimulation techniques have emerged as a promising option for chronic pain that is refractory to other treatments. While different neurostimulation strategies have been applied to many neural structures implicated in pain processing, there is variability in efficacy between patients, underscoring the need to optimize neurostimulation techniques for use in pain management. This optimization requires a deeper understanding of the mechanisms underlying neurostimulation-induced pain relief. Here, we discuss the most commonly used neurostimulation techniques for treating chronic pain. We present evidence that neurostimulation-induced analgesia is in part driven by the release of endogenous opioids and that this endogenous opioid release is a common endpoint between different methods of neurostimulation. Finally, we introduce technological and clinical innovations that are being explored to optimize neurostimulation techniques for the treatment of pain, including multidisciplinary efforts between neuroscience research and clinical treatment that may refine the efficacy of neurostimulation based on its underlying mechanisms.

Microstructural plasticity in nociceptive pathways after spinal cord injury

OBJECTIVE

To track the interplay between (micro-) structural changes along the trajectories of nociceptive pathways and its relation to the presence and intensity of neuropathic pain (NP) after spinal cord injury (SCI).

METHODS

A quantitative neuroimaging approach employing a multiparametric mapping protocol was used, providing indirect measures of myelination (via contrasts such as magnetisation transfer (MT) saturation, longitudinal relaxation (R1)) and iron content (via effective transverse relaxation rate (R2*)) was used to track microstructural changes within nociceptive pathways. In order to characterise concurrent changes along the entire neuroaxis, a combined brain and spinal cord template embedded in the statistical parametric mapping framework was used. Multivariate source-based morphometry was performed to identify naturally grouped patterns of structural variation between individuals with and without NP after SCI.

RESULTS

In individuals with NP, lower R1 and MT values are evident in the primary motor cortex and dorsolateral prefrontal cortex, while increases in R2* are evident in the cervical cord, periaqueductal grey (PAG), thalamus and anterior cingulate cortex when compared with pain-free individuals. Lower R1 values in the PAG and greater R2* values in the cervical cord are associated with NP intensity.

CONCLUSIONS

The degree of microstructural changes across ascending and descending nociceptive pathways is critically implicated in the maintenance of NP. Tracking maladaptive plasticity unravels the intimate relationships between neurodegenerative and compensatory processes in NP states and may facilitate patient monitoring during therapeutic trials related to pain and neuroregeneration.

Neuromodulation for Medically Refractory Neuropathic Pain: Spinal Cord Stimulation, Deep Brain Stimulation, Motor Cortex Stimulation, and Posterior Insula Stimulation

BACKGROUND

The treatment of neuropathic pain (NP) continues to be controversial as well as an economic health issue and a challenge to health care. Neurosurgery can offer different methods of neuromodulation that may improve patients' condition, including deep brain stimulation (DBS), motor cortex stimulation (MCS), spinal cord stimulation (SCS), and posterior insula stimulation (PIS). There is no consensus of opinion as to the final effects of these procedures, which stimulation parameters to select, the correct timing, or how to select the patients who will best benefit from these procedures.

OBJECTIVE

To review the evidence available regarding these 4 procedures and the management of NP.

METHODS

We conducted a PubMed, Embase, and Cochrane Library database search from 1990 to 2020. The strategy of the search concentrated on the following keywords: "neuropathic pain," "chronic pain," "deep brain stimulation," "motor cortex stimulation," "spinal cord stimulation," "insula stimulation," and "neuromodulation." Studies that provided data regarding the immediate and long-term effectiveness of the procedure, anatomic stimulation target, percentage of pain control, and cause of the NP were included.

RESULTS

The most frequent causes of NP were phantom limb pain and central poststroke pain in the MCS group; central poststroke pain, phantom limb pain, and spinal cord injury (SCI) in the DBS group; and complex regional pain syndrome and failed back surgery syndrome in the SCS group. Pain improvement varied between 35% and 80% in the MCS group and 50% and 60% in the DBS group. In the SCS group, successful rates varied between 38% and 89%.

CONCLUSIONS

This systematic review highlights the literature supporting SCS, DBS, MCS, and PIS methods for the treatment of NP. We found consistent evidence supporting MCS, DBS, and SCS as possible treatments for NP; however, we were not able to define which procedure should be indicated for each cause. Furthermore, we did not find enough evidence to justify the routine use of PIS. We conclude that unanswered points need to be discussed in this controversial field and emphasize that new research must be developed to treat patients with NP, to improve their quality of life.

Effects of botulinum toxin A on endometriosis‑associated pain and its related mechanism

Endometriosis (EMS) is a common disease in women aged 25–45 years, and pain is the main clinical symptom. The primary clinical treatment is surgical excision and drug therapy targeting the ectopic lesions, but these have not been very effective. Botulinum neurotoxin serotype A (BTX-A) has been reported to be useful in the treatment of pain in a variety of diseases. Based on this, the aim of the present study was to explore the therapeutic effect and mechanism of BTX-A on EMS. A model of nerve injury induced by oxygen glucose deprivation (OGD) was constructed in PC12 cells and EMS mice. Model cells and mice were treated with different concentrations of BTX-A to observe the changes in pain behavior, to detect cell viability and the secretion of norepinephrine (NE) and methionine enkephalin (M-EK) in cells and the spinal cord, and to evaluate the expression of apoptosis-related molecules in spinal cord nerves. The results revealed that BTX-A significantly reduced the amount of writhing in model mice, enhanced the activity of PC12 OGD cells, increased the secretion of NE and M-EK in model cells and the spinal cord of mice, and decreased the apoptosis of neural cells in the spinal cord of the model mice. Therefore, it was hypothesized that BTX-A may alleviate the pain induced by EMS by increasing the secretion of analgesic substances and promoting the repair of nerve injury. The present study provided a theoretical basis for the treatment of pain induced by EMS.

