Clinical Study Received: September 17, 2014 Accepted after revision: March 10, 2015 Published online: April 21, 2015
Stereotact Funct Neurosurg 2015;93:212–218 DOI: 10.1159/000381557
Long-Term Results of Motor Cortex Stimulation in the Treatment of Chronic, Intractable Neuropathic Pain Sang-hyuk Im a Sang-woo Ha a Deok-ryeong Kim c Byung-chul Son a, b
a
Department of Neurosurgery, Seoul St. Mary’s Hospital, College of Medicine, Catholic University of Korea, and Catholic Neuroscience Institute, College of Medicine, Catholic University of Korea, Seoul, and c Department of Neurosurgery, St. Vincent’s Hospital, College of Medicine, Suwon, Republic of Korea
b
Key Words Chronic pain · Motor cortex stimulation · Neuropathic pain · Central poststroke pain
1-way ANOVA). Conclusions: MCS was more effective in the treatment of chronic neuropathic pain of central poststroke pain and peripheral neuropathic pain types than in the treatment of SCI pain in the long-term follow-up. © 2015 S. Karger AG, Basel
© 2015 S. Karger AG, Basel 1011–6125/15/0933–0212$39.50/0 E-Mail [email protected] www.karger.com/sfn
Introduction
The unfavorable outcomes associated with traditional deep brain stimulation (DBS) in chronic pain, especially central pain syndromes [1, 2], marked the advent of a novel and less invasive alternative, epidural motor cortex stimulation (MCS), in the early 1990s [2, 3]. MCS was first proposed by Tsubokawa et al. [1, 4, 5] for the treatment of central poststroke pain. However, in a subsequent series, the efficacy of MCS was witnessed among patients with trigeminal neuropathic pain [6], and MCS has also been reported to be effective in peripheral neuropathic pain [7–13]. Several groups around the world similarly report mixed results with trends favoring pain of peripheral etiology [14–18], with poor response rates of 40–50% in central pain potentially due to damage to the central pain transmission pathways [16]. Byung-chul Son, MD, PhD Department of Neurosurgery, Seoul St. Mary’s Hospital Catholic Neuroscience Institute, College of Medicine, Catholic University of Korea 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Republic of Korea) E-Mail sbc @ catholic.ac.kr
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Abstract Background/Objectives: Although motor cortex stimulation (MCS) has been used for more than 20 years in the treatment of chronic neuropathic pain, there is still a debate about the efficacy of MCS. Methods: To investigate the longterm results and the factors associated with the long-term success of chronic MCS, 21 patients who underwent MCS trial were classified as having central poststroke pain, central pain after spinal cord injury (SCI) and peripheral neuropathic pain, and we investigated the clinical factors associated with long-term success and degree of pain relief. Results: Of the 21 patients, 16 (76.2%) had a successful trial and underwent chronic MCS. In the long-term follow-up (53 ± 39 months), only the diagnosis (central poststroke pain and peripheral neuropathic pain) was associated with long-term success defined as >30% pain relief compared with baseline (p < 0.05, χ2 test). The difference in pain relief was not significant in patients having SCI pain (p > 0.05, 1-way ANOVA). The other variables did not show any significant influence in the long-term success and degree of pain relief (p > 0.05,
Table 1. Demographics of MCS
Patient, Sex/age, Diagnosis No. years 1
M/47
2
M/50
CRPS-2 hemibody extension CP, TBI BG, insula
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
F/55 M/47 M/63 M/32 M/62 M/57 M/66 F/65 M/63 F/59 M/53 F/56 F/56 F/52 M/61 M/75 F/59 M/37 F/32
SCI, cervical CRPS-2 amputated stump SCI, TL CRPS-2 BPA SCI, cervical CPSP BG, insula CPSP brain stem SCI, thoracic CPRS-2 BPI, gunshot CPSP lt. thalamus SCI, thoracic segmental pain CPSP BG ICH CPSP BG ICH CPSP BG ICH CPSP BG ICH CPSP thalamus ICH CPSP thalamus CRPS-2 hemibody extension Cervical syrinx
Duration Location of pain, years of pain 3 3 2 5 39 6 3 3 5 2 37 12 2 5 5 3 2 1.5 4 3 5
lt. arm lt. hemibody rt. arm, leg rt. hemibody lt. arm shoulder lt. hand forearm bil. legs, rt. > lt. rt. arm rt. leg rt. arm lt. arm bi. legs rt. arm, trunk rt. arm rt. trunk lt. leg rt. trunk, leg rt. arm, leg rt. hand lt. arm lt. leg lt. leg, arm rt. arm
NRS preop.
