Disease applications of spinal cord stimulation: Chronic nonmalignant pain

Neuropathic pain is a chronic condition representing a significant burden for society. It is estimated 1 out of 10 people over the age of 30 that in the US have been diagnosed with neuropathic pain. Most of the available treatments for neuropathic pain have moderate efficacy over time which limit their use; therefore, other therapeutic approaches are needed for patients. Spinal cord stimulation is an established and cost-effective modality for treating severe chronic pain. In this article we will review the current approved indications for the use of spinal cord stimulation in the US and the novel therapeutic options which are now available using this therapy.

Postural Changes in Spinal Cord Stimulation Thresholds: Current and Voltage Sources

OBJECTIVE

Spinal cord stimulation (SCS) thresholds are known to change with body position; however, these changes have not been fully characterized for both "constant-voltage" and "constant-current" pulse generators. This study aimed to evaluate and quantify changes in psychophysical thresholds resulting from postural changes that may affect both conventional paresthesia-based SCS and novel paresthesia-free SCS technologies.

MATERIALS AND METHODS

We measured perceptual, usage, and discomfort thresholds in four body positions (prone, supine, sitting, standing) in 149 consecutive patients, with temporary lower thoracic percutaneous epidural electrodes placed for treating persistent low back and leg pain. We trialed 119 patients with constant-voltage stimulators and 30 patients with constant-current stimulators.

RESULTS

Moving from supine to the sitting, standing, or prone positions caused all three thresholds (perceptual, usage, and discomfort) to increase by 22% to 34% for constant-voltage stimulators and by 44% to 82% for constant-current stimulators. Changing from a seated to a supine position caused stimulation to exceed discomfort threshold significantly more often for constant-current (87%) than for constant-voltage (63%) stimulators (p = 0.01).

CONCLUSIONS

Posture-induced changes in SCS thresholds occurred consistently as patients moved from lying (supine or prone) to upright (standing or sitting) positions. These changes were more pronounced for constant-current than for constant-voltage pulse generators and more often led to stimulation-evoked discomfort. These observations are consistent with postural changes in spinal cord position measured in imaging studies, and with computer model predictions of neural recruitment for these different spinal cord positions. These observations have implications for the design, implantation, and clinical application of spinal cord stimulators, not only for conventional paresthesia-based SCS but also for paresthesia-free SCS.

A Definition of Neuromodulation and Classification of Implantable Electrical Modulation for Chronic Pain

OBJECTIVES

Neuromodulation therapies use a variety of treatment modalities (eg, electrical stimulation) to treat chronic pain. These therapies have experienced rapid growth that has coincided with escalating confusion regarding the nomenclature surrounding these neuromodulation technologies. Furthermore, studies are often published without a complete description of the effective stimulation dose, making it impossible to replicate the findings. To improve clinical care and facilitate dissemination among the public, payors, research groups, and regulatory bodies, there is a clear need for a standardization of terms.

APPROACH

We formed an international group of authors comprising basic scientists, anesthesiologists, neurosurgeons, and engineers with expertise in neuromodulation. Because the field of neuromodulation is extensive, we chose to focus on creating a taxonomy and standardized definitions for implantable electrical modulation of chronic pain.

RESULTS

We first present a consensus definition of neuromodulation. We then describe a classification scheme based on the 1) intended use (the site of modulation and its indications) and 2) physical properties (waveforms and dose) of a neuromodulation therapy.

CONCLUSIONS

This framework will help guide future high-quality studies of implantable neuromodulatory treatments and improve reporting of their findings. Standardization with this classification scheme and clear definitions will help physicians, researchers, payors, and patients better understand the applications of implantable electrical modulation for pain and guide informed treatment decisions.

Screening trials of spinal cord stimulation for neuropathic pain in England—A budget impact analysis

Screening trials of spinal cord stimulation (SCS) prior to full implantation of a device are recommended by expert guidelines and international regulators. The current study sought to estimate the budget impact of a screening trial of SCS and the costs or savings of discontinuing the use of a screening trial. A budget impact analysis was performed considering a study population that reflects the size and characteristics of a patient population with neuropathic pain in England eligible for SCS. The perspective adopted was that of the NHS with a 5-year time horizon. The base case analysis indicate that a no screening trial strategy would result in cost-savings to the NHS England of £400,000–£500,000 per year. Sensitivity analyses were conducted to evaluate different scenarios. If ≥5% of the eligible neuropathic pain population received a SCS device, cost-savings would be >£2.5 million/year. In contrast, at the lowest assumed cost of a screening trial (£1,950/patient), a screening trial prior to SCS implantation would be cost-saving. The proportion of patients having an unsuccessful screening trial would have to be ≥14.4% for current practice of a screening trial to be cost-saving. The findings from this budget impact analysis support the results of a recent UK multicenter randomized controlled trial (TRIAL-STIM) of a policy for the discontinuation of compulsory SCS screening trials, namely that such a policy would result in considerable cost-savings to healthcare systems.

