Intraepidermal Nerve Fiber Density Research Articles

Effects of Spinal Cord Stimulation in Patients with Small Fiber and Associated Comorbidities from Neuropathy After Multiple Etiologies.

Objectives: The aim of this study was to evaluate the effects of spinal cord stimulation (SCS) on pain, neuropathic symptoms, and other health-related metrics in patients with chronic painful peripheral neuropathy (PN) from multiple etiologies. Methods: A prospective single center observational longitudinal cohort study assessed SCS efficacy from April 2023 to May 2024, with follow-ups at 2, 4, 6, and 12 months in 19 patients suffering from the painful polyneuropathy of diverse etiologies: diabetic (DPN), idiopathic (CIAP), chemotherapy-induced (CIPN), and others. Patients were implanted with a neurostimulator (WaveWriter AlphaTM, Boston Scientific Corporation, Valencia, CA, USA) and percutaneous leads targeting the lower limbs (T10-T11) and, if necessary, the upper limbs (C4-C7). Stimulation programming was individualized based on patient preference and best response. Assessments were performed before and after implantation and included pain intensity (VAS and DN4), neuropathic pain symptoms (NPSI and SF-MPQ-2), autonomic symptoms (SFN-SIQ and SAS), sensory and small fiber nerve injury (UENS), functionality (GAF), sleep (CPSI), global impression of change (CGI and PGI), and quality of life (EQ-VAS and EQ-5D). Intra-epidermal nerve fiber density (IENFD) via skin biopsy was also performed at baseline (diagnostic) and after 12 months to assess potential small fiber re-growth. Statistical analyses were conducted to determine the evolution of treatment success. Results: To date, 19 patients have undergone implantation and completed follow-up. SCS produced a significant consistent and sustained improvement in pain intensity by 49% in DN4 and 76% in VAS, in neuropathic pain symptoms by 73%, in autonomic symptoms by 26-30%, in the sensorimotor physical exam by 8%, in functionality by 44%, in sleep by 74%, and in quality of life (69% for EQ-VAS and 134% EQ-5D). Both clinicians and patients had a meaningful global impression of change, at 1.1 and 1.3, respectively. Distal intra-epidermal nerve fiber density improved by 22% at 12 months while proximal intra-epidermal nerve fiber density decreased by 18%. Conclusions: SCS is an effective therapy for managing various types of PN.

Pain and small fiber pathology in men with fibromyalgia syndrome.

Small fiber pathology may be involved in the pathophysiology of pain in women with fibromyalgia syndrome (FMS). This prospective single-center case-control study provides detailed pain phenotyping and small fiber pathology data in a cohort of men with FMS on a morphological and functional level. Forty-two men with FMS underwent a comprehensive pain-related interview and neurological examination, a questionnaire and neurophysiological assessment, and specialized small fiber tests: skin punch biopsy, quantitative sensory testing including C-tactile afferents, and corneal confocal microscopy. Data were compared with those of healthy male controls. Men with FMS reported generalized and permanent pain with additional pain attacks and a mostly pressing pain character. Intraepidermal nerve fiber density was reduced at ≥1 biopsy site in 35 of 42 (83%) men with FMS (controls: 32/65, 49%). Compared with male controls, men with FMS had elevated cold (P < 0.05) and warm detection thresholds (P < 0.001) and an increased mechanical pain threshold (P < 0.05) as well as an impairment of C-tactile afferents (P < 0.05). Corneal nerve fiber density was lower in male patients with FMS vs healthy men (P < 0.01). Male FMS patients with pathological skin innervation at ≥1 biopsy site compared with those with normal skin innervation had a higher clinical Widespread Pain Index (P < 0.05) indicating an association between the severity of cutaneous denervation and symptom load. We show a distinct pain phenotype and small nerve fiber dysfunction and pathology in male patients with FMS. These findings may have implications for the diagnosis and management of men with FMS.

Cutaneous Carbonyl Stress Is Associated With Nerve Dysfunction in Recent-Onset Type 2 Diabetes.

