The influence of High Dose Spinal Cord Stimulation on the descending pain modulatory system in patients with failed back surgery syndrome

Effect of neuromodulation for chronic pain on the autonomic nervous system: a systematic review

Background

In recent years, there has been a growing interest in the use of neuromodulation as an alternative treatment option for chronic pain. Neuromodulation techniques, such as spinal cord stimulation (SCS), dorsal root ganglion (DRG) stimulation, deep brain stimulation (DBS), and peripheral nerve stimulation, have shown promising results in the management of various chronic pain conditions and involve targeted modulation of neural activity to alleviate pain and restore functional capacity. The autonomic nervous system (ANS) plays a crucial role in the regulation of various bodily functions including pain perception. However, the effects of neuromodulation on the ANS in the context of chronic pain remain poorly understood. This systematic review aimed to comprehensively assess the existing literature about the effects of neuromodulation on the ANS in chronic pain settings.

Methods

Searches were conducted using four electronic databases (PubMed, EMBASE, SCOPUS, and Web of Science). The study protocol was registered before initiation of the review process. The Office of Health Assessment and Translation (OHAT) Risk of Bias tool was used to evaluate risk of bias.

Results

A total of 43 studies were included, of which only one was an animal study. Several studies have reported more than one outcome parameter in the same population of chronic pain patients. Cardiovascular parameters were the most frequently used outcomes. More specifically, 18 outcome parameters were revealed to evaluate the function of the ANS, namely heart rate variability (n=17), arterial blood pressure (n=15), tissue oxygenation/perfusion (n=5), blood markers (n=6), multiunit postganglionic sympathetic nerve activity (n=4), skin temperature (n=3), skin conductance (n=3), cephalic autonomic symptoms (n=2), ventilatory frequency (n=2), vasomotor tone (n=1), baroreflex sensitivity (n=1), sympathetic innervation of the heart, neural activity of intrinsic cardiac neurons (n=1), vascular conductance (n=1), arterial diameter (n=1), blood pulse volume (n=1), and vagal efficiency (n=1). Most studies evaluated SCS (62.79%), followed by DBS (18.6%), peripheral nerve stimulation (9.3%), DRG stimulation (4.65%), and vagus nerve stimulation (4.65%). Overall, inconsistent results were revealed towards contribution of SCS, DBS, and peripheral nerve stimulation on ANS parameters. For DRG stimulation, included studies pointed towards a decrease in sympathetic activity.

Conclusions

There are indications that neuromodulation alters the ANS, supported by high or moderate confidence in the body of evidence, however, heterogeneity in ANS outcome measures drives towards inconclusive results. Further research is warranted to elucidate the indirect or direct mechanisms of action on the ANS, with a potential benefit for optimisation of patient selection for these interventions.

Systematic review protocol

PROSPERO (CRD42021297287).

Distinct Functional Connectivity Patterns for Intermittent Vs Constant Neuropathic Pain Phenotypes in Persistent Spinal Pain Syndrome Type 2 Patients

Background

Chronic low back pain (cLBP) has been associated with alterations in brain functional connectivity (FC) but based upon heterogeneous populations and single network analyses. Our goal is to study a more homogeneous cLBP population and focus on multiple cross-network (CN) connectivity analysis. We hypothesize that within this population: 1) altered CN FC, involving emotion and reward/aversion functions are related to their pain levels and 2) altered relationships are dependent upon pain phenotype (constant neuropathic vs intermittent pain).

Methods

In this case series, resting state fcMRI scans were obtained over a study duration of 60 months from 23 patients (13 constant neuropathic and 10 intermittent pain) with Persistent Spinal Pain Syndrome (PSPS Type 2) being considered for spinal cord stimulation (SCS) therapy at a single academic center. Images were acquired using a Discovery MR750 GE scanner. During the resting state acquisitions, they were asked to close their eyes and relax. The CN analysis was performed on 7 brain networks and compared to age-matched controls. Linear regression was used to test the correlation between CN connectivity and pain scores.

Results

CN FC involving emotion networks (STM: striatum network index) was significantly lower than controls in all patients, regardless of pain phenotype (P < 0.003). Pain levels were positively correlated with emotional FC for intermittent pain but negatively correlated for constant pain.

Conclusion

This is the first report of 1) altered CN FC involving emotion/reward brain circuitry in 2) a homogeneous population of cLBP patients with 3) two different pain phenotypes (constant vs intermittent) in PSPS Type 2 patients being considered for SCS. FC patterns were altered in cLBP patients as compared to controls and were characteristic for each pain phenotype. These data support fcMRI as a potential and objective tool in assessing pain levels in cLBP patients with different pain phenotypes.

