Neuropad: evaluation of three cut-off points of sudomotor dysfunction for early detection of polyneuropathy in recently diagnosed diabetes

Screening for diabetic peripheral neuropathy in resource-limited settings

BACKGROUND

Diabetic neuropathy is the most common microvascular complication of diabetes mellitus and a major risk factor for diabetes-related lower-extremity complications. Diffuse neuropathy is the most frequently encountered pattern of neurological dysfunction and presents clinically as distal symmetrical sensorimotor polyneuropathy. Due to the increasing public health significance of diabetes mellitus and its complications, screening for diabetic peripheral neuropathy is essential. Consequently, a review of the principles that guide screening practices, especially in resource-limited clinical settings, is urgently needed.

MAIN BODY

Numerous evidence-based assessments are used to detect diabetic peripheral neuropathy. In accordance with current guideline recommendations from the American Diabetes Association, International Diabetes Federation, International Working Group on the Diabetic Foot, and National Institute for Health and Care Excellence, a screening algorithm for diabetic peripheral neuropathy based on multiphasic clinical assessment, stratification according to risk of developing diabetic foot syndrome, individualized treatment, and scheduled follow-up is suggested for use in resource-limited settings.

CONCLUSIONS

Screening for diabetic peripheral neuropathy in resource-limited settings requires a practical and comprehensive approach in order to promptly identify affected individuals. The principles of screening for diabetic peripheral neuropathy are: multiphasic approach, risk stratification, individualized treatment, and scheduled follow-up. Regular screening for diabetes-related foot disease using simple clinical assessments may improve patient outcomes.

Sympathetic System in Wound Healing: Multistage Control in Normal and Diabetic Skin

In this review, we discuss sympathetic regulation in normal and diabetic wound healing. Experimental denervation studies have confirmed that sympathetic nerve endings in skin have an important and complex role in wound healing. Vasoconstrictor neurons secrete norepinephrine (NE) and neuropeptide Y (NPY). Both mediators decrease blood flow and interact with inflammatory cells and keratinocytes. NE acts in an ambiguous way depending on receptor type. Beta2-adrenoceptors could be activated near sympathetic endings; they suppress inflammation and re-epithelialization. Alpha1- and alpha2-adrenoceptors induce inflammation and activate keratinocytes. Sudomotor neurons secrete acetylcholine (ACh) and vasoactive intestinal peptide (VIP). Both induce vasodilatation, angiogenesis, inflammation, keratinocytes proliferation and migration. In healthy skin, all effects are important for successful healing. In treatment of diabetic ulcers, mediator balance could be shifted in different ways. Beta2-adrenoceptors blockade and nicotinic ACh receptors activation are the most promising directions in treatment of diabetic ulcers with neuropathy, but they require further research.

Concordance between sudomotor disorder and the clinical diagnosis of diabetic peripheral neuropathy, according to various clinical guidelines

AIM

To assess the concordance between variations in Neuropad® results and the those in different diagnostic criteria of Diabetic Peripheral Neuropathy, according to various clinical guidelines.

METHODS

A descriptive observational study was conducted of 111 patients with a confirmed diagnosis of diabetes mellitus. The criteria for inclusion in the study were that patients should be aged 18 years or more and have at least 10 years' history of diabetes mellitus.

RESULTS

73 (65.8%) were male and 38 (34.2%) were female. Their mean age was 57.92 ± 13.24 years (95% CI 55.45-60.38). Healthy Neuropad® findings were obtained for 35 right feet (31.5%) and 31 left feet (27.9%).

CONCLUSION

Neuropad® is an effective instrument for detecting macro and microvascular complications such as early-stage neuropathy, although its use should always be accompanied by a clinical examination of the foot.

