Acta Neurochir Suppl (2007) 97(1): 85–89 # Springer-Verlag 2007 Printed in Austria
Dual electrode spinal cord stimulation in chronic leg and back pain N. G. Rainov1;2, W. Demmel1 , and V. Heidecke1;2 1 2
Department of Neurosurgery, Central Clinic Augsburg, Augsburg, Germany Department of Neurosurgery, Martin-Luther-University Halle-Wittenberg, Halle, Germany
Summary Patients with chronic back and leg pain (CBLP) suffer from a disabling spinal condition of multifactorial origin and are often resistant to medical therapy. Spinal cord stimulation (SCS) is a minimally invasive option for treatment of chronic pain in these patients, which involves placement of epidural electrodes close to the midline of the spinal cord. SCS was originally introduced and used for decades with a single electrode. The development of fully implantable dual channel pulse generators connected to dual multicontact electrodes has given pain clinicians a more versatile tool to treat axial low back pain accompanied by radicular neuropathic pain with irregular and asymmetric distribution, a feature which is found in most CBLP patients. It has been hypothesized that using dual electrodes may improve long term outcome for CBLP patients compared with single electrodes. Current evidence however does not lend strong support to this assumption. Given the high cost of treatments for CBLP and of SCS itself, there is an urgent need for highquality evidence for the effectiveness of dual electrode SCS in relieving pain and=or improving function in patients with CBLP. Keywords: Chronic back and leg pain; CBLP; spinal cord stimulation.
Introduction Chronic pain of benign origin is a widespread but underestimated cause of physical and emotional distress to individuals and financial losses to society. One of the modalities available since the 1960s for treatment of chronic pain refractory to medical and physical therapy is spinal cord stimulation (SCS), a minimally invasive surgical method where weak pulses of electricity are applied in a controlled fashion close to the dorsal surface of the spinal cord [9, 24]. The mode of action of SCS is based on the gate-control theory [10]. After initial delay due to insufficiently advanced technology and less suitable indications, the method of SCS has achieved widespread clinical acceptance and recognition the last two decades [1, 2]. The introduction of routine single percutaneous electrode implantation in the early 1990s
made possible the minimally invasive trial stimulation, which is now thought to be an indispensable step in the selection of patients with maximum benefit from SCS [7, 15, 22]. SCS has become a viable therapeutic option for patients suffering from chronic benign pain resistant to any other standard treatment. The sympatholytic effect of SCS is the most obvious of its therapeutic properties [14, 23]. It seems that SCS abolishes continuous and evoked pain (in particular allodynia), while acute nociceptive pain such as wound pain, arthritis or ischaemic heart pain is unaffected. The precise mechanisms of action of SCS are however still insufficiently understood [7]. Patients with chronic back and leg pain (CBLP) suffer from a disabling spinal condition of multifactorial origin and are mostly resistant to medical pain therapy [3, 16, 18]. The term CBLP describes a heterogeneous pool of presumably different pathogenetic mechanisms leading to a common set of symptoms. CBLP patients have long clinical histories and require systematic follow-up because the severity of their condition may vary considerably over time. SCS with a single multipolar electrode has shown efficacy in CBLP patients, however it emerged in some cohorts that the radicular neuropathic component of CBLP may be better influenced by SCS than the axial low back pain (nociceptive pain) component [7, 13, 23]. Many clinicians use SCS to treat predominantly radicular rather than axial low back pain because of the technical difficulty in achieving coverage by paresthesia of axial low back pain with single electrode SCS systems [1]. The development of fully implantable dual channel pulse generators connected to dual multicontact electrodes has allowed pain clinicians to treat axial low back
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pain accompanied by radicular neuropathic pain with irregular and asymmetric distribution, which is found in most CBLP patients. It has been hypothesized that using dual electrodes and increasing the number of contacts may improve outcome for CBLP patients [11, 13]. There is an urgent and largely unmet need for highquality evidence regarding the effectiveness of SCS in relieving pain and improving function. This review summarizes the personal experience of the authors and reviews the available evidence for efficacy of dual electrode SCS systems in CBLP treatment.