Effect of acupuncture versus usual care on sleep quality in cancer survivors with chronic pain: Secondary analysis of a randomized clinical trial

BACKGROUND

Chronic pain negatively affects sleep; it is unclear whether pain relief from acupuncture contributes to sleep quality improvements in cancer survivors. This study aimed to evaluate the effect of acupuncture versus usual care on sleep quality among cancer survivors with comorbid sleep disturbance and chronic musculoskeletal pain.

METHODS

Sleep outcome data from the Personalized Electroacupuncture Versus Auricular Acupuncture Comparative Effectiveness (PEACE) randomized clinical trial were analyzed. Electroacupuncture or auricular acupuncture was compared with usual care for sleep quality improvement over 10 weeks of treatment among cancer survivors with clinically significant sleep disturbance and chronic musculoskeletal pain at baseline. Sleep quality was measured with the Pittsburgh Sleep Quality Index (PSQI) global score.

RESULTS

Among 268 participants (mean [standard deviation (SD)] age, 61.4 [12.6] years; 191 women [71.3%]; mean [SD] baseline PSQI global score, 10.3 [3.3] points), electroacupuncture and auricular acupuncture resulted in greater reductions in the PSQI global score from baseline to 10 weeks in comparison with usual care: 1.42 points (95% confidence interval [CI], 0.45-2.38; p = .004) and 1.59 points (95% CI, 0.62-2.55; p = .001), respectively. The improvement in sleep quality for the acupuncture groups was sustained for 24 weeks from randomization. Furthermore, a greater proportion of patients in the electroacupuncture and auricular acupuncture groups had clinically meaningful improvement in sleep quality compared to the usual care group (41.0% and 42.9% vs. 21.4%; p = .044).

CONCLUSIONS

Among cancer survivors with comorbid sleep disturbance and chronic pain, electroacupuncture and auricular acupuncture produced a clinically relevant and persistent improvement in sleep quality. These findings suggest that acupuncture may be an evidence-based nonpharmacologic intervention to improve sleep health for cancer survivors with pain.

PLAIN LANGUAGE SUMMARY

This study analyzed the sleep quality data from a published randomized clinical trial that evaluated the effect of electroacupuncture or auricular acupuncture versus usual care on pain relief among people who survived cancer. This analysis included a prespecified subgroup of 268 participants with co-occurring sleep disturbance and chronic musculoskeletal pain at baseline and found that patients who used acupuncture for pain relief demonstrated greater improvements in sleep quality compared with patients who received usual care. Sleep quality improvement by acupuncture was sustained after the treatment ended.

Case report: Utilizing diffusion-weighted MRI on a patient with chronic low back pain treated with spinal cord stimulation

Diffusion-weighted magnetic resonance imaging (dwMRI) has increasingly demonstrated greater utility in analyzing neuronal microstructure. In patients with chronic low back pain (cLBP), using dwMRI to observe neuronal microstructure can lead to non-invasive biomarkers which could provide clinicians with an objective quantitative prognostic tool. In this case report, we investigated dwMRI for the development of non-invasive biomarkers by conducting a region-based analysis of a 55-year-old male patient with failed back surgery syndrome (FBSS) treated with spinal cord stimulation (SCS). We hypothesized that dwMRI could safely generate quantitative data reflecting cerebral microstructural alterations driven by neuromodulation. Neuroimaging was performed at 6- and 12- months post-SCS implantation. The quantitative maps generated included diffusion tensor imaging (DTI) parameters; fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) computed from whole brain tractography. To examine specific areas of the brain, 44 regions of interest (ROIs), collectively representing the pain NeuroMatrix, were extracted and registered to the patient's diffusion space. Average diffusion indices were calculated from the ROIs at both 6- and 12- months. Regions with >10% relative change in at least 3 of the 4 maps were reported. Using this selection criterion, 8 ROIs demonstrated over 10% relative changes. These ROIs were mainly located in the insular gyri. In addition to the quantitative data, a series of questionnaires were administered during the 6- and 12-month visits to assess pain intensity, functional disability, and quality of life. Overall improvements were observed in these components, with the Pain Catastrophizing Scale (PCS) displaying the greatest change. Lastly, we demonstrated the safety of dwMRI for a patient with SCS. In summary, the results from the case report prompt further investigation in applying dwMRI in a larger cohort to better correlate the influence of SCS with brain microstructural alterations, supporting the utility of dwMRI to generate non-invasive biomarkers for prognostication.

Functional Connectivity Magnetic Resonance Imaging Sequences in Patients With Postsurgical Persistent Spinal Pain Syndrome Type 2 With Implanted Spinal Cord Stimulation Systems: A Safety, Feasibility, and Validity Study

BACKGROUND

Chronic pain has been associated with alterations in brain connectivity, both within networks (regional) and between networks (cross-network connectivity). Functional connectivity (FC) data on chronic back pain are limited and based on heterogeneous pain populations. Patients with postsurgical persistent spinal pain syndrome (PSPS) type 2 are good candidates for spinal cord stimulation (SCS) therapy. We hypothesize that 1) FC magnetic resonance imaging (fcMRI) scans can be safely obtained in patients with PSPS type 2 with implanted therapeutic SCS devices and that 2) their cross-network connectivity patterns are altered and involve emotion and reward/aversion functions.

