The metabolic syndrome and neuropathy: therapeutic challenges and opportunities

Hungry for relief: Potential for neurotensin to address comorbid obesity and pain

Chronic pain and obesity frequently occur together. An ideal therapy would alleviate pain without weight gain, and most optimally, could promote weight loss. The neuropeptide neurotensin (Nts) has been separately implicated in reducing weight and pain but could it be a common actionable target for both pain and obesity? Here we review the current knowledge of Nts signaling via its receptors in modulating body weight and pain processing. Evaluating the mechanism by which Nts impacts ingestive behavior, body weight, and analgesia has potential to identify common physiologic mechanisms underlying weight and pain comorbidities, and whether Nts may be common actionable targets for both.

Peripheral neuropathy in patients with gout, beyond focal nerve compression: a cross-sectional study

Neuropathies secondary to tophus compression in gout patients are well known; however, limited data exist on other types of peripheral neuropathies (PN). Our aim was to describe PN frequency, characteristics, distribution, patterns, and associated factors in gout patients through clinical evaluation, a PN questionnaire, and nerve conduction studies (NCS). This cross-sectional descriptive study included consecutive gout patients (ACR/EULAR 2015 criteria) from our clinic. All underwent evaluation by Rheumatology and Rehabilitation departments, with IRB approval. Based on NCS, patients were categorized as PN + (presence) or PN- (absence). PN + patients were further classified as local peripheral neuropathy (LPN) or generalized somatic peripheral neuropathy (GPN). We enrolled 162 patients, 98% male (72% tophaceous gout). Mean age (SD): 49.4 (12) years; mean BMI: 27.9 (6.0) kg/m2. Comorbidities included dyslipidemia (53%), hypertension (28%), and obesity (23.5%). Abnormal NCS: 65% (n = 106); 52% LPN, 48% GPN. PN + patients were older, had lower education, and severe tophaceous gout. GPN patients were older, had lower education, and higher DN4 scores compared to LPN or PN- groups (p = 0.05); other risk factors were not significant. Over half of gout patients experienced neuropathy, with 48% having multiplex mononeuropathy or polyneuropathy. This was associated with joint damage and functional impairment. Mechanisms and risk factors remain unclear. Early recognition and management are crucial for optimizing clinical outcomes and quality of life in these patients. Key Points Peripheral neuropathies in gout patients had been scarcely reported and studied. This paper report that: • PN in gout is more frequent and more diverse than previously reported. • Mononeuropathies are frequent, median but also ulnar, peroneal and tibial nerves could be injured. • Unexpected, generalized neuropathies (polyneuropathy and multiplex mononeuropathy) are frequent and associated to severe gout. • The direct role of hyperuricemia /or gout in peripheral nerves require further studies.

Impact of Obesity and Age on Mouse Corneal Innervation at the Epithelial-Stromal Interface

Purpose

The corneal epithelium is the most highly innervated structure in the body. Previously, we reported a novel event whereby stromal axons fuse with basal epithelial cells, limiting nerve penetration into the epithelium. Although corneal-epithelial nerves undergo changes in sensitivity and distribution throughout life and in response to an obesogenic diet, it is unknown if neuronal-epithelial cell fusion is altered. Here, we sought to determine if neuronal-epithelial cell fusion frequency correlates with obesogenic diet consumption and age.

Methods

Corneas were collected from C57BL/6 mice and evaluated for neuronal-epithelial cell fusion frequency using serial block-face scanning electron microscopy. To assess the correlation between diet-induced obesity and fusion frequency, 6-week-old mice were fed either a normal diet or an obesogenic diet for 10 weeks. To assess changes in fusion frequency between young and adult mice under normal dietary conditions, 9- and 24-week-old mice were used.

Results

Mice fed a 10-week obesogenic diet showed 87% of central-cornea stromal nerves engaged in fusion compared with only 54% in age-matched controls (16 weeks old). In 9-week-old normal-diet animals, 48% of central-cornea stromal nerves contained fusing axons and increased to 81% at 24 weeks of age. Corneal sensitivity loss correlated with increased body weight and adiposity regardless of age and diet.

Conclusions

Neuronal-epithelial cell fusion positively correlates with age and obesogenic diet consumption, and corneal nerve sensitivity loss correlates with increased body weight and adiposity, regardless of age and diet. As such, neuronal-epithelial cell fusion may play a role in corneal nerve density and sensitivity regulation.

The effects of Garcinia kola and curcumin on the dorsal root ganglion of the diabetic rat after peripheral nerve transection injury

OBJECTIVE

To test the protective effects of Garcinia kola and curcumin on the ganglion tissues of diabetic rats following the use of autologous vein graft in peripheral nerve transection injury.

METHODS

The sciatic nerve on the right side was transected, and anastomosis was performed between the proximal and distal ends using an autologous vein graft. Curcumin and Garcinia kola seed extract were administered daily by oral gavage. The ganglion tissues were harvested after a 90-day waiting period. Sensory neurons in the dorsal root ganglion at the L4 and L5 levels were used for stereological evaluations. Mean sensory neuron numbers were analyzed using a stereological technique. The size of the light and dark neurons was also estimated, and ultrastructural and immunohistochemical evaluations were performed.

RESULTS

A statistically significant difference in sensory neuron numbers was observed between the groups with and without Garcinia kola and curcumin applications. The immunohistochemical results showed that the s-100 protein is expressed selectively between cell types.

CONCLUSION

The results of this study show that curcumin and Garicinia kola prevented sensory neuron loss in diabetic rats following transection injury to the sciatic nerve.

Carpal tunnel syndrome

Median neuropathy at the wrist, commonly referred to as carpal tunnel syndrome (CTS), is the most common entrapment neuropathy. It is caused by chronic compression of the median nerve at the wrist within the space-limited carpal tunnel. Risk factors that contribute to the etiology of compression include female gender, obesity, work-related factors, and underlying medical conditions, such as hypothyroidism, pregnancy, and amyloidosis. The diagnosis is made on clinical grounds, although these can be confounded by anatomical variations. Electrodiagnostic studies, which are specific and sensitive in diagnosing CTS, support the diagnosis; however, a subgroup may present with normal results. The advent of imaging techniques, including ultrasound and MRI, further assists the diagnostic process. The management of CTS is divided into the nonsurgical approaches that include hand therapy, splinting and corticosteroid injection, and surgical decompression of the carpal tunnel. Although several surgical techniques have been developed, no one method is more effective than the other. Each of these management approaches are effective at providing symptom relief and are utilized at different severities of the condition. There is, however, a lack of consensus on standardized diagnostic criteria, as well as when and to whom to refer patients for surgery.

Minor and Major Amputation Rates Following Midfoot Charcot Reconstructive Surgery

Charcot neuroarthropathy (CNA) is a progressive disease that affects the bones and joints of the foot. To prevent collapse and loss of stability within the pedal architecture, CNA should be diagnosed and managed early. The objective of this retrospective study was to review patients who underwent midfoot CNA reconstructive surgery and evaluate subsequent rates of minor and major amputations. Secondary objectives include identifying patients that underwent midfoot CAN with and without a subtalar joint (STJ) arthrodesis. Out of the 72 patients, 4 (5.6%) underwent minor (digital, ray) amputation, 2 (2.8%) underwent proximal amputations (either below or above the knee), and none underwent midfoot amputation (transmetatarsal, Lisfranc, Chopart). A Fisher's exact test was employed to compare the outcomes of minor and major amputation rates in our CNA cohort with those who underwent midfoot CNA reconstruction with STJ arthrodesis and found no statistical significance (p = .15). Overall, a total progression to amputation was 8.4% following midfoot CNA reconstruction, with 2.8% of patients undergoing major amputation (below knee or above knee). Despite no statistical significance, we recommend surgeons to consider including an STJ arthrodesis in addition to midfoot CNA reconstruction to establish a stable and plantigrade foot.