Early Detection of Diabetic Peripheral Neuropathy: A Focus on Small Nerve Fibres

Diabetic peripheral neuropathy (DPN) is the most common complication of both type 1 and 2 diabetes. As a result, neuropathic pain, diabetic foot ulcers and lower-limb amputations impact drastically on quality of life, contributing to the individual, societal, financial and healthcare burden of diabetes. DPN is diagnosed at a late, often pre-ulcerative stage due to a lack of early systematic screening and the endorsement of monofilament testing which identifies advanced neuropathy only. Compared to the success of the diabetic eye and kidney screening programmes there is clearly an unmet need for an objective reliable biomarker for the detection of early DPN. This article critically appraises research and clinical methods for the diagnosis or screening of early DPN. In brief, functional measures are subjective and are difficult to implement due to technical complexity. Moreover, skin biopsy is invasive, expensive and lacks diagnostic laboratory capacity. Indeed, point-of-care nerve conduction tests are convenient and easy to implement however questions are raised regarding their suitability for use in screening due to the lack of small nerve fibre evaluation. Corneal confocal microscopy (CCM) is a rapid, non-invasive, and reproducible technique to quantify small nerve fibre damage and repair which can be conducted alongside retinopathy screening. CCM identifies early sub-clinical DPN, predicts the development and allows staging of DPN severity. Automated quantification of CCM with AI has enabled enhanced unbiased quantification of small nerve fibres and potentially early diagnosis of DPN. Improved screening tools will prevent and reduce the burden of foot ulceration and amputations with the primary aim of reducing the prevalence of this common microvascular complication.

Diabetic peripheral neuropathy: advances in diagnosis and strategies for screening and early intervention

Diabetic peripheral neuropathy (DPN) is a common complication of both type 1 and 2 diabetes. It is a leading cause of lower-limb amputation and disabling neuropathic pain. Amputations in patients with diabetes have a devastating effect on quality of life and are associated with an alarmingly low life expectancy (on average only 2 years from the amputation). Amputation also places a substantial financial burden on health-care systems and society in general. With the introduction of national diabetes eye screening programmes, the prevalence of blindness in working-age adults is falling. This is not the case, however, with diabetes related amputations. In this Review, we appraise innovative point-of-care devices that enable the early diagnosis of DPN and assess the evidence for early risk factor-based management strategies to reduce the incidence and slow the progression of DPN. We also propose a framework for screening and early multifactorial interventions as the best prospect for preventing or halting DPN and its devastating sequelae.

Novel Insights into Sensorimotor and Cardiovascular Autonomic Neuropathy from Recent-Onset Diabetes and Population-Based Cohorts

The most prevalent chronic complications of diabetes are diabetic neuropathies, among which distal sensorimotor polyneuropathy (DSPN) and cardiovascular autonomic neuropathy (CAN) are the best studied. Their major clinical sequelae such as foot ulcers, neuropathic pain, and orthostatic hypotension are associated with lower quality of life and increased risk of mortality. Here we discuss the recent insights into DSPN and CAN focusing on two prospective cohorts; that is, the German Diabetes Study (GDS) including recent-onset diabetes patients and the population-based Cooperative Health Research in the Region of Augsburg, Germany (KORA) surveys. The insights from these studies investigating novel tools for early detection and prediction of (pre)diabetic neuropathy as well as biomarkers of oxidative stress and inflammation should ultimately culminate in improving the health care of patients affected by this serious condition.

Emerging Biomarkers, Tools, and Treatments for Diabetic Polyneuropathy

Diabetic neuropathy, with its major clinical sequels, notably neuropathic pain, foot ulcers, and autonomic dysfunction, is associated with substantial morbidity, increased risk of mortality, and reduced quality of life. Despite its major clinical impact, diabetic neuropathy remains underdiagnosed and undertreated. Moreover, the evidence supporting a benefit for causal treatment is weak at least in patients with type 2 diabetes, and current pharmacotherapy is largely limited to symptomatic treatment options. Thus, a better understanding of the underlying pathophysiology is mandatory for translation into new diagnostic and treatment approaches. Improved knowledge about pathogenic pathways implicated in the development of diabetic neuropathy could lead to novel diagnostic techniques that have the potential of improving the early detection of neuropathy in diabetes and prediabetes to eventually embark on new treatment strategies. In this review, we first provide an overview on the current clinical aspects and illustrate the pathogenetic concepts of (pre)diabetic neuropathy. We then describe the biomarkers emerging from these concepts and novel diagnostic tools and appraise their utility in the early detection and prediction of predominantly distal sensorimotor polyneuropathy. Finally, we discuss the evidence for and limitations of the current and novel therapy options with particular emphasis on lifestyle modification and pathogenesis-derived treatment approaches. Altogether, recent years have brought forth a multitude of emerging biomarkers reflecting different pathogenic pathways such as oxidative stress and inflammation and diagnostic tools for an early detection and prediction of (pre)diabetic neuropathy. Ultimately, these insights should culminate in improving our therapeutic armamentarium against this common and debilitating or even life-threatening condition.