Sensory loss
Motor weakness
Mechanical allodynia
9
ms
ms
yes
7
ms
ms
yes
7 8 9 8 7 8 8 7 9 7 9 9 8 7 7 7 8 9 8
mi ms ms ms mi mi mi ms ms mi ms mi mi mi mi mi ms ms mi
mi no ms ms mi ms ms ms ms no ms ms no ms mi mi ms no no
no yes no no no no no no no no yes no no no no no yes yes no
BG = Basal ganglia; BPA = brachial plexus avulsion; BPI = brachial plexus injury; CP = central pain; CPSP = central poststroke pain; CRPS = complex regional pain syndrome (types 1 and 2); F = females; ICH = intracerebral hematoma; lt = left; M = males; mi = minimal; ms = moderate to severe; rt = right; TBI = traumatic brain injury; TL = thoracolumbar.
Methods Medical records of 21 patients, who underwent insertion of MCS electrodes for the treatment of chronic neuropathic pain, were reviewed. A trial of spinal cord stimulation was not effective in 3 of these. An MCS trial was considered for patients with a minimum numerical rating scale (NRS) score of 7/10. The mean age (±standard deviation) of the patients was 54.7 ± 10.1 years (range 32–75 years), and 8 of them were females. The mean duration of the pain was 7.1 ± 10.5 years (range 1.5–39 years). The patients were classified according to the anatomical location of the origin of the pain: central pain (n = 10), central pain of spinal cord origin [spinal cord injury (SCI) pain; (n = 6)], and peripheral neuropathic pain (n = 5). Table 1 summarizes the demographics of the patients who underwent MCS in our series.
Long-Term Results of MCS
Inclusion Criteria Patients who underwent MCS trials had been refractory to previous medical treatments including analgesics, opioid analgesics, physical therapy and pain blockers. MCS was considered for patients with a minimum NRS score of 7/10. Candidates with psychopathological or substance abuse problems and those with significant unresolved issues of secondary gain and worker’s compensation were excluded from this study. Procedures for MCS and Test Stimulation An anatomical localization of the central sulcus (CS) was performed using a 3-dimensional image-guided navigation system. After marking the course of the CS over the frontal convexity and vertex, an inverted U-shaped scalp incision was made immediately behind the frontal incision for DBS, and an about 5-cm sized craniotomy was performed along the course of the precentral gyrus and the CS. The surgical procedure performed in our series has been reported previously [9, 17, 18]. The localization of the CS was aided using phase reversal of the somatosensory evoked potential and evoked electromyography response of the muscle. In 9 out of 21 MCS trials, somatosensory evoked potential and evoked electromyography responses were not elicited for the somatosensory deficit, and the location of the stimulating electrode for the hand and forearm was determined according to the anatomical imaging
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We reviewed the medical record of patients who received MCS for chronic, central and peripheral neuropathic pain in 21 patients and investigated the long-term results of chronic MCS and factors associated with the success of MCS.
a
b
Fig. 1. a A skull X-ray showing a lead location after motor cortex stimulation. b An axial CT scan showing the placement of the lead over the somatosensory cortex. The black dotted line shows the course of the precentral sulcus, and the white dotted line indicates the location of the CS.
Assessment Two primary outcome variables were examined: first, whether or not the patients were using MCS and, secondly, the patients’ ratings of their worst pain as recorded on the NRS (0–10) [20] in the last follow-up and the percentage of pain relief (PPR) in the NRS. Baseline NRS was obtained before surgery and every 2–3 months after the procedure. Modifications in the drug regimens were not controlled over time in our study. As part of the physical examination, a detailed history of the pain complaint and associated treatments was obtained. Before the MCS trial, the patients gave their informed consent and answered a series of questions based on which of their demographic and clinical history was determined. Areas probed included age, sex, duration of pain, location of predominant pain (arm, leg, arm and leg, trunk, hemibody), diagnosis of pain, severity of pain at the time of MCS (NRS score), degree of sensory loss
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and motor weakness, and presence of mechanical allodynia in painful areas. We defined the long-term MCS treatment as successful when the patient achieved a significant mean reduction in the NRS score of at least 30% compared to the baseline. According to the IMMPACT guidelines, a 30% reduction in pain is considered to be a moderately important change and is equal to ‘much improved’ as measured by the Patient Global Impression of Change (PGIC) [21–23]. Failure was defined as a pain reduction of 30% of relief)
CPSP SCI pain PNeP
8/10 (80) 3/6 (50) 5/5 (100)
35.9±15.514 34±26.633 80.2±58.917
40.7±8.853 16.93±4.561 34.64±7.086
7/8 (87.5) 0/3 (0) 4/5 (80)
with peripheral neuropathic pain could achieve >50% pain relief. There were no significant differences between the two groups (success or failure in trial stimulation) in terms of sex, location of predominant pain, degree of sensory loss and motor weakness, presence of allodynia and diagnosis (p > 0.05, χ2 test). There was no correlation between age, sex, degree of pain, degree of preoperative pain and trial success (p > 0.05, logistic regression). Although the success rate of MCS trial was higher in patients with central poststroke pain and peripheral neuropathic pain than in patients with SCI pain, we could not determine
any correlation or factor related to the trial success in our series. In the long-term follow-up in chronic MCS patients, 7 out of 8 central poststroke pain patients, 4 out of 5 peripheral neuropathic pain patients and none of the 3 SCI patients achieved >30% pain relief compared to the baseline at the last follow-up and were classified as longterm success (table 3). The difference in pain relief (estimated by PPR in the last follow-up) was significant in patients with central poststroke pain and peripheral neuropathic pain (p < 0.05, 1-way ANOVA) but insig-
Long-Term Results of MCS
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Values represent numbers with precentages in parentheses or means ± standard deviation. CPSP = Central poststroke pain; PNeP = peripheral neuropathic pain; PPR = percentage pain relief.