Cellular Changes in Injured Rat Spinal Cord Following Electrical Brainstem Stimulation

Spinal cord injury (SCI) is a major cause of disability and pain, but little progress has been made in its clinical management. Low-frequency electrical stimulation (LFS) of various anti-nociceptive targets improves outcomes after SCI, including motor recovery and mechanical allodynia. However, the mechanisms of these beneficial effects are incompletely delineated and probably multiple. Our aim was to explore near-term effects of LFS in the hindbrain's nucleus raphe magnus (NRM) on cellular proliferation in a rat SCI model. Starting 24 h after incomplete contusional SCI at C5, intermittent LFS at 8 Hz was delivered wirelessly to NRM. Controls were given inactive stimulators. At 48 h, 5-bromodeoxyuridine (BrdU) was administered and, at 72 h, spinal cords were extracted and immunostained for various immune and neuroglial progenitor markers and BrdU at the level of the lesion and proximally and distally. LFS altered cell marker counts predominantly at the dorsal injury site. BrdU cell counts were decreased. Individually and in combination with BrdU, there were reductions in CD68 (monocytes) and Sox2 (immature neural precursors) and increases in Blbp (radial glia) expression. CD68-positive cells showed increased co-staining with iNOS. No differences in the expression of GFAP (glia) and NG2 (oligodendrocytes) or in GFAP cell morphology were found. In conclusion, our work shows that LFS of NRM in subacute SCI influences the proliferation of cell types implicated in inflammation and repair, thus providing mechanistic insight into deep brain stimulation as a neuromodulatory treatment for this devastating pathology.

The neural response to deep brain stimulation of the anterior nucleus of the thalamus: A MEMRI and c-Fos study

BACKGROUND

Deep brain stimulation (DBS) refers to the delivery of electric current to specific deep brain structures through implanted electrodes. Recently approved for use in United States, DBS to the anterior nucleus of thalamus (ANT) is a safe and effective alternative treatment for medically refractory seizures. Despite the anti-seizure effects of ANT DBS, preclinical and clinical studies have failed to demonstrate it actions at a whole brain level.

OBJECTIVE

Here, we used a magnetic resonance imaging (MRI)-based approach in healthy adult rats to investigate the effects of ANT DBS through the circuit of Papez, which has central role in the generation and propagation of limbic seizures, in temporal lobe epilepsy (TLE).

METHODS

After ANT electrode implantation and recovery, ANT DBS and SHAM (sham animals had electrodes implanted but were not stimulated) rats received one single injection of the contrast enhancer, manganese chloride (60 mg/kg, ip). Twelve hours after, rats underwent the baseline scan using the MEMRI (Manganese-Enhanced Magnetic Resonance Imaging) technique. We used the same MEMRI and parvalbumin sequence to follow the DBS delivered during 1 h (130 Hz and 200 μA). Perfusion was followed by subsequent c-Fos and parvalbumin immunostaining of brain sections.

RESULTS

Acute unilateral ANT DBS significantly reduced the overall manganese uptake and consequently, the MEMRI contrast in the circuit of Papez. Additionally, c-Fos expression was bilaterally increased in the cingulate cortex and posterior hypothalamus, areas directly connected to ANT, as well as in amygdala and subiculum, within the limbic circuitry.

CONCLUSION

Our data indicate that MEMRI can be used to detect whole-brain responses to DBS, as the high frequency stimulation parameters used here caused a significant reduction of cell activity in the circuit of Papez that might help to explain the antiepileptic effects of ANT DBS.

A pilot study of neuromuscular electrical stimulation for neuropathic pain caused by spinal cord injury

This pilot study retrospectively investigated the feasible effect and safety of neuromuscular electrical stimulation (NMES) for the management of neuropathic pain (NPP) caused by spinal cord injury (SCI).A total of 54 patient cases with NPP after SCI were included. Of these, 27 cases underwent carbamazepine plus NMES treatment, and were assigned to an NMES group; while the other 27 cases received carbamazepine only, and were assigned to a control group. The primary outcome of pain intensity was measured by numerical rating scale (NRS). The secondary outcome of quality of life was measured by the Short Form 36 (SF-36) Scale. Furthermore, adverse events were also documented in this study. All outcomes were measured and analyzed before and after 3-month treatment.After 3-month treatment, the cases in the NMES group neither reduced the pain intensity of NPP, measured by the NRS (P > .05), nor improved the quality of life, measured by the SF-36 (P > .05), compared with cases in the control group. Moreover, both groups had similar adverse events.The results of this study showed that NMES might be not efficacious for NPP caused by SCI after 3 months treatment with quite low intervention dose.