ECAP-controlled closed-loop versus open-loop SCS for the treatment of chronic pain: 36-month results of the EVOKE blinded randomized clinical trial

INTRODUCTION

The evidence for spinal cord stimulation (SCS) has been criticized for the absence of blinded, parallel randomized controlled trials (RCTs) and limited evaluations of the long-term effects of SCS in RCTs. The aim of this study was to determine whether evoked compound action potential (ECAP)-controlled, closed-loop SCS (CL-SCS) is associated with better outcomes when compared with fixed-output, open-loop SCS (OL-SCS) 36 months following implant.

METHODS

The EVOKE study was a multicenter, participant-blinded, investigator-blinded, and outcome assessor-blinded, randomized, controlled, parallel-arm clinical trial that compared ECAP-controlled CL-SCS with fixed-output OL-SCS. Participants with chronic, intractable back and leg pain refractory to conservative therapy were enrolled between January 2017 and February 2018, with follow-up through 36 months. The primary outcome was a reduction of at least 50% in overall back and leg pain. Holistic treatment response, a composite outcome including pain intensity, physical and emotional functioning, sleep, and health-related quality of life, and objective neural activation was also assessed.

RESULTS

At 36 months, more CL-SCS than OL-SCS participants reported ≥50% reduction (CL-SCS=77.6%, OL-SCS=49.3%; difference: 28.4%, 95% CI 12.8% to 43.9%, p<0.001) and ≥80% reduction (CL-SCS=49.3%, OL-SCS=31.3%; difference: 17.9, 95% CI 1.6% to 34.2%, p=0.032) in overall back and leg pain intensity. Clinically meaningful improvements from baseline were observed at 36 months in both CL-SCS and OL-SCS groups in all other patient-reported outcomes with greater levels of improvement with CL-SCS. A greater proportion of patients with CL-SCS were holistic treatment responders at 36-month follow-up (44.8% vs 28.4%), with a greater cumulative responder score for CL-SCS patients. Greater neural activation and accuracy were observed with CL-SCS. There were no differences between CL-SCS and OL-SCS groups in adverse events. No explants due to loss of efficacy were observed in the CL-SCS group.

CONCLUSION

This long-term evaluation with objective measurement of SCS therapy demonstrated that ECAP-controlled CL-SCS resulted in sustained, durable pain relief and superior holistic treatment response through 36 months. Greater neural activation and increased accuracy of therapy delivery were observed with ECAP-controlled CL-SCS than OL-SCS.

TRIAL REGISTRATION NUMBER

NCT02924129.

Durable multimodal and holistic response for physiologic closed-loop spinal cord stimulation supported by objective evidence from the EVOKE double-blind randomized controlled trial

INTRODUCTION

Chronic pain patients may experience impairments in multiple health-related domains. The design and interpretation of clinical trials of chronic pain interventions, however, remains primarily focused on treatment effects on pain intensity. This study investigates a novel, multidimensional holistic treatment response to evoked compound action potential-controlled closed-loop versus open-loop spinal cord stimulation as well as the degree of neural activation that produced that treatment response.

METHODS

Outcome data for pain intensity, physical function, health-related quality of life, sleep quality and emotional function were derived from individual patient level data from the EVOKE multicenter, participant, investigator, and outcome assessor-blinded, parallel-arm randomized controlled trial with 24 month follow-up. Evaluation of holistic treatment response considered whether the baseline score was worse than normative values and whether minimal clinical important differences were reached in each of the domains that were impaired at baseline. A cumulative responder score was calculated to reflect the total minimal clinical important differences accumulated across all domains. Objective neurophysiological data, including spinal cord activation were measured.

RESULTS

Patients were randomized to closed-loop (n=67) or open-loop (n=67). A greater proportion of patients with closed-loop spinal cord stimulation (49.3% vs 26.9%) were holistic responders at 24-month follow-up, with at least one minimal clinical important difference in all impaired domains (absolute risk difference: 22.4%, 95% CI 6.4% to 38.4%, p=0.012). The cumulative responder score was significantly greater for closed-loop patients at all time points and resulted in the achievement of more than three additional minimal clinical important differences at 24-month follow-up (mean difference 3.4, 95% CI 1.3 to 5.5, p=0.002). Neural activation was three times more accurate in closed-loop spinal cord stimulation (p<0.001 at all time points).

CONCLUSION

The results of this study suggest that closed-loop spinal cord stimulation can provide sustained clinically meaningful improvements in multiple domains and provide holistic improvement in the long-term for patients with chronic refractory pain.

TRIAL REGISTRATION NUMBER

NCT02924129.

Neurophysiological outcomes that sustained clinically significant improvements over 3 years of physiologic ECAP-controlled closed-loop spinal cord stimulation for the treatment of chronic pain

INTRODUCTION

A novel, spinal cord stimulation (SCS) system with a physiologic closed-loop (CL) feedback mechanism controlled by evoked compound action potentials (ECAPs) enables the optimization of physiologic neural dose and the accuracy of the stimulation, not possible with any other commercially available SCS systems. The report of objective spinal cord measurements is essential to increase the transparency and reproducibility of SCS therapy. Here, we report a cohort of the EVOKE double-blind randomized controlled trial treated with CL-SCS for 36 months to evaluate the ECAP dose and accuracy that sustained the durability of clinical improvements.

METHODS

41 patients randomized to CL-SCS remained in their treatment allocation and were followed up through 36 months. Objective neurophysiological data, including measures of spinal cord activation, were analyzed. Pain relief was assessed by determining the proportion of patients with ≥50% and ≥80% reduction in overall back and leg pain.

