Electrical neuromodulation for the treatment of chronic pain: derivation of the intrinsic barriers, outcomes and considerations of the sustainability of implantable spinal cord stimulation therapies

INTRODUCTION

For over 60 years, spinal cord stimulation has endured as a therapy through innovation and novel developments. Current practice of neuromodulation requires proper patient selection, risk mitigation and use of innovation. However, there are tangible and intangible challenges in physiology, clinical science and within society.

AREAS COVERED

We provide a narrative discussion regarding novel topics in the field especially over the last decade. We highlight the challenges in the patient care setting including selection, as well as economic and socioeconomic challenges. Physician training challenges in neuromodulation is explored as well as other factors related to the use of neuromodulation such as novel indications and economics. We also discuss the concepts of technology and healthcare data.

EXPERT OPINION

Patient safety and durable outcomes are the mainstay goal for neuromodulation. Substantial work is needed to assimilate data for larger and more relevant studies reflecting a population. Big data and global interconnectivity efforts provide substantial opportunity to reinvent our scientific approach, data analysis and its management to maximize outcomes and minimize risk. As improvements in data analysis become the standard of innovation and physician training meets demand, we expect to see an expansion of novel indications and its use in broader cohorts.

Research progress and prospects of benefit-risk assessment methods for umbilical cord mesenchymal stem cell transplantation in the clinical treatment of spinal cord injury

Over the past decade, we have witnessed the development of cell transplantation as a new strategy for repairing spinal cord injury (SCI). However, due to the complexity of the central nervous system (CNS), achieving successful clinical translation remains a significant challenge. Human umbilical cord mesenchymal stem cells (hUMSCs) possess distinct advantages, such as easy collection, lack of ethical concerns, high self-renewal ability, multilineage differentiation potential, and immunomodulatory properties. hUMSCs are promising for regenerating the injured spinal cord to a significant extent. At the same time, for advancing SCI treatment, the appropriate benefit and risk evaluation methods play a pivotal role in determining the clinical applicability of treatment plans. Hence, this study discusses the advantages and risks of hUMSCs in SCI treatment across four dimensions-comprehensive evaluation of motor and sensory function, imaging, electrophysiology, and autonomic nervous system (ANS) function-aiming to improve the rationality of relevant clinical research and the feasibility of clinical translation.

Electrophysiology Methods for Assessing of Neurodegenerative and Post-Traumatic Processes as Applied to Translational Research

Electrophysiological studies have long established themselves as reliable methods for assessing the functional state of the brain and spinal cord, the degree of neurodegeneration, and evaluating the effectiveness of therapy. In addition, they can be used to diagnose, predict functional outcomes, and test the effectiveness of therapeutic and rehabilitation programs not only in clinical settings, but also at the preclinical level. Considering the urgent need to develop potential stimulators of neuroregeneration, it seems relevant to obtain objective data when modeling neurological diseases in animals. Thus, in the context of the application of electrophysiological methods, not only the comparison of the basic characteristics of bioelectrical activity of the brain and spinal cord in humans and animals, but also their changes against the background of neurodegenerative and post-traumatic processes are of particular importance. In light of the above, this review will contribute to a better understanding of the results of electrophysiological assessment in neurodegenerative and post-traumatic processes as well as the possibility of translating these methods from model animals to humans.

Contribution of mechanoreceptors to spinal cord injury-induced mechanical allodynia

ABSTRACT

Evidence from previous studies supports the concept that spinal cord injury (SCI)-induced neuropathic pain (NP) has its neural roots in the peripheral nervous system. There is uncertainty about how and to which degree mechanoreceptors contribute. Sensorimotor activation-based interventions (eg, treadmill training) have been shown to reduce NP after experimental SCI, suggesting transmission of pain-alleviating signals through mechanoreceptors. The aim of the present study was to understand the contribution of mechanoreceptors with respect to mechanical allodynia in a moderate mouse contusion SCI model. After genetic ablation of tropomyosin receptor kinase B expressing mechanoreceptors before SCI, mechanical allodynia was reduced. The identical genetic ablation after SCI did not yield any change in pain behavior. Peptidergic nociceptor sprouting into lamina III/IV below injury level as a consequence of SCI was not altered by either mechanoreceptor ablation. However, skin-nerve preparations of contusion SCI mice 7 days after injury yielded hyperexcitability in nociceptors, not in mechanoreceptors, which makes a substantial direct contribution of mechanoreceptors to NP maintenance unlikely. Complementing animal data, quantitative sensory testing in human SCI subjects indicated reduced mechanical pain thresholds, whereas the mechanical detection threshold was not altered. Taken together, early mechanoreceptor ablation modulates pain behavior, most likely through indirect mechanisms. Hyperexcitable nociceptors seem to be the main drivers of SCI-induced NP. Future studies need to focus on injury-derived factors triggering early-onset nociceptor hyperexcitability, which could serve as targets for more effective therapeutic interventions.

Individuals With Prior Chronic Pain and Long-Term Opioid Treatment May Experience Persistence of That Pain Even After Subsequent Complete Cervical Spinal Cord Injury: Suggestions From a Prospective Case-Controlled Study

Objective

To determine whether chronic pain persists after complete spinal cord injury (SCI).

Design

Prospective observational study regarding the outcome of pre-existent chronic pain of inpatients admitted with new clinically diagnosed complete cervical SCI. For patients who acknowledged chronic pain of ≥3 years duration before the SCI, further questions explored whether they still experienced that pain, whether they were experiencing current posttraumatic pain, and whether they had any past exposure to opioids. The included patients were identified during the initial consultation in the trauma center for treatment of the SCI.

Setting

Level I trauma center.

Participants

From a total of 49 participants with acute cervical SCI with clinically diagnosed complete motor and sensory tetraplegia admitted between 2018 and 2020, 7 were selected on the basis of a history of chronic pain.

Intervention

Collected complete history and performed physical examination with serial follow-ups during the acute hospital stay until death or discharge.

Main Outcome Measures

The primary outcome was a finding of chronic pain experienced before new clinical diagnosis of complete SCI, compared with whether or not that pain continued after the SCI injury. The secondary outcome was the relation of persistent pain with opioid use; it was formulated after data collection.

Results

Among 49 patients with clinically diagnosed complete cervical SCIs, 7 had experienced prior chronic pain. Four participants experienced a continuation of the prior pain after their complete tetraplegia (4/7), whereas 3 participants did not (3/7). All the participants with continued pain had been previously treated with opioids, whereas those whose pain ceased had not received chronic opioid therapy.

Conclusions

There may be a unique form of chronic pain that is based in the brain, irrespective of peripheral pain or spinal mechanisms. Otherwise healthy people with longstanding antecedent chronic pain whose pain persists after acute clinically complete SCI with tetraplegia may provide a new model for evaluation of brain-based pain. Opioids may be requisite for this type of pain.

Can alternative medical methods evoke somatosensory responses and functional improvement?

Background

Evidence-based scientific studies focusing on complementary alternative medicine (CAM) and potential functional improvement after an insult of the central nervous system are lacking.

Aims

We aim to demonstrate that functional recovery after stimulation applied as a CAM treatment through cauterization might trigger neural repair and regenerative paths similarly as acupuncture, cupping, electrical or magnetic stimulations. Those paths are important in recovery of function.

Procedures

Medical records and information of ten patients, with initial presentations of cerebral trauma or spinal cord insult inducing paralysis, were studied. Patients ages ranged from 17 to 95-year-old. Patients consulted for alternative medical treatment one year or more after initial diagnosis.CAM treatment consisted in 10-point stimulation on the skull and 4-point stimulation located at the right and left calves and forearms. Stimulations consisted of a heated steel rod application (cautery) in a one-time session. The duration of each stimulation was about 0.5 s.

Results

Most studies using CAM stimulations (acupuncture, cautery, cupping, moxibustion, electrical and magnetic stimulations) describe improvement. In all 10 medical records and information from our practitioner, patients had improvement in their motor skills, including gain of weight support, unassisted small walks, independent and voluntary movements of limbs. Improvement was steady over a period of one to several years.

