The effects of dorsal column stimulation on measures of clinical and experimental pain in man

Implanted spinal neuromodulation interventions for chronic pain in adults

BACKGROUND

Implanted spinal neuromodulation (SNMD) techniques are used in the treatment of refractory chronic pain. They involve the implantation of electrodes around the spinal cord (spinal cord stimulation (SCS)) or dorsal root ganglion (dorsal root ganglion stimulation (DRGS)), and a pulse generator unit under the skin. Electrical stimulation is then used with the aim of reducing pain intensity.

OBJECTIVES

To evaluate the efficacy, effectiveness, adverse events, and cost-effectiveness of implanted spinal neuromodulation interventions for people with chronic pain.

SEARCH METHODS

We searched CENTRAL, MEDLINE Ovid, Embase Ovid, Web of Science (ISI), Health Technology Assessments, ClinicalTrials.gov and World Health Organization International Clinical Trials Registry from inception to September 2021 without language restrictions, searched the reference lists of included studies and contacted experts in the field.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing SNMD interventions with placebo (sham) stimulation, no treatment or usual care; or comparing SNMD interventions + another treatment versus that treatment alone. We included participants ≥ 18 years old with non-cancer and non-ischaemic pain of longer than three months duration. Primary outcomes were pain intensity and adverse events. Secondary outcomes were disability, analgesic medication use, health-related quality of life (HRQoL) and health economic outcomes.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened database searches to determine inclusion, extracted data and evaluated risk of bias for prespecified results using the Risk of Bias 2.0 tool. Outcomes were evaluated at short- (≤ one month), medium- four to eight months) and long-term (≥12 months). Where possible we conducted meta-analyses. We used the GRADE system to assess the certainty of evidence.

MAIN RESULTS

We included 15 unique published studies that randomised 908 participants, and 20 unique ongoing studies. All studies evaluated SCS. We found no eligible published studies of DRGS and no studies comparing SCS with no treatment or usual care. We rated all results evaluated as being at high risk of bias overall. For all comparisons and outcomes where we found evidence, we graded the certainty of the evidence as low or very low, downgraded due to limitations of studies, imprecision and in some cases, inconsistency. Active stimulation versus placebo SCS versus placebo (sham) Results were only available at short-term follow-up for this comparison. Pain intensity Six studies (N = 164) demonstrated a small effect in favour of SCS at short-term follow-up (0 to 100 scale, higher scores = worse pain, mean difference (MD) -8.73, 95% confidence interval (CI) -15.67 to -1.78, very low certainty). The point estimate falls below our predetermined threshold for a clinically important effect (≥10 points). No studies reported the proportion of participants experiencing 30% or 50% pain relief for this comparison. Adverse events (AEs) The quality and inconsistency of adverse event reporting in these studies precluded formal analysis. Active stimulation + other intervention versus other intervention alone SCS + other intervention versus other intervention alone (open-label studies) Pain intensity Mean difference Three studies (N = 303) demonstrated a potentially clinically important mean difference in favour of SCS of -37.41 at short term (95% CI -46.39 to -28.42, very low certainty), and medium-term follow-up (5 studies, 635 participants, MD -31.22 95% CI -47.34 to -15.10 low-certainty), and no clear evidence for an effect of SCS at long-term follow-up (1 study, 44 participants, MD -7 (95% CI -24.76 to 10.76, very low-certainty). Proportion of participants reporting ≥50% pain relief We found an effect in favour of SCS at short-term (2 studies, N = 249, RR 15.90, 95% CI 6.70 to 37.74, I² 0% ; risk difference (RD) 0.65 (95% CI 0.57 to 0.74, very low certainty), medium term (5 studies, N = 597, RR 7.08, 95 %CI 3.40 to 14.71, I² = 43%; RD 0.43, 95% CI 0.14 to 0.73, low-certainty evidence), and long term (1 study, N = 87, RR 15.15, 95% CI 2.11 to 108.91 ; RD 0.35, 95% CI 0.2 to 0.49, very low certainty) follow-up. Adverse events (AEs) Device related No studies specifically reported  device-related adverse events at short-term follow-up. At medium-term follow-up, the incidence of lead failure/displacement (3 studies N = 330) ranged from 0.9 to 14% (RD 0.04, 95% CI -0.04 to 0.11, I² 64%, very low certainty). The incidence of infection (4 studies, N = 548) ranged from 3 to 7% (RD 0.04, 95%CI 0.01, 0.07, I² 0%, very low certainty). The incidence of reoperation/reimplantation (4 studies, N =5 48) ranged from 2% to 31% (RD 0.11, 95% CI 0.02 to 0.21, I² 86%, very low certainty). One study (N = 44) reported a 55% incidence of lead failure/displacement (RD 0.55, 95% CI 0.35, 0 to 75, very low certainty), and a 94% incidence of reoperation/reimplantation (RD 0.94, 95% CI 0.80 to 1.07, very low certainty) at five-year follow-up. No studies provided data on infection rates at long-term follow-up. We found reports of some serious adverse events as a result of the intervention. These included autonomic neuropathy, prolonged hospitalisation, prolonged monoparesis, pulmonary oedema, wound infection, device extrusion and one death resulting from subdural haematoma. Other No studies reported the incidence of other adverse events at short-term follow-up. We found no clear evidence of a difference in otherAEs at medium-term (2 studies, N = 278, RD -0.05, 95% CI -0.16 to 0.06, I² 0%) or long term (1 study, N = 100, RD -0.17, 95% CI -0.37 to 0.02) follow-up. Very limited evidence suggested that SCS increases healthcare costs. It was not clear whether SCS was cost-effective.

AUTHORS' CONCLUSIONS

We found very low-certainty evidence that SCS may not provide clinically important benefits on pain intensity compared to placebo stimulation. We found low- to very low-certainty evidence that SNMD interventions may provide clinically important benefits for pain intensity when added to conventional medical management or physical therapy. SCS is associated with complications including infection, electrode lead failure/migration and a need for reoperation/re-implantation. The level of certainty regarding the size of those risks is very low. SNMD may lead to serious adverse events, including death. We found no evidence to support or refute the use of DRGS for chronic pain.

Quantitative Sensory Testing of Spinal Cord and Dorsal Root Ganglion Stimulation in Chronic Pain Patients

BACKGROUND/OBJECTIVES

The physiological mechanisms underlying the pain-modulatory effects of clinical neurostimulation therapies, such as spinal cord stimulation (SCS) and dorsal root ganglion stimulation (DRGS), are only partially understood. In this pilot prospective study, we used patient-reported outcomes (PROs) and quantitative sensory testing (QST) to investigate the physiological effects and possible mechanisms of action of SCS and DRGS therapies.