Chronic back and leg pain (CBLP) syndrome The so-called failed back surgery syndrome (FBSS) is common throughout the Western world and especially in the United States because of the high numbers of surgical procedures for low back and leg pain [4]. Treatments for this heterogeneous pain condition are varied, mostly unproven by evidence, and often rather costly [18]. CBLP is often used synonymously with FBSS, although unlike FBSS, CBLP may arise without prior surgery. CBLP represents a complex chronic pain syndrome usually defined by its anatomical localization in the lumbar spine and lower extremities. It is of multifactorial genesis and may be the consequence of various lumbar spinal diseases, including arachnoiditis, degenerative disc disease, epidural fibrosis, lumbar disc herniation, osteoporosis, or spinal canal stenosis [16]. Pain patterns in CBLP may include neuropathic components, but the main feature is usually nociceptive pain. Although degenerative or postsurgical disc pathology is thought to be a common cause of CBLP, the relationship between the extent of disc damage and the degree of clinical symptoms is not clear. A strictly mechanical or anatomical explanation for CBLP has proved inadequate [21]. Transition from acute to chronic low back and leg pain is further influenced by psychological and social factors [3, 17].
Rationale for dual electrode spinal cord stimulation for CBLP Despite the scarcity of published evidence, it seems universally accepted that SCS is clinically beneficial in patients with radicular neuropathic pain [1, 7, 14]. Most patients with CBLP however have a mixed pain pattern with neuropathic and nociceptive components and, in addition to the axial low back pain, scattered painful dermatomes over both buttocks and legs. It has been
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generally accepted that a single percutaneous electrode with 4 contacts cannot sufficiently cover pain in the midline and in bilateral dermatomes and therefore paresthesia, which is seen as the best prognostic indicator for pain relief by SCS, cannot be distributed evenly to cover all painful areas in the axial and lateral areas of the body [5, 13]. Dual electrode systems with 4 or 8 contacts each have been developed with the notion that two electrodes can be positioned close to the midline on each side, and that extended contact coverage in the lateral and cephalad-caudad planes will allow for generation of paresthesia in every necessary dermatome [20]. Separate programming of each electrode and of each contact has resulted in an almost unlimited numbers of combinations of the contacts on each electrode and between the pairs, which in turn demonstrated the necessity of some kind of computerized algorithm for selection of the most efficacious combinations [15].
Evidence for efficacy of SCS for CBLP Single electrode SCS An early systematic review of SCS for CBLP found the methodological quality of the then existing literature to be poor [24]. The lack of randomized trials precluded conclusions regarding the effectiveness of SCS relative to other treatments, placebo, or no treatment at all. Turner et al. have recently published an updated review to include data from new studies [25]. The authors concluded that still more methodologically robust studies are needed to establish the effectiveness of SCS, although a few randomized controlled trials (RCT) were carried out in the last decade. Mailis-Gagnon et al. conducted the first systematic Cochrane review of SCS for chronic benign pain [9]. Only one RCT fulfilled the inclusion criteria of the review and the authors concluded that currently there is insufficient evidence to determine the benefits and adverse effects of SCS [13]. In the RCT included in the Cochrane review, North et al. investigated SCS for lumbosacral radicular pain [14]. The authors reported that after 6 months therapy 17% (2=12) of SCS patients requested cross-over to back surgery in comparison to 67% (10=15) of the control group undergone surgery who sought cross-over to SCS. Another more recent RCT from the same group proved that in patients with persistent radicular pain SCS is significantly more effective than reoperation and in the great majority of patients obviates the need for reoperation [12].