Conclusion

We compared our findings to acupuncture, electrical, magnetic field effects to highlight common paths and to provide scientific evidence for recovery of the function. We believe that CAM treatments triggered existing or new neuronal networks as well as synaptic efficiency or reactivation, through highly increased, sensory nociceptive coupled to proprioceptive, afferences. Those results also highlight the need to further investigate neural function of cortical and subcortical areas through indirect pathways stimulations.

Positive Correlation Between Motor Function and Neuropathic Pain-Like Behaviors After Spinal Cord Injury: A Longitudinal Study of Mice

Abstract With the recovery of motor function, some spinal cord injury (SCI) patients still suffer from severe pain-like behaviors symptoms. Whether motor function correlates with neuropathic pain-like behaviors remain unclear. In this study, a longitudinal cohort study of mice with moderate thoracic 10 contusion was performed to explore the characteristics of neuropathic pain-like behaviors and its correlation with motor function in different sexes. Pain-like behaviors data up to 42 days post-injury (dpi) were collected and compared. Mice of both sexes were divided into three groups based on their Basso Mouse Scale at 42 dpi. There was no significant difference in motor function recovery between the sexes. Female mice showed more significant mechanical allodynia than males at 14 dpi, which was sustained until 42 dpi without significant dynamic changes. However, males showed a gradually worsening state and more severe mechanical allodynia than females at 28 dpi, and then the differences disappeared. Interestingly, male mice obtained more severe cold hyperalgesia symptoms than females. Additionally, we found that there was a correlation between the occurrence of mechanical allodynia and cold and thermal hyperalgesia. Importantly, motor function recovery was positively associated with the outcomes of neuropathic pain-like behaviors after SCI, which was more obvious in female mice. Our data not only revealed the characteristics of neuropathic pain-like behaviors but also clarified the correlations between motor function recovery and neuropathic pain-like behaviors after SCI. These findings may provide new opinions and suggestions for promoting the clinical diagnosis and treatment of neuropathic pain-like behaviors after SCI.

Application and underlying mechanism of acupuncture for the nerve repair after peripheral nerve injury: remodeling of nerve system

Peripheral nerve injury (PNI) is a structural event with harmful consequences worldwide. Due to the limited intrinsic regenerative capacity of the peripheral nerve in adults, neural restoration after PNI is difficult. Neurological remodeling has a crucial effect on the repair of the form and function during the regeneration of the peripheral nerve after the peripheral nerve is injured. Several studies have demonstrated that acupuncture is effective for PNI-induced neurologic deficits, and the potential mechanisms responsible for its effects involve the nervous system remodeling in the process of nerve repair. Moreover, acupuncture promotes neural regeneration and axon sprouting by activating related neurotrophins retrograde transport, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), N-cadherin, and MicroRNAs. Peripheral nerve injury enhances the perceptual response of the central nervous system to pain, causing central sensitization and accelerating neuronal cell apoptosis. Together with this, the remodeling of synaptic transmission function would worsen pain discomfort. Neuroimaging studies have shown remodeling changes in both gray and white matter after peripheral nerve injury. Acupuncture not only reverses the poor remodeling of the nervous system but also stimulates the release of neurotrophic substances such as nerve growth factors in the nervous system to ameliorate pain and promote the regeneration and repair of nerve fibers. In conclusion, the neurological remodeling at the peripheral and central levels in the process of acupuncture treatment accelerates nerve regeneration and repair. These findings provide novel insights enabling the clinical application of acupuncture in the treatment of PNI.

Neuropathic Pain in the Emergency Setting: Diagnosis and Management

Neuropathic pain, traditionally considered a chronic condition, is increasingly encountered in the emergency department (ED), accounting for approximately 20% of patients presenting with pain. Understanding the physiology and key clinical presentations of neuropathic pain is crucial for ED physicians to provide optimal treatment. While diagnosing neuropathic pain can be challenging, emphasis should be placed on obtaining a comprehensive medical history and conducting a thorough clinical examination. Patients often describe neuropathic pain as a burning or shock-like sensation, leading them to seek care in the ED after ineffective relief from common analgesics such as paracetamol and NSAIDs. Collaboration between emergency medicine specialists, neurologists, and pain management experts can contribute to the development of evidence-based guidelines specifically tailored for the emergency department setting. This article provides a concise overview of the common clinical manifestations of neuropathic pain that may prompt patients to seek emergency care.

A Silver Lining of Neuropathic Pain: Predicting Favorable Functional Outcome in Spinal Cord Injury

Background

Neuropathic pain (NP) is a common and severe problem following spinal cord injury (SCI). However, its relationship with functional outcome remains unclear.

Methods

A retrospective explorative analysis was performed on SCI patients admitted to a tertiary academic medical center between January 2018 and June 2022. The candidate predictor variables, including demographics, clinical characteristics and complications, were analyzed with logistic and linear regression. Spinal Cord Independence Measure (SCIM) scores at discharge and mean relative functional gain (mRFG) of SCIM were as outcome parameters.

Results

A total of 140 SCI patients included for the final analysis. Among them, 44 (31.43%) patients were tetraplegics, and 96 (68.57%) patients were paraplegics; 68 (48.57%) patients developed NP, and 72 (51.43%) patients did not. Logistic and linear regression analyses of SCIM at discharge both showed that NP [OR=3.10, 95% CI (1.29,7.45), P=0.01; unstandardized β=11.47, 95% CI (4.95,17.99), P<0.01; respectively] was significantly independent predictors for a favorable outcome (SCIM at discharge ≥ 50, logistic regression results) and higher SCIM total score at discharge (linear regression results). Besides, NP [unstandardized β=15.67, 95% CI (8.94,22.41), P<0.01] was also independently associated with higher mRFG of SCIM scores. Furthermore, the NP group had significantly higher mRFG, SCIM total scores and subscales (self-care, respiration and sphincter management, and mobility) at discharge compared to the non-NP group. However, there were no significant differences in mRFG, SCIM total score or subscales at discharge among the NP subgroups in terms of locations (at level pain, below level pain, and both) or timing of occurrence (within and after one month after SCI). This study also showed that incomplete injury, lumbar-sacral injury level and non-anemia were significantly independent predictors for a favorable outcome, and higher mRFG of SCIM scores (except for non-anemia).

Conclusion

NP appears independently associated with better functional recovery in SCI patients, suggesting the bright side of this undesirable complication. These findings may help to alleviate the psychological burden of NP patients and ultimately restore their confidence in rehabilitation.

Assessing the Feasibility of a Multimodal Approach to Pain Evaluation in Early Stages after Spinal Cord Injury

This research evaluates the feasibility of a multimodal pain assessment protocol during rehabilitation following spinal cord injury (SCI). The protocol amalgamates clinical workup (CW), quantitative sensory testing (QST), and psychosocial factors (PSF) administered at 4 (T1), 12 (T2), and 24 (T3) weeks post injury and at discharge (T4). Molecular blood biomarkers (BB) were evaluated via gene expression and proteomic assays at T1 and T4. Different pain trajectories and temporal changes were identified using QST, with inflammation and pain-related biomarkers recorded. Higher concentrations of osteopontin and cystatin-C were found in SCI patients compared to healthy controls, indicating their potential as biomarkers. We observed altered inflammatory responses and a slight increase in ICAM-1 and CCL3 were noted, pointing towards changes in cellular adhesion linked with spinal injury and a possible connection with neuropathic pain. Despite a small patient sample hindering the correlation of feasibility data, descriptive statistical analyses were conducted on stress, depression, anxiety, quality of life, and pain interferences. The SCI Pain Instrument (SCIPI) was efficient in distinguishing between nociceptive and neuropathic pain, showing a progressive increase in severity over time. The findings emphasize the need for the careful consideration of recruitment setting and protocol adjustments to enhance the feasibility of multimodal pain evaluation studies post SCI. They also shed light on potential early adaptive mechanisms in SCI pathophysiology, warranting the further exploration of prognostic and preventive strategies for chronic pain in the SCI population.