MATERIALS AND METHODS

We tested 16 chronic pain patients selected for SCS and DRGS therapy, before and after treatment. PROs included pain intensity, pain-related symptoms (e.g., pain interference, pain coping, sleep interference) and disability, and general health status. QST included assessments of vibration detection theshold (VDT), pressure pain threshold (PPT) and tolerance (PPToL), temporal summation (TS), and conditioned pain modulation (CPM), at the most painful site.

RESULTS

Following treatment, all participants reported significant improvements in PROs (e.g., reduced pain intensity [p < 0.001], pain-related functional impairment [or pain interference] and disability [p = 0.001 for both]; better pain coping [p = 0.03], sleep [p = 0.002]), and overall health [p = 0.005]). QST showed a significant treatment-induced increase in PPT (p = 0.002) and PPToL (p = 0.011), and a significant reduction in TS (p = 0.033) at the most painful site, but showed no effects on VDT and CPM. We detected possible associations between a few QST measures and a few PROs. Notably, higher TS was associated with increased pain interference scores at pre-treatment (r = 0.772, p = 0.009), and a reduction in TS was associated with the reduction in pain interference (r = 0.669, p = 0.034) and pain disability (r = 0.690, p = 0.027) scores with treatment.

CONCLUSIONS

Our preliminary findings suggest significant clinical and therapeutic benefits associated with SCS and DRGS therapies, and the possible ability of these therapies to modulate pain processing within the central nervous system. Replication of our pilot findings in future, larger studies is necessary to characterize the physiological mechanisms of SCS and DRGS therapies.

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain.

Effects of Tonic Spinal Cord Stimulation on Sensory Perception in Chronic Pain Patients: A Systematic Review

OBJECTIVES

Even if spinal cord stimulation (SCS) is widely used and effective in treating intractable chronic neuropathic pain conditions, little is known about its possible impacts on sensory perception. Quantitative sensory testing (QST) is a useful tool to assess this issue. The aim of this study was to review the impact of tonic SCS on somatosensory perception quantified by QST in chronic pain patients.

MATERIALS AND METHODS

Relevant articles and abstracts were searched in all languages from CINAHL, Cochrane, Embase, MEDLINE, and Web of Knowledge data bases. Data were extracted and included studies were assessed for risk of bias.

RESULTS

Out of 5610 records, 15 peer-reviewed articles were eligible and included. The results are heterogeneous due to inadequate comparability among studies for populations (a total of 224 patients diagnosed with more than 13 chronic pain conditions), QST parameters (22 measured with 25 different devices) and experimental procedures (study design, comparator, evaluation time, and area tested). The wide variety of studies, designs, populations, and measures included in this review did not lead to strong evidence on how conventional ("tonic") SCS affects sensory processing in patients with chronic pain.

CONCLUSIONS

The data available tend to suggest that conventional SCS does not interfere with perception of external stimuli. New studies that follow a standardized procedure and consider the possible influence of sensory profile, after-effect bias, and confounding factors are required to confirm this observation. Moreover, the impact on sensory perception of other SCS modalities and alternative electrical neuromodulation therapies could also be explored.

Spinal cord stimulation modulates descending pain inhibition and temporal summation of pricking pain in patients with neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) is an established treatment option for patients with refractory chronic pain conditions. While effects of SCS on dorsal horn neuronal circuitries are intensively studied, current knowledge on the impact of SCS on descending pain pathways is scarce and relies on preclinical data. We aimed to address this topic and hypothesized a significant effect of SCS on descending pain modulation. In light of current efforts to determine the sensitivity of "static" versus "dynamic" somatosensory parameters to characterize pathophysiological pain conditions, all SCS patients were carefully investigated using both classes of somatosensory outcome parameters.

METHODS

Descending pain pathways were investigated by using a "Cold Pressor Test." This test enables to evaluate the efficacy of conditioned pain modulation (CPM) at the individual level. CPM efficacy was assessed in eight neuropathic pain patients (age 55.5 ± 10.6) during the two conditions stimulator "ON" and "OFF." The impact of SCS on "static" and "dynamic" somatosensory parameters was explored by using a quantitative sensory testing (QST) battery.

RESULTS

CPM efficacy on pressure pain sensitivity was nearly absent during "OFF" (- 1.2 ± 5.6% facilitation), but increased significantly to 16.3 ± 3.4% inhibition during "ON" (p = 0.03). While most "static" nociceptive QST parameters, represented by mechanical/thermal pain thresholds, exhibited only small effects of SCS (p > 0.05), the wind-up ratio was strongly reduced to within the normal range during "ON" (p = 0.04; Cohen's d = 1.0). Dynamic mechanical allodynia was abolished in six of seven patients.

CONCLUSIONS

Our study provides first human evidence for an impact of SCS on descending pain pathways in the dorsolateral funiculus and emphasizes the significance of "dynamic" pain measures like "CPM"-efficacy and "temporal summation" to evaluate SCS treatment effects. Future prospective studies may use these measures of nociceptive processing to predict SCS therapy response.

Objective Measures to Characterize the Physiological Effects of Spinal Cord Stimulation in Neuropathic Pain: A Literature Review

OBJECTIVE

The physiological mechanisms behind the therapeutic effects of spinal cord stimulation (SCS) are only partially understood. Our aim was to perform a literature review of studies that used objective measures to characterize mechanisms of action of SCS in neuropathic pain patients.

MATERIALS AND METHODS

We searched the PubMed data base to identify clinical studies that used objective measures to assess the effects of SCS in neuropathic pain. We extracted the study factors (e.g., type of measure, diagnoses, painful area[s], and SCS parameters) and outcomes from the included studies.

RESULTS

We included 67 studies. Of these, 24 studies used neurophysiological measures, 14 studies used functional neuroimaging techniques, three studies used a combination of neurophysiological and functional neuroimaging techniques, 14 studies used quantitative sensory testing, and 12 studies used proteomic, vascular, and/or pedometric measures. Our findings suggest that SCS largely inhibits somatosensory processing and/or spinal nociceptive activity. Our findings also suggest that SCS modulates activity across specific regions of the central nervous system that play a prominent role in the sensory and emotional functions of pain.

CONCLUSIONS

SCS appears to modulate pain via spinal and/or supraspinal mechanisms of action (e.g., pain gating, descending pain inhibition). However, to better understand the mechanisms of action of SCS, we believe that it is necessary to carry out systematic, controlled, and well-powered studies using objective patient measures. To optimize the clinical effectiveness of SCS for neuropathic pain, we also believe that it is necessary to develop and implement patient-specific approaches.

Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms

Spinal cord stimulation (SCS) is a minimally invasive therapy used for the treatment of chronic neuropathic pain. SCS is a safe and effective alternative to medications such as opioids, and multiple randomized controlled studies have demonstrated efficacy for difficult-to-treat neuropathic conditions such as failed back surgery syndrome. Conventional SCS is believed mediate pain relief via activation of dorsal column Aβ fibers, resulting in variable effects on sensory and pain thresholds, and measurable alterations in higher order cortical processing. Although potentiation of inhibition, as suggested by Wall and Melzack's gate control theory, continues to be the leading explanatory model, other segmental and supraspinal mechanisms have been described. Novel, non-standard, stimulation waveforms such as high-frequency and burst have been shown in some studies to be clinically superior to conventional SCS, however their mechanisms of action remain to be determined. Additional studies are needed, both mechanistic and clinical, to better understand optimal stimulation strategies for different neuropathic conditions, improve patient selection and optimize efficacy.

Dynamic Changes in Nociception and Pain Perception After Spinal Cord Stimulation in Chronic Neuropathic Pain Patients

OBJECTIVES

Patients with an implanted spinal cord stimulation (SCS) system for pain management present an opportunity to study dynamic changes in the pain system in a situation where patients are not stimulated (ie, experiencing severe pain) compared with a situation in which patients have just been stimulated (ie, pain free or greatly reduced pain). The aims of this study were (1) to determine if there are differences in nociceptive withdrawal reflex thresholds (NWR-T) and electrical pain thresholds (EP-T) before and after SCS; and (2) to establish if these differences are related to psychological factors associated with chronic pain.

METHODS

Seventeen volunteers with chronic neuropathic pain participated in the experiment. Electrical stimuli were applied to assess the NWR-T and the EP-T. In addition, psychological factors (ie, pain characteristics, depression, anxiety, and disability indexes) were also recorded. The NWR-T and EP-T were assessed with the SCS system off (at least 8 h before the experiment), and then reassessed 1 hour after the SCS system was turned on.

RESULTS

Ongoing pain intensity ratings decreased (P=0.018), whereas the NWR-T increased (P=0.028) after the SCS was turned on, whereas no significant difference was found for EP-T (P=0.324). Psychological factors were significant predictors for EP-T but not for NWR-T.

DISCUSSION

The results of this study suggest that pain relief after SCS is partially mediated by a decrease in the excitability of dorsal horn neurons in the spinal cord.

Effects of Spinal Cord Stimulation on Pain Thresholds and Sensory Perceptions in Chronic Pain Patients

OBJECTIVE

Spinal cord stimulation (SCS) has been in clinical use for nearly four decades. In earliest observations, researchers found a significant increase in pain threshold during SCS therapy without changes associated with touch, position, and vibration sensation. Subsequent studies yielded diverse results regarding how SCS impacts pain and other sensory thresholds. This pilot study uses quantitative sensory testing (QST) to objectively quantify the impact of SCS on warm sensation, heat pain threshold, and heat pain tolerance.

MATERIALS AND METHODS

Nineteen subjects with an indwelling SCS device for chronic pain were subjected to QST with heat stimuli. QST was performed on an area of pain covered with SCS-induced paresthesia and an area without pain and without paresthesia, while the SCS was turned off and on. The temperature at which the patient detected warm sensation, heat pain, and maximal tolerable heat pain was used to define the thresholds.

RESULTS

We found that all three parameters, the detection of warm sensation, heat pain threshold, and heat pain tolerance, were increased during the period when SCS was on compared with when it was off. This increase was observed in both painful and non-painful sites.

CONCLUSION

The observed pain relief during SCS therapy seems to be related to its impact on increased sensory threshold as detected in this study. The increased sensory threshold on areas without pain and without the presence of SCS coverage may indicate a central (spinal and/or supra-spinal) influence from SCS.

The appropriate use of neurostimulation of the spinal cord and peripheral nervous system for the treatment of chronic pain and ischemic diseases: the Neuromodulation Appropriateness Consensus Committee

INTRODUCTION

The Neuromodulation Appropriateness Consensus Committee (NACC) of the International Neuromodulation Society (INS) evaluated evidence regarding the safety and efficacy of neurostimulation to treat chronic pain, chronic critical limb ischemia, and refractory angina and recommended appropriate clinical applications.

METHODS

The NACC used literature reviews, expert opinion, clinical experience, and individual research. Authors consulted the Practice Parameters for the Use of Spinal Cord Stimulation in the Treatment of Neuropathic Pain (2006), systematic reviews (1984 to 2013), and prospective and randomized controlled trials (2005 to 2013) identified through PubMed, EMBASE, and Google Scholar.

RESULTS

Neurostimulation is relatively safe because of its minimally invasive and reversible characteristics. Comparison with medical management is difficult, as patients considered for neurostimulation have failed conservative management. Unlike alternative therapies, neurostimulation is not associated with medication-related side effects and has enduring effect. Device-related complications are not uncommon; however, the incidence is becoming less frequent as technology progresses and surgical skills improve. Randomized controlled studies support the efficacy of spinal cord stimulation in treating failed back surgery syndrome and complex regional pain syndrome. Similar studies of neurostimulation for peripheral neuropathic pain, postamputation pain, postherpetic neuralgia, and other causes of nerve injury are needed. International guidelines recommend spinal cord stimulation to treat refractory angina; other indications, such as congestive heart failure, are being investigated.

CONCLUSIONS

Appropriate neurostimulation is safe and effective in some chronic pain conditions. Technological refinements and clinical evidence will continue to expand its use. The NACC seeks to facilitate the efficacy and safety of neurostimulation.

Dynamic Pain Phenotypes are Associated with Spinal Cord Stimulation-Induced Reduction in Pain: A Repeated Measures Observational Pilot Study

OBJECTIVE

Spinal cord stimulation (SCS) has become a widely used treatment option for a variety of pain conditions. Substantial variability exists in the degree of benefit obtained from SCS and patient selection is a topic of expanding interest and importance. However, few studies have examined the potential benefits of dynamic quantitative sensory testing (QST) to develop objective measures of SCS outcomes or as a predictive tool to help patient selection. Psychological characteristics have been shown to play an important role in shaping individual differences in the pain experience and may aid in predicting responses to SCS. Static laboratory pain-induction measures have also been examined in their capacity for predicting SCS outcomes.

METHODS

The current study evaluated clinical, psychological and laboratory pain measures at baseline, during trial SCS lead placement, as well as 1 month and 3 months following permanent SCS implantation in chronic pain patients who received SCS treatment. Several QST measures were conducted, with specific focus on examination of dynamic models (central sensitization and conditioned pain modulation [CPM]) and their association with pain outcomes 3 months post SCS implantation.

RESULTS

Results suggest few changes in QST over time. However, central sensitization and CPM at baseline were significantly associated with clinical pain at 3 months following SCS implantation, controlling for psycho/behavioral factors and pain at baseline. Specifically, enhanced central sensitization and reduced CPM were associated with less self-reported pain 3 months following SCS implantation.