RESULTS

The performance of the feedback loop resulted in high-dose accuracy by keeping the elicited ECAP within 4µV of the target ECAP set on the system across all timepoints. Percent time stimulating above the ECAP threshold was >98%, and the ECAP dose was ≥19.3µV. Most patients obtained ≥50% reduction (83%) and ≥80% reduction (59%) in overall back and leg pain with a sustained response observed in the rates between 3-month and 36-month follow-up (p=0.083 and p=0.405, respectively).

CONCLUSION

The results suggest that a physiological adherence to supra-ECAP threshold therapy that generates pain inhibition provided by ECAP-controlled CL-SCS leads to durable improvements in pain intensity with no evidence of loss of therapeutic effect through 36-month follow-up.

Long-term efficacy of high-frequency (10 kHz) spinal cord stimulation for the treatment of painful diabetic neuropathy: 24-Month results of a randomized controlled trial

AIMS

To evaluate the long-term efficacy of high-frequency (10 kHz) spinal cord stimulation (SCS) for treating refractory painful diabetic neuropathy (PDN).

METHODS

The SENZA-PDN study was a prospective, multicenter, randomized controlled trial that compared conventional medical management (CMM) alone with 10 kHz SCS plus CMM (10 kHz SCS+CMM) in 216 patients with refractory PDN. After 6 months, participants with insufficient pain relief could cross over to the other treatment. In total, 142 patients with a 10 kHz SCS system were followed for 24 months, including 84 initial 10 kHz SCS+CMM recipients and 58 crossovers from CMM alone. Assessments included pain intensity, health-related quality of life (HRQoL), sleep, and neurological function. Investigators assessed neurological function via sensory, reflex, and motor tests. They identified a clinically meaningful improvement relative to the baseline assessment if there was a significant persistent improvement in neurological function that impacted the participant's well-being and was attributable to a neurological finding.

RESULTS

At 24 months, 10 kHz SCS reduced pain by a mean of 79.9% compared to baseline, with 90.1% of participants experiencing ≥50% pain relief. Participants had significantly improved HRQoL and sleep, and 65.7% demonstrated clinically meaningful neurological improvement. Five (3.2%) SCS systems were explanted due to infection.

CONCLUSIONS

Over 24 months, 10 kHz SCS provided durable pain relief and significant improvements in HRQoL and sleep. Furthermore, the majority of participants demonstrated neurological improvement. These long-term data support 10 kHz SCS as a safe and highly effective therapy for PDN.

TRIAL REGISTRATION

ClincalTrials.gov Identifier, NCT03228420.

High-Frequency 10-kHz Spinal Cord Stimulation Improves Health-Related Quality of Life in Patients With Refractory Painful Diabetic Neuropathy: 12-Month Results From a Randomized Controlled Trial

Objective

To evaluate high-frequency (10-kHz) spinal cord stimulation (SCS) treatment in refractory painful diabetic neuropathy.

Patients and Methods

A prospective, multicenter randomized controlled trial was conducted between Aug 28, 2017 and March 16, 2021, comparing conventional medical management (CMM) with 10-kHz SCS+CMM. The participants had hemoglobin A1c level of less than or equal to 10% and pain greater than or equal to 5 of 10 cm on visual analog scale, with painful diabetic neuropathy symptoms 12 months or more refractory to gabapentinoids and at least 1 other analgesic class. Assessments included measures of pain, neurologic function, and health-related quality of life (HRQoL) over 12 months with optional crossover at 6 months.

Results

The participants were randomized 1:1 to CMM (n=103) or 10-kHz SCS+CMM (n=113). At 6 months, 77 of 95 (81%) CMM group participants opted for crossover, whereas none of the 10-kHz SCS group participants did so. At 12 months, the mean pain relief from baseline among participants implanted with 10-kHz SCS was 74.3% (95% CI, 70.1-78.5), and 121 of 142 (85%) participants were treatment responders (≥50% pain relief). Treatment with 10-kHz SCS improved HRQoL, including a mean improvement in the EuroQol 5-dimensional questionnaire index score of 0.136 (95% CI, 0.104-0.169). The participants also reported significantly less pain interference with sleep, mood, and daily activities. At 12 months, 131 of 142 (92%) participants were "satisfied" or "very satisfied" with the 10-kHz SCS treatment.

Conclusion

The 10-kHz SCS treatment resulted in substantial pain relief and improvement in overall HRQoL 2.5- to 4.5-fold higher than the minimal clinically important difference. The outcomes were durable over 12 months and support 10-kHz SCS treatment in patients with refractory painful diabetic neuropathy.

Trial registration

clincaltrials.gov Identifier: NCT03228420.

Effect of High-frequency (10-kHz) Spinal Cord Stimulation in Patients With Painful Diabetic Neuropathy: A Randomized Clinical Trial

Question

Will 10-kHz spinal cord stimulation improve pain relief for patients with painful diabetic neuropathy refractory to medical management?

Findings

In this randomized clinical trial including 216 patients, there was a significant benefit of 10-kHz spinal cord stimulation, with 79% of treatment responders whose underlying neurological deficits did not worsen compared with 5% of controls treated with conventional medical management.

Meaning

Patients with painful diabetic neuropathy with inadequate pain relief despite best available medical treatments should be considered for 10-kHz spinal cord stimulation.

Importance

Many patients with diabetic peripheral neuropathy experience chronic pain and inadequate relief despite best available medical treatments.

Objective

To determine whether 10-kHz spinal cord stimulation (SCS) improves outcomes for patients with refractory painful diabetic neuropathy (PDN).

Design, Setting, and Participants

The prospective, multicenter, open-label SENZA-PDN randomized clinical trial compared conventional medical management (CMM) with 10-kHz SCS plus CMM. Participants with PDN for 1 year or more refractory to gabapentinoids and at least 1 other analgesic class, lower limb pain intensity of 5 cm or more on a 10-cm visual analogue scale (VAS), body mass index (calculated as weight in kilograms divided by height in meters squared) of 45 or less, hemoglobin A_1c (HbA_1c) of 10% or less, daily morphine equivalents of 120 mg or less, and medically appropriate for the procedure were recruited from clinic patient populations and digital advertising. Participants were enrolled from multiple sites across the US, including academic centers and community pain clinics, between August 2017 and August 2019 with 6-month follow-up and optional crossover at 6 months. Screening 430 patients resulted in 214 who were excluded or declined participation and 216 who were randomized. At 6-month follow-up, 187 patients were evaluated.

