Psychological screening/phenotyping as predictors for spinal cord stimulation

Variables associated with nonresponders to high-frequency (10 kHz) spinal cord stimulation

INTRODUCTION

The use of spinal cord stimulation (SCS) therapy to treat chronic pain continues to rise. Optimal patient selection remains one of the most important factors for SCS success. However, despite increased utilization and the existence of general indications, predicting which patients will benefit from neuromodulation remains one of the main challenges for this therapy. Therefore, this study aims to identify the variables that may correlate with nonresponders to high-frequency (10 kHz) SCS to distinguish the subset of patients less likely to benefit from this intervention.

MATERIALS AND METHODS

This was a retrospective single-center observational study of patients who underwent 10 kHz SCS implant. Patients were divided into nonresponders and responders groups. Demographic data and clinical outcomes were collected at baseline and statistical analysis was performed for all continuous and categorical variables between the two groups to calculate statistically significant differences.

RESULTS

The study population comprised of 237 patients, of which 67.51% were responders and 32.49% were nonresponders. There was a statistically significant difference of high levels of kinesiophobia, high self-perceived disability, greater pain intensity, and clinically relevant pain catastrophizing at baseline in the nonresponders compared to the responders. A few variables deemed potentially relevant, such as age, gender, history of spinal surgery, diabetes, alcohol use, tobacco use, psychiatric illness, and opioid utilization at baseline were not statistically significant.

CONCLUSION

Our study is the first in the neuromodulation literature to raise awareness to the association of high levels of kinesiophobia preoperatively in nonresponders to 10 kHz SCS therapy. We also found statistically significant differences with greater pain intensity, higher self-perceived disability, and clinically relevant pain catastrophizing at baseline in the nonresponders relative to responders. It may be appropriate to screen for these factors preoperatively to identify patients who are less likely to respond to SCS. If these modifiable risk factors are present, it might be prudent to consider a pre-rehabilitation program with pain neuroscience education to address these factors prior to SCS therapy, to enhance successful outcomes in neuromodulation.

Long-term efficacy of spinal cord stimulation for chronic primary neuropathic pain in the contemporary era: a systematic review and meta-analysis

INTRODUCTION

Spinal cord stimulation (SCS) is a modern neuromodulation technique extensively proven to be an effective modality for treatment of chronic neuropathic pain. It has been mainly studied for complex regional pain syndrome (CRPS) and failed back surgery syndrome (FBSS) and recent data almost uniformly establishes its statistically significant positive therapeutic results. It has also been compared with other available treatment modalities across various studies. However, long term data on maintenance of its efficacious potential remains less explored. Few studies have reported data on long follow-up times (>= 12 months) and have compared its efficacy with other treatment options for chronic pain, respectively. Our study pools and analyzes the available data and compares SCS with other treatment options. It also analyzes the efficacy of SCS in long term management of patients with chronic pain.

EVIDENCE ACQUISITION

We reviewed all the data available on MEDLINE, Embase and Cochrane CENTRAL using a search strategy designed to fit our pre-set inclusion and exclusion criteria. Both single-arm and double-arm studies were included. The primary outcome was defined as decrease of visual analogue scale (VAS) by >50% at 6, 12 and/or 24 months after SCS.

EVIDENCE SYNTHESIS

According to the pooled data of double-arm studies, SCS has unanimously proven its superiority over other treatment options at 6 months follow-up; however it fails to prove statistically significant difference in results at longer treatment intervals. Dorsal root ganglion stimulation, a relatively recent technique with the same underlying physiologic mechanisms as SCS, showed far more promising results than SCS. Single-arm studies show around 70% patients experiencing greater than 50% reduction in their VAS scores at 6 and 12 months.

CONCLUSIONS

SCS is a viable option for management of chronic neuropathic pain secondary to FBSS and CRPS. However, data available for its long term efficacy remains scarce and show no further statistically significant results.

Factors Predicting Clinically Relevant Pain Relief After Spinal Cord Stimulation for Patients With Chronic Low Back and/or Leg Pain: A Systematic Review With Meta-Analysis and Meta-Regression

RATIONALE

To optimize results with spinal cord stimulation (SCS) for chronic low back pain (CLBP) and/or leg pain, including persistent spinal pain syndrome (PSPS), careful patient selection based on proved predictive factors is essential. Unfortunately, the necessary selection process required to optimize outcomes of SCS remains challenging.

OBJECTIVE

This review aimed to evaluate predictive factors of clinically relevant pain relief after SCS for patients with CLBP and/or radicular leg pain, including PSPS.

MATERIALS AND METHODS

In August 2023, PubMed, Cinahl, Cochrane, and EMBASE were searched to identify studies published between January 2010 and August 2023. Studies reporting the percentage of patients with ≥50% pain relief after SCS in patients with CLBP and leg pain, including PSPS at 12 or 24 months, were included. Meta-analysis was conducted to pool results for back, leg, and general pain relief. Predictive factors for pain relief after 12 months were examined using univariable and multivariable meta-regression.

RESULTS

A total of 27 studies (2220 patients) were included for further analysis. The mean percentages of patients with substantial pain relief were 68% for leg pain, 63% for back pain, and 73% for general pain at 12 months follow-up, and 63% for leg pain, 59% for back pain, and 71% for general pain at 24 months follow-up assessment. The implantation method and baseline Oswestry Disability Index made the multivariable meta-regression model for ≥50% back pain relief. Sex and pain duration made the final model for ≥50% leg pain relief. Variable stimulation and implantation method made the final model for general pain relief.

CONCLUSIONS

This review supports SCS as an effective pain-relieving treatment for CLBP and/or leg pain, and models were developed to predict substantial back and leg pain relief. To provide high-grade evidence for predictive factors, SCS studies of high quality are needed in which standardized factors predictive of SCS success, based on in-patient improvements, are monitored and reported.

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.

Percutaneous high cervical spinal cord stimulation for refractory trigeminal neuralgia

Background

Trigeminal neuralgia (TN) is a debilitating pain that affects the dermatomes associated with the trigeminal nerve (V1, V2, and V3). Unfortunately, many medical treatments and surgical procedures fail to sufficiently modulate the pain associated with this condition.

Case Description

This study presents two extreme cases of refractory TN (RTN) that progressed to atypical facial pain and describes successful mitigation of the neuralgia of said cases by percutaneous implantation of upper cervical spinal cord stimulation (SCS). The SCS was designed to target the descending spinal trigeminal tract.

Conclusion

Together, these cases collaborate with the limited literature and further delineate the use and potential advantages of SCS in the treatment of RTN.

Supraorbital Nerve Stimulation for Facial Pain

PURPOSE OF REVIEW

Chronic facial pain is considered one of the conditions that affect quality of daily life of patients significantly and makes them seek medical help. Intractable facial pain with failed trials of medical treatment and other pain management therapies presents a challenge for neurologists, pain specialists, and neurosurgeons. We describe the possibility of proposing peripheral nerve stimulation of the supraorbital nerves to treat patients with medically intractable facial pain. Stimulation of the supraorbital nerves is performed using percutaneously inserted electrodes that are positioned in the epi-fascial plane, traversing the course of the supraorbital nerves. The procedure has two phases starting with a trial by temporary electrodes that are inserted under fluoroscopic guidance and are anchored to the skin. This trial usually lasts for a few days to 2 weeks. If successful, we proceed to the insertion of a permanent electrode that is tunneled under the skin behind the ear toward the infraclavicular region in which we make a pocket for the implantable pulse generator.

RECENT FINDINGS

This procedure has been used in multiple patients with promising results which was published in literature. Literature shows that it provides relief of medically intractable pain, without the need for destructive procedures or more central modulation approaches with a preferable safety profile compared to other invasive procedures. Supraorbital nerve stimulation is now considered a valid modality of treatment for patients with medically intractable facial pain and can be offered as a reliable alternative for the patients while discussing the proper plan of management.