Neuropathic Pain and Spinal Cord Injury: Management, Phenotypes, and Biomarkers

Chronic neuropathic pain after a spinal cord injury (SCI) continues to be a complex condition that is difficult to manage due to multiple underlying pathophysiological mechanisms and the association with psychosocial factors. Determining the individual contribution of each of these factors is currently not a realistic goal; however, focusing on the primary mechanisms may be more feasible. One approach used to uncover underlying mechanisms includes phenotyping using pain symptoms and somatosensory function. However, this approach does not consider cognitive and psychosocial mechanisms that may also significantly contribute to the pain experience and impact treatment outcomes. Indeed, clinical experience supports that a combination of self-management, non-pharmacological, and pharmacological approaches is needed to optimally manage pain in this population. This article will provide a broad updated summary integrating the clinical aspects of SCI-related neuropathic pain, potential pain mechanisms, evidence-based treatment recommendations, neuropathic pain phenotypes and brain biomarkers, psychosocial factors, and progress regarding how defining neuropathic pain phenotypes and other surrogate measures in the neuropathic pain field may lead to targeted treatments for neuropathic pain after SCI.

The Potential Role of Etanercept in the Management of Post-stroke Pain: A Literature Review

Strokes are the second leading cause of death and disability worldwide. The brain injury resulting from stroke produces a persistent neuroinflammatory response in the brain, resulting in a spectrum of neurologic dysfunction affecting stroke survivors chronically, also known as post-stroke pain. Excess production of tumor necrosis factor alpha (TNF alpha) in the cerebrospinal fluid (CSF) of stroke survivors has been implicated in post-stroke pain. Therefore, this literature review aims to assess and review the role of perispinal etanercept in the management of post-stroke pain. Several studies have shown statistically significant evidence that etanercept, a TNF alpha inhibitor, can reduce symptoms present in post-stroke syndrome by targeting the excess TNF alpha produced in the CSF. Studies have also shown improvements in not only post-stroke pain but also in traumatic brain injury and dementia. Further research is needed to explore the effects of TNF alpha on stroke prognosis and determine the optimal frequency and duration of etanercept treatment for post-stroke pain.

Noxious radiant heat evokes bi-component nociceptive withdrawal reflexes in spinal cord injured humans-A clinical tool to study neuroplastic changes of spinal neural circuits

Investigating nocifensive withdrawal reflexes as potential surrogate marker for the spinal excitation level may widen the understanding of maladaptive nociceptive processing after spinal cord injury (SCI). The aim of this prospective, explorative cross-sectional observational study was to investigate the response behavior of individuals with SCI to noxious radiant heat (laser) stimuli and to assess its relation to spasticity and neuropathic pain, two clinical consequences of spinal hyperexcitability/spinal disinhibition. Laser stimuli were applied at the sole and dorsum of the foot and below the fibula head. Corresponding reflexes were electromyography (EMG) recorded ipsilateral. Motor responses to laser stimuli were analyzed and related to clinical readouts (severity of injury/spasticity/pain), using established clinical assessment tools. Twenty-seven participants, 15 with SCI (age 18-63; 6.5 years post-injury; AIS-A through D) and 12 non-disabled controls, [non-disabled controls (NDC); age 19-63] were included. The percentage of individuals with SCI responding to stimuli (70-77%; p < 0.001), their response rates (16-21%; p < 0.05) and their reflex magnitude (p < 0.05) were significantly higher compared to NDC. SCI-related reflexes clustered in two time-windows, indicating involvement of both A-delta- and C-fibers. Spasticity was associated with facilitated reflexes in SCI (Kendall-tau-b p ≤ 0.05) and inversely associated with the occurrence/severity of neuropathic pain (Fisher's exact p < 0.05; Eta-coefficient p < 0.05). However, neuropathic pain was not related to reflex behavior. Altogether, we found a bi-component motor hyperresponsiveness of SCI to noxious heat, which correlated with spasticity, but not neuropathic pain. Laser-evoked withdrawal reflexes may become a suitable outcome parameter to explore maladaptive spinal circuitries in SCI and to assess the effect of targeted treatment strategies. Registration: https://drks.de/search/de/trial/DRKS00006779.

Role of Sensory Pathway Injury in Central Post-Stroke Pain: A Narrative Review of Its Pathogenetic Mechanism

Central post-stroke pain (CPSP) is a severe chronic neuropathic pain syndrome that is a direct result of cerebrovascular lesions affecting the central somatosensory system. The pathogenesis of this condition remains unclear owing to its extensive clinical manifestations. Nevertheless, clinical and animal experiments have allowed a comprehensive understanding of the mechanisms underlying CPSP occurrence, based on which different theoretical hypotheses have been proposed. We reviewed and collected the literature and on the mechanisms of CPSP by searching the English literature in PubMed and EMBASE databases for the period 2002-2022. Recent studies have reported that CPSP occurrence is mainly due to post-stroke nerve injury and microglial activation, with an inflammatory response leading to central sensitization and de-inhibition. In addition to the primary injury at the stroke site, peripheral nerves, spinal cord, and brain regions outside the stroke site are involved in the occurrence and development of CPSP. In the present study, we reviewed the mechanism of action of CPSP from both clinical studies and basic research based on its sensory pathway. Through this review, we hope to increase the understanding of the mechanism of CPSP.

The Effects of an Acute Maximal Seated Lumbar Spine Flexion Exposure on Low Back Mechanical Pain Sensitivity

Viscoelastic creep generated in the lumbar spine following sustained spine flexion may affect the relationship between tissue damage and perceived pain. Two processes supporting this altered relationship include altered neural feedback and inflammatory processes. Our purpose was to determine how low back mechanical pain sensitivity changes following seated lumbar spine flexion using pressure algometry in a repeated-measures, cross-sectional laboratory design. Thirty-eight participants underwent a 10-minute sustained seated maximal flexion exposure with a 40-minute standing recovery period. Pressure algometry assessed pressure pain thresholds and the perceived intensity and unpleasantness of fixed pressures. Accelerometers measured spine flexion angles, and electromyography measured muscular activity during flexion. The flexion exposure produced 4.4° (2.7°) of creep that persisted throughout the entire recovery period. The perception of low back stimulus unpleasantness was elevated immediately following the exposure, 20 minutes before a delayed increase in lumbar erector spinae muscle activity. Women reported the fixed pressures to be more intense than men. Sustained flexion had immediate consequences to the quality of mechanical stimulus perceived but did not alter pressure pain thresholds. Neural feedback and inflammation seemed unlikely mechanisms for this given the time and direction of pain sensitivity changes, leaving a postulated cortical influence.

A Review on Autophagy in Orofacial Neuropathic Pain

Orofacial neuropathic pain indicates pain caused by a lesion or diseases of the somatosensory nervous system. It is challenging for the clinician to diagnose and manage orofacial neuropathic pain conditions due to the considerable variability between individual clinical presentations and a lack of understanding of the mechanisms underlying the etiology and pathogenesis. In the last few decades, researchers have developed diagnostic criteria, questionnaires, and clinical assessment methods for the diagnosis of orofacial neuropathic pain. Recently, researchers have observed the role of autophagy in neuronal dysfunction as well as in the modulation of neuropathic pain. On this basis, in the present review, we highlight the characteristics, classification, and clinical assessment of orofacial neuropathic pain. Additionally, we introduce autophagy and its potential role in the modulation of orofacial neuropathic pain, along with a brief overview of the pathogenesis, which in future may reveal new possible targets for treating this condition.

Altered bodily perceptions in chronic neuropathic pain conditions and implications for treatment using immersive virtual reality

Chronic neuropathic pain is highly disabling and difficult to treat and manage. Patients with such conditions often report altered bodily perceptions that are thought to be associated with maladaptive structural and functional alterations in the somatosensory cortex. Manipulating these altered perceptions using body illusions in virtual reality is being investigated and may have positive clinical implications for the treatment of these conditions. Here, we have conducted a narrative review of the evidence for the types of bodily distortions associated with a variety of peripheral and central neuropathic pain conditions. In addition, we summarize the experimental and clinical studies that have explored embodiment and body transformation illusions in immersive virtual reality for neuropathic pain relief, which are thought to target these maladaptive changes, as well as suggesting directions for future research.