Interventions

Implanted medical device delivering 10-kHz SCS.

Main Outcomes and Measures

The prespecified primary end point was percentage of participants with 50% pain relief or more on VAS without worsening of baseline neurological deficits at 3 months. Secondary end points were tested hierarchically, as prespecified in the analysis plan. Measures included pain VAS, neurological examination, health-related quality of life (EuroQol Five-Dimension questionnaire), and HbA_1c over 6 months.

Results

Of 216 randomized patients, 136 (63.0%) were male, and the mean (SD) age was 60.8 (10.7) years. Additionally, the median (interquartile range) duration of diabetes and peripheral neuropathy were 10.9 (6.3-16.4) years and 5.6 (3.0-10.1) years, respectively. The primary end point assessed in the intention-to-treat population was met by 5 of 94 patients in the CMM group (5%) and 75 of 95 patients in the 10-kHz SCS plus CMM group (79%; difference, 73.6%; 95% CI, 64.2-83.0; P < .001). Infections requiring device explant occurred in 2 patients in the 10-kHz SCS plus CMM group (2%). For the CMM group, the mean pain VAS score was 7.0 cm (95% CI, 6.7-7.3) at baseline and 6.9 cm (95% CI, 6.5-7.3) at 6 months. For the 10-kHz SCS plus CMM group, the mean pain VAS score was 7.6 cm (95% CI, 7.3-7.9) at baseline and 1.7 cm (95% CI, 1.3-2.1) at 6 months. Investigators observed neurological examination improvements for 3 of 92 patients in the CMM group (3%) and 52 of 84 in the 10-kHz SCS plus CMM group (62%) at 6 months (difference, 58.6%; 95% CI, 47.6-69.6; P < .001).

Conclusions and Relevance

Substantial pain relief and improved health-related quality of life sustained over 6 months demonstrates 10-kHz SCS can safely and effectively treat patients with refractory PDN.

Trial Registration

ClincalTrials.gov Identifier: NCT03228420

The Impact of Age on the Outcomes of Minimally Invasive Lumbar Decompression for Lumbar Spinal Stenosis

Background and Purpose

Minimally invasive lumbar decompression (mild^®) is an effective long-term therapy for patients with symptomatic lumbar spinal stenosis (LSS) resulting primarily from hypertrophic ligamentum flavum (HLF). Most subjects in clinical studies of the mild procedure have been older adults (age≥65). While the incidence of LSS increases with age, a substantial number of adults (age<65) also suffer from neurogenic claudication secondary to HLF. In this report, outcomes of mild were compared between adults and older adults.

Patients and Methods

All prospective studies of the mild procedure with a 1-year follow-up completed since the beginning of 2012 that allowed the inclusion of adult patients of all ages were reviewed. Outcomes of visual analog scale (VAS), Oswestry Disability Index (ODI), Pain Disability Index (PDI), Roland Morris Low Back Pain and Disability Questionnaire (RMQ), standing time and walking distance were compared for adults and older adults.

Results

Four studies met the inclusion criteria, resulting in an analysis of 49 adults and 160 older adults. Patients in both age groups experienced significant mean improvements in all but one outcome measure at 6- and 12-month follow-up. Differences between the two age groups in all scores at 6 and 12 months were not statistically significant.

Conclusion

Analysis of the four studies indicated that symptom improvements for adults and older adults were significant from baseline, and no statistically significant difference was observed between the two age groups. These results illustrate that mild can be an effective treatment for LSS due primarily to HLF, regardless of the adult patient age.

High-frequency spinal cord stimulation at 10 kHz for the treatment of painful diabetic neuropathy: design of a multicenter, randomized controlled trial (SENZA-PDN)

BACKGROUND

Painful diabetic neuropathy (PDN), a debilitating and progressive chronic pain condition that significantly impacts quality of life, is one of the common complications seen with long-standing diabetes mellitus. Neither pharmacological treatments nor low-frequency spinal cord stimulation (SCS) has provided significant and long-term pain relief for patients with PDN. This study aims to document the value of 10-kHz SCS in addition to conventional medical management (CMM) compared with CMM alone in patients with refractory PDN.

METHODS

In a prospective, multicenter, randomized controlled trial (SENZA-PDN), 216 subjects with PDN will be assigned 1:1 to receive 10-kHz SCS combined with CMM or CMM alone after appropriate institutional review board approvals and followed for 24 months. Key inclusion criteria include (1) symptoms of PDN for at least 12 months, (2) average pain intensity of at least 5 cm-on a 0- to 10-cm visual analog scale (VAS)-in the lower limbs, and (3) an appropriate candidate for SCS. Key exclusion criteria include (1) large or gangrenous ulcers or (2) average pain intensity of at least 3 cm on VAS in the upper limbs or both. Along with pain VAS, neurological assessments, health-related quality of life, sleep quality, and patient satisfaction will be captured. The primary endpoint comparing responder rates (≥50% pain relief) and safety rates between the treatment groups will be assessed at 3 months. Several secondary endpoints will also be reported on.

DISCUSSION

Enrollment commenced in 2017 and was completed in 2019. This study will help to determine whether 10-kHz SCS improves clinical outcomes and health-related quality of life and is a cost-effective treatment for PDN that is refractory to CMM.

TRIAL REGISTRATION

ClincalTrials.gov identifier: NCT03228420 (registered 24 July 2017).

