Diagnostic utility of corneal confocal microscopy and intra-epidermal nerve fibre density in diabetic neuropathy

The role and molecular mechanism of α synuclein in Parkinson's disease: A diagnostic model for corneal nerve fiber injury

The purpose of this study was to investigate the role of α-synuclein in Parkinson's disease and its molecular mechanism, and to establish an evaluation model for corneal nerve fiber injury. The function and mechanism of α-synuclein in Parkinson's disease were studied. The expression level of α-synuclein in corneal tissues of Parkinson's disease patients and normal control group was detected by immunohistochemistry and Western blot. At the same time, the morphological changes of corneal nerve fibers were observed by confocal microscopy, and the degree of corneal nerve injury was evaluated by corneal synesthetic nerve function test. The results showed that the expression level of α-synuclein in the corneal tissue of patients with Parkinson's disease was significantly increased, and the morphology and function of corneal nerve fibers were significantly abnormal. Corneal synesthetic nerve function test results also showed that the corneal sensory nerve conduction speed slowed down and sensitivity decreased in patients with Parkinson's disease.

Early diagnosis and risk factors of diabetic peripheral neuropathy in type 1 diabetes: insights from current perception threshold testing

Objective

This study investigates nerve fiber dysfunction in type 1 diabetes (T1D) patients and identifies risk factors for diabetic peripheral neuropathy (DPN). It evaluates the relationship between current perception threshold (CPT) tests and nerve conduction velocity (NCV), and assesses CPT's diagnostic accuracy for early DPN detection.

Research design and methods

This study enrolled 110 patients with T1D and 26 healthy controls between January 2020 and December 2021, in accordance with predefined inclusion/exclusion criteria. CPT testing at 2000 Hz, 250 Hz, and 5 Hz assessed Aβ, Aδ, and C fiber function, while NCV was measured in 47 patients. Subgroups were stratified by disease duration (>5 years vs ≤5 years). Multivariate logistic regression identified DPN risk factors, and CPT-NCV correlation was analyzed using Chi-square and Kappa tests. Receiver operating characteristic (ROC) curves evaluated CPT diagnostic efficacy.

Results

The incidence of DPN in 110 T1D patients was 78%, with no significant difference between disease duration subgroups (78.3% vs. 78.0%). Neurological abnormalities were significantly more common in the lower extremities compared to the upper extremities (67.27% vs. 49.09%, P < 0.05). Multivariate logistic regression analysis revealed that a waist-to-hip ratio (WHR) greater than 0.85 was an independent risk factor for DPN (OR = 3.01, 95% CI: 1.03-8.80, P < 0.05). Patients with a disease duration >5 years demonstrated significantly higher 2000Hz abnormality rates (68.09% vs. 46.15%, P < 0.05) and more severe neurological lesions (57.45% vs. 35.90%, P < 0.05). In contrast, those with disease duration ≤5 years exhibited elevated 5Hz abnormality rates (30.77% vs. 10.64%, P < 0.05) with predominantly milder lesions (56.41% vs. 31.91%, P < 0.05). Statistical analyses demonstrated a significant association between CPT and NCV (P<0.001), with moderate diagnostic consistency further supported by Cohen's Kappa Test (κ=0.515, P<0.001). ROC curve analysis demonstrated that CPT exhibited moderate diagnostic accuracy in detecting DPN at the 5Hz, with an area under the curve (AUC) of 0.723.

Conclusions

CPT showed moderate diagnostic accuracy for early unmyelinated (C) fibers detection, routine CPT screening in high-risk groups (central obesity/short disease duration) enables timely intervention to prevent irreversible damage.

Deafferentation in Pain Medicine: A Narrative Review of Mechanisms and Management

Deafferentation is an umbrella term that includes several clinical conditions. The exact mechanism is not yet known, and the different clinical conditions do not necessarily share common pathophysiology. It includes both non-painful and painful conditions, including cancer pain conditions. Clinical presentation can be immediate or delayed, sometimes years after the causative lesion. Patients experience neuropathic pain symptoms in an area of abnormal or absent sensation. Laboratory tests show denervation and loss of function. Pain management strategies can be directed toward alleviating symptoms rather than eradication. The site of origin of the pain can help decide the treatment modalities to be tried. Gabapentinoids, antidepressants, and sodium channel blockers can be used. This type of pain is typically opioid-nonresponsive, but some patients may benefit. Neuronal destructive procedures are indicated for brachial plexus avulsion injuries. Spinal cord stimulation, dorsal root entry zone rhizotomy, deep brain thalamic stimulation, and motor cortex stimulation have been suggested for the management of the complex clinical conditions under the umbrella of deafferentation.

Long-term Nerve Regeneration in Diabetic Keratopathy Mediated by a Novel NGF Delivery System

Diabetic keratopathy (DK) is a common chronic metabolic disorder that causes ocular surface complications. Among various therapeutic approaches, local delivery of nerve growth factor (NGF) remains the most effective treatment of DK. However, achieving a sustained therapeutic effect with NGF and the frequent drug delivery burden remain challenging during clinical practice. Here, we developed a novel adeno-associated virus (AAV)-based NGF delivery system that achieved 1-year-long-lasting effects by a single injection. We refined the corneal stromal injection technique, resulting in reduced corneal edema and improved AAV distribution homogeneity. AAV serotype AAV.rh10 exhibited high tropism and specificity to corneal nerves. A dose of 2 × 109 vector genomes was determined to achieve efficient Ngf gene expression without inducing corneal immune responses. Moreover, NGF protein was highly expressed in trigeminal ganglion through a retrograde transport mechanism, indicating the capacity for repairing corneal nerve damage at both the root and corneal nerve endings. In a mouse DK model, a single injection of AAV-Ngf into the corneal stroma led to marked corneal nerve regeneration for over 5 months. Together, we provide a novel therapeutic paradigm for long-term effective treatment of DK, and this therapeutic approach is superior to current DK therapies.

ARTICLE HIGHLIGHTS

Assessing corneal dendritic cells in glucose dysregulation small-fibre neuropathy

BACKGROUND AND AIMS

Small-fibre neuropathy (SFN) is associated with glucose dysregulation, including impaired glucose tolerance (IGT) and type 2 diabetes (T2D). Corneal confocal microscopy (CCM) offers a non-invasive tool to assess corneal nerve damage and dendritic cell density (DCD). In this study, we investigated corneal DCD in patients with SFN and glucose dysregulation, defined as IGT or T2D.

METHODS

We enrolled 38 patients with SFN + glucose dysregulation, 51 with SFN + non-glucose dysregulation and 20 healthy controls. All participants underwent neurological examination, neurophysiology and CCM.

RESULTS

Individuals with SFN and glucose dysregulation had higher DCD compared with healthy controls (p = .01), and mature DCD was higher in IGT SFN patients than in T2D patients.

INTERPRETATION

Higher DCD in IGT compared with controls and patients with established T2D may suggest that DCD is a biomarker of early neuropathy.

Cardiovascular autonomic neuropathy in diabetes: an update with a focus on management

Cardiovascular autonomic neuropathy (CAN) is an under-recognised yet highly prevalent microvascular complication of diabetes. CAN affects approximately 20% of people with diabetes, with recent studies highlighting the presence of CAN in prediabetes (impaired glucose tolerance and/or impaired fasting glucose), indicating early involvement of the autonomic nervous system. Understanding of the pathophysiology of CAN continues to evolve, with emerging evidence supporting a potential link between lipid metabolites, mitochondrial dysfunction and genetics. Recent advancements, such as streamlining CAN detection through wearable devices and monitoring of heart rate variability, present simplified and cost-effective approaches for early CAN detection. Further research on the optimal use of the extensive data provided by such devices is required. Despite the lack of specific pharmacological interventions targeting the underlying pathophysiology of autonomic neuropathy, several studies have suggested a favourable impact of newer glucose-lowering agents, such as sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide-1 receptor agonists, where there is a wealth of clinical trial data on the prevention of cardiovascular events. This review delves into recent developments in the area of CAN, with emphasis on practical guidance to recognise and manage this underdiagnosed condition, which significantly increases the risk of cardiovascular events and mortality in diabetes.