CONCLUSIONS

These findings suggest a potentially important role for dynamic pain assessment in individuals undergoing SCS, and hint at potential mechanisms through which SCS may impart its benefit.

Comparison of intensity-dependent inhibition of spinal wide-dynamic range neurons by dorsal column and peripheral nerve stimulation in a rat model of neuropathic pain

BACKGROUND

Spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS) are thought to reduce pain by activating a sufficient number of large myelinated (Aβ) fibres, which in turn initiate spinal segmental mechanisms of analgesia. However, the volume of neuronal activity and how this activity is associated with different treatment targets is unclear under neuropathic pain conditions.

METHODS

We sought to delineate the intensity-dependent mechanisms of SCS and PNS analgesia by in vivo extracellular recordings from spinal wide-dynamic range neurons in nerve-injured rats. To mimic therapeutic SCS and PNS, we used bipolar needle electrodes and platinum hook electrodes to stimulate the dorsal column and the tibial nerve, respectively. Compound action potentials were recorded to calibrate the amplitude of conditioning stimulation required to activate A-fibres and thus titrate the volume of activation.

RESULTS

Dorsal column stimulation (50 Hz, five intensities) inhibited the windup (a short form of neuronal sensitization) and the C-component response of wide-dynamic range neurons to graded intracutaneous electrical stimuli in an intensity-dependent manner. Tibial nerve stimulation (50 Hz, three intensities) also suppressed the windup in an intensity-dependent fashion but did not affect the acute C-component response.

CONCLUSIONS

SCS and PNS may offer similar inhibition of short-term neuronal sensitization. However, only SCS attenuates spinal transmission of acute noxious inputs under neuropathic pain conditions. Our findings begin to differentiate peripheral from spinal-targeted neuromodulation therapies and may help to select the best stimulation target and optimum therapeutic intensity for pain treatment.

Psychological screening/phenotyping as predictors for spinal cord stimulation

Spinal cord stimulation (SCS) is becoming a widely used treatment for a number of pain conditions and is frequently considered as a pain management option when conservative or less invasive techniques have proven to be ineffective. Potential indications for SCS include complex regional pain syndrome (CRPS), postherpetic neuralgia, traumatic nerve injury, failed back surgery syndrome, refractory angina pectoris, peripheral vascular disease, neuropathic pain, and visceral pain (Guttman et al. Pain Pract. 9:308-11, 2009). While research on SCS is in its infancy, it is clear that substantial variation exists in the degree of benefit obtained from SCS, and the procedure does not come without risks; thus focused patient selection is becoming very important. Psychological characteristics play an important role in shaping individual differences in the pain experience and may influence responses to SCS, as well as a variety of other pain treatments (Doleys Neurosurg Focus 21:E1, 2006). In addition to psychological assessment, quantitative sensory testing (QST) procedures offer another valuable resource in forecasting who may benefit most from SCS and may also shed light on mechanisms underlying the individual characteristics promoting the effectiveness of such procedures (Eisenberg et al. Pain Pract. 6:161-165, 2006). Here, we present a brief overview of recent studies examining these factors in their relationship with SCS outcomes.

Evaluation of the Bonapace Method: a specific educational intervention to reduce pain during childbirth

OBJECTIVE

As pain during childbirth is very intense, several educational programs exist to help women prepare for the event. This study evaluates the efficacy of a specific pain management program, the Bonapace Method (BM), to reduce the perception of pain during childbirth. The BM involves the father, or a significant partner, in the use of several pain control techniques based on three neurophysiological pain modulation models: (1) controlling the central nervous system through breathing, relaxation, and cognitive structuring; (2) using non-painful stimuli as described in the Gate Control Theory; and (3) recruiting descending inhibition by hyperstimulation of acupressure trigger points.

METHODS

A multicenter case control study in Quebec on pain perception during labor and delivery compared traditional childbirth training programs (TCTPs) and the BM. Visual analog scales were used to measure pain perception during labor. In all, 25 women (TCTP: n = 12; BM: n = 13) successfully reported their perceptions of pain intensity and unpleasantness every 15 minutes.

RESULTS

A POSITIVE CORRELATION BETWEEN THE PROGRESSION OF LABOR AND PAIN WAS FOUND (PAIN INTENSITY: P < 0.01; pain unpleasantness: P < 0.01). When compared to TCTP, the BM showed an overall significant lower pain perception for both intensity (45%; P < 0.01) and unpleasantness (46%; P < 0.01).

CONCLUSION

These significant differences in pain perception between TCTP and the BM suggest that the emphasis on pain modulation models and techniques during labor combined with the active participation of a partner in BM are important variables to be added to the traditional childbirth training programs for childbirth pain management.

Spinal cord stimulation: a 20-year retrospective analysis in 260 patients

Introduction. Spinal cord stimulation (SCS) is used clinically by many pain physicians and neurosurgeons alike without regard to their own outcome data. Methods. We reviewed our 20-year experience retrospectively of patients receiving SCS implants and analyzed our data by pain type and group. Results. We present 260 patients, 140 men and 120 women. The most frequent type of pain in our series was neuropathic pain in 44.25% and the most frequent diagnosis was peripheral vascular disease (PVD) with 98 cases. The second was failed back surgery syndrome (FBSS) with 65 cases and the third was complex regional pain syndrome type I (CRPS I), with 40 cases. In CRPS group, the mean visual analog scale (VAS) of this group was 77.89 ± 13.38. In total, 5% had no pain relief, 40% had poor pain relief, 47.5% had good pain relief, and 7.5% had excellent pain relief. In FBSS group, the mean VAS was 79.62 ± 11.69 mm. A total of 13.80% had no pain relief at all, 35.39% had poor pain relief, 50.76% had good pain relief, and there were no patients in this group who had complete pain relief. A total of 98 patients, 78 men and 20 women, were diagnosed with PVD. The mean VAS of this group was 69.75 ± 14.36 mm. A total of 11.22% had poor pain relief, 87.75% had good pain relief. One patient had complete pain relief and all patients in this group perceived at least some improvement in their symptoms. The rate of complications was close to 28% in our overall sample. Conclusions. In conclusion, we demonstrated the utility over time of this type of treatment is comparable with other series of efficacy of SCS. The analgesic efficacy was close to 65% in the overall group. The therapy was not free of complications. The preponderance of our patients was patients with the diagnosis of PVD and our results in this group of patients were excellent. These excellent results of more than 90% improvement suggest to us that SCS be considered as a first-line approach to the clinical management of patients with pain and ulcer of PVD.

