LongTerm Outcomes of Spinal Cord Stimulation With Paddle Leads in ...

Neuromodulation: Technology at the Neural Interface Received: January 11, 2011

Revised: March 2, 2011

Accepted: April 26, 2011

(onlinelibrary.wiley.com) DOI: 10.1111/j.1525-1403.2011.00372.x

Long-Term Outcomes of Spinal Cord Stimulation With Paddle Leads in the Treatment of Complex Regional Pain Syndrome and Failed Back Surgery Syndrome ner_372

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Nathaniel C. Sears, MS*, Andre G. Machado, MD, PhD†, Sean J. Nagel, MD†, Milind Deogaonkar, MD†, Michael Stanton-Hicks, MD‡, Ali R. Rezai, MD§, Jaimie M. Henderson, MD¶ Introduction: Spinal cord stimulation (SCS) is frequently used to treat chronic, intractable back, and leg pain. Implantation can be accomplished with percutaneous leads or paddle leads. Although there is an extensive literature on SCS, the long-term efficacy, particularly with paddle leads, remains poorly defined. Outcome measure choice is important when defining therapeutic efficacy for chronic pain. Numerical rating scales such as the NRS-11 remain the most common outcome measure in the literature, although they may not accurately correlate with quality of life improvements and overall satisfaction. Methods: We reviewed the medical records of patients with failed back surgery syndrome (FBSS) or complex regional pain syndrome (CRPS) implanted with SCS systems using paddle leads between 1997 and 2008 at the Cleveland Clinic with a minimum six-month follow-up. Patients were contacted to fill out a questionnaire evaluating outcomes with the NRS-11 as well as overall satisfaction. Results: A total of 35 eligible patients chose to participate. More than 50% of the patients with CRPS reported greater than 50% pain relief at a mean follow-up of 4.4 years. Approximately 30% of the FBSS patients reported a 50% or greater improvement at a mean follow-up of 3.8 years. However, 77.8% of patients with CRPS and 70.6% of patients with FBSS indicated that they would undergo SCS surgery again for the same outcome. Conclusion: Patients with CRPS and FBSS have a high degree of satisfaction, indexed as willingness to undergo the same procedure again for the same outcome at a mean follow-up of approximately four years. The percentage of satisfaction with the SCS system is disproportionally greater than the percentage of patients reporting 50% pain relief, particularly among patients with FBSS. This suggests that the visual analog scale may not be the optimal measure to evaluate long-term outcomes in this patient population. Keywords: Chronic pain, complex regional pain syndrome, failed back surgery syndrome, retrospective study, SCS Conflict of Interest: The authors reported no conflicts of interest.

INTRODUCTION

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Spinal cord stimulation (SCS) is a safe, reversible, and efficacious treatment option for select patients with medically intractable chronic pain syndromes such as failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS) (1–13). SCS systems are routinely implanted after a trial with percutaneous leads. The percutaneous lead inserted for the stimulation trial can be converted into a permanent system or it can be withdrawn and a new system implanted using either percutaneous leads or paddlestyle leads, which require a laminotomy or laminectomy. Although the implantation of SCS systems with percutaneous leads is less invasive, there are several distinct advantages to paddle-style SCS leads. Lead migration and positional effects are commonly observed with percutaneous leads. These effects can be minimized with paddle leads, which have been shown to provide more consistent coverage of the painful areas with paresthesia and www.neuromodulationjournal.com

Address correspondence to: Andre Machado, MD, PhD, Center for Neurological Restoration, Department of Neurosurgery, Cleveland Clinic, Cleveland, Ohio 44195, USA. Email: [email protected] * Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA; † Center for Neurological Restoration and Department of Neurosurgery, Neurological Institute, Cleveland Clinic, Cleveland, OH, USA; ‡ Department of Pain Management, Anesthesiology Institute, Cleveland Clinic, Cleveland, OH, USA ; § Department of Neurosurgery, The Ohio State University, Columbus, Ohio, USA; and ¶ Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA, USA For more information on author guidelines, an explanation of our peer review process, and conflict of interest informed consent policies, please go to http:// www.wiley.com/bw/submit.asp?ref=1094-7159&site=1

