Skin biopsy as a diagnostic tool in peripheral neuropathy

Changes in the Cutaneous Nerve Fiber Staining and Distribution of PGP9.5 in Clinically Uninvolved Skin in Leprosy Patients after Completion of Multidrug Therapy and Assessing PGP9.5 as a Marker of Treatment Response

Background

Subclinical involvement of nerves may sometimes be present much before the overt clinical manifestations become apparent. Protein gene product (PGP) 9.5, a ubiquitin-C-terminal hydrolase, has been widely used as a marker to study the involvement of peripheral nerve fibers in many diseases.

Aim and Objectives

To evaluate the change in cutaneous nerve fiber staining and distribution from pre-treatment and post completion of multidrug therapy through the expression of PGP9.5 and to assess PGP9.5 as a marker of treatment response.

Materials and Methods

In this prospective single-center observational study, skin biopsy was taken in patients with leprosy, having areas of nerve function impairment (NFI), based on findings of nerve conduction studies (NCSs), but not having lesions or impaired tactile or thermal impairment clinically. The thin nerve fiber density in the clinically normal skin in areas supplied by nerve showing changes of sensory neuropathy was evaluated to study the density of the fibers. A second biopsy was taken at the end of treatment from a site near the previous site to assess the changes in intra-epidermal nerve fiber staining and distribution.

Results

Thirty-three patients were recruited in the present study (24 males and 9 females). Pre-treatment, 27 patients had abnormal NCSs, while six patients did not have any evidence of neuropathy on NCSs. Staining for nerve fibers using PGP9.5; in the epidermis was positive in five patients pre-treatment and 11 patients post treatment (P = 0.181). Staining in the dermis revealed positivity in 14 pre-treatment, which increased to 18 post treatment (P = 0.342). Adnexae showed positivity in five patients pre-treatment and increased to 17 post treatment (P = 0.005).

Conclusion

A reduced PGP9.5 staining in the epidermal, dermal, and adnexal regions was seen in leprosy patients, which improved post treatment. Thus, PGP9.5 may serve as a marker of NFI and treatment response.

The Mas-related G protein-coupled receptor d (Mrgprd) mediates pain hypersensitivity in painful diabetic neuropathy

ABSTRACT

Painful diabetic neuropathy (PDN) is one of the most common and intractable complications of diabetes. Painful diabetic neuropathy is characterized by neuropathic pain accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability, axonal degeneration, and changes in cutaneous innervation. However, the complete molecular profile underlying the hyperexcitable cellular phenotype of DRG nociceptors in PDN has not been elucidated. This gap in our knowledge is a critical barrier to developing effective, mechanism-based, and disease-modifying therapeutic approaches that are urgently needed to relieve the symptoms of PDN. Using single-cell RNA sequencing of DRGs, we demonstrated an increased expression of the Mas-related G protein-coupled receptor d (Mrgprd) in a subpopulation of DRG neurons in the well-established high-fat diet (HFD) mouse model of PDN. Importantly, limiting Mrgprd signaling reversed mechanical allodynia in the HFD mouse model of PDN. Furthermore, in vivo calcium imaging allowed us to demonstrate that activation of Mrgprd-positive cutaneous afferents that persist in diabetic mice skin resulted in an increased intracellular calcium influx into DRG nociceptors that we assess in vivo as a readout of nociceptors hyperexcitability. Taken together, our data highlight a key role of Mrgprd-mediated DRG neuron excitability in the generation and maintenance of neuropathic pain in a mouse model of PDN. Hence, we propose Mrgprd as a promising and accessible target for developing effective therapeutics currently unavailable for treating neuropathic pain in PDN.

Near-Infrared Chemiluminescence Imaging of Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) has a high prevalence but is poorly managed for cancer patients due to the lack of reliable and sensitive diagnostic techniques. Molecular optical imaging can provide a noninvasive way for real-time monitoring of CIPN; However, this is not reported, likely due to the absence of optical probes capable of imaging deep into the spinal canal and possessing sufficient sensitivity for minimal dosage through local injection into the dorsal root ganglia. Herein, a near-infrared (NIR) chemiluminophore (MPBD) with a chemiluminescence quantum yield higher than other reported probes is synthesized and a NIR activatable chemiluminescent probe (CalCL) is developed for in vivo imaging of CIPN. CalCL is constructed by caging MPBD with calpain-cleavable peptide moiety while conjugating polyethylene glycol chain to endow water solubility. Due to the deep-tissue penetration of chemiluminescence and specific turn-on response of CalCL toward calpain (a hallmark of CIPN), it allows for sensitive detection of paclitaxel-mediated CIPN in living mice, which is unattainable by fluorescence imaging. This study thus not only develops a highly efficient chemiluminescent probe, but also presents the first optical imaging approach toward high-throughput screening of neurotoxic drugs.

Archival skin biopsy specimens as a tool for miRNA-based diagnosis: Technical and post-analytical considerations

Archived specimens, taken by standardized procedures in clinical practice, represent a valuable resource in translational medicine. Their use in retrospective molecular-based studies could provide disease and therapy predictors. Microfluidic array is a user-friendly and cost-effective method allowing profiling of hundreds of microRNAs (miRNAs) from a low amount of RNA. However, even though tissue miRNAs may include potentially robust biomarkers, non-uniformed post-analytical pipelines could hinder translation into clinics. In this study, epidermal RNA from archival skin biopsy specimens was isolated from patients with peripheral neuropathy and healthy individuals. Unbiased miRNA profiling was performed using RT-qPCR-based microfluidic array. We demonstrated that RNA obtained from archival tissue is appropriate for miRNA profiling, providing evidence that different practices in threshold selection could significantly influence the final results. We showed the utility of software-based quality control for amplification curves. We revealed that selection of the most stable reference and the calculation of geometric mean are suitable when utilizing microfluidic arrays without known references. By applying appropriate post-analytical settings, we obtained miRNA profile of human epidermis associated with biological processes and a list of suitable references. Our results, which outline technical and post-analytical considerations, support the broad use of archived specimens for miRNA analysis to unravel disease-specific molecular signatures.

Plasma exosomes improve peripheral neuropathy via miR-20b-3p/Stat3 in type I diabetic rats

BACKGROUND

Diabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes and the main cause of non-traumatic amputation, with no ideal treatment. Multiple cell-derived exosomes have been reported to improve the progression of DPN. Blood therapy is thought to have a powerful repairing effect. However, whether it could also improve DPN remains unclear.

RESULTS

In this study, we found that microRNA (miRNA) expression in plasma-derived exosomes of healthy rats (hplasma-exos) was significantly different from that of age-matched DPN rats. By injection of hplasma-exos into DPN rats, the mechanical sensitivity of DPN rats was decreased, the thermal sensitivity and motor ability were increased, and the nerve conduction speed was accelerated. Histological analysis showed myelin regeneration of the sciatic nerve, increased intraepidermal nerve fibers, distal local blood perfusion, and enhanced neuromuscular junction and muscle spindle innervation after hplasma-exos administration. Compared with plasma exosomes in DPN, miR-20b-3p was specifically enriched in exosomes of healthy plasma and was found to be re-upregulated in the sciatic nerve of DPN rats after hplasma-exos treatment. Moreover, miR-20b-3p agomir improved DPN symptoms to a level similar to hplasma-exos, both of which also alleviated autophagy impairment induced by high glucose in Schwann cells. Mechanistic studies found that miR-20b-3p targeted Stat3 and consequently reduced the amount of p-Stat3, which then negatively regulated autophagy processes and contributed to DPN improvement.