MATERIALS AND METHODS

Resting-state (RS) fcMRI (rsfcMRI) scans were obtained from nine patients with PSPS type 2 implanted with therapeutic SCS systems and 13 age-matched controls. Seven RS networks were analyzed, including the striatum.

RESULTS

Cross-network FC sequences were safely obtained on a 3T MRI scanner in all nine patients with PSPS type 2 with implanted SCS systems. FC patterns involving emotion/reward brain circuitry were altered as compared with controls. Patients with a history of constant neuropathic pain, experiencing longer therapeutic effects of SCS, had fewer alterations in their connectivity patterns.

CONCLUSIONS

To our knowledge, this is the first report of altered cross-network FC involving emotion/reward brain circuitry in a homogeneous population of patients with chronic pain with fully implanted SCS systems, on a 3T MRI scanner. All rsfcMRI studies were safe and well tolerated by all nine patients, with no detectable effects on the implanted devices.

Case report: The promising application of dynamic functional connectivity analysis on an individual with failed back surgery syndrome

Failed back surgery syndrome (FBSS), a chronic neuropathic pain condition, is a common indication for spinal cord stimulation (SCS). However, the mechanisms of SCS, especially its effects on supraspinal/brain functional connectivity, are still not fully understood. Resting state functional magnetic resonance imaging (rsfMRI) studies have shown characteristics in patients with chronic low back pain (cLBP). In this case study, we performed rsfMRI scanning (3.0 T) on an FBSS patient, who presented with chronic low back and leg pain following her previous lumbar microdiscectomy and had undergone permanent SCS. Appropriate MRI safety measures were undertaken to scan this subject. Seed-based functional connectivity (FC) was performed on the rsfMRI data acquired from the FBSS subject, and then compared to a group of 17 healthy controls. Seeds were identified by an atlas of resting state networks (RSNs), which is composed of 32 regions grouped into 8 networks. Sliding-window method and k-means clustering were used in dynamic FC analysis, which resulted in 4 brain states for each group. Our results demonstrated the safety and feasibility of 3T MRI scanning in a patient with implanted SCS system. Compared to the brain states of healthy controls, the FBSS subject presented very different FC patterns in less frequent brain states. The mean dwell time of brain states showed distinct distributions: the FBSS subject seemed to prefer a single state over the others. Although future studies with large sample sizes are needed to make statistical conclusions, our findings demonstrated the promising application of dynamic FC to provide more granularity with FC changes associated with different brain states in chronic pain.

Effects of transcutaneous spinal stimulation on spatiotemporal cortical activation patterns: A proof-of-concept EEG study

OBJECTIVE

Transcutaneous spinal cord stimulation (TSS) has been shown to be a promising non-invasive alternative to epidural spinal cord stimulation (ESS) for improving outcomes of people with spinal cord injury (SCI). However, studies on the effects of TSS on cortical activation are limited. Our objectives were to evaluate the spatiotemporal effects of TSS on brain activity, and determine changes in functional connectivity under several different stimulation conditions. As a control, we also assessed the effects of functional electrical stimulation (FES) on cortical activity.

APPROACH

Non-invasive scalp electroencephalography (EEG) was recorded during TSS or FES while five neurologically intact participants performed one of three lower-limb tasks while in the supine position: (1) A no contraction control task, (2) a rhythmic contraction task, or (3) a tonic contraction task. After EEG denoising and segmentation, independent components were clustered across subjects to characterize sensorimotor networks in the time and frequency domains. Independent components of the event related potentials (ERPs) were calculated for each cluster and condition. Next, a Generalized Partial Directed Coherence (gPDC) analysis was performed on each cluster to compare the functional connectivity between conditions and tasks.

RESULTS

Independent Component analysis of EEG during TSS resulted in three clusters identified at Brodmann areas (BA) 9, BA 6, and BA 4, which are areas associated with working memory, planning, and movement control. Lastly, we found significant (p < 0.05, adjusted for multiple comparisons) increases and decreases in functional connectivity of clusters during TSS, but not during FES when compared to the no stimulation conditions.

SIGNIFICANCE

The findings from this study provide evidence of how TSS recruits cortical networks during tonic and rhythmic lower limb movements. These results have implications for the development of spinal cord-based computer interfaces, and the design of neural stimulation devices for the treatment of pain and sensorimotor deficit.