45 40
Mean PPR
35 30 25 20 15 10 5 0
CPSP
SCI pain
PNeP
Fig. 2. Mean plot of PPR between the groups (pain type) in the
long-term. CPSP = Central poststroke pain; PNeP = peripheral neuropathic pain.
nificant in patients with SCI pain (p > 0.05, 1-way ANOVA) (fig. 2). In the long-term follow-up, only the diagnosis (central poststroke pain, SCI, peripheral neuropathic pain) was associated with long-term success defined as >30% pain relief compared with baseline (p < 0.05, χ2 test), and the other variables (sex, location of pain, degree of sensory loss, degree of motor weakness, presence of mechanical allodynia) did not show any significant association (p > 0.05, χ2 test). There was no correlation between age, duration of pain, degree of pain and the long-term success (p > 0.05, binary logistic regression). The other variables did not show any significant influence on the last follow-up PPR (p > 0.05, 1-way ANOVA).
Discussion
In our study, MCS was effective in relieving central pain and chronic neuropathic pain of peripheral origin but not SCI pain. According to a critical review on the efficacy of MCS by Fontaine et al. [24], the conditions that improved the most were trigeminal neuropathic pain, phantom limb pain and SCI pain. In our series, 3 out of 6 SCI pain patients (50%) responded to the initial MCS trial. However, we could achieve a PPR of only 16.9% (±4.56 216
Stereotact Funct Neurosurg 2015;93:212–218 DOI: 10.1159/000381557
standard deviation) in the long-term. This was significantly lower (p < 0.05) than the long-term PPR in patients with central poststroke pain and peripheral neuropathic pain (40.7 ± 8.85%, 34.6 ± 7.08%, respectively), and it seemed to be negligible. The effectiveness of MCS in treating SCI pain was initially reported by Nguyen et al. [14] in 1999 and by other researches [15, 24–26] in the early 2000s. In a review on the efficacy of DBS and MCS therapies for neuropathic pain in SCI patients by Prévinaire et al. [27], MCS was found to have a low level of evidence with an interesting potential with a long-term efficacy of 57% (4 out of 7 patients). In another review by Fontaine et al. [24], the reported number of MCS-treated SCI pain patients was 11, and 3 out of 6 patients (50%) who underwent chronic MCS showed a pain relief of >40–50% when more than a 1-year follow-up was considered. Although MCS has been reported to be effective in selected cases of SCI pain, the reported number of patients successfully treated with MCS seems to be too small to generalize the effectiveness results. Furthermore, due to the limited number of cases, it is difficult to determine the type of SCI pain (complete or incomplete injury, level of injury, etc.) that would be considered suitable for performing the MCS trial. To achieve long-term success in treating neuropathic pain with MCS, Velasco et al. [11] emphasized the importance of correct electrode placement in the cortical representation of pain territory over the motor cortex and the elimination of nonresponders to subacute stimulation from the group receiving long-term stimulation. In addition to 3-dimenional MR-neuronavigational guidance and conventional neurophysiologic study such as phasereversal polarity of N20-P20 components [28], corticocortical potentials induced by the stimulation of different pairs of grid contact [29] and motor and sensory responses to electrical stimulation [14] were recommended to accomplish a correct electrode placement [11]. The poor outcome in our series, especially in patients with SCI pain, might be explained by the technical points emphasized by experienced authors [11] as we only performed conventional neuronavigational guidance and analyzed N20-P20 phase reversal responses. However, we performed a thorough trial stimulation after the implantation of the electrodes, and chronic stimulation was applied the selected patients whose preoperative pain was successfully relieved during the trial stimulation. Indeed, the technical aspects of targeting the motor cortex varied significantly across the centers, and it is still difficult to find any significant correlation between the surgical technique and outcome [24]. Im/Ha/Kim/Son
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50