Comparison of intraepidermal nerve fiber density and confocal corneal microscopy for neuropathy

OBJECTIVE

Compare the diagnostic characteristics of intraepidermal nerve fiber density (IENFD) and confocal corneal microscopy (CCM) for distal symmetric polyneuropathy (DSP) and small fiber neuropathy (SFN).

METHODS

Participants with obesity were recruited from bariatric surgery clinics and testing was performed prior to surgery. DSP and SFN were determined using the Toronto consensus definitions of probable neuropathy. IENFD was assessed from 3 mm punch biopsies of the distal leg and proximal thigh. CCM was performed on both eyes with manual and automated counting. The Michigan Neuropathy Screening Instrument questionnaire (MNSIq) was also completed. Diagnostic capability was determined using areas under the receiver operating characteristics curve (AUC) from logistic regression.

RESULTS

We enrolled 140 participants (mean [standard deviation [SD]] age: 50.3 years [7.1], 77.1% female, BMI: 44.4 kg/m2 [6.7]). In this population, 22.9% had DSP and 14.3% had SFN. Distal leg IENFD had the largest AUC (95% confidence interval) for DSP (0.78, 0.68-0.89) and SFN (0.85, 0.75-0.96). Proximal thigh IENFD (DSP: AUC: 0.59, 0.48-0.69, SFN: AUC: 0.59, 0.46-0.73) and CCM metrics (DSP: AUC range: 0.55-0.60, SFN: AUC range: 0.45-0.62) had poorer diagnostic capability than distal leg IENFD for DSP/SFN (P < 0.05). MNSIq had similar diagnostic capability to distal leg IENFD for both DSP/SFN (DSP: AUC: 0.76, 0.68-0.85, SFN: AUC: 0.81, 0.73-0.88). More participants (52%) preferred skin biopsies to CCM.

INTERPRETATION

Distal leg IENFD was the best quantitative measure of DSP/SFN. CCM had poor diagnostic characteristics and fewer patients preferred this test to IENFD. The MNSIq had similar diagnostic characteristics to distal leg IENFD, indicating its value as a diagnostic tool in the clinical setting.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov: NCT03617185.

Assessing the diagnostic utility of urinary albumin-to-creatinine ratio as a potential biomarker for diabetic peripheral neuropathy in type 2 diabetes mellitus patients

BACKGROUND AND AIMS

Diabetic peripheral neuropathy (DPN) and diabetic nephropathy (DN) both have microcirculation dysfunction. Urinary albumin-to-creatinine ratio (UACR) is a biomarker for DN. We aimed to explore the links between DPN and UACR in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 195 T2DM patients were defined as Control or DPN group. Clinical parameters were compared, and the association between HbA1c (or UACR) and DPN was analyzed. Risk factors for DPN were observed, and the diagnostic values of HbA1c and UACR were assessed.

RESULTS

Compared with 104 participants without DPN, 91 individuals with DPN exhibited higher HbA1c and UACR levels. In all patients, increased HbA1c and UACR were identified as risk factors for DPN in individuals with T2DM. Moreover, increased HbA1c was a risk factor for DPN in volunteers without DN, whereas elevated UACR was determined as a risk factor for DPN in participants with DN. The cut-off point for HbA1c (7.65%) in patients without DN had a sensitivity of 86.0% and specificity of 44.6%, while the cut-off point for UACR (196.081 mg/g) in patients with DN had a sensitivity of 52.9% and specificity of 76.2%.

CONCLUSION

Elevated HbA1c and UACR levels are risk factors for DPN and may serve as potential biomarkers for DPN in T2DM patients.

Development of a transformer-based deep learning algorithm for diabetic peripheral neuropathy classification using corneal confocal microscopy images

Background

Diabetic peripheral neuropathy (DPN) is common and can go unnoticed until it is firmly developed. This study aims to establish a transformer-based deep learning algorithm (DLA) to classify corneal confocal microscopy (CCM) images, identifying DPN in diabetic patients.

Methods

Our classification model differs from traditional convolutional neural networks (CNNs) using a Swin transformer network with a hierarchical architecture backbone. Participants included those with (DPN+, n = 57) or without (DPN-, n = 37) DPN as determined by the updated Toronto consensus criteria. The CCM image dataset (consisting of 570 DPN+ and 370 DPN- images, with five images selected from each participant's left and right eyes) was randomly divided into training, validation, and test subsets at a 7:1:2 ratio, considering individual participants. The effectiveness of the algorithm was assessed using diagnostic accuracy measures, such as sensitivity, specificity, and accuracy, in conjunction with Grad-CAM visualization techniques to interpret the model's decisions.

Results

In the DPN + group (n = 12), the transformer model successfully predicted all participants, while in the DPN- group (n = 7), one participant was misclassified as DPN+, with an area under the curve (AUC) of 0.9405 (95% CI 0.8166, 1.0000). Among the DPN + images (n = 120), 117 were correctly classified, and among the DPN- images (n = 70), 49 were correctly classified, with an AUC of 0.8996 (95% CI 0.8502, 0.9491). For single-image predictions, the transformer model achieved a superior AUC relative to the ResNet50 model (0.8761, 95% CI 0.8155, 0.9366), the Inception_v3 model (0.8802, 95% CI 0.8231, 0.9374), and the DenseNet121 model (0.8965, 95% CI 0.8438, 0.9491).

Conclusion

Transformer-based networks outperform CNN-based networks in rapid binary DPN classification. Transformer-based DLAs have clinical DPN screening potential.

Comprehensive assessment of ocular parameters for identifying diagnostic indicators of diabetic peripheral neuropathy

PURPOSE

To explore variations in systemic and ocular parameters among patients with diabetes, both with and without diabetic peripheral neuropathy (DPN) and to identify sensitive indicators for DPN diagnosis.

METHODS

Ninty-five patients with type 2 diabetes mellitus (T2DM) were involved in this cross-sectional study, including 49 without DPN and 46 with DPN. Ocular parameters were obtained using optical coherence tomography angiography (OCTA) and corneal confocal microscopy (CCM).

RESULT

Patients with DPN presented with significantly higher HbA1c (p < 0.05) and glycated albumin (GA, p < 0.01) levels, increased prevalence of diabetic retinopathy (DR, p < 0.05), and lower serum albumin (ALB, p < 0.01) and red blood cell (RBC, p < 0.05) levels. Ocular assessments revealed reduced corneal nerve fiber length (CNFL, p < 0.001) and enlarged foveal avascular zone (FAZ) area (p < 0.05) in DPN group. Logistic regression analysis indicated a significant association of presence of DR, RBC, GA, ALB, CNFL and DPN (p < 0.05, respectively). In the binary logistic regression for DPN risk, all three models including the presence of DR and CNFL exhibited the area under the curve (AUC) exceeding 0.8.

CONCLUSION

The study establishes a strong correlation between ocular parameters and DPN, highlighting CCM's role in early diagnosis. Combining systemic and ocular indicators improves DPN risk assessment and early management.

Evaluation of a New Diabetes Mellitus Index Based on Measurements Using the Scheimpflug Analyzer Corvis ST

PURPOSE

Chronic hyperglycemia causes changes in corneal biomechanics that can be measured with the Scheimpflug Analyzer Corvis ST. The diagnostic reliability of the new diabetes mellitus (DM) index developed based on this should be evaluated.

METHODS

In a prospective cross-sectional study, the index was initially developed using data from 81 patients with DM and 75 healthy subjects based on logistic regression analysis. The reliability of the DM index was subsequently assessed using data from another 61 patients and 37 healthy individuals. In addition, the dependence of the DM index on indicators of disease severity was analyzed.

