The diagnostic utility of Sudoscan for distal symmetric peripheral neuropathy

Abstract

Aims: Diagnosis of early distal symmetric polyneuropathy (DSP) is challenging. Nerve conduction studies (NCS) are often normal. Skin biopsy for intraepidermal nerve fiber density (IENFD) has better sensitivity, but is invasive. Sudoscan is a novel technology that measures electrochemical skin conductance (ESC; microSiemens, μS), which is thought to be proportionate to the number of functional sweat glands. This study evaluated Sudoscan's diagnostic utility for DSP.

Methods: 55 patients with suspected DSP (22 with diabetes, 2 prediabetes, 31 idiopathic) and 42 controls underwent the Utah Early Neuropathy Scale (UENS) and Sudoscan. Each was offered skin biopsy. DSP participants underwent quantitative sudomotor axon reflex testing (QSART) and NCS.

Results: Feet and hands ESCs were reduced among DSP participants compared to controls (64±22 vs. 76±14 μS p<0.005, and 58±19 vs. 66±18 μS p<0.04). There was no difference between diabetic and idiopathic DSP. Receiver operating characteristic curve analysis revealed feet ESC and IENFD had similar areas under the curve (0.761 and 0.752). ESC correlated with Sural amplitude (0.337, p<0.02), UENS (-0.388, p<0.004), and MNSI (-0.398, p<0.005).

Conclusions: Sudoscan is a promising diagnostic test for diabetic and idiopathic DSP, with diagnostic performance similar to IENFD.

Keywords: Diabetes; Peripheral neuropathy; Skin biopsy; Sudomotor.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1. Electrochemical skin conductance (ESC) in the feet and hands was significantly reduced in those with abnormal Utah Early Neuropathy Score (UENS)

Mean ESC (with 95% confidence intervals) in the feet was 60.7 +/− 22.5 uS among those with abnormal UENS and 77.5 +/− 10.5 among those with normal UENS (p

Figure 2. Receiver operating characteristics (ROC) curves for Sudoscan and skin biopsy using abnormal Utah Early Neuropathy Score (UENS) as the gold standard

Area under the curve (AUC) for Sudoscan (ESC feet), and intraepidermal nerve fiber density (IENFD) were similar (0.761, 0.752 respectively).

Figure 3. Electrochemical skin conductance (ESC) in the feet correlated with neuropathy symptoms and signs

(A) The Michigan Neuropathy Screen Instrument and ESC feet had a Pearson correlation coefficient of −.398 (p2 of 11%. (B) The UENS and ESC feet had a Pearson correlation coefficient of −.398 (p<0.005) with an R2 of 15%.