Neuropathic pain modulation after spinal cord injury by breathing-controlled electrical stimulation (BreEStim) is associated with restoration of autonomic dysfunction

Complement Receptor 3 Pathway and NMDA Receptor 2B Subunit Involve Neuropathic Pain Associated with Spinal Cord Injury

Background

Neuropathic pain (NP) after spinal cord injury (SCI-evoked NP) is clinically challenging; the underlying mechanisms are not fully understood, leading to a lack of promising treatment options. NP occurs in only a subset of patients with SCI. The injured spinal cord exhibits a series of histopathological changes, and the complement system has been shown to play an important role in these processes. In addition, NMDA receptor subunit 2B (NR2B) is involved in the development and maintenance of NP. This preliminary study was performed to investigate the correlations of the complement receptor 3/complement component 3 (CR3/C3) pathway and NR2B with SCI-evoked NP.

Methods

A trauma-induced SCI animal model was established and SCI-evoked NP was evaluated by behavioural analysis. Transcriptome analysis was performed to identify genes in the CR3/C3 pathway related to synaptic modification, while the expression and distribution of NR2B in the injured spinal cord, and the relation to NP, were examined by immunohistochemical analysis.

Results

Nine of seventeen SCI rats (52.9%) developed NP. C3 mRNA expression was significantly decreased in SCI-evoked NP rats and significantly increased in the non-NP SCI rats. C1q mRNA and CR3 mRNA expression were significantly increased in all SCI rats, but higher levels of expression were observed in the non-NP SCI rats. NR2B mRNA expression was significantly increased in the SCI-evoked NP rats and significantly decreased in the non-NP SCI rats. In addition, significantly elevated expression of NR2B-positive cells was seen in lamina II of the superficial dorsal horn in SCI-evoked NP rats in comparison with non-NP SCI rats.

Conclusion

NP occurred in only a subset of SCI rats, and the CR3/C3 pathway and NR2B were involved in SCI-evoked NP. Further studies are required to determine the mechanisms underlying the SCI-evoked NP associated with the CR3/C3 pathway and NR2B.

Central Neuropathic Pain Syndromes: Current and Emerging Pharmacological Strategies

Central neuropathic pain is caused by a disease or lesion of the brain or spinal cord. It is difficult to predict which patients will develop central pain syndromes after a central nervous system injury, but depending on the etiology, lifetime prevalence may be greater than 50%. The resulting pain is often highly distressing and difficult to treat, with no specific treatment guidelines currently available. This narrative review discusses mechanisms contributing to central neuropathic pain, and focuses on pharmacological approaches for managing common central neuropathic pain conditions such as central post-stroke pain, spinal cord injury-related pain, and multiple sclerosis-related neuropathic pain. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, and gabapentinoids have some evidence for efficacy in central neuropathic pain. Medications from other pharmacologic classes may also provide pain relief, but current evidence is limited. Certain non-pharmacologic approaches, neuromodulation in particular, may be helpful in refractory cases. Emerging data suggest that modulating the primary afferent input may open new horizons for the treatment of central neuropathic pain. For most patients, effective treatment will likely require a multimodal therapy approach.

The CanPain SCI clinical practice guidelines for rehabilitation management of neuropathic pain after spinal cord injury: 2021 update

STUDY DESIGN

Clinical practice guidelines.

OBJECTIVES

The objective was to update the 2016 version of the Canadian clinical practice guidelines for the management of neuropathic pain in people with spinal cord injury (SCI).

SETTING

The guidelines are relevant for inpatient, outpatient and community SCI rehabilitation settings in Canada.

METHODS

The guidelines were updated in accordance with the Appraisal of Guidelines for Research and Evaluation II tool. A Steering Committee and Working Group reviewed the relevant evidence on neuropathic pain management (encompassing screening and diagnosis, treatment and models of care) after SCI. The quality of evidence was scored using Grading of Recommendations Assessment, Development and Evaluation (GRADE). A consensus process was followed to achieve agreement on recommendations and clinical considerations.

RESULTS

The working group identified and reviewed 46 additional relevant articles published since the last version of the guidelines. The panel agreed on 3 new screening and diagnosis recommendations and 8 new treatment recommendations. Two key changes to these treatment recommendations included the introduction of general treatment principles and a new treatment recommendation classification system. No new recommendations to model of care were made.

CONCLUSIONS

The CanPainSCI recommendations for the management of neuropathic pain after SCI should be used to inform practice.

Central Neuropathic Mechanisms in Pain Signaling Pathways: Current Evidence and Recommendations

Purpose

This is a comprehensive review of the current literature on central neuropathic pain mechanisms that is secondary to spinal cord injury. It reviews recent and seminal findings on the pathophysiology, diagnosis, and treatment and compares treatment options and recommendations.