RESULTS

The index initially achieved a sensitivity of 79% and specificity of 80% with a cutoff value of 0.58. The evaluation showed a sensitivity of 67% and specificity of 76% with an optimized cutoff of 0.51 (area under the curve = 0.737, P < 0.001). The DM index correlated weakly with the severity of diabetic retinopathy (r = 0.209, P = 0.014). It was increased in the presence of diabetic maculopathy ( P = 0.037) and in type 1 DM compared with patients with type 2 disease ( P = 0.039).

CONCLUSIONS

In this first evaluation, the new DM index achieved sufficiently good sensitivity and specificity and was weakly associated with disease-specific factors. With further improvements, it could complement the diagnostic options in DM with a simple, rapid, and noninvasive assessment method.

Sustained corneal nerve loss predicts the development of diabetic neuropathy in type 2 diabetes

Introduction

This study was undertaken to investigate whether sustained rather than a single measure of corneal nerve loss was associated with the onset of diabetic peripheral neuropathy (DPN) and the progression of neuropathic symptoms and deficits in individuals with type 2 diabetes (T2D).

Methods

Participants underwent clinical, metabolic testing and assessment of neuropathic symptoms, vibration perception threshold (VPT), sudomotor function, and corneal confocal microscopy (CCM) at baseline, 1, 2, and 4-7 years. Sustained corneal nerve loss was defined as abnormal corneal nerve fiber density (CNFD, <24 fibers/mm2), corneal nerve branch density (CNBD, <21 branches/mm2), and corneal nerve fiber length (CNFL, <16 mm/mm2) persisting for ≥50% of the study duration.

Results

A total of 107 participants with a mean duration of T2D of 13.3 ± 7.3 years, aged 54.8 ± 8.5 years, underwent baseline and follow-up assessments over a median duration of 4 years, ranging from 1 to 7 years. The DPN prevalence at baseline was 18/107 (16.8%), and of the 89 participants without DPN at baseline, 13 (14.6%) developed DPN during follow-up. Approximately half of the cohort had sustained corneal nerve damage, and corneal nerve measures were significantly lower in this group than those without sustained damage (p < 0.0001). Sustained corneal nerve damage was associated with the development of DPN (p < 0.0001), a progressive loss of vibration perception (p ≤ 0.05), an increased incidence of burning pain, numbness, or a combination of both (p = 0.01-0.001), and a borderline association with progressive sudomotor dysfunction (p = 0.07). Sustained abnormal CNFL effectively distinguished between participants who developed DPN and those who did not (AUC: 76.3, 95% CI: 65.9-86.8%, p < 0.0001), while baseline and other sustained measures did not predict DPN onset.

Conclusion

Sustained abnormal CCM is associated with more severe corneal nerve damage, DPN development, and the progression of neuropathic symptoms and deficits. Regular CCM monitoring may enable the identification of those at greater risk of developing and worsening DPN who may benefit from more aggressive risk factor reduction.

Corneal confocal microscopy detects early nerve regeneration after pharmacological and surgical interventions: Systematic review and meta-analysis

Corneal confocal microscopy (CCM) is an ophthalmic imaging technique that enables the identification of corneal nerve fibre degeneration and regeneration. To undertake a systematic review and meta-analysis of studies utilizing CCM to assess for corneal nerve regeneration after pharmacological and surgical interventions in patients with peripheral neuropathy. Databases (EMBASE [Ovid], PubMed, CENTRAL and Web of Science) were searched to summarize the evidence from randomized and non-randomized studies using CCM to detect corneal nerve regeneration after pharmacological and surgical interventions. Data synthesis was undertaken using RevMan web. Eighteen studies including 958 patients were included. CCM identified an early (1-8 months) and longer term (1-5 years) increase in corneal nerve measures in patients with peripheral neuropathy after pharmacological and surgical interventions. This meta-analysis confirms the utility of CCM to identify nerve regeneration following pharmacological and surgical interventions. It could be utilized to show a benefit in clinical trials of disease modifying therapies for peripheral neuropathy.

Discontinuity third harmonic generation microscopy for label-free imaging and quantification of intraepidermal nerve fibers

Label-free imaging methodologies for nerve fibers rely on spatial signal continuity to identify fibers and fail to image free intraepidermal nerve endings (FINEs). Here, we present an imaging methodology-called discontinuity third harmonic generation (THG) microscopy (dTHGM)-that detects three-dimensional discontinuities in THG signals as the contrast. We describe the mechanism and design of dTHGM and apply it to reveal the bead-string characteristics of unmyelinated FINEs. We confirmed the label-free capability of dTHGM through a comparison study with the PGP9.5 immunohistochemical staining slides and a longitudinal spared nerve injury study. An intraepidermal nerve fiber (IENF) index based on a discontinuous-dot-connecting algorithm was developed to facilitate clinical applications of dTHGM. A preliminary clinical study confirmed that the IENF index was highly correlated with skin-biopsy-based IENF density (Pearson's correlation coefficient R = 0.98) and could achieve differential identification of small-fiber neuropathy (p = 0.0102) in patients with diabetic peripheral neuropathy.

Corneal confocal microscopy may help to distinguish Multiple System Atrophy from Parkinson's disease

Multiple system atrophy (MSA) and Parkinson's disease (PD) have clinical overlapping symptoms, which makes differential diagnosis difficult. Our research aimed to distinguish MSA from PD using corneal confocal microscopy (CCM), a noninvasive and objective test. The study included 63 PD patients, 30 MSA patients, and 31 healthy controls (HC). When recruiting PD and MSA, questionnaires were conducted on motor and non-motor functions, such as autonomic and cognitive functions. Participants underwent CCM to quantify the corneal nerve fibers. Corneal nerve fiber density (CNFD) and corneal nerve fiber length (CNFL) values in MSA are lower than PD (MSA vs. PD: CNFD, 20.68 ± 6.70 vs. 24.64 ± 6.43 no./mm2, p < 0.05; CNFL, 12.01 ± 3.25 vs. 14.17 ± 3.52 no./mm2, p < 0.05). In MSA + PD (combined), there is a negative correlation between CNFD and the Orthostatic Grading Scale (OGS) (r = -0.284, p = 0.007). Similarly, CNFD in the only MSA group was negatively correlated with the Unified Multiple System Atrophy Rating Scale I and II (r = -0.391, p = 0.044; r = -0.382, p = 0.049). CNFD and CNFL were inversely associated with MSA (CNFD: β = -0.071; OR, 0.932; 95% CI, 0.872 ~ 0.996; p = 0.038; CNFL: β = -0.135; OR, 0.874; 95% CI, 0.768-0.994; p = 0.040). Furthermore, we found the area under the receiver operating characteristic curve (ROC) of CNFL was the largest, 72.01%. The CCM could be an objective and sensitive biomarker to distinguish MSA from PD. It visually reflects a more severe degeneration in MSA compared to PD.

High-resolution nerve ultrasound and corneal confocal microscopy in taxane-induced polyneuropathy

BACKGROUND AND PURPOSE

The role of high-resolution nerve ultrasound (HRUS) and corneal confocal microscopy (CCM) in the early detection of taxane-induced polyneuropathy (TIPN) is unclear. The present prospective longitudinal controlled observational pilot study estimates the role of HRUS and CCM in the early diagnosis of TIPN in breast cancer patients.

METHODS

Fifteen breast cancer patients receiving paclitaxel and 15 healthy age matched controls were included. Visits before and 3 weeks, 8 weeks and 6 months after treatment included clinical examination, the total neuropathy score, nerve conduction studies (NCS), monocular CCM including corneal nerve fibre length, density and branching and HRUS of bilateral median, ulnar, radial, tibial, peroneal and sural nerves. Patients were compared between different visits and to healthy controls.