Safety and Efficacy of Occipital Nerves Stimulation for the Treatment of Chronic Migraines: Randomized, Double-blind, Controlled Single-center Experience

BACKGROUND

A recent multicenter study presented 52-week safety and efficacy results from an open-label extension of a randomized, sham-controlled trial for patients with chronic migraine (CM) undergoing peripheral nerve stimulation of the occipital nerves. We present the data from a single center of 20 patients enrolled at the Cleveland Clinic's Pain Management Department.

METHODS

In this single center, 20 patients were implanted with a neurostimulation system, randomized to an active or control group for 12 weeks, and received open-label treatment for an additional 40 weeks. Outcomes collected included number of headache days, pain intensity, Migraine Disability Assessment (MIDAS), Zung Pain and Distress (PAD), direct patient reports of headache pain relief, quality of life, satisfaction, and adverse events (AEs).

RESULTS

Headache days per month were reduced by 8.51 (±9.81) days (P < 0.0001). The proportion of patients who achieved a 30% and 50% reduction in headache days and/or pain intensity was 60% and 35%, respectively. MIDAS and Zung PAD were reduced for all patients. Fifteen (75%) of the 20 patients at the site reported at least one AE. A total of 20 AEs were reported from the site.

CONCLUSION

Our results support the 12-month efficacy of 20 CM patients receiving peripheral nerve stimulation of the occipital nerves in this single-center trial.

A Comprehensive Outcome-Specific Review of the Use of Spinal Cord Stimulation for Complex Regional Pain Syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful, debilitating affliction that is often difficult to treat. It has become common international practice to use spinal cord stimulation (SCS) for the treatment of CRPS as other therapies fail to provide adequate relief, quality of life, or improvement in function. This comprehensive outcome-specific systematic review of the use of SCS for CRPS was performed to elucidate the available evidence with focus on clinically relevant patient-specific outcomes.

METHODS

A systematic review of the literature was conducted to evaluate the effects of SCS on patients with CRPS for the following outcomes and provide summary levels of evidence in regard to each outcome: perceived pain relief, pain score, resolution of CRPS signs, functional status, quality of life, psychological impact, sleep hygiene, analgesic medication utilization, and patient satisfaction with SCS therapy. Search terms included "complex regional pain syndrome," "spinal cord stimulation," and "reflex sympathetic dystrophy," without restriction of language, date, or type of publication, albeit only original data were included in analyses. Of 30 studies selected, seven systematic reviews were excluded, as were four studies reporting combination therapy that included SCS and other therapies (ie, concurrent peripheral nerve stimulation, intrathecal therapy) without clear delineation to the effect of SCS alone on outcomes. A total of 19 manuscripts were evaluated.

RESULTS

Perceived pain relief, pain score improvement, quality of life, and satisfaction with SCS were all rated 1B+, reflecting positive high-level (randomized controlled trial) evidence favoring SCS use for the treatment of CRPS. Evidence for functional status improvements and psychological effects of SCS was inconclusive, albeit emanating from a randomized controlled trial (evidence level 2B±), and outcomes evidence for both sleep hygiene and resolution of CRPS signs was either nonexistent or of too low quality from which to draw conclusions (evidence level 0). An analgesic sparing effect was observed in nonrandomized reports, reflecting an evidence level of 2C+.

CONCLUSIONS

Spinal cord stimulation remains a favorable and effective modality for treating CRPS with high-level evidence (1B+) supporting its role in improving CRPS patients' perceived pain relief, pain score, and quality of life. A paucity of evidence for functional improvements, resolution of CRPS signs, sleep hygiene, psychological impact, and analgesic sparing effects mandate further investigation before conclusions can be drawn for these specific outcomes.

Retrospective review of 707 cases of spinal cord stimulation: indications and complications

Appropriate patient selection and minimizing complications are critical for successful spinal cord stimulation (SCS) therapy in managing intractable pain. We thus reviewed electronic medical records of 707 consecutive cases of patients who received SCS therapy in the Cleveland Clinic from 2000 to 2005 with an emphasis on indications and complications. SCS was used to treat complex regional pain syndrome (CRPS) (345 cases), failed back surgery syndrome (235 cases), peripheral vascular disease (20 cases), visceral pain in the chest, abdomen, and pelvis (37 cases), and peripheral neuropathy (70 cases). CRPS and failed back surgery syndrome accounted for 82% of the cases. The implant-to-trial ratio was 75% on average, with the highest for CRPS type 2 (83%) and the lowest for peripheral vascular diseases (65%). The only documented complication associated with SCS trials was lead migration in 5 of 707 patients (0.7%). There were no permanent neurological deficits or deaths as a result of SCS implant or its complications. Hardware-related complications were common (38%) and included lead migration (22.6%), lead connection failure (9.5%), and lead breakage (6%). Revisions or replacements were required in these cases. Biologically related complications included pain at the generator site (12%) and clinical infection (4.5%; 2.5% with positive culture). The rates of infection varied among the different diagnoses with the highest in failed back surgery syndrome (6.3%). Patients with diabetes had an infection rate of 9%, over the 4% in non-diabetics. Infections were managed successfully with explantation and antibiotic therapy without permanent sequela.

Continuous cervical epidural analgesia for rehabilitation after shoulder surgery: a retrospective evaluation

BACKGROUND

Patients with frozen shoulder who fail conservative therapy need surgical treatment and aggressive post-operative rehabilitation.

OBJECTIVE

To evaluate the effect of continuous cervical epidural analgesia on pain scores and range of motion of the shoulder joint in patients undergoing surgery for treatment of refractory frozen shoulder.

