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Background and Objectives: Stellate ganglion blocks are an effective but invasive treatment of upper extremity pain. Linearly polarized red and near-infrared (IR) light is promoted as a safe alternative to this procedure, but its effects are poorly established. This study was designed to assess the physiological effects of this latter approach and to quantitate its benefits in people with upper extremity pain due to Complex Regional Pain Syndrome I (CRPS I, RSD)., Study Design/materials and Methods: This was a two-part study. In the first phase, six adults (ages 18-60) with normal neurological examinations underwent transcutaneous irradiation of their right stellate ganglion with linearly polarized 0.6-1.6 microm light (0.92 W, 88.3 J). Phase two consisted of a double-blinded evaluation of active and placebo radiation in 12 subjects (ages 18-72) of which 6 had upper extremity CRPS I and 6 served as "normal" controls. Skin temperature, heart rate (HR), sudomotor function, and vasomotor tone were monitored before, during, and for 30 minutes following irradiation. Analgesic and sensory effects were assessed over the same period as well as 1 and 2 weeks later., Results: Three of six subjects with CRPS I and no control subjects experienced a sensation of warmth following active irradiation (P = 0.025). Two of the CRPS I subjects reported a >50% pain reduction. However, four noted minimal or no change and improvement did not reach statistical significance for the group as a whole. No statistically significant changes in autonomic function were noted. There were no adverse consequences., Conclusions: Irradiation is well tolerated. There is a suggestion in this small study that treatment is beneficial and that its benefits are not dependent on changes in sympathetic tone. Further evaluation is warranted., (Copyright 2003 Wiley-Liss, Inc.)