Comparison of Minimally Invasive and Open Approaches for Midfoot Charcot Neuroarthropathy Reconstruction

Charcot neuroarthropathy (CNA) is a progressive disease affecting the bones and joints of the foot that can lead to instability, breakdown, and collapse. Minimally invasive surgery (MIS) techniques are becoming a popular option within musculoskeletal surgery of the foot and ankle and may be an alternative to aggressive dissection seen during corrective surgery. An MIS approach minimizes vascular disruption, provides structural stability at an osteotomy or arthrodesis site, and encourages early mobilization if indicated. This retrospective study compares 17 patients who underwent an open approach for midfoot CNA reconstruction with 17 patients who underwent an MIS approach for midfoot CNA reconstruction. Preoperative and postoperative radiographic parameters were measured: lateral talus-first metatarsal, anteroposterior (AP) talus-first metatarsal, calcaneal pitch, and cuboid height. Difficulties that occurred during treatment were gathered and sorted into postoperative problems (stage I), obstacles (stage II), and complications (stage III). Changes from preoperative to postoperative radiographic lateral talus-first metatarsal and AP talus-first metatarsal angles were statistically significant (p < .001) for both the MIS and open approach. No true postoperative complications (stage III) were observed at last follow-up. The most common difficulty encountered was pin-site infection (stage I; in 23.5% of patients) in the MIS group. In the open group, the most common complications were wound development (stage I; 23.5%) and nonunions (stage II; 23.5%). Our findings suggest that midfoot CNA reconstruction with MIS methods offers similar outcomes to the open approach.

Comparison of western diet-induced obesity and streptozotocin mouse models: insights into energy balance, somatosensory dysfunction, and cardiac autonomic neuropathy

Metabolic disorders such as obesity and type 2 diabetes (T2D) are increasingly prevalent worldwide, necessitating a deeper comprehension of their underlying mechanisms. However, translating findings from animal research to human patients remains challenging. This study aimed to investigate the long-term effects of Streptozotocin (STZ) on metabolic, cardiac, and somatosensory function in mice fed a Western diet (WD) of high fat, sucrose, and cholesterol with low doses of STZ administration compared to mice fed WD alone. In our research, we thoroughly characterized energy balance and glucose homeostasis, as well as allodynia and cardiac function, all of which have been previously shown to be altered by WD feeding. Notably, our findings revealed that the treatment of WD-fed mice with STZ exacerbated dysfunction in glucose homeostasis via reduced insulin secretion in addition to impaired peripheral insulin signaling. Furthermore, both WD and WD + STZ mice exhibited the same degree of cardiac autonomic neuropathy, such as reduced heart rate variability and decreased protein levels of cardiac autonomic markers. Furthermore, both groups developed the same symptoms of neuropathic pain, accompanied by elevated levels of activating transcription factor 3 (Atf3) in the dorsal root ganglia. These discoveries enhance our understanding of metabolic activity, insulin resistance, neuropathy, and cardiac dysfunction of diet-induced models of obesity and diabetes. The exacerbation of impaired insulin signaling pathways by STZ did not lead to or worsen cardiac and somatosensory dysfunction. Additionally, they offer valuable insights into suitable diet induced translational mouse models, thereby advancing the development of potential interventions for associated conditions.

Management of Midfoot Charcot: Minimally Invasive Techniques and Improved Fixation

The objective of this article is to review the etiology and pathophysiology of Charcot neuroarthropathy as it contributes to the breakdown of the midfoot. The article will also discuss the emerging techniques in minimally invasive surgery and how this is applied to Charcot reconstructive surgery as well as reflect on a newer thought processes to surgical intervention.

In vivo corneal confocal microscopy as a non-invasive test to assess obesity induced small fibre nerve damage and inflammation

PURPOSE

To investigate small nerve fibre damage and inflammation at the level of the sub-basal nerve plexus (SNP) of severe obese patients and compare the results with those of healthy subjects.

METHODS

This cross-sectional, observational study investigated the data of 28 patients (14 out of 28 prediabetic or diabetic) with severe obesity (Body Mass Index; BMI ≥ 40) and 20 healthy subjects. Corneal nerve fibre density (CNFD), branch density (CNBD), fibre length (CNFL), nerve fibre area (CNFA), nerve fibre width (CNFW), and nerve fractal dimension (CNFrD) and dendritic cell (DC) density were evaluated using in vivo confocal microscopy (IVCM, Heidelberg Retinal Tomograph III Rostock Cornea Module). Automatic CCMetrics software (University of Manchester, UK) was used for quantitative analysis of SNP.

RESULTS

Mean age was 48.4±7.4 and 45.1 ± 5.8 in the control and obese group, respectively (p = 0.09). Mean BMI were 49.1 ± 7.8 vs. 23.3 ± 1.4 in obese vs. control group, respectively (p < 0.001). Mean CNFD, CNBD, CNFL, CNFA, CNFW were significantly reduced in obese group compared with those in the control group (always p < 0.05, respectively). There were no significant differences in any ACCMetrics parameters between prediabetic/diabetic and non-diabetic obese patients. Increased DC densities were detected in obese group compared with those in control group (p < 0.0001). There were significant correlations between BMI scores and SNP parameters.

CONCLUSION

Imaging with IVCM is a feasible, non-invasive method to detect and quantify occult corneal nerve damage and increased inflammation in patients with obesity. This study suggests that obesity may be a separate risk factor for peripheral neuropathy regardless of DM.

Progression to Hindfoot Charcot Neuroarthropathy After Midfoot Charcot Correction in Patients With and Without Subtalar Joint Arthrodesis

Charcot neuroarthropathy (CNA) is a disabling and progressive disease that affects the bones and joints of the foot. Successful Charcot reconstruction focuses on restoring anatomic alignment, obtaining multiple joint arthrodesis, selecting stable fixation, preserving foot length, and creating a foot suitable for community ambulation in supportive shoegear. Intramedullary fixation arthrodesis of the medial and lateral columns has been previously reported to produce improvement in midfoot Charcot reconstruction. More recently, a growing trend of stabilization of the subtalar joint (STJ) has been incorporated alongside the medial and lateral column fusion. Our objectives were to retrospectively review patients who underwent midfoot Charcot reconstructive surgery, whether with or without accompanying STJ arthrodesis, and establish which patients progressed to ankle CNA. Of the 72 patients who underwent midfoot Charcot reconstruction, 28 (38.9%) underwent STJ arthrodesis, and 22 converted to ankle CNA (30.6%). Fourteen (63.6%) of 22 ankle CNA cases had not undergone STJ arthrodesis; 8 patients (36.4%) had it. A Fisher exact test was performed to identify the relationship between those without STJ arthrodesis and those progressing to ankle CNA; it revealed statistical significance (P = 0.001). Performing an STJ arthrodesis with midfoot Charcot reconstructive surgery may be beneficial to aiding in hindfoot stability, establishing a plantigrade foot, and providing further insight into the management of midfoot Charcot. LEVEL OF CLINICAL EVIDENCE: III.

Prevalence and Predictors of Carpal Tunnel Syndrome Symptoms Among Teachers in Riyadh: A Cross-Sectional Study

Background Carpal tunnel syndrome (CTS) is a musculoskeletal disorder (MSD) afflicting the upper limbs with a prevalence of approximately 14.4% in the general population. Previous studies have noted the increasing prevalence of MSDs among teachers but have not investigated in depth the prevalence and predictors of CTS symptoms in this population. The aim of this study was to help fill this gap in the literature by investigating teachers working in Riyadh, Saudi Arabia. Methods We conducted this cross-sectional study in Riyadh using an online survey. We distributed the Boston carpal tunnel questionnaire (BCTQ) to schoolteachers in the city through the social media applications Twitter, WhatsApp, and Telegram. We assessed the respondents' symptoms using Univariate association analyses with a Wilcoxon rank sum test for the continuous variables and Fisher's exact test and Pearson's chi-squared test for the categorical variables. We assessed the independent risk factors for CTS by constructing multivariate binary logistic regression models and expressed the results using the odds ratio (OR) and 95% confidence intervals (95% CIs), with p < 0.05 indicating statistical significance. Results The sample for this study included 490 teachers. Among them, the prevalence of moderate to severe CTS symptoms was 40.0%, and self-reported CTS was 9.1%. The teachers who were female, relatively old, left-handed, retired, and spent significant time using a pen, keyboard, and/or blackboard were more likely than those who were male, relatively young, right-handed, and did not spend significant time using a pen, keyboard, and/or blackboard to self-report CTS and exhibit moderate to severe symptoms. Conclusions We found a relatively high percentage (40.0%) of CTS symptoms among teachers working in Riyadh. This finding suggests that any sign of CTS symptoms should be checked to ensure early diagnosis and treatment, which contribute to positive outcomes, particularly given the recent increase in such risk factors for CTS as diabetes, hypothyroidism, and high BMI in populations worldwide.

