Corneal confocal microscopy: a new technique for early detection of diabetic neuropathy

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 in patients with distal symmetric polyneuropathy compared to controls

BACKGROUND

Diabetic neuropathy (DN) is a very common clinical condition throughout the world. The diagnostic tests currently recommended have low sensitivity, such as electromyography, or are invasive, such as skin biopsy. New techniques have been developed to identify the early involvement of the peripheral nerve. With the advent of corneal confocal microscopy (CCM), a reduction in corneal innervation in patients with DN has been observed.

OBJECTIVE

To compare, through CCM, diabetic patients with symptomatic distal symmetric polyneuropathy (DSP) and controls.

METHODS

In the present study, through CCM, we compared the morphological changes in the sub-basal epithelial corneal plexus of 35 diabetic patients with symptomatic DSP with 55 controls. Moreover, we sought to determine a pattern of change regarding the severity stages of DSP, comparing the clinical, laboratory, and nerve-conduction (NC) variables.

RESULTS

Differences between the control and diabetic groups were observed for the following variables, respectively: age (44.9 ± 13.24 years versus 57.02 ± 10.4 years; p < 0.001); fiber density (29.7 ± 10.2 versus 16.6 ± 10.2; p < 0.001); number of fibers (4.76 ± 1.30 versus 3.14 ± 1.63; p < 0.001); number of Langerhans cells (4.64 ± 8.05 versus 7.49 ± 10.3; p = 0.035); tortuosity (p < 0.05); and thickness (p < 0.05). Furthermore, inverse relationships were found regarding fiber density and age (p < 0.01) and fiber density and the severity of the disease (p < 0.05). A positive relationship between the conduction velocity of the fibular nerve and fiber density (p < 0.05) was also observed.

CONCLUSION

Corneal confocal microscopy proved to be a fast, noninvasive and reproducible method for the diagnosis, staging, and monitoring of diabetic DSP.

Differential effects of obstructive sleep apnea on the corneal subbasal nerve plexus and retinal nerve fiber layer

Purpose

Obstructive sleep apnea (OSA) is an established independent risk factor for peripheral neuropathy. Macro and microvascular changes have been documented in OSA, including high levels of potent vasoconstrictors. In diabetes, vasoconstriction has been identified as an underlying risk factor for corneal neuropathy. This study sought to establish a potential relationship between OSA and corneal nerve morphology and sensitivity, and to determine whether changes in corneal nerves may be reflective of OSA severity.

Design

Single center cross-sectional study.

Methods

Sixty-seven patients were stratified into two groups: those with OSA and healthy controls. Groups were matched for age, sex, race, smoking, and dry eye status. Outcome measures included serologies, a dilated fundus exam, dry eye testing, anthropometric parameters, corneal sensitivity, subbasal nerve plexus morphology, retinal nerve fiber layer (RNFL) thickness, and the use of questionnaires to assess symptoms of dry eye disease, risk of OSA, and continuous positive airway pressure (CPAP) compliance.

Results

No significant differences were observed in corneal nerve morphology, sensitivity, or the number of dendritic cells. In the OSA test group, RNFL thinning was noted in the superior and inferior regions of the optic disc and peripapillary region. A greater proportion of participants in the OSA group required a subsequent evaluation for glaucoma than in the control. In those with OSA, an increase in the apnea hypopnea index was associated with an increase in optic nerve cupping.

Conclusions

OSA does not exert a robust effect on corneal nerves. OSA is however, associated with thinning of the RNFL. Participants with glaucomatous optic nerve changes and risk factors for OSA should be examined as uncontrolled OSA may exacerbate glaucoma progression.

Performance Analysis of Conventional Machine Learning Algorithms for Diabetic Sensorimotor Polyneuropathy Severity Classification Using Nerve Conduction Studies

Background

Diabetic sensorimotor polyneuropathy (DSPN) is a major form of complication that arises in long-term diabetic patients. Even though the application of machine learning (ML) in disease diagnosis is very common and well-established in the field of research, its application in DSPN diagnosis using nerve conduction studies (NCS), is very limited in the existing literature.

Method

In this study, the NCS data were collected from the Diabetes Control and Complications Trial (DCCT) and its follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) clinical trials. The NCS variables are median motor velocity (m/sec), median motor amplitude (mV), median motor F-wave (msec), median sensory velocity (m/sec), median sensory amplitude (μV), Peroneal Motor Velocity (m/sec), peroneal motor amplitude (mv), peroneal motor F-wave (msec), sural sensory velocity (m/sec), and sural sensory amplitude (μV). Three different feature ranking techniques were used to analyze the performance of eight different conventional classifiers.

Results

The ensemble classifier outperformed other classifiers for the NCS data ranked when all the NCS features were used and provided an accuracy of 93.40%, sensitivity of 91.77%, and specificity of 98.44%. The random forest model exhibited the second-best performance using all the ten features with an accuracy of 93.26%, sensitivity of 91.95%, and specificity of 98.95%. Both ensemble and random forest showed the kappa value 0.82, which indicates that the models are in good agreement with the data and the variables used and are accurate to identify DSPN using these ML models.

Conclusion

This study suggests that the ensemble classifier using all the ten NCS variables can predict the DSPN severity which can enhance the management of DSPN patients.

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 Nerve Fiber and Sensitivity Loss After Repeated Intravitreal Anti-VEGF Injections: An In Vivo Confocal Microscopy Study

PURPOSE

The purpose of this study was to investigate corneal sensation, subbasal nerve plexus (SBNP), and ocular surface symptoms in patients who underwent multiple intravitreal antivascular endothelial growth factor (anti-VEGF) injections for age-related macular degeneration (AMD) and diabetic macular edema (DME).

METHODS

Forty patients with previous anti-VEGF intravitreal injections (20 AMD and 20 DME) and 30 healthy controls were included in this study. In vivo corneal confocal microscopy (IVCM) of the SBNP, corneal sensitivity measurement with a Cochet-Bonnet esthesiometer, noninvasive tear break-up times, and ocular surface disease score index (OSDI) calculation were performed for each participant. Corneal nerve fiber density, corneal nerve branch density, total length of all nerve fibers, corneal total branch density, corneal nerve fiber area, corneal nerve fiber width, and corneal nerve fiber fractal dimension parameters were obtained by automatic digital analysis.

