From the Electrodiagnostics Lab…

Abstract

Quantitative sudomotor axon reflex testing (QSART) evaluates peripheral postganglionic sympathetic small fiber function. With QSART, the sympathetic innervation of the sweat gland is reflexly stimulated by iontophoresis of acetylcholine through the skin. The resulting sweat output is measured at one upper and three lower extremity sites and compared with normal values [ [1] Low P.A Laboratory evaluation of autonomic function. in: Low P.A Clinical Autonomic Disorders. Lippincott-Raven, Philadelphia1997: 179-208 Google Scholar ]. Patients with small fiber neuropathy present with tingling, prickling and burning dysesthesias. QSART is 80% sensitive in detecting small fiber neuropathy [ [2] Tobin K Giuliani M.J Lacomis D Comparison of different modalities for detection of small fiber neuropathy. Clin Neurophysiol. 1999; 110: 1909-1912 Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar ]. Nerve conduction studies evaluate large nerve fiber function and are normal in these patients. Large and small nerve fibers may be simultaneously involved in patients with peripheral neuropathy; in these cases nerve conduction studies and QSART may both be abnormal [ [3] Lacomis D Small-fiber neuropathy. Muscle Nerve. 2002; 26: 173-188 Crossref PubMed Scopus (323) Google Scholar ]. QSART may be helpful in differentiating a central versus a peripheral nervous system abnormality as a cause of symptoms in patients who present with tingling, prickling and burning of the extremities (Fig. 1).