The most common use for SCS in the United States is failed back surgery syndrome (FBSS); whereas in Europe, peripheral ischemia is the predominant indication. With respect to clinical outcomes, it makes sense to subdivide the outcomes based on diagnosis. In a review of the available SCS literature, most evidence falls within the level IV (limited) or level V (indeterminate) categories due to the invasiveness of the modality and inability to provide blind treatment. Recognition also must be given to the time frame within which a study was performed due to rapidly evolving SCS technology. Basic science knowledge, implantation techniques, lead placement locations, contact array designs, and programming capabilities have changed dramatically since the time of the first implants. These improvements have led to decreased morbidity and much greater probability of obtaining adequate parasthesia coverage with subsequent improved outcomes.19 Thus, even a level II review study such as the one by Turner20 with FBSS patients from 1966 to 1994 reported less positive outcomes than Barolat's level IV FBSS study21 in 2001. This difference in efficacy may represent the effect of improving technology.
7.6.1 SCS Outcomes: Failed Back Surgery Syndrome (FBSS)
There has been one recent prospective, randomized study. North et al.22 selected fifty patients as candidates for repeat laminectomy. All patients had undergone previous surgery and were excluded from randomization if they presented with severe spinal canal stenosis, extremely large disc fragments, a major neurological deficit such as foot drop, or radiographic evidence of gross instability. In addition, patients were excluded for untreated dependency on narcotic analgesics or benzodiazepines, major psychiatric comorbidity, the presence of any significant or disabling chronic pain problem, or a chief complaint of low back pain exceeding lower extremity pain. Crossover between groups was permitted. The six-month follow-up report included twenty-seven patients. At this point, they became eligible for crossover. Of the fifteen patients who had undergone reoperation, 67% (ten patients) crossed over to SCS. Of the twelve patients who had undergone SCS, 17% (two patients) opted for crossover to reoperation. Additionally, of the nineteen patients who reached their six-month follow-up assessment after reoperation, 42% (eight patients) opted for spinal cord stimulation outside the study. For 90% of the patients, long-term (three-year follow-up) evaluation has shown that spinal cord stimulation continues to be more effective than reoperation, with significantly better outcomes by standard measures and significantly lower rates of crossover to the alternate procedure. Additionally, patients randomized to reoperation used significantly more opioids than those randomized to spinal cord stimulation. Other measures assessing activities of daily living and work status did not differ significantly. The preliminary results have been published in abstract format, but the definitive study has yet to be published.22
Two recent, prospective case series have been done. The first, by Barolat23 examined the outcomes of patients with intractable low-back pain treated with epidural SCS utilizing paddle electrodes and a radio-frequency (RF) stimulator. In four centers, forty-four patients were implanted and followed with the visual analog scale (VAS), the Oswestry Disability Questionnaire, the Sickness Impact Profile (SIP), and a patient satisfaction rating scale. All patients had back and leg pain, and all had at least one previous back surgery, with most (83%) having two or more back surgeries and 51% having had a spinal fusion. Data were collected at baseline, at six months, twelve months, and two years.
All patients showed a reported mean decrease in their ten-point VAS scores compared to baseline. The majority of patients reported fair to excellent pain relief in both the low back and legs. At six months, 91.6% of the patients reported fair to excellent relief in the legs and 82.7% of the patients reported fair to excellent relief in the low back. At one year, 88.2% of the patients reported fair to excellent relief in the legs and 68.8% of the patients reported fair to excellent relief in the low back. Significant improvement in function and quality of life was found at both the six-month and one-year follow-ups using the Oswestry and SIP, respectively. The majority of patients reported that the procedure was worthwhile (92% at six months, 88% at one year). The authors concluded that SCS proved beneficial at one year for the treatment of patients with chronic low back and leg pain.
The second multicenter prospective case series was published by Burchiel in 1996.24 The study included 182 patients with a permanent system after a percutaneous trial. Patient evaluation of pain and functional levels was performed before and three, six, and twelve months after implantation. Complications, medication usage, and work status also were monitored. A one-year follow-up evaluation was available for seventy patients. All pain and quality-of-life measures showed statistically significant improvement, whereas medication usage and work status did not significantly improve, during the treatment year. Complications requiring surgical interventions were experienced by 17% (twelve of seventy) of the patients.
There have been two systematic review articles on neurostimulation. Turner et al.25 completed a meta analysis from the articles related to the treatment of FBSS by SCS, from 1966 to 1994. They reviewed thirty-nine studies that met the inclusion criteria. The mean follow-up period was sixteen months with a range of one to forty-five months. Pain relief exceeding 50% was experienced by 59% of patients with a range of 15 to 100%. Complications occurred in 42% of patients, with 30% of patients experiencing one or more stimulator-related complications. However, all the studies were case-control investigations. Based on this review, the authors concluded that there was insufficient evidence from the literature for drawing conclusions about the effectiveness of spinal cord stimulation relative to no treatment or other treatments, or about the effects of spinal cord stimulation on patient work status, functional disability, and medication use.