Effects of Patient Assessment and Education by an Integrated Care Team on Postoperative Adherence and Failure Rates After Osteochondral Allograft and Meniscal Allograft Transplantation in the Knee

Background

Patient nonadherence with prescribed rehabilitation protocols is associated with up to 16 times higher likelihood of treatment failure after osteochondral allograft transplantation (OCA) and meniscal allograft transplantation.

Hypothesis

Patients who completed counseling with an orthopaedic health behavior psychologist as part of an evidence-based shift in practice at our institution would have significantly lower rates of nonadherence and surgical treatment failure versus patients who did not participate in counseling.

Study Design

Cohort study; Level of evidence, 2.

Methods

Patients in a prospective registry who underwent OCA and/or meniscal allograft transplantation between January 2016 and April 2021 were included for analysis when 1-year follow-up data were available. Of 292 potential patients, 213 were eligible for inclusion. Patients were categorized based on whether they participated in the preoperative counseling and postoperative patient management program: no health psych group (n = 172) versus health psych group (n = 41). Nonadherence was defined as documented evidence of a deviation from the prescribed postoperative rehabilitation protocol.

Results

In this cohort of patients, 50 (23.5%) were documented to be nonadherent. Patients in the no health psych cohort were significantly more likely to be nonadherent (P = .023; odds ratio [OR], 3.4). Tobacco use (OR, 7.9), higher preoperative Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Interference score, lower preoperative PROMIS Mental Health score, older age, and higher body mass index were also significantly associated with nonadherence (P < .001 for all). Patients who were nonadherent with the prescribed postoperative rehabilitation protocol during the first year after transplantation were 3 times more likely (P = .004) to experience surgical treatment failure than those who were adherent. Overall, 26.2% of patients in the no health psych group experienced surgical treatment failure versus 12.2% in the health psych cohort.

Conclusion

Data from the present study suggest that preoperative counseling with a health behavior psychologist is associated with an improved rate of patient adherence and a lower proportion of surgical treatment failure after OCA and meniscal allograft transplantation. Patients who remained adherent to the postoperative protocol were 3 times more likely to have a successful short-term (≥1 year) outcome.

The Association of Psychiatric Comorbidities With Short-Term and Long-Term Outcomes Following Spinal Cord Stimulator Placement

BACKGROUND

Outcomes after spinal cord stimulator (SCS) placement are affected by psychologic comorbidities. It is part of routine practice to do psychologic assessments prior to SCS trials to assess for the presence of maladaptive behavioral patterns. However, few studies have sought to quantify the effect of psychiatric comorbidities on complications, reoperation, and readmission rates. The purpose of this study was to assess the association of psychiatric comorbidities with postprocedural outcomes after SCS implantation.

MATERIALS AND METHODS

Inclusion criteria included SCS placement between 2015 and 2020 (percutaneous approach or an open laminectomy-based approach) using Healthcare Corporation of America National Database. Data on psychiatric comorbidities present at the time of SCS implantation surgery were collected. Outcomes of interest included complication rates (defined as lead migration, fracture, malfunction, battery failure, postoperative pain, infection, dural puncture, or neurological injury), reoperation rates (defined as either revision or explant [ie, removal]), and readmission rates within 30-day and 1-year time after SCS implantation. We measured the association between psychiatric comorbidities and outcomes using multivariable regression and reported odds ratio (OR) and respective 95% confidence intervals.

RESULTS

A total of 12,751 cases were included. The most common psychiatric comorbidities were major depressive disorder (16.1%) and anxiety disorder (13.4%). In unadjusted univariate analysis, patients with any psychiatric comorbidity had heightened rates of any complication (27.1% vs 19.4%), infection (5.9% vs 1.9%), lead displacement (2.2% vs 1.3%), surgical pain (2.1% vs 1.2%), explant (14.7% vs 8.8%), and readmission rates at one year (54.2% vs 33.8%) (all p < 0.001). In multivariable logistic regression, with each additional psychiatric comorbidity, a patient had increased odds of experiencing any complication (OR = 1.5, 95% CI = 1.36-1.57, p < 0.001), requiring a reoperation (OR = 1.5, 95% CI = 1.37-1.6, p < 0.001), and requiring readmission (OR = 1.7, 99% CI = 1.6-1.8, p < 0.001).

CONCLUSIONS

The presence of psychiatric comorbidities was found to be associated with postoperative complication rates, reoperation, and readmission rates after SCS placement. Furthermore, each consecutive increase in psychiatric comorbidity burden was associated with increased odds of complications, reoperation, and readmission. Future studies might consider examining the role of presurgical mental health screening (ie, patient selection, psychologic testing) and treatment in optimizing outcomes for patients with psychiatric comorbidities.

Identifying Predictors for Early Percutaneous Spinal Cord Stimulator Explant at One and Two Years: A Retrospective Database Analysis

OBJECTIVES

Placement of percutaneous spinal cord stimulator (SCS) implant has become a therapeutic option for various chronic pain conditions; however, early surgical explant still occurs. Unfortunately, evidence regarding the incidence of early surgical explant, and patient-specific factors and comorbidities associated with such, is limited and mixed. The objective of this retrospective analysis was to elucidate the incidence and predictors of percutaneous SCS explant within the first two years of device placement.

MATERIALS AND METHODS

The PearlDiver-Mariner Patient Record Database of all payer claims was used to identify patients who underwent percutaneous lead SCS implant (leads and generator) with subsequent explant within two years of initial device implant. The primary outcome was to determine the incidence of SCS explant within the first two years of device placement. Secondary outcomes included evaluating the effects of several patient-specific comorbidities on explant rates using univariate regression analysis.

RESULTS

Across the database, a total of 52,070 patients who underwent percutaneous lead SCS implant were included, of whom 3104 (5.96%) had SCS explant within the first two years. Most explants occurred within the first-year time interval at 72.8% (2260 patients), whereas only 27.2% (844 patients) had SCS explant between years one and two. At the one-year time interval, covariates associated with an increased odds ratio (OR) (95% CI) of SCS explant were 1) depression (1.39 [1.26, 1.52]), 2) chronic preoperative (1.27 [1.16, 1.39]) or postoperative (1.23 [1,13, 1.36]) opioid use, 3) cannabis abuse (1.58 [1.20, 2.02]), 4) tobacco use (1.13 [1.04, 1.23]), and 5) coagulopathy (1.22 [1.07, 1.38]). In contrast, the OR of explant was lower in patients who were older, men, or had diabetes (complicated or uncomplicated). All associated covariates became nonsignificant after the first year of SCS implant (ie, between the first and second years), and only depression and tobacco use remained as associated factors for device explant.

CONCLUSIONS

Our retrospective analysis highlights that the rate of percutaneous SCS explant appears to considerably decrease after the first year of device implant. Furthermore, this analysis sheds additional insights into patients who may be at risk of early percutaneous SCS explant, especially within the first year of device placement, and underscores the importance of a continued multidimensional/biopsychologic assessment in patients with chronic pain.

The post spinal surgery syndrome: A review

Post spinal surgery syndrome(PSSS) has always been considered only for the pain it causes. However, many other neurological deficits do happen after lower back surgery. The aim of this review is to look into the various other neurological deficits that could happen after a spinal surgery. Using the keywords, foot drop, cauda equina syndrome, epidural hematoma, nerve and dural injury in spine surgery, the literature was searched. Out of the 189 articles obtained, the most important were analyzed. The problems associated with spine surgery have been published in the literature but are much more than the failed back surgery syndrome and cause more discomfort to the patients. To bring about a more sustained and collective awareness and understanding of these complications following spinal surgery, we encompassed all these complications under the heading of PSSS.