Trends in Utilization and Cost of Inpatient Spinal Cord Stimulation: Analysis of Data from 2008 to 2014

OBJECTIVE

In this study, we sought to characterize contemporary trends in cost and utilization of spinal cord stimulation (SCS).

METHODS

The Healthcare Cost and Utilization Project-National Inpatient Sample was queried for inpatient admissions from 2008 to 2014 where SCS was performed. We then determined the rates and costs of SCS performed in this time frame to treat diagnoses that we classified as device-related complications, degenerative spine disease, pain syndromes, and neuropathies/neuritis/nerve lesions. Least-squares regression was performed to determine the yearly trends for each indication adjusted by the total number of yearly hospitalizations for that diagnosis.

RESULTS

We identified a total of 6876 admissions in whom an SCS was performed. The overall rate of inpatient SCS procedures performed has decreased by 45% from 2008 to 2014 (14.0 to 7.7 procedures per 100,000 admissions). Adjusted analysis for yearly trends also demonstrated a declining trend for all indications; however, this was not found to be statistically significant, except for device-related complications (P = 0.004). The median inflation-adjusted cost of an admission where SCS was performed increased slightly by 7.4% from $26,200 (IQR: $16,700-$33,800) in 2008 to $28,100 (IQR: $19,600-$36,900) in 2014. Billed hospital charges demonstrated a significant increase with median inflation-adjusted admission charge of $66,068 in 2008 to $110,672 in 2014.

CONCLUSIONS

Despite a declining contemporary trend in inpatient SCS, an increase was noted in admission costs and hospital charges. A significant declining trend was noted in revision SCS implantations due to device-related complications.

Examining the Need to Standardize Implanted Stimulator Connectors: NANS Survey Results

INTRODUCTION

Connectors between implanted stimulator electrodes and pulse generators allow revisions, including battery changes or generator upgrades, to proceed without disturbing uninvolved components, such as the electrode. As new devices are introduced, however, connector incompatibility, even with updated hardware from the same manufacturer, can lead to additional procedures, expense, and morbidity.

MATERIALS AND METHODS

Following the example of the cardiac pacemaker/defibrillator industry, the Institute of Neuromodulation (IoN) met to explore the possibility of creating connector standards for implanted neurostimulation devices. At a subsequent meeting of the Association for the Advancement of Medical Instrumentation, which coordinates the development of such standards, industry representatives asked for data defining the need for a new standard. Accordingly, IoN prepared an online survey to be sent to the North American Neuromodulation Society mailing list regarding experience with the connectivity of spinal cord stimulation (SCS) generators and electrodes.

RESULTS

The 87 respondents of 9657 surveyed included 77 clinicians, who reported a total of 42,572 SCS implants and revisions. More than a quarter of revisions (2741 of 9935) required the interconnection of devices made by separate manufacturers, in most cases (n = 1528) to take advantage of a new feature (e.g., rechargeability, new waveform) or because an original component could not be replaced (n = 642). Connector adapters provided by manufacturers were used in less than half (n = 1246) of these cases. Nearly all (94%) of the clinicians agreed that standardized connectors should be developed for SCS, and 86% opined that standardized connectors should be developed for other neurostimulation therapies.

CONCLUSION

Those who responded to our survey support the development of standard connectors for implanted stimulators, with voluntary compliance by manufacturers, to mitigate the need for adapters and facilitate interchanging components when appropriate. Other advantages to patients and manufacturers might accrue from the adoption of standards, as technology evolves and diversifies.

Systematic Review of Research Methods and Reporting Quality of Randomized Clinical Trials of Spinal Cord Stimulation for Pain

This systematic review assessed design characteristics and reporting quality of published randomized clinical trials of spinal cord stimulation (SCS) for treatment of pain in adults and adolescents. The study protocol was registered with PROSPERO (CRD42018090412). Relevant articles were identified by searching the following databases through December 31, 2018: MEDLINE, Embase, WikiStim, The Cochrane Database of Systematic Reviews, and The Cochrane Central Register of Controlled Trials. Forty-six studies were included. Eighty-seven percent of articles identified a pain-related primary outcome. Secondary outcomes included physical functioning, health-related quality of life, and reductions in opioid use. Nineteen of the 46 studies prespecified adverse events as an outcome, with 4 assessing them as a primary outcome. Eleven studies stated that they blinded participants. Of these, only 5 were assessed as being adequately blinded. The number of participants enrolled was generally low (median 38) and study durations were short (median 12 weeks), particularly in studies of angina. Fifteen studies employed an intention-to-treat analysis, of which only seven specified a method to accommodate missing data. Review of these studies identified deficiencies in both reporting and methodology. The review's findings suggest areas for improving the design of future studies and increasing transparency of reporting. PERSPECTIVE: This article presents a systematic review of research methods and reporting quality of randomized clinical trials of SCS for the treatment of various pain complaints. The review identifies deficiencies in both methodology and reporting, which may inform the design of future studies and improve reporting standards.