Advantages of early diagnosis of diabetic neuropathy in the prevention of diabetic foot ulcers

AIMS

To evaluate the utility of the sudomotor function test (SFT) as a clinical tool in the Risk Stratification System of diabetic patients and to demonstrate the earlier detection of the risk of developing diabetic foot ulcers (DFU) compared to the standard clinical tests.

METHODS

Prospective follow-up study on 263 patients enrolled consecutively over 3.5 years. Diabetic patients without active DFU were classified according to the International Working Group Risk Stratification System (RSS) and categorized according to the results of the Semmes-Wenstein Monofilament (SWM) and biothesiometer measurements or the SFT. The main outcome evaluated was the development of DFU.

RESULTS

Median follow-up was 42 [38-44] months. Sixty patients (22.8%) developed DFU after a median of 6.2 [3-17] months. Ten patients that were included in the no-risk group (group 0) based on the SWM and biothesiometer results developed DFU. Thus the sensitivity of this approach was 83.33% and the specificity was 50.47%. Based on the SFT results, all patients that developed DFU were included in the correct risk group. This approach had 100% sensitivity and 31.53% specificity. Regarding the diagnostic accuracy of the two Methods, the respective AUC values were 0.776 (95% CI 0.702-0.849) and 0.816 (95% CI 0.757-0.874).

CONCLUSIONS

SFT improved RSS in diabetic patients in a specialized diabetic foot unit. SFT categorized patients correctly according to the risk of developing DFU.

The Quest for more Research on Painful Diabetic Neuropathy

A 62-year-old diabetologist diagnosed himself to have diabetes type-2, with an HbA1c of 9.5. Five months after lifestyle intervention and a multi-drug approach, HbA1c was 6.3, systolic blood pressure was below 135mmHg and BMI reduced to 27. But he suffered from severe painful diabetic neuropathy. Therefore he decided to visit his friend, a famous neuroscientist at an even more famous university. He asked him several plain questions: 1. What is the natural course of painful diabetic neuropathy? 2. Why do I have, despite almost normalizing HbA1c, more problems than before? 3. Are you sure my problems are due to diabetes or should we do a nerve biopsy? 4. Are there imaging techniques helpful for the diagnosis of this diabetic complication, starting in the distal nerve endings of the foot and slowly moving ahead? 5. Can you suggest any drug, specific and effective, for relieving painful diabetic neuropathy? This review will use the experts' answers to the questions of the diabetologist, not only to give a summary of the current knowledge, but even more to highlight areas of research needed for improving the fate of patients with painful diabetic neuropathy. Based on the unknowns, which exceed the knowns in diabetic neuropathy, a quest for more public support of research is made.

Spatial analysis improves the detection of early corneal nerve fiber loss in patients with recently diagnosed type 2 diabetes

Corneal confocal microscopy (CCM) has revealed reduced corneal nerve fiber (CNF) length and density (CNFL, CNFD) in patients with diabetes, but the spatial pattern of CNF loss has not been studied. We aimed to determine whether spatial analysis of the distribution of corneal nerve branching points (CNBPs) may contribute to improving the detection of early CNF loss. We hypothesized that early CNF decline follows a clustered rather than random distribution pattern of CNBPs. CCM, nerve conduction studies (NCS), and quantitative sensory testing (QST) were performed in a cross-sectional study including 86 patients recently diagnosed with type 2 diabetes and 47 control subjects. In addition to CNFL, CNFD, and branch density (CNBD), CNBPs were analyzed using spatial point pattern analysis (SPPA) including 10 indices and functional statistics. Compared to controls, patients with diabetes showed lower CNBP density and higher nearest neighbor distances, and all SPPA parameters indicated increased clustering of CNBPs (all P<0.05). SPPA parameters were abnormally increased >97.5th percentile of controls in up to 23.5% of patients. When combining an individual SPPA parameter with CNFL, ≥1 of 2 indices were >99th or <1st percentile of controls in 28.6% of patients compared to 2.1% of controls, while for the conventional CNFL/CNFD/CNBD combination the corresponding rates were 16.3% vs 2.1%. SPPA parameters correlated with CNFL and several NCS and QST indices in the controls (all P<0.001), whereas in patients with diabetes these correlations were markedly weaker or lost. In conclusion, SPPA reveals increased clustering of early CNF loss and substantially improves its detection when combined with a conventional CCM measure in patients with recently diagnosed type 2 diabetes.

