Functional linkage between large and small fibers in diabetic polyneuropathy:

<p>[Aim] To examine relationship between peripheral small fiber dysfunction and large fiber failure in type 2 diabetes mellitus (T2DM), we recorded electrodermal skin conductance (ESC) by Sudoscan (SS), a peripheral C-fiber testing device recently developed in France, and nerve conduction studies (NCS). Since SS is not approved in the Japanese health insurance system, yet, we discuss the usefulness of SS for neuromuscular medicine. [Method] One hundred and sixty-eight patients with T2DM aged under 73 years were included, and those with other causes of peripheral neuropathy were strictly excluded. Nerve conduction studies (NCS) were carried out in the lower limb, and Baba’s diabetic neuropathy criteria (BDC) was applied to evaluate severity of the large fiber dysfunction, since validity and usefulness of BDC has been established by several validation studies. BDC criteria are as follows; BDC-0: no abnormalities by NCS, BDC-1: delay in CMAP, SCV and/or F-wave, BDC-2: fall in Sural SNAP less than 5 μV, BDC-3: fall in tibial CMAP between 2 mV and 5 mV, BDC-4: marked fall in tibial CMAP less than 2 mV. We set 70 μS as a cut off value of the feet ESC, since several large-scale studies and a study with intra-epidermal nerve fiber density of biopsied leg skin revealed 70 μS as a lower limit of healthy subjects. [Results] All subjects complained nothing during SS test. We found that ESC decreased symmetrically, and lower in the feet than in hands. Frequency of abnormally low ESC was seen in 47% of the subjects, while NCS abnormality was revealed in 70%. We confirmed that both frequency and degree of fall in ESC value had positive correlation with advance of BDC (p<0.001). On the other hand, 21% of the subjects with normal NCS (BDC-0 group) had low ESC. [Conclusion] SF dysfunction starts earlier in some T2DM patients, and SF function declines in parallel with development of LF dysfunction. Sudoscan is a useful tool to detect small C-fiber dysfunction emerging in early stage of DPN. Although SS is not approved in the Japanese health insurance medical system, yet, early adoption of SS is desired.</p>