© 2011 International Neuromodulation Society

Neuromodulation 2011; 14: 312–318

LONG-TERM OUTCOMES OF SCS The purpose of this study was to evaluate the long-term outcomes of patients treated with paddle lead SCS systems at a single center for two common indications: FBSS or CRPS. The focus of the study was to evaluate overall satisfaction with the therapy and attempt to correlate satisfaction with pain alleviation measured with the VAS.

optimize stimulation efficiency (14). Paddle leads also have been shown to be more clinically effective and to reduce long-term stimulation related side-effects (15) compared with percutaneous leads at relatively short follow-ups (16). However, few studies have so far addressed the question of long-term outcomes after implantation of SCS systems, particularly with paddle leads. A large 1993 study by North et al. (17) evaluated long-term outcomes, mostly in patients undergoing implantation with percutaneous leads. Several other studies focused on outcome assessment up to 24 months post implantation (12,13,18–20). Even though obtaining data from 24 months of follow-up is challenging enough, it is still a relatively short period of time compared with the lifetime of a typical SCS system. Hardware failure can occur in a distressingly large percentage of patients (21), leading to potentially risky interventions that must be balanced against long-term benefit. Evaluating outcomes at the longest possible follow-up is thus important to guide decision making for hardware implantation in this patient population. Evaluating long-term outcomes of interventions for chronic pain is not a trivial task. Following patients for long periods of time can be difficult as the proportion of patients lost to follow-up for a multitude of reasons tends to increase over time. To date, most studies reporting outcomes at up to 24 months rely on the visual analog scale (VAS) or other pain scales, typically defining efficacy as greater than 50% pain relief in greater than 50% of patients implanted (12,13,18–20). Defining long-term efficacy based on pain rating scales has limitations. The results observed with these different scales cannot be always compared directly with each other, making it difficult to compare and aggregate outcomes across different studies (22–24). Pain rating scales, such as the 0–10 numerical rating scale (NRS-11), have been shown to be poorly reproducible (25), which is particularly concerning for long-term outcome evaluation of a chronic pain disorder. Over time, patients may experience magnification of the residual pain, pain memory, and other factors, which may influence the ratings and result in underestimation or overestimation of an intervention performed several years before. Furthermore, there is little knowledge on how much a 50% improvement in NRS-11 levels correlates with improved quality of life and satisfaction.

METHODS We reviewed the medical records of patients implanted with SCS systems with paddle leads at the Cleveland Clinic Center for Neurological Restoration, Department of Neurosurgery between the years of 1997 and 2008. All patients included had been implanted longer than six months. In addition to chart review, patients were contacted to fill out a questionnaire regarding the effectiveness of SCS for their chronic pain syndrome (Fig. 1). Patients were excluded from the study if they were unwilling or unable to complete the questionnaire. This study was reviewed and approved by the Cleveland Clinic Institutional Review Board. Patients diagnosed with CRPS or FBSS were included in the study. The age, sex, duration of pain syndrome, treatment history, etiology of pain syndrome, severity of pain, prior pharmacologic treatment, and affected areas were documented (Table 1). The questionnaire assessed patients’ perceived stimulation coverage, usage habits, and pain reduction. Pain reduction was calculated from the pre- and post-operative VAS scores. As a comparison, patients also were asked if they would undergo implantation of the SCS system again if they were to have the same outcome. The quantitative sciences department at the Cleveland Clinic carried out statistical analysis. Because outcomes were defined by the study itself and the data revealed a nearly Gaussian distribution, parametric analyses were used. Pain scores were compared before and after implantation of the SCS system and analyzed through a Wilcoxon matched-pairs signed-rank test (Table 2). The percentage of patients with greater than 50% pain reduction in NRS-11 was tabulated by disease and in total. Patients with greater than 40% pain reduction were similarly analyzed. (Table 3) This second cut off,