Endogenous carbonyl stress leads to the formation of advanced glycation end products (AGEs). AGEs represent a potential target to prevent or treat diabetic sensorimotor polyneuropathy (DSPN). The current study aimed to characterize cutaneous carbonyl stress, oxidative stress, immune cells, and endothelial cell damage in early type 2 diabetes compared with normal glucose tolerance (NGT) using novel cutaneous biomarkers. Included were 160 individuals recently (≤12 months) diagnosed with type 2 diabetes and 144 with NGT from the German Diabetes Study baseline cohort. Nerve function was assessed using electrophysiological, quantitative sensory, and clinical testing. Skin biopsies were obtained to analyze intraepidermal nerve fiber density, AGEs autofluorescence, argpyrimidine area, and endothelial cell area. In addition, skin autofluorescence was measured noninvasively using the AGE reader. A subgroup with type 2 diabetes (n = 80) was reassessed 5 years later. After adjustment for sex, age, HbA1c, LDL cholesterol, and BMI, argpyrimidine area (17.5 ± 18.8 vs. 11.7 ± 12.7%) was higher in recent-onset type 2 diabetes than in NGT (P < 0.05). AGEs autofluorescence was inversely correlated with nerve conduction (e.g., peroneal motor nerve conduction velocity: r = -0.346) and positively with AGE reader measurements in type 2 diabetes (r = 0.358, all P < 0.05), but not in NGT. Higher baseline AGEs autofluorescence and lower endothelial cell area predicted the deterioration of clinical and neurophysiological measures after 5 years. Cutaneous AGEs markers were associated with neurophysiological deficits in recent-onset type 2 diabetes and predicted their progression after 5 years, substantiating the role of carbonyl stress in the development of early DSPN.

Structural changes in the nociceptive system induced by long-term conventional spinal cord stimulation in experimental painful diabetic polyneuropathy

BackgroundClinical studies suggest that long-term conventional spinal cord stimulation (LT-SCS) for painful diabetic peripheral neuropathy (PDPN) is initially effective but may decline in efficacy over time. Preclinical studies indicate that...

Visualization of Bortezomib Induced Peripheral Neuropathy By Dorsal Root Ganglion MRI in Patients with Multiple Myeloma

Background: Whereas most treatments in multiple myeloma (MM) are stopped due to their inefficiency over time and the development of drug resistance, the use of the proteasome inhibitor bortezomib (BTZ) is mainly limited by its neurotoxic effects and the induction of BTZ induced neuropathy (BIPN). Of particular pathophysiological importance is the dorsal root ganglion (DRG), which plays a central role in the development of BIPN (Argyriou et al. Blood 2008). As early BIPN diagnosis and treatment adjustment is critical, we here investigated the predictive potential of DRG MRI and measured the DRG T2 signal intensity as a biomarker of inflammation in BTZ treated MM patients. Methods: We recruited a total of 112 MM patients receiving BTZ either currently or in the past. Of these, 92 (82 %) had BIPN, which was painful in 37% (n=41) and mild and only detectable by sophisticated clinical-neurological diagnostics in 52% of patients (n = 58, severity Grade 1 with/without pain). DRG MRI was performed in a subset of 54 patients, including 45 of them with detectable BIPN (all grades), and additionally in 12 healthy controls. Using high-resolution three-dimensional T2-weighted fast spin-echo DRG MRI, we evaluated the lumbosacral DRG Th12-S2 bilaterally in all patients. Comparative analyses were performed using one-way ANOVA with Bonferroni correction. Pearson's Rho was used for the correlation analyses. Results: Analysis revealed a significant increase in DRG T2 signal intensity in MM patients with BIPN compared to MM patients without BIPN (p= 0.005) and healthy controls (p= 0.003). Furthermore, an inverse correlation was found between DRG T2 signal intensity and intraepidermal nerve fiber density (IENFD) (p= 0.035). The mean DRG volume on L5+S1 level (in mm³) did not differ significantly between the groups, however, IENFD was significantly decreased in BIPN MM patients (n=26; 3.41 fibers/mm) compared to the healthy controls (n=12, 5.28 fibers/mm; p = 0.031), MM patients without BIPN showed no difference in IENFD (4.45 fibers/mm) compared to healthy controls. Conclusion: DRG T2 signal intensity is a surrogate marker of inflammation, and our observations suggest that inflammatory changes at the DRG level underlie BIPN in MM patients. Our imaging holds potential to be used as a non-invasive biomarker for early BIPN detection and to define patients at risk. This is an ongoing study, and imaging from the full cohort and from additional longitudinal assessment will be presented at the meeting.

