Efficacy in Treating CRPS

The Neuromodulation Therapy Access Coalition found excellent evidence supporting the use of spinal cord stimulation (SCS) to treat CRPS ( ). The authors identified 3 randomized controlled trials (RCTs), 6 long-term follow-up studies, 6 short-term follow-up studies, and 10 case studies.

In the first RCT of SCS for CRPS, all patients met IASP CRPS Type I criteria ( ). All patients had their pain for more than 6 months and all had failed conventional treatment, consisting of medical management and physical therapy (PT). Patients were randomized to receive SCS plus PT (n = 36) or PT alone (n = 18). Only those patients who had a successful trial underwent an SCS implant. Intention-to-treat analysis demonstrated a significant reduction in pain for patients in the SCS group when compared to those in the PT group ( P < .001): 39% had an improved global perceived effect (GPE) compared to 6% in the control group. The quality of life (QOL) improved 11% overall in the 24 patients who received a permanent SCS system. In a 2-year follow-up the authors found the SCS/PT group maintained their significant GPE improvement compared with the PT-only group ( P ≤ .001 Neither group showed any clinically important improvement of functional status. The authors concluded that SCS provides long-term pain reduction and improved QOL in patients suffering from CRPS. A 5-year follow-up found no difference between pain scores, but the GPE results were significantly better in the SCS plus PT group ( P ≤ .02 ( ), and 95% of all SCS-treated patients stated they would repeat the treatment for the same result. undertook an interesting RCT in which the analgesic effects of carbamazepine were compared with sustained-release (SR) morphine in patients with CRPS. All patients were pretreated with SCS, and 43 had their SCS systems switched off before receiving their medication or placebo. Compared with placebo, those patients who received carbamazepine had a delayed onset of pain, but there was no effect in patients receiving morphine SR. Two patients receiving carbamazepine and one patient receiving morphine SR preferred to continue their medication. However, 35 patients chose to return to SCS. While most of the published studies regarding SCS for CRPS studies are retrospective in nature, a review of 10 studies by found an overall success rate of 82% (148/180) for patients with CRPS Type I and 79% (23/29) for CRPS Type II.

Recent case reports and studies reflect the extraordinary advances in technology and clinical applications that are currently being realized with SCS. A 65-year-old woman with CRPS of the left upper extremity, whose response after the initial success of SCS over a 2-year period became attenuated, with a numerical rating score (NRS) for pain that climbed to 8, underwent burst stimulation which reestablished the previous efficacy and resulted in the NRS returning to 2 ( ). Burst stimulation is a unique method of SCS consisting of delivering spikes of energy, and is discussed in the next section.

Along similar lines, completed an RCT that compared tonic SCS and high-frequency and burst stimulation in patients with CRPS. Five SCS modes (40, 500, 1200 Hz, burst, and placebo) were compared in a blinded manner after a successful trial and implantation using 40 Hz stimulation. After a 3-month follow-up assessment (T1), the remaining modes were tested in a cross-over fashion over 10 weeks. Each patient then chose the stimulation they preferred. This was assessed at the end of 3 months (T2). The answers from this trial will provide important information regarding the most appropriate type of stimulation that can provide optimal pain control and perhaps also improvement of function for patients with CRPS.

The combination of SCS and motor cortex stimulation (MCS) is one example of combining a single neuromodulation modality with another to regain a loss of clinical efficacy. Lopez et al. described the gradual loss of pain relief to SCS over 2 years in a patient with severe CRPS Type II after brachial plexus injury ( ). Using MCS in a cycling fashion with SCS, they were able to regain efficacy by 2 years, with pain reduction and improvement in QOL noted at follow-up. Similar improvements have been achieved by using the combination of SCS and peripheral nerve stimulation (PNS). Sanders et al. described the outcomes of a retrospective case series of 199 patients with failed back surgery syndrome (FBSS) or CRPS who were treated with SCS at an academic medical center over a 10-year period. The oral morphine equivalents and NRS scores decreased significantly from preimplantation levels at 6 months and 1 year ( P = <.02 and P = <.01, respectively) ( ).

