Altered C-Fiber Function as an Indicator of Early Peripheral Neuropathy in Individuals With Impaired Glucose Tolerance

OBJECTIVE: This study explored the importance of glycemic burden compared with features of the metabolic syndrome in the pathogenesis of diabetic neuropathy by comparing C-fiber function in people with type 1 diabetes to that in people with impaired glucose tolerance (IGT). RESEARCH DESIGN AND METHODS: The axon reflex–elicited flare areas (LDIflares) were measured with a laser Doppler imager (LDI) in age-, height-, and BMI-matched groups with IGT (n = 14) and type 1 diabetes (n = 16) and in healthy control subjects (n = 16). RESULTS: The flare area was reduced in the IGT group compared with the control (2.78 ± 1.1 vs. 5.23 ± 1.7 cm(2), P = 0.0001) and type 1 diabetic (5.16 ± 2.3 cm(2), P = 0.002) groups, whereas the flare area was similar in the type 1 diabetic and control groups. CONCLUSIONS: This technique suggests that small-fiber neuropathy is a feature of IGT. The absence of similar small-fiber neuropathy in those with longstanding type 1 diabetes suggests that glycemia may not be the major determinant of small-fiber neuropathy in IGT.