The Effect of Hesperidin and Diosmin Individually or in Combination on Metabolic Profile and Neuropathy among Diabetic Patients with Metabolic Syndrome: A Randomized Controlled Trial

Current evidence supports the association of metabolic syndrome (MetS) with neuropathy. Limited data are available on proper strategies to control metabolic disorders and neuropathy among patients with type2 diabetes mellitus (T2DM). We aimed to determine hesperidin and diosmin efficacy individually and in combination among T2DM patients with neuropathy and meet MetS criteria. In this parallel-group designed trial, 129 T2DM patients with MetS and neuropathy were recruited and randomized to receive their oral hypoglycemics with either hesperidin (1g/day), or diosmin (1g/day), or combination of both or oral hypoglycemics without intervention for 12 weeks. Diabetic neuropathy was evaluated using Michigan Neuropathy Screening Instrument (MNSI) at baseline and after trial. Anthropometric parameters, blood glucose and lipid profile were also assessed before and after the intervention using paired student t-test within groups. The trial is registered at clinicaltrials.gov as NCT05243238. By completion of the trial duration, both hesperidin and diosmin groups showed significant reduction in blood glucose, triglycerides (TGs) and low density lipoprotein (LDL) from baseline (p<0.05). However, the magnitude of improvement in metabolic components significantly increased with hesperidin and diosmin combination. Although MNSI scores improved significantly in both groups, the reduction was more significant with the combination of hesperidin and diosmin. Moreover, the change in MNSI score was significantly correlated with the improvement in metabolic profile components including LDL, TGs and fasting blood glucose. Oral supplementation of hesperidin and diosmin was associated with improvement in metabolic syndrome and diabetic neuropathy and the combination of both was superior in efficacy.

LXR agonist modifies neuronal lipid homeostasis and decreases PGD2 in the dorsal root ganglia in western diet-fed mice

The prevalence of peripheral neuropathy is high in diabetic and overweight populations. Chronic neuropathic pain, a symptom of peripheral neuropathy, is a major disabling symptom that leads to a poor quality of life. Glucose management for diabetic and prediabetic individuals often fail to reduce or improve pain symptoms, therefore, exploring other mechanisms is necessary to identify effective treatments. A large body of evidence suggest that lipid signaling may be a viable target for management of peripheral neuropathy in obese individuals. The nuclear transcription factors, Liver X Receptors (LXR), are known regulators of lipid homeostasis, phospholipid remodeling, and inflammation. Notably, the activation of LXR using the synthetic agonist GW3965, delayed western diet (WD)-induced allodynia in rodents. To further understand the neurobiology underlying the effect of LXR, we used translating ribosome affinity purification and evaluated translatomic changes in the sensory neurons of WD-fed mice treated with the LXR agonist GW3965. We also observed that GW3965 decreased prostaglandin levels and decreased free fatty acid content, while increasing lysophosphatidylcholine, phosphatidylcholine, and cholesterol ester species in the sensory neurons of the dorsal root ganglia (DRG). These data suggest novel downstream interplaying mechanisms that modifies DRG neuronal lipid following GW3965 treatment.

“Big Data” Approaches for Prevention of the Metabolic Syndrome

Metabolic syndrome (MetS) is characterized by the concurrence of multiple metabolic disorders resulting in the increased risk of a variety of diseases related to disrupted metabolism homeostasis. The prevalence of MetS has reached a pandemic level worldwide. In recent years, extensive amount of data have been generated throughout the research targeted or related to the condition with techniques including high-throughput screening and artificial intelligence, and with these “big data”, the prevention of MetS could be pushed to an earlier stage with different data source, data mining tools and analytic tools at different levels. In this review we briefly summarize the recent advances in the study of “big data” applications in the three-level disease prevention for MetS, and illustrate how these technologies could contribute tobetter preventive strategies.

Carpal Tunnel Syndrome and Diabetes—A Comprehensive Review

Carpal tunnel syndrome (CTS) is the most common compression neuropathy in the general population and is frequently encountered among individuals with type 1 and 2 diabetes. The reason(s) why a peripheral nerve trunk in individuals with diabetes is more susceptible to nerve compression is still not completely clarified, but both biochemical and structural changes in the peripheral nerve are probably implicated. In particular, individuals with neuropathy, irrespective of aetiology, have a higher risk of peripheral nerve compression disorders, as reflected among individuals with diabetic neuropathy. Diagnosis of CTS in individuals with diabetes should be carefully evaluated; detailed case history, thorough clinical examination, and electrophysiological examination is recommended. Individuals with diabetes and CTS benefit from surgery to the same extent as otherwise healthy individuals with CTS. In the present review, we describe pathophysiological aspects of the nerve compression disorder CTS in relation to diabetes, current data contributing to the explanation of the increased risk for CTS in individuals with diabetes, as well as diagnostic methods, treatment options, and prognosis of CTS in diabetes.

Weight-Related and Personal Risk Factors of Carpal Tunnel Syndrome in the Northern Finland Birth Cohort 1966

BACKGROUND

Excess body mass is a risk factor for carpal tunnel syndrome (CTS), but the mechanisms of this are unclear. This study aimed to evaluate the association between CTS and personal risk factors of body mass index (BMI), waist circumference and waist-to-hip ratio (WHR).

METHODS

The study sample consisted of the Northern Finland Birth Cohort 1966 (n = 9246). At the age of 31 in 1997 and at the age of 46 in 2012, the participants underwent a clinical examination. Cohort A consisted of complete cases with a follow-up from 1997 to 2012 (n = 4701), and Cohort B was followed up from 2012 to 2018 (n = 4548). The data on diagnosed CTS were provided by the Care Register for Health Care until the end of 2018.

RESULTS

After an adjustment for confounding factors, BMI was associated with CTS among women (hazard ratio (HR) 1.47, 95% Cl 0.98-2.20 for overweight women and HR 2.22, 95% Cl 1.29-3.83 for obese women) and among both sexes combined (HR 1.35 95% Cl 0.96-1.90 for overweight and HR 1.98 95% Cl 1.22-3.22 for obese participants). Neither waist circumference nor WHR was associated with CTS.

CONCLUSIONS

BMI is an independent risk factor for CTS and is more relevant for estimating the increased risk of CTS due to excess body mass than waist circumference or WHR.

The Effects of Obesity and Bariatric Surgery on Rates of Upper Extremity Compression Neuropathies

Objectives

To estimate the effects of obesity on all types of upper extremity compression neuropathies (UECN) (carpal tunnel syndrome and other median nerve, radial nerve, and ulnar nerve compression neuropathies) and to assess whether bariatric surgery modifies these effects.

Background

UECN are increasingly prevalent and decrease the quality of life of affected individuals. Studies suggest obesity as a risk factor for carpal tunnel syndrome, the most common type of UECN.

Methods

A retrospective cohort study was conducted using the PearlDiver Mariner Database, an all-payor claims database containing claims for over 53 million patients from 2010 to 2019 in all 50 US states. Rates and odds of all types of UECN were compared between 1:1:1 exact matched cohorts of obese patients who were medically managed, obese patients who underwent bariatric surgery, and nonobese patients (111,967 patients in each cohort).