Early implementation of SCS was emphasized by Prager and Chang to facilitate interdisciplinary management of CRPS. The externalized SCS lead remained in place for 4 weeks, but if a patient still required SCS for pain relief and promotion of functional restoration, a permanent SCS system would be implanted. This emphasizes the fact that not only may early use of SCS be an important adjunct to exercise therapy, but an externalized SCS (extended trial) may be both therapeutic and cost effective. A second set of 16 patients received a permanent implant if they failed to improve after 4 weeks of comprehensive therapy (exercise therapy with or without a behavioral component). Two patients of this latter group had their SCS system explanted because they were essentially pain free and no longer used their systems at 5 and 18 months after implant ( ). A recent paper by Goff et al. exemplifies the early application of SCS in a patient who developed spontaneous CRPS and was completely refractory to medical management, and whose rehabilitation dramatically responded after SCS, with unassisted ambulation, functional improvement, pain relief, and improved QOL ( ) in the paper by , these investigators also exempified early application of spinal cord stimulation for CRPS.

Singular advances in our understanding of the neural framework and possible sites within which SCS may achieve its clinical response on pain have taken place during the past 10 years. The traditional/conventional model of tonic (paresthesia-based) stimulation has finally been challenged by new waveforms and paradigms. With software and technological advances, tolerance as a byproduct of tonic SCS may be relegated to history. Without exploring the field of SCS mechanisms, which is more than adequately dealt with elsewhere (see Guan et al.), one recent study has suggested a mechanistic basis for clinical phenomena that respond to SCS. Dystonia, a frequent and frustrating phenomenon that occurs in CRPS, is difficult to treat and can prevent the adequate return of function. A case report by in which a 31-year-old female with severe refractory dystonia responded successfully to a combination of SCS, multidisciplinary care, and behavioral measures is an example. The authors make a strong argument that dystonia, in this case, is a consequence of multilevel (peripheral and central) pathological modifications in the nervous system brought about by CRPS ( ). As pointed out by , a number of CRPS pathophysiologies respond not only because of their effects on central autonomic and spinal inhibitory systems, but also because of the beneficial effects on the microvasculature via calcitonin gene-related peptide and nitric oxide, and on small-diameter nerve endings through the expression of transient receptor potential V1. In addition, the α-1a receptor, which is an integral component of CRPS pathophysiology (expression on nerve endings, blood vessels, and sclerocytes in the periphery), responds to SCS with the amelioration of this activity ( ).

In an animal model of a unilateral spinal nerve injury designed to look at the manner in which SCS modulates the descending antinociceptive system (DAS), found that while serotonergic and noradrenergic pathways in the DAS may be important, the dorsal raphe nucleus and, to a lesser extent, the locus coeruleus may be primarily responsible. They also noted that SCS does not potentiate the synthetic enzymes of 5HT and norepinephrine in the neuropathic spinal cord. The authors used methysergide, a 5HT ₁ and 5HT ₂ antagonist, and idazoxan, an α-2 adrenoceptor antagonist, both of which antagonized the antinociceptive effect of SCS ( ). A disturbance in the locus coeruleus of hemilateral pain processing, due to the disruption of pain-control mechanisms because of a sensitized nociceptive network in CRPS, might be a likely target for SCS. The spread of increased sensitivity and allodynia from an affected limb to the ipsilateral forehead as a reflection of disrupted pain mechanisms was commented on by .

Benefits and Risks of Spinal Cord Stimulation

Any pain treatment plan must balance benefit against risk. Consequently, the classic chronic pain treatment continuum begins with less invasive and costly options and progresses if they fail ( ). In this context, SCS has been relegated to the status of last-resort therapy. The potential benefits of SCS are listed in Table 48.1 .

