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The use of spinal cord stimulation in pain management

Practice Points

Krishna Kumar*, Mariam Abbas & Syed Rizvi „„ Chronic pain is a leading cause of disability, reduces the working span of an individual and incurs both

direct and indirect costs to society. „„ Spinal cord stimulation (SCS) is safe, efficacious and cost–effective in the management of neuropathic

pain such as failed back surgery syndrome, complex regional pain syndrome, refractory angina pectoris, diabetic neuropathy, post-herpetic neuralgia and peripheral vascular disease. „„ The effectiveness of SCS is time dependent. Implantation within 2 years of onset of symptoms secures

the best possible outcome. „„ A multidisciplinary approach is needed to ensure timely access to stimulation therapy, foster realistic

patient expectations and ensure ongoing, long-term follow-up. „„ SCS technology has advanced considerably and new developments on the horizon offer improved

pain control, including highly selective steerability, innovative lead design, multiarray placement and rechargeable pulse generators. „„ In the near future, SCS will effectively harness control of axial back pain, leads will become MRI compliant

and distance telemetry will become a reality.

SUMMARY

Pain is a complex behavior process, the anatomy and physiology of which is not completely understood, and is subject to continuous exploration and research. Following on the heels of Melzack and Wall’s gate control theory of pain (1965), Shealey et al., in 1967, were the first to implant stimulation electrodes over the dorsal columns in an attempt to provide relief for patients with chronic, intractable pain. Since then, significant strides in both the technological and therapeutic sides have facilitated the evolution of spinal cord stimulation (SCS) in the management of a variety of pain pathologies. High-quality evidence attests to the efficacy and cost–effectiveness of this modality. In contrast to conventional medical management, SCS offers long-lasting symptom relief, improved quality of life and functional capability, often achieving these goals at a reduced cost. This article illustrates the present status, challenges and future of SCS. Section of Neurosurgery, Department of Surgery, Regina General Hospital, University of Saskatchewan, Regina SK, S4P 0W5, Canada *Author for correspondence: Tel.: +1 306 781 6116; Fax: +1 306 781 6153; [email protected]

10.2217/PMT.11.83 © 2012 Future Medicine Ltd

Pain Manage. (2012) 2(2), 125–134

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ISSN 1758-1869

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management perspective  Kumar, Abbas & Rizvi Chronic pain is a leading cause of disability, afflicting at least 116 million adults in the USA: more than the number affected by heart disease, diabetes and cancer combined [1,2] . Pain is one of the most frequent causes for physician visits, among the most common reason for increased narcotic consumption and a major cause of work disability. Chronic pain affects both physical and mental functioning, quality of life and productivity. It imposes significant financial burden on the individual, their family, employers and the nation as a whole. The annual economic cost of chronic pain is estimated at US$560–630 billion annually in the USA alone [1] . For decades, spinal cord stimulation (SCS) has been successfully applied in the management of a variety of chronic pain syndromes, ranging from failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), refractory angina pectoris, peripheral vascular disease (PVD), diabetic peripheral neuropathy, postherpetic neuralgia, visceral pain and motility disorders of the intestine and bladder. Results are influenced by patient selection, timing of implantation, precise lead placement, underlying pathology being treated and operator experience. The advantages of SCS are its reversibility, minimally invasive technique, low morbidity and high efficacy in appropriately selected cases. Past & present The original premise behind SCS lies in the work of Melzack and Wall, who in 1965 proposed the gate control theory of pain [3] . The use of SCS has burgeoned over the past three decades with the number of implants having almost doubled in the past 10 years. It is estimated that current annual sales of SCS systems total 35,000 units globally, and the number is rising [4,101] . The growth of SCS has been propelled by the development of improved quality percutaneous leads, which are relatively easy to implant, carry a low risk of fracture and displacement and contain multiple contact points. These leads are available for both trial and permanent implantation. Similarly, paddle/surgical leads have improved in quality and number of contact points (ranging from four to 20), which facilitates management of complex pain cases. This procedure carries very low risks of morbidity and mortality. Newer leads and higher powered pulse generators, including rechargeable systems, are able to capture complex pain patterns and have fewer technical failures. Cumulatively, these advances have