1. Is the stimulator working and covering the area of pain? Yes / No 2. Do you turn the stimulator on for at least 1 hour per day? Yes / No 3. How bad was your average daily pain BEFORE surgery for implantation of the spinal cord stimulator? 0 indicates that you experienced no pain, 10 indicates the worst pain was the worst you’ve experienced. (please circle) 0

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5. If you could go back in time, would you undergo this surgery again in order to get the same pain relief you have now? (Yes or No – please circle) YES I would have surgery again in order to get the same degree of pain relief that I got from this spinal cord stimulator NO I would not have surgery again in order to get the same degree of pain relief that I got from this spinal cord stimulator.

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Figure 1. Questionnaire administered to patients at the time of follow-up. www.neuromodulationjournal.com



SEARS ET AL.

Table 1. Baseline Characteristics of Patients Included Their Age, Sex, Duration of Illness, Duration of Pain Before SCS, Treatment History, Etiology of Pain Syndrome, Severity of Pain, Prior Pharmacologic Treatment, and Areas Affected by Pain Syndrome.

Mean (SD)

Years of age at surgery Years pain at surgery Years after implantation VAS pain pre-surgery (1–10) Total Gender (female) Unilateral Greatest pain location Lower limb Back Upper limb Pharmacologic therapy: Opioids Antidepressants Gabapentin Pregabalin Oxcarbazepine Topiramate Tiagabine Lidocaine patch Alpha-2 agonist Muscle relaxant Other therapies: Physical therapy Nerve block Trigger point injection Epidural injection TENS

Count (%)

CRPS

FBSS

Total

44.3 (10.73) 9.6 (9.27) 5.0 (2.47) 9.2 (0.81) N = 18 (51.4%) N = 9 (50.0%) 11 (61.1%)

51.6 (11.91) 8.5 (1.18) 3.8 (1.62) 8.5 (1.18) N = 17 (48.6%) N = 8 (47.1%) 11 (78.6%)

47.8 (11.76) 8.9 (1.06) 4.4 (2.16) 8.9 (1.06) N = 35 (100%) N = 17 (48.6%) 22 (68.8%)

8 (44.4%) 4 (22.2%) 6 (33.3%)

6 (37.5%) 9 (56.3%) 1 (6.3%)

14 (41.2%) 13 (38.2%) 7 (20.6%)

12 (66.7%) 5 (27.8%) 7 (38.9%) 0 (0.0%) 2 (11.1%) 2 (11.1%) 1 (5.6%) 2 (11.1%) 1 (5.6%) 3 (16.7%)

8 (47.1%) 1 (5.9%) 7 (41.2%) 1 (5.9%) 1 (5.9%) 1 (5.9%) 0 (0.0%) 2 (11.8%) 0 (0.0%) 3 (17.7%)

20 (57.1%) 6 (17.1%) 14 (40.0%) 1 (2.9%) 3 (8.6%) 3 (8.6%) 1 (2.9%) 4 (11.4%) 1 (2.9%) 6 (17.1%)

2 (11.1%) 7 (38.9%) 2 (11.1%) 8 (44.4%) 2 (11.1%)

6 (35.3%) 4 (23.5%) 1 (5.9%) 3 (17.7%) 2 (11.8%)

8 (22.9%) 11 (31.4%) 3 (8.6%) 11 (31.4%) 4 (11.4%)

CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome; SCS, spinal cord stimulation; TENS, transcutaneous electrical nerve stimulation; VAS, visual analog scale.

Table 2. Pain Scores in Patients With CRPS or FBSS Before and After Treatment With a Paddle Electrode Spinal Cord Stimulation System Were Compared and Analyzed Through a Wilcoxon Matched-Pairs Signed-Rank Test. Group

Pre-surgical VAS pain score

Post-surgical VAS pain score

Mean reduction in VAS (p-value)

Percent reduction in VAS (SD)

CRPS FBSS Total

9.2 8.5 8.9

4.7 6.1 5.4

-4.5 (p < 0.0001) -2.4 (p = 0.0005) -3.5 (p < 0.0001)

49.6% (30.36) 28.5% (23.14) 39.3% (28.76)

CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome; VAS, visual analog scale.