METHODS

Twenty-one patients with refractory frozen shoulder who had failed conservative treatment and undergone surgical procedure (manipulation under anesthesia or capsular release) were identified and the data were collected retrospectively. These patients had cervical tunneled epidural catheter (TEC) placement for continuous infusion of a mixture of low-dose narcotic and local anesthetics at the time of surgery and were discharged home with the catheter in place. They were then involved in an active physical therapy program to increase the range of motion of the affected shoulder joint. The patients (N = 21) were followed for a median of 4.7 weeks. They were assessed for range of motion, function, visual analog pain scores (VAS), and opiate use before the surgery and after tunneled epidural catheter removal.

RESULTS

Statistically significant changes from the time of placement to the time of removal of the tunneled epidural catheter (TEC) were observed for VAS pain score and range of motion of the shoulder in forward flexion, external rotation, and internal rotation. The mean rate of change among the patients for pain score, forward flexion, external rotation, and internal rotation was also computed. The mean change per week in each of these 4 measurements significantly differed from zero. 33 percent of the patients returned to work within one week.

CONCLUSION

Our data show that the continuous infusion of epidural opioids and local anesthetics through a tunneled cervical epidural catheter during the rehabilitation phase after shoulder surgery for adhesive capsulitis may be a safe and effective tool for post-operative pain control and to facilitate rehabilitation.

Management of pain in addicted/illicit and legal substance abusing patients

Approximately one-third of the American population experiences chronic pain. This varies in origin and severity. It also has been documented that billions of dollars are lost yearly because of health care expenses and missed workdays for chronic pain. Addiction is a primary, chronic, neurobiological disease with genetic, psychological and environmental factors influencing its development and manifestations. Addictive disorders occur in 3% to 26% of the general population, 19% to 255 of hospitalized patients and 40% to 60% in patients who sustained major trauma. More specifically 13.9 million of people living in USA over the age of 12 years are currently using illicit drugs. Although patients with chronic pain may be at an increased risk for addiction, the general population has demonstrated similar addiction rates. Unfortunately, patients who have chronic pain and addition will only have one of these aspects addressed. The purpose of this article is to clarify specific definition of substance use, abuse and addiction. As well as examining the role of pain physicians in evaluating and treating the chronic pain patients who have a history of substance abuse, and lastly outline strategy for assessing patients at risks and evaluating the most practical way of dealing with their chronic pain issues.

Bupivacaine induces transient neurological symptoms after subarachnoid block

Bupivacaine is a long-acting amide local anesthetic that was introduced to clinical practice in the early 1980s. Since then it has been extensively used for both peripheral blocks as well as neuraxial blockade in concentrations varying from 0.125% to 0.75%. Despite the relatively narrow safety margin, bupivacaine has become the most frequently used local anesthetic in obstetric anesthesia. It is 95% metabolized in the liver and 5% excreted unchanged in urine. Bupivacaine cardiotoxicity is related to the total dose rather than to the concentration of bupivacaine administered. It produces a dose-dependent delay in the transmission of impulses through the cardiac conduction system by blocking sodium channels. Transient neurologic symptoms (TNS) defined as bilateral symmetrical pain in the lower back and buttocks with radiation to both lower extremities after 5% lidocaine spinal anesthetic was first described by Schneider in 1993. Several studies have failed to show TNS after spinal anesthesia using bupivacaine 0.5% or 0.75%. In the literature there is only 1 case report of TNS after spinal anesthesia using bupivacaine and morphine. The following report describes a case of TNS following spinal anesthesia with bupivacaine 0.75%.

Treatment of intractable discogenic low back pain. A systematic review of spinal fusion and intradiscal electrothermal therapy (IDET)

BACKGROUND

A growing number of patients suffer from severe low back pain of discogenic origin that is not responsive to conservative medical management. These patients must consider the option of surgical spinal fusion or minimally-invasive intradiscal electrothermal therapy (IDET).

OBJECTIVE

To conduct a systematic review of clinical outcomes in patients undergoing spinal fusion or the intradiscal electrothermal therapy (IDET) procedure for intractable discogenic low back pain.

DESIGN

Systematic literature review.

METHODS

English-language journal articles published from January 1995 to December 2005 were identified through computerized searches of the PubMed database and bibliographies of identified articles and review papers. Articles were selected if disc degeneration or disruption was the primary indication for spinal fusion or the IDET procedure and if follow-up outcome data included evaluations of back pain severity, condition-specific functional impairment and/or health-related quality of life. The literature reviewed encompassed 33 spinal fusion articles: 10 randomized controlled trials, 1 nonrandomized controlled trial, 9 before-after trials, and 13 case series. There were 18 IDET articles: 2 randomized controlled trial, 2 nonrandomized controlled trials, 11 before- after trials, and 3 case series. Data were extracted and summarized on patient characteristics, surgical methods, and clinical outcomes.

RESULTS

Overall, there were similar median percentage improvements realized after spinal fusion and the IDET procedure, respectively, for 2 of the 3 outcomes evaluated: pain severity (50%, 51%), back function (42%, 14%) and quality of life (46%, 43%). There was an identifiable randomized controlled trials trend of both treatments reporting a smaller magnitude of improvement in all 3 primary outcomes (pain severity, back function, quality of life) compared to other types of trials. Perioperative complications were commonly associated with spinal fusion (median: 14%, range: 2% to 54%, n = 31 study groups) whereas adverse events were rarely experienced with the IDET procedure (median: 0%, range: 0% to 16%, n = 14 studies). Randomized controlled trials of spinal fusion, in particular, had important methodological limitations.

CONCLUSION

The majority of patients reported improvement in symptoms following both spinal fusion and the IDET procedure. The IDET procedure appears to offer sufficiently similar symptom amelioration to spinal fusion without the attendant complications.

Tunneled Epidural Catheter Infections in Noncancer Pain: Increased Risk in Patients With Neuropathic Pain/Complex Regional Pain Syndrome

BACKGROUND AND OBJECTIVE

Tunneled epidural catheters are often used to control pain and facilitate rehabilitation in patients with regional pain syndromes. A cohort retrospective study design was undertaken to evaluate the risk of catheter-related infection in patients who underwent a TEC placement to manage their chronic noncancer regional pain over a 5-year period.