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reduced revision rates, and improved outcomes and patient acceptance [5] . Indications In the preceding section we summarized the varied indications for SCS. Due to space limitations, we have restricted our discussion to four major pain syndromes: „„ Failed back surgery syndrome

Low back pain is behind only hypertension and diabetes as the leading reason for frequent physician visits [6] . The incidence of FBSS ranges between 10 and 40% of low back pain cases and is a sequelae to lumbosacral spine surgery undertaken to alleviate radicular pain [7] . It is the most common indication for SCS and constitutes 60–70% of the caseload [8] . While several case series and meta-analyses have reported beneficial outcomes, only two randomized controlled trials (RCTs) have been published [9–11] . The primary outcome in both studies was the proportion of people who achieved 50% or greater radicular pain relief in comparison to other treatment modalities. In the PROCESS Study, 100  patients were recruited (52 patients were assigned to the SCS group and 48 patients to conventional medical management (CMM) with follow-up at 6, 12 and 24 months [9,10] . Compared with the CMM group, the SCS group experienced improved leg and back pain relief, quality of life and functional capacity, as well as greater treatment satisfaction (p ≤ 0.05 for all comparisons). In their RCT, North et al. demonstrated that patients initially randomized to SCS were significantly less likely to cross over than were those randomized to reoperation (five out of 24 patients vs 14 out of 26 patients, p = 0.02) [11] . Patients randomized to SCS had significantly reduced opiate intake compared with those randomized to reoperation (p 10 mmHg from baseline, as early predictors of long-term success [32] . SCS appears to improve perfusion in patients with end-stage nonreconstructable ischemic vascular disease. Kumar et al. found the best results were seen in patients that had severe claudication and pain at rest (but no trophic changes in the foot) [32] . Thus SCS may be considered a treatment modality in a subgroup of PVD patients for symptom relief and ulcer healing.

„„ Refractory angina pectoris

Patient selection The success of SCS hinges on careful patient selection, underlying pathology causing pain, failure of at least 6  months of conventional treatment under multidisciplinary supervision, remedial surgery not being feasible, absence of major psychiatric disorder, a willingness to cooperate, and, if possible, cease inappropriate drug use, lack of secondary gain or litigation, the ability to operate equipment and the ability to give informed consent. Other contraindications are planned or existing pregnancy, significant comorbidity, history of coagulation disorders and other general surgical contraindications in general. Once the patient is deemed a suitable candidate, psychological testing is desirable [8,33] . The issue of chronic pain and psychiatric overlay is complex. Conventional wisdom suggests significant psychological or psychiatric illness as contraindications to implant [8] . However, this may be problematic, as it excludes a large group of patients, some of whom would otherwise stand to benefit [34] . Ultimately, individual patient ana­lysis is a superior means of assessing candidacy for therapy [34] . The neuromodulation team must alert the patient to the fact that SCS will not completely abolish their pain as it does not correct the underlying anatomic or physiological etiology of the pain syndrome [35] . The objective is to reduce pain intensity and thus improve quality of life. Healthcare professionals must therefore foster realistic goals and remain mindful to patients’ level of acceptance and expectation.

In the ESBY study Mannheimer et al. concluded that coronary artery bypass grafting (CABG) and SCS appear to be equivalent methods in terms of symptom relief in this group of patients [17] . Effects on ischemia, morbidity and mortality were considered in the choice of treatment method. Taking all factors into account, they concluded that SCS may be a therapeutic alternative for patients with an increased risk of surgical complications. Ekre et al. also confirmed that SCS as well as CABG offered long-lasting improvement in quality of life [18] . Survival up to 5 years was comparable between the groups. Both methods can be considered as effective treatment options for patients with severe angina, increased surgical risks and those estimated to have no prognostic benefits from CABG. Andrell et al. studied cost–effectiveness of SCS versus CABG and summarized that SCS proved to be a less expensive symptomatic treatment modality of angina pectoris than CABG (p 

The use of spinal cord stimulation in pain management.

SUMMARY Pain is a complex behavior process, the anatomy and physiology of which is not completely understood, and is subject to continuous exploration...
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