Results

Compared with nonobese patients, patients with obesity were significantly more likely to develop any UECN (odds ratio [OR], 1.13; 95% confidence interval [CI], 1.09-1.18), carpal tunnel syndrome (OR, 1.15; 95% CI, 1.10-1.30), and 2 or more UECN (OR, 1.34; 95% CI, 1.20-1.48). Compared with obese patients who were managed medically, obese patients who underwent bariatric surgery were significantly less likely to develop any UECN (OR, 0.87; 95% CI, 0.84-0.91) and carpal tunnel syndrome (OR, 0.85; 95% CI, 0.81-0.89).

Conclusions

Obese patients have higher odds of both single and concomitant UECN, specifically carpal tunnel syndrome, compared with nonobese patients. Bariatric surgery decreases the odds of developing UECN compared with obese patients not undergoing surgical intervention.

LXR agonist improves peripheral neuropathy and modifies PNS immune cells in aged mice

Background

Peripheral neuropathy is a common and progressive disorder in the elderly that interferes with daily activities. It is of importance to find efficient treatments to treat or delay this age-related neurodegeneration. Silencing macrophages by reducing foamy macrophages showed significant improvement of age-related degenerative changes in peripheral nerves of aged mice. We previously demonstrated that activation of the cholesterol sensor Liver X receptor (LXR) with the potent agonist, GW3965, alleviates pain in a diet-induced obesity model. We sought to test whether LXR activation may improve neuropathy in aged mice.

Methods

21-month-old mice were treated with GW3965 (25 mg/Kg body weight) for 3 months while testing for mechanical allodynia and thermal hyperalgesia. At termination, flow cytometry was used to profile dorsal root ganglia and sciatic nerve cells. Immune cells were sorted and analyzed for cholesterol and gene expression. Nerve fibers of the skin from the paws were analyzed. Some human sural nerves were also evaluated. Comparisons were made using either t test or one-way ANOVA.

Results

Treatment with GW3965 prevented the development of mechanical hypersensitivity and thermal hyperalgesia over time in aged mice. We also observed change in polarization and cholesterol content of sciatic nerve macrophages accompanied by a significant increase in nerve fibers of the skin.

Conclusions

These results suggest that activation of the LXR may delay the PNS aging by modifying nerve-immune cell lipid content. Our study provides new potential targets to treat or delay neuropathy during aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02423-z.

Evaluation of thermal sensitivity is of potential clinical utility for the predictive, preventive, and personalized approach advancing metabolic syndrome management

A possible association between metabolic disorders and ambient temperature has been suggested, and cold exposure as a way of increasing energy expenditure has gained considerable interest for preventative/therapeutic measures toward metabolic disorders. Although thermal sensitivity, which has recently been studied in regard to its utility as a risk assessment/patient stratification for various diseases, might influence physiological responses to ambient temperature on an individual basis, more studies are needed. We aimed to investigate the association between self-identified thermal intolerance/sensation and metabolic syndrome (MetS) to verify the working hypothesis that individuals with altered thermal sensitivity may have a predisposition to MetS. We fitted generalized additive models for thermal intolerance/sensation using body mass index (BMI) and waist–hip ratio in women, and identified those with higher/lower thermal intolerance/sensation than those predicted by the models. Higher heat intolerance, higher heat sensation, and lower cold intolerance were associated with a higher prevalence of MetS. The risk of having MetS was increased in those who had two or three associated conditions compared with those with none of these conditions. In an analysis for MetS components, significant associations of thermal sensitivity were present with high glucose, triglyceride, and blood pressure levels. Overall, higher heat intolerance/sensation and lower cold intolerance were associated with increased prevalence of MetS even at a similar level of obesity. Our study indicates that evaluation of thermal sensitivity may help identify individuals at high risk for MetS, and lead to more advanced patient stratification and personalized treatment strategies for MetS, including cold-induced thermogenesis.

Evaluation of Risk Factors for Diabetic Peripheral Neuropathy Among Saudi Type 2 Diabetic Patients with Longer Duration of Diabetes

BACKGROUND

Neuropathy is the most common microvascular complications among diabetic patients. Diabetic peripheral neuropathy (DPN) is the predominant variety which may associate with increased in mortality and morbidity among type 2 diabetes mellitus (T2DM).

OBJECTIVE

To assess the prevalence of diabetic peripheral neuropathy and its correlation with risk factors among T2DM.

METHODS

This was a cross-sectional retrospective study, data was collected from a previous cohort study conducted at the University Diabetes Center, King Saud University Medical City (KSUMC), King Saud University, Riyadh, Saudi Arabia. The data of T2DM patients were collected from case report form, included demographic data, history of chronic diabetes neuropathy, and laboratory reports. Statistical analysis includes Student`s t test, chi square test, and Pearson correlation and logistic regression were performed.

RESULTS

A total of 430 patients with T2DM data was collected and analyzed, and of them 54% were females, with the mean age of 55.88 years. The prevalence of diabetic neuropathy among study participants were 40.2%, and 73.3% of them having the subtype polyneuropathy. The mean BMI; p = 0.006, FBS; p < 0.001, HbA1c; p < 0.001, cholesterol p = 0.001, LDL; p < 0.001, and triglyceride; p < 0.001 levels were a significantly higher among participants with diabetic neuropathy than without neuropathy. The male gender (Risk Ratio: 1.294, 95% CI:1.090, 1.536) p = 0.003, fasting blood glucose (Risk Ratio: 1.157, 95% CI:1.051, 1.273) p = 0.003 Cholesterol (Risk Ratio: 1.588, 95% CI:1.174, 2.147) p = 0.003, triglyceride (Risk Ratio: 1.290, 95% CI:1.086, 1.538), p = 0.004, and LDL (Risk Ratio: 1.299, 95% CI:1.073, 1.574), p = 0.007) were found to be significant risk factors for DPN.

CONCLUSION

DPN is highly prevalent among T2DM patients in Saudi Arabia. Poor glycemic control and hyperlipidemia were associated with significantly higher risk for DPN patients among T2DM.

Treatment for Diabetic Peripheral Neuropathy: What have we Learned from Animal Models?

INTRODUCTION

Animal models have been widely used to investigate the etiology and potential treatments for diabetic peripheral neuropathy. What we have learned from these studies and the extent to which this information has been adapted for the human condition will be the subject of this review article.

METHODS

A comprehensive search of the PubMed database was performed, and relevant articles on the topic were included in this review.

RESULTS

Extensive study of diabetic animal models has shown that the etiology of diabetic peripheral neuropathy is complex, with multiple mechanisms affecting neurons, Schwann cells, and the microvasculature, which contribute to the phenotypic nature of this most common complication of diabetes. Moreover, animal studies have demonstrated that the mechanisms related to peripheral neuropathy occurring in type 1 and type 2 diabetes are likely different, with hyperglycemia being the primary factor for neuropathology in type 1 diabetes, which contributes to a lesser extent in type 2 diabetes, whereas insulin resistance, hyperlipidemia, and other factors may have a greater role. Two of the earliest mechanisms described from animal studies as a cause for diabetic peripheral neuropathy were the activation of the aldose reductase pathway and increased non-enzymatic glycation. However, continuing research has identified numerous other potential factors that may contribute to diabetic peripheral neuropathy, including oxidative and inflammatory stress, dysregulation of protein kinase C and hexosamine pathways, and decreased neurotrophic support. In addition, recent studies have demonstrated that peripheral neuropathy-like symptoms are present in animal models, representing pre-diabetes in the absence of hyperglycemia.

CONCLUSION

This complexity complicates the successful treatment of diabetic peripheral neuropathy, and results in the poor outcome of translating successful treatments from animal studies to human clinical trials.

Dietary weight loss in people with severe obesity stabilizes neuropathy and improves symptomatology

OBJECTIVE

The aim of this study was to determine the effect of dietary weight loss on neuropathy outcomes in people with severe obesity.

