Painful and Painless Diabetic Neuropathies: What Is the Difference?

Efficacy and Safety of Trazodone and Gabapentin Fixed-Dose Combination in Patients Affected by Painful Diabetic Neuropathy: Randomized, Controlled, Dose-Finding Study

INTRODUCTION

Up to 50% of diabetic patients with neuropathy suffer from chronic pain, namely painful diabetic neuropathy (PDN), an unmet medical need with significant impact on quality of life. Gabapentin is widely used for PDN, albeit with frequent dose-limiting effects. Trazodone, an antidepressant with multi-modal action, has shown promising results when given at low doses as an add-on to gabapentin. Upon previous clinical trials and experimental evidence, a fixed-dose combination (FDC) of both compounds, at low doses, was developed for neuropathic pain.

METHODS

This was a phase II, randomized, double-blind, placebo and reference controlled, dose-finding, multicenter, international, prospective study. Male and female diabetic patients aged 18-75 years and affected by PDN were eligible for enrolment. Patients were randomized (1:1:1:1:2 ratio) to trazodone and gabapentin (Trazo/Gaba) 2.5/25 mg t.i.d. for 8 weeks, Trazo/Gaba 5/50 mg t.i.d. for 8 weeks, Trazo/Gaba 10/100 mg t.i.d. for 8 weeks, gabapentin (Gaba), or placebo (PLB). The aim of the study was to collect preliminary information on the effect of the 3 different FDCs of Trazo/Gaba on pain intensity based on the 11-point numeric rating score (NRS) after 8 weeks of treatment. The secondary objectives were the evaluation of the percentage of responders, neuropathic pain symptoms, anxiety, sleep, quality of life, safety, and tolerability. The primary efficacy endpoint was evaluated with last observation carried out forward (LOCF), using an analysis of covariance (ANCOVA), including treatment and centers as factors and baseline as covariate and applying linear contrast test, excluding the active treatment. Only if the linear contrast test was significant (p < 0.05), the step-down Dunnett test would be used to determine the minimum effective dose significantly different from PLB. If linearity was not verified, an adjusted ANCOVA model and comparisons with Dunnett test were performed. Before the application of the ANCOVA model, the non-significance of interaction treatment per baseline was verified.

RESULTS

A total of 240 patients were included in the modified intention-to-treat (m-ITT) population: 39 in Trazo/Gaba 2.5/25 mg, 38 in Trazo/Gaba 5/50 mg, 37 in Trazo/Gaba 10/100 mg, 83 in PLB, and 43 in Gaba. After 8 weeks of treatment, changes of the average daily pain score based on the 11-point NRS from baseline were - 2.52 ± 2.31 in Trazo/Gaba 2.5/25 mg group, - 2.24 ± 1.96 in Trazo/Gaba 5/50 mg group, - 2.46 ± 2.12 in Trazo/Gaba 10/100 mg group, - 1.92 ± 2.21 in Gaba group, and - 2.02 ± 1.95 in the PLB group. The linear contrast test did not result in significant differences (p > 0.05) among treatment groups. Consequently, the minimum effective dose against PLB was not determined. The multiple comparison with Dunnett adjustment did not show any statistically significant differences vs. PLB after 8 weeks of treatment: Trazo/Gaba 2.5/25 mg (95% confidence interval (CI) - 1.2739, 0.2026; p = 0.1539); Trazo/Gaba 5/50 mg (95% CI - 0.9401, 0.5390; p = 0.5931); Trazo/Gaba 10/100 mg (95% CI - 1.0342, 0.4582; p = 0.4471). However, patients receiving the lowest dose of Trazo/Gaba 2.5/25 mg showed a statistically significant difference to PLB after 6 weeks of treatment (95% CI - 1.6648, - 0.2126; p = 0.0116). Positive results were also found for responder patients, other items related to the pain, anxiety, depression, sleep, and quality of life, consistently in favor to the lowest Trazo/Gaba FDC. Two serious adverse events (SAEs) occurred but were judged unrelated to the study treatment. Treatment-emergent adverse events (TEAEs) were mainly mild-to-moderate in intensity and involved primarily nervous system, gastrointestinal disorders, and investigations.

CONCLUSIONS

The primary end point of the study was the change from baseline of the average daily pain score based on the 11-point NRS after 8 weeks of treatment. While the primary endpoint was not reached, patients treated with Trazo/Gaba 2.5/25 mg t.i.d. showed statistically significant improvement of pain and other scores after 6 weeks and reported consistent better results in comparison to PLB on primary and secondary endpoints for the overall study duration. According to these results, the lowest dose of Trazo/Gaba FDC may be the best candidate for further clinical development to confirm the potential benefits of the FDC drug for this condition.

CLINICAL TRIAL REGISTRATION

NCT03749642.

Eleven neurology-related proteins measured in serum are positively correlated to the severity of diabetic neuropathy

About 20% of patients with diabetes suffer from chronic pain with neuropathic characteristics. We investigated the multivariate associations between 92 neurology-related proteins measured in serum from 190 patients with painful and painless diabetic neuropathy. Participants were recruited from the Pain in Neuropathy Study, an observational cross-sectional multicentre study in which participants underwent deep phenotyping. In the exploration cohort, two groups were defined by hierarchical cluster analyses of protein data. The proportion of painless vs painful neuropathy did not differ between the two groups, but one group had a significantly higher grade of neuropathy as measured by the Toronto Clinical Scoring System (TCSS). This finding was replicated in the replication cohort. Analyzing both groups together, we found that a group of 11 inter-correlated proteins (TNFRSF12A, SCARB2, N2DL-2, SKR3, EFNA4, LAYN, CLM-1, CD38, UNC5C, GFR-alpha-1, and JAM-B) were positively associated with TCSS values. Notably, EFNA4 and UNC5C are known to be part of axon guidance pathways. To conclude, although cluster analysis of 92 neurology-related proteins did not distinguish painful from painless diabetic neuropathy, we identified 11 proteins which positively correlated to neuropathy severity and warrant further investigation as potential biomarkers.

Correlations between distal sensorimotor polyneuropathy and cardiovascular complications in diabetic patients in the North-Eastern region of Hungary

Distal sensorimotor polyneuropathy (DSPN) is the earliest detectable and the most frequent microvascular complication in diabetes mellitus. Several studies have previously demonstrated correlations between cardiovascular risk factors in diabetic patients and independent risk factors for diabetic neuropathy. Our objective was to retrospectively analyze data from diabetic patients in the North-East region of Hungary who underwent neuropathy screening at the Diabetic Neuropathy Center, University of Debrecen, between 2017 and 2021. We aimed to investigate the correlations between cardiovascular risk factors and microvascular complications among patients with DSPN. The median age of the patients was 67 years, 59,6% were female, and 91,1% had type 2 diabetes. The prevalence of DSPN among the study subjects was 71.7%. A significantly longer duration of diabetes (p<0.01) was noted in patients with DSPN. Those with DSPN demonstrated a significantly higher HbA1c level (p<0.001) and a greater frequency of insulin use (p = 0.001). We observed a significantly elevated albumin/creatinine ratio (p<0.001) and a significantly lower eGFR (p<0.001) in patients with DSPN. Diabetic retinopathy exhibited a significantly higher prevalence in patients with DSPN (p<0.001). A higher prevalence of myocardial infarction (p<0.05), ischemic heart disease (p<0.001), peripheral arterial disease (p<0.05) and a history of atherosclerosis (p<0.05) was observed in patients with DSPN. In a multivariate logistic regression analysis, the following factors were independently associated with the presence of DSPN: higher HbA1c (OR:2.58, 95% CI:1.89-3.52, p<0.001), age (OR:1.03, 95% CI:1.01-1.05, p = 0.006), albumin/creatinine ratio above 3 mg/mmol (OR:1.23, 95% CI:1.06-1.45, p = 0.008), retinopathy (OR:6.06, 95% CI:1.33-27.53, p = 0.02), and composite cardiovascular endpoint (OR:1.95, 95% CI:1.19-3.19, p = 0.008). Our study revealed that age, elevated HbA1c levels, significant albuminuria, retinopathy, and cardiovascular complications may increase the risk of DSPN. Further investigation of these associations is necessary to understand the impact of patient characteristics during the treatment of diabetic neuropathy.

Factors correlating to decisions for prescribing pharmacological treatment and referrals in suspected peripheral neuropathy cases in chat consultation-based application

Introduction

Since the COVID-19 pandemic, there has been increasing use ofchat-based telemedicine, including for patients with neuropathy complaints. It is imperative to learn how to effectively use telemedicine. This study describes the characteristics of patients with neuropathy complaints in chat-based telemedicine services in Indonesia and their influence on treatment decisions and referrals.

Methods

This is a retrospective cross-sectional study during the COVID-19 pandemic era (March 2020 to December 2021) using anonymous secondary data from patient chat databases on Indonesian application-based telemedicine services (Halodoc, Alodokter, Good Doctor, and Milvik). We applied bivariate and multivariate analysis.

Results

We obtained 1051 patients with suspected peripheral nerve complaints (4 per 10,000) from a total of 2,199,527 user consultations, with the majority being 40-64 years old females and diabetes mellitus was the leading comorbid (90.7%). Most patients received treatment (90.7%) and only 11.4% patients were referred. Multivariate analysis showed that treatment was more likely to be given by a neurologist (p < 0.01). Chronic symptoms (p < 0.01) and previous laboratory/other tests (p = 0.01) decreased the likelihood of medication prescription. Referrals were more likely to be given to chronic onset (p = 0.02), hypertension and heart disease (p < 0.01), and previous laboratory/other tests (p = 0.02). The opposite was true for age≥65 years, female (p = 0.04), and neurologists or other specialists as responders (p < 0.01).

Conclusion

We identified several factors that influence the treatment decision such as female patients and onset. Meanwhile, age, sex, chronic symptoms, history of hypertension and heart disease, and previous laboratory/other tests may influence the referral decisions. General practitioners were more likely to refer the patients whereas neurologists or other specialists were more likely to give treatment. Chat-based telemedicine services can still be developed in the future to be better.