RESULTS

Total neuropathy score increased from 2.2 at baseline to 5.8 (p < 0.001) at week 8. NCS showed a decreased sensory amplitude in the sural, radial, ulnar and median nerve after 6 months (p < 0.001). HRUS revealed a significant increase of cross-sectional area in the sural nerve (p = 0.004), the median nerve (p = 0.003) at the carpal tunnel and the ulnar nerve in the forearm (p = 0.006) after 6 months. CCM showed no changes at different visits.

CONCLUSIONS

Corneal confocal microscopy and HRUS do not detect early signs of TIPN during the paclitaxel treatment period. HRUS and NCS might detect congruent signs of an axonal, predominantly sensory polyneuropathy after 6 months. The clinical examination remains the most sensitive tool in the early detection of TIPN in breast cancer patients.

Corneal confocal microscopy in small and mixed fiber neuropathy-Comparison with skin biopsy and cold detection in a large prospective cohort

BACKGROUND AND AIMS

The diagnosis of small fiber neuropathy (SFN) is supported by reduced intraepidermal nerve fiber density (IENFD). The noninvasive method corneal confocal microscopy (CCM) has the potential to be a practical alternative. We aimed to estimate the diagnostic accuracy of CCM compared with IENFD and cold detection thresholds (CDT) in SFN and mixed fiber neuropathy (MFN).

METHODS

CCM was performed in an unselected prospective cohort of patients with a clinical suspicion of polyneuropathy. Predefined criteria were used to classify SFN and MFN. Neuropathy scores, including the Utah early neuropathy scale (UENS), were used to describe severity. Patients with established other diagnoses were used for diagnostic specificity calculations.

RESULTS

Data were taken from 680 patients, of which 244 had SFN or MFN. There was no significant difference in sensitivities [95%CI] of CCM (0.44 [0.38-0.51]), IEFND (0.43 [0.36-0.49]), and CDT (0.34 [0.29-0.41]). CCM specificity (0.75 [0.69-0.81]) was lower (p = .044) than for IENFD (0.99 [0.96-1.00]) but not than for CDT (0.81 [0.75-0.86]). The AUCs of the ROC curves of 0.63, 0.63 and 0.74 respectively, was lower for corneal nerve fiber density (p = .0012) and corneal nerve fiber length (p = .0015) compared with IENFD. While UENS correlated significantly with IENFD (p = .0016; R2  = .041) and CDT (p = .0002; R2  = .056), it did not correlate with CCM measures.

INTERPRETATION

The diagnostic utility of CCM in SNF and MFN is limited by the low specificity compared with skin biopsy. Further, CCM is less suitable than skin biopsy and CDT as a marker for neuropathy severity.

Evaluation of Corneal Nerve Regeneration After Minimally Invasive Corneal Neurotization

PURPOSE

To evaluate the corneal nerve regeneration after minimally invasive corneal neurotization (MICN) and to further clarify the recovery patterns of sensory and trophic functions of the corneal nerves.

DESIGN

A retrospective cohort study based in the Shanghai Ninth People's Hospital.

METHODS

Eighteen patients (18 eyes) who underwent MICN for neurotrophic keratopathy due to intracranial surgery was conducted to analyze their follow-up data at 6, 12, 18, and 24 months after surgery.

RESULTS

At 12 months postoperatively, the growth of the central and peripheral corneal nerve fiber density (CNFD) was 11.47±8.56 and 14.73±8.08 n/mm 2 with subsequent improvement slowing down, and the patient's corneal epithelium defect was healed ahead of the accomplishment of corneal nerve regeneration. The number of dendritic cells also reached its peak. At 18 months postoperatively, the recovery of central and peripheral corneal sensation was 37.22±23.06 mm and 39.38±18.08 mm with no subsequent improvement, and the growth of the central and peripheral corneal nerve branch density (CNBD) was 29.69±11.05 and 43.75±1.41 n/mm 2 , with a positive and significant correlation between corneal sensation and CNBD (at central r =0.632, P <0.005; at peripheral r =0.645, P <0.005). At 24 months postoperatively, mean CNFD, CNBD, and corneal sensation recovered significantly compared with preoperative, but a few patients' corneal sensation recovered insignificantly with good CNFD recovery and poor CNBD recovery.

CONCLUSIONS

After MICN, the trophic function of the corneal nerve recovers before the sensory function, and in particular, the recovery of sensation is based on the coexistence of the corneal nerve trunk and branches.

Corneal Confocal Microscopy Predicts Cardiovascular and Cerebrovascular Events and Demonstrates Greater Peripheral Neuropathy in Patients with Type 1 Diabetes and Foot Ulcers

OBJECTIVE

In this study, we evaluate small and large nerve fibre pathology in relation to diabetic foot ulceration (DFU) and incident cardiovascular and cerebrovascular events in type 1 diabetes (T1D).

METHODS

A prospective observational study was conducted on people with T1D without diabetic peripheral neuropathy (DPN) (n = 25), T1D with DPN (n = 28), T1D with DFU (n = 25) and 32 healthy volunteers. ROC analysis of parameters was conducted to diagnose DPN and DFU, and multivariate Cox regression analysis was performed to evaluate the predictive ability of corneal nerves for cardiac and cerebrovascular events over 3 years.

RESULTS

Corneal nerve fibre length (CNFL), fibre density (CNFD) and branch density (CNBD) were lower in T1D-DPN and T1D-DFU vs. T1D (all p < 0.001). In ROC analysis, CNFD (sensitivity 88%, specificity 87%; AUC 0.93; p < 0.001; optimal cut-off 7.35 no/mm2) and CNFL (sensitivity 76%, specificity 77%; AUC 0.90; p < 0.001; optimal cut-off 7.01 mm/mm2) had good ability to differentiate T1D with and without DFU. Incident cardiovascular events (p < 0.001) and cerebrovascular events (p < 0.001) were significantly higher in T1D-DPN and T1D-DFU. Corneal nerve loss, specifically CNFD predicted incident cardiovascular (HR 1.67, 95% CI 1.12 to 2.50, p = 0.01) and cerebrovascular (HR 1.55, 95% CI 1.06 to 2.26, p = 0.02) events.

CONCLUSIONS

Our study provides threshold values for corneal nerve fibre metrics for neuropathic foot at risk of DFU and further demonstrates that lower CNFD predicts incident cardiovascular and cerebrovascular events in T1D.

Where Art Thou O treatment for diabetic neuropathy: the sequel

INTRODUCTION

Having lived through a pandemic and witnessed how regulatory approval processes can evolve rapidly; it is lamentable how we continue to rely on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

AREAS COVERED

Small (Aδ and C) fibers are key to the genesis of pain, regulate skin blood flow, and play an integral role in the development of diabetic foot ulceration but continue to be ignored. This article challenges the rationale for the FDA insisting on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

EXPERT OPINION

Quantitative sensory testing, intraepidermal nerve fiber density, and especially corneal confocal microscopy remain an after-thought, demoted at best to exploratory secondary endpoints in clinical trials of diabetic neuropathy. If pharma are to be given a fighting chance to secure approval for a new therapy for diabetic neuropathy, the FDA needs to reassess the evidence rather than rely on 'opinion' for the most suitable endpoint(s) in clinical trials of diabetic neuropathy.

Comparison of Novel Wide-Field In Vivo Corneal Confocal Microscopy With Skin Biopsy for Assessing Peripheral Neuropathy in Type 2 Diabetes

Diabetic peripheral neuropathy (DPN) is a serious complication of diabetes, where skin biopsy assessing intraepidermal nerve fiber density (IENFD) plays an important diagnostic role. In vivo confocal microscopy (IVCM) of the corneal subbasal nerve plexus has been proposed as a noninvasive diagnostic modality for DPN. Direct comparisons of skin biopsy and IVCM in controlled cohorts are lacking, as IVCM relies on subjective selection of images depicting only 0.2% of the nerve plexus. We compared these diagnostic modalities in a fixed-age cohort of 41 participants with type 2 diabetes and 36 healthy participants using machine algorithms to create wide-field image mosaics and quantify nerves in an area 37 times the size of prior studies to avoid human bias. In the same participants, and at the same time point, no correlation between IENFD and corneal nerve density was found. Corneal nerve density did not correlate with clinical measures of DPN, including neuropathy symptom and disability scores, nerve conduction studies, or quantitative sensory tests. Our findings indicate that corneal and intraepidermal nerves likely mirror different aspects of nerve degeneration, where only intraepidermal nerves appear to reflect the clinical status of DPN, suggesting that scrutiny is warranted concerning methodologies of studies using corneal nerves to assess DPN.