Cohort profile: the German Diabetes Study (GDS)

Background

The German Diabetes Study (GDS) is a prospective longitudinal cohort study describing the impact of subphenotypes on the course of the disease. GDS aims at identifying prognostic factors and mechanisms underlying the development of related comorbidities.

Study design and methods

The study comprises intensive phenotyping within 12 months after clinical diagnosis, at 5-year intervals for 20 years and annual telephone interviews in between. Dynamic tests, including glucagon, mixed meal, intravenous glucose tolerance and hyperinsulinemic clamp tests, serve to assess beta-cell function and tissue-specific insulin sensitivity. Magnetic resonance imaging and multinuclei spectroscopy allow quantifying whole-body fat distribution, tissue-specific lipid deposition and energy metabolism. Comprehensive analyses of microvascular (nerve, eye, kidney) and macrovascular (endothelial, cardiorespiratory) morphology and function enable identification and monitoring of comorbidities. The GDS biobank stores specimens from blood, stool, skeletal muscle, subcutaneous adipose tissue and skin for future analyses including multiomics, expression profiles and histology. Repeated questionnaires on socioeconomic conditions, patient-reported outcomes as quality of life, health-related behavior as physical activity and nutritional habits are a specific asset of GDS. This study will recruit 3000 patients and a group of humans without familiy history of diabetes. 237 type 1 and 456 type 2 diabetes patients have been already included.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0374-9) contains supplementary material, which is available to authorized users.

Neuropad for the detection of cardiovascular autonomic neuropathy in patients with type 2 diabetes

BACKGROUND

Cardiovascular autonomic neuropathy (CAN) is a prevalent and neglected chronic complication of diabetes, with a large impact on morbidity and mortality. Part of the reason why it is not detected and treated opportunely is because of the complexity of the tests required for its diagnosis. We evaluated the Neuropad®, a test based on sudomotor function, as a screening tool for CAN in adult patients with type 2 diabetes in Bogotá, Colombia.

METHODS

This was a cross-sectional evaluation of Neuropad® for the detection of CAN. Patients were 20-75years of age and did not suffer from any other type of neuropathy. CAN was diagnosed using the Ewing battery of tests for R-R variability during deep breathing, Valsalva and lying-to-standing maneuvers. Additionally, distal symmetric polyneuropathy (DSP) was diagnosed using a sign-based scale (Michigan Neuropathy Disability Score - NDS) and a symptom-based score (Total Symptom Score - TSS). The primary outcome was the sensitivity and specificity of the Neuropad® for the diagnosis of CAN, and secondary outcomes were the sensitivity and specificity of Neuropad® for DSP.

RESULTS

We studied 154 patients (74 men and 80 women). Prevalence of CAN was extremely high (68.0% of study participants), but also DSP was prevalent, particularly according to the signs-based definition (45%). The sensitivity of the Neuropad® for any degree of CAN was 70.1%, being slightly higher for the deep breathing and Valsalva tests than for lying-to-standing. The specificity of the Neuropad® for any type of CAN was only 37.0%, as expected for a screening exam. The negative predictive value was higher for the deep breathing and Valsalva tests (69.4 and 81.6%, respectively). Neuropad showed also a good sensitivity and negative predictive value for DSP. The sensitivity and specificity of Neuropad were better among men, and among patients with diabetes duration above the group median.

CONCLUSIONS

The Neuropad is a simple and inexpensive device that demonstrated an adequate performance as a screening tool for cardiovascular autonomic neuropathy in Latin American patients with DM2.

Automated Quantification of Neuropad Improves Its Diagnostic Ability in Patients with Diabetic Neuropathy

Neuropad is currently a categorical visual screening test that identifies diabetic patients at risk of foot ulceration. The diagnostic performance of Neuropad was compared between the categorical and continuous (image-analysis (Sudometrics)) outputs to diagnose diabetic peripheral neuropathy (DPN). 110 subjects with type 1 and 2 diabetes underwent assessment with Neuropad, Neuropathy Disability Score (NDS), peroneal motor nerve conduction velocity (PMNCV), sural nerve action potential (SNAP), Deep Breathing-Heart Rate Variability (DB-HRV), intraepidermal nerve fibre density (IENFD), and corneal confocal microscopy (CCM). 46/110 patients had DPN according to the Toronto consensus. The continuous output displayed high sensitivity and specificity for DB-HRV (91%, 83%), CNFD (88%, 78%), and SNAP (88%, 83%), whereas the categorical output showed high sensitivity but low specificity. The optimal cut-off points were 90% for the detection of autonomic dysfunction (DB-HRV) and 80% for small fibre neuropathy (CNFD). The diagnostic efficacy of the continuous Neuropad output for abnormal DB-HRV (AUC: 91%, P = 0.0003) and CNFD (AUC: 82%, P = 0.01) was better than for PMNCV (AUC: 60%). The categorical output showed no significant difference in diagnostic efficacy for these same measures. An image analysis algorithm generating a continuous output (Sudometrics) improved the diagnostic ability of Neuropad, particularly in detecting autonomic and small fibre neuropathy.