CONCLUSIONS

This study demonstrated that miRNA of plasma exosomes was different between DPN and age-matched healthy rats. MiR-20b-3p was enriched in hplasma-exos, and both of them could alleviated DPN symptoms. MiR-20b-3p regulated autophagy of Schwann cells in pathological states by targeting Stat3 and thereby inhibited the progression of DPN.

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

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

Assessment of intraepidermal nerve fiber density and neurophysiological studies in patients with idiopathic polyneuropathy

Background

Idiopathic polyneuropathy is an asymmetrical, length-dependent neuropathy in which neurophysiology demonstrates axonal damage involving large fibers, along with insidious onset and slow progression over 6 months, with no identified etiology in spite of thorough investigations. This study aimed to evaluate the diagnostic role of clinical, electrophysiological, and histopathological studies in patients with idiopathic polyneuropathy.

Methods

Case–control study included 20 patients with clinical and neurophysiological evidence of sensory or sensory–motor neuropathy with no apparent etiology after laboratory investigation were recruited from 127 patients with sensory–motor neuropathy of unknown etiology (the patients group). Twenty apparently healthy individuals, age- and sex-matched, with no neuropathy symptoms (the control group), were recruited from the Neurology Clinic of Al-Azhar University, Assuit.

Results

Age of onset of patients with idiopathic polyneuropathy (44–70) years, duration of illness (1–6) years, 60% had painful neuropathy, diagnostic neuropathic pain questioner (DN4 score) (5–7), abnormal pin brick (80%), abnormal vibration (90%), abnormal fine touch (75%), distal weakness (70%), and lost ankle reflex (90%). In the control group, there were substantial differences with respect to prolonged latency, diminished sympathetic skin response amplitude, and significant intraepidermal nerve fiber density reduction in skin biopsy cases. In diagnosing idiopathic polyneuropathy, the specificity and sensitivity of sympathetic skin response were (80–86)% and (81–89.5)%, respectively, whereas those of diminished intraepidermal nerve fiber density were (92.5%) and (97.5%), respectively.

Conclusion

The assessment of intraepidermal nerve fiber density had an important good diagnostic role in cases presented with polyneuropathy.

Abnormalities of the oculomotor function in type 1 diabetes and diabetic neuropathy

AIMS

Abnormalities in the oculomotor system may represent an early sign of diabetic neuropathy and are currently poorly studied. We designed an eye-tracking-based test to evaluate oculomotor function in patients with type 1 diabetes.

METHODS

We used the SRLab-Tobii TX300 Eye tracker®, an eye-tracking device, coupled with software that we developed to test abnormalities in the oculomotor system. The software consists of a series of eye-tracking tasks divided into 4 classes of parameters (Resistance, Wideness, Pursuit and Velocity) to evaluate both smooth and saccadic movement in different directions. We analyzed the oculomotor system in 34 healthy volunteers and in 34 patients with long-standing type 1 diabetes.

RESULTS

Among the 474 parameters analyzed with the eye-tracking-based system, 11% were significantly altered in patients with type 1 diabetes (p < 0.05), with a higher proportion of abnormalities observed in the Wideness (24%) and Resistance (10%) parameters. Patients with type 1 diabetes without diabetic neuropathy showed more frequently anomalous measurements in the Resistance class (p = 0.02). The classes of Velocity and Pursuit were less frequently altered in patients with type 1 diabetes as compared to healthy subjects, with anomalous measurements mainly observed in patients with diabetic neuropathy.

CONCLUSIONS

Abnormalities in oculomotor system function can be detected in patients with type 1 diabetes using a novel eye-tracking-based test. A larger cohort study may further determine thresholds of normality and validate whether eye-tracking can be used to non-invasively characterize early signs of diabetic neuropathy.

TRIAL

NCT04608890.

Investigation of nerve fibers in the skin by biopsy: technical aspects, indications, and contribution to diagnosis of small-fiber neuropathy

Skin biopsy with investigation of small-diameter nerve fibers in human epidermis and dermis has been proven to be a useful method for confirming small-fiber neuropathy. In medical practice, small-fiber neuropathy is increasingly recognized as a leading cause of neuropathic pain. It is a prevalent complaint in medical offices, brought by patients often as a “painful burning sensation”. The prevalence of neuropathic pain is high in small-fiber neuropathies of different etiologies, especially in the elderly; 7% of population in this age group present peripheral neuropathy. Pain and paresthesia are symptoms which might cause disability and impair quality of life of patients. The early detection of small-fiber neuropathy can contribute to reducing unhealthy lifestyles, associated to higher incidence of the disease.

Preclinical nerve conduction: Nerve battery options for primate studies

Electrophysiological neurodiagnostic tests of nerve conduction (NC) are key assays included in preclinical safety and toxicology programs to assess the peripheral neuropathy (PN) liability of a new drug. Despite their increased use, standardization of nerve conduction studies (NCS) is lacking in the preclinical space, with limited regulatory guidelines stipulating type and number of nerves or minimum combinations appropriate for each stage of drug development or indication. Detection of subtle peripheral toxicities depends on choosing appropriate nerve targets for testing, especially when functional changes remain above the lower limit of normal values. To support robust preclinical toxicology study designs, the current short communication provides options and recommendations for selecting peripheral nerves for clinically translatable nerve conduction batteries applicable to toxicology and gene therapy, with a focus on clinically translatable primate models. A comprehensive compilation of accessible nerve locations is offered including lower and upper extremity motor nerves, and sensory nerves with origin at multiple DRG levels. Rankings of technique difficulty and repeatability across serial collections are presented for each assay informed by serial nerve conduction from 500 adult primates. The goal of this communication is to support the standardization and preclinical implementation of this important assay.

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.

Mitochondrial calcium uniporter deletion prevents painful diabetic neuropathy by restoring mitochondrial morphology and dynamics

ABSTRACT

Painful diabetic neuropathy (PDN) is an intractable complication affecting 25% of diabetic patients. Painful diabetic neuropathy is characterized by neuropathic pain accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability, resulting in calcium overload, axonal degeneration, and loss of cutaneous innervation. The molecular pathways underlying these effects are unknown. Using high-throughput and deep-proteome profiling, we found that mitochondrial fission proteins were elevated in DRG neurons from mice with PDN induced by a high-fat diet (HFD). In vivo calcium imaging revealed increased calcium signaling in DRG nociceptors from mice with PDN. Furthermore, using electron microscopy, we showed that mitochondria in DRG nociceptors had fragmented morphology as early as 2 weeks after starting HFD, preceding the onset of mechanical allodynia and small-fiber degeneration. Moreover, preventing calcium entry into the mitochondria, by selectively deleting the mitochondrial calcium uniporter from these neurons, restored normal mitochondrial morphology, prevented axonal degeneration, and reversed mechanical allodynia in the HFD mouse model of PDN. These studies suggest a molecular cascade linking neuropathic pain to axonal degeneration in PDN. In particular, nociceptor hyperexcitability and the associated increased intracellular calcium concentrations could lead to excessive calcium entry into mitochondria mediated by the mitochondrial calcium uniporter, resulting in increased calcium-dependent mitochondrial fission and ultimately contributing to small-fiber degeneration and neuropathic pain in PDN. Hence, we propose that targeting calcium entry into nociceptor mitochondria may represent a promising effective and disease-modifying therapeutic approach for this currently intractable and widespread affliction. Moreover, these results are likely to inform studies of other neurodegenerative disease involving similar underlying events.

Small Fiber Neuropathy in Diabetes Polyneuropathy: Is It Time to Change?