ARTICLE HIGHLIGHTS

Comparison of intraepidermal nerve fiber density with automated wide-field corneal nerve fiber density in participants with type 2 diabetes revealed no correlation between these parameters. Intraepidermal and corneal nerve fibers both detected neurodegeneration in type 2 diabetes, but only intraepidermal nerve fibers were associated with clinical measures of diabetic peripheral neuropathy. A lack of association of corneal nerves with peripheral neuropathy measures suggests that corneal nerve fibers may be a poor biomarker for diabetic peripheral neuropathy.

Painful Diabetic Peripheral Neuropathy: Practical Guidance and Challenges for Clinical Management

Painful diabetic peripheral neuropathy (PDPN) is present in nearly a quarter of people with diabetes. It is estimated to affect over 100 million people worldwide. PDPN is associated with impaired daily functioning, depression, sleep disturbance, financial instability, and a decreased quality of life. Despite its high prevalence and significant health burden, it remains an underdiagnosed and undertreated condition. PDPN is a complex pain phenomenon with the experience of pain associated with and exacerbated by poor sleep and low mood. A holistic approach to patient-centred care alongside the pharmacological therapy is required to maximise benefit. A key treatment challenge is managing patient expectation, as a good outcome from treatment is defined as a reduction in pain of 30-50%, with a complete pain-free outcome being rare. The future for the treatment of PDPN holds promise, despite a 20-year void in the licensing of new analgesic agents for neuropathic pain. There are over 50 new molecular entities reaching clinical development and several demonstrating benefit in early-stage clinical trials. We review the current approaches to its diagnosis, the tools, and questionnaires available to clinicians, international guidance on PDPN management, and existing pharmacological and non-pharmacological treatment options. We synthesise evidence and the guidance from the American Association of Clinical Endocrinology, American Academy of Neurology, American Diabetes Association, Diabetes Canada, German Diabetes Association, and the International Diabetes Federation into a practical guide to the treatment of PDPN and highlight the need for future research into mechanistic-based treatments in order to prioritise the development of personalised medicine.

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.

Methods for evaluation of corneal nerve fibres in diabetes mellitus by in vivo confocal microscopy: a scoping review protocol

INTRODUCTION

Globally, 422 million people have diabetes. Late complications of diabetes are blindness, kidney failure, heart attack, stroke and lower limb amputation. The prevalence of diabetic peripheral neuropathy and diabetic retinopathy is 50% and 35%, respectively. In vivo confocal microscopy (IVCM) is a rapid, non-invasive method to evaluate subbasal corneal nerve fibres, which are small fibres of the peripheral nervous system. Corneal nerve fibre changes can be a marker of diabetic peripheral neuropathy. There is currently no gold-standard procedure for IVCM imaging, image processing or quantitative analysis of the corneal nerve fibres in the subbasal plexus. This protocol describes a scoping review to map, summarise and critically evaluate current methods used with IVCM evaluation in people with diabetes mellitus.

METHODS

The scoping review will follow Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for scoping review. A comprehensive search of the literature will be conducted in MEDLINE, Embase, Cochrane, Scopus and Web of Science. The search strategy will include terms related to IVCM, diabetes and corneal nerve fibres. We will set inclusion and exclusion criteria prior to the search, and two reviewers will screen titles and abstracts independently. One reviewer will full text read eligible articles and chart data from the studies. A descriptive summary of the methods used in imaging, image processing and quantitative analysis of peripheral corneal nerve fibres by IVCM will be written.

ETHICS AND DISSEMINATION

Ethical approval is not required since this is a scoping review based on previously published articles. The findings will be published in a scientific peer-reviewed journal.

Cranial Nerve Affection in Adolescents with Type 1 Diabetes Assessed by Corneal Confocal Microscopy, Smell and Taste Tests

Aim

To determine whether adolescents with type 1 diabetes (T1D) have morphological changes of the corneal nerve fibers and reduced smell and taste function compared to healthy control subjects as a sign of cranial nerve affection and to evaluate possible associated risk factors for cranial nerve affection.

Methods

The study was a part of the T1DANES study including 60 adolescents (15-<19 years) and 23 healthy age-matched controls. First, clinical and biochemical data on the participants were obtained, and the second step involved a test day with neurological examinations including corneal confocal microscopy (CCM), olfactory testing with Sniffin' Sticks, and gustatory assessment with taste-drop test.

Results

The adolescents with T1D (mean diabetes duration 9.8 years, mean HbA1c 61 mmol/mol) had lower CCM parameters (corneal nerve fiber density, corneal nerve branch density, corneal nerve fiber length, and corneal nerve fiber fractal dimension) compared to control subjects (all p < 0.05). No differences in total score for smell test (p = 0.66) and taste test (p = 0.47) were found, but adolescents with T1D had reduced ability to taste sweet (p < 0.01). In total, 24% had two or more reduced CCM parameters, 12% had reduced smell test, and 23% had abnormal taste test. Higher waist to height ratio (WHtR) was the only risk factor found for reduced corneal nerve fiber density, and higher BMI-SDS and WHtR were found for impaired taste function. Having abnormal smell test increased the risk for having abnormal taste perception, and vice versa.

Conclusion

Up to 29% of adolescents with T1D had abnormal test scores indicating cranial nerve affection. Lower corneal nerve fiber density and reduced ability to taste sweet were found in adolescents with T1D compared to control subjects. Clinical attention to smell and taste function seems important because it requires intervention for advising adolescents with impaired smell and taste function.

Corneal nerve fiber involvement in chronic inflammatory demyelinating polyneuropathy

BACKGROUND

Despite the primary myelin-related pathophysiology, small fiber neuropathy (SFN) and axonal degeneration are also considered to be involved and associated with disabling symptoms and impaired quality of life in chronic inflammatory demyelinating polyneuropathy (CIDP). Demonstration of SFN usually requires complex or invasive investigations.

OBJECTS

In vivo corneal confocal microscopy (IVCCM) has evolved as a non-invasive, easily applied method for quantification of small fiber involvement in peripheral nerve disorders. We aimed to investigate the potential role of IVCCM in CIDP.

METHODS

In this cross-sectional study, 15 patients with CIDP underwent assessment with clinical disability scales, neuropathic pain (NP) and autonomic symptom questionnaires, nerve conduction studies, and IVCCM. IVCCM parameters were analyzed and compared to those from 32 healthy controls.

RESULTS

Corneal nerve fiber density (CNFD) and corneal nerve fiber length (CNFL) were significantly decreased in the CIDP group, compared to those in controls (p = 0.03 and p = 0.024, respectively). Langerhans cells and fiber tortuosity were increased in CIDP patients (p = 0.005 and p = 0.001, respectively). IVCCM parameters were significantly lower in patients with NP compared to those in patients without NP.

CONCLUSION

IVCCM shows promise as a non-invasive complementary biomarker in the assessment of demyelinating polyneuropathies, providing insights into the potential pathophysiology of these non-length-dependent neuropathies.

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.

