Differential impairment of the sudomotor and nociceptor axon‐reflex in diabetic peripheral neuropathy

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