Exploring Pruritus in Bullous Pemphigoid; Analysis of Quality-of-Life Metrics and Potential Biological Mechanisms

Bullous pemphigoid (BP) is a devastating autoimmune blistering disease with need for improved therapeutics. Limited data is available on the overall burden of pruritus and alterations over time, however treatment of itch specific pathways may provide novel therapeutics. In this paper, we analyzed the quality-of-life (QOL) impact particularly related to itch and determined corresponding changes in intraepidermal nerve fiber density (IENFD) and gene expression. 43 BP patients were followed prospectively on standard-of-care treatment and showed average BPDAI total activity score (TAS) decrease from 19.1 ± 19.2 to 8.2 ± 11.3 and improvement in QOL measures ABQoL, TABQoL and ItchyQoL. At baseline, IENFD in BP and Atopic Dermatitis (AD) patients were significantly lower than healthy controls (7.3 ± 1.5, 3.2 ± 2.0 and vs. 9.7 ± 5.4 fibers/mm, p=0.031) and increased from baseline to follow-up visit, (11.7 ± 0.4 and 5.8 ± 2.7) although only AD reached statistical significance (p=0.018). S100A8, S100A9, CCL17 and CCL18, genes were highly upregulated in the skin of BP patients compared to healthy controls. Our data provides evidence for improvements in itch-related QOL over time on standard of care therapies with unique alterations in inflammatory mediators related to early immune cell activation and recruitment.

Early-life cisplatin exposure induces neuroinflammation and chemotherapy-induced neuropathic pain.

Chemotherapy-induced neuropathic pain (CINP) is a common adverse health-related comorbidity that manifests later in life in patients with paediatric cancer. Current analgesia is ineffective, aligning closely with our lack of understanding of CINP. The aim of this study was to investigate how cisplatin induces nerve growth factor (NGF)-mediated neuroinflammation and nociceptor sensitisation. In a rat model of cisplatin-induced survivorship pain, cisplatin induced a neuroinflammatory environment in the dorsal root ganglia (DRG), demonstrated by NGF-positive macrophages infiltrating into the DRG. Cisplatin-treated CD11b- and F4/80-positive macrophages expressed more NGF compared to those treated with vehicle control. Mouse primary DRG sensory neuronal cultures demonstrated enhanced NGF-dependent TRPV1-mediated nociceptor activity after cisplatin treatment. Increased nociceptor activity was also observed when cultured mouse DRG neurons were treated with conditioned medium from cisplatin-activated macrophages. Elevated nociceptor activity was inhibited in a dose-dependent manner by an NGF-neutralising antibody. Intraperitoneal administration of the NGF-neutralising antibody reduced cisplatin-induced mechanical hypersensitivity and aberrant nociceptor intraepidermal nerve fibre density. These findings identify that a monocyte- or macrophage-driven NGF-TrkA pathway is a novel analgesic target for adult survivors of childhood cancer.

Hypertension is associated with the reduction in epidermal small fibres independently of sural nerve inflammation in type 2 diabetic subjects.

Diabetic polyneuropathy (DPN) is a multifactorial disease associated not only with hyperglycaemia but also with circulatory disturbances such as hypertension. A close interaction between the immune system and hypertension is known. It remains unclear whether the inflammatory response is associated with hypertension in the pathology of human DPN. Autopsied patients were evaluated: 7 non-diabetic patients (nDM), 11 non-diabetic patients with hypertension (nDMHT), 6 patients with diabetes (DM) and 9 patients with hypertension and diabetes (DMHT). Intraepidermal nerve fibre density (IENFD) was examined by immunofluorescent staining. Dissected sural nerve (SNs) were morphometrically quantified. Dermal and endoneurial macrophage infiltration was evaluated by double immunostaining using anti-CD68 and anti-CD206 antibodies. IENFD was significantly decreased in DM compared to nDM (p < 0.05) and was further decreased in DMHT (p < 0.05). Myelinated nerve fibre density (MNFD) in the SN was significantly decreased in DM compared with nDM (p < 0.05) and further decreased in DMHT (p < 0.01 vs. DM). The infiltration of CD206-/CD68+ proinflammatory macrophages in the SN was significantly increased in DM compared to nDM (p < 0.05), whilst the number of CD206+/CD68+ anti-inflammatory macrophages was decreased in DM (p < 0.05). Hypertension had no impact on macrophage infiltration. The ratio of CD206- and CD206+ macrophage was negatively correlated with MNFD (r = 0.42, p < 0.05) but not IENFD (r = 0.30, p = 0.09). Dermal CD206+ macrophage infiltration was similar amongst all groups. Diabetes complicated by hypertension significantly increased the total diffusion barrier thickness (p < 0.01 vs. DM). Total diffusion barrier thickness was inversely correlated with both IENFD (r = -0.59, p < 0.01) and MNFD (r =-0.62, p < 0.01). Our results suggest that vascular factors and inflammation might be synergistically involved in pathological changes in human diabetic patients through different mechanisms.

