Corneal Confocal Microscopy Predicts the Development of Diabetic Neuropathy: A Longitudinal Diagnostic Multinational Consortium Study

A muscarinic receptor antagonist reverses multiple indices of diabetic peripheral neuropathy: preclinical and clinical studies using oxybutynin

Preclinical studies indicate that diverse muscarinic receptor antagonists, acting via the M1 sub-type, promote neuritogenesis from sensory neurons in vitro and prevent and/or reverse both structural and functional indices of neuropathy in rodent models of diabetes. We sought to translate this as a potential therapeutic approach against structural and functional indices of diabetic neuropathy using oxybutynin, a muscarinic antagonist approved for clinical use against overactive bladder. Studies were performed using sensory neurons maintained in vitro, rodent models of type 1 or type 2 diabetes and human subjects with type 2 diabetes and confirmed neuropathy. Oxybutynin promoted significant neurite outgrowth in sensory neuron cultures derived from adult normal rats and STZ-diabetic mice, with maximal efficacy in the 1-100 nmol/l range. This was accompanied by a significantly enhanced mitochondrial energetic profile as reflected by increased basal and maximal respiration and spare respiratory capacity. Systemic (3-10 mg/kg/day s.c.) and topical (3% gel daily) oxybutynin reversed paw heat hypoalgesia in the STZ and db/db mouse models of diabetes and reversed paw tactile allodynia in STZ-diabetic rats. Loss of nerve profiles in the skin and cornea of db/db mice was also prevented by daily topical delivery of 3% oxybutynin for 8 weeks. A randomized, double-blind, placebo-controlled interventional trial was performed in subjects with type 2 diabetes and established peripheral neuropathy. Subjects received daily topical treatment with 3% oxybutynin gel or placebo for 6 months. The a priori designated primary endpoint, significant change in intra-epidermal nerve fibre density (IENFD) in skin biopsies taken before and after 20 weeks of treatments, was met by oxybutynin but not placebo. Secondary endpoints showing significant improvement with oxybutynin treatment included scores on clinical neuropathy, pain and quality of life scales. This proof-of-concept study indicates that muscarinic antagonists suitable for long-term use may offer a novel therapeutic opportunity for treatment of diabetic neuropathy. Trial registry number: NCT03050827.

Advances in diagnosis and management of distal sensory polyneuropathies

Distal sensory polyneuropathy (DSP) is characterised by length-dependent, sensory-predominant symptoms and signs, including potentially disabling symmetric chronic pain, tingling and poor balance. Some patients also have or develop dysautonomia or motor involvement depending on whether large myelinated or small fibres are predominantly affected. Although highly prevalent, diagnosis and management can be challenging. While classic diabetes and toxic causes are well-recognised, there are increasingly diverse associations, including with dysimmune, rheumatological and neurodegenerative conditions. Approximately half of cases are initially considered idiopathic despite thorough evaluation, but often, the causes emerge later as new symptoms develop or testing advances, for instance with genetic approaches. Improving and standardising DSP metrics, as already accomplished for motor neuropathies, would permit in-clinic longitudinal tracking of natural history and treatment responses. Standardising phenotyping could advance research and facilitate trials of potential therapies, which lag so far. This review updates on recent advances and summarises current evidence for specific treatments.

Correlation Between Corneal Whorl-Like Nerve and Retinal Neurodegenerative Changes and Their Association With Microvessel Perfusion in Diabetes

Purpose

The purpose of this study was to compare the evolution of changes in the corneal nerves, retinal nerves, and cells and blood vessels at a single time point in early diabetic retinopathy (DR).

Methods

Eighty participants (60 with diabetes and 20 nondiabetic controls) were examined. DR was graded according to the International Classification of Diabetic Retinopathy. Inferior whorl length (IWL), spiral orientation, central nerve fiber length (CNFL), retinal nerve fiber layer (RNFL) thickness, ganglion cell complex (GCC) layer thickness, global loss volume (GLV), focal loss volume (FLV) indices, superficial (sVD), and deep vessel densities (dVD) were examined.

Results

Compared with those of healthy controls, the IWL, CNFL, and FLV were decreased in the diabetic groups (P < 0.001). The IWL was significantly positively correlated with the RNFL and GCC thicknesses in the diabetic group (r = 0.248, P = 0.006 and r = 0.207, P = 0.023, respectively) and significantly negatively correlated with the FLV (r = -0.535, P < 0.001). The sVD was significantly positively correlated with the RNFL thickness (r = 0.314, P < 0.001) and negatively correlated with the GLV (r = -0.229, P = 0.012).