The Neuromodulation Access Coalition, in drawing up its practice parameters for SCS, classified its reported benefits as useful information, in part because there are no generally accepted standards for measuring many of the benefits of SCS and only two RCTs exist for consideration. Pain relief is the most obvious benefit of SCS and the intended goal of the therapy; the criterion of 50% pain reduction has been used as a definition of SCS success for decades ( ), but lacks standardization because pain itself fluctuates and the perception of pain is highly subjective and idiosyncratic. The commonly used visual analog scale (VAS) creates an individual framework for the temporal assessment of pain—a reduction in score representing success. Yet patients reporting relatively modest reductions in VAS may have disproportionately greater gains in function or decreases in pain medication. Given the intractable nature of the chronic pain syndromes treated with SCS, patients will view any reduction of their pain as a benefit, particularly if it allows functional improvement and less reliance on medications. A number of recent studies clearly demonstrate that SCS, by modifying or reversing pathological processes known to impact upon the patient by CRPS and the return toward normal function (neuromodulation), can engender a significant reduction in pain ( ).

In its review, the Neuromodulation Therapy Access Coalition ( ) found studies that demonstrated increased ability to undertake activities of daily living or improved QOL for patients treated with SCS. Seven years after SCS implantation, a majority of patients in one retrospective consecutive series of 205 patients had maintained improvements in activities of daily living ( ). To date, however, no standard measure of patient satisfaction with treatment exists. Among 153 patients followed for 4 years after implantation in Belgium, 68% rated their results as excellent to good ( ).

Depression invariably presents in patients with chronic pain, and is known to improve with successful treatment of CRPS by SCS ( ). In a prospective study, observed a trend toward improvement ( P < .06) in the Beck Depression Inventory in CRPS patients at an average of 7.9 months follow-up, with the scores dropping from 13.18 preimplantation to 5.18 postimplantation. A more recent paper has substantiated the benefit of SCS on depression ( ).

The risks of SCS relate to surgery, to the implanted devices, and to stimulation itself. Infection ranks as the primary surgery-related risk. In a survey of 31 studies, perioperative infections were reported in 5% (0%–12%) of cases ( ). Significant influences on the incidence of surgical infections (SIs) are preoperative skin preparation, perioperative antibiotics, double gloving, and postoperative occlusive dressing. These are described in the recently published “An international survey to understand infection control practices for spinal cord stimulation” ( ) and in the Neurostimulation Appropriateness Consensus Committee’s most recent publication ( ).

Chlorhexidine–alcohol is superior to povidine–iodine in reducing SIs (9.5% vs. 16.1%). The Centers for Disease Control issued guidelines for infection prevention in 1999, recommending that patients who are to undergo surgery wash their skin the day before and the morning of their surgery with a chlorhexidine–alcohol solution. There is no evidence that continuing perioperative antibiotics beyond 24 h has any further antimicrobial effect or impact on the incidence of SIs. There is a significant difference in infection rates between the use of an occlusive or a nonocclusive dressing (2.6% vs. 7.1%) ( ). Decolonization of methicillin-resistant staph aureus (MRSA) and MRSA (sensitive) carriers with mupirocin nasal ointment and chlorhexidine washings can reduce SIs in other implantable surgeries ( ).

Device-related complications used to present the greatest challenge to successful implementation of SCS as a therapy, occurring in as many as 50% of cases in a review of 13 studies published in 1995 ( ). Electrode migration posed the biggest difficulty, accounting for 24% of the device-related complications and frequently resulting in the loss of topical paresthesias. Surgical revision or replacement of a system component was necessary in 12 of 219 (5%) patients who were tracked by . As a result of technical improvements, improved materials, multiple channels, built-in accelerometers and systems that are safe with magnetic resonance imagery (MRI), device-related complications requiring surgical revision are decreasing.