RESULTS

Corneal nerve fiber density, corneal nerve branch density, total length of all nerve fibers, and corneal nerve fiber fractal dimension in IVCM imaging and corneal sensitivity were significantly decreased in both AMD and DME groups compared with the control group. Corneal nerve fiber width and OSDI scores were significantly increased in AMD and DME groups compared with the control group. None of the IVCM parameters were significantly different between AMD and DME groups. Corneal sensitivity was decreased in patients with DME compared with patients with AMD. Tear break-up time was not different among the groups.

CONCLUSIONS

Corneal SBNP parameters were affected, corneal sensitivity was decreased, and OSDI scores were increased in patients with multiple intravitreal anti-VEGF injections. IVCM parameters were not significantly different between AMD and DME groups.

A Review On digital image processing techniques for in-Vivo confocal images of the cornea

This work reviews the scientific literature regarding digital image processing for in vivo confocal microscopy images of the cornea. We present and discuss a selection of prominent techniques designed for semi- and automatic analysis of four areas of the cornea (epithelium, sub-basal nerve plexus, stroma and endothelium). The main context is image enhancement, detection of structures of interest, and quantification of clinical information. We have found that the preprocessing stage lacks of quantitative studies regarding the quality of the enhanced image, or its effects in subsequent steps of the image processing. Threshold values are widely used in the reviewed methods, although generally, they are selected empirically and manually. The image processing results are evaluated in many cases through comparison with gold standards not widely accepted. It is necessary to standardize values to be quantified in terms of sensitivity and specificity of methods. Most of the reviewed studies do not show an estimation of the computational cost of the image processing. We conclude that reliable, automatic, computer-assisted image analysis of the cornea is still an open issue, constituting an interesting and worthwhile area of research.

Validation of a Novel Confocal Microscopy Imaging Protocol With Assessment of Reproducibility and Comparison of Nerve Metrics in Dry Eye Disease Compared With Controls

PURPOSE

The purposes of this study were to assess the reproducibility of a novel standardized technique for capturing corneal subbasal nerve plexus images with in vivo corneal confocal microscopy and to compare nerve metrics captured with this method in participants with dry eye and control participants.

METHODS

Cases and controls were recruited based on their International Statistical Classification of Diseases and Related Health Problems (ICD-10) diagnoses. Participants completed the following 3 ocular symptom questionnaires: the Ocular Surface Disease Index, Neuropathic Pain Symptom Inventory, and Dry Eye Questionnaire 5. A novel eye fixation-grid system was used to capture 30 standardized confocal microscopy images of the central cornea. Each participant was imaged twice by different operators. Seven quantitative nerve metrics were analyzed using automated software (ACCmetrics, Manchester, United Kingdom) for all 30 images and a 6-image subset.

RESULTS

Forty-seven participants were recruited (25 classified as dry eye and 22 controls). The most reproducible nerve metrics were corneal nerve fiber length [intraclass correlation (ICC) = 0.86], corneal nerve fiber area (ICC = 0.86), and fractal dimension (ICC = 0.90). Although differences were not statistically significant, all mean nerve metrics were lower in those with dry eye compared with controls. Questionnaire scores did not significantly correlate with nerve metrics. Reproducibility of nerve metrics was similar when comparing the entire 30-image montage to a central 6-image subset.

CONCLUSIONS

A standardized confocal imaging technique coupled with quantitative assessment of corneal nerves produced reproducible corneal nerve metrics even with different operators. No statistically significant differences in in vivo corneal confocal microscopy nerve metrics were observed between participants with dry eye and control participants.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.

Performance analysis of noninvasive electrophysiological methods for the assessment of diabetic sensorimotor polyneuropathy in clinical research: a systematic review and meta-analysis with trial sequential analysis

Despite the availability of various clinical trials that used different diagnostic methods to identify diabetic sensorimotor polyneuropathy (DSPN), no reliable studies that prove the associations among diagnostic parameters from two different methods are available. Statistically significant diagnostic parameters from various methods can help determine if two different methods can be incorporated together for diagnosing DSPN. In this study, a systematic review, meta-analysis, and trial sequential analysis (TSA) were performed to determine the associations among the different parameters from the most commonly used electrophysiological screening methods in clinical research for DSPN, namely, nerve conduction study (NCS), corneal confocal microscopy (CCM), and electromyography (EMG), for different experimental groups. Electronic databases (e.g., Web of Science, PubMed, and Google Scholar) were searched systematically for articles reporting different screening tools for diabetic peripheral neuropathy. A total of 22 studies involving 2394 participants (801 patients with DSPN, 702 controls, and 891 non-DSPN patients) were reviewed systematically. Meta-analysis was performed to determine statistical significance of difference among four NCS parameters, i.e., peroneal motor nerve conduction velocity, peroneal motor nerve amplitude, sural sensory nerve conduction velocity, and sural sensory nerve amplitude (all p < 0.001); among three CCM parameters, including nerve fiber density, nerve branch density, and nerve fiber length (all p < 0.001); and among four EMG parameters, namely, time to peak occurrence (from 0 to 100% of the stance phase) of four lower limb muscles, including the vastus lateralis (p < 0.001), tibialis anterior (p = 0.63), lateral gastrocnemius (p = 0.01), and gastrocnemius medialis (p = 0.004), and the vibration perception threshold (p < 0.001). Moreover, TSA was conducted to estimate the robustness of the meta-analysis. Most of the parameters showed statistical significance between each other, whereas some were statistically nonsignificant. This meta-analysis and TSA concluded that studies including NCS and CCM parameters were conclusive and robust. However, the included studies on EMG were inconclusive, and additional clinical trials are required.