METHODS

A prospective cohort study of participants attending a medical weight-management program was followed. Weight loss was achieved with meal replacement of 800 kcal/d for 12 weeks and then transitioning to 1,200 to 1,500 kcal/d. The coprimary outcomes were changes in intraepidermal nerve fiber density (IENFD) at the distal leg and proximal thigh. Secondary outcomes included nerve conduction studies, Michigan Neuropathy Screening Instrument questionnaire and exam, Quality of Life in Neurological Disorders, and quantitative sensory testing.

RESULTS

Among 131 baseline participants, 72 (mean [SD] age: 50.1 [10.5] years, 51.4% female) completed 2 years of follow-up. Participants lost 12.4 (11.8) kg. All metabolic syndrome components improved with the exception of blood pressure. IENFD in the distal leg (0.4 [3.3], p = 0.29), and proximal thigh (0.3 [6.3], p = 0.74) did not significantly change. Improvements were observed on the Michigan Neuropathy Screening Instrument questionnaire, two Quality of Life in Neurological Disorders subdomains, and quantitative sensory testing cold threshold.

CONCLUSIONS

Dietary weight loss was associated with improvements in all metabolic parameters except blood pressure, and both IENFD outcomes remained stable after 2 years. Given that natural history studies reveal decreases in IENFD over time, dietary weight loss may halt this progression, but randomized controlled trials are needed.

Small Fiber Neuropathy Incidence, Prevalence, Longitudinal Impairments, and Disability

BACKGROUND AND OBJECTIVES

There are limited population-based data on small fiber neuropathy (SFN). We wished to determine SFN incidence, prevalence, comorbid conditions, longitudinal impairments, and disabilities.

METHODS

Test-confirmed patients with SFN in Olmsted, Minnesota, and adjacent counties were compared 3:1 to matched controls (January 1, 1998-December 31, 2017).

RESULTS

Ninety-four patients with SFN were identified, with an incidence of 1.3/100,000/y that increased over the study period and a prevalence of 13.3 per 100,000. Average follow-up was 6.1 years (0.7-43 years), and mean onset age was 54 years (range 14-83 years). Female sex (67%), obesity (body mass index mean 30.4 vs 28.5 kg/m²), insomnia (86% vs 54%), analgesic-opioid prescriptions (72% vs 46%), hypertriglyceridemia (180 mg/dL mean vs 147 mg/dL), and diabetes (51% vs 22%, p < 0.001) were more common (odds ratio 3.8-9.0, all p < 0.03). Patients with SFN did not self-identify as disabled with a median modified Rankin Scale score of 1.0 (range 0-6) vs 0.0 (0-6) for controls (p = 0.04). Higher Charlson comorbid conditions (median 6, range 3-9) occurred vs controls (median 3, range 1-9, p < 0.001). Myocardial infarctions occurred in 46% vs 27% of controls (p < 0.0001). Classifications included idiopathic (70%); diabetes (15%); Sjögren disease (2%); AL-amyloid (1%); transthyretin-amyloid (1%); Fabry disease (1%); lupus (1%); postviral (1%); Lewy body (1%), and multifactorial (5%). Foot ulcers occurred in 17, with 71% having diabetes. Large fiber neuropathy developed in 36%, on average 5.3 years (range 0.2-14.3 years) from SFN onset. Median onset Composite Autonomic Severity Score (CASS) was 3 (change per year 0.08, range 0-2.0). Median Neuropathy Impairment Scale (NIS) score was 2 at onset (range 0-8, change per year 1.0, range -7.9 to +23.3). NIS score and CASS change >1 point per year occurred in only AL-amyloid, hereditary transthyretin-amyloid, Fabry, uncontrolled diabetes, and Lewy body. Death after symptom onset was higher in patients with SFN (19%) vs controls (12%, p < 0.001), 50% secondary to diabetes complications.

DISCUSSION

Isolated SFN is uncommon but increasing in incidence. Most patients do not develop major neurologic impairments and disability but have multiple comorbid conditions, including cardiovascular ischemic events, and increased mortality from SFN onsets. Development of large fiber involvements and diabetes are common over time. Targeted testing facilitates interventional therapies for diabetes but also rheumatologic and rare genetic forms.

Replication of epidemiological associations of carpal tunnel syndrome in a UK population-based cohort of over 400,000 people

Introduction

Several phenotypic factors are associated in the literature with an increased risk of carpal tunnel syndrome (CTS). Along with female sex and older age, certain systemic diseases show an association with CTS, with varying degrees of evidence.

Methods

This study was performed using the UK Biobank resource – a cohort study of over 500,000 participants who have allowed linkage of phenotypic data with their medical records. We calculated the prevalence of CTS and a sex-specific prevalence ratio and compared the body mass index (BMI) between cases and controls. We performed a series of nested case-control studies to compute odds ratios for the association between CTS and three systemic diseases.

Results

There were 12,312 CTS cases within the curated UK Biobank dataset of 401,656 (3.1% prevalence), and the female:male ratio was 1.95:1. CTS cases had, on average, a BMI > 2.0 kg/m² greater than controls. Odds ratios for the association with CTS for three systemic diseases were 2.31 (95% CI 2.17–2.46) for diabetes, 2.70 (95% CI 2.44–2.99) for rheumatoid arthritis, and 1.47 (95% CI 1.38–1.57) for hypothyroidism. Adjusted for BMI, these odds ratios fell to 1.75 (95% CI 1.65–1.86), 2.43 (95% CI 2.20–2.69), and 1.35 (95% CI 1.26–1.43), respectively.

Discussion

We harnessed the size and power of UK Biobank to provide robust replication of evidence for the associations between CTS and female sex, raised BMI, and three systemic diseases, which are only mediated in part by raised BMI.

Advances in diet-induced rodent models of metabolically acquired peripheral neuropathy

Peripheral neuropathy (PN) is a severe complication that affects over 30% of prediabetic and 60% of type 2 diabetic (T2D) patients. The metabolic syndrome is increasingly recognized as a major driver of PN. However, basic and translational research is needed to understand the mechanisms that contribute to nerve damage. Rodent models of diet-induced obesity, prediabetes, T2D and PN closely resemble the human disease and have proven to be instrumental for the study of PN mechanisms. In this Perspective article, we focus on the development, neurological characterization and dietary fat considerations of diet-induced rodent models of PN. We highlight the importance of investigating sex differences and discuss some of the challenges in translation from bench to bedside, including recapitulating the progressive nature of human PN and modeling neuropathic pain. We emphasize that future research should overcome these challenges in the quest to better mimic human PN in animal models.

Theories behind the effect of starch‑ and sucrose‑reduced diets on gastrointestinal symptoms in irritable bowel syndrome (Review)

Increased amounts of starch and sugar have been added to the diet in the Western world during the last decades. Undigested carbohydrates lead to bacterial fermentation and gas production with diffusion of water, causing abdominal bloating, pain and diarrhea. Therefore, dietary advice is the first line of treatment of irritable bowel syndrome (IBS), a disease characterized by abdominal pain and altered bowel habits without any organic findings. Recently, a diet with a reduction of starch and sucrose led to a marked effect on gastrointestinal (GI) symptoms. The mechanism is unknown, but three possible mechanisms are presented in the present review. First, functional variants of the enzyme sucrase‑isomaltase (SI) have been described in IBS. A subgroup of patients with IBS may thus suffer from partial SI deficiency with reduced digestion of starch and sucrose. Second, fructose absorption is less efficient than glucose absorption, which may lead to a physiological fructose malabsorption when ingesting high amounts of sucrose. A third mechanism is that high‑sugar diets causing hyperglycemia, hyperinsulinemia and weight gain have led to painful neuropathy in animal models; whereas, improved metabolic control in humans has led to improvement of neuropathy. Starch‑ and sucrose‑reduced diets lead to decreased levels of C‑peptide, insulin, gastric inhibitory peptide, leptin and weight reduction. These metabolic changes may reduce the excitability of the hypersensitive nervous system often found in IBS and, thereby, lead to the reduced symptoms found after the diet. In conclusion, further studies are needed to investigate the pathophysiology behind development of symptoms after starch and sucrose intake, and the mechanisms behind symptom relief after reduced intake.