Spinal cord stimulation: neurophysiological and neurochemical mechanisms of action

Chronic neuropathic pain can significantly reduce quality of life and place an economic burden on individuals and society. Spinal cord stimulation (SCS) is an alternative approach to the treatment of neuropathic pain when standard pharmacological agents have failed. However, an improved understanding of the mechanisms by which SCS inhibits pain is needed to enhance its clinical utility. This review summarizes important findings from recent studies of SCS in animal models of neuropathic pain, highlights current understanding of the spinal neurophysiological and neurochemical mechanisms by which SCS produces an analgesic effect, and discusses the potential clinical applicability of these findings and future directions for research.

Effects of sub-perception threshold spinal cord stimulation in neuropathic pain: a randomized controlled double-blind crossover study

BACKGROUND

Recent studies suggest that perception of the paraesthesia elicited by spinal cord stimulation (SCS) is not necessarily required for the pain relieving effect.

OBJECTIVE

The purpose of the study was to determine the effect of sub-perception threshold SCS in patients with neuropathic pain.

METHODS

Ten patients with implanted SCS systems underwent continuous sub-threshold stimulation and no stimulation in a blinded randomized crossover design. Pain scores under these treatment modalities were compared with usual supra-threshold stimulation.

RESULTS

Sub-threshold stimulation elicited significantly lower pain relief than supra-perception threshold SCS. Mean pain scores were 3.6 [max 6.3, min 1.9, standard deviation (SD) 1.3] under supra-threshold stimulation, 5.6 (max 9.0, min 2.4, SD 1.9) under sub-threshold stimulation and 6.4 (max 10.0, min 4.0, SD 2.0) without stimulation.

CONCLUSION

Sub-threshold stimulation under otherwise conventional stimulation parameters has a measurable but not clinically sufficient effect. Thus, the pain relieving effect elicited by SCS is not necessarily linked to the perceptibility of stimulation but may instead be attributed to the intensity of the electric field.

Preoperative DTI and probabilistic tractography in an amputee with deep brain stimulation for lower limb stump pain

This study aimed to find out whether preoperative diffusion tensor imaging (DTI) and probabilistic tractography could help with surgical planning for deep brain stimulation in the periaqueductal/periventricular grey area (PAG/PVG) in a patient with lower leg stump pain. A preoperative DTI was obtained from the patient, who then received DBS surgery in the PAG/PVG area with good pain relief. The postoperative MRI scan showing electrode placement was used to calculate four seed areas to represent the contacts on the Medtronic 3387 electrode. Probabilistic tractography was then performed from the pre-operative DTI image. Tracts were seen to connect to many areas within the pain network from the four different contacts. These initial findings suggest that preoperative DTI scanning and probabilistic tractography may be able to assist surgical planning in the future.

Spinal cord stimulation: an update

Spinal cord stimulation has been used in the treatment of many chronic pain disorders since 1967. In this update, the indications for spinal cord stimulation are reviewed with attention to recent publications. A focused review of the literature on abdominal and visceral pain syndromes is also provided. Furthermore, the technology has evolved from the use of monopolar electrodes to complex electrode arrays. Similarly, the power source has changed from a radio frequency-driven system to a rechargeable impulse generator. These topics are covered, along with a short discussion of implant technique. Finally, we include a review of complications of such therapy. SCS as a technology and therapy continues to evolve.

Changes in Pain Perception and Descending Inhibitory Controls Start at Middle Age in Healthy Adults

OBJECTIVES

Previous studies have shown a reduction of diffuse noxious inhibitory controls (DNICs) in elderly adults compared with younger adults. Unfortunately, little is known regarding the developmental course of DNIC deficits and so it is still unclear whether middle-aged adults also show a DNIC deficit. The aims of the present study were to better characterize the developmental time course of the change in DNIC response by adding a middle-aged group. The role of expectations was also investigated.

METHODS

The pain thresholds (PTs) of 20 young, 20 middle-aged, and 20 healthy elderly volunteers were assessed before and during a cold pressor task (water at 7 degrees C). Acute nociceptive stimuli were administered using a thermode and consisted of a range of painless and painful heat pulses.

RESULTS

Analyses showed that thermal PTs increase by middle age but that the DNIC-induced increase in PT dampens progressively with advancing age. DNIC response was negatively correlated with advancing age, however, expectations regarding DNIC efficacy did not vary with age. This suggests that age-related changes in the size of the DNIC response are not best explained by an age-related change in expectation.

DISCUSSION

The findings tell us that changes in pain perception and endogenous pain modulation arrive earlier than previously suggested. Studies on aging and pain should include a middle-aged group when comparing pain measures across the adult lifespan.

Neurostimulation for chronic noncancer pain: an evaluation of the clinical evidence and recommendations for future trial designs

Object

Neurostimulation to treat chronic pain includes approved and investigational therapies directed at the spinal cord, thalamus, periaqueductal or periventricular gray matter, motor cortex, and peripheral nerves. Persistent pain after surgery and work-related or neural injuries are common indications for such treatments. In light of the risks, efforts, costs, and expectations associated with neurostimulation therapies, a careful reexamination of the methods used to gather evidence for this treatment’s long-term efficacy is in order.

Methods

The authors combed English-language publications to determine the nature of the evidence supporting the efficacy of neurostimulation therapies for chronic noncancer pain. To formulate recommendations for the design of future studies, the results of their analysis were compared with established guidelines for the evaluation of medical evidence.

Evidence supporting the efficacy of neurostimulation has been collected predominantly from retrospective series or from prospective studies whose design or methods of analysis make them subject to limited interpretation. To date, there has been no successful clinical study focused on establishing the efficacy of neurostimulation for pain and incorporating sufficient numbers of participants, matched control groups, sham stimulation, randomization, prospectively defined end points, and methods for controlling experimental bias. Currently available data provide little support for the common practices of psychological or pharmacological screening or trial stimulation to predict and/or improve long-term results.

Conclusions

These findings do not diminish the value of previous investigations or positive patient experiences and do not mean that the treatments are ineffective; rather, they reveal that new data are required to answer the questions raised in and by previous study data. Future analyses of emerging neurostimulation modalities for pain should, whenever feasible, require unambiguous diagnoses as an entry criterion and should involve the use of randomization, parallel control groups that receive sham stimulation, and blinding of patients, investigators, and device programmers. Given the chronicity of patient symptoms and stimulation therapies, efficacy should be studied for 1 year or longer after device implantation. Meticulous study methods are especially important to evaluate new therapies like motor cortex and occipital nerve stimulation.

Spinal cord stimulation for axial low back pain: a prospective, controlled trial comparing dual with single percutaneous electrodes

STUDY DESIGN

A prospective, controlled, clinical trial comparing single and dual percutaneous electrodes in the treatment of axial low back pain from failed back surgery syndrome.