Development of Machine Learning-Based Models to Predict Treatment Response to Spinal Cord Stimulation

BACKGROUND

Despite spinal cord stimulation's (SCS) proven efficacy, failure rates are high with no clear understanding of which patients benefit long term. Currently, patient selection for SCS is based on the subjective experience of the implanting physician.

OBJECTIVE

To develop machine learning (ML)-based predictive models of long-term SCS response.

METHODS

A combined unsupervised (clustering) and supervised (classification) ML technique was applied on a prospectively collected cohort of 151 patients, which included 31 features. Clusters identified using unsupervised K-means clustering were fitted with individualized predictive models of logistic regression, random forest, and XGBoost.

RESULTS

Two distinct clusters were found, and patients in the cohorts significantly differed in age, duration of chronic pain, preoperative numeric rating scale, and preoperative pain catastrophizing scale scores. Using the 10 most influential features, logistic regression predictive models with a nested cross-validation demonstrated the highest overall performance with the area under the curve of 0.757 and 0.708 for each respective cluster.

CONCLUSION

This combined unsupervised-supervised learning approach yielded high predictive performance, suggesting that advanced ML-derived approaches have potential to be used as a functional clinical tool to improve long-term SCS outcomes. Further studies are needed for optimization and external validation of these models.

Machine Learning to Predict Successful Opioid Dose Reduction or Stabilization After Spinal Cord Stimulation

BACKGROUND

Spinal cord stimulation (SCS) effectively reduces opioid usage in some patients, but preoperatively, there is no objective measure to predict who will most benefit.

OBJECTIVE

To predict successful reduction or stabilization of opioid usage after SCS using machine learning models we developed and to assess if deep learning provides a significant benefit over logistic regression (LR).

METHODS

We used the IBM MarketScan national databases to identify patients undergoing SCS from 2010 to 2015. Our models predict surgical success as defined by opioid dose stability or reduction 1 year after SCS. We incorporated 30 predictors, primarily regarding medication patterns and comorbidities. Two machine learning algorithms were applied: LR with recursive feature elimination and deep neural networks (DNNs). To compare model performances, we used nested 5-fold cross-validation to calculate area under the receiver operating characteristic curve (AUROC).

RESULTS

The final cohort included 7022 patients, of whom 66.9% had successful surgery. Our 5-variable LR performed comparably with the full 30-variable version (AUROC difference <0.01). The DNN and 5-variable LR models demonstrated similar AUROCs of 0.740 (95% CI, 0.727-0.753) and 0.737 (95% CI, 0.728-0.746) (P = .25), respectively. The simplified model can be accessed at SurgicalML.com.

CONCLUSION

We present the first machine learning-based models for predicting reduction or stabilization of opioid usage after SCS. The DNN and 5-variable LR models demonstrated comparable performances, with the latter revealing significant associations with patients' pre-SCS pharmacologic patterns. This simplified, interpretable LR model may augment patient and surgeon decision making regarding SCS.

Association of Spinal Cord Stimulator Implantation With Persistent Opioid Use in Patients With Postlaminectomy Syndrome

IMPORTANCE

The results of studies evaluating spinal cord stimulation (SCS) for postlaminectomy syndrome (PLS) have yielded mixed results. This has led to an increased emphasis on objective outcome measures such as opioid prescribing.

OBJECTIVE

To determine the association between SCS and long-term opioid therapy (LOT) for PLS.

DESIGN, SETTING, AND PARTICIPANTS

In this cohort study, adults with PLS were identified using the TriNetx Diamond Network and separated based on whether they underwent SCS. Patients were stratified according to baseline opioid use (opioid-naive or receiving LOT) and subsequent opioid therapy over the 12-month period ranging from 3 to 15 months post-SCS implantation or post-PLS index date. Statistical analysis was performed from June to December 2021.

EXPOSURE

SCS.

MAIN OUTCOMES AND MEASURES

The main outcome was cessation of opioid use among patients receiving LOT or abstinence from opioids among opioid-naive patients. Opioid-naive patients were defined as those receiving at most 2 opioid prescriptions per year, and patients on LOT were those receiving at least 6 opioid prescriptions per year.

RESULTS

Among 552 937 eligible patients treated between December 2015 and May 2021, 26 179 with PLS received an SCS implant. The median (IQR) patient age was 60 (51-69) years; 305 802 patients (55.3%) were female. Among those reporting racial identify (37.0% [204 758 patients]), 9.3% (18 971 patients) were African American, 0.3% (648 patients) were Asian, and 90.4% (185 139 patients) were White. Compared with those who did not receive an SCS, individuals who received an SCS were more likely to be using opioids preimplantation (mean [SD] prescriptions: 4.3 [8.5] vs 4.1 [9.3]; P < .001) but less likely to be using opioids after SCS implantation (mean [SD] prescriptions: 3.8 [8.2] vs 4.0 [9.4]; P = .006). In the 12-month study period, similar proportions in the SCS and no-SCS groups receiving baseline LOT remained on LOT (70.3% [n = 74 585] vs 69.2% [n = 3882], respectively; P = .10). In opioid-naive patients, SCS was associated with a small decreased likelihood of patients subsequently receiving LOT (7.6% vs 7.0%; difference, -0.6% [95% CI, -1.0% to -0.2%]; P = .003). In multivariable analysis, SCS was associated with an increased likelihood of not being on opioids in both opioid-naive (adjusted odds ratio [OR], 0.90 [95% CI, 0.85-0.96]; P < .001) and LOT patients (adjusted OR, 0.93 [95% CI, 0.88-0.99]; P = .02). White patients were significantly more likely to be diagnosed with PLS (ie, underwent surgery) (90.4% vs 85.2%; difference, 5.2% [95% CI, 5.1%-5.4%]; P < .001) and receive an SCS (93.7% vs 90.3%; difference, 3.4% [95% CI, 2.9% to 4.0%]; P < .001) than patients of other racial identities.

CONCLUSIONS AND RELEVANCE

These findings suggest that under real-life conditions, SCS was associated with small, clinically questionable associations with opioid discontinuation and not starting opioids in the context of PLS.

Peripheral Nerve Stimulation for Treatment of Headaches: An Evidence-Based Review

Headaches are one of the most common medical complaints worldwide, and treatment is often made difficult because of misclassification. Peripheral nerve stimulation has emerged as a novel treatment for the treatment of intractable headaches in recent years. While high-quality evidence does exist regarding its use, efficacy is generally limited to specific nerves and headache types. While much research remains to bring this technology to the mainstream, clinicians are increasingly able to provide safe yet efficacious pain control.

Machine Learning Algorithms Provide Greater Prediction of Response to SCS Than Lead Screening Trial: A Predictive AI-Based Multicenter Study

Persistent pain after spinal surgery can be successfully addressed by spinal cord stimulation (SCS). International guidelines strongly recommend that a lead trial be performed before any permanent implantation. Recent clinical data highlight some major limitations of this approach. First, it appears that patient outco mes, with or without lead trial, are similar. In contrast, during trialing, infection rate drops drastically within time and can compromise the therapy. Using composite pain assessment experience and previous research, we hypothesized that machine learning models could be robust screening tools and reliable predictors of long-term SCS efficacy. We developed several algorithms including logistic regression, regularized logistic regression (RLR), naive Bayes classifier, artificial neural networks, random forest and gradient-boosted trees to test this hypothesis and to perform internal and external validations, the objective being to confront model predictions with lead trial results using a 1-year composite outcome from 103 patients. While almost all models have demonstrated superiority on lead trialing, the RLR model appears to represent the best compromise between complexity and interpretability in the prediction of SCS efficacy. These results underscore the need to use AI-based predictive medicine, as a synergistic mathematical approach, aimed at helping implanters to optimize their clinical choices on daily practice.

Transcranial direct current stimulation for provoked vestibulodynia: What roles do psychosexual factors play in treatment response?