Vascular and nerve biomarkers in thigh skin biopsies differentiate painful from painless diabetic peripheral neuropathy.

Identifying distinct mechanisms and biomarkers for painful diabetic peripheral neuropathy (DPN) is required for advancing the treatment of this major global unmet clinical need. We previously provided evidence in calf skin biopsies that disproportion between reduced sensory small nerve fibers and increased blood vessels may distinguish painful from non-painful DPN. We proposed that overexposure of the reduced nerve fibers in DPN to increased hypoxemia-induced vasculature and related algogenic factors, e.g., nerve growth factor (NGF), leads to neuropathic pain. To further investigate this proposed mechanism, we have now studied more proximal thigh skin biopsies, to see if the same disproportion between increased vasculature and decreased nerve fibers generally differentiates painful DPN from painless DPN. A total of 28 subjects with type 2 diabetes (T2DM) and 13 healthy volunteers (HV) underwent detailed clinical and neurophysiological assessments, based on the neuropathy composite score of the lower limbs [NIS(LL)] plus 7 tests. T2DM subjects were subsequently divided into three groups: painful DPN (n = 15), painless DPN (n = 7), and no DPN (n = 6). All subjects underwent skin punch biopsy from the upper lateral thigh 20 cm below the anterior iliac spine. Skin biopsies showed decreased PGP 9.5-positive intraepidermal nerve fiber (IENF) density in both painful DPN (p < 0.0001) and painless DPN (p = 0.001). Vascular marker von Willebrand Factor (vWF) density was markedly increased in painful DPN vs. other groups, including painless DPN (p = 0.01). There was a resulting significant decrease in the ratio of intraepidermal nerve fiber density to vasculature and PGP9.5 to vWF, in painful DPN vs. painless DPN (p = 0.05). These results were similar in pattern to those observed in these HV and T2DM groups previously in distal calf biopsies; however, the increase in vWF was much higher and nerve fiber density much lower in the calf than thigh for painful DPN. Thigh skin vWF density was significantly correlated with several metabolic (waist/hip ratio, HbA1c), clinical (e.g., pain score), and neurophysiological measures. This study supports our proposal that increased dermal vasculature, and its disproportionate ratio to reduced nociceptors, may help differentiate painful DPN from painless DPN. This disproportion is greater in the distal calf than the proximal thigh skin; hence, neuropathic pain in DPN is length-dependent and first localized to the distal lower limbs, mainly feet.

From Sudoscan to bedside: theory, modalities, and application of electrochemical skin conductance in medical diagnostics.

The human body has two main types of sweat glands: apocrine and eccrine. Eccrine glands are widely distributed across the skin, including areas with hair. While the eccrine glands on palms and soles help improve grip, those on the rest of the body primarily aid in thermoregulation. Sudomotor function, which controls sweating, is regulated by the sympathetic division of the autonomic nervous system through cholinergic and adrenergic pathways. The activation of eccrine glands involves intricate processes, including neurotransmitter binding, ion channel modulation, and voltage generation. Sudoscan technology utilizes electrochemical skin conductance (ESC) to non-invasively measure sudomotor function. This method, which has been standardized for accuracy, has established normative benchmarks and has proven reliable across diverse populations. Sudoscan's diagnostic performance is comparable to invasive methods such as intraepidermal nerve fiber density testing, making it a valuable tool for diagnosing small fiber neuropathy. Moreover, it has been shown to correlate with corneal nerve fiber length, providing insights into various neuropathic conditions. Compared to traditional sudomotor function tests, Sudoscan proves superior in terms of its accessibility, simplicity, and reliability, with the potential to replace or complement existing diagnostic methods. It is important to differentiate ESC, as measured by Sudoscan, from other skin conductance measures, such as galvanic skin response (GSR) or electrodermal activity (EDA). Although these methods share a common physiological principle, ESC is specifically designed for diagnosing sudomotor function, unlike GSR/EDA, which is typically used for continuous monitoring. Sudoscan's success has led to its integration into consumer health devices, such as the BodyScan from Withings, showcasing its versatility beyond clinical settings. Future research may explore ESC applications in diverse medical fields, leveraging real-world data from integrated consumer devices. Collaborative efforts between researchers and engineers promise to offer new insights into sudomotor function and its implications for broader health monitoring. This study provides a comprehensive overview of ESC, including topics such as eccrine gland physiology, sudomotor function, Sudoscan technology, normative benchmarks, diagnostic comparisons, and potential future applications.