Cost-Effectiveness Model Shows Superiority of Wireless Spinal Cord Stimulation Implantation Without a Separate Trial

Objective

We evaluated the cost‐effectiveness of wireless spinal cord stimulation (Wireless SCS) with single stage “direct to permanent” implantation vs. screening with temporary electrodes and an external pulse generator followed by implantation of a system for long‐term use (IPG SCS).

Materials and Methods

We created a cost model that takes a 2019 United States (U.S.) payer perspective and is based on IPG SCS cost models for subjects with chronic back and/or leg pain. Our six‐month decision tree includes the screening trial period (success ≥50% relief) and leads to various levels of pain relief with or without complications for IPG SCS and Wireless SCS and without complications for conventional medical management (CMM). Every three months in the follow‐on 15‐year Markov model (with costs and quality‐adjusted life years discounted 3.5% annually), subjects remain stable or transition to deteriorated health or death. Subjects who fail SCS receive CMM. After 60 Markov cycles, a 100,000‐sample simulation reveals the impact of maximum willingness‐to‐pay (WTP) from $10,000 to $100,000 per quality‐adjusted life year on net monetary benefit (NMB). Sensitivity analyses considered the impact of the Wireless SCS screening success rate, Wireless SCS device cost, and IPG SCS device longevity.

Results

Compared with IPG SCS, Wireless SCS offers higher clinical effectiveness at a lower cost and a higher NMB for our WTP thresholds and is, thus, dominant. Wireless SCS is also cost‐effective compared with CMM. Results remain robust with 1) Wireless SCS screening success rates as low as 85% (dominant), 2) the cost of the Wireless SCS devices as high as $55,000 (cost‐effective), and 3) IPG SCS devices lasting 12 years (dominant).

Conclusions

In this model, compared with IPG SCS or with CMM, Wireless SCS is a superior strategy.

Randomized Placebo-/Sham-Controlled Trials of Spinal Cord Stimulation: A Systematic Review and Methodological Appraisal

OBJECTIVES

The recent availability of paraesthesia/sensation free spinal cord stimulation (SCS) modalities allow the design of clinical trials of SCS using placebo/sham controls and blinding of patients, clinicians, and researchers. The aims of this study were to: 1) systematically review the current evidence base of randomized controlled trials (RCTs) of SCS placebo/sham trials and 2) to undertake a methodological critique of their methods. Based on this critique, we developed a checklist for the design and reporting of future RCTs of SCS.

MATERIALS AND METHODS

Electronic data bases were searched from inception until January 2019 for RCTs of SCS using a placebo/sham control. RCTs with only an active comparator arm were excluded. The results are presented as a narrative synthesis.

RESULTS

Searches identified 12 eligible RCTs. SCS modalities included paraesthesia stimulation, subthreshold, burst, and high-frequency SCS and were mainly conducted in patients with failed back surgery syndrome, complex regional pain syndrome, and refractory angina. The quality and transparency of reporting of the methods of placebo stimulation, blinding of patients, clinicians, and researchers varied markedly across studies.

CONCLUSIONS

To date the methods of placebo/sham control and blinding in RCTs have been poorly reported, leading to concerns about the validity and replicability of the findings. Important aspects that need to be clearly reported in the design of placebo-/sham-controlled RCTs of SCS include the transparent reporting of stimulation programming parameters, patient position during perception threshold measurement, management of the patient handheld programmer, frequency of recharging, and assessment of the fidelity of blinding.

Redefining Spinal Cord Stimulation "Trials": A Randomized Controlled Trial Using Single-Stage Wireless Permanent Implantable Devices

BACKGROUND

"Traditional" spinal cord stimulation (SCS) trials with percutaneous electrodes externalized to a pulse generator (PG) are typically limited in duration due to risk of infection. Newer miniaturized wireless SCS technology eliminates the percutaneous extension (as well as PGs implanted for chronic use), thus facilitating a single-stage implantation after which the device can remain indefinitely.

OBJECTIVE

To evaluate fully implanted wireless SCS devices during a 30-day screening trial in subjects with chronic low back pain and leg pain and a history of lumbosacral spine surgery.