Diabetes polyneuropathy is an important complication of diabetes polyneuropathy, and its notable sequelae of foot ulceration, autonomic dysfunction, and neuropathic pain are associated with significant morbidity and mortality. Despite the major impact on quality of life and health economic costs, it remains underdiagnosed until late in its natural history, and there is lack of any intervention that can reverse its clinical progress. Assessment of small fiber neuropathy (SFN) in diabetes offers an opportunity to detect abnormalities at an early stage so that both interventional studies and preventative measures can be enacted to prevent progression to the devastating complications of foot ulceration and cardiac dysautonomic death. Over the last two decades, significant advances have been made in understanding the pathophysiology of diabetes neuropathy and its assessment. In this review, we discuss limitations of the screening methods recommended in current clinical guidelines which are based on large nerve fiber assessments. Thereafter, we discuss in detail the various methods currently available to assess small fiber structure and function and examine their individual strength and limitations. Finally, we discuss the reasons why despite the considerable body of evidence available, legislators and global experts have yet to incorporate the assessment of SFN as routine clinical surveillance in diabetes management. We hope that these insights will stimulate further discussion and be instrumental in the early adoption of these methods so as to reduce the burden of complications arising due to diabetes polyneuropathy.

Diabetic Peripheral Neuropathy

Diabetic painless and painful peripheral neuropathy remains the most frequent complication of diabetes mellitus, but the pathophysiology remains undescribed, there are no robust clinical endpoints and no efficient treatment exists. This hampers good clinical practice, fruitful clinical research and successful pharmacological trials, necessary for the development of early detection, prevention and treatment. This chapter supplies an update on background and treatment of diabetic peripheral neuropathy. Goals and perspectives for future clinical and scientific approaches are also described.

OUP accepted manuscript

Background

There is a lack of standardized objective and reliable assessment tools for chemotherapy-induced peripheral neuropathy (CIPN). In vivo reflectance confocal microscopy (RCM) imaging offers a non-invasive method to identify peripheral neuropathy markers, namely Meissner’s corpuscles (MC). This study investigated the feasibility and value of RCM in CIPN.

Patients and Methods

Reflectance confocal microscopy was performed on the fingertip to evaluate MC density in 45 healthy controls and 9 patients with cancer (prior, during, and post-chemotherapy). Quantification was completed by 2 reviewers (one blinded), with maximum MC count/3 × 3 mm image reported. Quantitative Sensory Testing (QST; thermal and mechanical detection thresholds), Grooved pegboard test, and patient-reported outcomes measures (PROMS) were conducted for comparison.

Results

In controls (25 females, 20 males; 24-81 years), females exhibited greater mean MC density compared with males (49.9 ± 7.1 vs 30.9 ± 4.2 MC/3 × 3 mm; P = .03). Differences existed across age by decade (P < .0001). Meissner’s corpuscle density was correlated with mechanical detection (ρ = −0.51), warm detection (ρ = −0.47), cold pain (ρ = 0.49) thresholds (P < .01); and completion time on the Grooved pegboard test in both hands (P ≤ .02). At baseline, patients had reduced MC density vs age and gender-matched controls (P = .03). Longitudinal assessment of MC density revealed significant relationships with QST and PROMS. Inter-rater reliability of MC count showed an intraclass correlation of 0.96 (P < .0001).

Conclusions

The findings support the clinical utility of RCM in CIPN as it provides meaningful markers of sensory nerve dysfunction. Novel, prospective assessment demonstrated the ability to detect subclinical deficits in patients at risk of CIPN and potential to monitor neuropathy progression.

Effect of video-based patient information on patients' anxiety and pain levels before skin biopsy: a randomized controlled study

OBJECTIVES

Effective use of technology can provide advantages for both patients and physicians in skin biopsy practice. We aimed to investigate the effects of video-based information on the anxiety, pain and satisfaction levels of patients undergoing biopsy.

METHODS

Patients were randomized and divided into two groups as video-informed and verbally informed. The anxiety levels were evaluated using the State-Trait Anxiety Inventory (STAI) and measuring the physiological parameters, systolic and diastolic blood pressure, heart rate, and respiratory rate. After the informing process, the STAI's state form was reevaluated, and physiological parameters were measured again. After the biopsy, the level of pain was evaluated using the visual analog scale (VAS), and patient satisfaction was assessed with the satisfaction scale.

RESULTS

Fifty-two in the video-informed group and 50 in the verbally informed group completed the study. Compared to the baseline values, the STAI and STAI-state scores, systolic blood pressure, heart rate and respiratory rate of the patients in the video-informed group decreased (p < 0.0001, p < 0.0001, p = 0.003, p = 0.007, and p < 0.0001, respectively), and the systolic blood pressure, diastolic blood pressure, heart rate and respiratory rate values decreased in the verbally informed group (p < 0.0001, p = 0.014, p = 0.005, and p < 0.0001, respectively). According to VAS, 98.1% of the patients in the video-informed group and 86% of those in the verbally informed group described no or mild pain, and pain levels were lower in the video-informed group (p = 0.030).

CONCLUSIONS

Video-based information prior to skin biopsy may be more useful in managing anxiety and pain in patients than traditional verbal information.

Non-length-dependent small fiber neuropathy: Not a matter of stockings and gloves

The clinical spectrum of small fiber neuropathy (SFN) encompasses manifestations related to the involvement of thinly myelinated A-delta and unmyelinated C fibers, including not only the classical distal phenotype, but also a non-length-dependent (NLD) presentation that can be patchy, asymmetrical, upper limb-predominant, or diffuse. This narrative review is focused on NLD-SFN. The diagnosis of NLD-SFN can be problematic, due to its varied and often atypical presentation, and diagnostic criteria developed for distal SFN are not suitable for NLD-SFN. The topographic pattern of NLD-SFN is likely related to ganglionopathy restricted to the small neurons of dorsal root ganglia. It is often associated with systemic diseases, but about half the time is idiopathic. In comparison with distal SFN, immune-mediated diseases are more common than dysmetabolic conditions. Treatment is usually based on the management of neuropathic pain. Disease-modifying therapy, including immunotherapy, may be effective in patients with identified causes. Future research on NLD-SFN is expected to further clarify the interconnected aspects of phenotypic characterization, diagnostic criteria, and pathophysiology.

Advantages of an Automated Method Compared With Manual Methods for the Quantification of Intraepidermal Nerve Fiber in Skin Biopsy

Intraepidermal nerve fiber density (IENFD) measurements in skin biopsy are performed manually by 1–3 operators. To improve diagnostic accuracy and applicability in clinical practice, we developed an automated method for fast IENFD determination with low operator-dependency. Sixty skin biopsy specimens were stained with the axonal marker PGP9.5 and imaged using a widefield fluorescence microscope. IENFD was first determined manually by 3 independent observers. Subsequently, images were processed in their Z-max projection and the intradermal line was delineated automatically. IENFD was calculated automatically (fluorescent images automated counting [FIAC]) and compared with manual counting on the same fluorescence images (fluorescent images manual counting [FIMC]), and with classical manual counting (CMC) data. A FIMC showed lower variability among observers compared with CMC (interclass correlation [ICC] = 0.996 vs 0.950). FIMC and FIAC showed high reliability (ICC = 0.999). A moderate-to-high (ICC = 0.705) was observed between CMC and FIAC counting. The algorithm process took on average 15 seconds to perform FIAC counting, compared with 10 minutes for FIMC counting. This automated method rapidly and reliably detects small nerve fibers in skin biopsies with clear advantages over the classical manual technique.