Conclusions

Our findings suggest a correlation between corneal whorl-like nerve plexus and retinal nerve changes in the early stages of DR and that the IWL of the cornea may be able to indicate the extent of DR. Retinal nerve changes are associated with retinal microvessel perfusion, and nerve changes may precede vessel lesions.

Corneal Confocal Microscopy Abnormalities in Children and Adolescents With Type 1 Diabetes

OBJECTIVE

Utility of corneal confocal microscopy (CCM) in children and adolescents with type 1 diabetes mellitus (T1DM) without neuropathic symptoms or signs and minimal abnormality in large and small nerve fiber function tests remains largely undetermined. This study aimed to evaluate the performance of CCM in comparison to thermal detection thresholds (TDT) testing and nerve conduction studies (NCS) for detecting neuropathy in children with T1DM.

METHODS

A cohort of children and adolescents with T1DM (n = 51) and healthy controls (n = 50) underwent evaluation for symptoms and signs of neurological deficits, including warm detection threshold, cold detection threshold, vibration perception threshold, NCS, and CCM.

RESULTS

Children with T1DM had no or very minimal neuropathic symptoms and deficits based on the Toronto Clinical Neuropathy Score, yet NCS abnormalities were present in 18 (35%), small fiber dysfunction defined by an abnormal TDT was found in 13 (25.5%) and CCM abnormalities were present in 25 (49%). CCM was abnormal in a majority of T1DM children with abnormal TDT (12/13, 92%) and abnormal NCS (16/18, 88%). CCM additionally was able to detect small fiber abnormalities in 13/38 (34%) in T1DM with a normal TDT and in 9/33 (27%) with normal NCS.

CONCLUSION

CCM was able to detect corneal nerve loss in children with and without abnormalities in TDT and NCS.

In-vivo corneal confocal microscopy: Imaging analysis, biological insights and future directions

In-vivo corneal confocal microscopy is a powerful imaging technique which provides clinicians and researcher with the capabilities to observe microstructures at the ocular surfaces in significant detail. In this Mini Review, the optics and image analysis methods with the use of corneal confocal microscopy are discussed. While novel insights of neuroanatomy and biology of the eyes, particularly the ocular surface, have been provided by corneal confocal microscopy, some debatable elements observed using this technique remain and these are explored in this Mini Review. Potential improvements in imaging methodology and instrumentation are also suggested.

Assessing Corneal Confocal Microscopy and Other Small Fiber Measures in Diabetic Polyneuropathy

BACKGROUND AND OBJECTIVES

Damage to small nerve fibers is common in diabetic polyneuropathy (DPN), and the diagnosis of DPN relies on subjective symptoms and signs in a combination with objective confirmatory tests, typically electrophysiology or intraepidermal nerve fiber density (IENFD) from skin biopsy. Corneal confocal microscopy (CCM) has been introduced as a tool to detect DPN. However, it is unclear if CCM can reliably be used to diagnose DPN and how the technique compares with other commonly used measures of small fiber damage, such as IENFD, cold detection threshold (CDT), and warm detection threshold (WDT). Therefore, we assessed and compared the use of CCM, IENFD, CDT, and WDT in the diagnosis of DPN in patients with type 2 diabetes.

METHODS

In this cohort study, the participants underwent detailed neurologic examination, electrophysiology, quantification of IENFD, CCM, and quantitative sensory testing. Definition of DPN was made in accordance with the Toronto criteria for diabetic neuropathy (without relying on IENFD and thermal thresholds).

RESULTS

A total of 214 patients with at least probable DPN, 63 patients without DPN, and 97 controls without diabetes were included. Patients with DPN had lower CCM measures (corneal nerve fiber length [CNFL], nerve fiber density, and branch density), IENFD, CDT, and WDT compared with patients without DPN (p ≤ 0.001, <0.001, 0.002, p < 0.001, p = 0.003, and <0.005, respectively), whereas there was no difference between controls and patients with diabetes without DPN. All 3 CCM measures showed a very low diagnostic sensitivity with CNFL showing the highest (14.4% [95% CI 9.8-18.4]) and a specificity of 95.7% (88.0-99.1). In comparison, the sensitivity of abnormal CDT and/or WDT was 30.5% (24.4-37.0) with a specificity of 84.9% (74.6-92.2). The sensitivity of abnormal IENFD was highest among all measures with a value of 51.1% (43.7-58.5) and a specificity of 90% (79.5-96.2). CCM measures did not correlate with IENFD, CDT/WDT, or neuropathy severity in the group of patients with DPN.