Patients occasionally report that stimulation has become uncomfortable or increases the underlying pain. Stimulation-related complications vary widely, and few studies have examined the precise reasons for failure. Five (3%) patients in the Burchiel study ( ) reported discomfort or loss of pain relief. Posture-induced changes in paresthesias were cited. Implantable pulse generators (IPGs) that have inbuilt accelerometers markedly reduce the nuisance of posture-induced changes in paresthesias. In a study by of 126 patients with 2-year follow-up, 26 (20%) had discontinued stimulation or requested removal of the system. He found three reasons for failure: disease progression in 12 patients (55%), appropriate paresthesia with loss of pain relief in 9 patients (41%), and painful hardware at the implant site in 1 patient. Four patients (3%) enjoyed such successful pain resolution that they no longer required SCS ( ).

On balance, the risks of SCS must be judged against the risks of other possible therapies or the option of doing nothing. In this calculus, patients should be told of the deleterious or adverse effects of opioid medications as a competitive therapy to SCS, including mental dependence, sedation, nausea, constipation, weight gain, and loss of libido ( ). The most frequent and serious complications of SCS are not related to stimulation itself or its long-term use. Thus a preimplantation screening trial, combined with careful, immediate, postimplant management, offers the potential to resolve any adverse effects early in the course of treatment. The adverse effects of pain medications, however, persist for the duration of their use.

Every patient contemplating SCS should be engaged in a detailed discussion of the risks and benefits that might be experienced. A well-informed patient becomes an active partner in the treatment plan. Patients should be aware that they have responsibilities, and their participation in preoperative, postoperative, and maintenance therapy will influence the outcome.

Patient Selection and the Screening Trial

There is virtual unanimity among pain specialists regarding the importance of appropriate selection criteria for patients who are candidates for SCS. Treatment algorithms rely on a stepwise approach that begins with therapies that are less invasive, are likely to have few adverse effects, and can be reversed. SCS is a minimally invasive procedure, and should therefore follow appropriate noninvasive therapies.

Most patients with chronic pain who are suitable for SCS will have a long medical history. Reviewing this is a crucial first step in the patient selection process. Distinguishing the diagnosis of CRPS I from CRPS II is also pertinent to the selection process, as this can affect the choice of appropriate modalities for pain care.

An MRI scan should be taken if there is any suspected spinal stenosis, disc herniation, or other spinal anomaly that might impact upon the procedural risk of SCS ( ). An MRI scan may also be used to gain information regarding the depth of the posterior epidural space and position of the spinal cord, the dimensions of which can vary among individuals. These metrics can influence the selection of electrode array, both percutaneous and paddle. Severe thoracic or cervical spinal stenosis may in some circumstances preclude the use of SCS.

Guidelines list patient inclusion and exclusion criteria ( ) and the relative and absolute contraindications for SCS ( ). These criteria should be carefully considered before undertaking SCS as a therapy, as inappropriate patient selection accounts for some of the disparate outcomes of SCS reported in the literature. The valuable and continuing work performed by the International Neuromodulation Society and its chapters, the IASP, and other groups has contributed to a more precise understanding of the patient selection criteria associated with successful neurostimulation (see Table 48.2 ).

Where controversies exist, such as the necessity for psychological testing of patients who are to undergo neuromodulation procedures, clinical judgment should come to the fore. Medicare and most health insurance agencies require psychological screening before implanting a permanent SCS system; without such a step, the SCS procedure is withheld ( ). Information from a well and professionally performed psychological assessment can expose psychological factors that should be treated, guide specific treatments that can help resolve psychological risk factors, facilitate patient selection, provide clues as to the patient’s possible response to SCS, and possibly improve outcomes. Doleys and Olson recommend looking for an accumulation of risk factors or an overall level of distress when conducting psychological testing. Severe pain by itself can cause psychological disturbances, and behavioral therapy can help patients control pain ( ). Such assessments may actually uncover psychological factors that are readily treatable and therefore enhance the chance for success. Screening trials can thus provide valid patient information not just on the efficacy of SCS, but on the patient’s and the physician’s assessment of the effects of SCS treatment on symptoms and the psyche.

Patient questionnaires can embrace pain history, its intensity (VAS), current medication, other therapies, and disability status ( ). Information provided by the patient should be carefully reviewed against records from the referring physician to provide corroborative evidence; these records also supply results from earlier diagnostic studies. The physical examination, including a complete neurologic assessment, should document the patient’s current pain symptoms. In certain cases a complete diagnostic workup may be necessary to rule out reversible, or identify treatable, causes of pain.

