Comparison of SSR and QSART in early diabetic neuropathy - the value of length-dependent pattern in QSART

We evaluated postganglionic sympathetic function using the sympathetic skin response (SSR) and quantitative sudomotor axon reflex test (QSART) on the feet of 31 patients with early diabetic neuropathy and 20 age-matched norma l controls. The amplitude of SSR and.. the sweat volume of QSART were signi ficantly decreased in the diabetic patients. We evaluated the sensitivity o f the tests in detecting autonomic failure. Out of 31 patients, 14 (45%) ha d abnormal SSR (14 absent; 17 present), while 16 of 31 patients (52%) had a bnormal QSART (1 absent; 5 absolutely reduced and 10 showed a length-depend ent pattern of reduction). More important than differences in sensitivity i s the specificity of QSART, which specifically evaluates the postganglionic axon (instead of polysynaptic pathways in SSR) and provides quantitative d ata on the severity and pattern of autonomic deficit. In normal controls un der 65 years of age, there was a significant correlation between the amplit ude of SSR and the sweat volume of QSART. However, there was no significant relationship between these in diabetic. patients. These results suggest th at QSART can evaluate early diabetic neuropathy more precisely than SSR.. ( C) 2001 Elsevier Science B.V. All rights reserved.