DISCUSSION

CCM measures showed the lowest sensitivity compared with other small fiber measures in the diagnosis of DPN. This indicates that CCM is not a sensitive method to detect DPN in recently diagnosed type 2 diabetes.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that CCM measures aid in the detection of DPN in recently diagnosed type 2 diabetics but with a low sensitivity when compared with other small fiber measures.

Pre-Ophthalmoscopic Quantitative Biomarkers in Diabetes Mellitus

Purpose

The purpose of this study was to assess whether retinal microvascular or corneal nerve abnormalities occur earlier in diabetes mellitus (DM) and to identify imaging biomarkers in order to help prevent the subsequent irreversible retinal and corneal complications.

Methods

The study comprised 35 eyes of 35 healthy volunteers and 52 eyes of 52 patients with type 1 and type 2 DM. Swept-source optical coherence tomography (OCT), OCT angiography, and in vivo corneal confocal microscopy were performed in both groups. Corneal sub-basal nerve plexus and vessel density (VD) of superficial capillary plexus (SCP) and deep capillary plexus (DCP) were evaluated.

Results

All corneal sub-basal nerve fiber parameters were decreased in patients with DM compared with healthy subjects and the difference was significant for each result except for nerve fiber width (P = 0.586). No significant correlation was obtained between any nerve fiber morphology parameters and disease duration or HbA1C. VD in SCP was significantly decreased in the superior (P < 0.0001), temporal (P = 0.001), and nasal quadrant (P = 0.003) in the diabetes group. In DCP, only superior VD (P = 0.036), decreased significantly in the diabetes group. Ganglion cell layer thickness in the inner ring showed a significantly lower value in patients with DM (P < 0.0001).

Conclusions

Our results implicate a more pronounced and earlier damage to the corneal nerve fibers compared to the retinal microvasculature in patients with DM.

Translational Relevance

In DM, an earlier and more pronounced damage to the corneal nerve fibers was observed compared to the retinal microvasculature.

Peripheral Neuropathy in Diabetes Mellitus: Pathogenetic Mechanisms and Diagnostic Options

Diabetic neuropathy (DN) is one of the main microvascular complications of both type 1 and type 2 diabetes mellitus. Sometimes, this could already be present at the time of diagnosis for type 2 diabetes mellitus (T2DM), while it appears in subjects with type 1 diabetes mellitus (T1DM) almost 10 years after the onset of the disease. The impairment can involve both somatic fibers of the peripheral nervous system, with sensory-motor manifestations, as well as the autonomic system, with neurovegetative multiorgan manifestations through an impairment of sympathetic/parasympathetic conduction. It seems that, both indirectly and directly, the hyperglycemic state and oxygen delivery reduction through the vasa nervorum can determine inflammatory damage, which in turn is responsible for the alteration of the activity of the nerves. The symptoms and signs are therefore various, although symmetrical painful somatic neuropathy at the level of the lower limbs seems the most frequent manifestation. The pathophysiological aspects underlying the onset and progression of DN are not entirely clear. The purpose of this review is to shed light on the most recent discoveries in the pathophysiological and diagnostic fields concerning this complex and frequent complication of diabetes mellitus.

The severity of corneal nerve loss differentiates motor subtypes in patients with Parkinson's disease

Background

Parkinson's disease (PD) is a heterogeneous movement disorder with patients manifesting with either tremor-dominant (TD) or postural instability and gait disturbance (PIGD) motor subtypes. Small nerve fiber damage occurs in patients with PD and may predict motor progression, but it is not known whether it differs between patients with different motor subtypes.

Objective

The aim of this study was to explore whether there was an association between the extent of corneal nerve loss and different motor subtypes.

Methods

Patients with PD classified as TD, PIGD, or mixed subtype underwent detailed clinical and neurological evaluation and corneal confocal microscopy (CCM). Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fiber length (CNFL) were compared between groups, and the association between corneal nerve fiber loss and motor subtypes was investigated.