Corneal nerves in diabetes-The role of the in vivo corneal confocal microscopy of the subbasal nerve plexus in the assessment of peripheral small fiber neuropathy

The cornea's intense innervation is responsible for corneal trophism and ocular surface hemostasis maintenance. Corneal diabetic neuropathy affects subbasal nerve plexus, with progressive alteration of nerves' morphology and density. The quantitative analysis of nerve fibers can be performed with in vivo corneal confocal microscopy considering the main parameters such as corneal nerve fibers length, corneal nerve fibers density, corneal nerve branching density, tortuosity coefficient, and beadings frequency. As the nerve examination permits the detection of early changes occurring in diabetes, the invivo corneal confocal microscopy becomes, over time, an important tool for diabetic polyneuropathy assessment and follow-up. In this review, we summarize the actual evidence about corneal nerve changes in diabetes and the relationship between the grade of alterations and the duration and severity of the disease. We aim at understanding how diabetes impacts corneal nerves and how it correlates with sensorimotor peripheral polyneuropathy and retinal complications. We also attempt to analyze the safety of the most common surgical procedures such as cataract and refractive surgery in diabetic patients and to highlight the specific risk factors. We believe that information about the corneal nerve fibers' condition obtained from the in vivo subbasal nerve plexus investigation may be crucial in monitoring peripheral small fiber polyneuropathy and that it will help with decision-making in ophthalmic surgery in diabetic patients.

An unbiased stereological method for corneal confocal microscopy in patients with diabetic polyneuropathy

Corneal confocal microscopy (CCM) derived corneal nerve measures are lower in diabetic sensorimotor polyneuropathy (DSPN). There are, however, methodological challenges in relation to adequate and unbiased sampling of images with objective corneal nerve quantification. Here we compare a new sampling method and adjusted area calculation with established methods of corneal nerve quantification in patients with and without DSPN and healthy controls. CCM images from 26 control subjects and 62 patients with type 1 diabetes with (n = 17) and without (n = 45) DSPN were analyzed. The images were randomly selected and corneal nerve fiber length (CNFL), corneal nerve fiber branch density (CNBD) and corneal nerve fiber density (CNFD) were determined in both a manual and automated manner. The new method generated 8–40% larger corneal nerve parameters compared to the standard procedure (p < 0.05). CNFL was significantly reduced using the new method for both manual and automated analysis; whilst CNFD and CNBD were significantly reduced using the automated method in both diabetic groups compared with controls. The new, objective method showed a reduction in corneal nerve parameters in diabetic patients with and without DSPN. We recommend using a randomized sampling method and area-dependent analysis to enable objective unbiased corneal nerve quantification.

Tear biomarkers and corneal sensitivity as an indicator of neuropathy in type 2 diabetes

AIMS

Explore potential of 31 tear biomarkers involved in screening for diabetic peripheral neuropathy (DPN). Assess the utility of aesthesiometry for measuring corneal damage in DPN and determine optimal cutoff point for detecting DPN.

METHODS

Screening test pilot study recruited 90 participants from a tertiary hospital in Lima, Peru. Participants were grouped by diabetes and neuropathy status. Tears collected on Schirmer strips, and proteins measured by both ELISA and multiplex-bead assay. Corneal sensitivity was measured by aesthesiometry, and DPN by vibration perception threshold testing.

RESULTS

There were 89 participants included in the analysis. The mean age was 55.7 ± 1.46, and 58.4% were female. MMP-9 and TGF-alpha concentrations were higher in participants with DPN versus diabetes alone, though not significant. Aesthesiometry was decreased in individuals with DPN when compared to participants with diabetes alone (p < 0.01) and normal controls (p < 0.01). Optimal cutoff point for aesthesiometry was found to be 5.8 cm, with 79% sensitivity and 75% specificity.

CONCLUSIONS

Tears are an insufficient standalone tool for detecting DPN based on the biomarkers analyzed. Aesthesiometry is a simple, inexpensive, and accurate method to assess corneal damage associated with moderate-severe DPN, and its integration into screening practices has potential to improve detection of DPN in poor-resource settings.

Progressive Loss of Corneal Nerve Fibers and Sensitivity in Rats Modeling Obesity and Type 2 Diabetes Is Reversible with Omega-3 Fatty Acid Intervention: Supporting Cornea Analyses as a Marker for Peripheral Neuropathy and Treatment

PURPOSE

To determine whether cornea nerve fiber density and/or corneal function are valid markers for early detection and treatment of peripheral neuropathy in rats modeling prediabetes and type 2 diabetes.

METHODS

High-fat feeding combined without or with low-dose streptozotocin was used to create rat models for prediabetes and type 2 diabetes that were longitudinally studied for loss of structure and function of sensory nerves in the cornea and skin as well as nerve conduction velocity and vascular reactivity of epineurial arterioles. There were three time points examined in each of the three conditions with 12 rats per group. The latest time point (24 weeks of high-fat diet with or without 16 weeks of hyperglycemia) was used to examine reversibility of neuro and vascular pathology following 16 weeks of treatment with menhaden oil, a natural source of long-chain omega-3 polyunsaturated fatty acids. The number of rats in the intervention study ranged from 6 to 17.

RESULTS

Our longitudinal study demonstrated that vascular and neural dysfunction associated with obesity or type 2 diabetes occur early and are progressive. Decrease in cornea nerve fiber length and function were valid markers of disease in both the pre-diabetic and diabetic rat models and were more sensitive than decrease in intraepidermal nerve fiber density of the skin and thermal nociception of the hindpaw. Late intervention with menhaden oil significantly reversed both vascular and peripheral nerve damage induced by chronic obesity or type 2 diabetes.

CONCLUSION

These studies provide support for examination of corneal structure and function as an early marker of peripheral neuropathy in prediabetes and type 2 diabetes. Furthermore, we demonstrate that omega-3 polyunsaturated fatty acids derived from fish oil are an effective treatment for peripheral neuropathy that occurs with chronic obesity or type 2 diabetes.

Pain-related evoked potentials in patients with large, mixed, and small fiber neuropathy

OBJECTIVE

To investigate A-delta fiber pathways in patients with large, mixed, and small fiber neuropathies using pain-related evoked potentials (PREP).

METHODS

We prospectively examined consecutive and unselected 108 patients with neuropathies using PREP. Patients were stratified according to impaired fiber types in those with large fiber neuropathy (LFN, n = 23), mixed fiber neuropathy (MFN, n = 80), and small fiber neuropathy (SFN, n = 5). Additionally, medical history, nerve conduction studies, quantitative sensory testing (QST), and skin punch biopsy were applied. Data was compared with those of 49 healthy controls.