OBJECTIVES

To clarify technical requirements and test the hypothesis that placing two linear arrays in parallel, thereby doubling the number of contacts, improves outcome.

SUMMARY OF BACKGROUND DATA

Technical improvements have enhanced outcomes of spinal cord stimulation for chronic axial low back pain. Dual, parallel electrodes reportedly improve these outcomes.

METHODS

Acting as their own controls, 20 patients who passed screening with single, 4-contact electrodes received permanent dual, 4-contact electrodes with 7- or 10-mm intercontact distances at the same vertebral level(s). We quantified and compared the technical and clinical results of the single and dual electrodes, adjusting stimulation parameters to specific psychophysical thresholds.

RESULTS

Single electrodes provided significant (P < 0.01) advantages in patient- and computer-calculated ratings of pain coverage by paresthesias and in the scaled amplitude necessary to cover the low back, compared with dual 7-mm electrodes. Slight advantages without statistical significance were observed for the single over the dual 10-mm electrodes. Amplitude requirements were significantly lower for the single electrode than for either dual electrode. At long-term follow-up, 53% of patients met the criteria for clinical success.

CONCLUSIONS

While we observed disadvantages for dual electrodes in treating axial low back pain, we achieved technical success with single or dual electrodes in most patients and maintained this success clinically with dual electrodes in 53%.

Temporal Analysis of Cortical Mechanisms for Pain Relief by Tactile Stimuli in Humans

The mechanisms by which vibrotactile stimuli relieve pain are not well understood, especially in humans. We recorded cortical magnetic responses to paired noxious (intra-epidermal electrical stimulation, IES) and innocuous (transcutaneous electrical stimulation, TS) stimuli applied to the back at a conditioning-test interval (CTI) of -500 to 500 ms. Results showed that IES-induced responses were remarkably attenuated when TS was applied 20-60 ms later and 0-500 ms earlier than IES (CTI = -60 to 500 ms). Since the signals evoked by IES reached the spinal cord (CTI = -60 to -20 ms conditions) and the cortex (-60 and -40 ms condition) earlier than those evoked by TS, the present results indicate that cortical responses to noxious stimuli can be inhibited by innocuous tactile stimuli at the cortical level, with minimal contribution at the spinal level.

Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review

OBJECT

The purpose of this report was to examine the available literature to determine the safety and efficacy of spinal cord stimulation (SCS) for the treatment of chronic pain of the trunk and limbs.

METHODS

The author identified 68 studies that fulfilled the efficacy inclusion/exclusion criteria, grouped on the basis of pain indication, with an overall population of 3679 patients. Fifty-one studies fulfilled all safety inclusion/exclusion criteria. Based on the literature review, the author found that SCS had a positive, symptomatic, long-term effect in cases of refractory angina pain, severe ischemic limb pain secondary to peripheral vascular disease, peripheral neuropathic pain, and chronic low-back pain, and that, in general, SCS was a safe and effective treatment for a variety of chronic neuropathic conditions.

CONCLUSIONS

Despite the positive findings, there is an urgent need for randomized, controlled, long-term studies on the efficacy of SCS involving larger patient sample sizes.

Analgesic and placebo effects of thalamic stimulation

Numerous clinical studies have reported successful relief of chronic pain with sensory thalamic stimulation. However, even with the extensive use of sensory thalamic stimulation as a clinical tool in the relief of chronic pain, the results are still inconsistent. This discrepancy could probably be explained by the fact that the majority of these studies are case reports or retrospective analyses, which have often used imprecise pain measurements that do not allow a rigorous statistical evaluation of pain relief. None of these studies measured the effect of stimulation on clinical pain for longer than a few hours per day, which is an important aspect considering that clinical pain can vary over time. Moreover, placebo controls are seldom included. In the current study, we measured patients' pain perception at home over a 2-week period, both during days of normal stimulation of the sensory thalamus and during days without stimulation. Patients also came to the laboratory to assess the effects of thalamic and placebo stimulation on clinical pain, experimental heat pain, innocuous air puff and visual stimulation. A potential relation between the perceived paresthesia and analgesic efficacy during thalamic and placebo stimulation was also explored. We found that thalamic stimulation significantly affected clinical and experimental pain perception, but that an important placebo component also exists. On the other hand, neither thalamic nor placebo stimulation affected air puff and visual ratings, suggesting that the effect applies specifically to pain and hence is not caused by a general change in attention. The level of paresthesia elicited during the placebo manipulation was also directly correlated with the degree of placebo pain relief. These results suggest that thalamic stimulation produces a small but significant reduction in pain perception, but that a significant placebo effect also exists.

Spinal cord stimulation for chronic pain of spinal origin: a valuable long-term solution

STUDY DESIGN

A literature review was conducted.

OBJECTIVE

To review the indications and efficacy of spinal cord stimulation, particularly in reference to chronic pain of spinal origin.

SUMMARY OF BACKGROUND DATA

The first spinal cord stimulation was implanted by Shealy in 1967 via a subarachnoid route. Early systems were plagued with a high rate of complications and technical problems. With the evolving technology, especially the advent of multichannel programmable systems and more precise epidural placement, the ability of spinal cord stimulation to treat various pain syndromes improved. This article reviews the literature on spinal cord stimulation from 1967 to the present.

METHODS

The literature is reviewed, with a particular focus on recent studies investigating the efficacy of spinal cord stimulation for low back pain.

RESULTS

Most studies are limited by the same flaws, namely, retrospective study design. At this writing, the few published randomized prospective studies have suggested that spinal cord stimulation may be superior to repeat surgery. Complication rates have declined to approximately 8%, and reoperation is necessary in approximately 4% of patients. When current percutaneous techniques are used, a lead migration rate lower than 3% may be achieved. For certain topographies, laminotomy leads may be superior, particularly with regard to low back pain.

CONCLUSIONS

The ultimate efficacy of spinal cord stimulation remains to be determined, primarily because of limitations associated with the published literature. However, on the basis of the current evidence, it may represent a valuable treatment option, particularly for patients with chronic pain of predominantly neuropathic origin and topographical distribution involving the extremities. The potential treatment of other pain topographies and etiologies by spinal cord stimulation continues to be studied.

Spinal cord stimulation for nonspecific limb pain versus neuropathic pain and spontaneous versus evoked pain

OBJECTIVE

To compare the outcome of spinal cord stimulation (SCS) in patients with nonspecific limb pain versus patients with neuropathic pain syndromes and in patients with spontaneous versus evoked pain.

METHODS

A retrospective review of 122 patients accepted for treatment with SCS between January 1990 and December 1998 was conducted. All patients first underwent a trial of SCS with a monopolar epidural electrode. Seventy-four patients had a successful trial and underwent permanent implantation of the monopolar electrode used for the trial (19 patients), or a quadripolar electrode (53 patients), or a Resume quadripolar electrode via laminotomy (2 patients).