Table 3. Percentage of Patients With Greater Than 50% or Greater Than 40% Pain Relief (by Disease), Percentage of Patients Who Would Undergo the Same Procedure Again for the Same Outcome and the Percent Reduction in Pain, by Disease, Among Those That Would Undergo the Procedure Again.

CRPS FBSS Total

Percentage of patients with >50% reduction in VAS


Percentage of patients who would undergo the procedure again for the same outcome

Percent reduction in VAS score among those that would undergo the procedure again for the same outcome

55.6% (10/18) 29.4% (5/17) 42.9% (15/35)

55.6% (10/18) 35.3% (6/17) 45.7% (16/35)

77.8% (14/18) 70.6% (12/17) 74.3% (26/35)

50.6% 33.4% 42.7%

Note that the disparity between those that would undergo the procedure again and the percentage of patients with greater than 40% or 50% relief is greater among FBSS patients. This is further explored in Table 4. CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome; VAS, visual analog scale.

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also arbitrary, is based on previous studies indicating that a 40% improvement can be meaningful to patients with chronic pain (26,27). The percentage of patients that would proceed with surgery again and the mean pain relief among each group was calculated www.neuromodulationjournal.com

(Table 3). Fisher’s exact test was used to compare the frequency of patients who would undergo surgery again to the proportion of patients with 50% or greater pain relief, by disease (Table 4). These two groups were further broken into those with less than four-year



LONG-TERM OUTCOMES OF SCS follow-up and those with greater than four-year follow-up. The reduction in pain in these subgroups was calculated and displayed in Table 5. All analysis was conducted using SAS® v9.2 (SAS Institute Inc., Cary, NC, USA). All patients included had undergone either a percutaneous trial of SCS followed by implantation of the paddle lead SCS system or had undergone initially implantation of SCS with percutaneous leads that were then replaced for a paddle lead. Three authors independently selected patients for percutaneous trials. Four authors implanted paddle leads. All patients included were implanted with thoracic SCS leads connected to implantable pulse generator. All permanent implants were performed under general anesthesia.

RESULTS Ninety-two patients fit the inclusion criteria. Forty were unwilling to participate or did not respond to the questionnaire. Of the remaining 52 patients, seven were excluded because of device removal. Another 10 patients were excluded because they had multiple implants or also had been implanted with peripheral nerve stimulators that confounded the analysis. As shown in Table 1, the study group consisted of 17 female and 18 male patients (total = 35) who underwent SCS for CRPS or FBSS. There were 18 CRPS patients and 17 FBSS patients. The CRPS group was evenly divided between men and women. Nearly half the CRPS patients had pain syndromes affecting their lower extremities, with the remaining patients split between syndromes affecting their back or upper extremities. In the FBSS group, there were eight women and nine men. More than half the FBSS patients had pain syndromes affecting their back and legs while 37.5% of patients had predominantly lower extremity pain. For CRPS, the mean (SD) age was 44.3 years (10.73), the duration of pain at the time of surgery was 9.6 years (9.27), and the duration of follow-up after surgery was

Table 4. Comparison of Proportion of Patients With Greater Than 50% Pain Relief (by Syndrome) and Willingness to Undergo the Same Procedure Again for the Same Outcome.

CRPS FBSS Total


Percentage of patients who would undergo the procedure again for the same outcome

p-value

55.6 (10/18) 29.4 (5/17) 42.9 (15/35)

77.8 (14/18) 70.6 (12/17) 74.3 (26/35)

0.1573 0.0196 0.0076

CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome; VAS, visual analog scale.

5.0 years (2.47). For FBSS, the mean age was 51.6 years (11.91), the duration of pain at the time of surgery was 8.5 years (1.18), and the duration of follow-up after surgery was 3.8 years (1.62). For the whole group, the mean age was 47.8 years (11.76), the duration of pain at the time of surgery was 8.9 years (1.06), and follow-up after surgery was 4.4 years (2.16).