Spinal cord stimulation in patients suffering from chronic pain after surgery for spinal intradural tumors: A case report and literature summary

BACKGROUND

The prevalence of pain after treatment of a spinal intradural tumor is remarkably high, approximately up to 40% of the patients suffer from central neuropathic pain. Publications on spinal cord stimulation (SCS) and its effect on pain caused by intradural spinal tumors are rare. We discuss the case of a patient suffering from chronic pain after removal of a Th7 level meningioma who was successfully treated with SCS and give an overview of the literature.

METHODS

MEDLINE database was searched for neuropathic pain and intradural tumors.

RESULTS

The initial search identified 35 articles, including hand-searched manuscripts. Six articles were included for analysis.

CASE REPORT

A 57-year-old female suffers from neuropathic pain in both legs after surgical removal of a Th7 level intradural meningioma. Postoperative magnetic resonance imaging shows no gross abnormalities, although she developed chronic pain in both legs. Pain in combination with side effects of analgesic intake are too disabling to have decent quality of life. A successful implantation of SCS is achieved at Th5 level as a treatment for the central neuropathic pain, and, at 36 months follow-up, there is significant pain relief and almost complete discontinuation of analgesics.

DISCUSSION

Central pain from spinal intradural tumors may have a different mechanism of origin than pain seen after an acute spinal cord injury (SCI). However, the basic principles of neuromodulation are the same in both etiologies, as for successful stimulation intact pathways in the spinal cord are necessary. The efficacy of SCS as treatment in intradural spinal tumors is rarely described as only a handful of case reports are published. Interestingly, the case reports show that stimulation both above and below the lesion can be effective. In patients with incomplete SCI or intradural tumor resection stimulation below the lesion could be considered and tried in a trial setting before definitive implantation.

Cold evoked potentials elicited by rapid cooling of the skin in young and elderly healthy individuals

Cold-evoked potentials (CEPs) constitute a novel electrophysiological tool to assess cold-specific alterations in somatosensory function. As an important step towards the clinical implementation of CEPs as a diagnostic tool, we evaluated the feasibility and reliability of CEPs in response to rapid cooling of the skin (-300 °C/s) and different stimulation sites in young and elderly healthy individuals. Time-locked electroencephalographic responses were recorded from at vertex in fifteen young (20-40 years) and sixteen elderly (50-70 years), individuals in response to 15 rapid cold stimuli (-300 °C/s) applied to the skin of the hand dorsum, palm, and foot dorsum. High CEP proportions were shown for young individuals at all sites (hand dorsum/palm: 100% and foot: 79%) and elderly individuals after stimulation of the hand dorsum (81%) and palm (63%), but not the foot (44%). Depending on the age group and stimulation site, test-retest reliability was "poor" to "substantial" for N2P2 amplitudes and N2 latencies. Rapid cooling of the skin enables the recording of reliable CEPs in young individuals. In elderly individuals, CEP recordings were only robust after stimulation of the hand, but particularly challenging after stimulation of the foot. Further improvements in stimulation paradigms are warranted to introduce CEPs for clinical diagnostics.

From acute to long-term alterations in pain processing and modulation after spinal cord injury: mechanisms related to chronification of central neuropathic pain

ABSTRACT

A severe and debilitating consequence of a spinal cord injury (SCI) is central neuropathic pain (CNP). Our aim was to investigate the processes leading to CNP emergence and chronification by analyzing causal relationship over time between spinothalamic function, pain excitability, and pain inhibition after SCI. This longitudinal follow-up study included 53 patients with acute SCI and 20 healthy controls. Spinothalamic, pain excitability, and intrasegmental and extrasegmental pain inhibition indices were repeatedly evaluated at 1.5, 3, and 6 months post-SCI. Between- and within-group analyses were conducted among those patients who eventually developed CNP and those who did not. Healthy controls were evaluated twice for repeatability analysis. Patients who developed CNP, compared with those who did not, exhibited increased thermal thresholds (P < 0.05), reduced pain adaptation (P < 0.01), and conditioned pain modulation (P < 0.05), early post-injury, and the CNP group's manifestations remained worse throughout the follow-up. By contrast, allodynia frequency was initially similar across SCI groups, but gradually increased in the subacute phase onward only among the CNP group (P < 0.001), along with CNP emergence. Early worse spinothalamic and pain inhibition preceded CNP and predicted its occurrence, and early worse pain inhibition mediated the link between spinothalamic function and CNP. Crossover associations were observed between early and late pain inhibition and excitability. Inefficient intrasegmental and extrasegmental inhibition, possibly resulting from spinothalamic deafferentation, seems to ignite CNP chronification. Pain excitability probably contributes to CNP maintenance, possibly via further exhaustion of the inhibitory control. Preemptive treatment promoting antinociception early post-SCI may mitigate or prevent CNP.

Identifying Discomplete Spinal Lesions: New Evidence from Pain-Autonomic Interaction in Spinal Cord Injury

The clinical evaluation of spinal afferents is an important diagnostic and prognostic marker for neurological and functional recovery after spinal cord injury (SCI). Particularly important regarding neuropathic pain following SCI is the function of the spinothalamic tract (STT) conveying nociceptive and temperature information. Here, we investigated the added value of neurophysiological methods revealing discomplete STT lesions; that is, residual axonal sparing in clinically complete STT lesions. Specifically, clinical pinprick testing and thermal thresholds were compared with objective contact heat-evoked potentials (CHEPs) and a novel measure of pain-autonomic interaction employing heat-induced sympathetic skin responses (SSR). The test stimuli (i.e., contact heat, pinprick) were applied below the lesion level in 32 subjects with thoracic SCI while corresponding heat-evoked responses (i.e., CHEPs and SSR) were recorded above the lesion (i.e., scalp and hand, respectively). Readouts of STT function were related to neuropathic pain characteristics. In subjects with abolished pinprick sensation, measures of thermosensation (10%), CHEPs (33%), and SSR (48%) revealed residual STT function. Importantly, SSRs can be used as an objective readout and when abolished, no other proxy indicated residual STT function. No relationship was found between STT function readouts and spontaneous neuropathic pain intensity and extent. However, subjects with clinically preserved STT function presented more often with allodynia (54%) than subjects with discomplete (13%) or complete STT lesions (18%). In individuals with absent pinprick sensation, discomplete STT lesions can be revealed employing pain-autonomic measures. The improved sensitivity to discerning STT lesion completeness might support the investigation of its association with neuropathic pain following SCI.

Markers of Central Neuropathic Pain in Higuchi Fractal Analysis of EEG Signals From People With Spinal Cord Injury

Central neuropathic pain (CNP) negatively impacts the quality of life in a large proportion of people with spinal cord injury (SCI). With no cure at present, it is crucial to improve our understanding of how CNP manifests, to develop diagnostic biomarkers for drug development, and to explore prognostic biomarkers for personalised therapy. Previous work has found early evidence of diagnostic and prognostic markers analysing Electroencephalogram (EEG) oscillatory features. In this paper, we explore whether non-linear non-oscillatory EEG features, specifically Higuchi Fractal Dimension (HFD), can be used as prognostic biomarkers to increase the repertoire of available analyses on the EEG of people with subacute SCI, where having both linear and non-linear features for classifying pain may ultimately lead to higher classification accuracy and an intrinsically transferable classifier. We focus on EEG recorded during imagined movement because of the known relation between the motor cortex over-activity and CNP. Analyses were performed on two existing datasets. The first dataset consists of EEG recordings from able-bodied participants (N = 10), participants with chronic SCI and chronic CNP (N = 10), and participants with chronic SCI and no CNP (N = 10). We tested for statistically significant differences in HFD across all pairs of groups using bootstrapping, and found significant differences between all pairs of groups at multiple electrode locations. The second dataset consists of EEG recordings from participants with subacute SCI and no CNP (N = 20). They were followed-up 6 months post recording to test for CNP, at which point (N = 10) participants had developed CNP and (N = 10) participants had not developed CNP. We tested for statistically significant differences in HFD between these two groups using bootstrapping and, encouragingly, also found significant differences at multiple electrode locations. Transferable machine learning classifiers achieved over 80% accuracy discriminating between groups of participants with chronic SCI based on only a single EEG channel as input. The most significant finding is that future and chronic CNP share common features and as a result, the same classifier can be used for both. This sheds new light on pain chronification by showing that frontal areas, involved in the affective aspects of pain and believed to be influenced by long-standing pain, are affected in a much earlier phase of pain development.