By approximating the conditions of long-term therapy, a screening trial for SCS seems to offer the best chance of assessing efficacy and tolerance. The trial should answer two fundamental questions. Does the patient’s pain respond to SCS therapy? Is the patient able to tolerate the treatment? Furthermore, in the context of interdisciplinary care, is the patient able to benefit from functional restoration (see Fig. 48.4 )? Both physician and patient should agree on the goals of the trial and on which measures are used to assess these goals. In general, patients should proceed to implantation if pain is reduced by 50% or more and, more importantly, if significant improvements of function occur in the affected extremity ( ). Other aspects of a successful trial with traditional/conventional SCS (newer paradigms such as burst SCS and KHz frequency SCS are paresthesia free) are a tolerance of paresthesias, which should be concordant with the area of pain ( ), and stable or reduced medication intake.

There are numerous screening protocols, but there is no unanimity concerning the duration of such protocols. Probably the duration of any protocol should be determined by the presentation and context of the patient’s medical and behavioral status. For example, there are those patients in whom circumstances may dictate that a trial of a few days to 1 week will be adequate to assess their response, while others, because of their personality and/or psychological makeup, may need 2 or more weeks to determine whether they are likely to be satisfactory responders and or will be suitable candidates for long-term SCS treatment. Screening for surgically placed paddle leads may vary from 24 h to 2 days as an inpatient procedure, which when successful is immediately followed by “internalization” or implantation of the IPG. A paper by describes a 5-day trial with a paddle lead in 22 patients that was followed by successful permanent implant in 16 patients. At 23 months all patients continued to have satisfactory control of their pain.

Sometimes governments or third-party payers dictate the length of the screening trial. Mention should also be made here of clinical reports of “on-table” screening trials that have proceeded to implantation and successful long-term outcomes ( ).

The merits of doing a screening trial, removing the screening electrode on its completion, and, if successful, doing the implant of a new electrode during the permanent implant procedure versus a two-stage procedure will often be determined by protocols of the particular surgical facility or of the implanting physician. In the case of a two-stage procedure, the trial electrode is permanently implanted, connected to an externally tunneled extension. If the trial is successful, the temporary and nonsterile extension is removed and the permanent electrode is either connected directly or indirectly to an IPG by way of a tunneled extension.

Most screening trials use percutaneous electrodes placed under fluoroscopy, because access to many levels of the spine is possible through a single epidural needle puncture ( ). A surgical plate/paddle, implanted by either neurosurgeons or orthopedic surgeons, is used in the minority of patients in whom the epidural space is otherwise inaccessible. Electrodes should be placed under local anesthesia so patients can describe paresthesia coverage to the area of their pain (with paresthesia-based SCS and not paresthesia-free SCS), react to changes in stimulation, and report any unusual intraoperative events.

Because patient cooperation is fundamental to the success of SCS, the evaluation process should include a discussion of the patient’s and family’s expectations of therapy. Patients should know in advance that complete pain relief is rare and 50% or greater relief should be considered optimal. They should also realize that regular follow-up appointments are necessary, and that some patients may experience postimplantation complications.

The infection rate of trial stimulation was evaluated in 84 patients during a trial period of 1–3 weeks ( ). Interestingly, the results reflected two implanters, one more experienced and the other less experienced. Experience is important to outcomes. The infection rates were 1.8% for the experienced planter versus 13% for the inexperienced implanter, respectively. During the trial, one infection (1.2%) resulted in removal of the lead. Three infections (3.6%) were successfully treated with antibiotics. The authors attributed the low incidence of infections to an adherence to strict asepsis, the use of a hydrocolloid dressing, prophylactic antibiotics, implanter experience, and patient education. No implants were explanted due to infection.