New vistas in the diagnosis of diabetic polyneuropathy

New modalities are now available to improve the diagnosis of diabetic polyneuropathy (DPN). The present review discusses the progress achieved in this area. First, the minimal diagnostic criteria have been better clarified. Moreover, there are now new bedside tests available, such as the indicator test Neuropad, NeuroQuick, Ipswich Touch Test (IpTT), Vibratip, NC-stat(®)/DPNCheck™ for automated nerve conduction study (NCS), tactile circumferential discriminator, steel ball-bearing, and SUDOSCAN(®), while more sophisticated modalities include skin biopsy and corneal confocal microscopy (CCM). Some tests can be used as screening tools, including primary care setting (Neuropad, IpTT, Vibratip, automated NCS), while others are more suitable for research, including evaluation of DPN in prospective studies (CCM, skin biopsy). Importantly, there is some evidence of earlier DPN diagnosis with the aid of some tests (Neuropad, skin biopsy, CCM). Further advantages provided by different tests are educational value and self-examination. Thus far, the potential of these tests has not been fully utilised. In particular, they have not been validated against standardised clinical examination scores in terms of predicting foot ulcers and amputations. Hence, it now remains to investigate the potential benefits from the widespread use of these tests for earlier and easier diagnosis of DPN in the everyday clinic.

The diagnostic accuracy of Neuropad for assessing large and small fibre diabetic neuropathy

AIMS

Neuropad is a simple visual indicator test, with moderate diagnostic performance for diabetic peripheral neuropathy. As it assesses sweating, which is a measure of cholinergic small nerve fibre function, we compared its diagnostic performance against established measures of both large and, more specifically, small fibre damage in patients with diabetes.

METHODS

One hundred and twenty-seven participants (89 without diabetic peripheral neuropathy and 38 with) aged 57 ± 9.7 years underwent assessment with Neuropad, large nerve fibre assessments: Neuropathy Disability Score, vibration perception threshold, peroneal motor nerve conduction velocity; small nerve fibre assessments: neuropathy symptoms (Diabetic Neuropathy Symptoms score) corneal nerve fibre length and warm perception threshold.

RESULTS

Neuropad has a high sensitivity but moderate specificity against large fibre neuropathy assessments: Neuropathy Disability Score (> 2) 70% and 50%, vibration perception threshold (> 14 V) 83% and 53%, and peroneal motor nerve conduction velocity (< 42 m/s) 81% and 54%, respectively. However, the diagnostic accuracy of Neuropad was significantly improved against corneal nerve fibre length (< 14 mm/mm2) with a sensitivity and specificity of 83% and 80%, respectively. Furthermore, the area under the curve for corneal nerve fibre length (85%) was significantly greater than with the Neuropathy Disability Score (66%, P = 0.01) and peroneal motor nerve conduction velocity (70%, P = 0.03). For neuropathic symptoms, sensitivity was 78% and specificity was 60%.

CONCLUSIONS

The data show the improved diagnostic performance of Neuropad against corneal nerve fibre length. This study underlines the importance of Neuropad as a practical diagnostic test for small fibre neuropathy in patients with diabetes.

Early detection of nerve fiber loss by corneal confocal microscopy and skin biopsy in recently diagnosed type 2 diabetes