RESULTS

Patients with MFN showed a distal loss of PREP (16/80, 20%) and prolonged PREP latencies after stimulation at the foot (MFN: 225.8 [135-293.6] ms, controls: 218 [135-394] ms, p < 0.05). Patients with demyelinating neuropathies had prolonged PREP latencies after stimulation at the hand (p < 0.05 each). QST showed an impairment of small and large fiber function in patients with MFN. PREP were mostly absent in patients at advanced stages of neuropathies: in 10/31 (30%) patients with no recordable sural nerve action potential (SNAP, preserved SNAP: 8/76, 10% missing) and in 4/17 (24%) patients with loss of distal epidermal innervation (preserved epidermal innervation: 7/60, 24%) PREP was not recordable. PREP peak-to-peak amplitude after stimulation at the face was lowered in patients with reduced proximal intraepidermal nerve fiber density (p < 0.02).

CONCLUSION

PREP is a useful screening method for A-delta fiber pathology also in patients with simultaneous large fiber pathology. Loss of PREP indicates advance stages of nerve fiber damage.

SIGNIFICANCE

PREP may be useful as a complementary method for detection of small fiber impairment also in patients with mixed fiber neuropathy and in advanced stages.

Corneal injury: Clinical and molecular aspects

Currently, over 10 million people worldwide are affected by corneal blindness. Corneal trauma and disease can cause irreversible distortions to the normal structure and physiology of the cornea often leading to corneal transplantation. However, donors are in short supply and risk of rejection is an ever-present concern. Although significant progress has been made in recent years, the wound healing cascade remains complex and not fully understood. Tissue engineering and regenerative medicine are currently at the apex of investigation in the pursuit of novel corneal therapeutics. This review uniquely integrates the clinical and cellular aspects of both corneal trauma and disease and provides a comprehensive view of the most recent findings and potential therapeutics aimed at restoring corneal homeostasis.

Emerging Biomarkers, Tools, and Treatments for Diabetic Polyneuropathy

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

Contact lens wear and the diabetic corneal epithelium: A happy or disastrous marriage?

Diabetes mellitus is an epidemic in the US and abroad. With the advent of new contact lens technology, the use of contact lenses as glucose sensors in lieu of the traditional finger stick is quickly becoming realized. This has the potential to rapidly expand the contact lens market into this growing patient population. The independent cellular and physiological effects of contact lens wear and diabetes on the corneal epithelium have been described. However, little evidence exists to date to support whether there is increased risk associated with contact lens wear in diabetes. The focus of this review is to discuss what is known about the cellular effects of contact lenses on the corneal epithelium, the pathophysiological changes in the corneal epithelium that occur in diabetes, and whether an increased risk for corneal epithelial damage and/or infection may negatively impact safety in diabetic contact lens wearers. Available data indicates that there are inherent risks associated with contact lens wear in diabetics. Importantly, eye care practitioners fitting contact lenses in the diabetic patient need to carefully consider the duration of disease, the level of glycemic control, the presence of retinopathy, and the patient's overall health.

Corneal confocal sub-basal nerve plexus evaluation: a review

The aim of this study was to review the most recent data about corneal sub-basal nerve plexus (SNP) evaluated with the use of corneal confocal microscopy (CCM). For this purpose, an electronic search was conducted based on PubMed and Google Scholar and Web of Science databases from 2008 up to the end of 2016. Ninety-eight articles in English were cited, as well as abstracts in other languages, concerning the morphology and function of corneal SNP in various diseases. Changes in corneal SNP as a result of local treatment were also introduced. Figures with scans from confocal microscopy from our Department were included. The main conclusion of this review was that both corneal SNP diminishment and high tortuosity as well as low sensitivity are in principle related to the presence or level of pathology. In addition, increased nerve tortuosity may represent a morphological determinant of nerve regeneration. However, the presented literature shows that SNP changes are not characteristic for one unified corneal pathology; rather, they reflect the non-specific pathological process present in many diseases. Future studies should use automatized biometric software and also examine the effects of new treatments on SNP.

Small-fiber neuropathy and pain sensitization in survivors of pediatric acute lymphoblastic leukemia

BACKGROUND

Chemotherapy-induced Peripheral Neuropathy (CIPN) of large-fibers affects up to 20% of survivors of pediatric acute lymphoblastic leukemia (ALL). We aimed to describe small-fiber toxicity and pain sensitization in this group.

METHODS

In a cross-sectional, bicentric study we assessed 46 survivors of pediatric ALL (Mean age: 5.7 ± 3.5 years at diagnosis, median 2.5 years after therapy; males: 28).

INCLUSION CRITERIA

≥6 years of age, ≥3 months after last administration of Vincristine, and cumulative dose of Vincristine 12 mg/m². We used a reduced version of the Pediatric-modified Total Neuropathy Score (Ped-mTNS) as bedside test and Quantitative Sensory Testing (QST) for assessment of small- and large-fiber neuropathy as well as pain sensitization. We employed Nerve Conduction Studies (NCS) as the most accurate tool for detecting large-fiber neuropathy.

RESULTS

Fifteen survivors (33%) had abnormal rPed-mTNS values (≥4 points) and 5 survivors (11%) reported pain. In QST, the survivor group showed significant (p < 0.001) inferior large-fiber function and pain sensitization when compared to healthy matched peers. We identified deficits of vibration in 33 (72%) and tactile hypoesthesia in 29 (63%), hyperalgesia to blunt pressure in 19 (41%), increased mechanical pain sensitivity in 12 (26%) and allodynia in 16 (35%) of 46 survivors. Only 7 survivors (15%) had pathologic NCS.

CONCLUSION

QST is a sensitive tool that revealed signs of large-fiber neuropathy in two thirds, small-fiber neuropathy and pain sensitization in one third of survivors. Prospective studies using QST in pediatric oncology may help to elucidate the pathophysiology of small-fiber neuropathy and pain sensitization as well as their relevance for quality of survival.