The second analysis, by North and Wetzel,26 consisted of a review of case-control studies and two prospective control studies. They concluded that if a patient reports a reduction in pain of at least 50% during a trial, as determined by standard rating methods, and demonstrates improved or stable analgesic requirements and activity levels, significant benefit may be realized from a permanent implant. The authors conclude that the bulk of the literature appears to support a role for spinal cord stimulation (in neuropathic pain syndromes), but also caution that the quality of the existing literature is marginal — largely case series.
7.6.2 SCS Outcomes: Complex Regional Pain Syndrome (CRPS)
Research of high quality regarding SCS and CRPS is limited, but existing data are overwhelmingly positive in terms of pain reduction, quality of life, analgesic usage, and function. Kemler and co-workers27 published a prospective, randomized, comparative trial to compare SCS versus conservative therapy for CRPS. Patients with a six-month history of CRPS of the upper extremities were randomized to undergo trial SCS (and implant if successful) + physiotherapy vs. physiotherapy alone. In this study, thirty-six patients were assigned to receive a standardized physical therapy program together with spinal cord stimulation, whereas eighteen patients were assigned to receive therapy alone. In twenty-four of the thirty-six patients randomized to spinal cord stimulation along with physical therapy, the trial was successful and permanent implantation was performed. At a six-month follow-up assessment, the patients in the spinal cord stimulation group had a significantly greater reduction in pain; and a significantly higher percentage was graded as much improved for the global perceived effect. However, there were no clinically significant improvements in functional status. The authors concluded that in the short term, spinal cord stimulation reduces pain and improves the quality of life for patients with CRPS involving the upper extremities.
Several important case series have been published on the use of neurostimulation in the treatment of CRPS. Calvillo et al.28 reported a series of thirty-six patients with advanced stages of complex regional pain syndrome (at least two years' duration) who had undergone successful SCS trial (>50% reduction in pain). They were treated with either spinal cord stimulation or peripheral nerve stimulation, and in some cases with both modalities. Thirty-six months after implantation, the reported pain measured on Visual Analog Scales was an average of 53% better; this change was statistically significant. Analgesic consumption decreased in the majority of patients, and 41% of patients had returned to work on modified duty. The authors concluded that in late stages of complex regional pain syndrome, neurostimulation (with SCS or PNS) is a reasonable option when alternative therapies have failed.
Another case series reported by Oakley and Weiner29 is remarkable in that it utilized a sophisticated battery of outcomes tools to evaluate treatment response in complex regional pain syndromes (CRPS) using spinal cord stimulation. The study followed nineteen patients and analyzed the results from the McGill Pain Rating Index, the Sickness Impact Profile, Oswestry Disability Profile, Beck Depression Inventory, and Visual Analog Scale. Nineteen patients were reported as a subgroup enrolled at two centers participating in a multicenter study of the efficacy/outcomes of spinal cord stimulation. Specific pre-implant and postimplant tests to measure outcome were administered. Statistically significant improvement in the Sickness Impact Profile physical and psychosocial subscales was documented. The McGill Pain Rating Index words chosen and sensory subscale also improved significantly, as did Visual Analog Scale (VAS) scores. The Beck Depression Inventory trended toward significant improvement. All patients received at least partial relief and benefit from their device, with 30% receiving full relief. Eighty percent (80%) of the patients obtained at least 50% pain relief through the use of their stimulators. The average percent of pain relief was 61%. The authors concluded that patients with CRPS benefit significantly from the use of spinal cord stimulation, based on average follow-up of 7.9 months.
A literature review by Stanton-Hicks of SCS for CRPS consisted of seven case series. These studies ranged in size from six to twenty-four patients. Results were noted as "good to excellent" in greater than 72% of patients over a time period of eight to forty months. The review concluded that SCS has proven a powerful tool in the management of patients with CRPS.30
A retrospective, three-year, multicenter study of 101 patients by Bennett et al.31 evaluated the effectiveness of SCS applied to complex regional pain syndrome I (CRPS I) and compared the effectiveness of octapolar vs. quadrapolar systems, as well as high-frequency and multi-program parameters. VAS was significantly decreased in the group using the dual-octapolar system with reductions in overall VAS approaching 70%. Of the dual-octapolar group, 74.8% used multiple arrays to maximize paresthesia coverage. VAS reduction in the group using quadrapolar systems approached 50%. And 86.3% of quadrapolar systems and 97.2% of dual-octapolar systems continued to be utilized. Overall satisfaction with stimulation was 91% in the dual-octapolar group and 70% in the quadrapolar group (p < 0.05). The authors concluded that SCS is effective in the management of chronic pain associated with CRPS I, and that use of dual-octapolar systems with multiple-array programming capabilities appeared to increase the paresthesia coverage and thus further reduce pain. High-frequency stimulation (>250 Hz) was found to be essential in obtaining adequate analgesia in 15% of the patients using dual-octapolar systems (this frequency level was not available to those with quadrapolar systems).
7.6.3 SCS Outcomes: Peripheral Ischemia and Angina
Cook and co-workers32 reported in 1976 that SCS effectively relieved pain associated with peripheral ischemia. This result has been repeated and noted to have particular efficacy in conditions associated with vasospasm, such as Raynaud's disease.33 Many studies have shown impressive efficacy of SCS to treat intractable angina.34 Reported success rates are consistently greater than 80%, and these indications, already widely used outside the United States, are certain to expand within the United States.
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