Artificial Intelligence Based Analysis of Corneal Confocal Microscopy Images for Diagnosing Peripheral Neuropathy: A Binary Classification Model

Diabetic peripheral neuropathy (DPN) is the leading cause of neuropathy worldwide resulting in excess morbidity and mortality. We aimed to develop an artificial intelligence deep learning algorithm to classify the presence or absence of peripheral neuropathy (PN) in participants with diabetes or pre-diabetes using corneal confocal microscopy (CCM) images of the sub-basal nerve plexus. A modified ResNet-50 model was trained to perform the binary classification of PN (PN+) versus no PN (PN-) based on the Toronto consensus criteria. A dataset of 279 participants (149 PN-, 130 PN+) was used to train (n = 200), validate (n = 18), and test (n = 61) the algorithm, utilizing one image per participant. The dataset consisted of participants with type 1 diabetes (n = 88), type 2 diabetes (n = 141), and pre-diabetes (n = 50). The algorithm was evaluated using diagnostic performance metrics and attribution-based methods (gradient-weighted class activation mapping (Grad-CAM) and Guided Grad-CAM). In detecting PN+, the AI-based DLA achieved a sensitivity of 0.91 (95%CI: 0.79-1.0), a specificity of 0.93 (95%CI: 0.83-1.0), and an area under the curve (AUC) of 0.95 (95%CI: 0.83-0.99). Our deep learning algorithm demonstrates excellent results for the diagnosis of PN using CCM. A large-scale prospective real-world study is required to validate its diagnostic efficacy prior to implementation in screening and diagnostic programmes.

Diabetic Retinopathy: Soluble and Imaging Ocular Biomarkers

Diabetic retinopathy (DR), the most common microvascular complication of diabetes mellitus, represents the leading cause of acquired blindness in the working-age population. Due to the potential absence of symptoms in the early stages of the disease, the identification of clinical biomarkers can have a crucial role in the early diagnosis of DR as well as for the detection of prognostic factors. In particular, imaging techniques are fundamental tools for screening, diagnosis, classification, monitoring, treatment planning and prognostic assessment in DR. In this context, the identification of ocular and systemic biomarkers is crucial to facilitate the risk stratification of diabetic patients; moreover, reliable biomarkers could provide prognostic information on disease progression as well as assist in predicting a patient's response to therapy. In this context, this review aimed to provide an updated and comprehensive overview of the soluble and anatomical biomarkers associated with DR.

Update on Corneal Confocal Microscopy Imaging

In vivo corneal confocal microscopy (IVCM) is a non-invasive ophthalmic imaging technique that provides images of the cornea at the cellular level. Despite the uses in ocular surface pathologies, in the last decades IVCM has been used to provide more knowledge in refractive surgery wound healing, in neuropathies diagnosis, etc. The observation of the corneal cells, both normal and inflammatory, and the possibility of quantification of the corneal nerve density with manual or automated tools, makes IVCM have a significant potential to improve the diagnosis and prognosis in several systemic and corneal conditions.

Assessing the corneal sub-basal nerve plexus by in vivo confocal microscopy in patients with blepharoptosis

BACKGROUND

To assess in vivo confocal microscopy features of corneal sub-basal nerve plexus in patients with congenital or aponeurogenic blepharoptosis using a fully automated software (ACCMetrics).

PATIENTS AND METHODS

This prospective study included 33 patients with blepharoptosis and 17 normal controls. The corneal sub-basal nerve plexus was assessed using in vivo confocal microscopy, and the ocular surface status was evaluated by tear break-up times.

RESULTS

The mean age of 33 patients with blepharoptosis and 17 normal controls were 38.77 ± 22.81 years and 48.35 ± 17.15 years, respectively. The mean duration of blepharoptosis was 16.42 ± 15.60 years. In 13 patients with unilateral blepharoptosis, there was no significant difference between affected eyes and contralateral eyes (all ps > .05), except for wider corneal nerve fibre width (CNFW) in affected eyes (0.024 ± 0.001 versus 0.023 ± 0.001 mm/mm², p = .021). In 20 patients with bilateral blepharoptosis, there was no significant difference between the eyes. No significant difference was detected between 19 cases with congenital blepharoptosis and 14 cases with aponeurogenic blepharoptosis. When compared with normal controls, eyes with both unilateral and bilateral blepharoptosis had significantly wider CNFW. But from the point of aetiology, only eyes with congenital blepharoptosis presented with wider CNFW (p = .001), rather than the eyes with aponeurogenic blepharoptosis (p = .093). Besides, four young patients with congenital blepharoptosis revealed very sparse sub-basal nerve plexus.

CONCLUSIONS

These data suggested that corneal confocal microscopy demonstrated no significant changes in patients with blepharoptosis as compared with normal controls, except for relatively wider CNFW in congenital affected eyes. However, in some children and young adults with congenital blepharoptosis, the density of corneal sub-basal nerve plexus was evidently decreased, which needs to be cautioned when ones with congenital blepharoptosis want to take corneal surgeries or wear contact lens.Key messagesWhen compared with normal controls, no significant effect was found in the influence of blepharoptosis on the most of corneal nerve parameters, except for corneal nerve fibre width (CNFW) in the group of congenital blepharoptosis.The age of onset of blepharoptosis may influence corneal nerve fibres, so timely surgical treatment of congenital blepharoptosis is not only conducive to the development of normal vision, but also beneficial to the reduction of corneal nerve lesions to some extent.We noted that some young blepharoptosis patients revealed sparse corneal nerve, which should be taken precaution when ones with congenital blepharoptosis who want to take corneal surgeries or wear contact lens.

Mosaic vs. Single Image Analysis with Confocal Microscopy of the Corneal Nerve Plexus for Diagnosis of Early Diabetic Peripheral Neuropathy

INTRODUCTION

The assessment of the corneal nerve fibre plexus with corneal confocal microscopy (CCM) is an upcoming but still experimental method in the diagnosis of early stage diabetic peripheral neuropathy (DPN). Using an innovative imaging technique-Heidelberg Retina Tomograph equipped with the Rostock Cornea Module (HRT-RCM) and EyeGuidance module (EG)-we were able to look at greater areas of subbasal nerve plexus (SNP) in order to increase the diagnostic accuracy. The aim of our study was to evaluate the usefulness of EG instead of single image analysis in diagnosis of early stage DPN.

METHODS

This prospective study was performed on 60 patients with type 2 diabetes mellitus, classified equally into two subgroups based on neuropathy deficient score (NDS): patients without DPN (group 1) or with mild DPN (group 2). The following parameters were analysed in the two subgroups: corneal nerve fibre length (CNFL; mm/mm²), corneal nerve fibre density (CNFD; no./mm²), corneal nerve branch density (CNBD; no./mm²). Furthermore, we compared the data calculated with the novel mosaic, EG-based method with those received from single image analysis using different quantification tools.

RESULTS

Using EG we did not find a significant difference between group 1 and group 2: CNFL (16.81 ± 5.87 mm/mm² vs. 17.19 ± 7.19 mm/mm², p = 0.895), CNFD (254.05 ± 115.36 no./mm² vs. 265.91 ± 161.63 no./mm², p = 0.732) and CNBD (102.68 ± 62.28 no./mm² vs. 115.38 ± 96.91 no./mm², p = 0.541). No significant difference between the EG method of analysing the SNP and the single image analysis of 10 images per patient was detected.

CONCLUSION

On the basis of our results it was not possible to differentiate between early stages of large nerve fibre DPN in patients with type 2 diabetes mellitus via SNP analysis. To improve sensitivity and specificity of this method newer technologies are under current evaluation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05326958.

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 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.

Relationship between time in range and corneal nerve fiber loss in asymptomatic patients with type 2 diabetes

BACKGROUND

Corneal confocal microscopy (CCM) is a noninvasive technique to detect early nerve damage of diabetic sensorimotor polyneuropathy (DSPN). Time in range (TIR) is an emerging metric of glycemic control which was reported to be associated with diabetic complications. We sought to explore the relationship between TIR and corneal nerve parameters in asymptomatic patients with type 2 diabetes (T2DM).

METHODS

In this cross-sectional study, 206 asymptomatic inpatients with T2DM were recruited. After 7 days of continuous glucose monitoring, the TIR was calculated as the percentage of time in the glucose range of 3.9 to 10.0 mmol/L. CCM was performed to determine corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length (CNFL). Abnormal CNFL was defined as ≤15.30 mm/mm 2 .