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In the virtual absence of RCT evidence, it is worth noting some lower class evidence from other studies. In a large prospective multicenter study, only 70 of 182 CBLP patients who received a permanent SCS implant (single percutaneous electrode or surgical plate electrode) completed the follow-up [2]. One-year follow-up data showed statistically significant improvement in measures of pain and quality of life, but not in medication use or work status. Dario et al. reported a study of SCS in CBLP. Twenty patients responded to medical treatment (medical group), 23 patients did not respond to medical treatment and received permanent SCS implants. Mean follow-up was 42 months. In terms of mean values for leg and back pain and for disability, the medical treatment group improved significantly more than the SCS group [5]. Kumar et al. treated 60 CBLP patients with permanently implanted SCS systems, 44 further cases failed trial SCS and were treated medically. At 5 year follow up, the SCS group improved by 27% and non-SCS group improved by 12% on disability measure, and 15% of the SCS group and none of the nonSCS group returned to work. However patient selection in this study may be biased by the non-random character of groups [8].
Dual electrode SCS Devulder et al. used a device consisting of two multicontact electrodes connected to a radiofrequency-coupled system (Mattrix+, Medronic, Inc., Minneapolis, MN, USA) to treat two patients with CBLP. The authors stated that dual channel stimulation helped steering better stimulation paresthesias. They claimed that better distribution of stimulation-induced paresthesias was achieved in the back and the legs, however the case reports allowed for descriptive evidence only [6]. North et al. published a prospective controlled clinical trial comparing single and dual percutaneous electrodes in the treatment of axial low back pain. The authors hypothesized that placing two parallel electrodes would improve outcome. Twenty patients who passed screening with single percutaneous electrodes received permanent dual electrodes at the same vertebral levels. Patients acted as their own controls in evaluating the effects of single versus dual electrodes. The authors found that single electrodes provided significant advantages (p < 0.01) in pain coverage by paresthesias compared with the same electrodes implanted as a pair. Amplitude requirements were significantly lower for the single electrode than for either dual electrode. A total of 53% of
patients with dual electrodes nevertheless met the criteria for long-term clinical success. The authors concluded that there are some disadvantages for dual electrodes in treating axial low back pain [13]. Rutten et al. examined the effects of dual electrodes (8 contacts each) in patients with postsurgical CBLP. Thirty-four patients received permanent implants. Dual electrode systems were implanted in 23 patients and single electrode systems in 11 patients. Follow-up was 24 months. The authors reported paresthetic coverage of painful areas in all patients, which remained constant over the whole follow-up period. All measurement scales confirmed reduction of pain and improved quality of life as a result of SCS, irrespective of the number of electrodes. No further comparisons were however reported between the dual electrode and single electrode groups [20].
Personal experience with dual electrode SCS systems The authors have used dual electrode=dual channel SCS systems in their clinical practice since 1997. Various hardware configurations and systems (ANS, Inc.; Medtronic, Inc.) were used in combination with percutaneous dual electrodes with 4 or 8 contacts each. Initially, a radiofrequency-coupled dual channel system (Mattrix+, Medtronic, Inc.) was used with standard 4-contact electrodes (Pisces Quad+, Medtronic, Inc.) to treat patients with CBLP who had bilateral leg pain combined with axial low back pain. We found that dual electrode stimulation using the Single StimTM technology (same amplitude and pulse width on both electrodes with at least one cathode and one anode on either electrode) significantly increased the ability of the SCS system to cover painful areas with precisely placed stimulation-induced paresthesias. Placement of the electrodes was parallel to each other on both sides of the physiological (not anatomical) midline and covering the same vertebral segments in the cephalad-caudad direction. With this system we were able to achieve better paresthesia coverage in the back and at the same time in various dermatomes in both legs, however the radiofrequency system with external pulse generator was inconvenient for the patients and a few became allergic to the material of the antenna. With the advent of fully implantable dual channel pulse generators (Synergy+, Medtronic, Inc.) we started using those instead of the radiofrequency systems for the same indications. Additional programming capability of