RESULTS

Of the 74 patients, 60.7% underwent implantation of a permanent device and were followed for an average of 3.9 years (range, 0.3-9 yr). Early failure (within 1 yr) occurred in 20.3% of patients, and late failure (after 1 yr) occurred in 33.8% of patients. Overall, 45.9% of patients were still receiving SCS at latest follow-up. Successful SCS (>50% reduction in pain for 1 yr) occurred in 83.3% of patients with nonspecific leg pain, 89.5% of patients with limb pain associated with root injury, and 73.9% of patients with nerve neuropathic pain. SCS was less effective for the control of allodynia or hyperpathia than for spontaneous pain associated with neuropathic pain syndromes. Third-party involvement did not influence outcome. There was a lesser incidence of surgical revisions when quadripolar leads were used than with monopolar electrodes.

CONCLUSION

SCS is as effective for treating nonspecific limb pain as it is for treating neuropathic pain, including limb pain associated with root damage.

Functional imaging and neurophysiological assessment of spinal and brain therapeutic modulation in humans

We summarize here our experience in the neurophysiological and neuroimaging assessment of spinal and brain neuromodulation for pain relief. Techniques reviewed include somatosensory evoked potentials (SEPs), nociceptive spinal (RIII) reflexes, and positron emission tomography (PET), which have been applied both to investigate the mechanisms and to optimize the application of neurostimulation procedures. SEPs are especially useful in the preoperative assessment of patients with neuropathic pain, as they allow the establishment of the functional state of the dorsal column system. Patients with strongly abnormal SEPs due to ganglionic or preganglionic pathology are not likely to benefit from spinal (SCS) or peripheral (TENS) neurostimulation, because ascending fibers disconnected from their soma will undergo rapid degeneration and not be excitable. In the postoperative period, nociceptive spinal reflexes yield objective data concerning the effects of neurostimulation on spinal circuitry. In our experience, the best clinical results are achieved in patients with preserved preoperative SEPs, in whom neurostimulation entails profound attenuation of nociceptive reflexes.PET-scan imaging techniques have recently been used to demonstrate changes in cerebral blood flow during new neuromodulation schemes such as motor cortex stimulation for pain control (MCS). PET studies highlight the thalamus as the key structure mediating functional MCS effects. Thalamic activation would trigger a cascade of synaptic events influencing activity in other pain-related structures including the anterior cingulate gyrus, insula, and upper brainstem. The combination of clinical electrophysiology and functional neuroimaging provides insight into the mechanisms of action of neuromodulation procedures, guides clinical decision, and contributes to optimize patient selection.

Inhibitory effects from various types of dorsal column and raphe magnus stimulations on nociceptive withdrawal flexion reflexes

Most of the clinical and research reports agree about the analgesic effects of dorsal column (DC) stimulation, but there is no unanimity about the neural mechanisms involved in this stimulation. The aim of the present study was to compare the effects of segmental and rostral activation of the DCs and to investigate whether these effects are mediated through a brainstem spinal loop. Decerebrate-decerebellate cats were subjected to selective DC lesions at C(1) and C(3) spinal cervical levels and their reflex reactions to natural or electrical nociceptive stimuli were monitored either as withdrawal flexion reflexes or as motorneuronal discharges. Conditioning stimulation was performed as train of shocks (100 Hz, for 1 to 10 min or 300 Hz for 30 ms) applied on the DCs either rostral (DCr) or caudal (DCc) to the spinal lesions or on the raphe magnus (RM). Conditioning trains for 5-10 min applied on DCr inhibited the withdrawal flexion reflexes recorded as toe flexion (90% of the control). Comparisons of the effects of DCr, DCc or RM of conditioning stimuli were made on the discharges of 110 motorneurons recorded in isolated ventral root fibers. Conditioning stimulation applied to DCc produced short lived inhibition (in about 60%) or facilitation (in about 30% of the neurons) while DCr or RM conditioning produced inhibition in 90% of neurons which outlasted the duration of the conditioning trains. It was also shown that repetitive application of conditioning train on either DCr or RM resulted in longer duration of inhibition than that observed following DCc conditioning. We conclude that the stronger inhibition of motorneuronal discharges, evoked by nociceptive stimuli, is obtained by rostral activation of the DCs and that long term effects of DCst are mediated through a DC-brainstem-spinal loop.

[Physiology of nociception]

Nociception is related to the mechanisms elicited by stimuli threatening the integrity of the organism. At the peripheral level, unmyelinated C fibres (C polymodal nociceptores) or fine myelinated A delta fibres are excited by noxious stimulation, directly or indirectly by inflammatory processes. Nociceptive afferent fibres terminate in the superficial laminae of the dorsal horn of the spinal cord where informations are integrated and controlled. These first synapses are modulated by excitatory amino acids (glutamate and aspartate) and many peptides (substance P, CGRP, CCK, endogenous opiods). The majority of ascending pathways involved in nociception are located in the ventrolateral controlateral quadrant of the cord (spinorelicular and spinothalamic tracts). Many supraspinal sites are activated following nociceptive stimuli, with relays in the reticular formation of the brain stem (including the subnucleus reticularis dorsalis), the ponto-mesencephalic regions (periaqueducal gray matter and parabrachial area) and thalamic sites. Amygdala and hypothamic targets could be involved in motivational reactions and neuroendocrine adaptations to a noxious event. The cingular, insular and somatosensory cortices also receive nociceptive informations. Nociceptive signals are modulated at all levels of their transmission; the more extensively studied controls are located at the spinal level. Segmental controls are inhibitory effects produced by non-noxious mechanical stimuli. Spinal signals can also be inhibited following activation of bulbopinal descending inhibitor pathways and release of serotonin, norepinephrine and, indirectly, endogenous opiods. Inhibitory controls triggered by noxious stimuli could facilitate the extraction of the nociceptive tone of informations having priority over other stimuli.