Results

Of the 73 patients studied, 29 (40%) had TD, 34 (46%) had PIGD, and 10 (14%) had a mixed subtype. CNFD (no./mm², 24.09 ± 4.58 versus 28.66 ± 4.27; p < 0.001), CNBD (no./mm², 28.22 ± 11.11 versus 37.37 ± 12.76; p = 0.015), and CNFL (mm/mm², 13.11 ± 2.79 versus 16.17 ± 2.37; p < 0.001) were significantly lower in the PIGD group compared with the TD group. Multivariate logistic regression showed that higher CNFD (OR = 1.265, p = 0.019) and CNFL (OR = 1.7060, p = 0.003) were significantly associated with the TD motor subtype. The receiver operating characteristic (ROC) analysis demonstrated that combined corneal nerve metrics showed excellent discrimination between TD and PIGD, with an area under the curve (AUC) of 0.832.

Conclusion

Greater corneal nerve loss occurs in patients with PIGD compared with TD, and patients with a higher CNFD or CNFL were more likely to have the TD subtype. CCM may have clinical utility in differentiating different motor subtypes in PD.

Impact of Chronic Kidney Disease on Corneal Neuroimmune Features in Type 2 Diabetes

Aim: To determine the impact of chronic kidney disease on corneal nerve measures and dendritic cell counts in type 2 diabetes. Methods: In vivo corneal confocal microscopy images were used to estimate corneal nerve parameters and compared in people with type 2 diabetes with chronic kidney disease (T2DM-CKD) (n = 29) and those with type 2 diabetes without chronic kidney disease (T2DM-no CKD) (n = 29), along with 30 healthy controls. Corneal dendritic cell densities were compared between people with T2DM-CKD and those with T2DM-no CKD. The groups were matched for neuropathy status. Results: There was a significant difference in corneal nerve fiber density (p < 0.01) and corneal nerve fiber length (p = 0.04) between T2DM-CKD and T2DM-no CKD groups. The two diabetes groups had reduced corneal nerve parameters compared to healthy controls (all parameters: p < 0.01). Immature central dendritic cell density was significantly higher in the T2DM-CKD group compared to the T2DM-no CKD group ((7.0 (3.8−12.8) and 3.5 (1.4−13.4) cells/mm2, respectively, p < 0.05). Likewise, central mature dendritic cell density was significantly higher in the T2DM-CKD group compared to the T2DM-no CKD group (0.8 (0.4−2.2) and 0.4 (0.6−1.1) cells/mm2, respectively, p = 0.02). Additionally, total central dendritic cell density was increased in the T2DM-CKD group compared to T2DM-no CKD group (10.4 (4.3−16.1) and 3.9 (2.1−21.0) cells/mm2, respectively, p = 0.03). Conclusion: The study showed that central corneal dendritic cell density is increased in T2DM-CKD compared to T2DM-no CKD, with groups matched for peripheral neuropathy severity. This is accompanied by a loss of central corneal nerve fibers. The findings raise the possibility of additional local factors exacerbating central corneal nerve injury in people with diabetic chronic kidney disease.

Association of Elevated Serum Uric Acid with Nerve Conduction Function and Peripheral Neuropathy Stratified by Gender and Age in Type 2 Diabetes Patients

Background: The relationship between serum uric acid (SUA) level and diabetic peripheral neuropathy (DPN) remains controversial. We aimed to investigate the association between SUA level and DPN and evaluate the effects of SUA level on nerve conduction function via electromyography in patients with type 2 diabetes (T2DM), stratified by gender and age. Methods: This cross-sectional study included 647 inpatients with T2DM from the First Affiliated Hospital of Wenzhou Medical University between February 2017 and October 2020. The diagnosis of DPN was confirmed according to the Toronto Expert Consensus. Clinical data, SUA level, and nerve conduction parameters were obtained from electronic medical records. Results: A total of 647 patients with T2DM were included, and 471 patients were diagnosed with DPN. The level of SUA was higher in the DPN group than in the Non-DPN group (330.58 ± 99.67 vs. 309.16 ± 87.04, p < 0.05). After adjustment, a higher SUA level was associated with the presence of DPN [odds ratio (OR) 1.003, 95% confidence interval (CI), 1.001−1.005; p = 0.017]. The area under the curve for the prediction of DPN was 0.558 (95% CI, 0.509−0.608; p = 0.022), and the optimized cut-off of SUA level was 297.5 µmol/L. The SUA > 297.5 µmol/L level was independently associated with DPN in the male subgroup (OR 2.507, 95% CI, 1.405−4.473; p = 0.002) rather than in the female subgroup. Besides, SUA > 297.5 µmol/L was independently associated with DPN in the younger subgroup (age < 65 years) (OR 2.070, 95% CI, 1.278−3.352; p = 0.003) rather than in the older subgroup. In multiple linear regression analysis, SUA was significantly correlated with certain nerve conduction study parameters in the all patients group, and was also observed in the male and younger subgroups. Conclusions: Elevated SUA was independently associated with poorer nerve conduction functions, and hyperuricemia was also significantly associated with a higher risk of developing DPN in T2DM patients, especially in male and younger patients.

