LAUSR

Dear Sir, We were interested in the recent article from Chahal et al. [1] who found low electrochemical skin conductance (ESC) in patients with type 2 diabetes and peripheral artery disease (PAD). This original finding seems relevant because ESC is usually considered as a marker of diabetic peripheral neuropathy (DPN) [2] related to the loss of small fibers in the skin and sweat glands [3]. The neurological evaluation of patients studied by Chahal et al. was not reported in the paper [1], and we wonder whether an abnormal Semmes-Weinstein monofilament (10 g) test could be related to an altered ESC in patients with diabetes. In 36 patients with diabetes (50% type 1, 50% type 2) free of PAD (no history of foot ulcer, distal pulses present), we measured the ESC (Sudoscan, Impeto Medical) and we performed neurological tests: 10 g monofilament test, vibration perception threshold (VPT; Neurothesiometer, Horwell) instead of a tuning fork, and sural nerve conduction velocity and amplitude potential (SNCV and SNAP; DPN-Check, Neurometrix). The comparison between the patients who did not perceive the monofilament and the patients who perceived it was performed by ANOVA and Chi-2 as appropriate and is summarized in Table 1. As expected, the patients who did not perceive the monofilament were more men, older, with a longer duration of diabetes, and their VPT and nerve conduction tests were altered. The ESC was reduced in our patients who did not perceive the monofilament (47 ± 8 μS), very near of the values reported by Chahal et al. (48 ± 8 μS). The difference between ESC in patients perceiving vs not perceiving the monofilament was still significant after adjusting for age, gender, and diabetes duration by multivariate regression analysis. In patients with diabetes, PAD and DPN usually coexist [4] and vascular risk factors have also been related to the polyneuropathy even in non-diabetic population [5]. A reduced ankle/brachial index as used by Chahal et al. has been related to a twice higher risk of diabetic neuropathy in the Verona study [6]. We therefore wonder whether neuropathy may contribute to the low ESC in patients with PAD, and we suggest that their conclusions would get stronger if the authors could adjust the relation between the ankle/brachial index and ESC to the presence of DPN. The most accurate approach for the evaluation of DPN would be the objective measurement of SNCV and SNAP or the quantified and more sensitive measurement of the VPT, which we performed. But our result shows that a simple, recommended, monofilament test may be used for this adjustment. It should, however, be noticed that SNCV, SNAP, and VPT only test for large nerve fibers. This is a limitation, considering that often the autonomic and small fiber impairment is unrelated to the presence of large nerve fiber neuropathy. The ESC, as A comment on: Chahal S, Vohra K, Syngle A. Association of sudomotor function with peripheral artery disease in type 2 diabetes. Neurol Sci (2017) 38:151–6