There will also be patients with CRPS who will not need an implant at all because a period of prolonged and temporary neurostimulation, say for 6–8 weeks, may facilitate their rehabilitation sufficiently to achieve a remission and relief of CRPS pain.

Patient Management

Because many patients with CRPS have suffered unrelenting pain for years, their approach to a procedure like SCS may be fraught with skepticism, fear, or unrealistic expectations. These considerations need to be addressed in the light of the patient’s history and by continuing patient education. Patients must be made aware that SCS, in the great preponderance of patients, reduces but does not eliminate pain. They should also know that SCS can be used with other pain-relieving modalities, as there is no indication of any cross-tolerance ( ).

If nondissolvable sutures have been used, they should be removed between 7 and 14 days after implant. All patients who have received an SCS system should be involved in functional rehabilitation as soon as their wounds have healed, generally about 4 weeks following surgery. The level or degree of rehabilitation will be determined by the severity of CRPS. It is also important that therapists be made aware of some initial limitations of physical modalities and exercises that are imposed by the recent implant.

Follow-up appointments are mandatory, particularly in the first 3 months, during which many adjustments to the programming of the SCS device may be necessary, and at least 6 and 12 months after implantation, or at any time there are problems or programming issues that arise in conjunction with the neurostimulator system.

Patients whose systems were implanted elsewhere should be considered new patients, so that the physician can become familiar with the patient’s pain condition and response. Every patient should know how to contact the implanting physician and device manufacturer in case of an emergency.

Cost Effectiveness

In the past decade the cost effectiveness of SCS when compared with conventional medical management (CMM) for CRPS has been studied and reported widely in several countries. In Kemler and Furnee calculated lifetime costs for 54 CRPS patients receiving either SCS or SCS and PT in the Netherlands. SCS plus PT costs were 25% less than for PT alone, €171,153 versus €229,624 respectively, over the lifetime of the patients.

One study from the United Kingdom ( ) and one study from the Netherlands ( ) used analytic cost–utility models over a 15-year projected timeframe. The study by Simpson found an incremental cost-effectiveness ratio (ICER) ²

2 The incremental cost-effectiveness ratio ( ICER ) is a statistic used in cost-effectiveness analysis to summarize the cost-effectiveness of a health care intervention. It is defined by the difference in cost between two possible interventions, divided by the difference in their effect. Taken from the internet: https://www.google.com/#q=define+icer& ∗.

3 The QALY is a generic measure of disease burden including both the quality and the quantity of life lived. It is used in economic evaluation to assess the value for money of medical interventions. One QALY equates to 1 year in perfect health. Taken from https://www.google.com/#q=define+qaly& ∗.

4 WTP is the maximum amount an individual, government, or third-party payer is willing to sacrifice to procure a good or avoid something undesirable. The price of any goods transaction will thus be any point between a buyer’s WTP and a seller’s willingness to accept. Taken from https://www.google.com/#q=willingness+to+pay& ∗.

In , Kumar and Rizvi in Canada, found an ICER of $11,216/QALY and an 89% probability that SCS is cost effective at the WTP of $50,000. Despite these figures, the overall cost of SCS plus CMM ($172,577) was higher than the cost of CMM alone ($148,799) ( ).

calculated actual healthcare costs for complications in 160 patients receiving SCS treatment. The mean cost of SCS implantation was $23,205 per patient. The mean annual maintenance cost of an uncomplicated case was $3609, compared to $7092 to rectify a complication over a 10-year period. The mean cost to explant a system was $1739. Preventing or reducing complications would certainly reduce the cost of SCS.

A recent study examined healthcare resource utilization costs associated with delays between a chronic pain diagnosis and implementation of SCS therapy in 762 patients ( ). Odds of being in the high versus low medical expenditure group increased by 33% for every 1-year delay in implementing SCS therapy. Prior opioid use in SCS patients also has an effect on long-term costs. For patients in the high opioid prescriptions group, the odds of being in the high versus low expenditure group increased by 39%. Similarly, the odds of being in the high versus low expenditure group increased by 44% for office visits, and by 55% for hospitalizations. The authors concluded that considering SCS earlier in the chronic pain care continuum could decrease treatment costs, improve outcomes, and reduce clinic visits, hospitalizations, and opioid use.

