Spinal Geometry and Paresthesia Coverage in Spinal Cord Stimulation

Objective . To test the following hypotheses, based on computer modeling studies of spinal cord stimulation, by the analysis of data from chronic pain patients: I. the probability-of-paresthesia in a dermatome is highest when the cathode is placed at the corresponding segmental level; II. variation of the rostrocaudal position of the cathode in the lower cervical/high thoracic region results in less variation of the probability-of-paresthesia in a dermatome than stimulation in more caudal regions; III. when stimulating in the midthoracic region, the probability-of-paresthesia in a dermatome is low in comparison to other regions when the cathode is not at the corresponding segmental level. Method . The probability-of-paresthesia in 16 body segments as a function of the rostrocaudal position of the cathode was analyzed from the paresthesia coverage with 3,897 bipolar and unipolar combinations from 106 chronic pain patients. Results . The distributions of the probability-of-paresthesia in the upper and lower limb are in accordance with the hypotheses, but different distributions were found in all trunk areas. Conclusion . The success to be expected from spinal cord stimulation in chronic pain management is inversely related to the thickness of the dorsal cerebrospinal fluid layer at the cathode level. Therefore, preoperative measurement from transverse images can be helpful as a predictor for success.     

Biomarker Optimization of Spinal Cord Stimulation Therapies

ObjectivesWe are in the process of designing and testing an intradural stimulation device that will shorten the distance between the location of the electrode array and the targeted neural tissue, thus improving the efficacy of electrical current delivery. Identifying a biomarker that accurately reflects the response to this intervention is highly valued because of the potential to optimize interventional parameters or predict a response before it is clinically measurable. In this report, we summarize the findings pertaining to the study of biomarkers so that we and others will have an up-to-date reference that critically evaluates the current approaches and select one or several for testing during the development of our device.Materials and MethodsWe have conducted a broad survey of the existing literature to catalogue the biomarkers that could be coupled to intradural spinal cord stimulation. We describe in detail some of the most promising biomarkers, existing limitations, and suitability to managing chronic pain.ResultsChronic, intractable pain is an all-encompassing condition that is incurable. Many treatments for managing chronic pain are nonspecific in action and intermittently administered; therefore, patients are particularly susceptible to large fluctuations in pain control over the course of a day. The absence of a reliable biomarker challenges assessment of therapeutic efficacy and contributes to either incomplete and inconsistent pain relief or, alternatively, intolerable side effects. Fluctuations in metabolites or inflammatory markers, signals captured during dynamic imaging, and genomics will likely have a role in governing how a device is modulated.ConclusionsEfforts to identify one or more biomarkers are well underway with some preliminary evidence supporting their efficacy. This has far-reaching implications, including improved outcomes, fewer adverse events, harmonization of treatment and individuals, performance gains, and cost savings. We anticipate that novel biomarkers will be used widely to manage chronic pain.     

Spinal Cord Stimulation Surgical Technique for the Nonsurgically Trained

The objective of this paper is to educate physicians who implant spinal cord stimulators in current surgical techniques. Many implanters have not gone through formal surgical residencies and learn their surgical techniques during a one year Fellowship or from proctoring experience. This paper utilizes current concepts from the literature to reinforce appropriate surgical practices, which are applicable to surgeons as well as interventional pain physicians. This should be a valuable resource for all Fellows whether they are in surgical programs or pain fellowship programs. In addition, a more detailed presentation is made at the end of this paper on a proposed simple one‐incision surgical technique for implantation of small internal pulse generators. This is the first publication in the literature describing such a technique and may be useful for less‐experienced implanters, as well as conferring potential advantages in surgical technique.     

Effects of Posture on Stimulation Parameters in Spinal Cord Stimulation

Objective . To examine the importance of posture on the efficacy of spinal cord stimulation in a population of chronic pain patients previously implanted with a spinal cord stimulator. Materials and Methods . Electrode leads (Octrode 2098, ANS) were placed percutaneously into the epidural space under fluoroscopic control (BV29, Phillips, Inc.) at either the cervical or thoracic vertebral level. Stimulation parameters were measured at least 24 h after initial Implantation, and as long as 3 y. All patients were asked to look forward and remain still in one of three positions: lying, sitting, and standing. At each posture, electrical stimulation was applied to the spinal cord. The voltages and pulse widths necessary to produce threshold paresthesia, therapeutic stimulation, and uncomfortable sensations were recorded. A stimulus frequency of 100 Hz was used for all subjects. Results . As previously described by Barolat 1 , we found the thresholds for stimulation to be highest in the thoracic level. We also measured the largest usage range to be at this level. However, we found that this range varied greatly between patients and between postures. In 20 patients the threshold for paresthesia was lowest when lying, while in three patients it was lowest when sitting. The mean range and SD of stimulation required to achieve paresthesia at all three posture levels was found to be 0.113 ± 0.062 μC for leads in the cervical region (N = 11) and 0.494 ± 0.297 μC for leads in the thoracic region (N = 19). Conclusions . To provide adequate stimulation at all postures, multiple stimulation settings (programs) would be required.     