Transient receptor potential vanilloid subtype 1 depletion mediates mechanical allodynia through cellular signal alterations in small-fiber neuropathy

Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodal nociceptor that monitors noxious thermal sensations. Few studies have addressed the role of TRPV1 in mechanical allodynia in small-fiber neuropathy (SFN) caused by sensory nerve damage. Accordingly, this article reviews the putative mechanisms of TRPV1 depletion that mediates mechanical allodynia in SFN. The intraepidermal nerve fibers (IENFs) degeneration and sensory neuronal injury are the primary characteristics of SFN. Intraepidermal nerve fibers are mainly C-polymodal nociceptors and Aδ-fibers, which mediated allodynic pain after neuronal sensitization. TRPV1 depletion by highly potent neurotoxins induces the upregulation of activating transcription factor 3 and IENFs degeneration which mimics SFN. TRPV1 is predominately expressed by the peptidergic than nonpeptidergic nociceptors, and these neurochemical discrepancies provided the basis of the distinct pathways of thermal analgesia and mechanical allodynia. The depletion of peptidergic nociceptors and their IENFs cause thermal analgesia and sensitized nonpeptidergic nociceptors respond to mechanical allodynia. These distinct pathways of noxious stimuli suggested determined by the neurochemical-dependent neurotrophin cognate receptors such as TrkA and Ret receptors. The neurogenic inflammation after TRPV1 depletion also sensitized Ret receptors which results in mechanical allodynia. The activation of spinal TRPV1(+) neurons may contribute to mechanical allodynia. Also, an imbalance in adenosinergic analgesic signaling in sensory neurons such as the downregulation of prostatic acid phosphatase and adenosine A1 receptors, which colocalized with TRPV1 as a membrane microdomain also correlated with the development of mechanical allodynia. Collectively, TRPV1 depletion-induced mechanical allodynia involves a complicated cascade of cellular signaling alterations.

Chemotherapy-induced peripheral neuropathy (CIPN): current therapies and topical treatment option with high-concentration capsaicin

Cancer diagnosis and treatment are drastic events for patients and their families. Besides psychological aspects of the disease, patients are often affected by severe side effects related to the cancer itself or as a result of therapeutic interventions. Particularly, chemotherapy-induced peripheral neuropathy (CIPN) is the most prevalent neurological complication of oral or intravenous chemotherapy. The disorder may require dose reduction of chemotherapy and is accompanied by multiple symptoms with long-term functional impairment affecting quality of life (QoL), e.g., sensory and functional deteriorations as well as severe pain. Although CIPN may reverse or improve after termination of the causative chemotherapy, approximately 30–40% of patients are faced with chronicity of the symptoms. Due to the advantages in cancer diagnosis and treatments, survival rates of cancer patients rise and CIPN may occur even more frequently in the future. In this review, we summarize current recommendations of leading national and international societies regarding prevention and treatment options in CIPN. A special focus will be placed on current evidence for topical treatment of CIPN with high-dose capsaicin. Finally, an algorithm for CIPN treatment in clinical practice is provided, including both pharmacologic and non-pharmacologic modalities based on the clinical presentation.

Neuropathic pain and symptoms of potential small-fiber neuropathy in fibromyalgic patients: A national on-line survey

OBJECTIVE

Recent studies have highlighted that about 50% of fibromyalgic patients has a neuropathy of small- and/or large-fibers which could partially explain the puzzling symptoms of fibromyalgia (FM). Our aim was to investigate the estimated prevalence of self-reported neuropathic pain and small-fiber neuropathic symptoms (SFNS) indicative for the presence of small-fiber pathology in FM patients.

METHODS

A nationwide sample of patients was recruited to participate in an on-line survey. Two groups of patients were considered in post-hoc analysis: those positive (FM+) to the Fibromyalgia Research Criteria (FRC) and those complaining typical symptoms of fibromyalgia without fulfilling the FRC (FM-).

RESULTS

We collected data from 854 patients (749 FM+ and 105 FM-). Patients that scored=50/100 at the Neuropathic Pain Symptoms Inventory (NPSI), indicating severe neuropathic pain, were 57.3% (62.4% in FM+ and 21.0% in FM-). Around 46% of patients presented three or more SFNS that could be suggestive of small fiber pathology, the most frequent being dry eyes/mouth, allodynia, and dyshidrosis. The NPSI score showed significant moderate/strong associations with disability (Spearman's rho=0.61), pain (rho=0.66), stiffness level (rho=0.46), number of painful sites (rho=0.40), and SFNS (rho=0.44). Despite the high prevalence of neuropathic pain and other symptoms attributable to potential small and/or large fibers pathology, neurophysiologic investigations were performed in 43.6% of cases and skin punch biopsy only in 1.9% of patients enrolled, as well as the assumption of anti-neuropathic pain drugs (13.2%).

CONCLUSIONS

Our findings underscore the high estimated prevalence of neuropathic pain and SFNS in FM patients.

Corneal confocal microscopy identifies small fibre damage and progression of diabetic neuropathy

Accurately quantifying the progression of diabetic peripheral neuropathy is key to identify individuals who will progress to foot ulceration and to power clinical intervention trials. We have undertaken detailed neuropathy phenotyping to assess the longitudinal utility of different measures of neuropathy in patients with diabetes. Nineteen patients with diabetes (age 52.5 ± 14.7 years, duration of diabetes 26.0 ± 13.8 years) and 19 healthy controls underwent assessment of symptoms and signs of neuropathy, quantitative sensory testing, autonomic nerve function, neurophysiology, intra-epidermal nerve fibre density (IENFD) and corneal confocal microscopy (CCM) to quantify corneal nerve fibre density (CNFD), branch density (CNBD) and fibre length (CNFL). Mean follow-up was 6.5 years. Glycated haemoglobin (p = 0.04), low-density lipoprotein-cholesterol (LDL-C) (p = 0.0009) and urinary albumin creatinine ratio (p < 0.0001) improved. Neuropathy symptom profile (p = 0.03), neuropathy disability score (p = 0.04), vibration perception threshold (p = 0.02), cold perception threshold (p = 0.006), CNFD (p = 0.03), CNBD (p < 0.0001), CNFL (p < 0.0001), IENFD (p = 0.04), sural (p = 0.02) and peroneal motor nerve conduction velocity (p = 0.03) deteriorated significantly. Change (∆) in CNFL correlated with ∆CPT (p = 0.006) and ∆Expiration/Inspiration ratio (p = 0.002) and ∆IENFD correlated with ∆CNFD (p = 0.005), ∆CNBD (p = 0.02) and ∆CNFL (p = 0.01). This study shows worsening of diabetic neuropathy across a range of neuropathy measures, especially CCM, despite an improvement in HbA1c and LDL-C. It further supports the utility of CCM as a rapid, non-invasive surrogate measure of diabetic neuropathy.

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.

Continuous glucose monitoring defined time-in-range is associated with sudomotor dysfunction in type 2 diabetes

BACKGROUND

Time in range (TIR), as a novel metric for glycemic control, has robust relevance with diabetic complications. Diabetic peripheral neuropathy (DPN) is characterized by sudomotor dysfunction.

AIM

To explore the relationship between TIR obtained from continuous glucose monitoring (CGM) and sudomotor function detected by SUDOSCAN in subjects with type 2 diabetes.

METHODS

The research enrolled 466 inpatients with type 2 diabetes. All subjects underwent 3-d CGM and SUDOSCAN. SUDOSCAN was assessed with electrochemical skin conductance in hands (HESC) and feet (FESC). Average feet ESC < 60 µS was defined as sudomotor dysfunction (+), otherwise it was sudomotor dysfunction (-). TIR refers to the percentage of time when blood glucose is between 3.9-10 mmol/L during 1 d period.