There is growing evidence that provoked vestibulodynia (PVD), a frequent and debilitating condition, is characterized by central sensitization. This study aimed to examine predictive factors of transcranial direct current stimulation (tDCS) efficacy in this chronic pain population. Exploratory analysis derived from a randomized controlled trial was performed to assess predictors of pain reduction among 39 women with PVD who received 10 daily sessions of either active or sham tDCS. Clinical characteristics (e.g. pain intensity, duration and pain sensitivity) and psychosexual factors (e.g. pain catastrophizing, pain-related fear, anxiety, depressive symptoms and vaginal penetration cognitions) were assessed at baseline and used to predict tDCS response at 3-month follow-up. Analysis revealed that higher depressive symptoms and lower negative self-image cognitions were significant predictors of pain reduction at follow-up and accounted for 62.3% of the variance in the active tDCS group. Higher genital incompatibility cognitions were related to poorer response, regardless of treatment group. These findings suggest that women with PVD presenting higher depressive symptoms and lower levels of negative self-image cognitions could derive greater benefits from tDCS. These results suggest that tDCS could be effective in a subgroup of women with PVD - a possibility worth exploring with future prospective larger studies.

Improving outcomes of hypoglossal nerve stimulation therapy: current practice, future directions and research gaps. Proceedings of the 2019 International Sleep Surgery Society Research Forum

Hypoglossal nerve stimulation (HGNS) has evolved as a novel and effective therapy for patients with moderate-to-severe obstructive sleep apnea (OSA). Despite positive published outcomes of HGNS, there exist uncertainties regarding proper patient selection, surgical technique, and the reporting of outcomes and individual factors that impact therapy effectiveness. According to current guidelines, this therapy is indicated for select patients, and recommendations are based on the Stimulation Therapy for Apnea Reduction (STAR) trial. Ongoing research and physician experiences continuously improve methods to optimize the therapy. An understanding of the way in which airway anatomy, OSA phenotypes, individual health status, psychological conditions and comorbid sleep disorders influence the effectiveness of HGNS is essential to improve outcomes and expand therapy indications. This manuscript presents discussions on current evidence, future directions, and research gaps for HGNS therapy from the 10th International Surgical Sleep Society expert research panel.

Surgical Technique and Patient Selection for Spinal Cord Stimulation for Chronic Pain

Spinal cord stimulation (SCS) is a neuromodulation surgical technique that allows the treatment of various causes of chronic pain. SCS is effective in the treatment of chronic low back pain, neuropathic pain, chronic regional pain syndrome, and failed back surgery syndrome, among others. The mechanisms underlying the efficacy are still under investigation and different mechanisms are likely responsible for the effects of different waveforms used in the therapy. Successful application of SCS to individual patients depends on patient selection and meticulous surgical technique. Important factors in patient selection depend on preoperative imaging, maximizing noninvasive therapy, and neuropsychological evaluation. Percutaneous and open techniques exist for placing both paddle-shaped epidural leads as well as typical cylindrical leads. Benefits and risks exist for both techniques and the exact technique that is optimal depends on surgeon experience and surgeon and patient preference. Complications are rare and can be minimized and managed with appropriate preoperative mitigation.

Implant- and anesthesia-related factors affecting cardiopulmonary threshold intensities for vagus nerve stimulation

Objective.Vagus nerve stimulation (VNS) is typically delivered at increasing stimulus intensity until a neurological or physiological response is observed ('threshold') for dose calibration, preclinically and therapeutically. Factors affecting VNS thresholds have not been studied systematically. In a rodent model of VNS we measured neural and physiological responses to increasing VNS intensity, determined neurological and physiological thresholds and examined the effect of implant- and anesthesia-related factors on thresholds.Approach.In acute and chronic vagus implants (45 and 20 rats, respectively) VNS was delivered under isoflurane, ketamine-xylazine, or awake conditions. Evoked compound action potentials (CAPs) were recorded and activation of different fiber types was extracted. Elicited physiological responses were registered, including changes in heart rate (HR), breathing rate (BR), and blood pressure (BP). CAP and physiological thresholds were determined.Main results. The threshold for evoking discernable CAPs (>10µV) (CAP threshold) is significantly lower than what elicits 5%-10% drop in heart rate (heart rate threshold, HRT) (25µA ± 1.8 vs. 80µA ± 5.1, respectively; mean ± SEM). Changes in BP and small changes in BR (bradypnea) occur at lowest intensities (70µA ± 8.3), followed by HR changes (80µA ± 5.1) and finally significant changes in BR (apnea) (310μA ± 32.5). HRT and electrode impedance are correlated in chronic (Pearson correlationr= 0.47;p< 0.001) but not in acute implants (r= -0.34;pNS); HRT and impedance both increase with implant age (r= 0.44;p< 0.001 andr= 0.64;p< 0.001, respectively). HRT is lowest when animals are awake (200µA ± 35.5), followed by ketamine-xylazine (640µA ± 151.5), and isoflurane (1000µA ± 139.5). The sequence of physiological responses with increasing VNS intensity is the same in anesthetized and awake animals. Pulsing frequency affects physiological responses but not CAPs.Significance. Implant age, electrode impedance, and type of anesthesia affect VNS thresholds and should be accounted for when calibrating stimulation dose.

Association of Outcomes of Spinal Cord Stimulation for Chronic Low Back Pain and Psoas Measurements Based on Size of Iliopsoas Muscles

INTRODUCTION

Patients experience variable long-term improvement in chronic back pain despite successful spinal cord stimulation (SCS) trials. Iliopsoas (IP) size has been shown to differ between patients with low back pain and healthy controls. In this study, we examine whether IP muscle cross-sectional area (CSA) is associated with SCS outcomes.

MATERIALS AND METHODS

We examined patients for whom we had lumbar MRIs 6.3 years prior to SCS and had baseline and one-year outcome data. Percent change from baseline to one year was calculated for Numeric Rating Scale (NRS), Oswestry Disability Index (ODI), Beck Depression Inventory (BDI), Pain Catastrophizing Scale (PCS), and McGill Pain Questionnaire (MPQ). Correlations between IP muscle CSA, ratio of iliopsoas muscle size to the vertebral body area (P/VBA), and the ratio of iliopsoas muscle size to BMI (P/BMI) were examined. Sex differences were considered.

RESULTS

A total of 73 subjects were included in this study including 30 females and 43 males. Males had significantly larger IP (males 15.70 ± 0.58, females 9.72 ± 0.43; p < 0.001), P/VBA (males 1.00 ± 0.04, females 0.76 ± 0.03, p < 0.001) and P/BMI ratio (males 0.51 ± 0.02, females 0.32 ± 0.01; p < 0.001) than females. In females, P/VBA predicted NRS worst pain scores (β = 0.82, p = 0.004, r² = 0.55) and BDI (β = 0.59, p = 0.02, r² = 0.24). In males, P/BMI was a significant predictor of BDI outcomes scores (β = 0.45, p = 0.03, r² = 0.16). Males who had more muscle mass measured by iliopsoas size had more depression as measured using BDI (p = 0.03, r = 0.61). Females with less muscle mass measured by P/VBA also experienced more depression (p = 0.02, r = 0.74).

CONCLUSIONS

Our study showed that psoas measurements correlated with various pain outcomes specifically. P/VBA was most predictive in females and P/BMI in males. Depression correlated with P/BMI, reinforcing the complex relationship between depression and constant chronic pain. Tertile analyses further showed a relationship between iliopsoas CSA and depression in males and females. We provide preliminary data of sex-specific psoas measurements as a risk factor for worse SCS outcomes.

Preoperative Elevated Levels for Depression, Anxiety, and Subjective Mental Stress Have No Influence on Outcome Measures of Peripheral Nerve Field Stimulation for Chronic Low Back Pain-A Prospective Study

OBJECTIVE

Peripheral nerve field stimulation (PNFS) is an effective alternative treatment for patients with chronic low back pain. The treatment of low back pain strongly depends on psychological factors like anxiety, depression, and mental stress. The aim of this study was to evaluate the impact of such factors on outcome measures after lead- and implantable pulse generator-implantation.

