VALUE OF AUTONOMIC TESTING IN REFLEX SYMPATHETIC DYSTROPHY

Objective: To attempt to characterize reflex sympathetic dystrophy (RS D) and to determine factors that would predict a response to sympathet ic block. Design: We undertook a retrospective analysis on 396 patient s with chronic limb pain referred for autonomic testing during a 5-yea r period. Material and Methods: Clinical endpoints were relief of pain after sympathetic block and a composite RSD diagnostic probability sc ore, based on the clinical attributes of allodynia, protopathia, swell ing, and vasomotor alterations. We compared the results of three auton omic tests-resting sweat output (RSO), resting skin temperature (RST), and quantitative sudomotor axon reflex test (QSART). Results: Increas ed RSO predicted the diagnosis of RSD with 94% specificity, and the sp ecificity was 98% when RSO was considered in conjunction with an abnor mal QSART result, the best laboratory correlate (P = 0.003) of the cli nical diagnosis. Shorter duration of pain correlated with a warmer lim b (P<0.001), even in the absence of RSD. Response to single sympatheti c block did correlate with the diagnosis (P = 0.031) but correlated mo st significantly with short duration of pain in the arm (P = 0.001) an d laboratory findings in the leg, where increased RST (P<0.001) and QS ART (P<0.001) were near-perfect predictors of response. Conclusion: Sw eating abnormalities correlate strongly with the clinical syndrome of RSD, and alterations in RST may be superior to clinical findings in pr edicting the response to sympathetic block. The findings provide physi ologic support for the unproven view of a natural disease progression (''stages''), with better treatment response and a warmer extremity in itially. Because certain physiologic trends occur in all patients, gen eral alterations of autonomic function with pain are suggested.