Regional homogeneity alterations in multi-frequency bands in tension-type headache: a resting-state fMRI study

OBJECTIVES

In this study, we aimed to investigate the spontaneous neural activity in the conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz, and slow-5: 0.01-0.027 Hz) in tension-type headache (TTH) patients with regional homogeneity (ReHo) analyses.

METHODS

Thirty-eight TTH patients and thirty-eight healthy controls (HCs) underwent resting-state functional magnetic resonance imaging (RS-fMRI) scanning to investigate abnormal spontaneous neural activity using ReHo analysis in conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz and slow-5: 0.01-0.027 Hz).

RESULTS

In comparison with the HC group, patients with TTH exhibited ReHo increases in the right medial superior frontal gyrus in the conventional frequency band (0.01-0.08 Hz). The between group differences in the slow-5 band (0.01-0.027 Hz) highly resembled the differences in the conventional frequency band (0.01-0.08 Hz); even the voxels with increased ReHo were spatially more extensive, including the right medial superior frontal gyrus and the middle frontal gyrus. In contrast, no region showed significant between-group differences in the slow-4 band (0.027-0.073 Hz). The correlation analyses showed no correlation between the ReHo values in TTH patients and VAS scores, course of disease and number of seizures per month in conventional band (0.01-0.08 Hz), slow-4 band (0.027-0.073 Hz), as well as in slow-5 band (0.01-0.027 Hz).

CONCLUSIONS

The results showed that the superior frontal gyrus and middle frontal gyrus were involved in the integration and processing of pain signals. In addition, the abnormal spontaneous neural activity in TTH patients was frequency-specific. Namely, slow-5 band (0.01-0.027 Hz) might contain additional useful information in comparison to slow-4 band (0.027-0.073 Hz). This preliminary exploration might provide an objective imaging basis for the understanding of the pathophysiological mechanism of TTH.

1-kHz high-frequency spinal cord stimulation alleviates chronic refractory pain after spinal cord injury: a case report

Background

Patients with spinal cord injury (SCI) frequently complain of intractable pain that is resistant to conservative treatments. Here, we report the successful application of 1-kHz high-frequency spinal cord stimulation (SCS) in a patient with refractory neuropathic pain secondary to SCI.

Case presentation

A 69-year-old male diagnosed with SCI (C4 American Spinal Injury Association Impairment Scale A) presented with severe at-level bilateral upper extremity neuropathic pain. Temporary improvement in his symptoms with a nerve block implied peripheral component involvement. The patient received SCS, and though the tip of the leads could not reach the cervical vertebrae, a 1-kHz frequency stimulus relieved the intractable pain.

Conclusions

SCI-related symptoms may include peripheral components; SCS may have a considerable effect on intractable pain. Even when the SCS electrode lead cannot be positioned in the target area, 1-kHz high-frequency SCS may still produce positive effects.

Celecoxib-Loaded Electrospun Fibrous Antiadhesion Membranes Reduce COX-2/PGE2 Induced Inflammation and Epidural Fibrosis in a Rat Failed Back Surgery Syndrome Model

To date, failed back surgery syndrome (FBSS) remains a therapy-refractory clinical condition after spinal surgery. The antiadhesion membrane is applied to prevent FBSS by isolating fibrosis; however, the inflammation stimulated by the foreign body and surgical trauma needs to be further resolved simultaneously. Therefore, we developed new electrospun polycaprolactone (PCL) fibrous membranes loaded with celecoxib (CEL) to prevent fibrosis and inflammation associated with FBSS. The CEL-loaded PCL fibers were randomly distributed, and the drug was released over two weeks. Fluorescence micrographs revealed that the fibroblasts proliferated less on the PCL-CEL fibrous membranes than in the PCL group and the blank control. In the rat laminectomy model after 4 weeks, magnetic resonance imaging of epidural fibrosis was least in the PCL-CEL group. Expression of COX-2 and PGE2 was lower in the PCL-CEL group. It concluded that the CEL-loaded PCL membrane could reduce fibrosis and inflammation in a rat model of FBSS via COX-2/PGE2 signaling pathways.

Current Perspectives on Neurostimulation for the Management of Chronic Low Back Pain: A Narrative Review

Neurostimulation techniques for the treatment of chronic low back pain (LBP) have been rapidly evolving; however, questions remain as to which modalities provide the most efficacious and durable treatment for intractable axial symptoms. Modalities of spinal cord stimulation, such as traditional low-frequency paresthesia based, high-density or high dose (HD), burst, 10-kHz high-frequency therapy, closed-loop, and differential target multiplexed, have been limitedly studied to determine their efficacy for the treatment of axial LBP. In addition, stimulation methods that target regions other than the spinal cord, such as medial branch nerve stimulation of the multifidus muscles and the dorsal root ganglion may also be viable treatment options. Here, current scientific evidence behind neurostimulation techniques have been reviewed with a focus on the management of chronic axial LBP.