MATERIALS AND METHODS

Between 2014 and 2019, a prospective cohort study of 39 patients with chronic lumbar pain was conducted. Hospital Anxiety and Depression Scale (HADS) score was assessed at baseline to measure symptoms of anxiety and depression. Symptom checklist-90 (SCL-90) was used to measure subjective psychopathology. Pain intensity (numeric pain rating scale [NRS]), SF12v2 with Physical Component Summary and Mental Component Summary (MCS) scores, and Oswestry Disability Index (ODI) were assessed pre- and postoperatively as well as three and six months after PNFS implantation. Outcome values were compared to baseline data. Statistical analysis was performed using depending t-test and analysis of variance (ANOVA). A p value <0.05 was considered significant.

RESULTS

The cohort consisted of 39 patients (18 females, 21 males) with a median age of 61 years (IQR^25-75  = 52-67 years). NRS, ODI, and SF12v2 showed significant improvement in the whole follow-up period compared to baseline values (p < 0.05). Elevated HADS scores for anxiety were seen in 64.1%, for depression in 76.9% of the patients at baseline. SCL-90 was pathologic in 71.8% of the cases. A one-way ANOVA revealed no differences between elevated HADS- and SCL-90 values and all outcome measures after PNFS implantation in the whole follow-up period (p > 0.05).

CONCLUSION

Chronic low back pain is often associated with psychological distress. Our study showed highly elevated levels for anxiety and depression as well as subjective mental stress in patients with chronic low back pain without negative impact on NRS, ODI, and SF12v2 in the whole follow-up after PNFS implantation.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for “precision medicine” or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

Spinal Cord Stimulation to Treat Low Back Pain in Patients With and Without Previous Spine Surgery

OBJECTIVES

Little is known about the effects of spinal cord stimulation (SCS) on chronic low back pain (CLBP) patients with no history of previous spine surgery. Using our prospectively collected database, we evaluate improvements in patients with and without previous spine surgery one-year post SCS implantation.

MATERIALS AND METHODS

Subjects completed outcome metrics pre-operatively and one-year post-implantation including Numeric Rating Scale (NRS), McGill Pain Questionnaire (MPQ), Oswestry Disability Index (ODI), Beck's Depression Inventory (BDI), and Pain Catastrophizing Scale (PCS).

RESULTS

We enrolled 134 patients; 82 patients had previous spine surgery and 52 patients did not. At one-year post-SCS implantation, patients with previous spine surgery showed improvements in worst pain experienced, least pain experienced, average pain experienced, pain felt currently, MPQ, MPQ sensory, MPQ affective, PCS, PCS helplessness, PCS rumination, PCS magnification, ODI, and BDI scores (p < 0.001, p = 0.005, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p = 0.03, p = 0.01, p = 0.02, p < 0.001, p = 0.05, p < 0.001, p = 0.017, respectively). Likewise, patients without previous spine surgery showed improvements in worst pain experienced, least pain experienced, average pain experienced, pain felt currently, MPQ, MPQ sensory, PCS, PCS helplessness, PCS rumination, PCS magnification, ODI, and BDI scores (p < 0.001, p = 0.005, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p = 0.008, p < 0.001, p < 0.001, respectively). Patients without previous spine surgery showed greater improvements for average pain PCS helplessness (p = 0.01).

CONCLUSIONS

Patients with and without previous spine surgery showed similar improvements in pain intensity, pain quality, feelings of rumination and magnification, functional disability, and depression severity. SCS can improve CLBP regardless of whether patients have had previous spine surgery.

Conditioned pain modulation-A comprehensive review

Conditioned pain modulation (CPM) is a centrally processed measure of the net effect of the descending pain pathway. This comprises both the facilitatory as well as the inhibitory effect. In the past, CPM or similar effects have been previously described using different terminologies such as diffuse noxious inhibitory control (DNIC), heterotopic noxious conditioning stimulation (HNCS) or endogenous analgesia (EA). A variety of patient-related factors such as age, gender, hormones, race, genetic and psychological factors have been thought to influence the CPM paradigms. CPM paradigms have also been associated with a wide range of methodological variables including the mode of application of the 'test' as well as the 'conditioning' stimuli. Despite all these variabilities, CPM seems to reliably lend itself to the pain modulation profile concept and could in future become one of the phenotypic biomarkers for pain and also a guide for mechanism-based treatment in chronic pain. Future research should focus on establishing consistent methodologies for measuring CPM and thereby enhancing the robustness of this emerging biomarker for pain.

Peripheral Neuromodulation for Chronic Pain

BACKGROUND

Chronic, focal, neuropathic pain is difficult to treat. Local nerve blocks are either ineffective or do not last. Regular neuromodulation modalities like spinal cord stimulation (SCS) or pain pump are invasive and affect a larger area.

OBJECTIVES

To discuss the indications, technique, nuances, programming, and outcomes of peripheral neuromodulation.

METHODS

The article reviews published literature and the author's own experience of over 500 cases of peripheral neuromodulation.

RESULTS AND CONCLUSION

Peripheral neuromodulation using peripheral nerve field stimulation (PNFS) is an effective, minimally invasive, targeted method of treatment. It is a relatively new modality in the field of neuromodulation but is used more often.

Quantitative sensory phenotyping in chronic neuropathic pain patients treated with unilateral L4-dorsal root ganglion stimulation

Background

In a previous study, we reported that selective dorsal root ganglion stimulation (DRG_STIM) at DRG level L4 promoted a favorable outcome for complex regional pain syndrome (CRPS) patients along with DRG_STIM-related changes of inflammatory biomarkers in blood and saliva. The impact on somatosensation is largely unknown. Herein, we assessed the quantitative sensory profile to quantify L4-DRG_STIM effects in CRPS patients.

Methods

Twelve refractory CRPS patients (4 female; 8 male; mean age 69 ± 9 years) received standardized quantitative sensory testing (QST) protocol at baseline and after 3 months of unilateral L4-DRG_STIM assessing nociceptive and non-nociceptive thermal and mechanical sensitivity of the knee affected by CRPS and the contralateral non-painful knee area.

Results

At baseline, CRPS subjects showed significantly increased thresholds for warmth, tactile and vibration detection (WDT, MDT and VDT) and exaggerated pain summation (WUR). After 3 months of unilateral L4-DRG_STIM all pain parameters exhibited trends towards normalization of sensitivity accumulating to a significant overall normalization for pain sensitivity (effect size: 0.91, p < 0.01), while with the one exception of WDT all non-nociceptive QST parameters remained unchanged. Overall change of non-nociceptive detection was negligible (effect size: 0.25, p > 0.40). Notably, reduction of pain summation (WUR) correlated significantly with pain reduction after 3 months of L4-DRG_STIM.

Conclusions

Selective L4-DRG_STIM lowered ongoing pain in CRPS patients and evoked significant normalization in the pain domain of the somatosensory profile. Thermoreception and mechanoreception remained unchanged. However, larger randomized, sham-controlled trials are highly warranted to shed more light on effects and mechanisms of dorsal root ganglion stimulation on quantitative sensory characteristics.

The study protocol was registered at the 15.11.2016 on German Register for Clinical Trials (DRKS ID 00011267).

https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00011267

Pain Catastrophizing Does Not Predict Spinal Cord Stimulation Outcomes: A Cohort Study of 259 Patients With Long-Term Follow-Up

OBJECTIVE

Spinal cord stimulation (SCS) is an important treatment modality used to treat chronic neuropathic pain. However, reported success rates of 26%-70% entail an increased focus on patient selection. An area of core interest is psychological evaluation, often using scales such as the Pain Catastrophizing Scale (PCS). The aim of this study was to assess the relation between baseline PCS scores obtained before implantation and SCS outcomes defined as (1) Rating on Patients' Global Impression of Change scale (PGIC), (2) Pain relief on the Numeric Rating Scale (NRS), (3) Cessation of pain medication, and (4) Risk of permanent explantation.