Obesity, Type 2 Diabetes, and the Risk of Carpal Tunnel Syndrome: A Two-Sample Mendelian Randomization Study

Some previous observational studies have reported an increased risk of carpal tunnel syndrome (CTS) in patients with obesity or type 2 diabetes (T2D), which was however, not observed in some other studies. In this study we performed a two-sample Mendelian randomization to assess the causal effect of obesity, T2D on the risk of CTS. Single nucleotide polymorphisms associated with the body mass index (BMI) and T2D were extracted from genome-wide association studies. Summary-level results of CTS were available through FinnGen repository. Univariable Mendelian randomization (MR) with inverse-variance-weighted method indicated a positive correlation of BMI with CTS risk [odds ratio (OR) 1.66, 95% confidence interval (CI), 1.39–1.97]. Genetically proxied T2D also significantly increased the risk of CTS [OR 1.17, 95% CI (1.07–1.29)]. The causal effect of BMI and T2D on CTS remained consistent after adjusting for each other with multivariable MR. Our mediation analysis indicated that 34.4% of BMI’s effect of CTS was mediated by T2D. We also assessed the effects of several BMI and glycemic related traits on CTS. Waist circumference and arm fat-free mass were also causally associated with CTS. However, the associations disappeared after adjusting for the effect of BMI. Our findings indicate that obesity and T2D are independent risk factors of CTS.

Corneal Keratocyte Density and Corneal Nerves Are Reduced in Patients With Severe Obesity and Improve After Bariatric Surgery

Purpose

Obesity is associated with peripheral neuropathy, which bariatric surgery may ameliorate. The aim of this study was to assess whether corneal confocal microscopy can show a change in corneal nerve morphology and keratocyte density in subjects with severe obesity after bariatric surgery.

Methods

Twenty obese patients with diabetes (n = 13) and without diabetes (n = 7) underwent assessment of hemoglobin A1c (HbA1c), lipids, IL-6, highly sensitive C-reactive protein (hsCRP), and corneal confocal microscopy before and 12 months after bariatric surgery. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and keratocyte density (KD) from the anterior, middle, and posterior stroma were quantified. Twenty-two controls underwent assessment at baseline only.

Results

CNFL (P < 0.001), CNBD (P < 0.05), and anterior (P < 0.001), middle (P < 0.001), and posterior (P < 0.001) keratocyte densities were significantly lower in obese patients compared to controls, and anterior keratocyte density (AKD) correlated with CNFL. Twelve months after bariatric surgery, there were significant improvements in body mass index (BMI; P < 0.001), HDL cholesterol (P < 0.05), hsCRP (P < 0.001), and IL-6 (P < 0.01). There were significant increases in CNFD (P < 0.05), CNBD (P < 0.05), CNFL (P < 0.05), and anterior (P < 0.05) and middle (P < 0.001) keratocyte densities. The increase in AKD correlated with a decrease in BMI (r = -0.55, P < 0.05) and triglycerides (r = -0.85, P < 0.001). There were no significant correlations between the change in keratocyte densities and corneal nerve fiber or other neuropathy measures.

Conclusions

Corneal confocal microscopy demonstrates early small fiber damage and reduced keratocyte density in obese patients. Bariatric surgery leads to weight reduction and improvement in lipids and inflammation and an improvement in keratocyte density and corneal nerve regeneration.

A Review of Alternative Treatment Options in Diabetic Polyneuropathy

Currently there is no recognized curative treatment for diabetic polyneuropathy (DPN). Strict glucose control and symptomatic pain relief are the first line management routes. DPN is a common complication of diabetes and has a major detrimental influence on the quality of life (QOL) for many patients. Due to the scope of the problem, it is imperative that treatment options which impede DPN's progression and restore sensorineural function should be researched comprehensively and made available to the masses at an economical cost. We reviewed a multitude of atypical treatment options for DPN including capsaicin, lidocaine, acupuncture, electrical nerve stimulation, alpha lipoic acid, benfotiamine, and acetyl-l-carnitine and explored the evidence to date regarding their safety and efficacy. Most of these options have been around for a long time and have promising pilot studies or small-scale trials focused on DPN treatment.

Cardiovascular health and chronic axonal polyneuropathy: A population-based study

Background and purpose

Chronic axonal polyneuropathy is a common, usually multifactorial, disease for which there is no treatment yet available. We investigated the association between cardiovascular health, defined by the health score of the American Heart Association, and chronic axonal polyneuropathy.

Methods

Between June 2013 and January 2017, we investigated participants of the Rotterdam Study, a population‐based cohort study. Participants were screened for polyneuropathy and categorized as having no, possible, probable or definite polyneuropathy. The cardiovascular health score (range 0–14; higher score reflecting better health) consisted of four health behaviours (diet, physical activity, smoking and body mass index) and three health factors (blood pressure, serum cholesterol and fasting glucose level).

Results

We included 1919 participants, of whom 120 (6.3%) had definite polyneuropathy. The median (interquartile range [IQR]) age was 69.0 (58.6–73.7) years and 53.4% were women. A higher cardiovascular health score was associated with a lower prevalence of definite polyneuropathy (per point increase: odds ratio [OR] 0.90, 95% confidence interval [CI] 0.84–0.96). Optimal cardiovascular health (score≥10) was strongly associated with a lower prevalence of definite polyneuropathy (OR 0.55, 95% CI 0.32–0.90). An increase in health factors and health behaviour scores separately was associated with a lower prevalence of polyneuropathy (per point increase: OR 0.82, 95% CI 0.71–0.95 and OR 0.86, 95% CI 0.78–0.96, respectively). The association between a lower cardiovascular health score and lower sural nerve amplitude was not significant after correction for covariates (difference 0.07µV, 95% CI −0.02–0.17).

Conclusions

Better cardiovascular health, consisting of both modifiable health behaviours and health factors, is associated with a lower prevalence of chronic axonal polyneuropathy.

Peripheral Neuropathy and All-Cause and Cardiovascular Mortality in U.S. Adults : A Prospective Cohort Study

BACKGROUND

Growing evidence indicates that peripheral neuropathy (PN) is common even in the absence of diabetes. However, the clinical sequelae of PN have not been quantified in the general population.

OBJECTIVE

To assess the associations of PN with all-cause and cardiovascular mortality in the general adult population of the United States.

DESIGN

Prospective cohort study.

SETTING

NHANES (National Health and Nutrition Examination Survey), 1999 to 2004.

PARTICIPANTS

7116 adults aged 40 years or older who had standardized monofilament testing for PN.

MEASUREMENTS

Cox regression to evaluate the associations of PN with all-cause and cardiovascular mortality after adjustment for demographic and cardiovascular risk factors, overall and stratified by diabetes status.

RESULTS

The overall prevalence of PN (±SE) was 13.5% ± 0.5% (27.0% ± 1.4% in adults with diabetes and 11.6% ± 0.5% in adults without diabetes). During a median follow-up of 13 years, 2128 participants died, including 488 of cardiovascular causes. Incidence rates (per 1000 person-years) of all-cause mortality were 57.6 (95% CI, 48.4 to 68.7) in adults with diabetes and PN, 34.3 (CI, 30.3 to 38.8) in adults with PN but no diabetes, 27.1 (CI, 23.4 to 31.5) in adults with diabetes but no PN, and 13.0 (CI, 12.1 to 14.0) in adults with no diabetes and no PN. In adjusted models, PN was significantly associated with all-cause mortality (hazard ratio [HR], 1.49 [CI, 1.15 to 1.94]) and cardiovascular mortality (HR, 1.66 [CI, 1.07 to 2.57]) in participants with diabetes. In those without diabetes, PN was significantly associated with all-cause mortality (HR, 1.31 [CI, 1.15 to 1.50]), but the association between PN and cardiovascular mortality was not statistically significant after adjustment (HR, 1.27 [CI, 0.98 to 1.66]).