Comparison of the efficacy of spinal cord stimulation and dorsal root ganglion stimulation in the treatment of painful diabetic peripheral neuropathy: a prospective, cohort-controlled study

Objective

The aim of this study was to compare the clinical outcomes of spinal cord stimulation (SCS) and dorsal root ganglion stimulation (DRG-S) in the treatment of painful diabetic peripheral neuropathy (PDPN).

Methods

In this prospective cohort study, 55 patients received dorsal column spinal cord stimulation (SCS group) and 51 patients received dorsal root spinal cord stimulation (DRG-S group). The primary outcome was a Numerical Rating Scale (NRS) remission rate of ≥50%, and secondary outcomes included the effects of SCS and DRG-S on quality of life scores (EQ-5D-3L), nerve conduction velocity, and HbA1c, respectively.

Results

The percentage of NRS remission rate ≥ 50% at 6 months was 80.43 vs. 79.55%, OR (95% CI): 1.06 (0.38-2.97) in the SCS and DRG-S groups, respectively, and the percentage of VAS remission rate ≥ 50% at 12 months was 79.07 vs. 80.95%, OR (95% CI): 0.89 (0.31-2.58). Compared with baseline, there were significant improvements in EQ-5D and EQ-VAS at 6 and 12 months (p < 0.05), but there was no difference in improvement between the SCS and DRG-S groups (p > 0.05). Nerve conduction velocities of the common peroneal, peroneal, superficial peroneal, and tibial nerves were significantly improved at 6 and 12 months compared with the preoperative period in both the SCS and PND groups (p < 0.05). However, at 6 and 12 months, there was no difference in HbA1c between the two groups (p > 0.05).

Conclusion

Both SCS and DRG-S significantly improved pain, quality of life, and lower extremity nerve conduction velocity in patients with PDPN, and there was no difference between the two treatments at 12 months.

4. Painful diabetic polyneuropathy

INTRODUCTION

Pain as a symptom of diabetic polyneuropathy (DPN) significantly lowers quality of life, increases mortality and is the main reason for patients with diabetes to seek medical attention. The number of people suffering from painful diabetic polyneuropathy (PDPN) has increased significantly over the past decades.

METHODS

The literature on the diagnosis and treatment of diabetic polyneuropathy was retrieved and summarized.

RESULTS

The etiology of PDPN is complex, with primary damage to peripheral nociceptors and altered spinal and supra-spinal modulation. To achieve better patient outcomes, the mode of diagnosis and treatment of PDPN evolves toward more precise pain-phenotyping and genotyping based on patient-specific characteristics, new diagnostic tools, and prior response to pharmacological treatments. According to the Toronto Diabetic Neuropathy Expert Group, a presumptive diagnosis of "probable PDPN" is sufficient to initiate treatment. Proper control of plasma glucose levels, and prevention of risk factors are essential in the treatment of PDPN. Mechanism-based pharmacological treatment should be initiated as early as possible. If symptomatic pharmacologic treatment fails, spinal cord stimulation (SCS) should be considered. In isolated cases, where symptomatic pharmacologic treatment and SCS are unsuccessful or cannot be used, sympathetic lumbar chain neurolysis and/or radiofrequency ablation (SLCN/SLCRF), dorsal root ganglion stimulation (DRGs) or posterior tibial nerve stimulation (PTNS) may be considered. However, it is recommended that these treatments be applied only in a study setting in a center of expertise.

CONCLUSIONS

The diagnosis of PDPN evolves toward pheno-and genotyping and treatment should be mechanism-based.

Improvement in Protective Sensation: Clinical Evidence From a Randomized Controlled Trial for Treatment of Painful Diabetic Neuropathy With 10 kHz Spinal Cord Stimulation

BACKGROUND

Painful diabetic neuropathy (PDN) can result in the loss of protective sensation, in which people are at twice the likelihood of foot ulceration and three times the risk of lower extremity amputation. Here, we evaluated the long-term effects of high-frequency (10 kHz) paresthesia-independent spinal cord stimulation (SCS) on protective sensation in the feet and the associated risk of foot ulceration for individuals with PDN.

METHODS

The SENZA-PDN clinical study was a randomized, controlled trial in which 216 participants with PDN were randomized to receive either conventional medical management (CMM) alone or 10 kHz SCS plus CMM, with optional treatment crossover after 6 months. At study visits (baseline through 24 months), 10-g monofilament sensory assessments were conducted at 10 locations per foot. Two published methods were used to evaluate protective sensation via classifying risk of foot ulceration.

RESULTS

Participants in the 10 kHz SCS group reported increased numbers of sensate locations as compared to CMM alone (P < .001) and to preimplantation (P < .01) and were significantly more likely to be at low risk of foot ulceration using both classification methods. The proportion of low-risk participants approximately doubled from preimplantation to 3 months postimplantation and remained stable through 24 months (P ≤ .01).

CONCLUSIONS

Significant improvements were observed in protective sensation from preimplantation to 24 months postimplantation for the 10 kHz SCS group. With this unique, disease-modifying improvement in sensory function, 10 kHz SCS provides the potential to reduce ulceration, amputation, and other severe sequelae of PDN.

TRIAL REGISTRATION

The SENZA-PDN study is registered on ClinicalTrials.gov with identifier NCT03228420.

Novel drugs affecting diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) poses a significant threat, affecting half of the global diabetic population and leading to severe complications, including pain, impaired mobility, and potential amputation. The delayed manifestation of diabetic neuropathy (DN) makes early diagnosis challenging, contributing to its debilitating impact on individuals with diabetes mellitus (DM). This review examines the multifaceted nature of DPN, focusing on the intricate interplay between oxidative stress, metabolic pathways, and the resulting neuronal damage. It delves into the challenges of diagnosing DN, emphasizing the critical role played by hyperglycemia in triggering these cascading effects. Furthermore, the study explores the limitations of current neuropathic pain drugs, prompting an investigation into a myriad of pharmaceutical agents tested in both human and animal trials over the past decade. The methodology scrutinizes these agents for their potential to provide symptomatic relief for DPN. The investigation reveals promising results from various pharmaceutical agents tested for DPN relief, showcasing their efficacy in ameliorating symptoms. However, a notable gap persists in addressing the underlying problem of DPN. The results underscore the complexity of DPN and the challenges in developing therapies that go beyond symptomatic relief. Despite advancements in treating DPN symptoms, there remains a scarcity of options addressing the underlying problem. This review consolidates the state-of-the-art drugs designed to combat DPN, highlighting their efficacy in alleviating symptoms. Additionally, it emphasizes the need for a deeper understanding of the diverse processes and pathways involved in DPN pathogenesis.

Serum levels of endocannabinoids and related lipids in painful vs painless diabetic neuropathy: results from the Pain in Neuropathy Study

ABSTRACT

N-arachidonoylethanolamine (also known as anandamide) and 2-arachidonoylglycerol are activators of the cannabinoid receptors. The endocannabinoid system also includes structurally and functionally related lipid mediators that do not target cannabinoid receptors, such as oleoylethanolamide, palmitoylethanolamide, and stearoylethanolamide. These bioactive lipids are involved in various physiological processes, including regulation of pain. The primary aim of the study was to analyze associations between serum levels of these lipids and pain in participants in the Pain in Neuropathy Study, an observational, cross-sectional, multicentre, research project in which diabetic patients with painless or painful neuropathy underwent deep phenotyping. Our hypothesis was that painful neuropathy would be associated with higher levels of the 5 lipids compared with painless neuropathy. Secondary aims were to analyze other patient-reported outcome measures and clinical data in relationship to lipid levels. The lipid mediators were analyzed in serum samples using liquid chromatography tandem mass spectrometry (LC-MS/MS). Serum levels of anandamide were significantly higher in the painful group, but the effect size was small (Cohen d = 0.31). Using cluster analysis of lipid data, patients were dichotomized into a "high-level" endocannabinoid group and a "low-level" group. In the high-level group, 61% of patients had painful neuropathy, compared with 45% in the low-level group ( P = 0.039). This work is of a correlative nature only, and the relevance of these findings to the search for analgesics targeting the endocannabinoid system needs to be determined in future studies.

Painful Diabetic Neuropathy: The Need for New Approaches

Painful diabetic neuropathy is a common vexing problem for people with diabetes and a costly problem for society. The pathophysiology is not well understood, and no safe and effective mechanistically-based treatment has been identified. Poor glycemic control is a risk factor for painful diabetic neuropathy. Excessive intraneuronal glucose in people with diabetes can be shunted away from physiological glycolysis into multiple pathological pathways associated with neuropathy and pain. The first three treatments that are traditionally offered consist of risk factor reduction, lifestyle modifications, and pharmacological therapy, which includes only three drugs that are approved for this indication by the United States Food and Drug Administration. All of these traditional treatments are often inadequate for relieving neuropathic pain, and thus, new approaches are needed. Modern devices based on neuromodulation technology, which act directly on the nervous system, have been recently cleared by the United States Food and Drug Administration for painful diabetic neuropathy and offer promise as next-in-line therapy when traditional therapies fail.

Impact of diabetic peripheral neuropathy on gait abnormalities in patients with type 2 diabetes mellitus

Background

Many patients with type 2 diabetes (T2DM) suffer from diabetic peripheral neuropathy (DPN) and impaired muscle coordination. These changes may lead to walking instability, and gait abnormalities resulting in increased fall risk and lower limb amputations. The aim of this study was to assess the impact of DPN and patient footwear on the gait in patients with diabetes, in addition to Comparing the peak plantar pressure (PPP) in patients with and without DPN and assessing its association with gait abnormalities.

Methodology

This is an observational case-control study. Forty Subjects with T2DM were divided into two age and sex-matched groups, 20 subjects each. Group A: subjects with DPN. Group B: subjects without DPN. All study participants were subjected to a thorough history taking, clinical examinations focusing on detailed foot examination, PPP assessment, and functional gait evaluation.

Results

The results obtained in this study showed a median gait assessment score of 21 (17.0-22.5) for group A and 26 (23.5-26.0) for group B which was statistically significant (p < 0.001). There was no statistically significant difference between both groups (p > 0.05) regarding the assessment of footwear appropriateness. Comparing the PPP measurement among both studied groups, the prevalence of an elevated PPP was 80% in group A compared to 65% in group B, which was statistically non-significant, p = 0.288.