MATERIALS AND METHODS

Using records from the Neurizon Neuromodulation Database, we performed a multicenter open cohort study of 259 permanently implanted SCS patients. Follow-up ranged from six months to nine years (median = three years). For each of the defined SCS outcomes, patients were grouped according to their latest follow-up registration. Subsequently, we used a one-way ANOVA and exact t-tests to compare mean baseline PCS scores between groups.

RESULTS

No difference in mean baseline PCS scores was found between PGIC groups. Baseline PCS scores was not associated with the probability of obtaining 30% or 50% pain relief on latest registration. Baseline PCS scores of patients able to cease all usage of tricyclic antidepressants, antiepileptics, or opioids during SCS treatment did not differ from baseline scores of continuous users. We found no association between baseline PCS scores and risk of permanent explantation.

CONCLUSION

This study did not demonstrate any associations between baseline PCS scores and SCS outcomes.

Pain phenotypes classified by machine learning using electroencephalography features

Pain is a multidimensional experience mediated by distributed neural networks in the brain. To study this phenomenon, EEGs were collected from 20 subjects with chronic lumbar radiculopathy, 20 age and gender matched healthy subjects, and 17 subjects with chronic lumbar pain scheduled to receive an implanted spinal cord stimulator. Analysis of power spectral density, coherence, and phase-amplitude coupling using conventional statistics showed that there were no significant differences between the radiculopathy and control groups after correcting for multiple comparisons. However, analysis of transient spectral events showed that there were differences between these two groups in terms of the number, power, and frequency-span of events in a low gamma band. Finally, we trained a binary support vector machine to classify radiculopathy versus healthy subjects, as well as a 3-way classifier for subjects in the 3 groups. Both classifiers performed significantly better than chance, indicating that EEG features contain relevant information pertaining to sensory states, and may be used to help distinguish between pain states when other clinical signs are inconclusive.

Pain Psychology for Surgeons and Otolaryngologists

Pain is one of the leading reasons that brings patients into health care facilities; yet, it often is left undertreated. The biopsychosocial model of pain, which recognizes that pain is multidimensional, explains the complexities that affect the pain experience and response to treatment. Inclusion of behavioral and psychological factors in medical and surgical evaluations can facilitate an optimal outcome. When pain no longer is acute but becomes chronic, access to psychotherapeutic interventions becomes necessary to improve course and prognosis. Techniques, such as psychoeducation, deep breathing, imagery, and addressing expectations and catastrophic beliefs, can be incorporated into medical and surgical practices.

Development of an Educational Curriculum for Spinal Cord Stimulation

BACKGROUND

Spinal cord stimulators (SCSs) are used for treating chronic pain. The number of SCSs implanted each year is on the increase. The North American Neuromodulation Society (NANS) education committee aimed to develop a SCS curriculum as a tool to guide physicians at different training levels, based on the most recent evidence.

MATERIAL AND METHODS

A multidisciplinary (anesthesiology, physical medicine, neurosurgery, and neurology), taskforce representing the education committee of the NANS met to develop a SCS curriculum following the Accreditation Council for Graduate Medical Education (ACGME) milestones. The task force used the best available evidence and knowledge to develop the curriculum. Once developed, the SCS curriculum was then approved by the NANS board.

RESULTS

The task force developed a SCS training curriculum. Milestones included patient care and procedural skills, system-based practice, medical knowledge, interpersonal communication, practice based learning and professionalism. Each milestone was defined for three categories, early learner, advanced learner, and practitioner.

CONCLUSION

A multidisciplinary task force of the NANS education committee developed a SCS training curriculum that defines ACGME milestones for basic learners, advanced learners, and practitioners.

In Vivo Testing of a Prototype Intradural Spinal Cord Stimulator in a Porcine Model

BACKGROUND

Chronic midline low back pain is the number one reason for disability in the United States despite the prolific use of medical and surgical interventions. Notwithstanding the widespread use of epidural spinal cord stimulators (SCSs), there remains a large portion of the population with inadequate pain control thought to be because of the limited volume of stimulated neural tissue. Intradural SCSs represent an underexplored alternative strategy with the potential to improve selectivity, power efficiency, and efficacy. We studied and carried out development of an intradural form of an SCS. Herein we present the findings of in vivo testing of a prototype intradural SCS in a porcine model.

METHODS

Six female juvenile pigs underwent surgical investigation. One control animal underwent a laminectomy only, whereas the 5 other animals had implantation of an intradural SCS prototype. One of the prototypes was fully wired to enable acute stimulation and concurrent electromyographic recordings. All animals underwent terminal surgery 3 months postimplantation, with harvesting of the spinal column. Imaging (microcomputed tomography scan) and histopathologic examinations were subsequently performed.

RESULTS

All animals survived implantation without evidence of neurologic deficits or infection. Postmortem imaging and histopathologic examination of the spinal column revealed no evidence of spinal cord damage, cerebrospinal fluid fistula formation, abnormal bony overgrowth, or dural defect. Viable dura was present between the intra- and extradural plates of the device. Electromyographic recordings revealed evoked motor units from the stimulator.

CONCLUSIONS

Chronically implanted intradural device in the porcine model demonstrated safety and feasibility for translation into humans.

Spinal cord stimulation failure: evaluation of factors underlying hardware explantation

OBJECTIVE

Spinal cord stimulation has been shown to improve pain relief and reduce narcotic analgesic use in cases of complex refractory pain syndromes. However, a subset of patients ultimately undergoes removal of the spinal cord stimulator (SCS) system, presumably because of surgical complications or poor efficacy. This retrospective study addresses the paucity of evidence regarding risk factors and underlying causes of spinal cord stimulation failures that necessitate this explantation.

METHODS

In this retrospective single-center review, 129 patients underwent explantation of SCS hardware during a 9-year period (2005-2013) following initial placement at the authors' institution or elsewhere. Medical history, including indication of implantation, device characteristics, revision history, and reported reasons for removal of hardware, were reviewed.

RESULTS

The 74 (57%) women and 55 (43%) men were a median of 49 years old (IQR 41-61 years) at explantation; the median time to explantation was 20 months (IQR 7.5-45.5 months). Thoracic or upper lumbar leads were placed in 89.9% of patients primarily for the diagnosis of postsurgical failed-back surgery syndrome (70.5%), chronic regional pain syndrome (14.7%), and neuropathic pain (8.5%). More than half of patients were legally disabled. Initial postoperative reduction in pain was reported in 81% of patients, and 37.8% returned to work. Among 15 patients with acute postsurgical complications (12 infections, 2 hemorrhages, 1 immediate paraplegia), the median time to removal was 2 months. Primary reasons for hardware removal were lack of stimulation efficacy (81%), electrode failure due to migration (14%), and allergic reactions to implanted hardware in 2 patients. The 72 patients who underwent formal psychiatric evaluation before implantation were affected by high rates of major depression (64%), anxiety (34%), posttraumatic stress disorder (PTSD) (12%), drug or alcohol abuse (12%), and physical or sexual abuse (22%).

CONCLUSIONS

The authors' findings provide insight regarding the mechanisms of spinal cord stimulation failure that resulted in total removal of the implanted system. The relationship between spinal cord stimulation failure and certain psychiatric disorders, such as PTSD, depression, and anxiety, is highlighted. Ultimately, this work may shed light on potential avenues to reduce morbidity and improve patient outcomes.

Are Multidimensional Pain Inventory Coping Strategy Profiles Associated with Long-Term Spinal Cord Stimulation Effectiveness?

Introduction

It is acknowledged that the way patients cope with pain may influence treatment outcome. In particular, psychological factors are deemed important when considering patients for suitability for spinal cord stimulation (SCS).