RESULTS

Abnormal CNFL was found in 30.6% (63/206) of asymptomatic subjects. Linear regression analyses revealed that TIR was positively correlated with CCM parameters both in the crude and adjusted models (all P   <  0.05). Each 10% increase in TIR was associated with a 28.2% (95% CI: 0.595-0.866, P  = 0.001) decreased risk of abnormal CNFL after adjusting for covariates. With the increase of TIR quartiles, corneal nerve fiber parameters increased significantly (all P for trend <0.01). The receiver operating characteristic curve indicated that the optimal cutoff point of TIR was 77.5% for predicting abnormal CNFL in asymptomatic patients.

CONCLUSIONS

There is a significant independent correlation between TIR and corneal nerve fiber loss in asymptomatic T2DM patients. TIR may be a useful surrogate marker for early diagnosis of DSPN.

Segmentation and Evaluation of Corneal Nerves and Dendritic Cells From In Vivo Confocal Microscopy Images Using Deep Learning

Purpose

Segmentation and evaluation of in vivo confocal microscopy (IVCM) images requires manual intervention, which is time consuming, laborious, and non-reproducible. The aim of this research was to develop and validate deep learning–based methods that could automatically segment and evaluate corneal nerve fibers (CNFs) and dendritic cells (DCs) in IVCM images, thereby reducing processing time to analyze larger volumes of clinical images.

Methods

CNF and DC segmentation models were developed based on U-Net and Mask R-CNN architectures, respectively; 10-fold cross-validation was used to evaluate both models. The CNF model was trained and tested using 1097 and 122 images, and the DC model was trained and tested using 679 and 75 images, respectively, at each fold. The CNF morphology, number of nerves, number of branching points, nerve length, and tortuosity were analyzed; for DCs, number, size, and immature–mature cells were analyzed. Python-based software was written for model training, testing, and automatic morphometric parameters evaluation.

Results

The CNF model achieved on average 86.1% sensitivity and 90.1% specificity, and the DC model achieved on average 89.37% precision, 94.43% recall, and 91.83% F₁ score. The interclass correlation coefficient (ICC) between manual annotation and automatic segmentation were 0.85, 0.87, 0.95, and 0.88 for CNF number, length, branching points, and tortuosity, respectively, and the ICC for DC number and size were 0.95 and 0.92, respectively.

Conclusions

Our proposed methods demonstrated reliable consistency between manual annotation and automatic segmentation of CNF and DC with rapid speed. The results showed that these approaches have the potential to be implemented into clinical practice in IVCM images.

Translational Relevance

The deep learning–based automatic segmentation and quantification algorithm significantly increases the efficiency of evaluating IVCM images, thereby supporting and potentially improving the diagnosis and treatment of ocular surface disease associated with corneal nerves and dendritic cells.

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.

Corneal in vivo Confocal Microscopy for Assessment of Non-Neurological Autoimmune Diseases: A Meta-Analysis

Purpose

This study aimed to evaluate the features of corneal nerve with in vivo confocal microscopy (IVCM) among patients with non-neurological autoimmune (NNAI) diseases.

Methods

We systematically searched PubMed, Web of Science, and Cochrane Central Register of Controlled Trials for studies published until May 2021. The weighted mean differences (WMDs) of corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), tortuosity, reflectivity, and beadings per 100 μm with a 95% CI between NNAI and control group were analyzed using a random-effects model.

Results

The results showed 37 studies involving collective totals of 1,423 patients and 1,059 healthy controls were ultimately included in this meta-analysis. The pooled results manifested significantly decreased CNFL (WMD: −3.94, 95% CI: −4.77–−3.12), CNFD (WMD: −6.62, 95% CI: −8.4–−4.85), and CNBD (WMD: −9.89, 95% CI: −14–−5.79) in NNAI patients. In addition, the NNAI group showed more tortuous corneal nerve (WMD: 1.19, 95% CI:0.57–1.81). The comparison between NNAI patients and healthy controls in beadings per 100 μm corneal nerve length was inconsistent. No significant difference was found in the corneal nerve fiber reflectivity between NNAI and the control group (WMD: −0.21, 95% CI: −0.65–0.24, P = 0.361).

Conclusions

The parameters and morphology of corneal nerves observed by IVCM proved to be different in NNAI patients from healthy controls, suggesting that IVCM may be a non-invasive technique for identification and surveillance of NNAI diseases.

Corneal Confocal Microscopy to Image Small Nerve Fiber Degeneration: Ophthalmology Meets Neurology

Neuropathic pain has multiple etiologies, but a major feature is small fiber dysfunction or damage. Corneal confocal microscopy (CCM) is a rapid non-invasive ophthalmic imaging technique that can image small nerve fibers in the cornea and has been utilized to show small nerve fiber loss in patients with diabetic and other neuropathies. CCM has comparable diagnostic utility to intraepidermal nerve fiber density for diabetic neuropathy, fibromyalgia and amyloid neuropathy and predicts the development of diabetic neuropathy. Moreover, in clinical intervention trials of patients with diabetic and sarcoid neuropathy, corneal nerve regeneration occurs early and precedes an improvement in symptoms and neurophysiology. Corneal nerve fiber loss also occurs and is associated with disease progression in multiple sclerosis, Parkinson's disease and dementia. We conclude that corneal confocal microscopy has good diagnostic and prognostic capability and fulfills the FDA criteria as a surrogate end point for clinical trials in peripheral and central neurodegenerative diseases.

Is Nerve Electrophysiology a Robust Primary Endpoint in Clinical Trials of Treatments for Diabetic Peripheral Neuropathy?

There is currently no FDA-approved disease-modifying therapy for diabetic peripheral neuropathy (DPN). Nerve conduction velocity (NCV) is an established primary endpoint of disease-modifying therapies in DPN and clinical trials have been powered with an assumed decline of 0.5 m/s/year. This paper sought to establish the time-dependent change in NCV associated with a placebo, compared to that observed in the active intervention group. A literature search identified twenty-one double-blind, randomised controlled trials in DPN of ≥1 year duration conducted between 1971 and 2021. We evaluated changes in neurophysiology, with a focus on peroneal motor and sural sensory NCV and amplitude in the placebo and treatment groups. There was significant variability in the change and direction of change (reduction/increase) in NCV in the placebo arm, as well as variability influenced by the anatomical site of neurophysiological measurement within a given clinical trial. A critical re-evaluation of efficacy trials should consider placebo-adjusted effects and present the placebo-subtracted change in NCV rather than assume a universal annual decline of 0.5 m/s/year. Importantly, endpoints such as corneal confocal microscopy (CCM) have demonstrated early nerve repair, whilst symptoms and NCV have not changed, and should thus be considered as a viable alternative.

Artificial intelligence utilising corneal confocal microscopy for the diagnosis of peripheral neuropathy in diabetes mellitus and prediabetes

AIMS/HYPOTHESIS

We aimed to develop an artificial intelligence (AI)-based deep learning algorithm (DLA) applying attribution methods without image segmentation to corneal confocal microscopy images and to accurately classify peripheral neuropathy (or lack of).

METHODS

The AI-based DLA utilised convolutional neural networks with data augmentation to increase the algorithm's generalisability. The algorithm was trained using a high-end graphics processor for 300 epochs on 329 corneal nerve images and tested on 40 images (1 image/participant). Participants consisted of healthy volunteer (HV) participants (n = 90) and participants with type 1 diabetes (n = 88), type 2 diabetes (n = 141) and prediabetes (n = 50) (defined as impaired fasting glucose, impaired glucose tolerance or a combination of both), and were classified into HV, those without neuropathy (PN-) (n = 149) and those with neuropathy (PN+) (n = 130). For the AI-based DLA, a modified residual neural network called ResNet-50 was developed and used to extract features from images and perform classification. The algorithm was tested on 40 participants (15 HV, 13 PN-, 12 PN+). Attribution methods gradient-weighted class activation mapping (Grad-CAM), Guided Grad-CAM and occlusion sensitivity displayed the areas within the image that had the greatest impact on the decision of the algorithm.