Conclusions

Gait abnormalities are common among patients with T2DM even in the absence of DPN. However, the presence of DPN was the strongest independent risk factor for gait abnormalities among the studied factors.

Adaptive Autonomic and Neuroplastic Control in Diabetic Neuropathy: A Narrative Review

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a worldwide socioeconomic burden, and is accompanied by a variety of metabolic disorders, as well as nerve dysfunction referred to as diabetic neuropathy (DN). Despite a tremendous body of research, the pathogenesis of DN remains largely elusive. Currently, two schools of thought exist regarding the pathogenesis of diabetic neuropathy: a) mitochondrial-induced toxicity, and b) microvascular damage. Both mechanisms signify DN as an intractable disease and, as a consequence, therapeutic approaches treat symptoms with limited efficacy and risk of side effects.

OBJECTIVE

Here, we propose that the human body exclusively employs mechanisms of adaptation to protect itself during an adverse event. For this purpose, two control systems are defined, namely the autonomic and the neural control systems. The autonomic control system responds via inflammatory and immune responses, while the neural control system regulates neural signaling, via plastic adaptation. Both systems are proposed to regulate a network of temporal and causative connections which unravel the complex nature of diabetic complications.

RESULTS

A significant result of this approach infers that both systems make DN reversible, thus opening the door to novel therapeutic applications.

Relationship of PIEZO1 and PIEZO2 vascular expression with diabetic neuropathy

Introduction: Diabetic distal symmetric polyneuropathy (DDSP) is the most prevalent form of diabetic peripheral neuropathy, and 25% of patients develop pain in their toes. DDSP is associated with increased cutaneous microvessel density (MVD), reduced skin blood flow, endothelial dysfunction, and impaired fluid filtration with vasodilation. The Piezo family of mechanosensitive channels is known to be involved in the control of vascular caliber by converting mechanical force into intracellular signals. Furthermore, Piezo2 is particularly involved in peripheral pain mechanisms of DDSP patients. To date, very little is known about the number, structure, and PIEZO expression in cutaneous blood vessels (BVs) of individuals with DDSP and their relation with pain and time span of diabetes. Methods and results: We studied microvessels using endothelial markers (CD34 and CD31) and smooth cell marker (α-SMA) by indirect immunohistochemical assay in sections of the glabrous skin of the toes from patients and controls. MVD was assessed through CD34 and CD31 immunoreaction. MVD determined by CD34 is higher in short-term DDSP patients (less than 15 years of evolution), regardless of pain. However, long-term DDSP patients only had increased BV density in the painful group for CD31. BVs of patients with DDSP showed structural disorganization and loss of shape. The BVs affected by painful DDSP underwent the most dramatic structural changes, showing rupture, leakage, and abundance of material that occluded the BV lumen. Moreover, BVs of DDSP patients displayed a Piezo1 slight immunoreaction, whereas painful DDSP patients showed an increase in Piezo2 immunoreaction. Discussion: These results suggest that alterations in the number, structure, and immunohistochemical profile of specific BVs can explain the vascular impairment associated with painful DDSP, as well as the temporal span of diabetes. Finally, this study points out a possible correlation between increased vascular Piezo2 immunostaining and pain and decreased vascular Piezo1 immunostaining and the development of vasodilation deficiency.

Acupuncture for painful diabetic peripheral neuropathy: a systematic review and meta-analysis

Background

Painful Diabetic Peripheral Neuropathy (PDPN) is a common complication of diabetes, it severely affects the quality of life of patients. Acupuncture has been shown to be effective in the treatment of PDPN. To evaluate the efficacy and safety of acupuncture for pain relief in patients diagnosed with diabetic peripheral neuropathy, we conducted a systematic review and meta-analysis.

Method

We thoroughly searched specific databases, which included PUBMED, EMBASE, Web of Science, the Cochrane Library, the Chinese Biomedical Literature Database, the Chinese National Knowledge Infrastructure, China Science and Technology Journal Database and the Wanfang Data. All randomized controlled trials of acupuncture therapy for PDPN with pain change scales were included. Included studies were assessed for methodological quality according to the risk of bias from the Cochrane handbook. Meta-analyses were carried out to analyze the outcomes, subgroup analyses, sensitivity analyses, and funnel plot analyses were undertaken.

Results

This systematic review evaluated a total of 25 trials of acupuncture therapy in combination with conventional treatment, involving a total of 1,561 patients with PDPN. According to the results, among 16 trials using VAS scores with a total of 1,552 patients, 2 acupoint injection trials (MD -2.38, 95% CI: -2.76 to -2.01, p < 0.00001), 12 acupuncture trials (MD -1. 31, 95% CI: -1.60 to -1.02, p < 0.00001) and 2 moxibustion trials showed that acupuncture therapy combined with conventional treatment improved pain better than conventional treatment (MD -2.50, 95% CI: -2.76 to -2.24, p < 0.00001). In the subgroup analysis of the acupuncture group, the results of the 5 trials in which the location of acupuncture was only in the limbs (MD -1.27, 95% CI: -1.54 to -1.01, p < 0.00001) and the 7 trials both in limbs and torso (MD -1.38, 95% CI: -1.81 to -0.95, p < 0.00001) also demonstrated that acupuncture was effective in pain improvement.

Conclusion

This meta-analysis analyzed the possible efficacy of acupuncture in combination with conventional treatment for pain in diabetic peripheral neuropathy, particularly when acupoints are located in the limbs. However, there are limitations to this meta-analysis and future clinical studies are needed to confirm these findings.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023449447, identifier (CRD42023449447).

BTD: A TRPC5 activator ameliorates mechanical allodynia in diabetic peripheral neuropathic rats by modulating TRPC5-CAMKII-ERK pathway

Mechanical allodynia is a serious complication of painful diabetic neuropathy (PDN) with limited treatment options. The transient receptor potential canonical 5 (TRPC5) channel is a promising target in pain; however, its role in painful diabetic neuropathy has not yet been elucidated. In this study, we have investigated the role of TRPC5 channels using BTD [N-{3-(adamantan-2-yloxy)-propyl}-3-(6-methyl-1,1-dioxo-2H-1λ6,2,4-benzothiadiazin-3-yl)-propanamide)],a potent TRPC5 activator and HC070, as TRPC5 channel inhibitor in rat model of PDN. In this study, streptozotocin was used to induce diabetes in male Sprague-Dawley rats. The alterations in mechanical and thermal pain thresholds, nerve functional deficits in diabetic animals were assessed by various behavioral and functional parameters.TRPC5 involvement was investigated by treating neuropathic rats with BTD, TRPC5 channel activator (1 and 3 mg/kg, i.p. for 14 days) and HC070, a TRPC5 channel inhibitor (1 and 3 mg/kg). BTD and HC070 effects in pain reduction were assessed by western blotting, estimating oxidative stress and inflammatory markers in the lumbar spinal cord. BTD treatment (3 mg/kg, i.p.) once daily for 14 days ameliorated mechanical allodynia but not thermal hyposensation or nerve functional deficit in diabetic neuropathic rats. BTD treatment down-regulated TRPC5 expression by increasing the activity of protein kinase C. It also subsequently down-regulated the downstream pain markers (CAMKII, ERK) in the spinal cord. Additionally, a decrease in inflammatory cytokines (TNF-α, IL-6) also demonstrated BTD's potent anti-inflammatory properties in reducing mechanical allodynia. On the other hand, HC070 did not exert any beneficial effects on behavioural and nerve functional parameters. The study concludes that BTD ameliorated mechanical allodynia in a rat model of painful diabetic neuropathy not only through modulation of the TRPC5-CAMKII-ERK pathway but also through its anti-inflammatory and anti-apoptotic properties. Overall, BTD is a promising therapeutic molecule in the treatment of mechanical allodynia in painful diabetic neuropathy.

Effects of acupuncture therapy in diabetic neuropathic pain: A systematic review and meta-analysis

OBJECTIVE

To evaluate the effectiveness of acupuncture in relieving diabetic neuropathic pain and to establish a more reliable and efficient foundation for acupuncture practice in diabetes care.

METHODS

The Chinese National Knowledge Infrastructure, Wanfang database, Chongqing Weipu, Chinese Biomedical Literature Database, PubMed, Embase, and Cochrane Library were all searched for a randomized controlled trial research of acupuncture for DNP. Two researchers independently performed literature screening, quality evaluation, and data extraction. After selecting studies and extracting data, we conducted the data analysis using RevMan 5.4 and Stata 14.0. The quality was assessed using the Cochrane Risk of Bias Assessment Tool.

RESULTS

An extensive review of 19 studies involving 1276 patients up to April 29, 2023, found that acupuncture was successful in improving pain intensity [MD= -1.09; 95% CI (-1.28, -0.89), P < 0.00001], clinical efficacy indicating pain changes [RR= 1.22; 95% CI (1.15, 1.29), P < 0.00001], and clinical neuropathy [MD= -1.55; 95% CI ( -3.00, -0.09), P = 0.04] in DNP patients. Quality of life was also improved, with few side effects reported.

CONCLUSION

According to this meta-analysis, acupuncture therapy significantly improved the clinical efficacy of pain intensity, pain changes, and clinical neuropathy in patients with DNP, improved the quality of life of patients to a certain extent, and had lower side effects. This discovery provides evidence-based and practical recommendations for the treatment of DNP patients.

Pharmacological and Nonpharmacological Treatments for Painful Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most prevalent chronic complications of diabetes. The lifetime prevalence of DPN is thought to be >50%, and 15%-25% of patients with diabetes experience neuropathic pain, referred to as "painful DPN." Appropriate treatment of painful DPN is important because this pain contributes to a poor quality of life by causing sleep disturbance, anxiety, and depression. The basic principle for the management of painful DPN is to control hyperglycemia and other modifiable risk factors, but these may be insufficient for preventing or improving DPN. Because there is no promising diseasemodifying medication for DPN, the pain itself needs to be managed when treating painful DPN. Drugs for neuropathic pain, such as gabapentinoids, serotonin-norepinephrine reuptake inhibitors, tricyclic antidepressants, alpha-lipoic acid, sodium channel blockers, and topical capsaicin, are used for the management of painful DPN. The U.S. Food and Drug Administration (FDA) has approved pregabalin, duloxetine, tapentadol, and the 8% capsaicin patch as drugs for the treatment of painful DPN. Recently, spinal cord stimulation using electrical stimulation is approved by the FDA for the treatment for painful DPN. This review describes the currently available pharmacological and nonpharmacological treatments for painful DPN.