Objective

The aim of the study is to observe how pre-implantation psychological characteristics impact the effectiveness of SCS for chronic pain.

Methods

The analysis comprised data from 137 patients who underwent an SCS implant. Screening evaluation included a coping strategies profile (Multidimensional Pain Inventory) and psychiatric disorders (Mini-International Neuropsychiatric Interview). Based on SCS implant outcome collected during follow-up visits, patients were divided into three groups: subjects with long-term pain relief (long-term group), subjects who failed the SCS treatment and decided to explant trial device (trial explanter group [TE]), and those who chose a permanent device (permanent explanter group [PE]).

Results

Results showed that most of the patients who failed with the SCS (TE and PE groups) demonstrated a dysfunctional coping profile and showed a higher presence of psychiatric disorders, which significantly influenced the experience and perception of pain.

Conclusions

The findings of this study support the value of a multidisciplinary screening. Addressing psychological issues before SCS implantation can reduce the failure rate of SCS.

Evolving Techniques and Indications in Peripheral Nerve Stimulation for Pain

Peripheral nerve stimulation is the direct electrical stimulation of named nerves outside the central neuraxis to alleviate pain in the distribution of the targeted peripheral nerve. These treatments have shown efficacy in treating a variety of neuropathic, musculoskeletal, and visceral refractory pain pathologies; although not first line, these therapies are an important part of the treatment repertoire for chronic pain. With careful patient selection and judicious choice of stimulation technique, excellent results can be achieved for a variety of pain etiologies and distributions. This article reviews current and past practices of peripheral nerve stimulation and upcoming advancements in the field.

Designing and conducting proof-of-concept chronic pain analgesic clinical trials

Introduction:

The evolution of pain treatment is dependent on successful development and testing of interventions. Proof-of-concept (POC) studies bridge the gap between identification of a novel target and evaluation of the candidate intervention's efficacy within a pain model or the intended clinical pain population.

Methods:

This narrative review describes and evaluates clinical trial phases, specific POC pain trials, and approaches to patient profiling.

Results:

We describe common POC trial designs and their value and challenges, a mechanism-based approach, and statistical issues for consideration.

Conclusion:

Proof-of-concept trials provide initial evidence for target use in a specific population, the most appropriate dosing strategy, and duration of treatment. A significant goal in designing an informative and efficient POC study is to ensure that the study is safe and sufficiently sensitive to detect a preliminary efficacy signal (ie, a potentially valuable therapy). Proof-of-concept studies help avoid resources wasted on targets/molecules that are not likely to succeed. As such, the design of a successful POC trial requires careful consideration of the research objective, patient population, the particular intervention, and outcome(s) of interest. These trials provide the basis for future, larger-scale studies confirming efficacy, tolerability, side effects, and other associated risks.

Reliability and Validity of the Minnesota Multiphasic Personality Inventory - 2 - Restructured Form (MMPI-2-RF) in Spine Surgery and Spinal Cord Stimulator Samples

It is not uncommon for patients to report diminished outcomes as a result of spine surgery or a spinal cord stimulator implant. Presurgical psychological evaluations are increasingly used to identify patients at increased risk for such outcomes and use of personality assessment instruments in these evaluations provides incremental information beyond a clinical interview and medical chart review. This investigation explores the psychometric properties of the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF) in a sample of spine surgery patients (n = 810) and in a sample of spinal cord stimulator patients (n = 533). Results indicated that MMPI-2-RF substantive scale scores are reliable, with evidence of good convergent and discriminant validity in both samples. Incorporating the MMPI-2-RF as part of the presurgical evaluation of spine surgery and spinal cord stimulator patients can provide meaningful insight into patients' functioning and help guide pre- and postsurgical treatment in these settings.

Prospective, Randomized, Sham-Control, Double Blind, Crossover Trial of Subthreshold Spinal Cord Stimulation at Various Kilohertz Frequencies in Subjects Suffering From Failed Back Surgery Syndrome (SCS Frequency Study)

INTRODUCTION

The increasing use of high frequency paresthesia-free spinal cord stimulation has been associated with improved outcomes in the therapy of neuropathic pain. What is unknown is the effect of varying frequency on pain relief and the placebo effect.

MATERIALS AND METHODS

This is a prospective, randomized, sham-controlled double blind crossover study. Subjects with predominantly axial low back pain undergoing spinal cord stimulation therapy for failed back surgery syndrome were randomized to sham, 1200 Hz, 3030 Hz, and 5882 Hz with a four-phase crossover design over 12 weeks.

RESULTS

Twenty-four patients were randomized in the study. The mean low back pain score at baseline was 7.75. The mean low back pain scores on a 10 cm visual analog scale during the randomized crossover phase were 4.83, 4.51, 4.57, and 3.22, for sham, 1200 Hz, 3030 Hz, and 5882 Hz, respectively, with the lowest low back pain score observed in the 5882 Hz frequency group (p = 0.002). Of note, sham stimulation resulted in a reduction of pain by -2.92 cm and was not significantly different from stimulation at 1200 Hz and 3030 Hz.

CONCLUSIONS

This randomized crossover study demonstrated that 5882 Hz stimulation can produce significant pain relief for axial low back pain compared with lower frequencies and sham stimulation. Sham stimulation produced similar analgesic effects to 1200 Hz and 3030 Hz and this effect may influence future neuromodulation clinical trial designs.

Measuring Emotional Intelligence Enhances the Psychological Evaluation of Chronic Pain

The assessment of emotional factors, in addition to other psychosocial factors, has been recommended as a means of identifying individuals with chronic pain who may not respond to certain pain treatments. Systematic reviews of the evidence regarding the prediction of responsiveness to a treatment called the spinal cord stimulator (SCS) have yielded inconclusive results. Emotional intelligence is a term which refers to the ability to identify and manage emotions in oneself and others and has been shown to be inversely associated with emotional distress and acute pain. This study aims to investigate the relationship between emotional intelligence, chronic pain, and the more established psychosocial factors usually used for SCS evaluations by clinical psychologists in medical settings. A sample of 112 patients with chronic pain on an acute hospital waiting list for SCS procedures in a pain medicine service were recruited. Psychological measures were completed including: a novel measure of emotional intelligence; usual measures of emotional distress and catastrophizing; and a numerical rating scale designed to assess pain intensity, pain-related distress, and interference. As predicted, findings revealed significant associations between most of the measures analyzed and current pain intensity. When entered into a simultaneous regression analysis, emotional intelligence scores remained the only significant predictor of current pain intensity. There are potential clinical, ethical, and organizational implications of emotional intelligence processes partially predicting pain in patients on a waiting list for a medical procedure. These results may offer new insight, understanding, and evaluation targets for clinical psychologists in the field of pain management.

Complex regional pain syndrome-up-to-date

Complex regional pain syndrome (CRPS) was described for the first time in the 19th century by Silas Weir Mitchell. After the exclusion of other causes, CRPS is characterised by a typical clinical constellation of pain, sensory, autonomic, motor, or trophic symptoms which can no longer be explained by the initial trauma. These symptoms spread distally and are not limited to innervation territories. If CRPS is not improved in the acute phase and becomes chronic, the visible symptoms change throughout because of the changing pathophysiology; the pain, however, remains. The diagnosis is primarily clinical, although in complex cases further technical examination mainly for exclusion of alternative diagnoses is warranted. In the initial phase, the pathophysiology is dominated by a posttraumatic inflammatory reaction by the activation of the innate and adaptive immune system. In particular, without adequate treatment, central nociceptive sensitization, reorganisation, and implicit learning processes develop, whereas the inflammation moderates. The main symptoms then include movement disorders, alternating skin temperature, sensory loss, hyperalgesia, and body perception disturbances. Psychological factors such as posttraumatic stress or pain-related fear may impact the course and the treatability of CRPS. The treatment should be ideally adjusted to the pathophysiology. Pharmacological treatment maybe particularly effective in acute stages and includes steroids, bisphosphonates, and dimethylsulfoxide cream. Common anti-neuropathic pain drugs can be recommended empirically. Intravenous long-term ketamine administration has shown efficacy in randomised controlled trials, but its repeated application is demanding and has side effects. Important components of the treatment include physio- and occupational therapy including behavioural therapy (eg, graded exposure in vivo and graded motor imaging). If psychosocial comorbidities exist, patients should be appropriately treated and supported. Invasive methods should only be used in specialised centres and in carefully evaluated cases. Considering these fundamentals, CRPS often remains a chronic pain disorder but the devastating cases should become rare.