RESULTS

Among the enrolled subjects, 135 (28.97%) presented with sudomotor dysfunction. Patients with sudomotor dysfunction (+) showed a decreased level of TIR (P < 0.001). Compared to the lowest tertile of TIR, the middle and the highest tertiles of TIR was associated with an obviously lower prevalence of sudomotor dysfunction (20.51% and 21.94% vs 44.52%) (P < 0.001). In addition, with the increase of TIR, HESC and FESC increased (P < 0.001). Regression analysis demonstrated that TIR was inversely and independently linked with the prevalence of sudomotor dysfunction after adjusting for confounding values (odds ratio = 0.979, 95%CI: 0.971-0.987, P < 0.001).

CONCLUSION

The tight glycemic control assessed by TIR is of vitally protective value for sudomotor dysfunction in type 2 diabetes mellitus.

Detection of nerve enlargement with ultrasound and correlation with skin biopsy findings in painful sensory neuropathy associated with Sjögren's syndrome

OBJECTIVES

We evaluated usefulness of peripheral nerve ultrasound (US) in detecting abnormality in painful sensory neuropathy (PSN) associated with primary Sjögren's syndrome (pSS), and associations among various clinical factors, US findings, and intraepidermal nerve fiber density (IENFD).

METHODS

We conducted a retrospective, single-center, observational study of patients with pSS-PSN. US image was obtained to measure cross sectional area (CSA) of peripheral nerves and compared with matched pSS control.

RESULTS

We included 11 patients with pSS-PSN (10 women; age 70.5 ± 5.66) and 17 pSS controls (15 women; age 62.5 ± 16.7). Sural nerve CSA were significantly increased in pSS-PSN group (3.48 ± 1.0 mm² vs 2.05 ± 0.65 mm², p = .001). US of sural nerve showed the area under the ROC curve of 0.872 (95% CI, 0.732 - 1). Sural nerve CSA and IENFD of lower leg showed positive correlation. Compared with pSS-PSN patients with abnormal IENFD, those with normal IENFD showed significantly larger sural nerve CSA, and trends toward less systemic disease activity and small fiber impairment with sparing of large fibers.

CONCLUSION

US was useful in discriminating pSS patients with PSN from those without. Additionally, US may disclose distinct subsets of pSS-PSN with different clinical findings and IENFD.

Diagnostic utility of corneal confocal microscopy in type 2 diabetic peripheral neuropathy

Aims/Introduction

The early pathological changes of diabetic peripheral neuropathy (DPN) are mainly small nerve fiber injuries. Corneal confocal microscopy (CCM) is an easy, rapid, non‐invasive and repeatable technique to detect the damage of small nerve fibers. The purpose of this study was to explore the application of CCM in DPN and other chronic complications of type 2 diabetes mellitus.

Materials and Methods

A total of 220 individuals (48 normal healthy control participants and 172 patients with type 2 diabetes mellitus) were included in the study. All participants were assessed and scored for neurological symptoms and neurological deficits, quantitative sensory test, neuroelectrophysiological test, and CCM.

Results

Corneal nerve fiber density, corneal nerve fiber length and corneal nerve branch density were significantly reduced in patients with type 2 diabetes mellitus compared with normal healthy control subjects (P < 0.001, P < 0.001 and P < 0.001, respectively). In the DPN group, corneal nerve fiber density, corneal nerve branch density and corneal nerve fiber length were significantly lower than for patients without DPN (P < 0.001, P < 0.001 and P < 0.001, respectively). Receiver operating characteristic analysis showed that the optimal cut‐off values were 24.68, 39 and 15.315, respectively, in which corneal nerve fiber density and corneal nerve fiber length had moderate sensitivity and specificity.

Conclusion

This study provides more support for the clinical use of CCM to diagnose type 2 diabetes mellitus‐related complications, especially DPN.

Nerve growth factor in metabolic complications and Alzheimer's disease: Physiology and therapeutic potential

As the population ages, obesity and metabolic complications as well as neurological disorders are becoming more prevalent, with huge economic burdens on both societies and families. New therapeutics are urgently needed. Nerve growth factor (NGF), first discovered in 1950s, is a neurotrophic factor involved in regulating cell proliferation, growth, survival, and apoptosis in both central and peripheral nervous systems. NGF and its precursor, proNGF, bind to TrkA and p75 receptors and initiate protein phosphorylation cascades, resulting in changes of cellular functions, and are associated with obesity, diabetes and its complications, and Alzheimer's disease. In this article, we summarize changes in NGF levels in metabolic and neuronal disorders, the signal transduction initiated by NGF and proNGF, the physiological and pathophysiological relevance, and therapeutic potential in treating chronic metabolic diseases and cognitive decline.

A novel method to quantify cutaneous vascular innervation

INTRODUCTION

To develop a new method to quantify the density of nerves, vessels, and the neurovascular contacts, we studied skin biopsies in diabetes and control subjects.

METHODS

Skin biopsies with dual immunofluorescent staining were used to visualize nerves and blood vessels. The density of nerves, vessels, and their neurovascular contacts were quantified with unbiased stereology. Results were compared with examination findings, validated questionnaires, and autonomic function.

RESULTS

In tissue from 19 controls and 20 patients with diabetes, inter-rater and intra-rater intraclass correlation coefficients were high (>0.85; P < .001) for all quantitative methods. In diabetes, the nerve densities (P < .05), vessel densities (P < .01), and the neurovascular densities (P < .01) were lower compared with 20 controls. Results correlated with autonomic function, examination and symptom scores.

DISCUSSION

We report an unbiased, stereological method to quantify the cutaneous nerve, vessel and neurovascular density and offer new avenues of investigation into cutaneous neurovascular innervation in health and disease.

Exosomes Derived From Schwann Cells Ameliorate Peripheral Neuropathy in Type 2 Diabetic Mice

Schwann cell-derived exosomes communicate with dorsal root ganglia (DRG) neurons. The current study investigated the therapeutic effect of exosomes derived from healthy Schwann cells (SC-Exos) on diabetic peripheral neuropathy (DPN). We found that intravenous administration of SC-Exos to type 2 diabetic db/db mice with peripheral neuropathy remarkably ameliorated DPN by improving sciatic nerve conduction velocity and increasing thermal and mechanical sensitivity. These functional improvements were associated with the augmentation of epidermal nerve fibers and remyelination of sciatic nerves. Quantitative RT-PCR and Western blot analysis of sciatic nerve tissues showed that SC-Exo treatment reversed diabetes-reduced mature form of miRNA (miR)-21, -27a, and -146a and diabetes-increased semaphorin 6A (SEMA6A); Ras homolog gene family, member A (RhoA); phosphatase and tensin homolog (PTEN); and nuclear factor-κB (NF-κB). In vitro data showed that SC-Exos promoted neurite outgrowth of diabetic DRG neurons and migration of Schwann cells challenged by high glucose. Collectively, these novel data provide evidence that SC-Exos have a therapeutic effect on DPN in mice and suggest that SC-Exo modulation of miRs contributes to this therapy.

Evaluation of the Neuropathic Component of Chronic Low Back Pain

OBJECTIVES

Assessment of neuropathic pain in chronic low back syndromes is important. However, there is currently no gold standard for its diagnosis. The aim of this observational cross-sectional study was to assess the neuropathic component of pain in various chronic low back pain syndromes using a range of diagnostic tests.

MATERIALS AND METHODS

Included in this study were 63 patients with chronic axial low back pain (ALBP), 48 patients with chronic radicular syndromes (CRS) comprising 23 with discogenic compression (CDRS) and 25 with lumbar spinal stenosis (LSS), and 74 controls. PainDETECT questionnaire (PDQ), quantitative sensory testing (QST), and skin biopsy with evaluation of intraepidermal nerve fiber density (IENFD) were used to assess the neuropathic pain component.

