Percutaneous Spinal Cord Stimulation for Chronic Pain

Percutaneous spinal cord stimulation has a clinical benefit in selected patients with chronic neuropathic pain related to failed back surgery syndrome and complex regional pain syndrome. Patients with other peripheral neuropathic pain syndromes may also respond favorably. The cause of the chronic pain must be established to rule out remediable causes. Drug abuse or aberrant drug-related behaviors should be assessed before proceeding. A psychological evaluation identifies patients who may not benefit. Risk factors for infection should be corrected where possible. This safe, reversible treatment should be considered early for patients with intractable peripheral neuropathic pain.

Key points

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Percutaneous spinal cord stimulation (pSCS) is an effective treatment of patients with complex regional pain syndrome or failed back surgery syndrome refractory to conventional medical management.
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Although frequently used for other indications, the data supporting the use of pSCS remain limited for other types of chronic, peripheral, neuropathic pain.
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Selecting patients who may benefit from pSCS is based on the cause of the pain, rigorous psychological evaluation, and medical comorbidities, including opioid dependence and risk of perioperative infection.

Introduction

Percutaneous spinal cord stimulation (pSCS) or dorsal column stimulation is a safe, minimally invasive, reversible treatment of patients with chronic neuropathic pain refractory to conventional medical management (CMM). Electrical stimulation of the dorsal columns was shown to inhibit pain transmission more than 40 years ago by Shealy. Since then, multiple studies have demonstrated superior clinical benefit to other treatments in properly selected patients. It is cost-effective over the long-term and complements other therapies in multimodal treatment. However, these devices continue to be used as a treatment of last resort despite known advantages.

Introduction

Indications

Spinal cord stimulation (SCS) is currently approved in the United States by the Food and Drug Administration for the treatment of chronic pain of the back or limbs. In Europe, SCS for refractory angina pectoris (RAP) is frequently used in some centers but it is not considered a routine treatment in all countries. Several studies, including eight randomized controlled trials (RCTs) have tested SCS for RAP. However, the studies were small and several had methodological flaws. The Refractory Angina Spinal Cord stimulation and usuAL care (RASCAL), a pilot RCT on the effectiveness and cost-effectiveness of SCS for refractory angina, was recently completed at three centers in the United Kingdom. SCS has also been extensively studied in the treatment of inoperable chronic critical leg ischemia. A 2013 Cochrane review concluded that SCS may be better than conservative treatment alone in both pain relief and amputation risk reduction in select patients. However, the surgical risk of implanting an SCS, coupled with the costs of the implant in patients with expected short life spans (10%–30% mortality in 6 months), continues to favor amputation.

Over the last several years, several international expert panels have convened to establish the indications for pSCS based on a review of the available literature. Though a clear consensus has not been reached on many of the indications, the recommendations for SCS are relatively consistent with some notable exceptions. Almost universally, the panels agree that patients with failed back surgery syndrome (FBSS) or complex regional pain syndrome (CRPS) benefit from pSCS. Those with peripheral neuropathic pain due to illness or injury, including plexopathies, also seem to benefit. However, to date, this has not been evaluated with a properly powered study. Patients with central pain syndromes originating in the brain or spinal cord, including root avulsion, seem to benefit less with SCS except when the posterior columns are only minimally injured in the case of spinal cord injury. A synthesis of these recommendations is compiled into Table 1 . SCS has only been studied in a rigorous RCT on three occasions (see later discussion).