We defined the long-term MCS treatment as successful when the patient achieved a significant mean reduction in the NRS score of at least 30% compared to the baseline. The reason for considering a 30% mean reduction in the NRS score as the successful outcome was the lack of consistency across studies regarding the methods used to evaluate the outcome, as pointed out by Fontaine et al. [24]. For example, 40% pain relief was considered as a good outcome by some authors, while others required an improvement of >50% [24]. It was suggested that this kind of variability in the outcome measures used in clinical trials hinders the evaluation of the efficacy and effectiveness of treatments and the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) guidelines [21]. According to the IMMPACT guidelines [21], a 30% reduction in pain is considered a moderately important change and is equal to ‘much improved’ as measured by the PGIC [21–23], and it is now commonly used in the subjective evaluation of clinical trials for various kinds of pain treatment [23]. The problem associated with the mere description of ‘>40–50% pain relief’ in the evaluation of the efficacy of a specific treatment has already been reported [15, 30, 31]. For example, Sears et al. [30] documented that 29.4% of the patients with failed back surgery syndrome reported a 50% or greater reduction in pain after spinal cord stimulation with paddle leads at a mean follow-up of 3.8 years. However, 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. This discrepancy between the visual analogue scale (VAS) or NRS-11 outcome and overall satisfaction has been reported in spinal cord stimulation studies as well as in studies of MCS for chronic pain by Nuti et al. [15]. Although MCS has been used for >20 years in the treatment of chronic neuropathic pain, there is still a debate about the true efficacy of MCS, and its application is empirical. Authors of previous case series have reported
satisfactory results in 40–75% of patients [24]. However, there is criticism that the literature on MCS is heterogeneous, and there are still relatively few clinical series in small samples; also, there is a lack of a double-blinded evaluation for the efficacy of MCS [32]. A recent, retrospective analysis of MCS in 14 patients with neuropathic pain by Sach et al. [33] did not show long-term success with a mean follow-up of 55.5 weeks. Only 5 out of 14 patients exhibited a transient improvement of >50%, and only 2 patients maintained a >50% improvement to their last clinic visit. The median time from best to final VAS was only 50 days. Thus, the clinical findings do not unequivocally substantiate the therapeutic utility of cerebral neuromodulation such as MCS in chronic pain management [24, 32]. In the meanwhile, Fontaine et al. [24] reviewed the outcomes of 210 patients who underwent MCS implantation for different conditions in 14 studies published between 1991 and 2006 and reported that, overall, 57.6% of the patients had ‘good’ postoperative pain relief (defined as pain relief ≥40–50% depending on the studies). They suggested that MCS significantly improved the symptoms in patients with severe and medically resistant pain, for whom no other treatment was available, despite the multiple biases [24]. Therefore, it seems necessary to evaluate the practical efficacy of MCS by performing a double-blinded, placebo-controlled randomized study in the near future.
Conclusions
In our retrospective analysis of the long-term results of MCS, only the diagnosis was associated with long-term success defined as >30% pain relief compared with the baseline. MCS was effective in the treatment of chronic neuropathic pain of central poststroke pain and peripheral neuropathic pain types in the long-term follow-up but not in the treatment of SCI pain.
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Long-Term Results of MCS
4 Tsubokawa T, Katayama Y, Yamamoto T, Hirayama T, Koyama S: Chronic motor cortex stimulation for the treatment of central pain. Acta Neurochir Suppl (Wien) 1991; 52: 137– 139. 5 Tsubokawa T, Katayama Y, Yamamoto T, Hirayama T, Koyama S: Treatment of thalamic pain by chronic motor cortex stimulation. Pacing Clin Electrophysiol 1991; 14: 131–134.