We sought to determine whether early nerve damage may be detected by corneal confocal microscopy (CCM), skin biopsy, and neurophysiological tests in 86 recently diagnosed type 2 diabetic patients compared with 48 control subjects. CCM analysis using novel algorithms to reconstruct nerve fiber images was performed for all fibers and major nerve fibers (MNF) only. Intraepidermal nerve fiber density (IENFD) was assessed in skin specimens. Neurophysiological measures included nerve conduction studies (NCS), quantitative sensory testing (QST), and cardiovascular autonomic function tests (AFTs). Compared with control subjects, diabetic patients exhibited significantly reduced corneal nerve fiber length (CNFL-MNF), fiber density (CNFD-MNF), branch density (CNBD-MNF), connecting points (CNCP), IENFD, NCS, QST, and AFTs. CNFD-MNF and IENFD were reduced below the 2.5th percentile in 21% and 14% of the diabetic patients, respectively. However, the vast majority of patients with abnormal CNFD showed concomitantly normal IENFD and vice versa. In conclusion, CCM and skin biopsy both detect nerve fiber loss in recently diagnosed type 2 diabetes, but largely in different patients, suggesting a patchy manifestation pattern of small fiber neuropathy. Concomitant NCS impairment points to an early parallel involvement of small and large fibers, but the precise temporal sequence should be clarified in prospective studies.

A simple plaster for screening for diabetic neuropathy: a diagnostic test accuracy systematic review and meta-analysis

OBJECTIVE

Neuropad is an adhesive indicator test applied at the plantar surface of the foot that detects sweating through color change. We examined the diagnostic accuracy of this simple plaster as triage test for screening for clinically relevant diabetic sensorimotor polyneuropathy in adult outpatients with type 1 or type 2 diabetes.

MATERIALS/METHODS

Systematic review and meta-analysis of diagnostic accuracy studies. We searched Medline, Embase, Cochrane Library, Biosis Previews, Web of Science, Scopus and gray literature without date or language restrictions. We pooled estimates of sensitivity and specificity, and fitted hierarchical models to produce summary receiver operating characteristic curves. We assessed methodological quality of included studies utilizing the Quality Assessment of Diagnostic Accuracy Studies 2 tool.

RESULTS

Eighteen studies with 3470 participants met the inclusion criteria. Average sensitivity and specificity were 86% (95% CI 79 to 91) and 65% (95% CI 51 to 76) respectively. Likelihood ratios (LRs) were LR+=2.44 and LR-=0.22. Subgroup analyses per reference standard utilized provided similar estimates. Most studies were at risk of bias for patient selection and use of index or reference test, and had concerns regarding applicability due to patient selection.

CONCLUSION

The adhesive indicator test has reasonable sensitivity and could be used for triage of diabetic neuropathy to rule out foot at risk. Patients who tested positive should be referred to specialized care to establish a definite diagnosis. There is insufficient evidence for effectiveness on patient-important outcomes and cost-effectiveness of implementation in the diagnostic pathway compared with the standard clinical examination.

Pronounced reduction of cutaneous Langerhans cell density in recently diagnosed type 2 diabetes

Immune-mediated processes have been implicated in the pathogenesis of diabetic polyneuropathy. Langerhans cells (LCs) are the sole dendritic cell type located in the healthy epidermis and exert tolerogenic immune functions. We aimed to determine whether alterations in cutaneous LC density and intraepidermal nerve fiber density (IENFD) are present in patients with recently diagnosed type 2 diabetes. Skin biopsy specimens from the distal leg from 96 type 2 diabetic patients and 75 healthy control subjects were used for quantification of LC density and IENFD. LCs and IENFs were labeled using immunohistochemistry. Nerve conduction studies, quantitative sensory testing, and neurological examination were used to assess peripheral nerve function. LC density was markedly reduced in the diabetic group compared with the control group, but did not correlate with reduced IENFD or peripheral nerve function. Multivariate linear regression analysis revealed a strong association between LC density and whole-body insulin sensitivity in women but not in men with diabetes. Prospective studies should establish whether the pronounced reduction of cutaneous LCs detected in recently diagnosed type 2 diabetes could promote a cutaneous immunogenic imbalance toward inflammation predisposing to polyneuropathy and foot ulcers.

Correlation between sudomotor function, sweat gland duct size and corneal nerve fiber pathology in patients with type 2 diabetes mellitus

AIMS/INTRODUCTION

To study the correlation between sudomotor function, sweat gland duct size and corneal nerve fiber pathology in type 2 diabetes.

MATERIALS AND METHODS

Sudomotor function was quantified by Neuropad test, and sweat gland duct and corneal nerve fibers were visualized by confocal microscopy in 78 patients with type 2 diabetes stratified by diabetic neuropathy and 28 control participants.