Peripheral Neuropathy in Beta-Thalassemia: Corneal Confocal Microscopy-Based Study

Background Peripheral neuropathy is a controversial but serious complication of beta-thalassemia (β-Th). Although few studies have reported no relationship between neuropathy and thalassemia, many have linked it with increasing age, iron overload, and iron chelator toxicity. This study aims to investigate the presence of neuropathy in β-Th using corneal nerve fibers. Methodology A cross-sectional study was conducted using corneal confocal microscopy on individuals with intermediate and major β-Th who were compared to healthy individuals. The main outcome variables were corneal main nerve and branch nerve densities which were calculated using Image J software. The comparison between groups was done using the independent-samples F-test and Bonferroni post-hoc analysis. Results There was reduced corneal main nerve and branch nerve density in β-Th intermediate and major patients compared to the control group, and the results were statistically significant (p-value <0.05). However, a significant correlation was not observed between serum ferritin levels and corneal nerve parameters. Conclusions The reduction in corneal nerve parameters in β-Th patients compared to healthy controls can be an indication of peripheral neuropathy in β-Th. Further work is needed to confirm these findings.

Diabetic corneal neuropathy as a surrogate marker for diabetic peripheral neuropathy

Diabetic neuropathy is a prevalent microvascular complication of diabetes mellitus, affecting nerves in all parts of the body including corneal nerves and peripheral nervous system, leading to diabetic corneal neuropathy and diabetic peripheral neuropathy, respectively. Diabetic peripheral neuropathy is diagnosed in clinical practice using electrophysiological nerve conduction studies, clinical scoring, and skin biopsies. However, these diagnostic methods have limited sensitivity in detecting small-fiber disease, hence they do not accurately reflect the status of diabetic neuropathy. More recently, analysis of alterations in the corneal nerves has emerged as a promising surrogate marker for diabetic peripheral neuropathy. In this review, we will discuss the relationship between diabetic corneal neuropathy and diabetic peripheral neuropathy, elaborating on the foundational aspects of each: pathogenesis, clinical presentation, evaluation, and management. We will further discuss the relevance of diabetic corneal neuropathy in detecting the presence of diabetic peripheral neuropathy, particularly early diabetic peripheral neuropathy; the correlation between the severity of diabetic corneal neuropathy and that of diabetic peripheral neuropathy; and the role of diabetic corneal neuropathy in the stratification of complications of diabetic peripheral neuropathy.

Corneal confocal microscopy differentiates patients with Parkinson’s disease with and without autonomic involvement

Autonomic dysregulation in Parkinson’s disease (PD) can precede motor deficits and is associated with reduced quality of life, disease progression, and increased mortality. Objective markers of autonomic involvement in PD are limited. Corneal confocal microscopy (CCM) is a rapid ophthalmic technique that can quantify small nerve damage in a range of peripheral and autonomic neuropathies. Here we investigated whether CCM can be used to assess autonomic symptoms in PD. Based on the scale for outcomes in Parkinson’s disease for autonomic symptoms (SCOPA-AUT), patients with PD were classified into those without autonomic symptoms (AutD-N), with single (AutD-S), and multiple (AutD-M) domain autonomic dysfunction. Corneal nerve fiber pathology was quantified using CCM, and the relationship with autonomic symptoms was explored. The study enrolled 71 PD patients and 30 control subjects. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and CNBD/CNFD ratio were lower in PD patients with autonomic symptoms compared to those without autonomic symptoms. Autonomic symptoms correlated positively with CNFD (r = −0.350, p = 0.004), and were not related to Levodopa equivalent daily dose (r = 0.042, p = 0.733) after adjusting for age, disease severity, disease duration or cognitive function. CCM parameters had high sensitivity and specificity in distinguishing patients with PD with and without autonomic symptoms. PD patients with autonomic symptoms have corneal nerve loss, and CCM could serve as an objective ophthalmic imaging technique to identify patients with PD and autonomic symptoms.