METHODS

In a randomized controlled trial of single-stage wireless SCS using a wireless percutaneous system, 99 subjects received either 10 kHz high frequency stimulation (HFS) or lower frequency stimulation (LFS) below 1500 Hz (Bolash R, Creamer M, Rauck R, et al. Wireless high frequency spinal cord stimulation (10 kHz) compared to multi-waveform low frequency spinal cord stimulation in the management of chronic pain in failed back surgery syndrome subjects: preliminary results of a multicenter, prospective, randomized controlled study. Pain Med 2019, https://doi.org/10.1093/pm/pnz019). In this report, we assess the 30-day trial success rate (≥50% pain relief from baseline) and complications.

RESULTS

The overall trial success rate was 88% (87/99): 92% (46/50) for HFS and 84% (41/49) for LFS (NS). The trial success rate in the 64 subjects with predominant low back pain was 92% (59/64) vs. 80% (28/35) in those with leg pain ≥ low back pain (NS). During the screening trial, one infection occurred (1%) and one subject withdrew and was explanted (1%). Electrode migrations were seen on routine follow-up x-rays in 10 cases (10%).

CONCLUSION

Using wireless SCS devices that allow for an extended trial period and evaluation of various waveforms, we observed a high rate trial success rate with both HFS and LFS waveforms, with minimal incidence of infection. Long-term follow-up will address the cost-effectiveness and morbidity associated with this technology, which facilitates single-stage treatment.

WIKISTIM.org: An On-Line Database of Published Neurostimulation Studies

INTRODUCTION

Primary data reported in scientific publications provide guidance for improving patient care, expanding indications, identifying research gaps, educating patients, justifying reimbursement, and gaining regulatory approval. Finding and analyzing pertinent publications among the huge volume noted in databases such as PUBMED, however, costs time and effort. This situation demands innovative ways to locate citations of (and the possibility of abstracting data from) papers reporting primary findings.

METHODS

We created WIKISTIM.org, a searchable easily navigated website, to meet this challenge in our field and devised a taxonomy of data categories specific for various stimulation targets for extracting and posting primary data. We included a discussion section unlimited by time or space to overcome limits posed by traditional letters to the editor.

RESULTS

Registrants can download single or multiple citations from search results or from the list of papers (sortable by author, title, publication, and year) into a single table. The downloadable data category lists are used to submit completed data entry sheets for upload and for evidence-based comparison across studies as well as for study design, manuscript preparation, and peer review. Registration for WIKISTIM access continues to grow as do the curated citation lists, which are updated monthly and are comprehensive for deep brain stimulation, dorsal root ganglion stimulation, gastric electric stimulation, spinal cord stimulation, and sacral nerve stimulation.

CONCLUSIONS

Most WIKISTIM entries are limited to citation information and links to published abstracts. As the number of completed datasheets and of stimulation target sections increase, the value of WIKISTIM will increase.

Tonic and burst spinal cord stimulation waveforms for the treatment of chronic, intractable pain: study protocol for a randomized controlled trial

Background

Burst stimulation is a novel form of neurostimulation for the treatment of chronic pain which has demonstrated promise in small uncontrolled studies, but has not yet gained approval for use in the U.S. We report the study methods for an ongoing multicenter, randomized, controlled, cross-over study designed to gain United States Food and Drug Administration (FDA) approval for burst stimulation.

Methods

Participants who are candidates for a currently approved neurostimulation device were enrolled and screened. Participants who fail a tonic trial evaluation, have significant depressive symptoms, or evidence lack of compliance with study procedures by failing to complete 7 days of a Pain Diary are excluded. Participants receiving a permanent implant are randomized to receive: (1) 12 weeks of tonic followed by 12 weeks of burst stimulation or (2) 12 weeks of burst stimulation followed by 12 weeks of tonic stimulation. Assessments occur at 6, 12, 18, and 24 weeks. After 24 weeks, participants choose their preferred therapy and are assessed every 6 months for up to 2 years. All patients had the device leads inserted at the site of a successful tonic stimulation trial. Assessments include: a Pain Diary using a Visual Analog Scale (VAS) for overall, trunk, and limb pain, the Beck Depression Inventory, the Pain Catastrophizing Scale, the Oswestry Disability Index, paresthesia, satisfaction, and therapy preference. Reported adverse events are collected throughout the study. The primary endpoint is the noninferiority of burst stimulation compared to tonic measured by the within-subject difference in the mean overall VAS score at the end of each 12-week stimulation period.

Discussion

This trial represents the largest controlled trial of burst stimulation to date, and is expected to yield important information regarding the safety and efficacy of burst stimulation.