RESULTS

In patients with diabetic neuropathy, sudomotor function, as judged by the time required for complete color change of a Neuropad, was impaired compared with that of controls (P < 0.0001), thereby showing deterioration was related to the severity of diabetic neuropathy (P < 0.0001). Sweat gland ducts were smaller in patients without neuropathy than in controls (P < 0.0001), and further shrinking was seen in patients with severe diabetic neuropathy (P < 0.05). Patients without diabetic neuropathy showed reduced density and length (P < 0.001) of corneal nerve fibers and beading frequency (P < 0.0001), and increased tortuosity (P < 0.0001) compared with controls, and these changes deteriorated in patients with severe diabetic neuropathy. Sudomotor function was negatively associated with corneal nerve fibers (P < 0.002) and branches (P < 0.01), and influenced by the severity of diabetic neuropathy (P < 0.0001); sweat gland duct size correlated with serum triglycerides (P < 0.02), uric acid (P < 0.01), corneal nerve branch (P < 0.03), sudomotor function (P < 0.03) and severity of neuropathy (P < 0.03).

CONCLUSIONS

Type 2 diabetic patients had sudomotor dysfunction and smaller sweat gland ducts compared with controls. The stage of diabetic neuropathy and corneal nerve fiber pathology were independent predictors of sudomotor dysfunction, and serum triglycerides, uric acid, corneal nerve branch, stage of diabetic neuropathy and sudomotor function were predictors of sweat gland duct size.

Influence of peripheral arterial occlusive disease on the Neuropad(®) test performance in patients with diabetes

AIMS

The specificity of the Neuropad(®) test to screen for peripheral neuropathy is moderate, but this test has several advantages, such as self-use, educative value and good sensitivity. Use of the Neuropad is usually contra-indicated in the presence of peripheral arterial occlusive disease, a condition associated with skin dryness. The aim of this study was to assess the influence of peripheral arterial occlusive disease on the performance of the Neuropad for screening peripheral neuropathy, and to compare it with the monofilament test.

METHODS

We included 200 patients with diabetes. Peripheral neuropathy was defined by a neuropathy disability score ≥ 6. The Neuropad was determined as normal or abnormal at 10 and 20 min, respectively, and its performance was compared in patients with and without peripheral arterial occlusive disease diagnosed by colour duplex ultrasonography. The performances of the Neuropad and of the monofilament test were compared.

RESULTS

Prevalences of peripheral neuropathy and of peripheral arterial occlusive disease were 15.8 and 44%, respectively. At 10 min, sensitivity and negative predictive value were high (93.8 and 95.1%), while specificity and positive predictive value were poor (23.2 and 18.9%). The Neuropad performance was not significantly different between patients with and without arteriopathy. Between 10 and 20 min, there was significant loss of sensitivity and gain in specificity. The Neuropad at 10 min was more sensitive but less specific than the monofilament test.

CONCLUSIONS

The reliability of the Neuropad is not significantly different in the presence or absence of peripheral arterial occlusive disease.

A simple new non-invasive sweat indicator test for the diagnosis of diabetic neuropathy

A simple non-invasive indicator test (Neuropad(®)) has been developed for the assessment of sweating and, hence, cholinergic innervation in the diabetic foot. The present review summarizes current knowledge on this diagnostic test. The diagnostic ability of this test is based on a colour change from blue to pink at 10 min, with excellent reproducibility, which lends itself to patient self-examination. It has a high sensitivity (65.1-100%) and negative predictive value (63-100%), with moderate specificity (32-78.5%) and positive predictive value (23.3-93.2%) for the diagnosis of diabetic peripheral neuropathy. It also has moderate to high sensitivity (59.1-89%) and negative predictive value (64.7-91%), but low to moderate specificity (27-78%) and positive predictive value (24-48.6%) for the diagnosis of diabetic cardiac autonomic neuropathy. There are some data to suggest that Neuropad can detect early diabetic neuropathy, but this needs further evaluation. It remains to be established whether this test can predict foot ulceration and amputation, thereby contributing to the identification of high-risk patients.

Evaluation of the Neuropad sudomotor function test as a screening tool for polyneuropathy in the elderly population with diabetes and pre-diabetes: the KORA F4 survey

BACKGROUND

Neuropad is a novel indicator test for sudomotor dysfunction, which has not been validated as a screening tool in a population-based study. This study aimed to evaluate the utility of Neuropad as a screening tool for distal symmetric polyneuropathy among elderly subjects with diabetes and pre-diabetes in the general population.

METHODS

Eligible subjects aged 61-82 years (n = 940) from the KORA F4 survey were examined, 201 of whom had diabetes and 231 had pre-diabetes (WHO 1999 criteria). Polyneuropathy was defined by the Michigan Neuropathy Screening Instrument (MNSI) score >3.