In Vivo Corneal Confocal Microscopy Detects Improvement of Corneal Nerve Parameters following Glycemic Control in Patients with Type 2 Diabetes

AIM

This study aimed to investigate whether in vivo corneal confocal microscopy (CCM) can detect the improvement of corneal nerve parameters following glycemic control in patients with type 2 diabetes in natural history.

METHODS

Thirty-two patients with diabetes complicated by DPN and 12 age-matched control subjects underwent detailed clinical examination and were assessed per the Toronto Clinical Scoring Scale for DPN, nerve conduction studies, and IVCCM at baseline and after approximately one year from the first visit.

RESULTS

At follow-up, 16 diabetic patients had improved glycemic control (group A, HbA1c < 7.0%, 7.78 ± 1.62% versus 6.52 ± 0.59%, P = 0.005), while the remainder continued to have elevated HbA1c levels (group B, HbA1c ≥ 7.0%, 8.55 ± 1.57% versus 8.79 ± 1.05%, P = 0.527). For patients in group A, corneal nerve fiber density (CNFD) (18.55 ± 5.25 n/mm² versus 21.78 ± 6.13 n/mm², P = 0.005) and corneal nerve fiber length (CNFL) (11.62 ± 2.89 mm/mm² versus 13.04 ± 2.44 mm/mm², P = 0.029) increased significantly compared to baseline. For patients in group B, sural sensory nerve conduction velocity (47.93 ± 7.20 m/s versus 44.67 ± 6.43 m/s, P = 0.024), CNFD (17.19 ± 5.31 n/mm² versus 15.67 ± 4.16 n/mm², P = 0.001), corneal nerve branch density (19.33 ± 12.82 n/mm² versus 14.23 ± 6.56 n/mm², P = 0.033), and CNFL (11.16 ± 2.57 mm/mm² versus 9.90 ± 1.75 mm/mm², P = 0.011) decreased significantly.

CONCLUSIONS

The results of this study suggest that morphological repair of corneal nerve fibers can be detected when glycemic control improves. In vivo CCM could be a sensitive method that can be applied in future longitudinal or interventional studies on DPN.

The Quest for more Research on Painful Diabetic Neuropathy

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

Corneal confocal microscopy is a rapid reproducible ophthalmic technique for quantifying corneal nerve abnormalities

PURPOSE

To assess the effect of applying a protocol for image selection and the number of images required for adequate quantification of corneal nerve pathology using in vivo corneal confocal microscopy (IVCCM).

METHODS

IVCCM was performed in 35 participants by a single examiner. For each participant, 4 observers used a standardized protocol to select 6 central corneal nerve images to assess the inter-observer variability. Furthermore, images were selected by a single observer on two occasions to assess intra-observer variability and the effect of sample size was assessed by comparing 6 with 12 images. Corneal nerve fiber density (CNFD), branch density (CNBD) and length (CNFL) were quantified using fully automated software. The data were compared using the intra class correlation coefficient (ICC) and Bland-Altman agreement plots for all experiments.

RESULTS

The ICC values for CNFD, CNBD and CNFL were 0.93 (P<0.0001), 0.96 (P<0.0001) and 0.95 (P<0.0001) for inter-observer variability and 0.95 (P<0.0001), 0.97 (P<0.001) and 0.97 (P<0.0001) for intra-observer variability. For sample size variability, ICC values were 0.94 (P<0.0001), 0.95 (P<0.0001), and 0.96 (P<0.0001) for CNFD, CNBD and CNFL. Bland-Altman plots showed excellent agreement for all parameters.

CONCLUSIONS

This study shows that implementing a standardized protocol to select IVCCM images results in high intra and inter-observer reproducibility for all corneal nerve parameters and 6 images are adequate for analysis. IVCCM could therefore be deployed in large multicenter clinical trials with confidence.

Declining Skeletal Muscle Function in Diabetic Peripheral Neuropathy

PURPOSE

The present review highlights current concepts regarding the effects of diabetic peripheral neuropathy (DPN) in skeletal muscle. It discusses the lack of effective pharmacologic treatments and the role of physical exercise intervention in limb protection and symptom reversal. It also highlights the importance of magnetic resonance imaging (MRI) techniques in providing a mechanistic understanding of the disease and helping develop targeted treatments.

METHODS

This review provides a comprehensive reporting on the effects of DPN in the skeletal muscle of patients with diabetes. It also provides an update on the most recent trials of exercise intervention targeting DPN pathology. Lastly, we report on emerging MRI techniques that have shown promise in providing a mechanistic understanding of DPN and can help improve the design and implementation of clinical trials in the future.

FINDINGS

Impairments in lower limb muscles reduce functional capacity and contribute to altered gait, increased fall risk, and impaired balance in patients with DPN. This finding is an important concern for patients with DPN because their falls are likely to be injurious and lead to bone fractures, poorly healing wounds, and chronic infections that may require amputation. Preliminary studies have shown that moderate-intensity exercise programs are well tolerated by patients with DPN. They can improve their cardiorespiratory function and partially reverse some of the symptoms of DPN. MRI has the potential to bring new mechanistic insights into the effects of DPN as well as to objectively measure small changes in DPN pathology as a result of intervention.

IMPLICATIONS

Noninvasive exercise intervention is particularly valuable in DPN because of its safety, low cost, and potential to augment pharmacologic interventions. As we gain a better mechanistic understanding of the disease, more targeted and effective interventions can be designed.

Improved sampling and analysis of images in corneal confocal microscopy

INTRODUCTION

Corneal confocal microscopy (CCM) is a noninvasive clinical method to analyse and quantify corneal nerve fibres in vivo. Although the CCM technique is in constant progress, there are methodological limitations in terms of sampling of images and objectivity of the nerve quantification. The aim of this study was to present a randomized sampling method of the CCM images and to develop an adjusted area-dependent image analysis. Furthermore, a manual nerve fibre analysis method was compared to a fully automated method.

METHODS

23 idiopathic small-fibre neuropathy patients were investigated using CCM. Corneal nerve fibre length density (CNFL) and corneal nerve fibre branch density (CNBD) were determined in both a manual and automatic manner. Differences in CNFL and CNBD between (1) the randomized and the most common sampling method, (2) the adjusted and the unadjusted area and (3) the manual and automated quantification method were investigated.