METHODS

There were 260 tunneled epidural catheters placed in 218 patients accounting for a total of 10,985 catheter-days. Of these, 230 catheters were placed in patients with neuropathic pain (90% of whom had complex regional pain syndrome) and 30 catheters in patients with somatic pain.

RESULTS

There were 24 epidural space infections in symptomatic patients, 23 of whom were in the neuropathic pain group-22 had complex regional pain syndrome. Additionally, tunneled epidural catheters had to be discontinued in 34 patients because of superficial infection or suspicion of infection; 33 of these were in the neuropathic pain group. The differences in the infection rates were significantly higher in the neuropathic pain group compared to the somatic group. When analyzed to an infection index per 1,000 catheter-days, the rate of infection rate was 5.51 for the patients with neuropathic pain and 2.43 for the patients with somatic pain. The rates for deep and superficial infections were 2.26 and 3.25, respectively, per 1000 catheter-days for the neuropathic pain group compared to 1.22 for both deep and superficial infections in the patients with somatic pain. There were 6 frank epidural abscesses upon contrast-enhanced magnetic resonance imaging examinations of the spine, 1 epidural phlegmon and 2 patients displayed mild or questionable epidural enhancement on magnetic resonance imaging, suggestive of epidural inflammation. All these magnetic resonance imaging abnormalities were detected in patients with complex regional pain syndrome. Two of the patients with epidural abscesses underwent surgical exploration and drainage of the epidural abscess, though no neurologic deficits were observed in any of the patients.

CONCLUSIONS

The higher risk of tunneled epidural catheter infection observed in patients with neuropathic pain (particularly complex regional pain syndrome) warrants further study.

Epidural steroid therapy for back and leg pain: mechanisms of action and efficacy

BACKGROUND CONTEXT

Epidural steroid injection (ESI) is one of the most common nonsurgical interventions prescribed for back and leg pain symptoms. Although the use of ESI is widespread, proof of efficacy among the broad population of low back pain patients is lacking and use is predicated to a great extent on the cost and morbidity of the perceived "next step" in many patient's care-surgery.

PURPOSE

To review the relative indications and clinical features that predict success with ESI therapy, and to provide a physiological rationale to guide clinical decision-making.

STUDY DESIGN/SETTING

Review of literature and clinical experience.

RESULTS

Clinical studies have alternately supported and refuted the efficacy of ESI in the treatment of patients with back and leg pain. Steroid medications do benefit some patients with radicular pain, but the benefit is often limited in duration, making efficacy difficult to prove over time. Steroids appear to speed the rate of recovery and return to function, however, allowing patients to reduce medication levels and increase activity while awaiting the natural improvement expected in most spinal disorders. Fluoroscopic verification of needle placement, with contrast injection, greatly improves steroid delivery while reducing risks. Although it is assumed that the benefit of steroids is related to their effect on inflammation, that remains unproven, and it is possible that benefit is gained through an unrecognized action.

CONCLUSIONS

Randomized, controlled trials are needed to conclusively identify those patients most likely to benefit from ESI, and when and for how long. Until then, epidural steroids provide a reasonable alternative to surgical intervention in selected patients with back and/or leg pain, whose symptoms are functionally limiting. When appropriate goals are established and proper patients are selected, sufficient short-term benefit has been documented to warrant continued use of this tool.

Cost benefit analysis of neurostimulation for chronic pain

OBJECTIVES

To assess the healthcare utilization of patients with intractable chronic neuropathic pain treated with spinal cord stimulation and peripheral nerve stimulation and to provide a cost-benefit analysis.

METHODS

The case records of 222 consecutive patients who received spinal cord stimulation or peripheral nerve stimulation implants at the Cleveland Clinic Foundation between 1990 and 1998 were reviewed retrospectively. Patients were asked to complete a Neurostimulation Outcome Questionnaire designed to gather data on utilization of healthcare resources starting 1 year before surgical implantation. These data were pooled and net differences in events per patient per year, before and after device implantation were calculated and modeled to 2000 cost data obtained from the Medicare Fee Schedule and Healthcare Financing Administration.

RESULTS

Neurostimulation Outcome Questionnaires were returned by 128 patients. The mean patient age was 46 +/- 12.5 years (range 21-71 years) and the mean implant duration was 3.1 +/- 2.3 years (range 0.5-8.9 years). The mean per patient total reimbursement of spinal cord stimulation/peripheral nerve stimulation absent pharmacotherapy was $38,187. Patients treated with spinal cord stimulation/peripheral nerve stimulation for pain management achieved reductions in physician office visits, nerve blocks, radiologic imaging, emergency department visits, hospitalizations, and surgical procedures, which translated into a net annual savings of approximately $30,221 and a savings of $93,685 over the 3.1-year implant duration. The large reduction in healthcare utilization following spinal cord stimulation/peripheral nerve stimulation implantation resulted in a net per patient per year cost savings of approximately $17,903.

DISCUSSION

The reduced demand for healthcare resources by patients receiving neurostimulation suggests that peripheral nerve stimulation and spinal cord stimulation treatment, although associated with relatively high initial costs, demonstrates substantial long-term economic benefits. Thus, neurostimulation should be considered as a viable option for the early treatment of patients with intractable chronic neuropathic pain.

Epidural steroids for back and leg pain: mechanism of action and efficacy

Epidural injections of glucocorticoids may help some patients with back and leg pain. The efficacy of this therapy has not been conclusively proved; however, when weighed against the risks, cost, and outcomes of spinal surgery, epidural glucocorticoids are a reasonable alternative in selected patients whose back and leg pain is functionally limiting. We review the rationale, available data, techniques, and indications for these injections.