Occurrence of corneal sub-epithelial microneuromas and axonal swelling in people with diabetes with and without (painful) diabetic neuropathy

AIMS/HYPOTHESIS

Non-invasive in vivo corneal confocal microscopy is gaining ground as an alternative to skin punch biopsy to evaluate small-diameter nerve fibre characteristics. This study aimed to further explore corneal nerve fibre pathology in diabetic neuropathy.

METHODS

This cross-sectional study quantified and compared corneal nerve morphology and microneuromas in participants without diabetes (n=27), participants with diabetes but without distal symmetrical polyneuropathy (DSPN; n=33), participants with non-painful DSPN (n=25) and participants with painful DSPN (n=18). Clinical and electrodiagnostic criteria were used to diagnose DSPN. ANCOVA was used to compare nerve fibre morphology in the central cornea and inferior whorl, and the number of corneal sub-epithelial microneuromas between groups. Fisher's exact tests were used to compare the type and presence of corneal sub-epithelial microneuromas and axonal swelling between groups.

RESULTS

Various corneal nerve morphology metrics, such as corneal nerve fibre length and density, showed a progressive decline across the groups (p<0.001). In addition, axonal swelling was present more frequently (p=0.018) and in higher numbers (p=0.03) in participants with painful compared with non-painful DSPN. The frequency of axonal distension, a type of microneuroma, was increased in participants with painful and non-painful DSPN compared to participants with diabetes but without DSPN and participants without diabetes (all p≤0.042). The combined presence of all microneuromas and axonal swelling was increased in participants with painful DSPN compared with all other groups (p≤0.026).

CONCLUSIONS/INTERPRETATION

Microneuromas and axonal swelling in the cornea increase in prevalence from participants with diabetes to participants with non-painful DSPN and participants with painful DSPN.

Health care resource utilization and costs in patients with painful diabetic neuropathy treated with 10 kHz spinal cord stimulation therapy

BACKGROUND: Diabetic peripheral neuropathy, a common comorbidity of diabetes, is a neurodegenerative disorder that targets sensory, autonomic, and motor nerves frequently associated with painful diabetic neuropathy (PDN). PDN carries an economic burden as the result of reduced work and productivity. A recent multicenter randomized controlled trial, SENZA-PDN (NCT03228420), assessed the impact of high-frequency (10 kHz) spinal cord stimulation (SCS) on pain relief. The effects of high-frequency SCS on health care resource utilization and medical costs are not known. OBJECTIVE: To evaluate the effect of high-frequency (10 kHz) SCS on health care resource utilization (HRU) and medical costs in patients with PDN using data from the SENZA-PDN trial. METHODS: Participants with PDN were randomly assigned 1:1 to receive either 10 kHz SCS plus conventional medical management (CMM) (SCS treatment group) or CMM alone (CMM treatment group). Patient outcomes and HRU up to the 6-month follow-up are reported here. Costs (2020 USD) for each service was estimated based on publicly available Medicare fee schedules, Medicare claims data, and literature. HRU metrics of inpatient and outpatient contacts and costs are reported as means and SDs. Univariate and bivariate analyses were used to compare SCS and CMM treatment groups at 6 months. RESULTS: At 6-month follow up, the SCS arm experienced approximately half the mean rate of hospitalizations per patient compared with the CMM treatment group (0.08 vs 0.15; P = 0.066). The CMM treatment group's total health care costs per patient were approximately 51% higher compared with the SCS treatment group (equivalent to mean annual cost per patient of $9,532 vs $6,300). CONCLUSIONS: Our analysis of the SENZA-PDN trial indicates that the addition of 10 kHz SCS therapy results in lower rates of hospitalization and consequently lower health care costs among patients with PDN compared with those receiving conventional management alone.

Long-term efficacy of high-frequency (10 kHz) spinal cord stimulation for the treatment of painful diabetic neuropathy: 24-Month results of a randomized controlled trial

AIMS

To evaluate the long-term efficacy of high-frequency (10 kHz) spinal cord stimulation (SCS) for treating refractory painful diabetic neuropathy (PDN).

METHODS

The SENZA-PDN study was a prospective, multicenter, randomized controlled trial that compared conventional medical management (CMM) alone with 10 kHz SCS plus CMM (10 kHz SCS+CMM) in 216 patients with refractory PDN. After 6 months, participants with insufficient pain relief could cross over to the other treatment. In total, 142 patients with a 10 kHz SCS system were followed for 24 months, including 84 initial 10 kHz SCS+CMM recipients and 58 crossovers from CMM alone. Assessments included pain intensity, health-related quality of life (HRQoL), sleep, and neurological function. Investigators assessed neurological function via sensory, reflex, and motor tests. They identified a clinically meaningful improvement relative to the baseline assessment if there was a significant persistent improvement in neurological function that impacted the participant's well-being and was attributable to a neurological finding.

RESULTS

At 24 months, 10 kHz SCS reduced pain by a mean of 79.9% compared to baseline, with 90.1% of participants experiencing ≥50% pain relief. Participants had significantly improved HRQoL and sleep, and 65.7% demonstrated clinically meaningful neurological improvement. Five (3.2%) SCS systems were explanted due to infection.

CONCLUSIONS

Over 24 months, 10 kHz SCS provided durable pain relief and significant improvements in HRQoL and sleep. Furthermore, the majority of participants demonstrated neurological improvement. These long-term data support 10 kHz SCS as a safe and highly effective therapy for PDN.

TRIAL REGISTRATION

ClincalTrials.gov Identifier, NCT03228420.

Effect of Diabetic Neuropathy on Reparative Ability and Immune Response System

The effects of diabetes can be divided into short, medium and long term and various human organ systems can be effected. The present study aimed to determine how much the duration of diabetes mellitus (DM) affect the reparative ability of the body, immune response and the development of DM complications. Interleukin 1-β (IL-1β) and Interleukin 6 (IL-6) were monitored as specific indicators of inflammatory reaction and C-reactive protein (CRP), leukocyte count (WBC) and sedimentation rate (ESR) as general markers of inflammatory reaction. Tumour necrosis factor α (TNF-α) and transforming growth factor β1 (TGF-β1) were observed as indicators of reparative ability and polyneuropathy. All interleukins were determined by ELISA and evaluated spectrophotometrically. Michigan Neuropathy Screening Instrument (MNSI) is performed for neuropathy examination. Patients with diabetes mellitus were divided into 3 groups, according to duration of diabetes mellitus. IL-6 levels correlated with clinical stage of diabetic polyneuropathy at p = 0.025 R = 0.402; with CRP at p = 0.0001, R = 0.784 as well as correlation of CRP and MNSI score (R = 0.500, p = 0.034) in a group of patients with DM lasting up to 10 years. The reparative ability of the body is reduced by physiological age and ages of DM duration. The immune response is weakened in DM additionally. The dual activity of cytokines IL-6 and TGF-β1 is present in long-duration Diabetes Mellitus.

A Drosophila model of diabetic neuropathy reveals a role of proteasome activity in the glia

Diabetic peripheral neuropathy (DPN) is the most common chronic, progressive complication of diabetes mellitus. The main symptom is sensory loss; the molecular mechanisms are not fully understood. We found that Drosophila fed a high-sugar diet, which induces diabetes-like phenotypes, exhibit impairment of noxious heat avoidance. The impairment of heat avoidance was associated with shrinkage of the leg neurons expressing the Drosophila transient receptor potential channel Painless. Using a candidate genetic screening approach, we identified proteasome modulator 9 as one of the modulators of impairment of heat avoidance. We further showed that proteasome inhibition in the glia reversed the impairment of noxious heat avoidance, and heat-shock proteins and endolysosomal trafficking in the glia mediated the effect of proteasome inhibition. Our results establish Drosophila as a useful system for exploring molecular mechanisms of diet-induced peripheral neuropathy and propose that the glial proteasome is one of the candidate therapeutic targets for DPN.

MACHINE LEARNING ANALYSIS OF THE UK BIOBANK REVEALS PROGNOSTIC AND DIAGNOSTIC IMMUNE BIOMARKERS FOR POLYNEUROPATHY AND NEUROPATHIC PAIN IN DIABETES

AIMS

We assessed the health data of 11,047 people with diabetes in the UK Biobank to rank 329 risk factors for diabetic polyneuropathy (DPN) and DPN with chronic neuropathic pain without a priori assumption.

METHODS

The Integrated Disease Explanation and Risk Scoring (IDEARS) platform applies machine learning algorithms to multimodal data to determine individual disease risk, and rank risk factor importance using mean SHapley Additive exPlanations (SHAP) score.

RESULTS

IDEARS models showed discriminative performances with AUC > 0.64. Lower socioeconomic status, being overweight, poor overall health, cystatin C, HbA1C, and immune activation marker, C-reactive protein (CRP), predict DPN risk. Neutrophils and monocytes were higher in males and lymphocytes lower in females with diabetes that develop DPN. Neutrophil-to-Lymphocyte Ratio (NLR) was increased and IGF-1 levels decreased in people with type 2 diabetes that later develop DPN. CRP was significantly elevated in those with DPN and chronic neuropathic pain compared to DPN without pain.

CONCLUSIONS

Lifestyle factors and blood biomarkers predict the later development of DPN and may relate to DPN pathomechanisms. Our results are consistent with DPN as a disease involving systemic inflammation. We advocate for the use of these biomarkers clinically to predict future DPN risk and improve early diagnosis.