The Evolving Landscape of Small Fiber Neuropathy.

Small fiber neuropathy (SFN) belongs to a heterogeneous group of disorders in which thinly myelinated Aδ and unmyelinated C-fibers are primarily affected, leading to neuropathic pain and autonomic symptoms. SFN can be associated with systemic conditions such as diabetes, autoimmune diseases, exposure to drugs and toxins, and infection, with the list of associated diseases continuing to expand. Variants in the SCN9A, SCN10A, and SCN11A genes encoding Nav 1.7, Nav 1.8, and Nav 1.9 sodium channel subunits, as well as in the TRPA1 gene, have been found in SFN patients, expanding the spectrum of underlying conditions and enhancing our understanding of pathophysiological mechanisms. There is also growing interest in immune-mediated forms that could help identify potentially treatable subgroups. According to international criteria, diagnosis is established through clinical examination, the assessment of intraepidermal nerve fiber density, and/or quantitative sensory testing. Autonomic functional tests allow for a better characterization of dysautonomia in SFN, which can be subclinical. Other tests can support the diagnosis. Currently, the management of SFN prioritizes treating the underlying condition, if identified, within a multidisciplinary approach that combines symptomatic pain therapy, lifestyle changes, and biopsychological interventions. Emerging insights from the molecular characterization of SFN channelopathies hold promise for improving diagnosis, potentially leading to the discovery of new drugs and refining trial designs in the future. This article reviews the clinical presentation, diagnostic workup, and advancing knowledge of associated conditions and interventional management of SFN.

Postsurgical tactile-evoked pain: a role for brain-derived neurotrophic factor-tropomyosin receptor kinase B-dependent novel tactile corpuscles.

Millions of people undergo surgical procedures each year with many developing postsurgical pain. Dynamic allodynia can arise when, for example, clothing brushing close to the surgical site elicits pain. The allodynia circuits that enable crosstalk between afferent tactile inputs and central pain circuits have been studied, but the peripheral tactile drive has not been explored. Investigate the innervation of the skin in the rat plantar hindpaw skin-muscle incision model. Incision increased epidermal thickness and cell layers and reduced intraepidermal nerve fibre density, identified with PGP9.5 immunostaining. Strikingly, Collagen IV immunostaining revealed the development of dermal protrusions, oriented towards the incision site, that were reminiscent of the dermal papillae that exist in glabrous footpads. S100 immunostaining for lamellar Schwann cells revealed the presence of novel tactile corpuscles (S100-positive bulb) within incision-induced putative dermal papillae. The occurrence of these novel tactile corpuscles coincided with behavioural observations of dynamic allodynia. Tactile corpuscles require brain-derived neurotrophic factor- tropomyosin receptor kinase B (BDNF-TrkB) signalling to form during development, and an increase in BDNF-immunostaining intensity was observed close to the incision site. Local acute administration of TrkB-Fc, to block BDNF-TrkB signalling, reduced, by approximately 50%, both tactile corpuscle size (S100+ bulb area) and dynamic allodynia. Surgery induces the development of novel tactile corpuscles in the incision surround, in a BDNF-TrKB-dependent manner, that contributes to postsurgical tactile-evoked pain.

10 kHz spinal cord stimulation improves metrics of spinal sensory processing in a male STZ rat model of diabetes

To explore why clinical 10 kHz spinal cord stimulation (10 kHz SCS) might improve neurological function in a model of painful diabetic neuropathy (PDN), the short-term behavioral, electrophysiological, and histological effects of 10 kHz SCS were studied using adult male streptozotocin (STZ)-induced diabetic Sprague-Dawley rats. Four testing groups were established: Naïve controls (N = 8), STZ controls (N = 7), STZ+Sham SCS (N = 9), and STZ+10 kHz SCS (N = 11). After intraperitoneal injection (60 mg/kg) of STZ caused the rats to become hyperglycemic, SCS electrodes were implanted in the dorsal epidural space over the L5-L6 spinal segments in the STZ+Sham SCS and STZ+10 kHz SCS groups and were stimulated for 14 days. The von Frey filament paw withdrawal threshold was measured weekly. At termination, animals were anesthetized and the electrophysiologic response of dorsal horn neurons (receptive field size, vibration, radiant warmth) of the ipsilateral foot was measured. Tissue from the plantar paw surface was obtained post-euthanization for intraepidermal nerve fiber density measurements. In comparison to other control groups, while no significant effect of 10 kHz SCS on peripheral intraepidermal nerve fiber density was observed, 10 kHz SCS ‘normalized’ the central neural response to vibration, receptive field, and paw withdrawal threshold, and elevated the neural response to tissue recovery from warm stimuli. These results suggest that short-term, low intensity 10 kHz SCS operates in the spinal cord to ameliorate compromised sensory processing, and may compensate for reduced peripheral sensory functionality from chronic hyperglycemia, thereby treating a broader spectrum of the sensory symptoms in diabetic neuropathy.