Trial registration

ClinicalTrials.gov, NCT02011893. Registered on 10 December 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1706-5) contains supplementary material, which is available to authorized users.

A review of economic factors related to the delivery of health care for chronic low back pain

INTRODUCTION AND METHODS

We describe tools used to evaluate the economic impact of health care interventions, discuss the economic burden of chronic low back pain, and review evidence on the cost-effectiveness of treating failed back surgery syndrome with spinal cord stimulation, intrathecal drug delivery, acupuncture, epidural injections, disc prosthesis, lumbar fusion, and noninvasive therapies. We also mention the lack of cost studies for emerging therapies, such as vibrotherapy and peripheral nerve field stimulation. Topics include types of cost studies; the economic perspectives taken by such studies; direct and indirect costs; measures of success; definitions of cost-effectiveness, incremental cost-effectiveness, incremental cost-utility ratios, and quality-adjusted life years; the concept of maximum willingness to pay; and the use of cost-effectiveness models.

CONCLUSION

The fact that chronic low back pain arises from a variety of causes makes choosing appropriate treatment difficult. Determining the cost-effectiveness of various treatments for chronic low back pain depends on well-designed and well-executed randomized controlled trials with parallel economic evaluations. Researchers can use economic models to extrapolate costs and outcomes over the long term.

Prevention of percutaneous spinal cord stimulation electrode migration: a 15-year experience

OBJECTIVES

Percutaneous spinal cord stimulation electrodes have a propensity to migrate longitudinally, which is a costly complication that often compromises therapeutic effect. After implementing simple changes to our percutaneous electrode anchoring technique, we no longer encounter this migration. The current retrospective study updates previously reported results.

MATERIALS AND METHODS

We retrospectively examined data in a consecutive series of patients in whom we had secured a new percutaneous electrode by injecting < 0.1 cm(3) of adhesive into the silicone elastomer lead anchor. From 1998 through 2006, we used whichever anchor was supplied with each lead until we observed one case of migration through a short anchor; thereafter, we used a long, tapered anchor exclusively. From 2007 through 2013, we further modified our technique by adding a fascial incision to accommodate the tip of the anchor and by increasing the strength of our suture material.

RESULTS

In the first series of 291 patients, followed through July 2007 (mean 4.75 years, range 1.1-9.0 years), 4 (1.37%) experienced electrode migration requiring surgical revision. Only one lead had moved with respect to its anchor; the other three anchors remained securely bonded to their leads. No migration (0.00%) occurred in the second series of 142 patients, followed through 2013 (mean follow-up 2.86 years, range 0.10-5.45 years).

CONCLUSION

Improvements to our simple, inexpensive technique apparently have eliminated the most common complication of spinal cord stimulation.

Spinal cord stimulation for predominant low back pain in failed back surgery syndrome: study protocol for an international multicenter randomized controlled trial (PROMISE study)

BACKGROUND

Although results of case series support the use of spinal cord stimulation in failed back surgery syndrome patients with predominant low back pain, no confirmatory randomized controlled trial has been undertaken in this patient group to date. PROMISE is a multicenter, prospective, randomized, open-label, parallel-group study designed to compare the clinical effectiveness of spinal cord stimulation plus optimal medical management with optimal medical management alone in patients with failed back surgery syndrome and predominant low back pain.

METHOD/DESIGN

Patients will be recruited in approximately 30 centers across Canada, Europe, and the United States. Eligible patients with low back pain exceeding leg pain and an average Numeric Pain Rating Scale score ≥5 for low back pain will be randomized 1:1 to spinal cord stimulation plus optimal medical management or to optimal medical management alone. The investigators will tailor individual optimal medical management treatment plans to their patients. Excluded from study treatments are intrathecal drug delivery, peripheral nerve stimulation, back surgery related to the original back pain complaint, and experimental therapies. Patients randomized to the spinal cord stimulation group will undergo trial stimulation, and if they achieve adequate low back pain relief a neurostimulation system using the Specify® 5-6-5 multi-column lead (Medtronic Inc., Minneapolis, MN, USA) will be implanted to capture low back pain preferentially in these patients. Outcome assessment will occur at baseline (pre-randomization) and at 1, 3, 6, 9, 12, 18, and 24 months post randomization. After the 6-month visit, patients can change treatment to that received by the other randomized group. The primary outcome is the proportion of patients with ≥50% reduction in low back pain at the 6-month visit. Additional outcomes include changes in low back and leg pain, functional disability, health-related quality of life, return to work, healthcare utilization including medication usage, and patient satisfaction. Data on adverse events will be collected. The primary analysis will follow the intention-to-treat principle. Healthcare use data will be used to assess costs and long-term cost-effectiveness.

