Value of autonomic testing in reflex sympathetic dystrophy

To attempt to characterize reflex sympathetic dystrophy (RSD) and to determine factors that would predict a response to sympathetic block.

We undertook a retrospective analysis on 396 patients with chronic limb pain referred for autonomic testing during a 5-year period.

Clinical endpoints were relief of pain after sympathetic block and a composite RSD diagnostic probability score, based on the clinical attributes of allodynia, protopathia, swelling, and vasomotor alterations. We compared the results of three autonomic tests--resting sweat output (RSO), resting skin temperature (RST), and quantitative sudomotor axon reflex test (QSART).

Increased RSO predicted the diagnosis of RSD with 94% specificity, and the specificity was 98% when RSO was considered in conjunction with an abnormal QSART result, the best laboratory correlate (P = 0.003) of the clinical diagnosis. Shorter duration of pain correlated with a warmer limb (P < 0.001), even in the absence of RSD. Response to a single sympathetic block did correlate with the diagnosis (P = 0.031) but correlated most significantly with short duration of pain in the arm (P = 0.001) and laboratory findings in the leg, where increased RST (P < 0.001) and QSART (P < 0.001) were near-perfect predictors of response.

Sweating abnormalities correlate strongly with the clinical syndrome of RSD, and alterations in RST may be superior to clinical findings in predicting the response to sympathetic block. The findings provide physiologic support for the unproven view of a natural disease progression ("stages"), with better treatment response and a warmer extremity initially. Because certain physiologic trends occur in all patients, general alterations of autonomic function with pain are suggested.