• autonomic function;
  • axon-reflex;
  • c-fiber;
  • diabetes;
  • dysautonomia;
  • laser Doppler flowmetry;
  • silastic imprint method


It is not known whether C-fiber functional subclasses are differentially affected by diabetes mellitus or whether the patterns of C-fiber dysfunction are different between type 1 and type 2 diabetes. We therefore examined efferent sympathetic sudomotor and primary afferent nociceptor C-fiber function in diabetic patients. Acetylcholine (10%) was used to evoke C-fiber (axon-reflex)–mediated responses. The nociceptor (flare) response was measured using a laser Doppler device. The sudomotor response was quantified with silastic imprints. The nociceptor C-fiber–mediated flare response was reduced in type 2 diabetic patients (P < 0.008) but was similar to controls in type 1 diabetic patients. The sympathetic C-fiber–mediated responses, including sweat volume (P < 0.05) and the number of activated sweat glands (P = 0.003), were increased in patients with type 1 diabetes. There also was a trend toward a larger axon-reflex sweat area in patients with type 1 diabetes (P = 0.09). No differences in these sweat responses were found in patients with type 2 diabetes compared to controls. These findings suggest that the functional abnormalities in diabetic peripheral neuropathy are not homogeneous and that C-fiber subclasses are differentially affected in type 1 and 2 diabetes mellitus. Muscle Nerve, 2006