Complex regional pain syndrome: redefining reflex sympathetic dystrophy and causalgia

Complex regional pain syndrome (CRPS) is the new nomenclature that encompasses the older diagnostic entities of reflex sympathetic dystrophy (now CRPS 1) and causalgia (CRPS 2). CRPS arises after injuries such as sprains, strains, or fractures, but in some patients the cause is unknown. Although a perennial suspect in the pathogenesis of this entity, the sympathetic nervous system's role in CRPS remains unclear. New studies provide insight into the contribution of the sympathetic nervous system to CRPS and allow reevaluation of clinical features, diagnostic criteria, testing methods, and treatment modalities.

Epidural Infusion of Opiates and Local Anesthetics for Complex Regional Pain Syndrome

Complex Regional Pain Syndrome Type-I (CRPS-I) is a neuropathic pain syndrome resulting from complex pain mechanisms that involve several levels and components of the nervous system. CRPS-I consists of multiple signs, including autonomic dysfunction, in the form of edema, vasomotor changes, motor dysfunctions, muscle spasms, tremors and dystonia, as well as burning pain, hypersensitivity and allodynia that could present in any combination. The treatment is progressive physical therapy rehabilitation program. Multiple analgesic modalities have been used to facilitate the rehabilitation program with varying rates of success. The most successful treatment is a multi-disciplinary comprehensive approach, where initial pain control allows for physical and psychological interventions that are believed to be the basis for successful treatment.(1) The pain in CRPS-I may be mediated through the sympathetic nervous system, sympathetic maintained pain (SMP) or sympathetic independent pain (SIP)(2).

Management of an Epidural Abscess After Continuous Epidural Catheter Infusion

OBJECTIVE

To increase awareness of the possibility of epidural infection after continuous epidural infusion. Outline the salient diagnostic features of epidural infection. Outline a strategy to manage epidural infection and minimize morbidity.

SETTING

Academic multidisciplinary pain clinic.

PATIENT

A patient with a left knee meniscal tear with a history of Chronic Regional Pain Syndrome Type I (CRPS I) of the left foot.

INTERVENTIONS

Attempted control of CRPS I symptoms with a tunnelled epidural catheter infusion.

RESULTS AND CONCLUSIONS

The patient developed an epidural abscess diagnosed on the 11th postoperative day. The catheter was removed and the patient was treated successfully with intravenous antibiotics.

Common nerve blocks in chronic pain management

Anesthesiologists have become increasingly involved with the management of chronic pain patients in the operating room, on the surgical floor, and in the outpatient pain facility setting (often interdisciplinary). Based upon the authors' practice of regional anesthesia, the most specific contribution to chronic pain management arguably remains the practice of diagnostic, prognostic, and therapeutic injections of the neuraxis, peripheral nerves, and the autonomic nervous system.

Implantable spinal cord stimulator to treat the ischemic manifestations of thromboangiitis obliterans (Buerger's disease)

Thromboangiitis obliterans (Buerger's disease) is a segmental inflammatory vasculitis that involves the small-sized and medium-sized arteries, veins, and nerves. It is causally related to tobacco use. The diagnosis is usually made on the basis of the presence of distal arterial disease in individuals who smoke and in whom other disease entities have been excluded. The most effective treatment for Buerger's disease is smoking cessation. Without strict adherence to tobacco avoidance, disease progression is likely. Methods to control ischemic pain include medications, sympathectomy, or surgical revascularization. The effect of sympathectomy is unpredictable, and the chances of a successful revascularization procedure are rare because distal target vessels often are extensively diseased. Herein, we describe a patient whose condition did not respond to the usual conservative therapy but did respond dramatically to the implantation of a permanent spinal cord stimulator. Although these devices have been used for more than 20 years in various other peripheral arterial diseases, their use in Buerger's disease has been limited.

Hemodynamic responses to dobutamine during acute normovolemic hemodilution

The effects of dobutamine (DOB) on myocardial performance, systemic hemodynamics, and oxygen delivery during acute normovolemic hemodilution in anesthetized rats were studied. Forty-two Sprague Dawley rats (body weight 375 to 425 g) were divided into six equal groups. Hemodynamic and cardiac indices were measured or calculated at baseline, 30 minutes after the initiation of hemodilution (HD), and 15 minutes after DOB or saline infusion. Myocardial performance in response to acute pressure or volume loads was studied in all groups of animals. HD to a hematocrit (Hct) value of 20% resulted in no change in heart rate (HR), increased CI, SVI, and LV dP/dt, and decreased MAP, SVRI, and oxygen delivery index (O2DI). HD increased peak SV and CI after preload stress while the left ventricular developed pressure (LVDP) was unchanged. Infusion of DOB as 7.5 or 15 micrograms/kg/min increased HR, CI, and LV dP/dt as well as LVDP. At the same time, DOB decreased MAP and SVR, whereas the SVI remained unchanged. In non-HD animals both doses of DOB increased LVDP, but only the larger dose increased CI, whereas peak SV decreased with the smaller dose. Arterial carbon dioxide tension (PaCO2) increased, whereas pH and arterial oxygen tension (PaO2) decreased; however, O2DI remained unchanged. Concomitant hemodilution and DOB infusion resulted in attenuation of HR response to DOB, exaggerated the drop in MAP and SVR, and increased LV dP/dt. Only the larger dose of DOB increased the CI, whereas neither dose could alter the SVI in HD animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Fentanyl stimulates atrial natriuretic peptide secretion