Netrin-3 Suppresses Diabetic Neuropathic Pain by Gating the Intra-epidermal Sprouting of Sensory Axons

Diabetic neuropathic pain (DNP) is the most common disabling complication of diabetes. Emerging evidence has linked the pathogenesis of DNP to the aberrant sprouting of sensory axons into the epidermal area; however, the underlying molecular events remain poorly understood. Here we found that an axon guidance molecule, Netrin-3 (Ntn-3), was expressed in the sensory neurons of mouse dorsal root ganglia (DRGs), and downregulation of Ntn-3 expression was highly correlated with the severity of DNP in a diabetic mouse model. Genetic ablation of Ntn-3 increased the intra-epidermal sprouting of sensory axons and worsened the DNP in diabetic mice. In contrast, the elevation of Ntn-3 levels in DRGs significantly inhibited the intra-epidermal axon sprouting and alleviated DNP in diabetic mice. In conclusion, our studies identified Ntn-3 as an important regulator of DNP pathogenesis by gating the aberrant sprouting of sensory axons, indicating that Ntn-3 is a potential druggable target for DNP treatment.

Microbiological and Physiological Effects of Pain

Pain is an important innate defense mechanism that can dramatically alter a person's quality of life. Understanding the microbiological and physiological effects of pain may be important in the pursuit of novel pain interventions. The three descriptors of pain recognized by the International Association for the Study of Pain are nociceptive, neuropathic, and nociplastic pain. Our review examined the current understanding of all three pain types, focusing on the key molecules involved in the manifestation of each type as well as physiological effects. Additionally, we compared the differences in painful and painless neuropathies and discussed the neuroimmune interaction involved in the manifestation of pain.

Histone deacetylase 5-induced deficiency of signal transducer and activator of transcription-3 acetylation contributes to spinal astrocytes degeneration in painful diabetic neuropathy

Diabetes patients with painful diabetic neuropathy (PDN) show severe spinal atrophy, suggesting pathological changes of the spinal cord contributes to central sensitization. However, the cellular changes and underlying molecular mechanisms within the diabetic spinal cord are less clear. By using a rat model of type 1 diabetes (T1D), we noted an extensive and irreversible spinal astrocyte degeneration at an early stage of T1D, which is highly associated with the chronification of PDN. Molecularly, acetylation of astrocytic signal transducer and activator of transcription-3 (STAT3) that is essential for maintaining the homeostatic astrocytes population was significantly impaired in the T1D model, resulting in a dramatic loss of spinal astrocytes and consequently promoting pain hypersensitivity. Mechanistically, class IIa histone deacetylase, HDAC5 were aberrantly activated in spinal astrocytes of diabetic rats, which promoted STAT3 deacetylation by direct protein-protein interactions, leading to the PDN phenotypes. Restoration of STAT3 signaling or inhibition of HDAC5 rescued astrocyte deficiency and attenuated PDN in the T1D model. Our work identifies the inhibitory axis of HDAC5-STAT3 induced astrocyte deficiency as a key mechanism underlying the pathogenesis of the diabetic spinal cord that paves the way for potential therapy development for PDN.

Prevalence of painful diabetic peripheral neuropathy in type 2 diabetes mellitus and diabetic peripheral neuropathy: A nationwide cross-sectional study in mainland China

AIM

The study aimed to assess the prevalence and risk factors of painful diabetic peripheral neuropathy (PDPN) in patients with type 2 diabetes mellitus (T2DM) and diabetic peripheral neuropathy (DPN) in mainland China.

METHODS

This nationwide cross-sectional study enrolled T2DM patients with DPN from 25 provinces in China between July 2017 and December 2017. The prevalence, characteristics, and risk factors of PDPN were analyzed.

RESULTS

Among 25,710 patients with T2DM and DPN, 14,699 (57.2%) had PDPN. The median age was 63 years old. Age over 40 years old, education level, hypertension, myocardial infarction, duration of diabetes of over five years, diabetic retinopathy and nephropathy, moderate total cholesterol, moderate and higher low-density lipoprotein (LDL) increased uric acid (UA) and decreased estimated glomerular filtration rate (eGFR) were independently associated with PDPN (all P < 0.05). Compared with low levels of C-peptide, moderate levels were independently associated with a higher risk of PDPN, while high levels were associated with a lower risk (all P < 0.001).

CONCLUSIONS

In mainland China, more than half of the patients with DPN have neuropathic pain. Patients with older age, lower education level, longer duration of diabetes, lower LDL, increased UA, decreased eGFR, and comorbidities had an increased risk of PDPN.

Effects of 1-methyl-1, 2, 3, 4-tetrahydroisoquinoline on a diabetic neuropathic pain model

Background: Neuropathy is a prevalent and debilitating complication of poorly managed diabetes, contributing towards poor quality of life, amputation risk, and increased mortality. The available therapies for diabetic neuropathic pain (DPN) have limitations in terms of efficacy, tolerability and patient compliance. Dysfunction in the peripheral and central monoaminergic system has been evidenced in various types of neuropathic and acute pain. The objective of the present study was to investigate 1-methyl 1, 2, 3, 4-tetrahydroisoquinoline (1MeTIQ), an endogenous amine found in human brain with a known neuroprotective profile, in a model of streptozotocin (STZ) induced neuropathic pain. Methods: Diabetic neuropathy in male BALB/c mice was induced by intraperitoneal injection of a single dose of STZ (200 mg/kg). Upon development of DPN after 4 weeks, mice were investigated for mechanical allodynia (von Frey filament pressure test) and thermal hyperalgesia (tail immersion test). Ondansetron (1.0 mg/kg i.p.), naloxone (3.0 mg/kg i.p.) and yohimbine (2.0 mg/kg i.p.) were used to elucidate the possible mechanism involved. Postmortem frontal cortical, striatal and hippocampal tissues were dissected and evaluated for changes in levels of dopamine, noradrenaline and serotonin using High-Performance Liquid Chromatography (HPLC) with UV detection. Results: Acute administration of 1MeTIQ (15-45 mg/kg i.p.) reversed streptozotocin-induced diabetic neuropathic static mechanical allodynia (von Frey filament pressure test) and thermal hyperalgesia (tail immersion test), these outcomes being comparable to standard gabapentin. Furthermore, HPLC analysis revealed that STZ-diabetic mice expressed lower concentrations of serotonin in all three brain regions examined, while dopamine was diminished in the striatum and 1MeTIQ reversed all these neurotransmitter modifications. These findings suggest that the antihyperalgesic/antiallodynic activity of 1MeTIQ may be mediated in part via supraspinal opioidergic and monoaminergic modulation since they were naloxone, yohimbine and ondansetron reversible. Conclusion: It was also concluded that acute treatment with 1MeTIQ ameliorated STZ-induced mechanical allodynia and thermal hyperalgesia and restored brain regionally altered serotonin and dopamine concentrations which signify a potential for 1MeTIQ in the management of DPN.

The upregulation of NLRP3 inflammasome in dorsal root ganglion by ten-eleven translocation methylcytosine dioxygenase 2 (TET2) contributed to diabetic neuropathic pain in mice

BACKGROUND

The nucleotide oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) in dorsal root ganglion (DRG) contributes to pain hypersensitivity in multiple neuropathic pain models, but the function of the NLRP3 in diabetic neuropathic pain (DNP) and the regulation mechanism are still largely unknown. Epigenetic regulation plays a vital role in the controlling of gene expression. Ten-eleven translocation methylcytosine dioxygenase 2 (TET2) is a DNA demethylase that contributes to transcriptional activation. TET2 is also involved in high glucose (HG)-induced pathology.

METHODS

DNP was induced in mice via the intraperitoneal injection of streptozotocin (STZ) for five consecutive days and the mechanical threshold was evaluated in STZ-diabetic mice by using von Frey hairs. The expression level of the NLRP3 pathway and TET2 in DRG were determined through molecular biology experiments. The regulation of the NLRP3 pathway by TET2 was examined in in vitro and in vivo conditions.

RESULTS

In the present research, we first established the DNP model and found that NLRP3 pathway was activated in DRG. The treatment of NLRP3 inhibitor MCC950 alleviated the mechanical allodynia of DNP mice. Then we revealed that in STZ-diabetic mice DRG, the genomic DNA was demethylated, and the expression of DNA demethylase TET2 was increased evidently. Using RNA-sequencing analysis, we found that the expression of Txnip, a gene that encodes a thioredoxin-interacting protein (TXNIP) which mediates NLRP3 activation, was elevated in the DRG after STZ treatment. In addition, knocking down of TET2 expression in DRG using TET2-siRNA suppressed the mRNA expression of Txnip and subsequently inhibited the expression/activation of NLRP3 inflammasome in vitro and in vivo as well as relieved the pain sensitivity of DNP animals.

CONCLUSION

The results suggested that the upregulation of the TXNIP/NLRP3 pathway by TET2 in DRG was involved in the pain hypersensitivity of the DNP model.

Diabetic foot ulcers: A devastating complication of diabetes mellitus continues non-stop in spite of new medical treatment modalities

Diabetic foot ulcer is a devastating complication of diabetes mellitus and significant cause of mortality and morbidity all over the world and can be complex and costly. The development of foot ulcer in a diabetic patient has been estimated to be 19%-34% through their lifetime. The pathophysiology of diabetic foot ulcer consist of neuropathy, trauma and, in many patients, additional peripheral arterial disease. In particular, diabetic neuropathy leads to foot deformity, callus formation, and insensitivity to trauma or pressure. The standard algorithms in diabetic foot ulcer management include assessing the ulcer grade classification, surgical debridement, dressing to facilitate wound healing, off-loading, vascular assessment (status and presence of a chance for interventional vascular correction), and infection and glycemic control. Although especially surgical procedures are sometimes inevitable, they are poor predictive factors for the prognosis of diabetic foot ulcer. Different novel treatment modalities such as nonsurgical debridement agents, oxygen therapies, and negative pressure wound therapy, topical drugs, cellular bioproducts, human growth factors, energy-based therapies, and systematic therapies have been available for patients with diabetic foot ulcer. However, it is uncertain whether they are effective in terms of promoting wound healing related with a limited number of randomized controlled trials. This review aims at evaluating diabetic foot ulcer with regard to all aspects. We will also focus on conventional and novel adjunctive therapy in diabetic foot management.