RESULTS

The CNFL values were significantly lower when using the randomized sampling method compared to the most common method (p = 0.01). There was not a statistical significant difference in the CNBD values between the randomized and the most common sampling method (p = 0.85). CNFL and CNBD values were increased when using the adjusted area compared to the standard area. Additionally, the study found a significant increase in the CNFL and CNBD values when using the manual method compared to the automatic method (p ≤ 0.001).

CONCLUSION

The study demonstrated a significant difference in the CNFL values between the randomized and common sampling method indicating the importance of clear guidelines for the image sampling. The increase in CNFL and CNBD values when using the adjusted cornea area is not surprising. The observed increases in both CNFL and CNBD values when using the manual method of nerve quantification compared to the automatic method are consistent with earlier findings. This study underlines the importance of improving the analysis of the CCM images in order to obtain more objective corneal nerve fibre measurements.

Diabetic complications in the cornea

Diabetic corneal alterations, such as delayed epithelial wound healing, edema, recurrent erosions, neuropathy/loss of sensitivity, and tear film changes are frequent but underdiagnosed complications of both type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes mellitus. The disease affects corneal epithelium, corneal nerves, tear film, and to a lesser extent, endothelium, and also conjunctiva. These abnormalities may appear or become exacerbated following trauma, as well as various surgeries including retinal, cataract or refractive. The focus of the review is on mechanisms of diabetic corneal abnormalities, available animal, tissue and organ culture models, and emerging treatments. Changes of basement membrane structure and wound healing rates, the role of various proteinases, advanced glycation end products (AGEs), abnormal growth and motility factors (including opioid, epidermal, and hepatocyte growth factors) are analyzed. Experimental therapeutics under development, including topical naltrexone, insulin, inhibitors of aldose reductase, and AGEs, as well as emerging gene and cell therapies are discussed in detail.

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

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

Early vs. late intervention of high fat/low dose streptozotocin treated C57Bl/6J mice with enalapril, α-lipoic acid, menhaden oil or their combination: Effect on diabetic neuropathy related endpoints

We have previously demonstrated that enalapril, α-lipoic acid and menhaden (fish) oil has potential as a treatment for diabetic peripheral neuropathy. In this study we sought to determine the efficacy of these treatments individually or in combination on multiple neuropathic endpoints in a high fat fed low dose streptozotocin treated mouse, a model of type 2 diabetes, following early or late intervention. Four or twelve weeks after the onset of hyperglycemia, diabetic mice were treated with enalapril, α-lipoic acid, menhaden oil or their combination for 12 weeks. Afterwards, endpoints including glucose tolerance, motor and sensory nerve conduction velocity, thermal nociception, and intraepidermal and cornea nerve fiber density was determined. Glucose clearance was impaired in diabetic mice and significantly improved only with combination treatment and early intervention. Diabetes caused steatosis, slowing of motor and sensory nerve conduction velocity, thermal hypoalgesia and reduction in intraepidermal and cornea nerve fiber density. Treating diabetic mice with enalapril, α-lipoic acid or menhaden oil partially protected diabetic mice from these deficits, whereas the combination of these three treatments was more efficacious following early or late intervention. These studies suggest that a combination therapy may be more effective for treating neural complications of type 2 diabetes.

Intraepidermal Nerve Fiber Density: Diagnostic and Therapeutic Relevance in the Management of Chronic Pruritus: a Review

In recent years, measurement of the intraepidermal nerve fiber (IENF) density has gained relevance in the diagnostics of chronic pruritus. This method allows the objectification and quantification of a small-fiber neuropathy, which may manifest clinically with pruritus, pain or dysesthetic sensory symptoms, such as burning, stinging and tingling sensations or numbness. Upon suspicion of a small-fiber neuropathy as a cause for chronic pruritus, targeted diagnostic procedures are essential for the early detection of the neuroanatomical changes. After a punch biopsy of the lower leg, the obtained tissue undergoes an immunofluorescence staining process with a primary antibody against the protein gene product 9.5. The IENFs can thus be detected and are quantified according to pre-determined guidelines based on an international consensus. In addition to morphological changes, functional impairment of small-fibers can be assessed using quantitative sensory testing by assessing detection and pain thresholds of various thermal and mechanic modalities. This method, however, is time-consuming and requires a specialized investigator, and thus it is not routinely used in the diagnostic investigation of chronic pruritus. Diagnosing a small-fiber neuropathy underlying chronic pruritus has therapeutic relevance. If possible, the underlying cause of the neuropathy should be treated. Alternatively, symptomatic therapy options include topical (capsaicin) and systemic (anticonvulsants and/or antidepressants) agents. Chronification processes may lead to refractory pruritus, and thus treatment should be initiated as soon as possible. The aim of this review is to present and discuss the measurement of the IENF density as a diagnostic tool and its role in the management of patients with chronic pruritus. A brief case report is presented to better illustrate the role of this diagnostic method in the clinical setting.

Neuronal Changes in the Diabetic Cornea: Perspectives for Neuroprotection

Diabetic neuropathy is associated with neurotrophic ulcerations of the skin and cornea. Decreased corneal sensitivity and impaired innervation lead to weakened epithelial wound healing predisposing patients to ocular complications such as corneal infections, stromal opacification, and surface irregularity. This review presents recent findings on impaired corneal innervation in diabetic individuals, and the findings suggest that corneal neuropathy might be an early indicator of diabetic neuropathy. Additionally, the recent findings for neuroprotective and regenerative therapy for diabetic keratopathy are presented.

In vivo corneal confocal microscopy in diabetes: Where we are and where we can get

In vivo corneal confocal microscopy (IVCCM) is a novel, reproducible, easy and noninvasive technique that allows the study of the different layers of the cornea at a cellular level. As cornea is the most innervated organ of human body, several studies investigated the use of corneal confocal microscopy to detect diabetic neuropathies, which are invalidating and deadly complications of diabetes mellitus. Corneal nerve innervation has been shown impaired in subjects with diabetes and a close association between damages of peripheral nerves due to the diabetes and alterations in corneal sub-basal nerve plexus detected by IVCCM has been widely demonstrated. Interestingly, these alterations seem to precede the clinical onset of diabetic neuropathies, paving the path for prevention studies. However, some concerns still prevent the full implementation of this technique in clinical practice. In this review we summarize the most recent and relevant evidences about the use of IVCCM for the diagnosis of peripheral sensorimotor polyneuropathy and of autonomic neuropathy in diabetes. New perspectives and current limitations are also discussed.