The effects of fentanyl on ultrastructure, protein biosynthesis, and atrial natriuretic peptide (ANP) secretion were studied in neonatal rat cardiomyocytes (CM). Ventricles from 2-day-old American Wistar rats were digested with 1% collagenase in perfusion buffer. Eight hundred thousand to 1.0 million cells/ml were incubated in tissue culture media, to which fentanyl citrate (Sublimaze) was added in a dose of 10-50 ng/ml. Fentanyl increased the spontaneous CM beating rate, which became rather fibrillary in nature. Protein biosynthesis also increased in a time-related manner. Simultaneous incubation with naloxone (10(-6) M) did not alter the beating rate or protein synthesis. Ultrastructurally, several criteria of myocyte growth were observed: an increase in myofilaments and the appearance of newly formed organized sarcomeres, which were preceded by an increase in the ribosomes and cisternae of rough endoplasmic reticulum, and the appearance of large, adult-type mitochondria with increased matrix granules and long parallel cristae. The latter replaced the elongated thin fetal mitochondria. This was associated with a network of developing sarcoplasmic reticulum and T-tubular system as well as the formation of intercalated discs between the CM. Furthermore, exposure to fentanyl increased ANP immunoreactivity in the culture media while simultaneous incubation with naloxone blocked the effect of fentanyl on ANP secretion. On the other hand, naloxone alone did not alter ANP secretion. Therefore, it could be concluded that fentanyl stimulated protein biosynthesis and ANP secretion as evidenced both biochemically and ultrastructurally. Although the molecular mechanism of ANP secretion by fentanyl is still unclear, yet an opioid receptor mediation could be possible as ANP secretion was blocked by an opioid receptor antagonist (naloxone).

The localization of cholecystokinin immunoreactivity in the rat ovary and uterine tube

The presence of cholecystokinin (CCK) immunoreactive nerve fibres in the rat ovary and uterine tubes was detected using the peroxidase antiperoxidase (PAP) technique. The antibody used was anti CCK 4562 which reacts with CCK-4, CCK-8, CCK-12 and CCK-33 (Larsson and Rehfeld, 1977). CCK-immunoreactive nerve fibres were found between the interstitial cells of the ovary, along blood vessels, and close to smooth muscle fibres in the ovary and tubal wall. A possible role of CCK-nerves in modulation of the sensitivity of the ovarian components to other humoral and nervous stimuli is discussed. The possible control of CCK over smooth muscle fibres in the ovary and the uterine tube and its role in ovulation is a matter of further studies.

Portal-like microcirculation in rat sympathetic ganglia

The fine structure of intraganglionic blood vessels of rat superior cervical sympathetic ganglia is studied with the light microscope and with both conventional and ultrastructural histochemical methods. Two sets of small capillaries together with larger sinusoidal ones are identified. One set of capillaries is associated with the clustered (type II) small catecholamine-containing (CC) cells and exhibits features suggestive of fluid transport function (multiple wide fenestrae and active pinocytosis). The second set of capillaries is in direct relation to the sympathetic neurons (SN) and shows characteristics suggestive of absorptive function (microvilli and pinocytotic vesicles). The larger sinusoidal capillaries are observed in the vicinity of type II CC cells, extend parallel to the long axes of the perikarya of the neurons and occasionally form loops around them. The latter are assumed to be larger blood spaces connecting the two capillary sets and serve to slow the circulation around the neurons. A pattern of portal-like intraganglionic microcirculation through which type II CC cells participate in modulating the SN is postulated. Type II CC cells secrete a catecholamine modulator which, driven by concentration gradient, gains access to the circulation through the fenestrated capillaries. The sinusoidal capillaries serve to perfuse the SN with a slow stream of blood rich in the catecholamine modulator. The latter can be filtered through the microvilli and pinocytotic vesicles of the second set of capillaries to induce slow inhibitory postsynaptic potential on the SN.

Propranolol-induced changes in the catecholamine-containing cells and vesicles of SHR sympathetic ganglia

The ultrastructural effects of long-term propranolol administration on the catecholamine-containing (CC) cells of cervical sympathetic ganglia were studied in spontaneously hypertensive rats. After 2 months of propranolol administration, there were hydrops of mitochondria, together with swelling and vesiculation of Golgi complex and rough endoplasmic reticulum. Such swollen organelles seemed to coalesce with each other, resulting in transformation of major parts of the cytoplasm into large membrane bound saccules. In that group of animals, the number of CC vesicles showed a significant decrease (P less than 0.025) compared to the control. Moreover, such vesicles looked more electron dense, with decreased electron-lucent haloes compared to the control. Blood pressure recording via rat tail cuff showed a significant drop (P less than 0.0001) of the mean systolic blood pressure in the treated animals. One month after stopping propranolol administration, resorption of the cytoplasmic saccules occurred, but the cytoplasm looked lighter and lost its granular appearance. The mitochondria regained their normal shape, though they appeared fewer in number. The CC vesicles were significantly reduced in number (P less than 0.001) and were less electron dense compared to the control. The possible implications of these findings on the mechanism of action of propranolol as an antihypertensive agent are discussed.

New synapses associated with the granule-containing cells of rat sympathetic ganglia

The synapses of the rat superior cervical sympathetic ganglion were studied with both conventional and ultrastructural histochemical methods. Besides the cholinergic synapses polarized from preganglionic fibers to sympathetic ganglion neurons, two morphologically and functionally different types of synapses were observed in relation to the small granule-containing (catecholamine-containing) cells of the rat superior cervical ganglion. The first type is an efferent adrenergic synapse polarized from granule-containing cells to the dendrites of the sympathetic ganglion neurons. This type of synapse might mediate the inhibitory effects (slow inhibitory postsynaptic potentials) induced by catecholamines on the sympathetic neurons. The second type is a reciprocal type of synapse between the granule-containing cells and the cholinergic preganglionic fibers. Through such synapses, these cells could exert a modulating effect on the excitatory preganglionic fibers. Therefore, we propose that these cells, through their multiple synaptic connections, exhibit a local modulatory feedback system in the rat sympathetic ganglia and may serve as interneurons between the preganglionic and postganglionic sympathetic neurons.