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the software (DualStimTM mode with different amplitudes and pulse widths on both electrodes) allowed for further increase in the possible contact combinations and for the usage of dual electrodes placed close to the midline with their contacts covering two spinal segments instead of one. This we found helpful when there were thoracic and sacral dermatomes affected at the same time. In general, our clinical practice has shown that the cathodes () on each electrode should be localized ipsilateral or median to the painful sides, proximal to the most proximal pain dermatomes, and flanked by two anodes (guarded cathode). After more than 20 CBLP patients implanted with dual electrode systems, our experience confirms that dual electrodes actually shorten the duration of the test implantation procedure because their greater paresthetic coverage is more forgiving and only calls for approximate intraoperative placement. This in turn considerably shortens intraoperative test times and reduces the need of X-ray fluorography in the operating theatre, compared to single electrodes. Further advantages of the dual electrode system are significantly better ability to cover irregular pain patterns and capacity of almost unlimited programming combinations of channels and contacts. On the other hand, dual electrodes have higher energy requirements and reduce battery life of the implanted pulse generator. We have not seen increased rates of hardware failure with dual electrode systems compared with single electrode ones. Although a prospective comparative analysis has not been carried out yet, we did investigate a cohort of 42 CBLP patients with long term single electrode SCS (6 to 74 months duration). Twelve surgical corrections of the hardware were carried out in a total of 10 patients over the assessment period. In 8 patients there was a single corrective procedure, in 2 additional cases there were two surgically corrected hardware failures each. The most often encountered type of hardware failure was electrode breakage or disruption of insulation (in Pisces Quad+ percutaneous electrodes only) leading to short-circuiting and dysfunction (n ¼ 8). Second in frequency were failures due to insulation leakage at the pulse generator plug connection site (n ¼ 2). In one further case, extension cable breakage caused dysfunction of the system, and another dysfunction was caused by distal extension cable disconnection [19]. There is no evidence from our clinical practice and in the published literature to suggest that dual electrode SCS results in a significantly increased rate of complications or side effects [13, 20]. However reported complication rates for single and dual electrode systems vary
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widely across studies, and differences in patients. SCS equipment, clinical settings, complication assessment and reporting, length of follow-up and other factors may strongly influence the reported numbers of complications [23–25]. According to Turner et al., the median percentages of complications from single electrode SCS were as follows: superficial infection 4% (range 0–12%), hardware failures 6.5% (range 0–40%), pulse generator revision (additional operation) for reasons other than battery change 21.5% (range 0–81%), pulse generator removal 6% (range 0–47%). Sample sizes in the reviewed studies were however small and lengths of follow-up and reported complication rates were highly variable [25]. Conclusions At the present time there is little high-class evidence that SCS is effective for chronic benign pain, although clinical practice confirms its efficacy and safety. Most published trials are retrospective case collections and use single electrode SCS for radicular neuropathic pain. Only a few published trials deal with dual electrode SCS for axial low back pain and CBLP. There is a clear need for large scale RCT to evaluate SCS in comparison to other standard therapies for CBLP. There is also a need to evaluate different hardware configurations for SCS in homogeneous patient groups and with unified criteria. Based on our own experience and on a comprehensive review of the current literature, we conclude that evidence is inadequate to make definitive statements about the difference in efficacy of dual electrode systems compared to single electrode SCS. However it should be noted that dual electrode SCS has considerable practical advantages in CBLP cases and that hardware complication rates seem to be comparable to those of single electrode SCS. References 1. Barolat G (2000) Spinal cord stimulation for chronic pain management. Arch Med Res 31: 258–262 2. Burchiel KJ, Anderson VC, Brown FD, Fessler RG, Friedman WA, Pelofsky S, Weiner RL, Oakley J, Shatin D (1996) Prospective, multicenter study of spinal cord stimulation for relief of chronic back and extremity pain. Spine 21: 2786–2794 3. Burton AK, Tillotson KM, Main CJ, Hollis S (1995) Psychosocial predictors of outcome in acute and subchronic low back trouble. Spine 20: 722–728 4. Cherkin DC, Deyo RA, Loeser JD, Bush T, Waddell G (1994) An international comparison of back surgery rates. Spine 19: 1201–1206
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Correspondence: Nikolai G. Rainov, Department of Neurosurgery, Central Clinic Augsburg, Stenglinstr. 2, D-86156 Augsburg, Germany. e-mail:
[email protected]