Clinical Outcomes Pain scores at the time of the questionnaire follow-up were significantly reduced for both FBSS and CRPS (Table 2). Overall, the mean pain reduction (SD) was 39.3% (28.8). Mean pain relief (SD) for CRPS and FBSS patients was 49.6% (30.4) and 28.5% (23.1), respectively. For CRPS, the difference in mean NRS-11 pain score was -4.5 points in pain scores (p < 0.0001). For FBSS, the difference was -2.4 points (p = 0.0005). In total, the difference was -3.5 (p < 0.0001). For patients with CRPS, 55.6% achieved greater than 50% pain relief at the time of the questionnaire follow-up (Table 3). For FBSS, 29.4% of patients achieved a 50% or greater reduction in pain. When the pain improvement cut off was reduced to 40%, this number was unchanged for the CRPS patients, while for FBSS the percentage of patients reporting pain relief at 40% or greater increased to 35.3%. At the time of the questionnaire follow-up, 14 CRPS patients (77.8%) and 12 FBSS patients (70.6%) indicated that they would undergo SCS surgery again for the same outcome. For those that would undergo the surgery again, the mean pain relief (SD) after implantation was 50.6% (SD = 29.2) among CRPS patients and 33.4% (SD = 22.1) for FBSS patients. The percentage of patients willing to undergo the procedure again was compared with the percentage of patients reporting greater than 50% pain relief. Among those with CRPS, there was a greater proportion of patients reporting willingness to undergo the procedure again than reporting 50% or greater pain relief. This difference was greater and statistically significant among patients with FBSS. The effect of the post-surgical follow-up time on both NRS-11 outcome and willingness to undergo the procedure again was evaluated, with a cut off of four years. With regard to NRS-11 outcome, a decline in efficacy was noted in both groups. Among patients with CRPS, 66.7% (4/6 subjects) of those with less than four years of follow-up maintained a 50% or greater reduction in pain compared with 50% (6/12 subjects) among those with four years or greater follow-up. For FBSS, 37.5% (3/8 subjects) of those with less than four years of post-surgical follow-up maintained a 50% reduction in pain. Among those with four years or more of follow-up 22.2% (2/9 subjects) maintained a 50% reduction in pain intensity (Table 5). With regard to satisfaction for CRPS, the trend was reversed. Among those with less than four years of follow-up, 66.7% (4/6 subjects) would undergo the procedure again compared with 80.0% (10/12 subjects) among those with four years or greater follow-up. Of the FBSS patients with less than four years of follow-up, 75% (6/8 subjects)

Table 5. Comparison of Outcome Reporting Among Patients With Less Than Four Years of Follow-Up and Four Years or More of Follow-Up. Percent of patients who report >50% reduction

CRPS FBSS

Less than four-year follow-up

Greater than or equal to four-year follow-up

Percent of patients that would undergo the procedure again for the same result Less than four-year follow-up Greater than four-year follow-up

66.7% (4/6) 37.5% (3/8)

50.0% (6/12) 22.2% (2/9)

66.7% (4/6) 75.0% (6/8)

80.0% (10/12) 66.7% (6/9)

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CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome.

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SEARS ET AL. would undergo the procedure again compared with 66.7% (6/9) of those with four years and greater follow-up. Patient age, pain duration at the time of surgery, patient willingness to undergo the procedure again for the same outcome, usage patterns, or pain location were not associated with pain relief in this sample. However, pain relief was associated with antidepressant use at the time of surgery (p = 0.0152).