The relationship between vascular endothelial growth factor-A serum level and the severity of diabetic peripheral neuropathy

Background and aims

Diabetic peripheral neuropathy (DPN) is a common microvascular complication in type 2 diabetes mellitus (T2DM). The nerve fibers injury is caused by the interaction between metabolic and vascular factors. Vascular endothelial growth factor (VEGF) is an essential growth factor for vascular endothelial cells. We aimed to investigate the relation between VEGF-A serum level and the degree of DPN.

Results

This cross-sectional study was conducted on 81 patients with T2DM. Based on the combined clinical and electrophysiological assessment, 67 patients (82.7%) were diagnosed with peripheral neuropathy of which 32 patients (39.5%) had subclinical neuropathy, whereas 35 patients (43.2%) were confirmed cases of DPN. Patients with DPN had longer duration of DM and higher values of glycosylated hemoglobin (HbA1c). Although the mean serum VEGF-A level in diabetic patients without neuropathy was higher than that in diabetic patients with DPN, this difference did not reach statistical significance (P = 0.07). However, patients with subclinical DPN had significantly higher serum VEGF-A level compared to patients with confirmed DPN (P < 0.001).

Conclusion

DPN was found to be a common finding in the studied sample of T2DM patients. Longer duration of DM and poor glycemic control may be risk factors for development of severe DPN. Low VEGF-A serum levels may lead to more severe DPN in patients with T2DM.

Chronic Pain and Cannabidiol in Animal Models: Behavioral Pharmacology and Future Perspectives

The incidence of chronic pain is around 8% in the general population, and its impact on quality of life, mood, and sleep exceeds the burden of its causal pathology. Chronic pain is a complex and multifaceted problem with few effective and safe treatment options. It can be associated with neurological diseases, peripheral injuries or central trauma, or some maladaptation to traumatic or emotional events. In this perspective, animal models are used to assess the manifestations of neuropathy, such as allodynia and hyperalgesia, through nociceptive tests, such as von Frey, Hargreaves, hot plate, tail-flick, Randall & Selitto, and others. Cannabidiol (CBD) has been considered a promising strategy for treating chronic pain and diseases that have pain as a consequence of neuropathy. However, despite the growing body of evidence linking the efficacy of CBD on pain management in clinical and basic research, there is a lack of reviews focusing on chronic pain assessments, especially when considering pre-clinical studies, which assess chronic pain as a disease by itself or as a consequence of trauma or peripheral or central disease. Therefore, this review focused only on studies that fit our inclusion criteria: (1) used treatment with CBD extract; (2) used tests to assess mechanical or thermal nociception in at least one of the following most commonly used tests (von Frey, hot plate, acetone, Hargreaves, tail-flick, Randall & Selitto, and others); and (3) studies that assessed pain sensitivity in chronic pain induction models. The current literature points out that CBD is a well-tolerated and safe natural compound that exerts analgesic effects, decreasing hyperalgesia, and mechanical/thermal allodynia in several animal models of pain and patients. In addition, CBD presents several molecular and cellular mechanisms of action involved in its positive effects on chronic pain. In conclusion, using CBD seems to be a promising strategy to overcome the lack of efficacy of conventional treatment for chronic pain.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Is metformin a possible treatment for diabetic neuropathy?

Metformin is a hypoglycemic drug widely used in the treatment of type 2 diabetes. It has been proven to have analgesic and neuroprotective effects. Metformin can reverse pain in rodents, such as diabetic neuropathic pain, neuropathic pain caused by chemotherapy drugs, inflammatory pain and pain caused by surgical incision. In clinical use, however, metformin is associated with reduced plasma vitamin B12 levels, which can further neuropathy. In rodent diabetes models, metformin plays a neuroprotective and analgesic role by activating adenosine monophosphate-activated protein kinase, clearing methylgloxal, reducing insulin resistance, and neuroinflammation. This paper also summarized the neurological adverse reactions of metformin in diabetic patients. In addition, whether metformin has sexual dimorphism needs further study.

High-normal serum carcinoembryonic antigen levels and increased risk of diabetic peripheral neuropathy in type 2 diabetes

BACKGROUND

Increased serum carcinoembryonic antigen (CEA) levels are reported to be associated with various metabolic and inflammatory diseases. This study assessed whether high-normal serum CEA is related to diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes (T2D).

METHODS

All subjects received DPN assessment based on neuropathic symptoms, neuropathic signs, and nerve conduction studies to calculate composite Z scores of nerve latency, amplitude and conduction velocity (NCV). DPN was confirmed by both at least a presentation of neuropathic symptoms/signs and an abnormal nerve conduction index. Serum CEA levels and other clinical indices were also synchronously detected. Multivariable linear regression analyses were used to determine the independent effects of serum CEA levels on nerve conduction indices, multivariable logistic regression analyses were used to determine the independent impact of CEA levels on the risk of DPN, and receiver operating characteristic (ROC) curve analysis was used to assess the diagnostic capability of CEA levels to discriminate DPN.

RESULTS

We ultimately recruited 402 eligible subjects with normal ranges of serum CEA for this study, and 25.4% (n = 102) were determined to have DPN. After adjusting for other clinical covariates, serum CEA levels were independently associated with the composite Z score for latency (β = 0.132, t = 2.330, p = 0.021), amplitude (β = - 0.164, t = - 2.838, p = 0.005) and NCV (β = - 0.210, t = - 3.662, p < 0.001). Moreover, the prevalence of DPN in the first, second, third and fourth quartiles of CEA level was 12.9%, 19.0%, 29.4% and 40.4%, respectively (p for trend < 0.001); the corresponding adjusted odds ratios and 95% CIs for DPN in CEA quartiles were 1, 1.47 (0.45-4.82), 1.72 (0.54-5.53) and 4.58 (1.39-15.06), respectively. Furthermore, the optimal cut-off value of high-normal serum CEA to discriminate DPN was ≥ 2.66 ng/mL, with a Youden index of 0.28, sensitivity of 66.67% and specificity of 61.00%.

CONCLUSIONS

Increased serum CEA levels within the normal range are closely linked to dysfunction of peripheral nerve conduction and the risk of DPN, and high-normal serum CEA levels are a potential risk factor for DPN in T2D.

Impact of pain severity on functioning domains, sleep, and cognition in painful diabetic peripheral polyneuropathy patients

Background

Several studies have observed that painful diabetic peripheral polyneuropathy (PDPN) had an impact on the level of functioning domains and quality of sleep as well as cognitive functions. This study is aimed to explore the relationship between severity of pain and level of functioning, sleep quality, and cognitive functions among these patients. We recruited 100 diabetics with a mean HbA1C% of 7.3±0.9, diagnosed with PDPN, and included in the study with a mean age of 51±12.8 years and disease duration of 10.2±7.4 years. The following assessment was done for each patient; clinical and neurophysiology assessment, routine laboratory assessment, measuring pain severity, and average pain severity interference scores using pain visual analog scale (VAS) and brief pain inventory (BPI) short form, respectively, sleep quality assessment using Pittsburgh Sleep Quality Index (PSQI) and Montreal cognitive function assessment (MOCA) scales.

Results

Moderate to severe pain was recorded in 71% of patients according to the VAS pain score. The severe pain group recorded the significant highest average pain severity and interference scores in BPI and domains compared to other less pain groups with average pain intensity scores of 7.5±0.6 vs 5.3±0.8 in the moderate and 3.3±0.4 in mild pain groups. Poor sleep quality and pattern were observed in these patients with a mean PSQI score of 6.8±3.1, and the severe pain group had a significant highest score of 9.4±2.3 compared to other less group scores of 7±2.3 and 3.7±1.8. Their mean MOCA score was low 24.2±2.2. Out of them 48/100 patients had mild cognitive impairment and recorded high frequency in the severe pain group (28/32) followed by the moderate pain (15/39) group. There is a significant correlation between the score of VAS and PSQI as well as MOCA.

Conclusions

Painful DPN patients had a poor level of functioning and sleep quality as well as cognitive impairment based on pain intensity.

Trial registration

This study was registered on a clinical trial with registration number NCT03275233 on 7 September 2017.

Factors related to cognitive function in type-2 diabetes and neuropathic pain patients, the role of mood and sleep disorders in this relationship

To compare cognitive function in patients with diabetes mellitus type-2 (T2DM) both with and without diabetic neuropathic pain (DNP). To analyse the relationship between mood and sleep disorders, quality of life and cognitive function in patients with DNP. Cross-sectional study conducted in patients with T2DM and neuropathy. The presence of DNP, cognitive function, mood status, sleep quality, health-related quality of life, pain intensity and phenotype of pain were measured. Descriptive, bivariate and multivariate analyses were performed. A total of 149 patients (71 with DNP) were included. Patients with and without DNP presented similar scores on the TYM (41.46; SD = 6.70 vs. 41.97; SD = 5.50) and those with DNP had a slightly higher frequency of cognitive impairment (TYM score ≤ 41: 40.8% vs. 43.6%). The patients without DNP performed better in the verbal fluency dimension (mean = 3.53; SD = 0.98 vs. mean = 3.82; SD = 0.66). Being older (B = − 0.258) and under treatment with insulin (B = − 2.919) were related with greater cognitive impairment. Obesity (OR = 17.277) and a longer duration of diabetes (OR = 1.317) were also related to greater risk of cognitive impairment. Impaired cognitive function in patients with DNP is more related to T2DM factors than pain factors. The presence of depression and a worse quality of life were related to a greater risk of cognitive impairment. Identifying and controlling these factors should be an essential intervention for maintaining the cognitive function in patients with T2DM and DNP.

A randomized placebo-compared study on the efficacy of classical ayurvedic pharmaceutical form versus aqueous alcoholic extracts of Phyllanthus niruri Linn. Plus Sida cordifolia Linn. In patients of diabetic sensory polyneuropathy

Background

In routine, Ayurveda practitioners prefer classical pharmaceutical form of herbal medicines in compare to modern extracts.

Objective

To explore the difference of efficiency between whole drug powder of Phyllanthus niruri plus root decoction of Sida cordifolia and modern extracts of the same in compared to placebo in patients of diabetic poly-neuropathy.

