1 Pain Management and Research Centre, Department of Anaesthesiology, 2 Department of Surgery and 3 Department of Clinical Epidemiology and Medical Technology Assessment, University Hospital Maastricht, Maastricht, The Netherlands
*Corresponding author: M. van Kleef, Pain Management and Research Centre, University Hospital Maastricht,P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. E-mail: MVK@sane.azm.nl
Accepted for publication: October 3, 2003
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Abstract |
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Methods. Thirty-six patients with a definitive implant were included in this study. A pain diary was obtained from all patients before treatment and 6 months and 1 and 2 years after implantation. All patients were asked to complete a seven-point Global Perceived Effect (GPE) scale and the Euroqol-5D (EQ-5D) at each post-implant assessment point.
Results. The pain intensity was reduced at 6 months, 1 and 2 years after implantation (P<0.05). However, the repeated measures ANOVA showed a statistically significant, linear increase in the visual analogue scale score (P=0.03). According to the GPE, at least 42% of the cervical SCS patients and 47% of the lumbar SCS patients reported at least much improvement. The health status of the patients, as measured on the EQ-5D, was improved after treatment (P<0.05). This improvement was noted both from the social and from the patients perspective. Complications and adverse effects occurred in 64% of the patients and consisted mainly of technical defects. There were no differences between cervical and lumbar groups with regard to outcome measures.
Conclusion. SCS reduced the pain intensity and improves health status in the majority of the CRPS I patients in this study. There was no difference in pain relief and complications between cervical and lumbar SCS.
Br J Anaesth 2004; 92: 34853
Keywords: complications, complex regional pain syndrome; spinal cord, electrical stimulation, cervical; spinal cord, electrical stimulation, lumbar
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Introduction |
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Spinal cord stimulation (SCS) is widely used in the treatment of CRPS I,713 and we were able to show its effectiveness in a randomized controlled study.14 Follow-up in this study, however, was only 6 months. As there is anecdotal evidence that the clinical effects of SCS decrease over time and there is controversy regarding the use of SCS in the cervical region, we undertook a prospective study to address these issues. We prospectively measured pain, global perceived effect, quality of life, complications and side-effects of SCS in 36 CRPS I patients. Of these, 19 had devices positioned in the cervical region and 17 in the lumbar region.
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Patients and methods |
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After a test period of 7 days the temporary lead was removed. During the test period, patients were advised to perform all normal daily activities in order to obtain a good impression of the implants effect. The permanent SCS system was implanted when, during the testing period, the patient reported either at least 50% reduction in pain intensity as measured on a 10 cm visual analogue scale (VAS), which was anchored by the two extremes of pain (no pain on the left and the worst possible pain on the right), or much improvement on the seven-point global perceived effect (GPE) scale. The GPE was translated from English into Dutch.14 The GPE categories include: best ever, much improved, improved, not improved/not worse, much worse, and worst ever.
Implantation of the SCS system
The Quad lead was implanted in the same fashion as the test lead. After the lead had been positioned, the patient was sedated and a pulse generator (Itrel 3, model 7425; Medtronic) was implanted in the subcutaneous tissue in the left lower anterior abdominal wall, and connected to the electrode by a tunnelled extension lead (model 749551 or 749566; Medtronic). After closing the skin, the pulse generator was activated and adjusted using a console programmer (model 7432; Medtronic). Initial stimulation was started at a rate of 85 Hz and a pulse width of 210 µs. Patients could control the stimulation intensity by adjusting the amplitude from 0 to 10 V with a patient programmer (model 7434-NL; Medtronic). After implantation, patients remained in the hospital for 24 h, during which period they received two doses of cefuroxim (750 mg) i.v. The following day, after the position of the electrode had been verified by x-ray, the patient was discharged. Further adjustments in the programming could be made on an outpatient basis. After implantation no restrictions were placed on patient activities.
Patient assessment during follow-up
The assessments were done before treatment and 6, 12 and 24 months after implantation. All patients were asked to score their pain three times per day over the course of 4 days on a 10-cm VAS.1618 In addition, all patients rated the GPE on pain on a seven-point scale, as indicated above.
All patients completed the Euroqol 5D (EQ-5D)19 before the treatment and at follow-up after 1 and 2 yr. The EQ-5D consists of two parts. The first part records self-reported health problems in five dimensions: mobility, self-care, usual activities, pain or discomfort, and anxiety or depression. Each dimension is subdivided into three categories: no problem, moderate problems and extreme problems. By combining one category from each of the five dimensions, a total of 243 health states are defined. The second part records the perception of the patients overall health on a 100-mm VAS (0 denoting death and 100 perfect health). The data of the EQ-5D are represented in three distinct forms:20 (i) as a profile, based on the patients category of problem in each of the five dimensions (EQ-5D profile); (ii) as a social score by applying a suitable weighting system obtained from the UK national survey; some patients score negatively, indicating that, from a social perspective their state is regarded as worse than death; and (iii) on a VAS, representing a quantitative measure of the patients valuation of his own global health status (EQ-5D VAS).