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Stereotact Funct Neurosurg 2015;93:212–218 DOI: 10.1159/000381557
Long-Term Results of Motor Cortex Stimulation in the Treatment of Chronic, Intractable Neuropathic Pain Sang-hyuk Im a Sang-woo Ha a Deok-ryeong Kim c Byung-chul Son a, b
a
Department of Neurosurgery, Seoul St. Mary’s Hospital, College of Medicine, Catholic University of Korea, and Catholic Neuroscience Institute, College of Medicine, Catholic University of Korea, Seoul, and c Department of Neurosurgery, St. Vincent’s Hospital, College of Medicine, Suwon, Republic of Korea
b
Key Words Chronic pain · Motor cortex stimulation · Neuropathic pain · Central poststroke pain
1-way ANOVA). Conclusions: MCS was more effective in the treatment of chronic neuropathic pain of central poststroke pain and peripheral neuropathic pain types than in the treatment of SCI pain in the long-term follow-up. © 2015 S. Karger AG, Basel
© 2015 S. Karger AG, Basel 1011–6125/15/0933–0212$39.50/0 E-Mail [email protected] www.karger.com/sfn
Introduction
The unfavorable outcomes associated with traditional deep brain stimulation (DBS) in chronic pain, especially central pain syndromes [1, 2], marked the advent of a novel and less invasive alternative, epidural motor cortex stimulation (MCS), in the early 1990s [2, 3]. MCS was first proposed by Tsubokawa et al. [1, 4, 5] for the treatment of central poststroke pain. However, in a subsequent series, the efficacy of MCS was witnessed among patients with trigeminal neuropathic pain [6], and MCS has also been reported to be effective in peripheral neuropathic pain [7–13]. Several groups around the world similarly report mixed results with trends favoring pain of peripheral etiology [14–18], with poor response rates of 40–50% in central pain potentially due to damage to the central pain transmission pathways [16]. Byung-chul Son, MD, PhD Department of Neurosurgery, Seoul St. Mary’s Hospital Catholic Neuroscience Institute, College of Medicine, Catholic University of Korea 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Republic of Korea) E-Mail sbc @ catholic.ac.kr
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Abstract Background/Objectives: Although motor cortex stimulation (MCS) has been used for more than 20 years in the treatment of chronic neuropathic pain, there is still a debate about the efficacy of MCS. Methods: To investigate the longterm results and the factors associated with the long-term success of chronic MCS, 21 patients who underwent MCS trial were classified as having central poststroke pain, central pain after spinal cord injury (SCI) and peripheral neuropathic pain, and we investigated the clinical factors associated with long-term success and degree of pain relief. Results: Of the 21 patients, 16 (76.2%) had a successful trial and underwent chronic MCS. In the long-term follow-up (53 ± 39 months), only the diagnosis (central poststroke pain and peripheral neuropathic pain) was associated with long-term success defined as >30% pain relief compared with baseline (p < 0.05, χ2 test). The difference in pain relief was not significant in patients having SCI pain (p > 0.05, 1-way ANOVA). The other variables did not show any significant influence in the long-term success and degree of pain relief (p > 0.05,
Table 1. Demographics of MCS
Patient, Sex/age, Diagnosis No. years 1
M/47
2
M/50
CRPS-2 hemibody extension CP, TBI BG, insula
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
F/55 M/47 M/63 M/32 M/62 M/57 M/66 F/65 M/63 F/59 M/53 F/56 F/56 F/52 M/61 M/75 F/59 M/37 F/32
SCI, cervical CRPS-2 amputated stump SCI, TL CRPS-2 BPA SCI, cervical CPSP BG, insula CPSP brain stem SCI, thoracic CPRS-2 BPI, gunshot CPSP lt. thalamus SCI, thoracic segmental pain CPSP BG ICH CPSP BG ICH CPSP BG ICH CPSP BG ICH CPSP thalamus ICH CPSP thalamus CRPS-2 hemibody extension Cervical syrinx
Duration Location of pain, years of pain 3 3 2 5 39 6 3 3 5 2 37 12 2 5 5 3 2 1.5 4 3 5
lt. arm lt. hemibody rt. arm, leg rt. hemibody lt. arm shoulder lt. hand forearm bil. legs, rt. > lt. rt. arm rt. leg rt. arm lt. arm bi. legs rt. arm, trunk rt. arm rt. trunk lt. leg rt. trunk, leg rt. arm, leg rt. hand lt. arm lt. leg lt. leg, arm rt. arm
NRS preop.
Sensory loss
Motor weakness
Mechanical allodynia
9
ms
ms
yes
7
ms
ms
yes
7 8 9 8 7 8 8 7 9 7 9 9 8 7 7 7 8 9 8
mi ms ms ms mi mi mi ms ms mi ms mi mi mi mi mi ms ms mi
mi no ms ms mi ms ms ms ms no ms ms no ms mi mi ms no no
no yes no no no no no no no no yes no no no no no yes yes no
BG = Basal ganglia; BPA = brachial plexus avulsion; BPI = brachial plexus injury; CP = central pain; CPSP = central poststroke pain; CRPS = complex regional pain syndrome (types 1 and 2); F = females; ICH = intracerebral hematoma; lt = left; M = males; mi = minimal; ms = moderate to severe; rt = right; TBI = traumatic brain injury; TL = thoracolumbar.
