Original articleNon-invasive and quantitative assessment of sudomotor function for peripheral diabetic neuropathy evaluationMesure non invasive et quantitative de la fonction sudorale pour mieux évaluer la neuropathie périphérique chez le patient☆
Introduction
Diabetic polyneuropathy (DPN) is a nerve-length-dependent process [1]. Early detection of symmetrical distal sensory–motor DPN can decrease morbidity and the risk of foot complications [2]. Sensory function is considered one of the major initiating risk factors in the pathogenesis of diabetic foot ulcer [3]. As no gold standard is available for early diagnosis of DPN, vibration perception threshold (VPT), using a biothesiometer, and pressure perception, using Semmes–Weinstein monofilaments, have been proposed to identify patients at risk, but none of these investigates peripheral autonomic involvement [4].
Peripheral autonomic neuropathy (PAN) results in the atrophy of sweat glands and decreased sudomotor response that may affect the skin suppleness and flexibility that prevent skin cracks and ulceration, and may also reduce sweating, leading to abnormal skin conditions such as dryness, fissures and blisters [5], [6]. The prevalence of PAN, as determined by the presence of two or more clinical signs, has recently been estimated to affect 43% of diabetic patients aged 40–70 years [7], [8]. PAN is usually evaluated through sweat function, using the sympathetic skin response (SSR), or by quantitative sudomotor axon reflex testing (QSART) [9]. These methods require specialized training to perform and are also time-consuming procedures. Neuropad® is another alternative test targeted for use by the patient, although it is less sensitive and semi-quantitative [10].
Sudoscan™, a new non-invasive and rapid technique, has recently been developed to allow the precise quantitative evaluation of sweat gland function through measurement of electrochemical sweat conductance (ESC) on the hands and feet based on sweat chloride concentrations [11]. The aim of the present study was to analyze in diabetic patients the relationship between VPT and foot ESC, the reproducibility and effect of blood glucose levels on ESC measurements, and the relationship between ESC results and foot fissure presence.
Section snippets
Participants and study protocol
Altogether, 142 consecutive patients were recruited from the diabetes clinic at Haut-Lévêque University Hospital after their informed consent was obtained. Patients were accepted on the condition of having had a diagnosis of diabetes with different degrees of peripheral nerve involvement, but no progressive skin lesion that might induce foot ulceration. They were divided according to peripheral somatic neuropathy, as assessed by their VPT value as a reference (consecutive patients to obtain the
Results
Of our 142 diabetic patients, 55 had a VPT threshold less than 15 V, 30 had a threshold between 15–25 V and 57 had a threshold greater than 25 V. Their main characteristics by VPT are presented in Table 1. Patients were older and had longer diabetes durations as VPT increased from less than 15 V to greater than 25 V, whereas no statistical difference was found among the different diabetic groups in mean HbA1c.
Also, among our study patients, 66 had no sudomotor dysfunction (foot ESC > 60 μS), 43 had
Discussion
This study shows that the assessment of sudomotor function based on sweat chloride concentration through reverse iontophoresis is a quantitative reproducible method that is not influenced by glycaemia. Foot ESC correlates with different degrees of peripheral sensory neuropathy, as estimated by VPT measurement and monofilament tests, and there is also progressive worsening of ESC measurements with increasing VPT and monofilament results. Moreover, sudomotor dysfunction as assessed by ESC results
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
Acknowledgments
We would like to thank P. Brunswick, X. Neveu and J.H. Calvet for their technical assistance, analysis of data and contribution to discussions.
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This work was funded by Impeto Medical, 17, rue Campagne Première, 75014 Paris, France.