Supraspinal nociceptive networks in neuropathic pain after spinal cord injury

Neuropathic pain following spinal cord injury involves plastic changes along the whole neuroaxis. Current neuroimaging studies have identified grey matter volume (GMV) and resting-state functional connectivity changes of pain processing regions related to neuropathic pain intensity in spinal cord injury subjects. However, the relationship between the underlying neural processes and pain extent, a complementary characteristic of neuropathic pain, is unknown. We therefore aimed to reveal the neural markers of widespread neuropathic pain in spinal cord injury subjects and hypothesized that those with greater pain extent will show higher GMV and stronger connectivity within pain related regions. Thus, 29 chronic paraplegic subjects and 25 healthy controls underwent clinical and electrophysiological examinations combined with neuroimaging. Paraplegics were demarcated based on neuropathic pain and were thoroughly matched demographically. Our findings indicate that (a) spinal cord injury subjects with neuropathic pain display stronger connectivity between prefrontal cortices and regions involved with sensory integration and multimodal processing, (b) greater neuropathic pain extent, is associated with stronger connectivity between the posterior insular cortex and thalamic sub-regions which partake in the lateral pain system and (c) greater intensity of neuropathic pain is related to stronger connectivity of regions involved with multimodal integration and the affective-motivational component of pain. Overall, this study provides neuroimaging evidence that the pain phenotype of spinal cord injury subjects is related to the underlying function of their resting brain.

Thalamic anterior part of the ventral posterolateral nucleus and central lateral nucleus in the genesis of central post-stroke pain

BACKGROUND

The genesis of central post-stroke pain (CPSP) is important but difficult to understand. We evaluated the involvement of the thalamic anterior part of the ventral posterolateral nucleus (VPLa) and central lateral nucleus (CL) in the occurrence of CPSP.

METHOD

Stereotactic thalamotomy was performed on the posterior part of the ventral lateral nucleus (VLp)-VPLa and CL in 9 patients with CPSP caused by deep-seated intracerebral hemorrhage. Computed tomography (CT) did not reveal definite thalamic lesion in 5 patients but did in 4 patients. Electrophysiological studies of these thalamic nuclei were carried out during the surgery. Anatomical studies using CT were performed in another 20 patients with thalamic hemorrhage who had clear consciousness but had sensory disturbance at onset.

RESULTS

Neural activities were preserved and hyperactive and unstable discharges (HUDs) were often recognized along the trajectory in the thalamic VLp-VPLa in 5 patients without thalamic lesion. Surgical modification of this area ameliorated pain, particularly movement-related pain. Neural activities were hypoactive in the other 4 patients with thalamic lesion. However, neural activities were preserved and HUDs were sometimes recognized in the CL. Sensory responses were seen, but at low rate, in the sensory thalamus. Anatomical study showed that the thalamic lesion was obviously smaller in the patients with developing pain in the chronic stage.

CONCLUSIONS

Change in neural activities around the cerebrovascular disease lesion in the thalamic VPLa or CL might affect the perception of sensory impulses or sensory processing in those thalamic nuclei, resulting in the genesis of CPSP.

Characterization of Hyperacute Neuropathic Pain after Spinal Cord Injury: A Prospective Study

There is currently a lack of information regarding neuropathic pain in the very early stages of spinal cord injury (SCI). In the present study, neuropathic pain was assessed using the Douleur Neuropathique 4 Questions (DN4) for the patient's worst pain within the first 5 days of injury (i.e., hyperacute) and on follow-up at 3, 6, and 12 months. Within the hyperacute time frame (i.e., 5 days), at- and below-level neuropathic pain were reported as the worst pain in 23% (n = 18) and 5% (n = 4) of individuals with SCI, respectively. Compared to the neuropathic pain observed in this hyperacute setting, late presenting neuropathic pain was characterized by more intense painful electrical and cold sensations, but less itching sensations. Phenotypic differences between acute and late neuropathic pain support the incorporation of timing into a mechanism-based classification of neuropathic pain after SCI. The diagnosis of acute neuropathic pain after SCI is challenged by the presence of nociceptive and neuropathic pains, with the former potentially masking the latter. This may lead to an underestimation of the incidence of neuropathic pain during the very early, hyperacute time points post-injury. TRIAL REGISTRATION: ClinicalTrials.gov (Identifier: NCT01279811) PERSPECTIVE: This article presents distinct pain phenotypes of hyperacute and late presenting neuropathic pain after spinal cord injury and highlights the challenges of pain assessments in the acute phase after injury. This information may be relevant to clinical trial design and broaden our understanding of neuropathic pain mechanisms after spinal cord injury.

Alteration of White Matter in Patients with Central Post-Stroke Pain

A stroke may be followed by central post-stroke pain (CPSP), which is characterized by chronic neuropathic pain. The exact mechanism has not yet been fully uncovered. We investigated alterations in the white matters in patients with CPSP, compared with stroke patients without CPSP and normal controls. Our retrospective cross-sectional, case-control study participants were assigned to three groups: CPSP (stroke patients with CPSP (n = 17)); stroke control (stroke patients without CPSP (n = 26)); and normal control (normal subjects (n = 34)). The investigation of white matter for CPSP was focused on the values of fiber numbers (FN) and fractional anisotrophy (FA) for spinothalamic tract (STT), anterior thalamic radiation (ATR), superior thalamic radiation (STR) and posterior thalamic radiation (PTR), and corticospinal tract (CST) was measured. The FA for the STT and STR of the CPSP group were lower than those for the stroke control and normal control groups. The FA of CST and ATR did not differ between the CPSP and stroke groups, but both differed from the normal control. The FA of PTR in the stroke control group differed from the normal control group, but not from the CPSP group. The FN of CST, STT, ATR, and STR for the CPSP and stroke control groups did not differ from each other, but both differed from those of normal controls. FN of PTR did not differ between the CPSP and normal control groups. The alterations in the spinothalamic tract and superior thalamic radiation after stroke would play a role in the pathogenesis of CPSP.

Pain, depression, and quality of life in adults with MOG-antibody-associated disease

BACKGROUND AND PURPOSE

Myelin oligodendrocyte glycoprotein-antibody-associated disease (MOGAD) is an inflammatory autoimmune condition of the central nervous system. However, data on pain and depression have remained scarce. The aim of this study was to assess features of chronic pain and depression as well as their impact on health-related quality of life (hr-QoL) in MOGAD.

METHODS

Patients with MOGAD were identified in the Neuromyelitis Optica Study Group registry. Data were acquired by a questionnaire, including clinical, demographic, pain (PainDetect, Brief Pain Inventory-Short Form, McGill Pain Questionnaire-Short Form), depression (Beck Depression Inventory-II), and hr-QoL (Short Form-36 Health Survey) items.

RESULTS

Twenty-two of 43 patients suffered from MOGAD-related pain (11 nociceptive, eight definite neuropathic, three possible neuropathic) and 18 from depression. Patients with neuropathic pain had the highest pain intensity and most profound activities of daily living (ADL) impairment. Fifteen patients reported spasticity-associated pain, including four with short-lasting painful tonic spasms. Later disease onset, profound physical impairment, and depression were associated with chronic pain. Physical QoL was more affected in pain sufferers (p < 0.001) than in pain-free patients, being most severely reduced by neuropathic pain (p = 0.016). Pain severity, visual impairment, and gait impairment independently predicted lower physical QoL. Depression was the only factor reducing mental QoL. Twelve patients still suffering from moderate pain (pain severity 4.6 ± 2.3) received pain medication. Only four out of 10 patients with moderate to severe depression took antidepressants.

CONCLUSIONS

Being highly prevalent, pain and depression strongly affect QoL and ADL in MOGAD. Both conditions remain insufficiently controlled in real-life clinical practice.