Sacral Nerve and Spinal Cord Stimulation for Intractable Neuropathic Pain Caused by Spinal Cord Infarction

Central cord pain is very difficult to relieve, even with the many kinds of medical and surgical treatments available. Following spinal cord infarctions, central cord pain can develop. The problems that may arise could include limb pain, pelvic pain, difficulties voiding, and difficulties defecating. We are reporting a case of central cord pain caused by a spinal cord infarction of the conus medullaris. Limb pain was reduced by spinal cord stimulation. Voiding and defecation difficulties and pelvic pain were reduced by sacral nerve stimulation. Thus, in a case involving both intractable limb and pelvic pain, a combination therapy of these two stimulations might be an effective treatment modality.     

Treatment of Multifocal Pain with Spinal Cord Stimulation

Introduction: We report a retrospective case study of combined treatment of cancer‐related pain and chronic low back and lower extremity pain related to postlaminectomy syndrome (PLS) with one spinal cord stimulation (SCS) system. Methods: The patient underwent an uneventful SCS trial with percutaneous placement of two temporary eight‐electrode leads (Medtronic Inc., Minneapolis, MN) placed at the level of T8‐T9‐T10 and T5‐T6‐T7. Results: After successful trial, he was implanted with permanent leads and generator, reporting sustained pain relief at 12‐month follow‐up visit. Discussion: SCS is a trialable, reversible, and interactive therapy permitting patients to control the level of stimulation they feel based on their degree of pain. Conclusion: SCS provides an effective, alternative treatment for select patients with cancer‐related chest wall pain and pain related to PLS who have failed conservative treatment.     

Spinal Cord Stimulation Enhances Microglial Activation in the Spinal Cord of Nerve-Injured Rats

Microglia can modulate spinal nociceptive transmission. Yet, their role in spinal cord stimulation (SCS)-induced pain inhibition is unclear. Here, we examined how SCS affects microglial activation in the lumbar cord of rats with chronic constriction injury (CCI) of the sciatic nerve. Male rats received conventional SCS (50 Hz, 80% motor threshold, 180 min, 2 sessions/day) or sham stimulation on days 18–20 post-CCI. SCS transiently attenuated the mechanical hypersensitivity in the ipsilateral hind paw and increased OX-42 immunoreactivity in the bilateral dorsal horns. SCS also upregulated the mRNAs of M1-like markers, but not M2-like markers. Inducible NOS protein expression was increased, but brain-derived neurotrophic factor was decreased after SCS. Intrathecal minocycline (1 μg–100 μg), which inhibits microglial activation, dose-dependently attenuated the mechanical hypersensitivity. Pretreatment with low-dose minocycline (1 μg, 30 min) prolonged the SCS-induced pain inhibition. These findings suggest that conventional SCS may paradoxically increase spinal M1-like microglial activity and thereby compromise its own ability to inhibit pain.     

Heterogeneous Cortical Effects of Spinal Cord Stimulation

ObjectivesThe understanding of the cortical effects of spinal cord stimulation (SCS) remains limited. Multiple studies have investigated the effects of SCS in resting-state electroencephalography. However, owing to the large variation in reported outcomes, we aimed to describe the differential cortical responses between two types of SCS and between responders and nonresponders using magnetoencephalography (MEG).Materials and MethodsWe conducted 5-minute resting-state MEG recordings in 25 patients with chronic pain with active SCS in three sessions, each after a one-week exposure to tonic, burst, or sham SCS. We extracted six spectral features from the measured neurophysiological signals: the alpha peak frequency; alpha power ratio (power 7–9 Hz/power 9–11 Hz); and average power in the theta (4–7.5 Hz), alpha (8–12.5 Hz), beta (13–30 Hz), and low-gamma (30.5–60 Hz) frequency bands. We compared these features (using nonparametric permutation t-tests) for MEG sensor and cortical map effects across stimulation paradigms, between participants who reported low (< 5, responders) vs high (≥ 5, nonresponders) pain scores, and in three representative participants.ResultsWe found statistically significant (p < 0.05, false discovery rate corrected) increased MEG sensor signal power below 3 Hz in response to burst SCS compared with tonic and sham SCS. We did not find statistically significant differences (all p > 0.05) between the power spectra of responders and nonresponders. Our data did not show statistically significant differences in the spectral features of interest among the three stimulation paradigms or between responders and nonresponders. These results were confirmed by the MEG cortical maps. However, we did identify certain trends in the MEG source maps for all comparisons and several features, with substantial variation across participants.ConclusionsThe considerable variation in cortical responses to the various SCS treatment options necessitates studies with sample sizes larger than commonly reported in the field and more personalized treatment plans. Studies with a finer stratification between responders and nonresponders are required to advance the knowledge on SCS treatment effects.     