Methods Medical records of 21 patients, who underwent insertion of MCS electrodes for the treatment of chronic neuropathic pain, were reviewed. A trial of spinal cord stimulation was not effective in 3 of these. An MCS trial was considered for patients with a minimum numerical rating scale (NRS) score of 7/10. The mean age (±standard deviation) of the patients was 54.7 ± 10.1 years (range 32–75 years), and 8 of them were females. The mean duration of the pain was 7.1 ± 10.5 years (range 1.5–39 years). The patients were classified according to the anatomical location of the origin of the pain: central pain (n = 10), central pain of spinal cord origin [spinal cord injury (SCI) pain; (n = 6)], and peripheral neuropathic pain (n = 5). Table 1 summarizes the demographics of the patients who underwent MCS in our series.
Long-Term Results of MCS
Inclusion Criteria Patients who underwent MCS trials had been refractory to previous medical treatments including analgesics, opioid analgesics, physical therapy and pain blockers. MCS was considered for patients with a minimum NRS score of 7/10. Candidates with psychopathological or substance abuse problems and those with significant unresolved issues of secondary gain and worker’s compensation were excluded from this study. Procedures for MCS and Test Stimulation An anatomical localization of the central sulcus (CS) was performed using a 3-dimensional image-guided navigation system. After marking the course of the CS over the frontal convexity and vertex, an inverted U-shaped scalp incision was made immediately behind the frontal incision for DBS, and an about 5-cm sized craniotomy was performed along the course of the precentral gyrus and the CS. The surgical procedure performed in our series has been reported previously [9, 17, 18]. The localization of the CS was aided using phase reversal of the somatosensory evoked potential and evoked electromyography response of the muscle. In 9 out of 21 MCS trials, somatosensory evoked potential and evoked electromyography responses were not elicited for the somatosensory deficit, and the location of the stimulating electrode for the hand and forearm was determined according to the anatomical imaging
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We reviewed the medical record of patients who received MCS for chronic, central and peripheral neuropathic pain in 21 patients and investigated the long-term results of chronic MCS and factors associated with the success of MCS.
a
b
Fig. 1. a A skull X-ray showing a lead location after motor cortex stimulation. b An axial CT scan showing the placement of the lead over the somatosensory cortex. The black dotted line shows the course of the precentral sulcus, and the white dotted line indicates the location of the CS.
Assessment Two primary outcome variables were examined: first, whether or not the patients were using MCS and, secondly, the patients’ ratings of their worst pain as recorded on the NRS (0–10) [20] in the last follow-up and the percentage of pain relief (PPR) in the NRS. Baseline NRS was obtained before surgery and every 2–3 months after the procedure. Modifications in the drug regimens were not controlled over time in our study. As part of the physical examination, a detailed history of the pain complaint and associated treatments was obtained. Before the MCS trial, the patients gave their informed consent and answered a series of questions based on which of their demographic and clinical history was determined. Areas probed included age, sex, duration of pain, location of predominant pain (arm, leg, arm and leg, trunk, hemibody), diagnosis of pain, severity of pain at the time of MCS (NRS score), degree of sensory loss
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and motor weakness, and presence of mechanical allodynia in painful areas. We defined the long-term MCS treatment as successful when the patient achieved a significant mean reduction in the NRS score of at least 30% compared to the baseline. According to the IMMPACT guidelines, a 30% reduction in pain is considered to be a moderately important change and is equal to ‘much improved’ as measured by the Patient Global Impression of Change (PGIC) [21–23]. Failure was defined as a pain reduction of 30% of relief)
CPSP SCI pain PNeP
8/10 (80) 3/6 (50) 5/5 (100)
35.9±15.514 34±26.633 80.2±58.917
40.7±8.853 16.93±4.561 34.64±7.086
7/8 (87.5) 0/3 (0) 4/5 (80)
with peripheral neuropathic pain could achieve >50% pain relief. There were no significant differences between the two groups (success or failure in trial stimulation) in terms of sex, location of predominant pain, degree of sensory loss and motor weakness, presence of allodynia and diagnosis (p > 0.05, χ2 test). There was no correlation between age, sex, degree of pain, degree of preoperative pain and trial success (p > 0.05, logistic regression). Although the success rate of MCS trial was higher in patients with central poststroke pain and peripheral neuropathic pain than in patients with SCI pain, we could not determine
any correlation or factor related to the trial success in our series. In the long-term follow-up in chronic MCS patients, 7 out of 8 central poststroke pain patients, 4 out of 5 peripheral neuropathic pain patients and none of the 3 SCI patients achieved >30% pain relief compared to the baseline at the last follow-up and were classified as longterm success (table 3). The difference in pain relief (estimated by PPR in the last follow-up) was significant in patients with central poststroke pain and peripheral neuropathic pain (p < 0.05, 1-way ANOVA) but insig-
Long-Term Results of MCS
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Values represent numbers with precentages in parentheses or means ± standard deviation. CPSP = Central poststroke pain; PNeP = peripheral neuropathic pain; PPR = percentage pain relief.