Biomarkers for predicting central neuropathic pain occurrence and severity after spinal cord injury: results of a long-term longitudinal study

Central neuropathic pain (CNP) after spinal cord injury (SCI) is debilitating and immensely impacts the individual. Central neuropathic pain is relatively resistant to treatment administered after it develops, perhaps owing to irreversible pathological processes. Although preemptive treatment may overcome this shortcoming, its administration necessitates screening patients with clinically relevant biomarkers that could predict CNP early post-SCI. The aim was to search for such biomarkers by measuring pronociceptive and for the first time, antinociceptive indices early post-SCI. Participants were 47 patients with acute SCI and 20 healthy controls. Pain adaptation, conditioned pain modulation (CPM), pain temporal summation, wind-up pain, and allodynia were measured above, at, and below the injury level, at 1.5 months after SCI. Healthy control were tested at corresponding regions. Spinal cord injury patients were monitored for CNP emergence and characteristics at 3 to 4, 6 to 7, and 24 months post-SCI. Central neuropathic pain prevalence was 57.4%. Central neuropathic pain severity, quality, and aggravating factors but not location somewhat changed over 24 months. Spinal cord injury patients who eventually developed CNP exhibited early, reduced at-level pain adaptation and CPM magnitudes than those who did not. The best predictor for CNP emergence at 3 to 4 and 7 to 8 months was at-level pain adaptation with odds ratios of 3.17 and 2.83, respectively (∼77% probability) and a cutoff value with 90% sensitivity. Allodynia and at-level CPM predicted CNP severity at 3 to 4 and 24 months, respectively. Reduced pain inhibition capacity precedes, and may lead to CNP. At-level pain adaptation is an early CNP biomarker with which individuals at risk can be identified to initiate preemptive treatment.

Modelling at-level allodynia after mid-thoracic contusion in the rat

BACKGROUND

The rat mid-thoracic contusion model has been used to study at-level tactile allodynia, a common type of pain that develops after spinal cord injury (SCI). An important advantage of this model is that not all animals develop hypersensitivity. Therefore, it can be used to examine mechanisms that are strictly related to the development of pain-like behaviour separately from mechanisms related to the injury itself. However, how to separate animals that develop hypersensitivity from those that do not is unclear.

METHODS

The aims of the current study were to identify where hypersensitivity and spasticity develop and use this information to identify metrics to separate animals that develop hypersensitivity from those that do not to study differences in their behaviour. To accomplish these aims, a grid was used to localize hypersensitivity on the dorsal trunk relative to thoracic dermatomes and supraspinal responses to tactile stimulation were tallied. These supraspinal responses were used to develop a hypersensitivity score to separate animals that develop hypersensitivity, or pain-like response to nonpainful stimuli.

RESULTS

Similar to humans, the development of hypersensitivity could occur with the development of spasticity or hyperreflexia. Moreover, the time course and prevalence of hypersensitivity phenotypes (at-, above-, or below level) produced by this model were similar to that observed in humans with SCI.

CONCLUSION

However, the amount of spared spinal matter in the cord did not explain the development of hypersensitivity, as previously reported. This approach can be used to study the mechanisms underlying the development of hypersensitivity separately from mechanisms related to injury alone.

Multimodal sensory evaluation of neuropathic spinal cord injury pain: an experimental study

STUDY DESIGN

An experimental study.

OBJECTIVES

To investigate the changes in somatosensory functions using the combined application of quantitative sensory testing (QST), contact heat-evoked potentials (CHEPs) and laser-evoked potentials (LEPs) studies in individuals with spinal cord injury (SCI) in relation to neuropathic pain (NeP).

SETTING

Centre for Pain Medicine, Swiss Paraplegic Centre, Nottwil, Switzerland.

METHODS

Individuals with SCI were compared: 12 with NeP (SCI NeP) and 12 without NeP (SCI no NeP). Tools used were QST, CHEPs, LEPs and self-reported questionnaires. Tests were applied to the control (hand) and test (dermatome of altered sensation) sites, and compared to the able-bodied group.

RESULTS

QST, LEPs and CHEPs assessments showed abnormalities both on the test and control sites, which did not differ between the groups with SCI. QST showed higher prevalence of allodynia in SCI NeP. CHEPs and LEPs demonstrated diminished amplitudes in both groups with SCI in comparison to able-bodied individuals. Only reaction time (RT) analysis revealed the difference of SCI NeP from the other two groups, expressed in partially preserved responses to the laser C-fibre stimulations.

CONCLUSIONS

Combination of assessments in our study allowed to examine spinothalamic and dorsal column functions in individuals with SCI. Changes in QST, CHEPs and LEPs were detected below the level of injury independent of NeP and at the control site indicating modifications in sensory processing rostral to the spinal lesion. Analysis of RT during laser stimulation could be an essential component when evaluating the somatosensory functions related to NeP in persons with SCI.

Poststroke Pain

Pain is common but often underrecognized after stroke. Poststroke pain (PSP) hinders recovery, impairs quality of life, and is associated with the psychological state of patients with stroke. The most common subtypes of PSP include central PSP, complex regional pain syndrome, shoulder pain, spasticity-related pain, and headache. The pathophysiologies of these PSP subtypes are not yet clearly understood, and PSP is refractory to conventional treatment in many patients. However, recent studies have proposed potential pathophysiologies of PSP subtypes, which may help prioritize therapies that target specific mechanisms.

Tissue bridges predict neuropathic pain emergence after spinal cord injury

OBJECTIVE

To assess associations between preserved spinal cord tissue quantified by the width of ventral and dorsal tissue bridges and neuropathic pain development after spinal cord injury.

METHODS

This retrospective longitudinal study includes 44 patients (35 men; mean (SD) age, 50.05 (18.88) years) with subacute (ie, 1 month) spinal cord injury (25 patients with neuropathic pain, 19 pain-free patients) and neuroimaging data who had a follow-up clinical assessment at 12 months. Widths of tissue bridges were calculated from midsagittal T2-weighted images and compared across groups. Regression analyses were used to identify relationships between these neuroimaging measures and previously assessed pain intensity and pin-prick score.

RESULTS

Pin-prick score of the 25 patients with neuropathic pain increased from 1 to 12 months (Δmean=10.08, 95% CI 2.66 to 17.50, p=0.010), while it stayed similar in pain-free patients (Δmean=2.74, 95% CI -7.36 to 12.84, p=0.576). They also had larger ventral tissue bridges (Δmedian=0.80, 95% CI 0.20 to 1.71, p=0.008) at 1 month when compared with pain-free patients. Conditional inference tree analysis revealed that ventral tissue bridges' width (≤2.1 or >2.1 mm) at 1 month is the strongest predictor for 12 months neuropathic pain intensity (1.90±2.26 and 3.83±1.19, p=0.042) and 12 months pin-prick score (63.84±28.26 and 92.67±19.43, p=0.025).

INTERPRETATION

Larger width of ventral tissue bridges-a proxy for spinothalamic tract function-at 1 month post-spinal cord injury is associated with the emergence and maintenance of neuropathic pain and increased pin-prick sensation. Spared ventral tissue bridges could serve as neuroimaging biomarkers of neuropathic pain and might be used for prediction and monitoring of pain outcomes and stratification of patients in interventional trials.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

Electrical Thalamic Stimulation in the Anterior Part of the Ventral Posterolateral Nucleus for the Treatment of Patients With Central Poststroke Pain

OBJECTIVES

The effects of thalamic stimulation of the anterior part of the ventral posterolateral nucleus (VPLa) for central poststroke pain (CPSP) and the pain-related electrophysiological characteristics of this structure were investigated.

MATERIALS AND METHODS

Nine patients with CPSP manifesting as hemibody pain were enrolled. Stereotactic thalamic VPLa stimulation was implemented, and intraoperative electrophysiological studies on hyperactive and unstable discharges (HUDs) and responses to sensory and electrical stimulation were performed in the sensory thalamus. A preoperative somatosensory-evoked potential (SEP) study was carried out in all nine patients and in eight other patients with localized pain.

RESULTS

The patients were classified into two groups: a HUD-dominant group (group H, n = 5) and a sensory response-dominant group (group R, n = 4). HUDs were frequently encountered in the thalamic VPLa in the former group. The total number of HUDs and the number along the trajectory to the VPLa in group H were significantly larger than those in group R. The improvements on the pain numeric rating scale in group H were significantly higher than those in group R two years after surgery. The amplitude ratio of the SEP N20s in the ipsilateral to the contralateral side of CVD lesion in the study group was significantly lower than in the localized pain group.