Efficacy in Treating CRPS

The Neuromodulation Therapy Access Coalition found excellent evidence supporting the use of spinal cord stimulation (SCS) to treat CRPS ( ). The authors identified 3 randomized controlled trials (RCTs), 6 long-term follow-up studies, 6 short-term follow-up studies, and 10 case studies.

In the first RCT of SCS for CRPS, all patients met IASP CRPS Type I criteria ( ). All patients had their pain for more than 6 months and all had failed conventional treatment, consisting of medical management and physical therapy (PT). Patients were randomized to receive SCS plus PT (n = 36) or PT alone (n = 18). Only those patients who had a successful trial underwent an SCS implant. Intention-to-treat analysis demonstrated a significant reduction in pain for patients in the SCS group when compared to those in the PT group ( P < .001): 39% had an improved global perceived effect (GPE) compared to 6% in the control group. The quality of life (QOL) improved 11% overall in the 24 patients who received a permanent SCS system. In a 2-year follow-up the authors found the SCS/PT group maintained their significant GPE improvement compared with the PT-only group ( P ≤ .001 Neither group showed any clinically important improvement of functional status. The authors concluded that SCS provides long-term pain reduction and improved QOL in patients suffering from CRPS. A 5-year follow-up found no difference between pain scores, but the GPE results were significantly better in the SCS plus PT group ( P ≤ .02 ( ), and 95% of all SCS-treated patients stated they would repeat the treatment for the same result. undertook an interesting RCT in which the analgesic effects of carbamazepine were compared with sustained-release (SR) morphine in patients with CRPS. All patients were pretreated with SCS, and 43 had their SCS systems switched off before receiving their medication or placebo. Compared with placebo, those patients who received carbamazepine had a delayed onset of pain, but there was no effect in patients receiving morphine SR. Two patients receiving carbamazepine and one patient receiving morphine SR preferred to continue their medication. However, 35 patients chose to return to SCS. While most of the published studies regarding SCS for CRPS studies are retrospective in nature, a review of 10 studies by found an overall success rate of 82% (148/180) for patients with CRPS Type I and 79% (23/29) for CRPS Type II.

Recent case reports and studies reflect the extraordinary advances in technology and clinical applications that are currently being realized with SCS. A 65-year-old woman with CRPS of the left upper extremity, whose response after the initial success of SCS over a 2-year period became attenuated, with a numerical rating score (NRS) for pain that climbed to 8, underwent burst stimulation which reestablished the previous efficacy and resulted in the NRS returning to 2 ( ). Burst stimulation is a unique method of SCS consisting of delivering spikes of energy, and is discussed in the next section.

Along similar lines, completed an RCT that compared tonic SCS and high-frequency and burst stimulation in patients with CRPS. Five SCS modes (40, 500, 1200 Hz, burst, and placebo) were compared in a blinded manner after a successful trial and implantation using 40 Hz stimulation. After a 3-month follow-up assessment (T1), the remaining modes were tested in a cross-over fashion over 10 weeks. Each patient then chose the stimulation they preferred. This was assessed at the end of 3 months (T2). The answers from this trial will provide important information regarding the most appropriate type of stimulation that can provide optimal pain control and perhaps also improvement of function for patients with CRPS.

The combination of SCS and motor cortex stimulation (MCS) is one example of combining a single neuromodulation modality with another to regain a loss of clinical efficacy. Lopez et al. described the gradual loss of pain relief to SCS over 2 years in a patient with severe CRPS Type II after brachial plexus injury ( ). Using MCS in a cycling fashion with SCS, they were able to regain efficacy by 2 years, with pain reduction and improvement in QOL noted at follow-up. Similar improvements have been achieved by using the combination of SCS and peripheral nerve stimulation (PNS). Sanders et al. described the outcomes of a retrospective case series of 199 patients with failed back surgery syndrome (FBSS) or CRPS who were treated with SCS at an academic medical center over a 10-year period. The oral morphine equivalents and NRS scores decreased significantly from preimplantation levels at 6 months and 1 year ( P = <.02 and P = <.01, respectively) ( ).