RESULTS

The results were as follows: HV: recall of 1.0 (95% CI 1.0, 1.0), precision of 0.83 (95% CI 0.65, 1.0), F₁-score of 0.91 (95% CI 0.79, 1.0); PN-: recall of 0.85 (95% CI 0.62, 1.0), precision of 0.92 (95% CI 0.73, 1.0), F₁-score of 0.88 (95% CI 0.71, 1.0); PN+: recall of 0.83 (95% CI 0.58, 1.0), precision of 1.0 (95% CI 1.0, 1.0), F₁-score of 0.91 (95% CI 0.74, 1.0). The features displayed by the attribution methods demonstrated more corneal nerves in HV, a reduction in corneal nerves for PN- and an absence of corneal nerves for PN+ images.

CONCLUSIONS/INTERPRETATION

We demonstrate promising results in the rapid classification of peripheral neuropathy using a single corneal image. A large-scale multicentre validation study is required to assess the utility of AI-based DLA in screening and diagnostic programmes for diabetic neuropathy.

Diabetes Distal Peripheral Neuropathy: Subtypes and Diagnostic and Screening Technologies

Diabetes distal symmetrical peripheral neuropathy (DSPN) is the most prevalent form of neuropathy in industrialized countries, substantially increasing risk for morbidity and pre-mature mortality. DSPN may manifest with small-fiber disease, large-fiber disease, or a combination of both. This review summarizes: (1) DSPN subtypes (small- and large-fiber disease) with attention to clinical signs and patient symptoms; and (2) technological diagnosis and screening for large- and small-fiber disease with inclusion of a comprehensive literature review of published studies from 2015-present (N = 66). Review findings, informed by the most up-to-date research, advance critical understanding of DSPN large- and small-fiber screening technologies, including those designed for point-of-care use in primary care and endocrinology practices.

Corneal and Epidermal Nerve Quantification in Chemotherapy Induced Peripheral Neuropathy

Chemotherapy-induced neurotoxicity is an increasingly recognized clinical issue in oncology. in vivo confocal microscopy (IVCM) of corneal nerves has been successfully used to diagnose peripheral neuropathies, including diabetic neuropathy. The purpose of this study was to test if the combination of corneal nerve density and morphology assessed by IVCM is useful to monitor the neurotoxic effects of chemotherapy compared to epidermal nerve quantification. Overall, 95 adult patients with different cancer types were recruited from the oncology and hematology departments of the San Raffaele Hospital. Neurological examination, including clinical Total Neuropathy Score, and in vivo corneal confocal microscopy (IVCM), were performed before and after chemotherapy. In a group of 14 patients, skin biopsy was performed at the first and last visit. In the group of 14 patients who underwent both skin biopsy and corneal nerve imaging, clinical worsening (+69%, p = 0.0018) was paralleled by corneal nerve fiber (CNF) density reduction (−22%, p = 0.0457). Clinical Total neuropathy score significantly worsened from the first to the last visit (+62%, p < 0.0001). CNF length was not significantly reduced overall. However, CNF density/tortuosity ratio significantly decreased after therapy. Correlation analysis showed that the CNF density/tortuosity ratio was also correlated with the number of chemotherapy cycles (r = −0.04790, P = 0.0009). Our data confirm that in vivo corneal confocal microscopy is a helpful, non-invasive tool which shows promise for the diagnosis of chemotherapy-induced peripheral neuropathies. IVCM could allow a rapid, reproducible and non-invasive quantification of peripheral nerve pathology in chemotherapy-associated neuropathy.

Corneal Confocal Microscopy Findings in Neuro Lyme Disease: A Case Report

Neuro Lyme disease is caused by several bacteriae of the Borreliaceae family, such as Borrelia Miyamotoi. In late stages of illness, patients with Lyme disease may develop chronic neurologic symptoms such as cognitive disturbances or small fiber peripheral neuropathy. Confocal microscopy is a non-invasive method designed to evaluate the human cornea in vivo. Thus, all the corneal layers, including the cells and the sub-basal nerve plexus, can be easily visualized and analyzed. This is the first report of the morphology of small-fiber peripheral neuropathy analyzed by confocal microscopy in a patient diagnosed of neuro Lyme disease. The decrease in the number of unmyelinated sub-basal nerve fibers with abundant presence of dendritic cells (DC) in comparison with healthy corneas strongly supports the diagnosis of small fiber peripheral neuropathy in a case of neuroborreliosis disease.

Corneal confocal microscopy for the diagnosis of diabetic peripheral neuropathy: A systematic review and meta-analysis

INTRODUCTION

Corneal confocal microscopy (CCM) is a rapid non-invasive ophthalmic imaging technique that identifies corneal nerve fiber damage. Small studies suggest that CCM could be used to assess patients with diabetic peripheral neuropathy (DPN).

AIM

To undertake a systematic review and meta-analysis assessing the diagnostic utility of CCM for sub-clinical DPN (DPN- ) and established DPN (DPN+ ).

DATA SOURCES

Databases (PubMed, Embase, Central, ProQuest) were searched for studies using CCM in patients with diabetes up to April 2020.

STUDY SELECTION

Studies were included if they reported on at least one CCM parameter in patients with diabetes.

DATA EXTRACTION

Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and inferior whorl length (IWL) were compared between patients with diabetes with and without DPN and controls. Meta-analysis was undertaken using RevMan V.5.3.

DATA SYNTHESIS

Thirty-eight studies including ~4,000 participants were included in this meta-analysis. There were significant reductions in CNFD, CNBD, CNFL, and IWL in DPN- vs controls (P < 0.00001), DPN+ vs controls (P < 0.00001), and DPN+ vs DPN- (P < 0.00001).

CONCLUSION

This systematic review and meta-analysis shows that CCM detects small nerve fiber loss in subclinical and clinical DPN and concludes that CCM has good diagnostic utility in DPN.

Implementation of corneal confocal microscopy for screening and early detection of diabetic neuropathy in primary care alongside retinopathy screening: Results from a feasibility study

OBJECTIVE

Screening for diabetic peripheral neuropathy (DPN) is essential for early detection and timely intervention. Quantitative assessment of small nerve fiber damage is key to the early diagnosis and assessment of its progression. Corneal confocal microscopy (CCM) is a non-invasive, in-vivo diagnostic technique that provides an accurate surrogate biomarker for small-fiber neuropathy. In this novel study for the first time, we introduced CCM to primary care as a screening tool for DPN alongside retinopathy screening to assess the level of neuropathy in this novel cohort.

RESEARCH DESIGN AND METHODS

450 consecutive subjects with type 1 or type 2 diabetes attending for annual eye screening in primary care optometry settings underwent assessment with CCM to establish the prevalence of sub-clinical diabetic peripheral neuropathy. Subjects underwent assessment for neurological and ocular symptoms of diabetes and a history of diabetic foot disease, neuropathy and diabetic retinopathy (DR).

RESULTS

CCM examination was completed successfully in 427 (94.9%) subjects, 22% of whom had neuropathy according to Diabetic Neuropathy Symptom (DNS) score. The prevalence of sub-clinical neuropathy as defined by abnormal corneal nerve fiber length (CNFL) was 12.9%. In the subjects with a short duration of type 2 diabetes, 9.2% had abnormal CNFL. CCM showed significant abnormalities in corneal nerve parameters in this cohort of subjects with reduction of corneal nerve fiber density (CNFD, p<0.001), CNFL (p<0.001) and corneal nerve branch density (CNBD, p<0.001) compared to healthy subjects. In subjects who had no evidence of DR (67% of all subjects), 12.0% had abnormal CNFL.

CONCLUSIONS

CCM may be a sensitive biomarker for early detection and screening of DPN in primary care alongside retinopathy screening.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

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.