Table 1

Summary of selected recommendations on the indications for SCS

Diagnosis	European Federation of Neurologic Societies (EFNS) ^a(2007)	Practice Parameters for the Use of Spinal Cord Stimulation in the Treatment of Chronic Neuropathic Pain (2007)	British Pain Society (2009)	Austral-Asian Neurostimulation Working Group (2011)	Canadian Pain Society Special Interest Group on Neuropathic Pain (2012)
FBSS	Level B (probably effective) class II evidence: RCT that does not meet class I criteria	A: Well-designed RCTs; well-designed clinical studies; weighing risk vs potential benefit and expert consensus reveals a high likelihood of a favorable outcome	Neuropathic leg pain: good indication (likely to respond); axial pain: intermediate indication	Good indication (likely to respond)	Evidence quality: good; certainty: moderate; strength of recommendation; B
Failed Neck Surgery Syndrome	No evidence	N/A	Neuropathic arm pain: good indication (likely to respond)	Neuropathic arm pain: good indication (likely to respond)	N/A
CRPS I	Level B (probably effective), class II evidence: RCT that does not meet class I criteria	A: Well-designed RCTs; well-designed clinical studies; weighing risk vs potential benefit and expert consensus reveals a high likelihood of a favorable outcome	Good indication (likely to respond)	Intermediate indication (may respond)	Evidence quality: good; certainty: moderate; strength of recommendation; B
CRPS II	D, IV positive case series	A: Well-designed RCTs; well-designed clinical studies; weighing risk vs potential benefit and expert consensus reveals a high likelihood of a favorable outcome	Good indication (likely to respond)	Intermediate indication (may respond)	Evidence quality: good; certainty: moderate; strength of recommendation; B
Peripheral Nerve Injury	D, IV positive case series	Consider as other peripheral neuropathic pain	Good indication (likely to respond)	Intermediate indication (may respond)	Evidence quality: fair; certainty: moderate; strength of recommendation: grade C
Other Peripheral Neuropathy	D, IV positive case series	B: Well-designed clinical studies; case reports; weighing risk vs potential benefit and expert consensus reveals a good likelihood of a favorable outcome	Intermediate indication (may respond)	Intermediate indication (may respond)	Evidence quality: poor; certainty: low; strength of recommendation: grade I
Postherpetic Neuralgia	D, IV positive case series	B: Well-designed clinical studies; case reports; weighing risk vs potential benefit and expert consensus reveals a good likelihood of a favorable outcome B	Intermediate indication (may respond)	Not indicated (rarely respond)	Evidence quality: poor; certainty: low; strength of recommendation grade I
Intercostal Neuralgia	No evidence	Consider as other peripheral neuropathic pain	Intermediate indication (may respond)	Intermediate indication (may respond)	Evidence quality: poor; certainty: low; strength of recommendation: grade I
Brachial Plexus Injury	D, Class IV: positive case series	B: Well-designed clinical studies; case reports; weighing risk vs potential benefit and expert consensus reveals a good likelihood of a favorable outcome B	Brachial plexopathy: traumatic (partial); postirradiation: good indication (likely to respond)	N/A	Evidence quality: fair; certainty: moderate; strength of recommendation: grade C
Brachial Plexus Root Avulsion	D, IV negative case series for avulsion	N/A	Root avulsion: unresponsive	Avulsion: not indicated (rarely respond)	N/A
Amputation Pain	D, IV positive case series	B: Well-designed clinical studies; case reports; weighing risk vs potential benefit and expert consensus reveals a good likelihood of a favorable outcome	Intermediate indication (may respond)	Not indicated (rarely respond)	N/A
Central Pain of Spinal Cord origin	D, IV better success with incomplete lesion	B: Well-designed clinical studies; case reports; weighing risk vs potential benefit and expert consensus reveals a good likelihood of a favorable outcome	Intermediate indication (may respond) unless complete loss of posterior column function (poor response); complete spinal cord transection: unresponsive	Not indicated (rarely respond)	N/A
Central Pain of Brain Origin	D, IV negative case series	N/A	Poor indication (rarely respond)	Not indicated (rarely respond)	N/A
Refractory Angina Pectoris Pain	N/A	N/A	Good indication (likely to respond)	Good indication (likely to respond)	N/A
Peripheral Vascular Disease Pain	N/A	N/A	Good indication (likely to respond)	Intermediate indication (may respond)	N/A
Other	Facial pain: insufficient evidence; diabetic peripheral neuropathy: D, IV positive case series		Perineal or anorectal: poor indication (rarely respond); nonischemic nociceptive pain: unresponsive	Neuropathic pain secondary to peripheral nerve lesion: good indication (likely to respond); nociceptive axial back pain: not indicated (rarely respond)	N/A

Data from Refs.

a Class IV studies in the EFNS guidelines included uncontrolled studies, case series, case reports, or expert opinion. A Level D grade was not published in the original guidelines by the EFNS. In some instances, the diagnoses were inconsistent from one guideline to the next, requiring minor modifications in organizing the recommendations.