Beyond pain: Using Unsupervised Machine Learning to Identify Phenotypic Clusters of Small Fiber Neuropathy.

Small fiber neuropathy (SFN) is characterized by dysfunction and loss of peripheral unmyelinated and thinly myelinated nerve fibers, resulting in a phenotype that includes varying combinations of somatosensory and dysautonomia symptoms, which can be profoundly disabling and lead to decreased quality of life. Treatment aimed mainly at pain reduction, which may not target the underlying pathophysiology, is frequently ineffective. Another impediment to the effective management of SFN may be the significant between-patient heterogeneity. Accordingly, we launched this study to gain insights into the symptomatic variability of SFN and determine if SFN patients can be sub-grouped based on clinical characteristics. To characterize the phenotype and investigate how patients with SFN differ from those with large fiber involvement, 105 patients with skin-biopsy proven SFN and 45 with mixed fiber neuropathy (MFN) were recruited. Using unsupervised machine learning, SFN patients were clustered based upon symptom concurrence and severity. Demographics, clinical data, symptoms, and skin biopsy- and laboratory findings were compared between the groups. MFN- as compared to SFN patients, were more likely to be male, older, had a lower intraepidermal nerve fiber density at the ankle and more frequent abnormal immunofixation. Beyond these differences, symptom prevalence and intensities were similar in the two cohorts. SFN patients comprised three distinct phenotypic clusters, which differed significantly in symptom severity, co-occurrence, localization, and skin biopsy findings. Only one subgroup, constituting about 20% of the patient population, was characterized by intense neuropathic pain, which was always associated with several other SFN symptoms of similarly high intensities. A pauci-symptomatic cluster comprised patients who experienced few SFN symptoms, generally of low to moderate intensity. The largest cluster was characterized by intense fatigue, myalgias and subjective weakness, but lower intensities of burning pain and paresthesia. This data-driven study introduces a new approach to subgrouping patients with SFN. Considering both neuropathic pain and pernicious symptoms beyond pain, we identified three clusters, which may be related to distinct pathophysiological mechanisms. Although additional validation will be required, our findings represent a step towards stratified treatment approaches and, ultimately, personalized treatment.

Painful stimulation increases functional connectivity between supplementary motor area and thalamus in patients with small fibre neuropathy.

The lead symptom of small fibre neuropathy (SFN) is neuropathic pain. Recent functional magnetic resonance imaging (fMRI) studies have indicated central changes in SFN patients of different etiologies. However, less is known about brain functional connectivity during acute pain processing in idiopathic SFN. We conducted fMRI with thermal heat pain application (left volar forearm) in 32 idiopathic SFN patients and 31 healthy controls. We performed functional connectivity analyses with right supplementary motor area (SMA), left insula, and left caudate nucleus (CN) as seed regions, respectively. Since pathogenic gain-of-function variants in voltage gated sodium channels (Nav) have been linked to SFN pathophysiology, explorative connectivity analyses were performed in a homogenous subsample of patients carrying rare heterozygous missense variants. For right SMA, we found significantly higher connectivity with the right thalamus in SFN patients compared to controls. This connectivity correlated significantly with intraepidermal nerve fibre density, suggesting a link between peripheral and central pain processing. We found significantly reduced connections between right SMA and right middle frontal gyrus in patients with Nav variants. Likewise, connectivity between left CN and right frontal pole was decreased. Aberrant functional connectivity in SFN is in line with previous research on other chronic pain syndromes. Functional connectivity changes may be linked to SFN, highlighting the need to determine if they result from peripheral changes causing abnormal somatosensory processing. This understanding may be crucial for assessing their impact on painful symptoms and therapy response. We found increased functional connectivity between SMA and thalamus during painful stimulation in patients with idiopathic SFN. Connectivity correlated significantly with intraepidermal nerve fibre density, suggesting a link between peripheral and central pain processing. Our findings emphasize the importance of investigating functional connectivity changes as a potential feature of SFN.