RESULTS

Positive PDQ (≥19) was obtained more frequently in patients with CDRS and LSS (26.1% and 12.0%, respectively) compared with patients with ALBP (1.6%, P<0.001). The proportion of patients with sensory loss confirmed by QST was lowest in the ALBP subgroup (23.8%) compared with CDRS (47.8%), and LSS (68.0%) subgroups (P<0.001). A reduction in IENFD was disclosed in a proportion of up to 52.0% of affected roots in patients with CRS.

DISCUSSION

Neuropathic pain is quite frequent in CRS, and QST reveals sensory loss as a frequent abnormality in patients with CRS. Using a cut-off value of 19, PDQ identified a neuropathic component in a relatively low proportion of patients with CRS. CRS may be associated with a reduction in IENFD.

Neuromuscular ultrasound for taxane peripheral neuropathy in breast cancer

BACKGROUND

Our study aim was to evaluate neuromuscular ultrasound (NMUS) for the assessment of taxane chemotherapy-induced peripheral neuropathy (CIPN), the dose-limiting toxicity of this agent.

METHODS

This cross-sectional study of breast cancer patients with taxane CIPN measured nerve cross-sectional area (CSA) by NMUS and compared with healthy historical controls. Correlations were determined between CSA and symptom scale, nerve conduction studies, and intraepidermal nerve fiber density (IENFD).

RESULTS

A total of 20 participants reported moderate CIPN symptoms at a median of 3.8 months following the last taxane dose. Sural nerve CSA was 1.2 mm² smaller than healthy controls (P ≤ .01). Older age and time since taxane were associated with smaller sural nerve CSA. For each 1 mm² decrease in sural nerve CSA, distal IENFD decreased by 2.1 nerve/mm (R² 0.30; P = .04).

CONCLUSIONS

These data support a sensory predominant taxane neuropathy or neuronopathy and warrant future research on longitudinal NMUS assessment of CIPN.

Orbit Image Analysis: An open-source whole slide image analysis tool

We describe Orbit Image Analysis, an open-source whole slide image analysis tool. The tool consists of a generic tile-processing engine which allows the execution of various image analysis algorithms provided by either Orbit itself or from other open-source platforms using a tile-based map-reduce execution framework. Orbit Image Analysis is capable of sophisticated whole slide imaging analyses due to several key features. First, Orbit has machine-learning capabilities. This deep learning segmentation can be integrated with complex object detection for analysis of intricate tissues. In addition, Orbit can run locally as standalone or connect to the open-source image server OMERO. Another important characteristic is its scale-out functionality, using the Apache Spark framework for distributed computing. In this paper, we describe the use of Orbit in three different real-world applications: quantification of idiopathic lung fibrosis, nerve fibre density quantification, and glomeruli detection in the kidney.

Intraepidermal Nerve Fiber Analysis in Human Patients and Animal Models of Peripheral Neuropathy: A Comparative Review

Analysis of intraepidermal nerve fibers (IENFs) in skin biopsy samples has become a standard clinical tool for diagnosing peripheral neuropathies in human patients. Compared to sural nerve biopsy, skin biopsy is safer, less invasive, and can be performed repeatedly to facilitate longitudinal assessment. Intraepidermal nerve fiber analysis is also more sensitive than conventional nerve histology or electrophysiological tests for detecting damage to small-diameter sensory nerve fibers. The techniques used for IENF analysis in humans have been adapted for large and small animal models and successfully used in studies of diabetic neuropathy, chemotherapy-induced peripheral neuropathy, HIV-associated sensory neuropathy, among others. Although IENF analysis has yet to become a routine end point in nonclinical safety testing, it has the potential to serve as a highly relevant indicator of sensory nerve fiber status in neurotoxicity studies, as well as development of neuroprotective and neuroregenerative therapies. Recently, there is also interest in the evaluation of IENF via skin biopsy as a biomarker of small fiber neuropathy in the regulatory setting. This article provides an overview of the anatomic and pathophysiologic principles behind IENF analysis, its use as a diagnostic tool in humans, and applications in animal models with focus on comparative methodology and considerations for study design.

Diabetic neuropathy

The global epidemic of prediabetes and diabetes has led to a corresponding epidemic of complications of these disorders. The most prevalent complication is neuropathy, of which distal symmetric polyneuropathy (for the purpose of this Primer, referred to as diabetic neuropathy) is very common. Diabetic neuropathy is a loss of sensory function beginning distally in the lower extremities that is also characterized by pain and substantial morbidity. Over time, at least 50% of individuals with diabetes develop diabetic neuropathy. Glucose control effectively halts the progression of diabetic neuropathy in patients with type 1 diabetes mellitus, but the effects are more modest in those with type 2 diabetes mellitus. These findings have led to new efforts to understand the aetiology of diabetic neuropathy, along with new 2017 recommendations on approaches to prevent and treat this disorder that are specific for each type of diabetes. In parallel, new guidelines for the treatment of painful diabetic neuropathy using distinct classes of drugs, with an emphasis on avoiding opioid use, have been issued. Although our understanding of the complexities of diabetic neuropathy has substantially evolved over the past decade, the distinct mechanisms underlying neuropathy in type 1 and type 2 diabetes remains unknown. Future discoveries on disease pathogenesis will be crucial to successfully address all aspects of diabetic neuropathy, from prevention to treatment.

Diabetic neuropathy

The global epidemic of prediabetes and diabetes has led to a corresponding epidemic of complications of these disorders. The most prevalent complication is neuropathy, of which distal symmetric polyneuropathy (for the purpose of this Primer, referred to as diabetic neuropathy) is very common. Diabetic neuropathy is a loss of sensory function beginning distally in the lower extremities that is also characterized by pain and substantial morbidity. Over time, at least 50% of individuals with diabetes develop diabetic neuropathy. Glucose control effectively halts the progression of diabetic neuropathy in patients with type 1 diabetes mellitus, but the effects are more modest in those with type 2 diabetes mellitus. These findings have led to new efforts to understand the aetiology of diabetic neuropathy, along with new 2017 recommendations on approaches to prevent and treat this disorder that are specific for each type of diabetes. In parallel, new guidelines for the treatment of painful diabetic neuropathy using distinct classes of drugs, with an emphasis on avoiding opioid use, have been issued. Although our understanding of the complexities of diabetic neuropathy has substantially evolved over the past decade, the distinct mechanisms underlying neuropathy in type 1 and type 2 diabetes remains unknown. Future discoveries on disease pathogenesis will be crucial to successfully address all aspects of diabetic neuropathy, from prevention to treatment.

Quantification of intraepidermal nerve fiber density using three-dimensional microscopy

Three-dimensional microscopy provides more extended depth of penetration compared with conventional light microscopy and is known to be useful in clinical evaluation of thick biological specimens. Skin nerve biopsy together with the quantification of intraepidermal nerve fibers in multiple thick sections has been widely adopted for evaluating peripheral neuropathies. The aim of the present study was to evaluate the effectivity of three-dimensional microscopy in reducing the required time and inter-rater discrepancies, especially in the case of personnel not familiar with the quantification methods. A total of six cryo-sectioned specimens were analyzed for the study and the skin samples were collected from one patient with postherpetic neuralgia who voluntarily participated in the study. Two investigators, a physician and non-physician assessed the intraepidermal nerve fiber densities and required analysis time using three different methods including direct visualization of tissue slides, and analysis with two- and three-dimensional images. Three-dimensional microscopy could produce images that enabled reliable evaluation of intraepidermal nerve fibers; the accuracy of analysis was statistically comparable between the physician and non-physician (p > .05). Three-dimensional microscopy also enabled the non-physician to proceed meaningfully faster evaluation compared with the direct visualization method (p = .03). Three-dimensional microscopy could be one of the useful methods to improve accuracy and convenience of the analysis of intraepidermal nerve fibers especially appropriate for unaccustomed physician or non-physician. RESEARCH HIGHLIGHTS: Three-dimensional microscopy is capable of producing images with more extended depth of penetration compared with conventional light microscopy and has been known to be suitable for clinical evaluation of thick biological specimens. Cutaneous nerve biopsy and the quantification of nerve fibers in thick sections has been widely adopted for evaluating peripheral neuropathies. Three-dimensional microscopy could be especially appropriate for unaccustomed physician or non-physician to improve accuracy and convenience of the analysis of intraepidermal nerve fibers.