FBSS

In the United States, the most common indication for an SCS implant is FBSS. Patients with FBSS who did not achieve the goals of the spinal operation, specifically the anticipated pain relief, or who developed recurrent pain following surgery and have limited response to nonsurgical therapies may be candidates for SCS. In the United States in 2002, more than 1 million spinal procedures were performed and it estimated that the rate of back surgery is nearly 40% higher in the United States than in any other country. It is difficult to measure the frequency of FBSS in the general population but it is estimated that between 0.02% and 2% of lumbar spinal surgeries have unsuccessful outcomes. Furthermore, the health-related quality of life and economic costs often exceed other chronic pain and medical conditions. Even if only a small portion of these patients were candidates for pSCS, the potential for improvement in health and cost savings could be considerable.

In addition to multiple long-term outcome studies and retrospective case series that support the use of SCS, there were two published RCTs in the last decade that specifically addressed the use of SCS for FBSS. In 2005, North and colleagues published the results from a RCT comparing reoperation to SCS for FBSS in an effort to move SCS ahead of reoperation in the treatment algorithm. Only subjects with radicular pain that exceeded or was equal to the axial back pain were included in the study. Subjects who experienced at least 50% pain relief with the trial were offered a permanent implant with a paddle electrode. Although the sample size was relatively small (24 in the SCS treatment arm and 26 in the reoperation arm), there were statistically significant differences between the two groups. At a mean follow-up of 2.9 years (+/− 1.1 SD), 47% of subjects randomized to SCS versus 12% of subjects randomized to reoperation achieved pain relief of at least 50% ( P <.01). Narcotic use remained stable or decreased in subjects randomized to SCS compared with reoperation subjects ( P <.025) and 54% of subjects who initially underwent reoperation crossed over compared with only 21% in the SCS group ( P = .02). In this study, improvements in work status and activities of daily living were not improved following treatment.

In 2007, Kumar and colleagues reported the outcomes from a RCT that compared SCS to CMM for subjects with FBSS. The Prospective Randomised Controlled Multicentre Trial of the Effectiveness of Spinal Cord Stimulation (PROCESS) tested the hypothesis that SCS plus CMM (SCS+CMM) is more effective than CMM alone. Permanent lead type, percutaneous or paddle, was at the discretion of the surgeon. Unlike the study by North and colleagues, this was not a single institutional experience. The primary endpoint of the study was to calculate the proportion of subjects with at least 50% relief of leg pain at 6 months. One hundred subjects were initially included in the randomization. At 6-month follow-up, 44 subjects in the CMM-alone group were available for follow-up and 50 in the SCS+CMM group. After the 6 months, 28 (64%) of the subjects in the CMM group crossed over and received an implantable system. Twenty-four (48%) of the subjects in the SCS+CMM achieved the primary endpoint versus only four subjects (9%) in the CMM-alone group. Secondary outcomes at 6 months showed statistical significance favoring SCS+CMM versus CMM alone, including improvements in health-related quality of life, superior function, and greater treatment satisfaction. Nine subjects were able to wean off opioids in the SCS+CMM versus only one subject in the CMM group. There was no difference in return to work status between the two groups.

CRPS

Although less common in the general population, especially compared with FBSS, the treatment of CRPS with SCS is well established and includes one RCT. The trial compared SCS plus physical therapy (PT; SCS+PT) in 36 subjects with PT alone in 18 subjects. At 6 months, pain was reduced by 3.6 cm (in those who received the implant) on the visual analogue scale in the SCS+PT group and it was increased by 0.2 cm ( P <.001) in the PT-alone group. The functional status and health-related quality of life did not improve in the SCS+PT group at the 6 month mark. Follow-up was available for subjects implanted in the initial study at 24 months and at 5 years. Visual analogue scores, which were significantly better in the SCS+PT group at 2 years (3.0 cm–0 cm; P <.001), showed no difference at 5 years (1.7 cm SCS+PT vs 1.0 cm; P = .25). However, 95% reported they would undergo the treatment again for the same result.

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