Material and methods

A randomized, partly-double-blinded, placebo-controlled trial evaluated the efficacy of two different pharmaceutical forms of herbal medicines over placebo in 90 patients (30 in each group) of diabetic sensory polyneuropathy for first three weeks period. After three weeks, active herbal medication groups were continued with their assigned medicaments for next 5 weeks period and all placebo-patients were randomized again into 2 groups of active medication and treated for next 8 weeks. Patients were assessed with Neuropathy Total Symptom Score 6 and sensation thresholds.

Results

Significant effect of both form of herbal medicines over placebo was found in aching pain [F (2, 49) = 6.79, p = 0.002], allodynia [F (2, 59) = 6.74, p = 0.002], burning pain [F (2, 82) = 14.66, p < 0.0001], numbness [F (2, 77) = 16.37, p < 0.0001] and pricking pain [F (2, 50) = 14.23, p < 0.0001]. After the 8 weeks period, no significant difference was identified between the effect of both the herbal treatment on aching pain (U = 220, p = 0.03), allodynia (U = 421.5, p = 0.29), burning pain (U = 881.5, p = 0.846), numbness (U = 778, p = 0.92) and pricking pain (U = 260, p = 0.15).

Conclusion

Both herbal groups have significant effect to reduce NTSS-6 score in compare to placebo. No significant difference found between the effect of two different pharmaceutical forms of Phyllanthus niruri and S. cordifolia.

•Ayurvedist prefer more classical pharmaceutical form than modern extracts of herbs.

•In this RCT, after 3 weeks period, placebo patients randomized again in both active herbal groups.

•Multiple statistical tests applied for each outcome variable.

•Both herbal groups have significant effect to reduce the NTSS-6 score in compare to placebo.

•No significant difference found between the effect of classical pharmaceutical forms and modern extract form of herbs.

HIF-1α Ameliorates Diabetic Neuropathic Pain via Parkin-Mediated Mitophagy in a Mouse Model

Mitochondrial dysfunction, which can be regulated by mitophagy, plays a central role in diabetic neuropathic pain (DNP). Mitophagy that was involved in nerve damage-induced neuropathic pain has been reported. Hyperglycemia and cellular hypoxic were the two main characters of diabetes. Hypoxia-inducible factor 1α subunit (HIF-1α) plays a vital role in mitochondrial homeostasis under hypoxia. However, it remains unclear whether mitophagy was changed and could be regulated by HIF-1α in DNP. In this study, the results showed that mitophagy was activated and HIF-1α was upregulated in the spinal cord of diabetic mice. HIF-1α agonist dimethyloxalylglycine (DMOG) could further elevate HIF-1α and Parkin protein, enhance mitophagy, decrease mitochondrial dysfunction, and hyperalgesia. Furthermore, Park2 (encoding Parkin) knockout aggravated hyperalgesia and mitochondrial dysfunction in diabetic mice. Furthermore, mitophagy could not be activated and induced by HIF-1α agonist DMOG in Park2^−/− diabetic mice. In this study, we first demonstrated that HIF-1α could upregulate mitophagy in the spinal cord of mice with DNP through modulating the Parkin signaling pathway, promoting new insights into the mechanisms and research of treatment strategies for patients with DNP.

Diabetic Neuropathy in Hands: An Endemic Complication Waiting to Unfold?

In this cross-sectional study we aimed to quantify the somatosensory dysfunction in the hand in people with diabetes with distal symmetrical polyneuropathy (DSPN) in hands and explore early signs of nerve dysfunction in people with diabetes without DSPN in hands. The clinical diagnosis of DSPN was confirmed with electrodiagnosis and corneal confocal microscopy. Thermal and mechanical nerve function in the hand was assessed with quantitative sensory tests. Measurements were compared between healthy participants (n = 31), individuals with diabetes without DSPN (n = 35), individuals with DSPN in feet but not hands (DSPNFEET ONLY) (n = 31), and individuals with DSPN in hands and feet (DSPNHANDS & FEET) (n = 28) with one-way between-group ANOVA. The somatosensory profile of the hand in people with DSPNHANDS & FEET showed widespread loss of thermal and mechanical detection. This profile in hands is comparable with the profile in the feet of people with DSPN in feet. Remarkably, individuals with DSPNFEET ONLY already showed a similar profile of widespread loss of nerve function in their hands. People with diabetes without DSPN in feet already had some nerve dysfunction in their hands. These findings suggest that nerve function assessment in hands should become more routine in people with diabetes.

Effects of Neural Mobilization on Sensory Dysfunction and Peripheral Nerve Degeneration in Rats With Painful Diabetic Neuropathy

OBJECTIVE

This study aims to evaluate the effectiveness of neural mobilization (NM) in the management of sensory dysfunction and nerve degeneration related to experimental painful diabetic neuropathy (PDN).

METHODS

This is a pre-clinical animal study performed in the streptozocin-induced diabetic rat model. Three groups were included: a treatment group of rats with PDN receiving NM under anesthesia (PDN-NM, n = 10), a sham treatment group of rats with PDN that received only anesthesia (PDN-Sham, n = 9), and a vehicle control group with nondiabetic animals (Vehicle, n = 10). Rats in the PDN-NM and PDN-Sham groups received 1 treatment session on days 10, 12, and 14 after streptozocin injection, with a 48-hour rest period between sessions. Behavioral tests were performed using von Frey and Plantar tests. Evaluation for peripheral nerve degeneration was performed through measuring protein gene product 9.5-positive intra-epidermal nerve fiber density in hind-paw skin biopsies. All measurements were performed by a blinded investigator.

RESULTS

The behavioral tests showed that a single NM session could reduce hyperalgesia, which was maintained for 48 hours. The second treatment session further improved this treatment effect, and the third session maintained it. These results suggest that it requires multiple treatment sessions to produce and maintain hypoalgesic effects. Skin biopsy analysis showed that the protein gene product 9.5-positive intra-epidermal nerve fiber density was higher on the experimental side of the PDN-NM group compared with the PDN-Sham group, suggesting NM may mitigate the degeneration of peripheral nerves.

CONCLUSION

This study demonstrated that NM may be an effective method to manage experimentally induced PDN, potentially through mitigation of nerve degeneration. Further studies are needed to develop standardized protocols for clinical use.

IMPACT

These findings provide neurophysiological evidence for the use of NM in PDN and can form the basis for the development of physical therapy-based programs in clinics.

Pathogenesis of Distal Symmetrical Polyneuropathy in Diabetes

Distal symmetrical polyneuropathy (DSPN) is a serious complication of diabetes associated with significant disability and mortality. Although more than 50% of people with diabetes develop DSPN, its pathogenesis is still relatively unknown. This lack of understanding has limited the development of novel disease-modifying therapies and left the reasons for failed therapies uncertain, which is critical given that current management strategies often fail to achieve long-term efficacy. In this article, the pathogenesis of DSPN is reviewed, covering pathogenic changes in the peripheral nervous system, microvasculature and central nervous system (CNS). Furthermore, the successes and limitations of current therapies are discussed, and potential therapeutic targets are proposed. Recent findings on its pathogenesis have called the definition of DSPN into question and transformed the disease model, paving the way for new research prospects.

Peripheral Ion Channel Gene Screening in Painful- and Painless-Diabetic Neuropathy

Neuropathic pain is common in diabetic peripheral neuropathy (DN), probably caused by pathogenic ion channel gene variants. Therefore, we performed molecular inversion probes-next generation sequencing of 5 transient receptor potential cation channels, 8 potassium channels and 2 calcium-activated chloride channel genes in 222 painful- and 304 painless-DN patients. Twelve painful-DN (5.4%) patients showed potentially pathogenic variants (five nonsense/frameshift, seven missense, one out-of-frame deletion) in ANO3 (n = 3), HCN1 (n = 1), KCNK18 (n = 2), TRPA1 (n = 3), TRPM8 (n = 3) and TRPV4 (n = 1) and fourteen painless-DN patients (4.6%-three nonsense/frameshift, nine missense, one out-of-frame deletion) in ANO1 (n = 1), KCNK18 (n = 3), KCNQ3 (n = 1), TRPA1 (n = 2), TRPM8 (n = 1), TRPV1 (n = 3) and TRPV4 (n = 3). Missense variants were present in both conditions, presumably with loss- or gain-of-functions. KCNK18 nonsense/frameshift variants were found in painless/painful-DN, making a causal role in pain less likely. Surprisingly, premature stop-codons with likely nonsense-mediated RNA-decay were more frequent in painful-DN. Although limited in number, painful-DN patients with ion channel gene variants reported higher maximal pain during the night and day. Moreover, painful-DN patients with TRP variants had abnormal thermal thresholds and more severe pain during the night and day. Our results suggest a role of ion channel gene variants in neuropathic pain, but functional validation is required.

Diabetic neuropathy is a generalized phenomenon with impact on hand functional performance and quality of life

BACKGROUND

Diabetic sensorimotor peripheral neuropathy (DSPN) is usually considered to affect predominantly the lower limbs (LL-N), while the impact of upper limb neuropathy (UL-N) on hand functional performance and quality of life (QoL) has not been evaluated systematically. This study aims to investigate the prevalence and characteristics of UL-N and its functional and psychosocial consequences in type 2 diabetes.

METHODS

Individuals with type 2 diabetes (n=141) and an age- and sex-matched control group (n=73) underwent comprehensive assessment of neuropathy, hand functional performance and psychosocial status.

RESULTS

The prevalence of UL-N was 30.5% in patients with diabetes and that of LL-N 49.6%, with 25.5% exhibiting both. Patients with diabetes showed similar sensory phenotype regarding both large and small fiber functions in hands and feet. Patients with UL-N showed reduced manual dexterity, but normal hand grip force. Additionally, there was a correlation between reduced dexterity and sensory deficits. Patients with UL-N had reduced estimates of psychosocial health including health-related QoL compared to control subjects and patients without UL-N. UL-N correlated with the severity of LL-N, but not with duration of diabetes, glycaemia, age, or sex.