Spinal Cord Stimulation for Failed Back Surgery Syndrome

Objective. The purpose of this study is to evaluate the effectiveness of modern spinal cord stimulation (SCS) for the treatment of failed back surgery syndrome (FBSS). Materials and Methods. Thirty patients were treated with SCS between December 1992 and January 1998 for low back and radicular pain after multiple failed back surgeries. Permanent systems were implanted if trial stimulation led to > 50% pain reduction. Median long‐term follow‐up was 34 months (range, 6–66 months). Severity of pain was determined postoperatively by a disinterested third party. Results. Overall, 12 of the 16 patients (75%) who received permanent implants continued to report at least 50% relief of pain at follow‐up. All six patients who underwent placement of laminectomy‐styled electrode for SCS in the thoracic region had > 50% pain relief at long‐term follow‐up. Visual analog scores decreased an average of 3.2 (from 8.6 preoperatively to 5.4 postoperatively). Patients undergoing SCS placement via laminectomy in the thoracic region experienced an average decrease of 4.9 in VAS, whereas those who underwent percutaneous placement of thoracic leads had an average decrease of 2.5. Conclusions. SCS is an effective treatment for chronic low back and lower extremity pain which is refractory to conservative therapy and which is not amenable to corrective anatomic surgery. Though our patient population is small, our results imply that the laminectomy‐style electrodes in the thoracic region achieve better long‐term effectiveness than percutaneous leads.     

Which Neuronal Elements are Activated Directly by Spinal Cord Stimulation

The purpose of this paper is to discuss which nerve fibers in the various quadrants of the spinal cord are immediately activated under normal conditions of spinal cord stimulation, ie, at voltages within the therapeutic range. The conclusions are based on both empirical and computer modeling data. The recruitment of dorsal column (DC) fibers is most likely restricted to Aβ fibers with a diameter ≥ 10.7 μm in a 0.20–0.25 mm layer under the pia mater and fibers of 9.4–10.7 μm in an even smaller outer layer when a conventional SCS lead is used. In a 0.25‐mm outer layer of the T11 segment the number of Aβ fibers ≥ 10.7 μm, as estimated in a recent morphometric study, is about 56 in each DC. Because a DC at T11 innervates 12 dermatomes, a maximum of 4–5 fibers (≥ 10.7 μm) may be recruited in each dermatome near the discomfort threshold. The dermatome activated just below the discomfort threshold is likely to be stimulated by just a single fiber, suggesting that paresthesia and pain relief may be effected in a dermatome by the stimulation of a single large Aβ fiber. The depth of stimulation in the DCs, and thereby the number of recruited Aβ fibers, may be increased 2–3 fold when stimulation is applied by an optimized electrode configuration (a narrow bi/tripole or a transverse tripole). Assuming that the largest Aβ fibers in a dorsal root have a diameter of 15 μm, the smallest ones recruited at discomfort threshold would be 12 μm. The latter are presumably of proprioceptive origin and responsible for segmental reflexes and uncomfortable sensations. Furthermore, it is shown to be unlikely that, apart from dorsal roots and a thin outer layer of the DCs, any other spinal structures are recruited when stimulation is applied in the dorsal epidural space. Finally, anodal excitation and anodal propagation block are unlikely to occur with SCS.     

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.     

Accidental Subdural Spinal Cord Stimulator Lead Placement and Stimulation

Objectives: Neuromodulation with spinal cord stimulation has become an increasingly employed intervention for treatment of a variety of neuropathic pain states. As prevalence increases, so does the incidence of complications. Currently, there is sparse literature describing spinal cord stimulation lead placement and stimulation characteristics in the subdural space. In this case report we describe subdural lead placement and the associated stimulation parameters, and provide evidence‐based support to initiate a dialog to further reduce procedural morbidity and mortality. Materials and Methods: This study is a case report following lead placement during permanent percutaneous spinal cord stimulator placement and stimulation testing. The lead placement and stimulation characteristics were suggestive of extra‐epidural lead placement. Results: Using the same cathode/anode configuration (1:anode, 3:cathode, 5:anode), frequency of 40 Hz and pulse width of 650 microseconds, sequential stimulation was performed. Summarizing, the testing demonstrated similar impedance for the left and right leads (within 30 ohms) of approximately 300 ohms, and a large discrepancy in current of 3.2 mA for the left and 0.9 mA for the right. The patient reported “painful intense” stimulation with right lead stimulation. Conclusions: Evidence suggesting subdural lead placement include the lack of cerebrospinal‐fluid despite lavage, the absence of post‐dural puncture headache, the recent evidence of intentional and reproducible subdural anesthesia, and the conductive properties of the dural spinal elements. It can be argued that subdural lead placement may occur unrecognized more frequently than originally anticipated.     