RESULTS

Polyneuropathy was diagnosed in 60 (29.9%) subjects with diabetes and in 45 (19.5%) subjects with pre-diabetes, respectively (p = 0.013). The sensitivity and negative predictive value of Neuropad (reading time: 10 min) for the diagnosis of polyneuropathy were moderately high, reaching 76.7% and 78.1% in subjects with diabetes and 57.8% and 76.5% in those with pre-diabetes, respectively. Conversely, the specificity and positive predictive value for the diagnosis of polyneuropathy were rather low: 35.5% and 33.6% in diabetic individuals and 33.3% and 17.3% in subjects with pre-diabetes, respectively. Use of the >2 cut-off and MNSI combined with monofilament examination did not improve the diagnostic performance of Neuropad.

CONCLUSIONS

In the elderly general population with diabetes and pre-diabetes, Neuropad has reasonable sensitivity but rather low specificity for the diagnosis of polyneuropathy. It is a useful simple and inexpensive tool to screen for and to exclude polyneuropathy as desired, while its low specificity implies that a longer reading time merits consideration.

APOE gene polymorphisms and diabetic peripheral neuropathy

Genetic factors may influence the natural course of diabetic peripheral neuropathy and explain some of its variability. The aim of this review was to examine the association between apolipoprotein E (apoE) gene polymorphisms and diabetic peripheral neuropathy. Four relevant studies were identified. The two earlier works provided evidence that the ɛ4 allele is a risk factor for this complication, while the two more recent studies were negative. Important differences in the methodology used and in the populations included are obvious, rendering difficult the comparison between studies. In conclusion, the association between APOE gene polymorphisms and diabetic peripheral neuropathy is still unclear. Available evidence is rather limited and results have so far been contradictory. Future studies should employ more robust methodology, adjusting for potential confounders and for the prevalence of neuropathy in the general population with diabetes.

Quick and simple evaluation of sudomotor function for screening of diabetic neuropathy

Objective. The aim of this study was to compare SUDOSCAN, a new device to evaluate sweat function (reflecting peripheral small C-fiber status), with conventional measures of peripheral and cardiac neuropathy in patients with type 2 diabetes. Methods. 265 diabetic patients were tested for symptoms and clinical signs of neuropathy using Michigan Neuropathy Screening Instrument (MNSI), vibration perception threshold (VPT) using biothesiometer, and cardiac autonomic neuropathy (CAN) using Ewing's protocol. Sudomotor function was investigated with SUDOSCAN through measurement of electrochemical skin conductance (ESC) of hands and feet. Lower ESC is suggestive of sudomotor dysfunction. Results. Lower ESC at feet was significantly associated both with increasing symptoms (MNSI A) and increasing score on physical abnormalities (MNSI B). Lower ESC at feet was also significantly associated with increasing VPT by biothesiometry (P < 0.01), and with higher number of abnormal CAN results (P < 0.05). ESC was associated with postural fall in blood pressure (sympathetic abnormality) (P < 0.05), but not with heart rate variability (HRV) tests (parasympathetic abnormalities). Conclusions. Sudomotor dysfunction testing may be a simple test to alert physicians to peripheral nerve and cardiac sympathetic dysfunction. Ease of performance could make it useful in a busy diabetic clinic. Further studies with hard clinical outcomes are indicated.

Increased serum levels of uric acid are associated with sudomotor dysfunction in subjects with type 2 diabetes mellitus

The aim of this paper was to assess serum uric acid (SUA) levels in patients with type 2 diabetes mellitus (T2DM) with or without sudomotor dysfunction (evaluated by the Neuropad test). We included 36 T2DM patients with sudomotor dysfunction (group A: mean age 63.1 ± 2.6 years) and 40 age-, gender-, renal function- and T2DM duration-matched patients without sudomotor dysfunction (group B: mean age 62.1 ± 3.1 years). SUA was significantly higher in group A (P < 0.001). There was a significant correlation between SUA and Neuropad time to colour change in both groups (group A: r_s = 0.819, P < 0.001; group B: r_s = 0.774, P < 0.001). There was also a significant positive correlation between SUA and CRP in both groups (group A: r_s = 0.947, P < 0.001; group B: r_s = 0.848, P < 0.001). In conclusion, SUA levels were higher in T2DM patients with sudomotor dysfunction than those without this complication. The potential role of SUA in sudomotor dysfunction merits further study.