Corneal Confocal Microscopy as a Quantitative Imaging Biomarker of Diabetic Peripheral Neuropathy: A Review

Distal symmetric polyneuropathy (DPN), particularly chronic sensorimotor DPN, represents one of the most frequent complications of diabetes, affecting 50% of diabetic patients and causing an enormous financial burden. Whilst diagnostic methods exist to detect and monitor this condition, they have significant limitations, mainly due to their high subjectivity, invasiveness, and non-repeatability. Corneal confocal microscopy (CCM) is an in vivo, non-invasive, and reproducible diagnostic technique for the study of all corneal layers including the sub-basal nerve plexus, which represents part of the peripheral nervous system. We reviewed the current literature on the use of CCM as an instrument in the assessment of diabetic patients, particularly focusing on its role in the study of sub-basal nerve plexus alterations as a marker of DPN. CCM has been demonstrated to be a valid in vivo tool to detect early sub-basal nerve plexus damage in adult and pediatric diabetic patients, correlating with the severity of DPN. Despite its great potential, CCM has still limited application in daily clinical practice, and more efforts still need to be made to allow the dissemination of this technique among doctors taking care of diabetic patients.

Corneal toxicity associated with belantamab mafodotin is not restricted to the epithelium: neuropathy studied with confocal microscopy

PURPOSE

The purpose of this study was to investigate epithelial and neuronal changes in patients with refractory/relapsed multiple myeloma (RRMM) before/during belantamab mafodotin (belamaf) treatment using confocal microscopy.

DESIGN

Retrospective case series.

METHODS

RRMM patients underwent best corrected visual acuity (BCVA) testing and slit-lamp examination/photography, followed by corneal confocal microscopy (CCM) to evaluate the epithelium and subbasal nerve plexus (SNP) to measure corneal nerve fiber density (CNFD), -branch density (CNBD), and -fiber length (CNFL) before and during belamaf treatment.

RESULTS

In 14 eyes of 7 patients (4 female, 68±10 years) with complete follow-up (4±2 months), the median BCVA dropped from 20/25 (20/25-20/20) to 20/40 (20/200-20/32) in the worse eye at the end of follow-up. Microcystic epithelial changes and ocular surface disease were demonstrated biomicroscopically. CCM showed "grape-like" hyperreflective spots in the central basal epithelium that changed to polymorphous-structured cysts in the superficial epithelium, with no pathology detected at the(peri-)limbal structures. The baseline, normal SNP morphology with a mean CNFD, CNBD, and CNFL of 20.25±7.06/mm², 19.49±12.34/mm², and 11.8±3.74mm/mm² respectively, showed severe fiber fragmentation during follow-up, and an observed complete loss of the SNP at the end of follow-up in all eyes.

CONCLUSIONS

This study is the first to illustrate neurotoxic effects of belamaf on the human cornea.

Corneal Confocal Microscopy Identifies People with Type 1 Diabetes with More Rapid Corneal Nerve Fibre Loss and Progression of Neuropathy

There is a need to accurately identify patients with diabetes at higher risk of developing and progressing diabetic peripheral neuropathy (DPN). Fifty subjects with Type 1 Diabetes Mellitus (T1DM) and sixteen age matched healthy controls underwent detailed neuropathy assessments including symptoms, signs, quantitative sensory testing (QST), nerve conduction studies (NCS), intra epidermal nerve fiber density (IENFD) and corneal confocal microscopy (CCM) at baseline and after 2 years of follow-up. Overall, people with type 1 diabetes mellitus showed no significant change in HbA1c, blood pressure, lipids or neuropathic symptoms, signs, QST, neurophysiology, IENFD and CCM over 2 years. However, a sub-group (n = 11, 22%) referred to as progressors, demonstrated rapid corneal nerve fiber loss (RCNFL) with a reduction in corneal nerve fiber density (CNFD) (p = 0.0006), branch density (CNBD) (p = 0.0002), fiber length (CNFL) (p = 0.0002) and sural (p = 0.04) and peroneal (p = 0.05) nerve conduction velocities, which was not related to a change in HbA1c or cardiovascular risk factors. The majority of people with T1DM and good risk factor control do not show worsening of neuropathy over 2 years. However, CCM identifies a sub-group of people with T1DM who show a more rapid decline in corneal nerve fibers and nerve conduction velocity.