Automated immunohistochemistry of intra-epidermal nerve fibres in skin biopsies: A proof-of-concept study.

To develop a standardised, automated protocol for detecting protein gene product 9.5 (PGP9.5) positive intra-epidermal nerve fibres (IENFs) in skin biopsies, transitioning from the established manual technique to an automated platform. This automated method, although currently intended for research applications, may improve the accessibility of this diagnostic test for small fibre neuropathy in clinical settings. Skin biopsies (n = 274) from 100 participants (fibromyalgia syndrome n = 62; idiopathic small fibre neuropathy: n = 16; healthy volunteers: n = 22) were processed using an automated immunohistochemistry platform. IENF quantification was performed by blinded examiners, with reliability assessed via a two-way mixed-effects model to evaluate inter- and intra-observer variability. The automated staining system reproduced intra-epidermal nerve fibre density (IENFD) counts consistent with free-floating sections (mean ± standard deviation: free-floating: 5.6 ± 3.4 fibres/mm; automated: 5.9 ± 3.2 fibres/mm). A median difference of 0.3 with a lower bound 95% Confidence Interval (CI) at -0.00005 established non-inferiority against a margin of -0.4 (p = .08). Specifically, the inter-class correlation coefficient (class denotes consistency in measured observations) was 99% (95% CI: 0.9-1), indicating excellent agreement between free-floating and automated methods. The inter- and intra-class coefficient between examiners were both 99% (95% CI: 0.9-0.1) for IENFD, demonstrating high reliability using sections stained using the automated method. Automated immunohistochemistry provides high-throughput reliable and reproducible intra-epidermal nerve fibre quantification. This method, although currently proof-of-concept, for research use only, may be more widely deployed in histopathology laboratories to increase the adoption of IENFD assessment for the diagnosis of peripheral neuropathies.

Neuroinflammation evoked mechanisms for neuropathic itch in the spared nerve injury mouse model of neuropathic pain

A large portion of neuropathic pain suffering patients may also concurrently experience neuropathic itch, with a negative impact on the quality of life. The limited understanding of neuropathic itch and the low efficacy of current anti-itch therapies dictate the urgent need of a better comprehension of molecular mechanisms involved and development of relevant animal models. This study was aimed to characterize the itching phenotype in a model of trauma-induced peripheral neuropathy, the spared nerve injury (SNI), and the molecular events underlying the overlap with the nociceptive behavior. SNI mice developed hyperknesis and spontaneous itch 7–14 days after surgery that was prevented by gabapentin treatment. Itch was associated with pain hypersensitivity, loss of intraepidermal nerve fiber (IENF) density and increased epidermal thickness. In coincidence with the peak of scratching behavior, SNI mice showed a spinal overexpression of IBA1 and GFAP, microglia and astrocyte markers respectively. An increase of the itch neuropeptide B-type natriuretic peptide (BNP) in NeuN+ cells, of its downstream effector interleukin 17 (IL17) along with increased pERK1/2 levels occurred in the spinal cord dorsal horn and DRG. A raise in BNP and IL17 was also detected at skin level. Stimulation of HaCat cells with conditioned medium from BV2-stimulated SH-SY5Y cells produced a dramatic reduction of HaCat cell viability. This study showed that SNI mice might represent a model for neuropathic itch and pain. Collectively, our finding suggest that neuropathic itch might initiate at spinal level, then affecting skin epidermis events, through a glia-mediated neuroinflammation-evoked BNP/IL17 mechanism.

Development and Progression of Polyneuropathy Over 5 Years in Patients With Type 2 Diabetes.