DISCUSSION

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Spinal cord stimulation has been shown to be effective for patients with chronic pain syndromes including FBSS and CRPS (7,28,29). Most studies regarding SCS for these indications, however, have had follow-up periods of six months to one year, with few studies evaluating longer-term follow-up (13,30). North and colleagues reported the long-term follow-up of SCS in 171 patients that had received permanent SCS implantation, mostly with percutaneous leads (14,16). The majority of patients had a diagnosis of FBSS. At a mean follow-up of seven years, approximately 50% of patients reported 50% or greater pain relief, a result superior to the present series. However, a greater proportion of patients in the present series reported willingness to undergo the procedure again for the same results (74% compared with 60%). The questionnaire relied on the patient’s memory of the chronic pain and on its progress over time, before and after SCS. Memory of pain is often considered a contributing factor—if not the core—to the pathophysiology of chronic pain. The persistence of pain prevents extinction of pain memory as new painful stimuli (i.e., touch in a patient with CRPS related allodynia) further reinforces pain memory (31,32). This memory, in turn, is likely related to pain related disability as patients are likely to avoid activities that evoke a memory of pain. In this sense, the large proportion of patients reporting that the procedure is worthwhile undergoing again is particularly relevant. It indicates that, although patients continue to have pain, SCS provided a degree of alleviation meaningful enough to reduce pain related suffering. Furthermore, we can speculate that, by reducing daily pain, SCS may have reduced pain memory reinforcement from routine environmental stimuli. Few studies have evaluated the long-term outcomes of paddle leads alone or directly compared paddle with percutaneous leads in the treatment of chronic pain located in the back and legs (14,16,33). These studies have indicated so far that paddle leads tend to provide pain control on par with or greater than percutaneous leads. In 2001, Barolat et al. prospectively examined the outcomes of 41 patients with intractable low back pain treated with paddle leads (33). At one-year follow-up, 68.8% of the patients reported fair to excellent relief of pain in the low back and 88.2% reported fair to excellent relief in the legs (33). North et al., in a prospective, controlled trial, studied pain relief in patients with FBSS randomized to percutaneous or paddle leads. With a mean follow-up of 1.9 years, 10 out of 12 patients with paddle electrodes reported a successful outcome versus just 5 out of 10 in the percutaneous group (16). Villavicencio et al. directly compared paddle leads and percutaneous leads with a median follow-up of 34 months (34). Both groups showed a significant decrease in the VAS scores compared with baseline. However, paddle leads were superior to percutaneous in reducing pain in patients followed up longer-term. In the present study, we evaluated the long-term effects of paddle lead SCS systems implanted at a single institution. We evaluated the percent pain improvement at the time of questionnaire evaluation and compared with the overall satisfaction of www.neuromodulationjournal.com

patients, indexed by the willingness to undergo the same procedure again for the same outcome. The efficacy of chronic pain therapies is often measured by the percentage of patients reaching a threshold of 50% or greater in pain relief compared with before the therapy was initiated. In this sample, more than 50% of the patients with CRPS reported greater than 50% pain relief compared with prior to SCS implant, indicating that SCS can be efficacious at a mean follow-up of 4.4 years for patients with lower extremity CRPS. This finding is equivalent to a previous study (35). However, the sustained long-term efficacy of SCS for CRPS in this sample was superior to that observed in a previous long-term cohort (36), in which the benefits were to a large extent lost by the third year of follow-up. This may be due to the characteristics of the sample as well as sampling bias in the present study. However, it also is possible that SCS with paddle leads from the present series provided better and more stable stimulation over time compared with cylindrical leads. Patients with FBSS reported worse NRS-11 outcomes at the time of the questionnaire follow-up compared with CRPS. Approximately 30% of the FBSS patients reported a 50% or greater improvement and 35% reported a 40% or greater improvement. The results in this sample indicate the SCS can provide good long-term pain relief in patients with FBSS and CRPS but shows that a greater proportion of CRPS patients benefit when analgesia is measured in the 0–10 pain intensity scale. There was a loss of efficacy over time with respect to the pain scale for both groups of patients. It is possible—and plausible—that this difference represents a true decline in efficacy of SCS over time. This was more significant in the FBSS group. However, this study was not a prospective analysis and it cannot be affirmed that the effect of follow-up time on outcome was indeed related to a gradual loss of efficacy over time. Other explanations for comparatively less efficacy among those with longer follow-up could be the effect of a learning curve for implantation and programming or maintenance, given that patients implanted more recently were more prone to have greater than 50% pain relief than those implanted several years prior. Furthermore, technology could have played a role. SCS is a rapidly developing technological field and significant advances were made in the recent years with new multichannel paddle leads with various configurations, sizes, and shapes. Likewise, new features became available in pulse generators, with more programming options and flexibility. It is hence possible that those patients implanted in the last two or three years will enjoy better outcomes than patients implanted with more rudimentary systems in prior years. Prospective follow-up will be necessary to evaluate long-term efficacy of these patients and measure any decay in efficacy over time. The present study had several limitations, mostly related to it being a retrospective chart review combined with a recent questionnaire survey to assess present efficacy. Hence, sampling bias cannot be ruled out and may have affected the results positively or negatively. For example, it is possible that patients with better or worse outcomes were more prone to respond to an efficacy survey, influencing the analysis. The number of patients who responded is relatively small compared with the total number of implants performed, contributing to possible interpretation bias. It cannot be ruled out that patients who did not contribute to the data could have skewed the results to a different conclusion. The addition of the questionnaire was important to assess longterm outcomes as it allowed for evaluation of the patients’ willingness to undergo the procedure again, months or years after the implant. The percentage of patients reporting that they would