Clinical features of pain in amyotrophic lateral sclerosis: A clinical challenge

Pain in amyotrophic lateral sclerosis (ALS) is paradoxical in this disease of the upper and lower motor neurons. As such, it remains an underestimated and neglected clinical problem because it is poorly identified by physicians, its mechanisms are numerous and its treatments are generally not effective. Pain may be primary in the form of cramps, spasticity and neuropathy, or secondary as nociceptive pain, and may arise before the first motor symptoms. It may also lead to depression and, in all cases, affect patients' daily activities and quality of life. Given the high frequency of pain in ALS, the use of analgesic or sedative drugs is necessary and should reduce the course of the disease. Nevertheless, it is important to understand the pathophysiological mechanisms of pain in ALS, and to train physicians how to detect ALS pain early on and provide dedicated treatments. In France, the implementation of ALS centers is a positive response to the public-health problem resulting from this disorder.

Laser capture microdissection for transcriptomic profiles in human skin biopsies

Background

The acquisition of reliable tissue-specific RNA sequencing data from human skin biopsy represents a major advance in research. However, the complexity of the process of isolation of specific layers from fresh-frozen human specimen by laser capture microdissection, the abundant presence of skin nucleases and RNA instability remain relevant methodological challenges. We developed and optimized a protocol to extract RNA from layers of human skin biopsies and to provide satisfactory quality and amount of mRNA sequencing data.

Results

The protocol includes steps of collection, embedding, freezing, histological coloration and relative optimization to preserve RNA extracted from specific components of fresh-frozen human skin biopsy of 14 subjects. Optimization of the protocol includes a preservation step in RNALater^® Solution, the control of specimen temperature, the use of RNase Inhibitors and the time reduction of the staining procedure. The quality of extracted RNA was measured using the percentage of fragments longer than 200 nucleotides (DV₂₀₀), a more suitable measurement for successful library preparation than the RNA Integrity Number (RIN). RNA was then enriched using the TruSeq^® RNA Access Library Prep Kit (Illumina^®) and sequenced on HiSeq^® 2500 platform (Illumina^®). Quality control on RNA sequencing data was adequate to get reliable data for downstream analysis.

Conclusions

The described implemented and optimized protocol can be used for generating transcriptomics data on skin tissues, and it is potentially applicable to other tissues. It can be extended to multicenter studies, due to the introduction of an initial step of preservation of the specimen that allowed the shipment of biological samples.

Electronic supplementary material

The online version of this article (10.1186/s12867-018-0108-5) contains supplementary material, which is available to authorized users.

Reduced intraepidermal nerve fibre density, glial activation, and sensory changes in HIV type-1 Tat-expressing female mice: involvement of Tat during early stages of HIV-associated painful sensory neuropathy

INTRODUCTION

HIV infection is associated with chronic pain states, including sensory neuropathy, which affects greater than 40% of patients.

OBJECTIVES AND METHODS

To determine the impact of HIV-Tat induction on nociceptive behaviour in female mice conditionally expressing HIV Tat1-86 protein through a doxycycline (DOX)-driven glial fibrillary acidic protein promoter, intraepidermal nerve fibre density and immune cell activation in the dorsal root ganglion (DRG) and spinal cord were assessed by immunohistochemistry. Mice were assessed for mechanical and thermal sensitivity for 9 weeks using von-Frey and Hargreaves tests.

RESULTS

Intraepidermal nerve fibre density was significantly reduced after 6 weeks of Tat induction, similar to sensory neuropathy seen in clinical HIV infection. Tat induction through DOX caused a significant reduction in paw withdrawal thresholds in a time-dependent manner starting the 4th week after Tat induction. No changes in paw withdrawal latencies were seen in Tat(-) control mice lacking the tat transgene. Although reductions in paw withdrawal thresholds increased throughout the study, no significant change in spontaneous motor activity was observed. Spinal cord (cervical and lumbar), DRG, and hind paw skin were collected at 8 days and 6 weeks after Tat induction. HIV-Tat mRNA expression was significantly increased in lumbar DRG and skin samples 8 days after DOX treatment. Tat induced a significant increase in the number of Iba-1 positive cells at 6 weeks, but not after 8 days, of exposure. No differences in glial fibrillary acidic protein immunoreactivity were observed.

CONCLUSION

These results suggest that Tat protein contributes to painful HIV-related sensory neuropathy during the initial stages of the pathogenesis.

Clinical correlates of sudomotor dysfunction in patients with type 2 diabetes and peripheral neuropathy

AIMS

To investigate the factors associated with abnormal electrochemical skin conductance (ESC) in patients with type 2 diabetes mellitus (T2D) and early diabetic peripheral neuropathy (DPN).

METHODS

We recruited 523 consecutive patients with T2D (median age: 50 [interquartile range: 16] years; median T2D duration: 4 [5] years). Sudomotor dysfunction was defined as an ESC <60 µS, and DPN as a neuropathy disability score (NDS) ≥6. Logistic regression was performed to determine the predictors of sudomotor dysfunction in patients with DPN.

RESULTS

The prevalence of sudomotor dysfunction was 29% for all patients and 84.5% for patients with DPN. A significant negative correlation was observed between the NDS and ESC measurements (r = -0.52, p < 0.0001). In the univariate analysis, abnormal ESC measures were associated with age, diabetes duration, glycated hemoglobin, diabetic retinopathy, insulin therapy, and foot abnormalities. In the multivariate analysis, ESC abnormalities were associated with age, diabetes duration, glycated hemoglobin levels, insulin therapy, and foot deformities. There was a robust association between foot deformities and abnormal ESC (p = 0.049; odds ratio = 16.02) in patients with DPN.

CONCLUSION

Sudomotor dysfunction is highly prevalent in patients with T2D, especially in those with DPN. Various diabetes-related factors were linked to lower ESC values, indicating an association between chronic hyperglycemia and sudomotor function. We also observed a strong relationship between foot deformities and ESC abnormalities. We conclude that the factors associated with DPN are also relevant to sudomotor dysfunction.

Reducing CXCR4-mediated nociceptor hyperexcitability reverses painful diabetic neuropathy

Painful diabetic neuropathy (PDN) is an intractable complication of diabetes that affects 25% of patients. PDN is characterized by neuropathic pain and small-fiber degeneration, accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability and loss of their axons within the skin. The molecular mechanisms underlying DRG nociceptor hyperexcitability and small-fiber degeneration in PDN are unknown. We hypothesize that chemokine CXCL12/CXCR4 signaling is central to this mechanism, as we have shown that CXCL12/CXCR4 signaling is necessary for the development of mechanical allodynia, a pain hypersensitivity behavior common in PDN. Focusing on DRG neurons expressing the sodium channel Nav1.8, we applied transgenic, electrophysiological, imaging, and chemogenetic techniques to test this hypothesis. In the high-fat diet mouse model of PDN, we were able to prevent and reverse mechanical allodynia and small-fiber degeneration by limiting CXCR4 signaling or neuronal excitability. This study reveals that excitatory CXCR4/CXCL12 signaling in Nav1.8-positive DRG neurons plays a critical role in the pathogenesis of mechanical allodynia and small-fiber degeneration in a mouse model of PDN. Hence, we propose that targeting CXCR4-mediated DRG nociceptor hyperexcitability is a promising therapeutic approach for disease-modifying treatments for this currently intractable and widespread affliction.