Neuropathic Pain and Spinal Cord Injury: Phenotypes and Pharmacological Management

Chronic neuropathic pain is a complicated condition after a spinal cord injury (SCI) that often has a lifelong and significant negative impact on life after the injury; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Thus, identifying human neuropathic pain phenotypes based on pain symptoms, somatosensory changes, or cognitive and psychosocial factors that reflect specific spinal cord or brain mechanisms of neuropathic pain is an important goal. Once a pain phenotype can be reliably replicated, its relationship with biomarkers and clinical treatment outcomes can be analyzed, and thereby facilitate translational research and further the mechanistic understanding of individual differences in the pain experience and in clinical trial outcomes. The present article will discuss clinical aspects of SCI-related neuropathic pain, neuropathic pain phenotypes, pain mechanisms, potential biomarkers and pharmacological interventions, and progress regarding how defining neuropathic pain phenotypes may lead to more targeted treatments for these difficult pain conditions.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for "precision medicine" or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

Neuropathic pain

Neuropathic pain is caused by a lesion or disease of the somatosensory system, including peripheral fibres (Aβ, Aδ and C fibres) and central neurons, and affects 7-10% of the general population. Multiple causes of neuropathic pain have been described and its incidence is likely to increase owing to the ageing global population, increased incidence of diabetes mellitus and improved survival from cancer after chemotherapy. Indeed, imbalances between excitatory and inhibitory somatosensory signalling, alterations in ion channels and variability in the way that pain messages are modulated in the central nervous system all have been implicated in neuropathic pain. The burden of chronic neuropathic pain seems to be related to the complexity of neuropathic symptoms, poor outcomes and difficult treatment decisions. Importantly, quality of life is impaired in patients with neuropathic pain owing to increased drug prescriptions and visits to health care providers, as well as the morbidity from the pain itself and the inciting disease. Despite challenges, progress in the understanding of the pathophysiology of neuropathic pain is spurring the development of new diagnostic procedures and personalized interventions, which emphasize the need for a multidisciplinary approach to the management of neuropathic pain.

Neuropathic pain

Neuropathic pain is caused by a lesion or disease of the somatosensory system, including peripheral fibres (Aβ, Aδ and C fibres) and central neurons, and affects 7-10% of the general population. Multiple causes of neuropathic pain have been described and its incidence is likely to increase owing to the ageing global population, increased incidence of diabetes mellitus and improved survival from cancer after chemotherapy. Indeed, imbalances between excitatory and inhibitory somatosensory signalling, alterations in ion channels and variability in the way that pain messages are modulated in the central nervous system all have been implicated in neuropathic pain. The burden of chronic neuropathic pain seems to be related to the complexity of neuropathic symptoms, poor outcomes and difficult treatment decisions. Importantly, quality of life is impaired in patients with neuropathic pain owing to increased drug prescriptions and visits to health care providers, as well as the morbidity from the pain itself and the inciting disease. Despite challenges, progress in the understanding of the pathophysiology of neuropathic pain is spurring the development of new diagnostic procedures and personalized interventions, which emphasize the need for a multidisciplinary approach to the management of neuropathic pain.

10 kHz High-Frequency Spinal Cord Stimulation for Chronic Axial Low Back Pain in Patients With No History of Spinal Surgery: A Preliminary, Prospective, Open Label and Proof-of-Concept Study

OBJECTIVE

To explore the effectiveness of 10 kHz high frequency spinal cord stimulation (HF10 therapy) treatment of chronic low back pain in patients who have not had spinal surgery.

METHODS

Patients with chronic low back pain without prior spinal surgery were evaluated by a team of spine surgeons to rule out any spinal pathology amenable to surgical interventions and by a multidisciplinary pain team to confirm eligibility for the study. After a successful (>50% back pain reduction) trial of HF10 therapy, enrolled subjects underwent permanent system implantation and were followed-up one year post-implant.

RESULTS

About 95% of the enrolled subjects (20/21) received the permanent system. At 12 months post-implant, both back pain VAS score and ODI were significantly reduced compared with baseline values (by 73% and 48%, respectively); an estimated quality-adjusted life year gain of 0.47 and a reduction in opioid use by 64% was observed. Four more patients among those unable to work at baseline due to back pain were employed at 12 months post-implant. There were no serious adverse events.

CONCLUSION

HF10 therapy may provide significant back pain relief, reduction in disability, improvement quality of life, and reduction in opioid use in chronic low back pain not resulting from spinal surgery.

Psychological risk factors in back pain patients at an orthopaedic outpatient clinic

BACKGROUND

Psychological risk factors have shown to be important prognostic indicators of back surgery outcome. Prevalence of these risk factors has rarely been examined in an outpatient clinic population. Furthermore, it is unclear to which extent they play a role, in absence of routinely used psychological screening tools, in treatment assignment.

OBJECTIVE

First aim of this study was to examine the prevalence of psychological risk factors in back pain patients at an orthopaedic outpatient clinic. Second aim was to investigate the prognostic value of these identified risk factors in treatment assignment by the orthopaedic surgeons (conservative vs. surgery).

METHODS

Sixty-six adult back pain patients were included. Psychological risk factor prevalence was determined with the Hospital Anxiety and Depression Scale, Tampa Scale of Kinesiophobia and Pain Catastrophizing Scale. Prognostic value of these risk factors in treatment assignment was examined using statistics.

RESULTS

Respectively, 30 (45% HADS Anxiety), 27 (41%, HADS Depression), 19 (29%, PCS) and 37 (56%, TSK) patients scored above cut-off. No prognostic value of risk factors in treatment assignment, was found.

CONCLUSIONS

The majority of patients in our study is at risk of poor surgical outcome due to presence of psychological risk factors. Future studies should target the development of screening tools for an early identification of those at risk.

Presurgical Psychological Assessments as Correlates of Effectiveness of Spinal Cord Stimulation for Chronic Pain Reduction

BACKGROUND

Spinal Cord Stimulator (SCS) is a surgically implanted device for patients with certain types of chronic pain. While some studies show the value of psychological screening of potential SCS candidates, no consensus exists. This single-site study analyzed the association of SCS success with psychological assessments (e.g., Millon Behavioral Medicine Diagnostic), beliefs regarding SCS efficacy, self-reported pain and quality of life (QOL) among patients approved for SCS.

METHODS

Potential SCS candidates (N = 200) were contacted 3-7 years after initial psychological and medical clearance for SCS; 59 consented to a structured telephone interview. Thirty-four of the 59 had received a SCS; 25 had not received a SCS. Of the 34 that had received a SCS, 22 were approved by routine psychological evaluation while 12 went through in-depth psychological testing.

RESULTS

The majority of respondents (62%) reported effective pain reduction, and 64% of SCS recipients reported improved QOL. Younger patients reported higher pre-implantation pain scores, and participants with higher levels of pain preimplantation were more likely say they would undergo the procedure again. Finally, persons reporting preoperative alcohol problems were more likely to report lower levels of post-SCS pain.

CONCLUSION

Predictors of pain relief and QOL following SCS may depend on expectations of the device and on individuals' interpretation of pain or psychosocial health.