LONG-TERM OUTCOMES OF SCS undergo SCS implantation again in order to have the same results was higher than the percentage of patients with greater than 50% pain relief (Tables 4 and 5). This was true for both groups, but the difference was particularly pronounced and significant among patients with FBSS. While 29.4% of the FBSS patients reported a >50% reduction in pain at the time of the questionnaire follow-up, 70.6% of the same group of patients reported that they were satisfied with the surgery to the point of undergoing it again for the same outcome. Although not statistically significant, a similar trend was seen in CRPS. This discrepancy between NRS-11 outcomes and overall satisfaction has been reported before in SCS studies (30) as well as in studies of motor cortex stimulation for chronic pain (27). These results call into question the use of an arbitrary efficacy cut off of at least 50% reduction in the NRS-11 (37,38) and raise the question of how much pain “resetting” there is over time. The patient’s willingness to undergo the procedure was sustained across the follow-up periods. It likely represents the long-term efficacy of SCS better than the NRS-11. Maybe it is time to replace the numerical pain scales as the yardsticks for efficacy in neuromodulation for pain for other outcome measures.

CONCLUSIONS Spinal cord stimulation implantation with paddle leads is an effective long-term treatment for a proportion of patients with CRPS and FBSS. The reduction in the pain rating scores for CRPS exceeded scores for FBSS. However, the proportion of patients in each group that would undergo the procedure again for the same outcome was similar. Patients implanted more recently with SCS leads had better reported analgesic effects in the NRS-11 at the time of the questionnaire than those implanted earlier in the series. This could indicate a decay in efficacy over time but also may reflect the inadequacy of numerical pain scales for measuring long-term outcomes in chronic pain. This is corroborated by the significantly better FBSS results observed when outcomes are indexed by the proportion of those who would undergo the procedure again instead of the proportion of patients with greater than 50% pain relief.

Authorship Statements Nathaniel Sears and Dr. Andre Machado prepared the manuscript and designed and conducted the study, including patient recruitment, data collection, and data analysis. Dr. Andre Machado assisted with data analysis and manuscript work. Eric Novak helped with statistical analysis of the data. Drs. Milind Deogaonkar, Michael Stanton-Hicks, Ali R. Rezai, and Jaimie M. Henderson helped with manuscript preparation. Nathaniel Sears and Dr. Andre Machado had complete access to the study data.