45 40
Mean PPR
35 30 25 20 15 10 5 0
CPSP
SCI pain
PNeP
Fig. 2. Mean plot of PPR between the groups (pain type) in the
long-term. CPSP = Central poststroke pain; PNeP = peripheral neuropathic pain.
nificant in patients with SCI pain (p > 0.05, 1-way ANOVA) (fig. 2). In the long-term follow-up, only the diagnosis (central poststroke pain, SCI, peripheral neuropathic pain) was associated with long-term success defined as >30% pain relief compared with baseline (p < 0.05, χ2 test), and the other variables (sex, location of pain, degree of sensory loss, degree of motor weakness, presence of mechanical allodynia) did not show any significant association (p > 0.05, χ2 test). There was no correlation between age, duration of pain, degree of pain and the long-term success (p > 0.05, binary logistic regression). The other variables did not show any significant influence on the last follow-up PPR (p > 0.05, 1-way ANOVA).
Discussion
In our study, MCS was effective in relieving central pain and chronic neuropathic pain of peripheral origin but not SCI pain. According to a critical review on the efficacy of MCS by Fontaine et al. [24], the conditions that improved the most were trigeminal neuropathic pain, phantom limb pain and SCI pain. In our series, 3 out of 6 SCI pain patients (50%) responded to the initial MCS trial. However, we could achieve a PPR of only 16.9% (±4.56 216
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standard deviation) in the long-term. This was significantly lower (p < 0.05) than the long-term PPR in patients with central poststroke pain and peripheral neuropathic pain (40.7 ± 8.85%, 34.6 ± 7.08%, respectively), and it seemed to be negligible. The effectiveness of MCS in treating SCI pain was initially reported by Nguyen et al. [14] in 1999 and by other researches [15, 24–26] in the early 2000s. In a review on the efficacy of DBS and MCS therapies for neuropathic pain in SCI patients by Prévinaire et al. [27], MCS was found to have a low level of evidence with an interesting potential with a long-term efficacy of 57% (4 out of 7 patients). In another review by Fontaine et al. [24], the reported number of MCS-treated SCI pain patients was 11, and 3 out of 6 patients (50%) who underwent chronic MCS showed a pain relief of >40–50% when more than a 1-year follow-up was considered. Although MCS has been reported to be effective in selected cases of SCI pain, the reported number of patients successfully treated with MCS seems to be too small to generalize the effectiveness results. Furthermore, due to the limited number of cases, it is difficult to determine the type of SCI pain (complete or incomplete injury, level of injury, etc.) that would be considered suitable for performing the MCS trial. To achieve long-term success in treating neuropathic pain with MCS, Velasco et al. [11] emphasized the importance of correct electrode placement in the cortical representation of pain territory over the motor cortex and the elimination of nonresponders to subacute stimulation from the group receiving long-term stimulation. In addition to 3-dimenional MR-neuronavigational guidance and conventional neurophysiologic study such as phasereversal polarity of N20-P20 components [28], corticocortical potentials induced by the stimulation of different pairs of grid contact [29] and motor and sensory responses to electrical stimulation [14] were recommended to accomplish a correct electrode placement [11]. The poor outcome in our series, especially in patients with SCI pain, might be explained by the technical points emphasized by experienced authors [11] as we only performed conventional neuronavigational guidance and analyzed N20-P20 phase reversal responses. However, we performed a thorough trial stimulation after the implantation of the electrodes, and chronic stimulation was applied the selected patients whose preoperative pain was successfully relieved during the trial stimulation. Indeed, the technical aspects of targeting the motor cortex varied significantly across the centers, and it is still difficult to find any significant correlation between the surgical technique and outcome [24]. Im/Ha/Kim/Son
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50