CONCLUSIONS

Adequate and stable pain relief with thalamic VPLa stimulation is obtainable in patients with CPSP who exhibit hyperactivity and electrical instability along the trajectory to this nucleus. Both responders and nonresponders were found to have severe dysfunction of the lemniscal system.

Metabolites of neuroinflammation relate to neuropathic pain after spinal cord injury

OBJECTIVE

To determine whether cervical cord levels of metabolites are associated with pain sensation after spinal cord injury (SCI) by performing magnetic resonance spectroscopy in patients with SCI with and without neuropathic pain (NP).

METHODS

Cervical cord single-voxel spectroscopic data of 24 patients with SCI (14 with NP, 10 pain-free) and 21 healthy controls were acquired at C2/3 to investigate metabolite ratios associated with neuroinflammation (choline-containing compounds to myoinositol [tCho/mI]) and neurodegeneration (total N-acetylaspartate to myo-inositol [tNAA/mI]). NP levels were measured, and Spearman correlation tests assessed associations between metabolite levels, cord atrophy, and pinprick score.

RESULTS

In patients with NP, tCho/mI levels were increased (p = 0.024) compared to pain-free patients and negatively related to cord atrophy (p = 0.006, r = 0.714). Better pinprick score was associated with higher tCho/mI levels (p = 0.032, r = 0.574). In pain-free patients, tCho/mI levels were not related to cord atrophy (p = 0.881, r = 0.055) or pinprick score (p = 0.676, r = 0.152). tNAA/mI levels were similar in both patient groups (p = 0.396) and were not associated with pinprick score in patients with NP (p = 0.405, r = 0.242) and pain-free patients (p = 0.117, r = 0.527).

CONCLUSIONS

Neuroinflammatory metabolite levels (i.e., tCho/mI) were elevated in patients with NP, its magnitude being associated with less cord atrophy and greater pain sensation (e.g., pinprick score). This suggests that patients with NP have more residual spinal tissue and greater metabolite turnover than pain-free patients. Neurodegenerative metabolite levels (i.e., tNAA/mI) were associated with greater cord atrophy but unrelated to NP. Identifying the metabolic NP signature provides new NP treatment targets and could improve patient stratification in interventional trials.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that levels of magnetic resonance spectroscopy-identified metabolites of neuroinflammation were elevated in patients with SCI with NP compared to those without NP.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

Central Nervous System Reorganization and Pain After Spinal Cord Injury: Possible Targets for Physical Therapy-A Systematic Review of Neuroimaging Studies

BACKGROUND

Pain is one of the main symptoms associated with spinal cord injury (SCI) and can be associated with changes to the central nervous system (CNS).

PURPOSE

This article provides an overview of the evidence relating to CNS changes (structural and functional) associated with pain in SCIs.

DATA SOURCES

A systematic review was performed, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, on PubMed, Embase, and Web of Science in March 2018.

STUDY SELECTION

Studies were selected if they concerned changes in the CNS of patients with SCI, regardless of the type of imagery.

DATA EXTRACTION

Data were extracted by 2 blinded reviewers.

DATA SYNTHESIS

There is moderate evidence for impaired electroencephalographic function and metabolic abnormalities in the anterior cingulate in patients experiencing pain. There is preliminary evidence that patients with pain have morphological and functional changes to the somatosensory cortex and alterations to thalamic metabolism. There are conflicting data regarding the relationships between lesion characteristics and pain. In contrast, patients without pain can display protective neuroplasticity.

LIMITATIONS AND CONCLUSION

Further studies are required to elucidate fully the relationships between pain and neuroplasticity in patients with SCIs. However, current evidence might support the use of physical therapist treatments targeting CNS plasticity in patients with SCI pain.

An unusual presentation of neuropathic pain following cervical spinal cord injury: a case report

Background

We report a patient with unusual occipital neuropathic pain (at-level neuropathic pain) due to a small central cervical spinal cord injury (SCI).

Case presentation

A 50-year-old man presented with severe bilateral occipital pain after falling from a height of 2 m, 2 weeks ago. The degree of pain was evaluated to be 9 out of 10 using the numeric rating scale (NRS). The nature of the pain was tingling, burning, and piercing, and hyperalgesia was present over the bilateral posterior head regions. Greater occipital nerve block with bupivacaine and dexamethasone was not effective. On axial T2-cervical magnetic resonance imaging (MRI), a focal high signal change was observed in the central portion of the spinal cord at the C2 level. We deliberated that the patient’s pain was due to the SCI observed on MRI, and after administration of oral medications, the NRS pain score reduced from 9 to 2.

Conclusions

Neuropathic pain caused by SCI varies according to the location and degree of injury of the pain-related neural tracts; therefore, clinicians should closely observe the pain patterns and findings on imaging in patients with SCI to determine the cause of pain accurately.

Preserved somatosensory conduction in complete spinal cord injury: Discomplete SCI

OBJECTIVE

Spinal cord injury (SCI) disrupts the communication between brain and body parts innervated from below-injury spinal segments, but rarely results in complete anatomical transection of the spinal cord. The aim of this study was to investigate residual somatosensory conduction in clinically complete SCI, to corroborate the concept of sensory discomplete SCI.

METHODS

We used fMRI with a somatosensory protocol in which blinded and randomized tactile and nociceptive stimulation was applied on both legs (below-injury level) and one arm (above-injury level) in eleven participants with chronic complete SCI. The experimental design accounts for possible confounding mechanical (e.g. vibration) and cortico-cortical top-down mechanisms (e.g. attention/expectation).

RESULTS

Somatosensory stimulation on below-level insensate body regions activated the somatotopically corresponding part of the contralateral primary somatosensory cortex in six out of eleven participants.

CONCLUSIONS

Our results represent afferent-driven cortical activation through preserved somatosensory connections to the brain in a subgroup of participants with clinically complete SCI, i.e. sensory discomplete SCI.

SIGNIFICANCE

Identifying patients with residual somatosensory connections might open the door for new rehabilitative and restorative strategies as well as inform research on SCI-related conditions such as neuropathic pain and spasticity.

Skilled reaching deterioration contralateral to cervical hemicontusion in rats is reversed by pregabalin treatment conditional upon its early administration

Introduction

Gabapentinoids are first-line treatments for painful traumatic and nontraumatic central nervous system disorders. Evidence from a large human study suggests that early use of gabapentinoids after spinal cord injury improves motor scores. The underlying mechanism is unknown.

Objectives

We sought to examine the effects of early pregabalin (PGB, a gabapentinoid) treatment on performance in a fine motor task (skilled reaching) after cervical hemicontusion. We also asked whether early PGB administration affected PGB responsiveness later on.

Methods

Rats received C4/5 cervical hemicontusions. Injury severities ranged from 80 to 150 kdyn. We monitored evidence of skin irritation (peri-incisional and elsewhere) and quantified food pellet retrieval using the Montoya staircase test. Behaviours were assessed in rats receiving early (for 3 weeks from injury induction) and/or late (resuming or beginning at week 8) PGB treatment in animals with 150-kdyn injuries.

Results

Contralateral skilled reaching waned in control animals with 150-kdyn injuries. This was prevented in animals, which received early PGB as long as treatment continued. Deterioration of skilled reaching was reversed by later (week 8) PGB only in animals that had received early treatment. Ipsilateral reaching impairment was not improved by PGB. Relief of skin irritation verified early PGB efficacy.

Conclusion

Hemicontusive spinal cord injury produces a contralateral motor phenotype evocative of on-going neuropathic pain. Early PGB preserves sensitivity to subsequent PGB treatment, indicating that motor function is impaired by neuropathic pain and can be improved indirectly by early PGB administration. Direct effects of PGB on motor circuitry cannot be excluded but are not supported by our data.

Pathophysiology of Central Poststroke Pain

Background and Purpose—

Central poststroke pain (CPSP) is a disabling condition in stroke patients, and evidence suggests that altered corticospinal and motor intracortical excitability occurs in neuropathic pain. The objective of this study was to investigate changes in motor cortex excitability and sensorimotor interaction and their correlates with clinical manifestations and alterations in somatosensory systems in CPSP patients.