LIMITATION

Prevalent cardiovascular disease was self-reported, and PN was defined by monofilament testing only.

CONCLUSION

Peripheral neuropathy was common and was independently associated with mortality in the U.S. population, even in the absence of diabetes. These findings suggest that decreased sensation in the foot may be an underrecognized risk factor for death in the general population.

PRIMARY FUNDING SOURCE

National Institute of Diabetes and Digestive and Kidney Diseases and National Heart, Lung, and Blood Institute of the National Institutes of Health.

The metabolic drivers of neuropathy in India

AIMS

To determine the association between the metabolic syndrome (MetS) and neuropathy in Chennai, India.

METHODS

We recruited participants attending the M.V. Hospital for Diabetes. Neuropathy was defined using the Michigan Neuropathy Screening Instrument combined index and MetS was defined using the updated National Cholesterol Education Program criteria. Multivariable logistic regression models were used to assess the associations between individual metabolic components and neuropathy.

RESULTS

Of the 652 participants (42% female and mean (SD) age of 45.5 (9.7)) included in the study, the prevalence of neuropathy was 9.8%. Neuropathy prevalence increased with worsening glycemic status (p < 0.01), but not as the number of MetS components increased (p = 0.12). Among normoglycemic participants, an increasing neuropathy trend was observed as the number of MetS components increased (p = 0.04). Multivariable logistic regression found that diabetes (OR:3.41,1.28-9.11) was associated with neuropathy, but waist circumference was not (OR:1.002,0.88-1.14).

CONCLUSIONS

Similar to previous studies, diabetes was the most important metabolic risk factor for neuropathy in a population from Chennai, India. In contrast to other population-based studies, waist circumference was not associated with neuropathy. Whether the distribution of obesity affects nerves differently in Indian populations requires future studies with more precise anthropometric measures.

Evidence of Altered Peripheral Nerve Function in a Rodent Model of Diet-Induced Prediabetes

Peripheral neuropathy (PN) is a debilitating complication of diabetes that affects >50% of patients. Recent evidence suggests that obesity and metabolic disease, which often precede diabetes diagnosis, may influence PN onset and severity. We examined this in a translationally relevant model of prediabetes induced by a cafeteria (CAF) diet in Sprague–Dawley rats (n = 15 CAF versus n = 15 control). Neuropathy phenotyping included nerve conduction, tactile sensitivity, intraepidermal nerve fiber density (IENFD) and nerve excitability testing, an in vivo measure of ion channel function and membrane potential. Metabolic phenotyping included body composition, blood glucose and lipids, plasma hormones and inflammatory cytokines. After 13 weeks diet, CAF-fed rats demonstrated prediabetes with significantly elevated fasting blood glucose, insulin and impaired glucose tolerance as well as obesity and dyslipidemia. Nerve conduction, tactile sensitivity and IENFD did not differ; however, superexcitability was significantly increased in CAF-fed rats. Mathematical modeling demonstrated this was consistent with a reduction in sodium–potassium pump current. Moreover, superexcitability correlated positively with insulin resistance and adiposity, and negatively with fasting high-density lipoprotein cholesterol. In conclusion, prediabetic rats over-consuming processed, palatable foods demonstrated altered nerve function that preceded overt PN. This work provides a relevant model for pathophysiological investigation of diabetic complications.

Cardiometabolic risk factors as determinants of peripheral nerve function: the Maastricht Study

AIMS/HYPOTHESIS

We aimed to examine associations of cardiometabolic risk factors, and (pre)diabetes, with (sensorimotor) peripheral nerve function.

METHODS

In 2401 adults (aged 40-75 years) we previously determined fasting glucose, HbA_1c, triacylglycerol, HDL- and LDL-cholesterol, inflammation, waist circumference, blood pressure, smoking, glucose metabolism status (by OGTT) and medication use. Using nerve conduction tests, we measured compound muscle action potential, sensory nerve action potential amplitudes and nerve conduction velocities (NCVs) of the peroneal, tibial and sural nerves. In addition, we measured vibration perception threshold (VPT) of the hallux and assessed neuropathic pain using the DN4 interview. We assessed cross-sectional associations of risk factors with nerve function (using linear regression) and neuropathic pain (using logistic regression). Associations were adjusted for potential confounders and for each other risk factor. Associations from linear regression were presented as standardised regression coefficients (β) and 95% CIs in order to compare the magnitudes of observed associations between all risk factors and outcomes.

RESULTS

Hyperglycaemia (fasting glucose or HbA_1c) was associated with worse sensorimotor nerve function for all six outcome measures, with associations of strongest magnitude for motor peroneal and tibial NCV, β_{fasting glucose} = -0.17 SD (-0.21, -0.13) and β_{fasting glucose} = -0.18 SD (-0.23, -0.14), respectively. Hyperglycaemia was also associated with higher VPT and neuropathic pain. Larger waist circumference was associated with worse sural nerve function and higher VPT. Triacylglycerol, HDL- and LDL-cholesterol, and blood pressure were not associated with worse nerve function; however, antihypertensive medication usage (suggestive of history of exposure to hypertension) was associated with worse peroneal compound muscle action potential amplitude and NCV. Smoking was associated with worse nerve function, higher VPT and higher risk for neuropathic pain. Inflammation was associated with worse nerve function and higher VPT, but only in those with type 2 diabetes. Type 2 diabetes and, to a lesser extent, prediabetes (impaired fasting glucose and/or impaired glucose tolerance) were associated with worse nerve function, higher VPT and neuropathic pain (p for trend <0.01 for all outcomes).

CONCLUSIONS/INTERPRETATION

Hyperglycaemia (including the non-diabetic range) was most consistently associated with early-stage nerve damage. Nonetheless, larger waist circumference, inflammation, history of hypertension and smoking may also independently contribute to worse nerve function.

Diabetes mellitus as a risk factor for compression neuropathy: a longitudinal cohort study from southern Sweden

INTRODUCTION

Compression neuropathies (CN) in the upper extremity, the most common being carpal tunnel syndrome (CTS) and ulnar nerve entrapment (UNE), are frequent among patients with diabetes mellitus (DM). Earlier studies have shown contradicting results regarding DM as a risk factor for CN. Thus, the aim of the present population-based, longitudinal study was to explore potential associations between DM, CTS, and UNE during long-term follow-up.

RESEARCH DESIGN AND METHODS

A total of 30 466 participants aged 46-73 years, included in the population-based Malmö Diet and Cancer Study during 1991-1996, were followed up in Swedish national registries regarding incident CTS and UNE until 2016. Associations between prevalent DM at baseline and incident CTS or UNE were calculated using Cox proportional hazard models, adjusted for baseline confounders, such as sex, age at study entry, smoking, hypertension, use of antihypertensive treatment, alcohol consumption, and body mass index (BMI). HbA1c and fasting plasma glucose levels had been measured at baseline in a subgroup of 5508 participants and were related to incident CTS and UNE in age and sex-adjusted binary logistic regression models.

RESULTS

A total of 1081 participants developed CTS and 223 participants developed UNE during a median follow-up of 21 years. Participants with incident CTS or UNE had higher prevalence of DM and higher BMI at baseline. Using multivariate Cox regression models, prevalent DM at baseline was independently associated with both incident CTS (HR 2.10; 95% CI 1.65 to 2.70, p<0.0001) and incident UNE (HR 2.20; 95% CI 1.30 to 3.74, p=0.003). Higher levels of HbA1c and plasma glucose were associated with an increased risk for CTS, but not for UNE.

CONCLUSION

This study establishes DM as a major risk factor in the development of both CTS and UNE. Furthermore, a higher BMI is associated with both CTS and UNE. Finally, hyperglycemia seems to affect the median and ulnar nerves differently.