We defined the long-term MCS treatment as successful when the patient achieved a significant mean reduction in the NRS score of at least 30% compared to the baseline. The reason for considering a 30% mean reduction in the NRS score as the successful outcome was the lack of consistency across studies regarding the methods used to evaluate the outcome, as pointed out by Fontaine et al. [24]. For example, 40% pain relief was considered as a good outcome by some authors, while others required an improvement of >50% [24]. It was suggested that this kind of variability in the outcome measures used in clinical trials hinders the evaluation of the efficacy and effectiveness of treatments and the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) guidelines [21]. According to the IMMPACT guidelines [21], a 30% reduction in pain is considered a moderately important change and is equal to ‘much improved’ as measured by the PGIC [21–23], and it is now commonly used in the subjective evaluation of clinical trials for various kinds of pain treatment [23]. The problem associated with the mere description of ‘>40–50% pain relief’ in the evaluation of the efficacy of a specific treatment has already been reported [15, 30, 31]. For example, Sears et al. [30] documented that 29.4% of the patients with failed back surgery syndrome reported a 50% or greater reduction in pain after spinal cord stimulation with paddle leads at a mean follow-up of 3.8 years. However, 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. This discrepancy between the visual analogue scale (VAS) or NRS-11 outcome and overall satisfaction has been reported in spinal cord stimulation studies as well as in studies of MCS for chronic pain by Nuti et al. [15]. Although MCS has been used for >20 years in the treatment of chronic neuropathic pain, there is still a debate about the true efficacy of MCS, and its application is empirical. Authors of previous case series have reported
satisfactory results in 40–75% of patients [24]. However, there is criticism that the literature on MCS is heterogeneous, and there are still relatively few clinical series in small samples; also, there is a lack of a double-blinded evaluation for the efficacy of MCS [32]. A recent, retrospective analysis of MCS in 14 patients with neuropathic pain by Sach et al. [33] did not show long-term success with a mean follow-up of 55.5 weeks. Only 5 out of 14 patients exhibited a transient improvement of >50%, and only 2 patients maintained a >50% improvement to their last clinic visit. The median time from best to final VAS was only 50 days. Thus, the clinical findings do not unequivocally substantiate the therapeutic utility of cerebral neuromodulation such as MCS in chronic pain management [24, 32]. In the meanwhile, Fontaine et al. [24] reviewed the outcomes of 210 patients who underwent MCS implantation for different conditions in 14 studies published between 1991 and 2006 and reported that, overall, 57.6% of the patients had ‘good’ postoperative pain relief (defined as pain relief ≥40–50% depending on the studies). They suggested that MCS significantly improved the symptoms in patients with severe and medically resistant pain, for whom no other treatment was available, despite the multiple biases [24]. Therefore, it seems necessary to evaluate the practical efficacy of MCS by performing a double-blinded, placebo-controlled randomized study in the near future.
Conclusions
In our retrospective analysis of the long-term results of MCS, only the diagnosis was associated with long-term success defined as >30% pain relief compared with the baseline. MCS was effective in the treatment of chronic neuropathic pain of central poststroke pain and peripheral neuropathic pain types in the long-term follow-up but not in the treatment of SCI pain.
1 Tsubokawa T, Katayama Y, Yamamoto T, Hirayama T, Koyama S: Chronic motor cortex stimulation in patients with thalamic pain. J Neurosurg 1993;78:393–401. 2 Raslan AM: Deep brain stimulation for chronic pain: can it help? Pain 2006;120:1–2. 3 Plow EB, Pascual-Leone A, Machado A: Brain stimulation in the treatment of chronic neuropathic and non-cancerous pain. J Pain 2012;13:411–424.
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4 Tsubokawa T, Katayama Y, Yamamoto T, Hirayama T, Koyama S: Chronic motor cortex stimulation for the treatment of central pain. Acta Neurochir Suppl (Wien) 1991; 52: 137– 139. 5 Tsubokawa T, Katayama Y, Yamamoto T, Hirayama T, Koyama S: Treatment of thalamic pain by chronic motor cortex stimulation. Pacing Clin Electrophysiol 1991; 14: 131–134.
6 Meyerson BA, Lindblom U, Linderoth B, Lind G, Herregodts P: Motor cortex stimulation as treatment of trigeminal neuropathic pain. Acta Neurochir Suppl (Wien) 1993; 58: 150–153. 7 Nguyen JP, Keravel Y, Feve A, Uchiyama T, Cesaro P, Le Guerinel C, Pollin B: Treatment of deafferentation pain by chronic stimulation of the motor cortex: report of a series of 20 cases. Acta Neurochir Suppl 1997;68:54–60.
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