The Yin and Yang of the Opioid Growth Regulatory System: Focus on Diabetes-The Lorenz E. Zimmerman Tribute Lecture

The Opioid Growth Regulatory System consists of opioid growth factor (OGF), [Met5]-enkephalin, and its unique receptor (OGFr). OGF inhibits cell division when bound to OGFr. Conversely, blockade of the interaction of OGF and OGFr, using the potent, long-acting opioid receptor antagonist, naltrexone (NTX), results in increased DNA synthesis and cell division. The authors have demonstrated both in vitro and in vivo that the addition of exogenous OGF or an increase in available OGFr decreases corneal epithelial cell division and wound healing. Conversely, blockade of the OGF-OGFr interaction by NTX or a decrease in the production of the OGFr increases corneal epithelial cell division and facilitates corneal epithelial wound healing. The authors also have demonstrated that depressed corneal and cutaneous wound healing, dry eye, and abnormal corneal sensitivity in type 1 and type 2 diabetes in animals can be reversed by OGF-OGFr blockade by NTX. Thus, the function of the Opioid Growth Regulatory System appears to be disordered in diabetic animals, and its function can be restored with NTX treatment. These studies suggest a fundamental role for the Opioid Growth Regulatory System in the pathobiology of diabetic complications and a need for studies to elucidate this role further.

Evaluation of sural nerve automated nerve conduction study in the diagnosis of peripheral neuropathy in patients with type 2 diabetes mellitus

INTRODUCTION

New tests for improved diagnosis of diabetic peripheral neuropathy (DPN) are useful.

MATERIAL AND METHODS

We evaluated the utility of automated nerve conduction study (NCS) of the sural nerve with a new portable device for the diagnosis of DPN in patients with type 2 diabetes mellitus (T2DM). This study included 114 T2DM patients (58 men) with mean age 64.60 ±8.61 years. Exclusion criteria were B12 depletion, alcohol abuse and other causes of peripheral neuropathy. The reference method was the Neuropathy Disability Score (NDS) with a threshold NDS ≥ 3. Sural nerve automated NCS was carried out with the portable NC-stat DPNCheck device. Sensory nerve conduction velocity and sensory nerve action potential amplitude were measured bilaterally. Automated NCS was considered abnormal when ≥ 1 of the two aforementioned neurophysiological parameters was abnormal in at least one leg.

RESULTS

Examination with NC-stat DPNCheck exhibited 90.48% sensitivity, 86.11% specificity, 79.17% positive predictive value (PPV) and 93.94% negative predictive value (NPV). The positive likelihood ratio (LR+) was 6.51 and the negative likelihood ratio (LR-) was 0.11.

CONCLUSIONS

Sural nerve automated NCS with the NC-stat DPNCheck device exhibits high sensitivity and specificity for the diagnosis of DPN in T2DM.

Simplified Diagnosis of Cardiovascular Autonomic Neuropathy in Type 2 Diabetes Using Ewing's Battery

AIM

To find a potential simplification of the established Ewing's battery for the diagnosis of cardiovascular autonomic neuropathy (CAN) in type 2 diabetes (T2D).

METHODS

We included 152 patients (92 men) with mean age 64.51 ± 7.85 years and median diabetes duration of 12 years. Ewing's battery was used as the gold standard for the diagnosis of CAN. Against this, we compared the results from each test and their combinations.

RESULTS

The 30:15 ratio exhibited the best diagnostic performance (AUC = 0.817, 95% CI: 0.730-0.903, p < 0.001), with 96% sensitivity, 65% specificity, and 94% negative predictive value (NPV). The corresponding values for the Valsalva ratio (VR) were 62%, 92%, and 85%, respectively. The 30:15 ratio was the strongest independent predictor of neuropathy in multivariate regression analysis; low levels yielded an odds ratio (OR) of 21.14 for CAN. The rise in diastolic blood pressure and the expiration/inspiration/VR ratio (E/I/VR) were also identified as independent predictors of CAN, with 9.45 and 10.79 ORs, respectively.

CONCLUSIONS

The 30:15 ratio has the best diagnostic accuracy, primarily in the exclusion of CAN, by virtue of its very high sensitivity and NPV. If this ratio is positive for CAN, the VR, the rise in diastolic blood pressure, and the E/I/VR may be useful to increase diagnostic accuracy. This procedure is a simplified diagnostic approach that merits further evaluation to enable wider screening for CAN.

Risk Factors and Comorbidities in Diabetic Neuropathy: An Update 2015

Distal symmetric sensorimotor polyneuropathy (DSPN) is the most common neurological manifestation in diabetes. Major risk factors of DSPN include diabetes duration, hyperglycemia, and age, followed by prediabetes, hypertension, dyslipidemia, and obesity. Height, smoking, insulin resistance, hypoinsulinemia, and others represent an additional risk. Importantly, hyperglycemia, hypertension, dyslipidemia, obesity, and smoking are modifiable. Stringent glycemic control has been shown to be effective in type 1, but not to the same extent in type 2 diabetes. Antilipidemic treatment, especially with fenofibrate, and multi-factorial intervention have produced encouraging results, but more experience is necessary. The major comorbidities of DSPN are depression, autonomic neuropathy, peripheral arterial disease, cardiovascular disease, nephropathy, retinopathy, and medial arterial calcification. Knowledge of risk factors and comorbidities has the potential to enrich the therapeutic strategy in clinical practice as part of the overall medical care for patients with neuropathy. This article provides an updated overview of DSPN risk factors and comorbidities.

