| Abstract: | Pain relief in complex regional pain syndrome due to spinal cord stimulation does not depend on vasodilation. (Maastricht University Hospital, Maastricht, The Netherlands) Anesthesiology 2000;92:1653–1660. This study aimed to assess whether pain relief in complex regional pain syndrome (CRPS after spinal cord stimulation (SCS) is, in fact, dependent on vasodilation. In addition, the study attempted to determine which of the potential mechanisms may cause the vasodilatory effect that is generally found after SCS. Twenty‐four of 36 patients with unilateral CRPS responded to the test of SCS. Twenty‐two of the 24 responders (hand, n = 14; foot, n = 8) who had undergone previous sympathectomy were enrolled in the study. In addition, 20 control subjects (10 controls for each extremity) were studied. By means of laser Doppler flowmetry, the skin microcirculation of the patients was measured bilaterally while the SCS system was switched off and while it was activated. Control subjects were tested only once. The ratio of the rest flow at heart level and the dependent position was defined as the vasoconstricted index. Both in affected hands and feet, patients were found to have lower vasoconstriction indices (P < 0.01) as compared with controls, indicating a decreased sympathetic tone. Applying SCS did not result in any microcirculatory change as compared with the baseline or the contralateral clinically unaffected side. Conclude that the study failed to show that SCS influences skin microcirculation in patients with CRPS and a low sympathetic tone. Therefore, it was also concluded that pain relief in CRPS due to SCS is possible without vasodilation. Because sympathetic activity was greatly decreased in the patients, these results support the hypothesis that the vasodilation that is normally found with SCS is due to an inhibitory effect on sympathetically maintained vasoconstriction. Comment by Hemmo A. Bosscher, MD. SCS probably provides pain relief independent of increases in blood flow to the affected area. There may be several weaknesses in this study. All patients underwent prior sympathectomy. As every pain management specialist knows, the results of these procedures are variable. That leaves a group of pain patients with CRPS I that is either predominantly sympathetically mediated or sympathetically independent, with variable degrees of sympathetic blockade. In addition, only part of the peripheral circulation is measured with a device which accuracy has not yet been confirmed. Many variables are introduced in this study making a statement that there are no differences between the treatment group and the control somewhat strong. In my opinion: pain relief in complex regional pain syndrome due to spinal cord stimulation may not depend on vasodilatation. |