Spinal cord stimulation in animal models of mononeuropathy: effects on the withdrawal response and the flexor reflex

Spinal cord stimulation (SCS) is efficacious for pain due to injury of peripheral nerves, and therefore models of mononeuropathy appear to be particularly suitable for an experimental approach to the study of mechanisms underlying the clinical effect of this mode of treatment in chronic neuropathic pain. Virtually all previous experimental studies on SCS have utilized acute and nociceptive types of peripheral pain stimuli to explore the attenuating effects of SCS. In the present study we made use of the two models of supposedly painful neuropathy developed by Bennett and Xie (1988) and Seltzer et al. (1990) to explore the effect of SCS applied with stimulus parameters similar to those used in clinical practice. In rats subjected to ligatures of the sciatic nerve according to these two methods, SCS was applied via chronically implanted electrodes, or acutely via a laminectomy in the lower thoracic region. In awake, freely moving animals SCS produced a marked increase of the withdrawal thresholds to innocuous mechanical stimuli in the form of von Frey filaments. This threshold elevation lasted for up to 40 min after 10 min of SCS. In about one-half of the animals there was also a moderate, but short-lasting increase in the intact leg. The degree and duration of the withdrawal threshold elevation was clearly related to the intensity of SCS which was kept below the level of which a response in the thoracic or leg musculature was produced. In a second series of experiments the effect of SCS, applied acutely via a laminectomy, on the early component (latency: 8-12 msec) of the flexor reflex was studied. As a result of nerve ligation with either of the methods used, the thresholds for evoking the early as well as the late component in the nerve-ligated leg were significantly lower than in the intact one. SCS resulted in a marked and long-lasting increase of the threshold of the early component in the nerve-ligated leg. On the intact side only a slight and short-lasting increase was observed. The late, C fibre-mediated component was not influenced by SCS. The first component of the flexor reflex is conceivably mediated by A beta-fibre activation and it presumably corresponds to the withdrawal response induced by innocuous mechanical stimuli. The lack of effect of SCS on the late reflex component indicates that it selectively influences transmission of A-fibre activity. (ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of spinal cord projections from the medullary subnucleus reticularis dorsalis and the adjacent cuneate nucleus: a Phaseolus vulgaris-leucoagglutinin study in the rat

The distribution and organization of descending spinal projections from the dorsal part of the caudal medulla were studied in the rat following injections of Phaseolus vulgaris-leucoagglutinin into small areas of the subnucleus reticularis dorsalis (SRD) and the adjacent cuneate nucleus (Cu). The caudal aspect of the Cu projected only to the dorsal horn of the ipsilateral cervical cord via the dorsal funiculus. These projections were mainly to laminae I, IV, and V. More ventrally located reticular structures projected to the full length of the cord. Fibers originating from the SRD travelled through the ipsilateral dorsolateral funiculus and terminated within the deep dorsal horn and upper layers of the ventral horn, mainly in laminae V-VII. Fibers originating from subnucleus reticularis ventralis (SRV) travelled ipsilaterally through the lateral and ventrolateral funiculi and bilaterally through the ventromedial funiculus. These fibers terminated within the ventral horn. The density of labeling within the gray matter varied at different levels of the cord was as follows: cervical > sacral > thoracic > lumbar. The reciprocal connections between the caudal medulla and the spinal cord suggest that the former is an important link in feedback loops that regulate spinal outflow.

Dorsal column inhibition of nociceptive thalamic cells mediated by gamma-aminobutyric acid mechanisms in the cat

Cells in posterior parts of the cat thalamus were investigated. Responses in single units excited by electrical stimulation in the lateral funiculus (LF), the dorsal column nucleus (DCN) or the canine tooth pulp (TP) were analysed. All cells had a spontaneous resting activity which could be increased by extracellular iontophoretic application of DL-homocysteic acid (DLH) and decreased by gamma-aminobutyric acid (GABA). No effect on the spontaneous firing rate was observed following iontophoresis of the selective GABA-antagonists, picrotoxin (GABA-A receptor antagonist) or saclofen (GABA-B receptor antagonist). However, the decreased firing following GABA application was partially blocked by picrotoxin but not by saclofen. A phasic inhibition induced by DCN stimulation in nociceptive thalamic cells is indicated since simultaneous administration of picrotoxin increased the evoked response. This type of inhibitory mechanism could not be detected following LF or TP stimulation. The extracellular activity evoked by electrical stimulation of LF or TP was significantly depressed by preceding electrical stimulation in the DCN. This inhibition was reversed by simultaneous administration of picrotoxin, indicating an involvement of GABA-A receptors. The reversal of the DCN-induced depression of the late responses following LF stimulation occurred after application of saclofen. It is suggested that this effect is partly mediated via GABA-B receptors. Results from the present study indicate an interaction in the thalamus between presumed low-threshold (DCN) and presumed nociceptive afferents (LF and TP) similar to that previously described in the spinal cord.

What is the maximum number of levels needed in pain intensity measurement?

An important issue that has yet to be resolved in pain measurement literature concerns the number of levels needed to assess self-reported pain intensity. An examination of treatment outcome literature shows a large variation in the number of levels used, from as few as 4 (e.g., 4-point Verbal Rating scales (VRS)) to as many as 101 (e.g., 101-point Numerical Rating scales (NRS)). The purpose of this study was to provide an empirically derived guideline for determining the number of levels needed. Chronic pain patients (n = 124) provided pre- and post-treatment measures of pain intensity using 101-point NRS for least, most, current, and average pain. The patients' responses to the measures were examined closely to determine the actual number of levels used. In addition, their responses to the 101-point scales were recorded to form 7 scales of varying levels (2- to 101-point scales). The sensitivity of the 7 recorded scales was examined. The results indicated that little information is lost if 101-point scales are coded as 11- or 21-point scales. Moreover, examination of the actual responses to the 101-point measure showed that almost all patients treated it as a 21-point scale by providing responses in multiples of 5 or 10, while a substantial number of patients treated it as an 11-point scale, providing responses in multiples of 10 only. The results suggest that 10- and 21-point scales provide sufficient levels of discrimination, in general, for chronic pain patients to describe pain intensity.

Spinal cord stimulation in Belgium: a nation-wide survey on the incidence, indications and therapeutic efficacy by the health insurer

The present report describes a nation-wide survey on the incidence, the indications and the efficacy of spinal cord stimulation (SCS), as assessed by the Belgian health authorities. The direct motive for this survey was the rapidly growing expenditures resulting from the increasing use of SCS. Between 1983 and 1992, nearly 700 SCS devices were implanted for a population of less than 10 million inhabitants. The most common indication for SCS was failed back survey (61.4%). Whereas SCS was initially only performed in university teaching hospitals, it is now also widely practised in general hospitals. In 3 studies, the efficacy of SCS was assessed. In a first study, success was defined in terms of resumption of professional activities. After a mean follow-up of more than 1 year, less than 5% of the 147 patients treated with SCS had returned to work. A second study investigated the subjective evaluation of the therapy by the patient. Seventy patients with a mean follow-up of 3.5 years were studied. In 52% of the patients, the effect of SCS was judged as good to very good. Men scored better than women. In addition, the results obtained in the teaching hospitals were significantly better than those obtained in general hospitals. In a third study, the impact of psychiatric screening on patient selection was evaluated. Of the 100 candidates, 36 were withheld from implantation with a SCS device because of psychiatric contra-indications. Patients who had received a positive psychiatric advice showed a significantly better therapeutic outcome than patients for whom the psychiatrist had made reservations.