Small-Fiber Neuropathy: A Diabetic Microvascular Complication of Special Clinical, Diagnostic, and Prognostic Importance

Damage of small nerve fibers may lead to a large variety of clinical symptoms. Small-fiber neuropathy underlies the symptoms of painful diabetic neuropathy, which may decrease quality of life. It also contributes to the poor prognosis of diabetic neuropathy because it plays a key role in the pathogenesis of foot ulceration and autonomic neuropathy. Impairment of small nerve fibers is considered the earliest alteration in the course of diabetic neuropathy. Therefore, assessment of functional and morphological abnormalities of small nerve fibers may enable timely diagnosis. The definition, symptoms, and clinical significance of small-fiber neuropathy are considered in the present review. An apparently more complex interaction between small-fiber impairment and microcirculation is extensively discussed. Diagnostic modalities include morphometric and functional methods. Corneal confocal microscopy and punch skin biopsy are considered gold standards, but noninvasive functional tests are also diagnostically useful. However, in routine clinical practice, small-fiber neuropathy is diagnosed by its typical clinical presentation. Finally, prompt treatment should be initiated following diagnosis.

Diabetic foot syndrome and corneal subbasal nerve plexus changes in congolese patients with type 2 diabetes

BACKGROUND

To study the severity of diabetic neuropathy, diabetic retinopathy and grades of diabetic foot syndrome for correlations with corneal subbasal nerve plexus (SBP) changes in Congolese patients with type 2 diabetes.

METHODOLOGY/PRINCIPAL FINDINGS

Twenty-eight type 2 diabetes patients with diabetes-related foot ulceration were recruited in a diabetic care unit in Kinshasa, Democratic Republic of Congo. Corneal SBP was investigated by confocal laser-scanning microscopy to analyse nerve fibre density (NFD) [µm/ µm²], number of branches [n] and number of connectivity points [n]. Foot ulceration was graded using the Wagner ulcer classification. Corneal sensitivity (Cochet-Bonnet), Neuropathy Symptom Score (NSS), Neuropathy Disability Score (NDS), ankle-brachial index (ABI) and ophthalmological status were evaluated. Foot ulceration was ranked as mild (Wagner 0-1: 13 patients/46.4%), moderate (Wagner 2-3: 10 patients/35.7%) and severe (Wagner 4-5: 5 patients/17.9%). The correlation between Wagner Score and NFD (p=0.017, r = - 0,454), NDS and NFD (p=0,039, r = - 0.400) as well as Wagner Score and HbA1c (p=0,007, r = - 0.477) was stated. Significant differences in confocal SBP parameters were observed between Wagner 0-1 and Wagner 4 5 (number of branches (p=0.012), number of connectivity points (p=0.001), nerve fibre density (p=0.033)) and ABI (p=0.030), and between Wagner 2-3 and Wagner 4-5 (number of branches (p=0.003), number of connectivity points (p=0.005) and nerve fibre density (p=0.014)). Differences in NDS (p=0.001) and corneal sensation (p=0.032) were significant between Wagner 0-1 and Wagner 2-3. Patients with diabetic retinopathy had significantly longer diabetes duration (p=0.03) and higher NDS (p=0.01), but showed no differences in SBP morphology or corneal sensation.

CONCLUSIONS/SIGNIFICANCE

While confirming the diabetic aetiology of foot ulceration due to medial arterial calcification, this study indicates that the grade of diabetic foot syndrome correlates with corneal SBP changes and corneal sensation in patients in sub-Saharan Africa.

Corneal confocal microscopy: Recent progress in the evaluation of diabetic neuropathy

The present brief review discusses recent progress with corneal confocal microscopy for the evaluation of diabetic sensorimotor polyneuropathy. Corneal confocal microscopy is a new, non-invasive and reproducible diagnostic modality, and it can also be easily applied for patient follow up. It enables new perspectives of studying the natural history of diabetic sensorimotor polyneuropathy, severity of nerve fiber pathology and documenting early nerve fiber regeneration after therapeutic intervention. It shows moderate to high sensitivity and specificity for the timely diagnosis of diabetic sensorimotor polyneuropathy. Currently, corneal confocal microscopy is mainly used in specialized centers, but deserves more widespread application for the assessment of diabetic sensorimotor polyneuropathy. Finally, further progress is required in terms of technical improvements for automated nerve fiber quantification and for analysis of larger images.

Corneal confocal microscopy for assessment of diabetic peripheral neuropathy: a meta-analysis

PURPOSE

To evaluate the diagnostic performance of corneal confocal microscopy (CCM) in assessing corneal nerve parameters in patients with diabetic peripheral neuropathy (DPN).

METHODS

Studies in the literature that focused on CCM and DPN were retrieved by searching PubMed, Excerpt Medica Database (EMBASE) and China National Knowledge Infrastructure (CNKI) databases. RevMan V.5.3 software was used for the meta-analysis. The results are presented as weighted mean difference (WMD) with a corresponding 95% CI.

RESULTS

13 studies with a total of 1680 participants were included in the meta-analysis. The pooled results showed that the corneal nerve fibre density, nerve branch density and nerve fibre length were significantly reduced (all p<0.00001) in the patients with DPN compared with healthy controls ((WMD=-18.07, 95% CI -21.93 to -14.20), (WMD=-25.35, 95% CI -30.96 to -19.74) and (WMD=-6.37, 95% CI -7.44 to -5.30)) and compared with the diabetic patients without DPN ((WMD=-8.83, 95% CI -11.49 to -6.17), (WMD=-13.54, 95% CI -20.41 to -6.66) and (WMD=-4.19, 95% CI -5.35 to -3.04)), respectively. No significant difference was found in the corneal nerve fibre tortuosity coefficient between diabetic patients with DPN and healthy controls (p=0.80) or diabetic patients without DPN (p=0.61).

CONCLUSIONS

This meta-analysis suggested that CCM may be valuable for detecting and assessing early nerve damage in DPN patients.

Progress in the treatment of small fiber peripheral neuropathy

Small fiber neuropathy is a syndrome of diverse disease etiology because of multiple pathophysiologic mechanisms with major presentations of neuropathic pain and autonomic symptoms. Over the past decade, there has been substantial progress in the treatments for neuropathic pain, dysautonomia and disease-modifying strategy. In particular, anticonvulsants and antidepressants alleviate neuropathic pain based on randomized clinical trials.

New vistas in the diagnosis of diabetic polyneuropathy

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

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

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