BOND study: a randomised double-blind, placebo-controlled trial over 12 months to assess the effects of benfotiamine on morphometric, neurophysiological and clinical measures in patients with type 2 diabetes with symptomatic polyneuropathy

INTRODUCTION

Diabetic sensorimotor polyneuropathy (DSPN) affects approximately 30% of people with diabetes, while around half of cases are symptomatic. Currently, there are only few pathogenetically oriented pharmacotherapies for DSPN, one of which is benfotiamine, a prodrug of thiamine with a high bioavailability and favourable safety profile. While benfotiamine has shown positive effects in preclinical and short-term clinical studies, no long-term clinical trials are available to demonstrate disease-modifying effects on DSPN using a comprehensive set of disease-related endpoints.

METHODS AND ANALYSIS

The benfotiamine on morphometric, neurophysiological and clinical measures in patients with type 2 diabetes trial is a randomised double-blind, placebo-controlled parallel group monocentric phase II clinical trial to assess the effects of treatment with benfotiamine compared with placebo in participants with type 2 diabetes and mild to moderate symptomatic DSPN. Sixty participants will be 1:1 randomised to treatment with benfotiamine 300 mg or placebo two times a day over 12 months. The primary endpoint will be the change in corneal nerve fibre length assessed by corneal confocal microscopy (CCM) after 12 months of benfotiamine treatment compared with placebo. Secondary endpoints will include other CCM measures, skin biopsy and function indices, variables from somatic and autonomic nerve function tests, clinical examination and questionnaires, general health, health-related quality of life, cost, safety and blood tests.

ETHICS AND DISSEMINATION

The trial was approved by the competent authority and the local independent ethics committee. Trial results will be published in peer-reviewed journals, conference abstracts, and via online and print media.

TRIAL REGISTRATION NUMBER

DRKS00014832.

Corneal Confocal Microscopy in the Diagnosis of Small Fiber Neuropathy: Faster, Easier, and More Efficient Than Skin Biopsy?

Chronic pain may affect 30–50% of the world’s population and an important cause is small fiber neuropathy (SFN). Recent research suggests that autoimmune diseases may be one of the most common causes of small nerve fiber damage. There is low awareness of SFN among patients and clinicians and it is difficult to diagnose as routine electrophysiological methods only detect large fiber abnormalities, and specialized small fiber tests, like skin biopsy and quantitative sensory testing, are not routinely available. Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible method for quantifying small nerve fiber degeneration and regeneration, and could be an important tool for diagnosing SFN. This review considers the advantages and disadvantages of CCM and highlights the evolution of this technique from a research tool to a diagnostic test for small fiber damage, which can be a valuable contribution to the study and management of autoimmune disease.

Translating morphology from bench side to bed side via neurophysiology: 8-min protocol for peripheral neuropathy research

BACKGROUND

Peripheral neuropathy treatment is not always satisfactory. To fill this gap, inferences from bench side are warranted, where morphological and pathogenetic determinations can be performed. Nerve conduction studies (NCS) are ideal to translate results from preclinical to clinical setting.

NEW METHODS

We propose a comprehensive 8-minute protocol for sensory-motor neurophysiological assessment, similar to routine clinical practice: sensory proximal and distal caudal nerves, motor caudal nerve, and sensory digital nerve recordings were used and tested in 2 different experimental settings. In Experiment 1 we compared control (CTRL) animals to a severe sensory-motor polyneuropathy (animals treated with vincristine [VCR]), and in Experiment 2 CTRL animals were compared to a mild sensory polyneuropathy (animals treated with oxaliplatin [OHP]). NCS were performed after 1-month of chemotherapy and matched with confirmatory neuropathological analyses.

RESULTS

VCR treated animals showed, at NCS, a relevant sensory-motor polyneuropathy ensued at the end of treatment; whereas, OHP animals showed a mild distal sensory neuropathy. These patterns were confirmed by neuropathological analysis.

COMPARISON WITH EXISTING METHODS

In literature, the majority of proposed neurophysiological protocols relies mainly on a single nerve testing, rather than a combination of them, and only a few studies tested both caudal and sciatic nerve branches, nevertheless not aiming at fully reproduce clinical protocols (e.g., seeking for length-dependency); to provide evidence of appropriateness of our protocol we applied a gold standard: neuropathology.

CONCLUSION

The simple and rapid protocol here presented can be suggested as a good translation outcome measure in preclinical setting.