Review of Spinal Cord Stimulation in Peripheral Arterial Disease

Ever since its initial development in the late 1960s, spinal cord stimulation (SCS) has been used to treat a number of painful conditions. European practice, in contrast to that in North America, has used peripheral arterial disease (PAD) as a primary indication for SCS. First employed in patients with PAD in 1976, SCS was shown by Cook et al. to heal chronic leg ulcers. Numerous subsequent retrospective studies of SCS in PAD show improvements in multiple outcomes such as exercise tolerance, limb salvage, and pain. Previous retrospective studies are likely flawed with respect to author bias, inadequate sample size, and possible placebo effects. Further, they have not identified clinical criteria for selecting SCS therapy. Recent randomized prospective studies have questioned some of the conclusions from these preceding retrospective data. In addition to the questions related to outcomes, theories regarding exact mechanisms by which SCS improves circulatory parameters remain unclear. A thorough Medline literature review on the subject of SCS in peripheral vascular disease was thus undertaken to attempt to clarify questions regarding which patients are best suited for SCS therapy, pinpoint possible methodologic flaws in previous studies, and to review the background, outcomes, mechanisms of action, complications, and alternatives for SCS in patients with PAD.     

Spinal Cord Stimulation With Additional Peripheral Nerve/Field Stimulation Versus Spinal Cord Stimulation Alone on Back Pain and Quality of Life in Patients With Persistent Spinal Pain Syndrome

IntroductionPersistent spinal pain syndrome (PSPS) or failed back surgery syndrome (FBSS) refers to new or persistent pain following spinal surgery for back or leg pain in a subset of patients. Spinal cord stimulation (SCS) is a neuromodulation technique that can be considered in patients with predominant leg pain refractory to conservative treatment. Patients with predominant low back pain benefit less from SCS. Another neuromodulation technique for treatment of chronic low back pain is subcutaneous stimulation or peripheral nerve field stimulation (PNFS). We investigated the effect of SCS with additional PNFS on pain and quality of life of patients with PSPS compared with that of SCS alone after 12 months.Materials and MethodsThis is a comparative study of patients with PSPS who responded to treatment with either SCS + PNFS or SCS only following a multicenter randomized clinical trial protocol. In total, 75 patients completed the 12-month follow-up: 21 in the SCS-only group and 54 in the SCS + PNFS group. Outcome measures were pain (visual analog scale), quality of life (36-Item Short Form Survey [SF-36]), anxiety and depression (Hospital Anxiety and Depression Scale [HADS]), overall health (EuroQol Five-Dimension [EQ-5D]), disability (Oswestry Disability Index [ODI]), and pain assessed by the McGill questionnaire.ResultsThere were no significant differences in baseline characteristics between the two groups. Both groups showed a significant reduction in back and leg pain at 12 months compared with baseline measurements. No significant differences were found between the groups in effect on both primary (pain) and secondary parameters (SF-36, HADS, EQ-5D, ODI, and McGill pain).ConclusionIn a subgroup of patients with chronic back and leg pain, SCS alone provided similar long-term pain relief and quality-of-life improvement as PNFS in addition to SCS. In patients with refractory low back pain not responding to SCS alone, adding PNFS should be recommended.Clinical Trial RegistrationThe Clinicaltrials.gov registration number for the study is NCT01776749.     

Epidural Spinal Cord Stimulation: Anatomical and Electrical Properties of the Intraspinal Structures Relevant to Spinal Cord Stimulation and Clinical Correlations

Epidural spinal cord stimulation (SCS) has gained a secure place in the armamentarium of the surgeon treating chronic pain conditions 1 , 2 . The complexity of the intraspinal structures and their different susceptibility to electrical signals, however, has made it difficult to characterize the effects of the stimulation, Some important recent work has helped shed light on the electrical properties of the intraspinal structures and on the electrical field potentials generated with epidural spinal cord stimulation. This work, initially pioneered by Sin and Coburn, has successfully been expanded and perfected by Holsheimer and Strujik at the University of Twente, The Netherlands ( 3 - 8 ). The Dutch scientists developed a computerized volume conductor model of the spinal cord to represent in extreme detail the electrical properties of all the intraspinal structures, including the dorsal column and dorsal root fibers. The model can simulate the effects of epidural stimulation with different electrode geometries and configurations 8 . The data generated from the model were then validated by comparing them to a large number of data collected by the author in implanted subjects ( 9 - 12 ). The author also conducted a detailed analysis of the clinical properties of the activation of the intraspinal structures at various electrode positions in the spine 13 , 14 .