Methods—

Fourteen patients with CPSP but no motor weakness were compared with age- and sex-matched healthy controls for motor cortex excitability and sensorimotor interaction assessed by transcranial magnetic stimulation to measure resting motor thresholds, short-interval intracortical inhibition, intracortical facilitation, and afferent inhibitions. The sensory pathway was evaluated by quantitative sensory testing, contact heat evoked potential, and somatosensory evoked potentials. Clinical pain and quality of life were assessed with validated tools.

Results—

The duration of CPSP was 3.3±3.0 years (ranging 0.5–10 years), and pain significantly impaired quality of life. Compared with the unaffected hemisphere, the stroke hemisphere had higher thermal thresholds, lower contact heat evoked potential amplitudes, and prolonged cortical somatosensory evoked potential latencies. There was no difference in resting motor thresholds between the stroke and unaffected hemisphere or between patients and controls. CPSP patients had a reduction in short-interval intracortical inhibition in the stroke hemisphere compared with that in the unaffected hemispheres of patients and controls. No changes were noted in afferent inhibitions between the stroke and unaffected hemispheres. The short-interval intracortical inhibition of the stroke hemisphere was negatively correlated with self-rated health on a visual analog scale and positively correlated with cortical somatosensory evoked potential latencies.

Conclusions—

CPSP patients with intact corticospinal tracts showed reduced motor intracortical inhibition in the stroke hemisphere, suggesting defective gamma-aminobutyric acid-ergic inhibition. This disinhibition was associated with impaired quality of life and was related to dorsal column–medial lemniscus pathway dysfunction.

Mechanisms of Below-Level Pain Following Spinal Cord Injury (SCI)

Mechanisms of below-level pain are discoverable as neural adaptations rostral to spinal injury. Accordingly, the strategy of investigations summarized here has been to characterize behavioral and neural responses to below-level stimulation over time following selective lesions of spinal gray and/or white matter. Assessments of human pain and the pain sensitivity of humans and laboratory animals following spinal injury have revealed common disruptions of pain processing. Interruption of the spinothalamic pathway partially deafferents nocireceptive cerebral neurons, rendering them spontaneously active and hypersensitive to remaining inputs. The spontaneous activity among these neurons is disorganized and unlikely to generate pain. However, activation of these neurons by their remaining inputs can result in pain. Also, injury to spinal gray matter results in a cascade of secondary events, including excitotoxicity, with rostral propagation of excitatory influences that contribute to chronic pain. Establishment and maintenance of below-level pain results from combined influences of injured and spared axons in the spinal white matter and injured neurons in spinal gray matter on processing of nociception by hyperexcitable cerebral neurons that are partially deafferented. A model of spinal stenosis suggests that ischemic injury to the core spinal region can generate below-level pain. Additional questions are raised about demyelination, epileptic discharge, autonomic activation, prolonged activity of C nocireceptive neurons, and thalamocortical plasticity in the generation of below-level pain. PERSPECTIVE: An understanding of mechanisms can direct therapeutic approaches to prevent development of below-level pain or arrest it following spinal cord injury. Among the possibilities covered here are surgical and other means of attenuating gray matter excitotoxicity and ascending propagation of excitatory influences from spinal lesions to thalamocortical systems involved in pain encoding and arousal.

Diffusional plasticity induced by electroacupuncture intervention in rat model of peripheral nerve injury

Electroacupuncture (EA) is an adjuvant therapy for peripheral nerve injury (PNI). Both peripheral and central alterations contribute to the rehabilitation process. We employed diffusion tensor imaging (DTI) to investigate the diffusion plasticity of afferent and efferent pathways caused by EA in model of peripheral nerve injury and reparation. Twenty-four rats were divided into three groups: normal group, model group and intervention group. Rats of the model group and the intervention group underwent sciatic nerve transection and anastomosis. EA intervention was performed on the intervention group at ST-36 and GB-30 for three months. Gait assessment and DTI were conducted at days post-operative (DPO) 30, 60 and 90. We selected corticospinal tract, spinothalamic tract and internal capsule as regions of interest and analyzed diffusion metrics including fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). FA values and RD values displayed significant differences or obvious tendency while AD values maintained a stable level. RD values displayed better indicative performance than FA in internal capsule. The intervention group presented significant correlation between RD values and Regularity Index (RI) during the intervention period. The effect of EA on peripheral nerve injury repairing rats appeared to be accelerated recovery process of sensory and motor neural pathway. We proposed that RD was a potential in vivo indicator for structural plasticity caused by EA and PNI.

Uncovering the Cells and Circuits of Touch in Normal and Pathological Settings

The sense of touch is fundamental as it provides vital, moment-to-moment information about the nature of our physical environment. Primary sensory neurons provide the basis for this sensation in the periphery; however, recent work demonstrates that touch transduction mechanisms also occur upstream of the sensory neurons via non-neuronal cells such as Merkel cells and keratinocytes. Within the spinal cord, deep dorsal horn circuits transmit innocuous touch centrally and also transform touch into pain in the setting of injury. Here non-neuronal cells play a key role in the induction and maintenance of persistent mechanical pain. This review highlights recent advances in our understanding of mechanosensation, including a growing appreciation for the role of non-neuronal cells in both touch and pain.

Application of electrophysiological measures in spinal cord injury clinical trials: a narrative review

STUDY DESIGN

Narrative review.

OBJECTIVES

To discuss how electrophysiology may contribute to future clinical trials in spinal cord injury (SCI) in terms of: (1) improvement of SCI diagnosis, patient stratification and determination of exclusion criteria; (2) the assessment of adverse events; and (3) detection of therapeutic effects following an intervention.

METHODS

An international expert panel for electrophysiological measures in SCI searched and discussed the literature focused on the topic.

RESULTS

Electrophysiology represents a valid method to detect, track, and quantify readouts of nerve functions including signal conduction, e.g., evoked potentials testing long spinal tracts, and neural processing, e.g., reflex testing. Furthermore, electrophysiological measures can predict functional outcomes and thereby guide rehabilitation programs and therapeutic interventions for clinical studies.

CONCLUSION

Objective and quantitative measures of sensory, motor, and autonomic function based on electrophysiological techniques are promising tools to inform and improve future SCI trials. Complementing clinical outcome measures, electrophysiological recordings can improve the SCI diagnosis and patient stratification, as well as the detection of both beneficial and adverse events. Specifically composed electrophysiological measures can be used to characterize the topography and completeness of SCI and reveal neuronal integrity below the lesion, a prerequisite for the success of any interventional trial. Further validation of electrophysiological tools with regard to their validity, reliability, and sensitivity are needed in order to become routinely applied in clinical SCI trials.

White matter hyperintensities are related to pain intensity in an outpatient memory clinic population: preliminary findings

Background: The association between pain and dementia is complicated and may depend on underlying brain pathology. It was hypothesized that both medial temporal atrophy (MTA) and global cortical atrophy (GCA) predicted no/mild pain, while white matter hyperintensities (WMH) predicted moderate/severe pain.

Objectives: To study the association between pain intensity and measures of brain pathology, more specifically MTA, GCA, and WMH.

Methods: In total, 115 consecutive patients visiting an outpatient memory clinic were included. In total, diagnoses included dementia (N=70), mild cognitive impairment (N=30), and subjective cognitive impairment (N=15). Without administering stimuli, pain intensity was assessed with the Brief Pain Inventory. MTA, GCA, and WMH were measured with a MRI visual rating scale. Logistic regression analyses to examine the relationship between WMH, MTA, GCA, and self-reported pain intensity (no/mild pain versus moderate/severe pain) were adjusted for confounders.

Results: Mean age of the patients was 81 years (IQR: 78–85, 53% female). Moderate/severe pain was reported by 23.5% and associated with greater WMH (OR =3.34, 95% CI =1.01–10.97, p=0.047), but not MTA or GCA.

Conclusions: In contrast to the present results, earlier studies have reported either a positive or negative relationship between pain and brain volume. It is suggested that the presence of dementia may explain the absence of a relationship between pain and brain volume. WMH is positively related with pain in an older memory outpatient population. Considering the small sample size, our findings should be interpreted with caution. Hence, our conclusions are preliminary findings, warranting future replication.