DISCUSSION

Recruitment began in January 2013 and will continue until 2016.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT01697358 (http://www.clinicaltrials.gov).

Spinal cord stimulator adjustment to maximize implanted battery longevity: a randomized, controlled trial using a computerized, patient-interactive programmer

Internally powered, implanted pulse generators (IPGs) have been an important advance in spinal cord stimulation for the management of pain, but they require surgical replacement, with attendant cost and risk, when the implanted battery is depleted. Battery life is determined by the programmed settings of the implant, but until now the technical means to optimize settings for maximal battery life, delaying surgical replacement as long as possible, Materials and Methods.  We have developed a patient-interactive, computerized programmer for use with IPGs. It has been designed for easy operation and comprehensive data management, which have not been features of the standard programmers available until now. It automatically and rapidly presents to the patient a sequence of settings (contact combinations and pulse parameters) specified by the practitioner. Test results are analyzed and sorted to determine the optimal settings by multiple criteria, including battery life. In the present study we used new, improved algorithms to estimate battery life.  We have compared the computerized, patient-interactive system with standard practitioner-operated, manual programming methods in a randomized, controlled trial in 44 patients at two study centers.  In 95% of patients (41/43), the computerized, patient-interactive system identified new settings with improved estimated battery life (and corresponding anticipated cost savings) which had not been recognized as such using manual methods. The estimated battery life for the setting chosen by each patient using manual methods averaged 25.4 ± 49.5 (mean ± standard deviation) months; the longest battery life identified by computerized methods averaged 55.0 ± 71.7, a 2.2-fold or 29.6 month improvement. Seventy-two percent of patients (31/43) achieved better battery life at settings with technical results (visual analog scale rating of overlap or coverage of pain by stimulation paresthesias) equal or superior to those achieved by manual methods. The overall improvement over the setting chosen by manual methods was 1.41-fold or 10.5 months; averaged by patient, the improvement was 1.63-fold. Estimated cost savings averaged just over one-third. As reported previously, the new system also yields significantly (p < 0.0001) better technical results than traditional, manual methods in achieving coverage of pain by stimulation paresthesias; the very best technical results were achieved at some expense in estimated battery life (assuming the same frequency of use). We conclude that significant potential savings in longevity of the implanted battery are possible in the majority of patients with implanted spinal cord stimulators, but have not been realized until now for lack of appropriate methods. Computerized, patient-interactive programming addresses this problem and allows optimization of estimated battery life along with other treatment goals. Long-term clinical followup will be required to establish the full magnitude of the resulting savings.

Spinal cord stimulation with interleaved pulses: a randomized, controlled trial

Objectives.  The development of multicontact electrodes and programmable, implanted pulse generators has increased the therapeutic success of spinal cord stimulation (SCS) by enhancing the ability to capture and maintain pain/paresthesia overlap. This study sought to determine if interleaved stimulation and/or frequency doubling improves pain/paresthesia overlap in patients with failed back surgery syndrome. Methods.  Using a patient-interactive computer system that quantifies SCS performance and presents stimulation settings in randomized, double-blind fashion, we compared the effect on pain/paresthesia overlap of interleaved stimulation (rapidly interleaved pulse trains using two different contact combinations) vs. standard treatment with a single contact combination, controlling for frequency doubling. Stimulation amplitude (charge per phase, as determined by varying pulse voltage or width) was adjusted to a subjectively comfortable intensity (usage amplitude), which was maintained for all trials in each patient. The number of percutaneous spinal electrodes used (one or two) and the phase angle between interleaved pulses were additional study variables. Results.  Multivariate analysis of 266 test results from 15 patients revealed a statistically significant (p ≤ 0.05) association between increased computer-calculated pain/paresthesia overlap and 1) high- and low-frequency interleaved stimulation using two combinations of contacts and 2) frequency doubling using one combination. We found no significant effect for electrode configuration (single or dual), pulse width matching, or phase angle. Conclusions.  The statistically significant advantages we observed for SCS with interleaved stimulation are explained, at least in part, by the effects of frequency doubling. These findings have important implications for the design and adjustment of pulse generators.

Postural changes in spinal cord stimulation perceptual thresholds

Introduction. Spinal cord stimulation voltage thresholds have been observed to change with body position, but previously have not been characterized in detail. Design. Prospective case series. Methods. We have obtained voltage measurements at the threshold of perception in three body postures for patients with percutaneous dorsal epidural leads. Results. In our sample of 42 patients, we observed a significant (p = 0.000) increase in voltage requirements when moving from supine to sitting or standing positions. This increase can be represented as a linear slope (1.25) across a range of baseline voltage amplitudes. Ninety-five percent of patients experienced an increase, primarily between 11 and 25%. Conclusions. These observations have implications for the design, implantation, and clinical application of spinal cord stimulators.