CONCLUSIONS

This study points to a substantial prevalence of UL-N in type 2 diabetes. The sensory phenotype of patients with UL-N was similar to LL-N and was characterized by loss of sensory function. Our study demonstrated an association of UL-N with impaired manual dexterity and reduced health-related QoL. Thus, upper limb sensorimotor functions should be assessed early in patients with diabetes.

Conditioned pain modulation is more efficient in patients with painful diabetic polyneuropathy than those with nonpainful diabetic polyneuropathy

ABSTRACT

Endogenous pain modulation, as tested by the conditioned pain modulation (CPM) protocol, is typically less efficient in patients with chronic pain compared with healthy controls. We aimed to assess whether CPM is less efficient in patients with painful diabetic polyneuropathy (DPN) compared with those with nonpainful DPN. Characterization of the differences in central pain processing between these 2 groups might provide a central nervous system explanation to the presence or absence of pain in diabetic neuropathy in addition to the peripheral one. Two hundred seventy-one patients with DPN underwent CPM testing and clinical assessment, including quantitative sensory testing. Two modalities of the test stimuli (heat and pressure) conditioned to cold noxious water were assessed and compared between patients with painful and nonpainful DPN. No significant difference was found between the groups for pressure pain CPM; however, patients with painful DPN demonstrated unexpectedly more efficient CPMHEAT (-7.4 ± 1.0 vs -2.3 ± 1.6; P = 0.008). Efficient CPMHEAT was associated with higher clinical pain experienced in the 24 hours before testing (r = -0.15; P = 0.029) and greater loss of mechanical sensation (r = -0.135; P = 0.042). Moreover, patients who had mechanical hypoesthesia demonstrated more efficient CPMHEAT (P = 0.005). More efficient CPM among patients with painful DPN might result from not only central changes in pain modulation but also from altered sensory messages coming from tested affected body sites. This calls for the use of intact sites for proper assessment of pain modulation in patients with neuropathy.

Hepatocyte growth factor, colony-stimulating factor 1, CD40, and 11 other inflammation-related proteins are associated with pain in diabetic neuropathy: exploration and replication serum data from the Pain in Neuropathy Study

ABSTRACT

One in 5 patients with diabetes suffers from chronic pain with neuropathic characteristics, but the pathophysiological mechanisms underlying the development of neuropathic pain in patients with diabetic distal symmetrical polyneuropathy (DSP) are poorly understood. Systemic low-grade inflammation has been implicated, but there is still a considerable knowledge gap concerning its scope and meaning in this context. The aim of the study was to establish the broad inflammatory signature of painful diabetic DSP in serum samples from the Pain in Neuropathy Study, an observational cross-sectional multicentre study in which participants underwent deep phenotyping. In the present two cohorts exploration-replication study (180 participants in each cohort), serum samples from Pain in Neuropathy Study participants were analyzed with the Olink INFLAMMATION panel (Olink Bioscience, Uppsala, Sweden) that enables the simultaneous measurement of 92 inflammation-related proteins (mainly cytokines, chemokines, and growth factors). In both the exploration and the replication cohort, we identified a high-inflammation subgroup where 14 inflammation-related proteins in particular were associated with more neuropathy and higher pain intensity. The top 3 proteins were hepatocyte growth factor, colony-stimulating factor 1, and CD40 in both cohorts. In the exploratory cohort, additional clinical data were available, showing an association of inflammation with insomnia and self-reported psychological distress. Hence, this cross-sectional exploration-replication study seems to confirm that low-grade systemic inflammation is related to the severity of neuropathy and neuropathic pain in a subgroup of patients with diabetic DSP. The pathophysiological relevance of these proteins for the development of neuropathic pain in patients with diabetic DSP must be explored in more depth in future studies.

Sciatic nerve microvascular permeability in type 2 diabetes decreased in patients with neuropathy

Objectives

Clinical and histological studies have found evidence that nerve ischemia is a major contributor to diabetic neuropathy (DN) in type 2 diabetes (T2D). The aim of this study was to investigate peripheral nerve microvascular permeability using dynamic contrast enhanced (DCE) magnetic resonance neurography (MRN) to analyze potential correlations with clinical, electrophysiological, and demographic data.

Methods

Sixty‐five patients (35/30 with/without DN) and 10 controls matched for age and body mass index (BMI) underwent DCE MRN of the distal sciatic nerve with an axial T1‐weighted sequence. Microvascular permeability (K^trans), plasma volume fraction (v_p), and extravascular extracellular volume fraction (v_e) were determined with the extended Tofts model, and subsequently correlated with clinical data.

Results

K^trans and v_e were lower in T2D patients with DN compared to patients without DN (0.037 min⁻¹ ± 0.010 vs. 0.046 min⁻¹ ± 0.014; p = 0.011, and 2.35% ± 3.87 vs. 5.11% ± 5.53; p = 0.003, respectively). In individuals with T2D, K^trans correlated positively with tibial, peroneal, and sural NCVs (r = 0.42; 95%CI = 0.18 to 0.61, 0.50; 95%CI = 0.29 to 0.67, and 0.44; 95%CI = 0.19 to 0.63, respectively), with tibial and peroneal CMAPs (r = 0.27; 95%CI = 0.01 to 0.49 and r = 0.32; 95%CI = 0.07 to 0.53), and with the BMI (r = 0.47; 95%CI = 0.25 to 0.64). Negative correlations were found with the neuropathy deficit score (r = −0.40; 95%CI = −0.60 to −0.16) and age (r = −0.51; 95%CI = −0.67 to −0.31). No such correlations were found for v_p.

Conclusion

This study is the first to find associations of MR nerve perfusion parameters with clinical and electrophysiological parameters related to DN in T2D. The results indicate that a decrease in microvascular permeability but not plasma volume may result in nerve ischemia that subsequently causes demyelination.

Nerve and Vascular Biomarkers in Skin Biopsies Differentiate Painful From Painless Peripheral Neuropathy in Type 2 Diabetes

Painful diabetic peripheral neuropathy can be intractable with a major impact, yet the underlying pain mechanisms remain uncertain. A range of neuronal and vascular biomarkers was investigated in painful diabetic peripheral neuropathy (painful-DPN) and painless-DPN and used to differentiate painful-DPN from painless-DPN. Skin biopsies were collected from 61 patients with type 2 diabetes (T2D), and 19 healthy volunteers (HV). All subjects underwent detailed clinical and neurophysiological assessments. Based on the neuropathy composite score of the lower limbs [NIS(LL)] plus seven tests, the T2D subjects were subsequently divided into three groups: painful-DPN (n = 23), painless-DPN (n = 19), and No-DPN (n = 19). All subjects underwent punch skin biopsy, and immunohistochemistry used to quantify total intraepidermal nerve fibers (IENF) with protein gene product 9.5 (PGP9.5), regenerating nerve fibers with growth-associated protein 43 (GAP43), peptidergic nerve fibers with calcitonin gene-related peptide (CGRP), and blood vessels with von Willebrand Factor (vWF). The results showed that IENF density was severely decreased (p < 0.001) in both DPN groups, with no differences for PGP9.5, GAP43, CGRP, or GAP43/PGP9.5 ratios. There was a significant increase in blood vessel (vWF) density in painless-DPN and No-DPN groups compared to the HV group, but this was markedly greater in the painful-DPN group, and significantly higher than in the painless-DPN group (p < 0.0001). The ratio of sub-epidermal nerve fiber (SENF) density of CGRP:vWF showed a significant decrease in painful-DPN vs. painless-DPN (p = 0.014). In patients with T2D with advanced DPN, increased dermal vasculature and its ratio to nociceptors may differentiate painful-DPN from painless-DPN. We hypothesized that hypoxia-induced increase of blood vessels, which secrete algogenic substances including nerve growth factor (NGF), may expose their associated nociceptor fibers to a relative excess of algogens, thus leading to painful-DPN.

Magnetic Resonance Neurography Reveals Smoking-Associated Decrease in Sciatic Nerve Structural Integrity in Type 2 Diabetes

Objective

It is controversially discussed in how far smoking contributes to diabetic polyneuropathy (DPN) in type 2 diabetes (T2D). Diffusion-weighted magnetic resonance neurography (MRN) at 3 Tesla has been shown to provide objective values for structural nerve integrity in patients with T2D. The aim of this study was to investigate the contribution of cigarette smoking on structural nerve integrity in T2D.

Methods

This cross-sectional prospective cohort study investigated the structural integrity of the sciatic nerve in 10 smokers, 40 never-smokers, and 20 ex-smokers with T2D and 10 healthy control subjects, using diffusion tensor imaging MRN at 3 Tesla and semi-automated nerve fiber tracking. Results were correlated with clinical, electrophysiological, and serological data.

Results

The sciatic nerve’s fractional anisotropy (FA), a parameter for structural nerve integrity, was significantly lower in smokers with T2D when compared to controls (p = 0.002) and never-smokers (p = 0.015), and lower in ex-smokers when compared to controls (p = 0.015). In addition, sciatic nerve radial diffusivity, a marker of myelin damage, was increased in smokers versus controls and never-smokers (p = 0.048, p = 0.049, respectively). Furthermore, FA in T2D patients was negatively correlated with clinical and electrophysiological markers of DPN. FA also showed negative correlations with the pulse wave velocity, a marker of arterial stiffness and associated microangiopathy, in controls (r = −0.70; p = 0.037), never-smokers (r = −0.45; p = 0.004), ex-smokers (r = −0.55; p = 0.009), and a similar trend in smokers (r = −0.63; p = 0.076). Negative correlations were found between FA and skin auto-fluorescence, a marker of tissue advanced glycation end product accumulation and therefore long-term glycemic stress in T2D, in never-smokers (r = −0.39; p = 0.020) and smokers (r = −0.84; p = 0.004), but not in ex-smokers (r = −0.07; p = 0.765).

Conclusion

The findings indicate that smoking contributes to sciatic nerve damage in T2D, potentially worsening DPN due to glycemic stress and less microangiopathy-associated myelin damage in active smokers, while angiopathic effects predominate in ex-smokers. To stop smoking may therefore pose a promising preventive measure to slow the progression of DPN in T2D.