Brachial Plexus Injuries in Sport Medicine: Clinical Evaluation, Diagnostic Approaches, Treatment Options, and Rehabilitative Interventions

The brachial plexus represents a complex anatomical structure in the upper limb. This "network" of peripheral nerves permits the rearrangement of motor efferent fibers, coming from different spinal nerves, in several terminal branches directed to upper limb muscles. Moreover, afferent information coming from different cutaneous regions in upper limb are sorted in different spinal nerves through the brachial plexus. Severe brachial plexus injuries are a rare clinical condition in the general population and in sport medicine, but with dramatic consequences on the motor and sensory functions of the upper limb. In some sports, like martial arts, milder injuries of the brachial plexus can occur, with transient symptoms and with a full recovery. Clinical evaluation represents the cornerstone in the assessment of the athletes with brachial plexus injuries. Electrodiagnostic studies and imaging techniques, like magnetic resonance and high-frequency ultrasound, could be useful to localize the lesion and to define an appropriate treatment and a functional prognosis. Several conservative and surgical techniques could be applied, and multidisciplinary rehabilitative programs could be performed to guide the athlete toward the recovery of the highest functional level, according to the type of injury.

Insulin Treatment Attenuates Small Nerve Fiber Damage in Rat Model of Type 2 Diabetes

INTRODUCTION

Current clinical guidelines for management of diabetic peripheral neuropathy (DPN) emphasize good glycemic control. However, this has limited effect on prevention of DPN in type 2 diabetic (T2D) patients. This study investigates the effect of insulin treatment on development of DPN in a rat model of T2D to assess the underlying causes leading to DPN.

METHODS

Twelve-week-old male Sprague-Dawley rats were allocated to a normal chow diet or a 45% kcal high-fat diet. After eight weeks, the high-fat fed animals received a mild dose of streptozotocin to induce hyperglycemia. Four weeks after diabetes induction, the diabetic animals were allocated into three treatment groups receiving either no insulin or insulin-releasing implants in a high or low dose. During the 12-week treatment period, blood glucose and body weight were monitored weekly, whereas Hargreaves' test was performed four, eight, and 12 weeks after treatment initiation. At study termination, several blood parameters, body composition, and neuropathy endpoints were assessed.

RESULTS

Insulin treatment lowered blood glucose in a dose-dependent manner. In addition, both doses of insulin lowered lipids and increased body fat percentage. High-dose insulin treatment attenuated small nerve fiber damage assessed by Hargreaves' test and intraepidermal nerve fiber density compared to untreated diabetes and low-dose insulin; however, neuropathy was not completely prevented by tight glycemic control. Linear regression analysis revealed that glycemic status, circulating lipids, and sciatic nerve sorbitol level were all negatively associated with the small nerve fiber damage observed.

CONCLUSION

In summary, our data suggest that high-dose insulin treatment attenuates small nerve fiber damage. Furthermore, data also indicate that both poor glycemic control and dyslipidemia are associated with disease progression. Consequently, this rat model of T2D seems to fit well with progression of DPN in humans and could be a relevant preclinical model to use in relation to research investigating treatment opportunities for DPN.

Coaching of lifestyle recommendations improves sensory neurophysiological parameters in neuropathies related to glycemic disorder or metabolic syndrome. A pilot study

OBJECTIVES

Metabolic abnormalities, such as, glycemic disorders and metabolic syndrome (GDMS) are one of the main causes of peripheral neuropathies. The objective of this study was to evaluate the impact of adding specific coaching care (CC) to standard care (SC) of therapeutic education based on lifestyle recommendations for neuropathies associated with GDMS.

METHODS

This prospective randomized study included two groups of four patients (SC vs. CC) with examiners blinded to group allocation. The SC group had one day of therapeutic education on lifestyle measures (physical activity and diet recommendations) followed by only one phone call of reinforcement. The CC group received an additional weekly phone call of reinforcement for 3 months. Clinical, biological and neurophysiological variables were compared between the two groups at baseline and for the percentage of change at 3 months.

RESULTS

All patients (4 men and 4 women) had diabetes or pre-diabetes, which was associated with metabolic syndrome in 5 cases. There was no difference on any variable at baseline, but at 3 months, Mann-Whitney test showed a difference (P=0.0008) between the two groups regarding the sensory neurophysiological variable, which deteriorated in the SC group (median: -6.0%) and improved in the CC group (median: +12.4%). No significant difference was observed between the two groups for the other variables at 3 months.

CONCLUSION

The weekly coaching of recommendations for lifestyle measures over a period of three months allows an improvement of GDMS neuropathies, at least in terms of sensory aspects, as evidenced by neurophysiological assessments.

Phenotypic Characterization of Paclitaxel-Induced Peripheral Neuropathy in Cancer Survivors

CONTEXT

Although paclitaxel is one of the most commonly used drugs to treat breast, ovarian, and lung cancers, little is known about the impact of paclitaxel-induced peripheral neuropathy (PIPN) on cancer survivors.

OBJECTIVES

The purposes of this study were to evaluate for differences in demographic and clinical characteristics as well as measures of sensation, balance, upper extremity function, perceived stress, symptom burden, and quality of life (QOL) between survivors who received paclitaxel and did (n = 153) and did not (n = 58) develop PIPN.

METHODS

Pain characteristics associated with PIPN are described in detail. Both subjective and objective measures were used to evaluate the impact of PIPN.

RESULTS

Survivors with PIPN were significantly older, had a higher body mass index, and a worse comorbidity profile. The duration of PIPN was almost four years, and pain scores were in the moderate range. Compared with survivors without PIPN, survivors with PIPN had a higher number of upper and lower extremity sites that had lost light touch, cold, and pain sensations. Survivors with PIPN had worse upper extremity function, more problems with balance, a higher symptom burden, and higher levels of perceived stress. In addition, survivors with PIPN had worse QOL scores particularly in the domain of physical functioning.

CONCLUSION

The findings from this large descriptive study are the first to document the impact of PIPN on survivors' symptom burden, functional status, and QOL.

Value-Added Electrodiagnostics: Targeting Interventions for Fall Risk Reduction

Walking confers numerous health benefits, particularly for middle-aged and older patients with diabetes and metabolic syndrome. Nevertheless, it brings a risk of injurious falls, especially among populations with diabetes and metabolic syndrome-related distal neuromuscular decline and frank neuropathy. Those who stand to benefit most from walking are at greatest risk. Development of practical clinical tools to more precisely quantify neuromuscular function and link it to mobility outcomes will help clinicians target interventions toward those at risk for falls. Electrodiagnosis, with inclusion of several newer techniques, serves as a promising tool for objective evaluation of distal neuromuscular function.

A ketogenic diet reduces metabolic syndrome-induced allodynia and promotes peripheral nerve growth in mice

Current experiments investigated whether a ketogenic diet impacts neuropathy associated with obesity and prediabetes. Mice challenged with a ketogenic diet were compared to mice fed a high-fat diet or a high-fat diet plus exercise. Additionally, an intervention switching to a ketogenic diet following 8 weeks of high-fat diet was performed to compare how a control diet, exercise, or a ketogenic diet affects metabolic syndrome-induced neural complications. When challenged with a ketogenic diet, mice had reduced bodyweight and fat mass compared to high-fat-fed mice, and were similar to exercised, high-fat-fed mice. High-fat-fed, exercised and ketogenic-fed mice had mildly elevated blood glucose; conversely, ketogenic diet-fed mice were unique in having reduced serum insulin levels. Ketogenic diet-fed mice never developed mechanical allodynia contrary to mice fed a high-fat diet. Ketogenic diet fed mice also had increased epidermal axon density compared all other groups. When a ketogenic diet was used as an intervention, a ketogenic diet was unable to reverse high-fat fed-induced metabolic changes but was able to significantly reverse a high-fat diet-induced mechanical allodynia. As an intervention, a ketogenic diet also increased epidermal axon density. In vitro studies revealed increased neurite outgrowth in sensory neurons from mice fed a ketogenic diet and in neurons from normal diet-fed mice given ketone bodies in the culture medium. These results suggest a ketogenic diet can prevent certain complications of prediabetes and provides significant benefits to peripheral axons and sensory dysfunction.