Long-Time Course of Idiopathic Small Fiber Neuropathy

Background: Small fiber neuropathy (SFN) is a challenging subtype of peripheral neuropathies. Once the diagnosis has been established, there is an uncertainty how SFN may progress, whether larger fibers will become involved over time, whether quality of life may be compromised, or whether repeated diagnostic workup in patients with unknown underlying cause may increase the yield of treatable causes of SFN. Methods: We evaluated 16 patients with documented long-time course of idiopathic SFN. Results: Clinical and electrophysiological course remained stable in 75% of the patients, while 25% SFN-patients developed large fiber neuropathies. Conclusions: Our data suggest that SFN represents a benign disease course in the majority of patients without severely limiting the quality of life.

Preserved Expression of Skin Neurotrophic Factors in Advanced Diabetic Neuropathy Does Not Lead to Neural Regeneration despite Pancreas and Kidney Transplantation

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes with potential severe consequences. Its pathogenesis involves hyperglycemia-linked mechanisms, which may include changes in the expression of neurotrophic growth factors. We analyzed the expression of 29 factors potentially related to nerve degeneration and regeneration in skin biopsies from 13 type 1 diabetic pancreas and kidney recipients with severe DPN including severe depletion of intraepidermal nerve fibers (IENF) in lower limb skin biopsies (group Tx1 1st examination). The investigation was repeated after a median 28-month period of normoglycemia achieved by pancreas transplantation (group Tx1 2nd examination). The same tests were performed in 13 stable normoglycemic pancreas and kidney recipients 6-12 years posttransplantation (group Tx2), in 12 matched healthy controls (group HC), and in 12 type 1 diabetic subjects without severe DPN (group DM). Compared to DM and HC groups, we found a significantly higher (p < 0.05-0.001) expression of NGF (nerve growth factor), NGFR (NGF receptor), NTRK1 (neurotrophic receptor tyrosine kinase 1), GDNF (glial cell-derived neurotrophic factor), GFRA1 (GDNF family receptor alpha 1), and GFAP (glial fibrillary acidic protein) in both transplant groups (Tx1 and Tx2). Enhanced expression of these factors was not normalized following the median 28-month period of normoglycemia (Tx1 2nd examination) and negatively correlated with IENF density and with electrophysiological indices of DPN (vibration perception threshold, electromyography, and autonomic tests). In contrast to our expectation, the expression of most of 29 selected factors related to neural regeneration was comparable in subjects with severe peripheral nerve fiber depletion and healthy controls and the expression of six factors was significantly upregulated. These findings may be important for better understanding the pathophysiology of nerve regeneration and for the development of intervention strategies.

A prospective, observational study of patients with uncommon distal symmetric painful small-fiber neuropathy

Objective

To investigate the clinical characteristics of patients with uncommon distal symmetric painful small-fiber neuropathy (DSPSFN).

Methods

From September 2012 to September 2014, participants between 18–70 years of age that had DSPSFN defined by clinical signs/symptoms and ID pain > 2 or DN4 > 4 on questionnaires for more than 1 month were included. Participants who had previous historical or laboratory evidence of common etiologies of DSPSFN were excluded. Enzyme activity and genetic studies for Fabry diseaseand familial amyloid polyneuropathy were performed after participants fulfilled the inclusion and exclusion criteria. The cryoglobulin test, autoantibodies studies and electrophysiological studies were performed in these participants.

Results

In total, 100 cases were enrolled in the current study. Three cases of subclinical diabetes mellitus and two cases of fibromyalgia were found. Fabry disease (1%) and familial amyloid polyneuropathy (3%) with Ala97Ser transthyretin (TTR) mutations were also detected. The cryoglobulin test was positive in 30% of participants, and these participants had higher DN4 scores than the negative group. In the autoantibodies studies, 59% of the participants had abnormal anti-Ro/SSA and/or anti-La/SSB antibodies.

Conclusions

Cryoglobulinemia is not a rare etiology of uncommon DSPSFN. The long-term prognosis is quite good in these participants. From our structuralized protocol, Fabry disease and familial amyloid polyneuropathy could be easily detected in these cases of uncommon DSPSFN.

Clinical and Laboratory Profiles of Idiopathic Small Fiber Neuropathy in Children: Case Series

The role of autoimmune mechanisms in idiopathic small fiber neuropathy (SFN) is not completely understood. Serum IgM binding to trisulfated disaccharide IdoA2S-GlcNS-6S (TS-HDS) and IgG to fibroblast growth factor receptor 3 were associated with sensory motor polyneuropathies and sensory neuronopathy among others. In this retrospective case review, we describe the clinical and laboratory findings of idiopathic SFN in a small cohort of pediatric patients. Eight children were diagnosed with SFN clinically and confirmed by reduced epidermal nerve fiber density. No involvement of large fibers was confirmed by clinical examination and electrophysiological tests. Possible triggering factors were infectious mononucleosis in 4 patients and human papilloma virus vaccination in 1 patient. Tilt table test was positive in 1 patient, and clinical autonomic dysfunctions were noted in 6 patients. Five patients had positive IgM against TS-HDS, 3 of whom had lower extremity predominant paresthesia. In conclusion, a high proportion of patients with idiopathic SFN in our cohort had a positive IgM TS-HDS antibody.

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

Objectives

Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible technique that quantifies small nerve fibres. We have compared the diagnostic capability of CCM against a range of established measures of nerve damage in patients with diabetic neuropathy.

Methods

In this cross sectional study, thirty subjects with Type 1 diabetes without neuropathy (T1DM), thirty one T1DM subjects with neuropathy (DSPN) and twenty seven non-diabetic healthy control subjects underwent detailed assessment of neuropathic symptoms and neurologic deficits, quantitative sensory testing (QST), electrophysiology, skin biopsy and corneal confocal microscopy (CCM).

Results

Subjects with DSPN were older (C vs T1DM vs DSPN: 41.0±14.9 vs 38.8±12.5 vs 53.3±11.9, P = 0.0002), had a longer duration of diabetes (P<0.0001), lower eGFR (P = 0.006) and higher albumin-creatinine ratio (P = 0.03) with no significant difference for HbA1c, BMI, lipids and blood pressure. Patients with DSPN were representative of subjects with diabetic neuropathy with clinical signs and symptoms of neuropathy and greater neuropathy deficits quantified by QST, electrophysiology, intra-epidermal nerve fibre density and CCM. Corneal nerve fibre density (CNFD) (Spearman’s Rho = 0.60 P<0.0001) and IENFD (Spearman’s Rho = 0.56 P<0.0001) were comparable when correlated with peroneal nerve conduction velocity. For the diagnosis of diabetic neuropathy the sensitivity for CNFD was 0.77 and specificity was 0.79 with an area under the ROC curve of 0.81. IENFD had a diagnostic sensitivity of 0.61, specificity of 0.80 and area under the ROC curve of 0.73.

Conclusions

CCM is a valid accurate non-invasive method to identify small nerve fibre pathology and is able to diagnose DPN.

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.