Spinal cord stimulation paresthesia and activity of primary afferents

A patient with failed back surgery syndrome reported paresthesia in his hands and arms during a spinal cord stimulation (SCS) screening trial with a low thoracic electrode. The patient's severe thoracic stenosis necessitated general anesthesia for simultaneous decompressive laminectomy and SCS implantation for chronic use. Use of general anesthesia gave the authors the opportunity to characterize the patient's unusual distribution of paresthesia. During SCS implantation, they recorded SCS-evoked antidromic potentials at physiologically relevant amplitudes in the legs to guide electrode placement and in the arms as controls. Stimulation of the dorsal columns at T-8 evoked potentials in the legs (common peroneal nerves) and at similar thresholds, consistent with the sensation of paresthesia in the arms, in the right ulnar nerve. The authors' electrophysiological observations support observations by neuroanatomical specialists that primary afferents can descend several (in this case, at least 8) vertebral segments in the spinal cord before synapsing or ascending. This report thus confirms a physiological basis for unusual paresthesia distribution associated with thoracic SCS.

DYSPHAGIA AND NEUROPATHIC FACIAL PAIN TREATED WITH MOTOR CORTEX STIMULATION

OBJECTIVE

We report on a patient with a neuropathic facial pain syndrome, including elements of trigeminal neuralgia, glossopharyngeal neuralgia, and dysphagia. After failing medical and surgical decompressive treatments, the patient underwent implantation of a motor cortex stimulation (MCS) system.

CLINICAL PRESENTATION

A 54-year-old woman presented with a 14-year history of left-sided facial pain, throat pain, and associated nausea and vomiting. The patient failed several open surgical and percutaneous procedures for her facial pain syndrome. Additionally, several medication trial attempts were unsuccessful. Imaging studies were normal.

INTERVENTION

The patient underwent placement of a right-sided MCS system for treatment of her neuropathic facial pain syndrome. The procedure was tolerated well, and the trial stimulator provided promising results. The permanent MCS generator needed to be reprogrammed at the time of the 5-week follow-up visit to optimize symptom relief. The patient demonstrated dramatic improvements in her neuropathic facial and oral pain, including improvements in swallowing toleration, after the 5-week follow-up examination with subthreshold MCS. A decline in treatment efficacy also occurred 2 years after implantation due to generator depletion. Symptom improvement returned with stimulation after the generator was replaced.

CONCLUSION

A novel implantable MCS system was used to treat this patient's neuropathic facial pain. Durable improvements were noted not only in her facial pain, but also in swallowing toleration. The ultimate role of MCS in the treatment of pain conditions is still not well-defined but might play a part in refractory cases and, as in this case, might improve other functional issues, including dysphagia.

The effects of spinal cord stimulation in neuropathic pain are sustained: a 24-month follow-up of the prospective randomized controlled multicenter trial of the effectiveness of spinal cord stimulation

OBJECTIVE

After randomizing 100 failed back surgery syndrome patients to receive spinal cord stimulation (SCS) plus conventional medical management (CMM) or CMM alone, the results of the 6-month Prospective Randomized Controlled Multicenter Trial of the Effectiveness of Spinal Cord Stimulation (i.e., PROCESS) showed that SCS offered superior pain relief, health-related quality of life, and functional capacity. Because the rate of crossover favoring SCS beyond 6 months would bias a long-term randomized group comparison, we present all outcomes in patients who continued SCS from randomization to 24 months and, for illustrative purposes, the primary outcome (>50% leg pain relief) per randomization and final treatment.

METHODS

Patients provided data on pain, quality of life, function, pain medication use, treatment satisfaction, and employment status. Investigators documented adverse events. Data analysis included inferential comparisons and multivariate regression analyses.

RESULTS

The 42 patients continuing SCS (of 52 randomized to SCS) reported significantly improved leg pain relief (P < 0.0001), quality of life (P <or= 0.01), and functional capacity (P = 0.0002); and 13 patients (31%) required a device-related surgical revision. At 24 months, of 46 of 52 patients randomized to SCS and 41 of 48 randomized to CMM who were available, the primary outcome was achieved by 17 (37%) randomized to SCS versus 1 (2%) to CMM (P = 0.003) and by 34 (47%) of 72 patients who received SCS as final treatment versus 1 (7%) of 15 for CMM (P = 0.02).

CONCLUSION

At 24 months of SCS treatment, selected failed back surgery syndrome patients reported sustained pain relief, clinically important improvements in functional capacity and health-related quality of life, and satisfaction with treatment.