Early implementation of SCS was emphasized by Prager and Chang to facilitate interdisciplinary management of CRPS. The externalized SCS lead remained in place for 4 weeks, but if a patient still required SCS for pain relief and promotion of functional restoration, a permanent SCS system would be implanted. This emphasizes the fact that not only may early use of SCS be an important adjunct to exercise therapy, but an externalized SCS (extended trial) may be both therapeutic and cost effective. A second set of 16 patients received a permanent implant if they failed to improve after 4 weeks of comprehensive therapy (exercise therapy with or without a behavioral component). Two patients of this latter group had their SCS system explanted because they were essentially pain free and no longer used their systems at 5 and 18 months after implant ( ). A recent paper by Goff et al. exemplifies the early application of SCS in a patient who developed spontaneous CRPS and was completely refractory to medical management, and whose rehabilitation dramatically responded after SCS, with unassisted ambulation, functional improvement, pain relief, and improved QOL ( ) in the paper by , these investigators also exempified early application of spinal cord stimulation for CRPS.

Singular advances in our understanding of the neural framework and possible sites within which SCS may achieve its clinical response on pain have taken place during the past 10 years. The traditional/conventional model of tonic (paresthesia-based) stimulation has finally been challenged by new waveforms and paradigms. With software and technological advances, tolerance as a byproduct of tonic SCS may be relegated to history. Without exploring the field of SCS mechanisms, which is more than adequately dealt with elsewhere (see Guan et al.), one recent study has suggested a mechanistic basis for clinical phenomena that respond to SCS. Dystonia, a frequent and frustrating phenomenon that occurs in CRPS, is difficult to treat and can prevent the adequate return of function. A case report by in which a 31-year-old female with severe refractory dystonia responded successfully to a combination of SCS, multidisciplinary care, and behavioral measures is an example. The authors make a strong argument that dystonia, in this case, is a consequence of multilevel (peripheral and central) pathological modifications in the nervous system brought about by CRPS ( ). As pointed out by , a number of CRPS pathophysiologies respond not only because of their effects on central autonomic and spinal inhibitory systems, but also because of the beneficial effects on the microvasculature via calcitonin gene-related peptide and nitric oxide, and on small-diameter nerve endings through the expression of transient receptor potential V1. In addition, the α-1a receptor, which is an integral component of CRPS pathophysiology (expression on nerve endings, blood vessels, and sclerocytes in the periphery), responds to SCS with the amelioration of this activity ( ).

In an animal model of a unilateral spinal nerve injury designed to look at the manner in which SCS modulates the descending antinociceptive system (DAS), found that while serotonergic and noradrenergic pathways in the DAS may be important, the dorsal raphe nucleus and, to a lesser extent, the locus coeruleus may be primarily responsible. They also noted that SCS does not potentiate the synthetic enzymes of 5HT and norepinephrine in the neuropathic spinal cord. The authors used methysergide, a 5HT ₁ and 5HT ₂ antagonist, and idazoxan, an α-2 adrenoceptor antagonist, both of which antagonized the antinociceptive effect of SCS ( ). A disturbance in the locus coeruleus of hemilateral pain processing, due to the disruption of pain-control mechanisms because of a sensitized nociceptive network in CRPS, might be a likely target for SCS. The spread of increased sensitivity and allodynia from an affected limb to the ipsilateral forehead as a reflection of disrupted pain mechanisms was commented on by .

Benefits and Risks of Spinal Cord Stimulation

Any pain treatment plan must balance benefit against risk. Consequently, the classic chronic pain treatment continuum begins with less invasive and costly options and progresses if they fail ( ). In this context, SCS has been relegated to the status of last-resort therapy. The potential benefits of SCS are listed in Table 48.1 .

Table 48.1

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