The questionnaires were sent to the patients by post. They were asked to complete the questionnaires and return them by post.
Complications and adverse effects were also documented during clinic follow-up. Complications were defined as unpleasant, new, physical experiences for the patient, and included spinal tap, post-spinal headache, and infection. Adverse effects were defined as technical failure, including: technical procedure problems during the implantation; revision of the pulse generator pocket; lead dislocation; defective pulse lead; pulse generator failure; device removal; device re-implantation; and pain resulting from pulse generator, lead or plug and electrical stimulation elsewhere.
Statistical analysis
Changes in variables were tested using the paired t-test and the McNemar test. Differences between cervical and lumbar SCS were tested using two-way ANOVA and the 2 test.
The change/progress of pain, using more than two points of time, was analysed with repeated measures ANOVA with the VAS 0.5, 1 and 2 yr after the intervention. P<0.05 was considered statistically significant.
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Results |
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In Figure 2 the unweighted response to the EQ-5D is presented at baseline and at two follow-up periods. At the follow-up periods the number of patients reporting extreme problems for the categories usual activities and pain and discomfort decreased in both the cervical and the lumbar group (P<0.01). In the dimension anxiety and depression, 50% of the patients noted no problems at baseline, which increased in both groups at the follow-up periods (P<0.02). The other EQ-5D dimensions did not change significantly. Differences between cervical and lumbar SCS were not significant.
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Thirty-one adverse effects were noted in 20 patients. Because of a rotation of the pulse generator and subsequent painful sensations, revision of the pulse generator pocket was performed in five patients. Substantial weight loss resulted in pocket revision in two other cases. Inadequate paraesthesiae or paraesthesiae in other locations required repositioning of the lead in one patient with CRPS I in the lower extremity and in five patients with affected upper extremity. In two cases no satisfactory repositioning was obtained. Lead failure resulted in replacement in four patients. Because of technical failure, replacement of the pulse generator was needed in two cases.
The complete SCS system was removed in two patients with a cervical SCS and two patients with a lumbar SCS, which resulted in stopping the treatment. Dislocation of the cervical lead occurred more frequently, but this was not significant compared with the lumbar group (P=0.17). In one patient the complete permanent system was removed because of suspicion of infection. However, bacteriological cultures were negative. Reimplantation resulted in the same complaints as the first implant, which may indicate a reaction to the constituents of the implant. The reimplant was also removed. One patient suffered from secondary ulcerative colitis (UC). A relationship between the SCS system and UC disease activity was suggested, which resulted in the removal of the lead system.13 In one case the system was removed because of increased pain during stimulation, and in one other because of inability to obtain effective stimulation.
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Discussion |
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Spinal cord stimulation has been suggested as a therapy for pain relief when other treatment modalities have failed.23 The exact physiological mechanism of pain relief by SCS in patients with CRPS is poorly understood. It has been suggested that SCS works through a spectrum of neurophysiological mechanisms.24 Studies in nerve-lesioned rats showed that SCS results in increased release of GABA in the dorsal horn, resulting in a decrease in the excitatory amino acids glutamate and aspartate.25
The clinical effects of SCS in CRPS have been established in a limited number of uncontrolled studies.12 26 We recently documented the clinical short-term effects in a randomized controlled study.14 Little is known about the long-term effect and complications of SCS.
In 4461% of patients the CRPS is located in the upper extremity.27 28 This means that in most patients treatment with SCS cervical lead placement is indicated. It is widely held that SCS should be used with caution in the cervical region. In the cervical region, the posterior epidural space is the smallest and may prevent adequate lead placement. The mobility of the cervical spine and the local anatomy should restrict effectiveness and may lead to more and worse complications. The present study addresses these two issues.
Contrary to the prevailing view, we found that the SCS device was slightly more effective in patients with a cervical implant than a lumbar implant, although this difference was not significant. All patients reported a significant reduction in pain relief, of at least 50% after 6 months after implantation.
After 1 and 2 yr of follow-up there was a slight but significant increase in pain in both groups, indicating that the effect was declining. The reductions in VAS after 2 yr of 3.1 points in the cervical group and 3.4 points in the lumbar group are considered to be clinically relevant.22 The decrease in pain was reflected in health status. Health status of the patients measured on the EO-5D increased after SCS (Fig. 2). This increase was the same in both groups and was mainly due to decrease in pain, discomfort, anxiety and depression.
Complications of the procedure (i.e. spinal taps, post-spinal headache, no access to the epidural space and infection) were seen in six of the 36 patients. Spinal taps occurred only in the first 10 patients; thereafter we changed the technique for identifying the epidural space from loss of resistance to full fluoroscopic control. Adverse effects (i.e. technical failures) were seen in both the cervical and the lumbar group. Dislocation of the lead occurred somewhat more frequently in the cervical group, but this difference was not significant.
In conclusion, SCS was effective in patients with chronic CRPS I in our study, even after 2 yr of treatment. There were no significant differences in pain and quality of life between cervical and lumbar implantation of the lead. Cervical implantation was not associated with a higher complication rate.
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