Automated vs. Manual Spinal Cord Stimulator Adjustment: A Sensitivity Analysis of Lifetime Cost Data From a Randomized Controlled Trial

Objective.  In a randomized controlled trial comparing manual with automated computerized adjustment of spinal cord stimulators in patients with implanted power generators, automated adjustment conferred the following advantages: 1) more settings tested in a given time, 2) significantly greater pain/paresthesia overlap, 3) increased battery life, and 4) a $303,756 (95% confidence intervals = $116,503-491,009) reduction in lifetime per patient cost. The current study analyzes the sensitivity of this cost-savings to usage time/day, inflation, discount rate, and years of use. Methods.  We analyzed cost-sensitivity with a standard spreadsheet method and suitably adjusted standard equation. Results.  Regardless of hours of use/day, inflation, discount rate, or years of use, spinal cord stimulation remains significantly less expensive with automated rather than manual adjustment. This savings is attributable to increased battery life. Conclusion.  Sensitivity analyzes reveal that the significant cost-savings achieved with computerized, patient-directed adjustment of spinal cord stimulation in selected patients with chronic pain is robust across a representative range of parameters.

Spinal cord stimulation versus conventional medical management for neuropathic pain: a multicentre randomised controlled trial in patients with failed back surgery syndrome

Patients with neuropathic pain secondary to failed back surgery syndrome (FBSS) typically experience persistent pain, disability, and reduced quality of life. We hypothesised that spinal cord stimulation (SCS) is an effective therapy in addition to conventional medical management (CMM) in this patient population. We randomised 100 FBSS patients with predominant leg pain of neuropathic radicular origin to receive spinal cord stimulation plus conventional medical management (SCS group) or conventional medical management alone (CMM group) for at least 6 months. The primary outcome was the proportion of patients achieving 50% or more pain relief in the legs. Secondary outcomes were improvement in back and leg pain, health-related quality of life, functional capacity, use of pain medication and non-drug pain treatment, level of patient satisfaction, and incidence of complications and adverse effects. Crossover after the 6-months visit was permitted, and all patients were followed up to 1 year. In the intention-to-treat analysis at 6 months, 24 SCS patients (48%) and 4 CMM patients (9%) (p<0.001) achieved the primary outcome. Compared with the CMM group, the SCS group experienced improved leg and back pain relief, quality of life, and functional capacity, as well as greater treatment satisfaction (p<or=0.05 for all comparisons). Between 6 and 12 months, 5 SCS patients crossed to CMM, and 32 CMM patients crossed to SCS. At 12 months, 27 SCS patients (32%) had experienced device-related complications. In selected patients with FBSS, SCS provides better pain relief and improves health-related quality of life and functional capacity compared with CMM alone.

Spinal Cord Stimulation versus Reoperation for Failed Back Surgery Syndrome: A Cost Effectiveness and Cost Utility Analysis Based on a Randomized, Controlled Trial

OBJECTIVE:

We analyzed the cost-effectiveness and cost–utility of treating failed back–surgery syndrome using spinal cord stimulation (SCS) versus reoperation.

MATERIALS AND METHODS

A disinterested third party collected charge data for the first 42 patients in a randomized controlled crossover trial. We computed the difference in cost with regard to success (cost–effectiveness) and mean quality–adjusted life years (cost–utility). We analyzed the patient–charge data with respect to intention to treat (costs and outcomes as a randomized group), treated as intended (costs as randomized; crossover failure assigned to a randomized group), and final treatment costs and outcomes.

RESULTS:

By our mean 3.1–year follow–up, 13 of 21 patients (62%) crossed to reoperation versus 5 of 19 patients (26%) who crossed to SCS (P &lt; 0.025). The mean cost per success was US $117,901 for crossovers to SCS. No crossovers to reoperation achieved success despite a mean per-patient expenditure of US $260,584. The mean per-patient costs were US $31,530 for SCS versus US $38,160 for reoperation (intention to treat), US $48,357 for SCS versus US $105,928 for reoperation (treated as intended), and US $34,371 for SCS versus US $36,341 for reoperation (final treatment). SCS was dominant (more effective and less expensive) in the incremental cost–effectiveness ratios and incremental cost–utility ratios. A bootstrapped simulation for incremental costs and quality–adjusted life years confirmed SCS's dominance, with approximately 72% of the cost results occurring below US policymakers' “maximum willingness to pay” threshold.

CONCLUSION:

SCS was less expensive and more effective than reoperation in selected failed back–surgery syndrome patients, and should be the initial therapy of choice. SCS is most cost–effective when patients forego repeat operation. Should SCS fail, reoperation is unlikely to succeed.