Recent Findings

Neuropathic pain (NP) is a common complication of spinal cord injury (SCI). Chronicity of NP is attributed to increased abundance of inflammatory mediators and ion channel dysfunction leading to afferent nerve sensitization; nerve damage and nerve–glia cross talk have also been implicated. Conventional treatment is medical and has had limited success. Recent studies have made headway in identifying novel biomarkers, including microRNA and psychosocial attributes that can predict progress from SCI to chronic NP (CNP). Recent advances have provided evidence of efficacy for two promising drugs. Baclofen was able to provide good, long-lasting pain relief. Ziconotide, a voltage-gated calcium channel blocker, was studied in a small trial and was able to provide good analgesia in most participants. However, several participants had to be withdrawn because of worrisome creatine phosphokinase (CPK) elevations, and further studies are required to define its safety profile. Non-medical interventions include brain sensitization and biofeedback techniques. These methods have recently had encouraging results, albeit preliminary. Case reports of non-conventional techniques, such as hypnosis, were also reported.

Summary

CNP is a common complication of SCI and is a prevalent disorder with significant morbidity and disability. Conventional medical treatment is limited in efficacy. Recent studies identified baclofen and ziconotide as possible new therapies, alongside non-medical interventions. Further research into the pathophysiology is required to identify further therapy candidates. A multidisciplinary approach, including psychosocial support, medical and non-medical interventions, is likely needed to achieve therapeutic effects in this difficult to treat syndrome.

Observations of Autonomic Variability Following Central Neuromodulation for Chronic Neuropathic Pain in Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) persons with chronic neuropathic pain (NP) demonstrate maladaptive autonomic profiles compared to SCI counterparts without NP (SCI - NP) or able-bodied (AB) controls. These aberrations may be secondary to maladaptive neuroplasticity in the shared circuitry of the pain neuromatrix-central autonomic network interface (PNM-CAN). In this study, we explored the proposed PNM-CAN mechanism in SCI + NP and AB cohorts following centrally-directed neuromodulation to assess if the PNM and CAN are capable of being differentially modulated.

MATERIALS AND METHODS

Central neuromodulation was administered via breathing-controlled electrical stimulation (BreEStim), previously evidenced to operate at the PNM. To quantify CAN activity, conventional heart rate variability (HRV) recordings were used to gather time and frequency domain parameters of autonomic modulation. SCI + NP (n = 10) and AB (n = 13) cohorts received null and active BreEStim randomly in crossover fashion. HRV data were gathered pretest and 30 minutes posttest. Pain modulation was quantified at both time-points by visual analog scale (VAS) for SCI + NP persons and electrical detection and pain threshold levels (EDT, EPT) for AB persons.

RESULTS

Following active BreEStim only, SCI + NP persons demonstrated increased parasympathetic tone (increased NN50, p = 0.03, and pNN50, p = 0.02, HRV parameters). This parasympathetic restoration was associated with analgesia (VAS reduction, p < 0.01). Similarly, AB persons demonstrated increased noxious tolerance (increased EPT, p = 0.03, with preserved EDL, p = 0.78) only following active BreEStim. However, this increased pain threshold was not associated with autonomic changes.

CONCLUSIONS

Central modulation targeting the PNM produced autonomic changes in SCI + NP persons but not AB persons. These findings suggest that AB persons exhibit intact CAN mechanisms capable of compensating for PNM aberrations or simply that SCI + NP persons exhibit altered PNM-CAN machinery altogether. Our collective findings confirm the interconnectedness and maladaptive plasticity of PNM-CAN machinery in SCI + NP persons and suggest that the PNM and CAN circuitry can be differentially modulated.

Heart rate variability in spinal cord injury: Asymptomatic orthostatic hypotension is a confounding variable

STUDY DESIGN

observational study.

OBJECTIVES

Heart rate variability (HRV) studies have shown that the low-frequency (LF) domain is decreased in postural challenge of spinal cord injury (SCI). However, there are inconsistencies in the literature regarding HRV with postural challenge. We believed that asymptomatic orthostatic hypotension (OH) may contribute to the discrepancies in the literature. We also evaluated the time-domain parameters of HRV to evaluate for changes in SCI postural challenge. We looked at the association of Frequency and Time-domain HRV parameters to blood pressure (BP) and postural challenge in SCI based on groups with and without OH.

SETTING

SCI clinic.

METHODS

Patients from SCI clinic were enrolled and 5-minute electrocardiogram (ECG) recordings were performed before and after a postural challenge from supine to sitting position with blood pressure (BP) recordings at each time point. Between and within group analyses were performed based on tetraplegia, paraplegia, and the presence of asymptomatic OH.

RESULTS

There were 6 controls and 18 SCI subjects, 4 with OH based on change in diastolic BP. After postural challenge, mean heart rate was lower in tetraplegia compared to controls in all groupings. When OH was removed from the groups, total power was consistently reduced in tetraplegia compared to paraplegia across all positions. There were both time- and frequency-domain differences observed in SCI with OH compared to SCI without.

CONCLUSIONS

Autonomic variability is increased in SCI with OH and can lead to misinterpretation of findings if asymptomatic OH is included in samples. Our data suggest that there are frequency- and time-domain differences in HRV variables in those with OH compared to those without. Future HRV studies should account for asymptomatic OH and include analyses of the time-domain variables in postural challenge of SCI.