How to Cite this Article: Sears N.C., Machado A.G., Nagel S.J., Deogaonkar M., Stanton-Hicks M., Rezai A.R., Henderson J.M. 2011. Long-Term Outcomes of Spinal Cord Stimulation With Paddle Leads in the Treatment of Complex Regional Pain Syndrome and Failed Back Surgery Syndrome. Neuromodulation 2011; 14: 312–318

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COMMENTS This informative paper adds to the evidence for the efficacy of spinal cord stimulation but also illustrates several problems. First are the issues inherent in retrospective series; for example less than half the original cohort was included in the analysis. While obviously unlikely, the others might have been failures. Second, it is refreshing to see a discussion of the shortcomings of simple numerical rating scales in assessing long-term pain and its long-term treatment. More holistic assessments are published increasingly but are still far from universal despite the need for such an approach having been flagged up three decades ago (1,2). The results reported here by Sears and colleagues reprise almost exactly those of Ohnmeiss et al (3) from 15 years ago, who reported "50% or more pain relief" in only 26% at two years but 70% would recommend the therapy to others (and two thirds stopped or reduced their medication). Third, this paper raises the central issue of the influence of memory. The preoperative score on a Visual Analogue Scale (VAS) was taken exclusively from the questionnaire, not from contemporaneous records. Whatever the shortcomings of the VAS in real-time assessments of chronic pain, the substantial literature would suggest that memory for previous pain is significantly corruptible. Thus chronic pain is poorly remembered (4), it distorts the memory of previous pain intensity (5,6), and pain memory is susceptible to many other influences (7). Finally, the increasing evidence for superior performance of paddle over percutaneous electrodes raises the intriguing issue of the fallibility of the latter in selecting for the former.

REFERENCES 1. Long DM, Erickson D, Campbell J and North R. Electrical stimulation of the spinal cord and peripheral nerves for pain control. A 10-year experience. Appl Neurophysiol 1981;44:207–217. 2. Koeze TH, Williams AC de C and Reiman S. Spinal cord stimulation and the relief of chronic pain. J Neurol Neurosurg Psychiat 1987;50:1424–1429. 3. Ohnmeiss DD, Rashbaum RF, and Bogdanffy GM. Prospective outcome evaluation of spinal cord stimulation in patients with intractable leg pain. Spine 1996;21:1344–1351. 4. Erskine A, Morley S and Pearce S. Memory for pain: a review. Pain 1990;41:255–265. 5. Linton SJ and Melin L. The accuracy of remembering chronic pain. Pain 1982;13:281–285. 6. Bryant RA. Memory for pain and affect in chronic pain patients. Pain 1993;54:347–351. 7. Jamison RN, Sbrocco T and Parris WCV. The influence of physical and psychosocial factors on accuracy of memory for pain in chronic pain patients. Pain 1989;37:289–294.

*** This is a good long-term (unfortunately) retrospective study on SCS with paddle leads for the management of pain in patients with CRPS and FBSS. As the authors noted, the percentage of satisfaction with the SCS system is disproportionately greater than the percentage of patients reporting 50% pain relief, particularly among patients with FBSS. Again, this suggests that the VAS may not be the optimal measure to evaluate long-term outcomes in this patient population. The results are, however, impressive at a 4 + year follow-up. Very few treatment modalities, in advanced cases like the ones in this study, can boast similar results. Of course the study showed that, as with every other treatment modality for chronic pain, there is a certain degree of loss of efficacy over time. The results show how grateful patients with chronic pain can be when exposed to a modality that gives them some real benefits over a long period of time. Giancarlo Barolat, M.D. INS Founder & Director at Large Medical Director, Barolat Neuroscience Denver, CO, USA *** The first objective of this paper has been, as stated by the authors themselves, to evaluate the long term results of SCS using paddle leads in two common chronic pain syndromes (CRPS and FBSS). They take the opportunity to raise and discuss several questions such as the problem of how measure the result (pain score, patients satisfaction etc). The main bias of this work is that 40 out of 92 patients who met the inclusion criteria were unwilling to participate or did not respond to the questionnaire. The problem is correctly underlined by the authors as well as the need for prospective studies, but reduces the value of the reported percentage of success. More meaningful is the comparison of the outcome in the two pain syndromes studied (CRPS and FBSS). Mario Meglio, M.D. Catholic University Hospital Rome, Italy

Comments not included in the Early View version of this paper.

Brian A. Simpson, M.D., FRCS University Hospital of Wales, Cardiff, Wales, United Kingdom

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