Distal site testing of sympathetic skin response (big toe) in diabetic polyneuropathy.

The aim of this study was to determine whether the sympathetic skin response (SSR) recorded from the big toe is more sensitive than standard SSR recorded from the sole for the detection of sudomotor fiber dysfunction in diabetic neuropathy. We recorded big toe SSR (SSRBT) and plantar SSR (SSRP) in 17 diabetic patients with non-disabling neuropathy (group A), 13 patients with disabling neuropathy (group B) and 30 age-matched normal controls. With regard to controls, SSRP amplitude was reduced only in group B. In contrast, SSRBT amplitude was reduced in both groups of patients (p<0.0001). In 8 patients in group B, SSRBT was not recordable while the SSRP still persisted. Our results suggest that SS-RBT is a more sensitive test than SSRP in detecting distal sudomotor failure in patients with diabetic neuropathy.