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Complex Regional Pain Syndrome Diagnostic Tests
Quantitative Sudomotor Axon Reflex Test (QSART)
The quantitative sudomotor axon reflex test (QSART) is used to assess the small nerve fibers, which are linked to the sweat glands. It is often used to diagnose painful small fiber neuropathy when nerve conduction test results are normal, disturbances of the autonomic nervous system, and complex pain disorders (9). QSART measures sweat response and gives information on the function of the sudomotor reflex loops. It is a valuable test, but because it examines axon reflex, it cannot be used to test the effect of an inhibition to the sympathetic stimulus (5). By testing responses to outside stimuli, this test is useful for quantifying the allodynia often associated with CRPS. A combination of abnormal resting sweat output and QSART produces a specificity of 98%, which corresponds with the observed symptoms of CRPS (3).
R. Norman Harden, MD, Director of the Center for Pain Studies at the Rehabilitation Institute of Chicago says, "Since there has been no validation research for QSART, it must be considered experimental and is not considered diagnostic in any context. Its 'accuracy' (ie, sensitivity and specificity) has not been properly assessed. QSART is generally unavailable except in a few academic centers, and therefore is not generally available nor of general utility."
The test itself involves the technologist or physician placing four electrodes filled with acetylcholine on three areas of the leg and one area on the wrist (19). A mild electrical stimulation is then run through the electrodes, which in turn stimulates the sweat glands. This produces a tingling sensation that is measured subjectively.
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Updated December 20, 2007 |