There is a need for knowledge regarding the natural course of diabetic polyneuropathy (DPN), a complication in type 2 diabetes (T2D). The aim of this study was to examine the development of DPN over time. Patients with newly diagnosed T2D, recruited from a national cohort, and controls without diabetes of similar age and sex, underwent sensory phenotyping in 2016-2018. The Toronto consensus criteria were used to classify patients into possible, probable, and confirmed DPN. For this 5-year, observational, follow-up, cohort study, all participants were invited to a reexamination combining bedside sensory examination, quantitative sensory testing (QST), nerve conduction studies (NCSs), and skin biopsies measuring intraepidermal nerve fiber density (IENFD) in order to compare phenotypic and diagnostic changes over time. Of the baseline 389 patients and 97 controls, 184 patients (median [interquartile range] diabetes duration 5.9 [4.1-7.4] years, mean hemoglobin A1c [HbA1c] 51 ± 11 mmol/mol at baseline) and 43 controls completed follow-up (46.9%). Confirmed DPN was present in 35.8% and 50.3%, probable DPN in 27.2% and 14.6%, possible DPN in 17.2% and 16.6%, and no DPN in 15.2% and 17.9% at baseline and follow-up, respectively. The estimated prevalence (95% CI) of confirmed DPN was 33.5% (24.9-42.1) compared with 22.7% (17.5-28.0) at baseline. During the follow-up period, 43.9% of patients with probable DPN developed confirmed DPN. Progression of neuropathy occurred in 16.5% and 24.7% and regression in 5.9% and 18.6% of patients based on NCS and IENFD, respectively. Progression based on NCS and/or IENFD was associated with higher baseline waist circumference and triglycerides, and regression with lower baseline HbA1c. Patients with at least probable DPN at baseline but neither patients without DPN nor controls developed increased spread of hyposensitivity, more hyposensitivity on QST and lower NCS z-scores at follow-up, and worsening of nerve parameters at follow-up correlated with higher baseline triglycerides. In patients with well-regulated T2D, the proportion of patients with confirmed DPN increased over 5 years driven by progression from probable DPN. A large proportion of patients progressed, and a smaller proportion regressed on nerve parameters. Higher triglycerides correlated with this progression and may constitute a risk factor.

A phase 2a study investigating the effects of ritlecitinib on brainstem auditory evoked potentials and intraepidermal nerve fiber histology in adults with alopecia areata.

Reversible axonal swelling and brainstem auditory evoked potential (BAEP) changes were observed in standard chronic (9-month) toxicology studies in dogs treated with ritlecitinib, an oral Janus kinase 3/tyrosine kinase expressed in hepatocellular carcinoma family kinase inhibitor, at exposures higher than the approved 50-mg human dose. To evaluate the clinical relevance of the dog toxicity finding, this phase 2a, double-blind study assessed BAEP changes and intraepidermal nerve fiber (IENF) histology in adults with alopecia areata treated with ritlecitinib. Patients were randomized to receive oral ritlecitinib 50 mg once daily (QD) with a 4-week loading dose of 200 mg QD or placebo for 9 months (placebo-controlled phase); they then entered the active-therapy extension and received ritlecitinib 50 mg QD (with a 4-week loading dose of 200 mg in patients switching from placebo). Among the 71 patients, no notable mean differences in change from baseline (CFB) in Waves I-V interwave latency (primary outcome) or Wave V amplitude on BAEP at a stimulus intensity of 80 dB nHL were observed in the ritlecitinib or placebo group at Month 9, with no notable differences in interwave latency or Wave V amplitude between groups. The CFB in mean or median IENF density and in percentage of IENFs with axonal swellings was minimal and similar between groups at Month 9. Ritlecitinib treatment was also not associated with an imbalanced incidence of neurological and audiological adverse events. These results provide evidence that the BAEP and axonal swelling finding in dogs are not clinically relevant in humans.

Insights into phenotypic variability caused by GARS1 pathogenic variants.

Pathogenic variants of the glycyl-tRNA synthetase 1 (GARS1) gene have been described as a cause of Charcot-Marie-Tooth disease type 2D, motor axonal neuropathy with upper limb predominance (distal hereditary motor neuropathy [dHMN] type V), and infantile spinal muscular atrophy. This cross-sectional, retrospective, observational study was carried out on 12 patients harboring the c.794C>T (p.Ser265Phe) missense pathogenic variant in GARS1. The patients' clinical data, nerve conduction studies, magnetic resonance imaging (MRI), and intraepidermal nerve fiber density in skin biopsies were reviewed. The mean age at onset was 9.5 years; the intrinsic hand muscles were affected before or at the same time as the distal leg musculature. The clinical examination revealed greater weakness of the distal muscles, with a more pronounced involvement of the thenar complex and the first dorsal interosseous in upper limbs. Electrophysiological studies were concordant with an exclusively motor axonal neuropathy. A pathologic split hand index was found in six patients. Muscle MRI showed predominant fatty infiltration and atrophy of the anterolateral and superficial posterior compartment of the legs. Most patients reported distal pinprick sensory loss. A reduced intraepidermal nerve fiber density was evident in skin biopsies from proximal and distal sites in nine patients. GARS1 variants may produce a dHMN phenotype with "split hand" and sensory disturbances, even when sensory nerve conduction studies are normal. This could be explained by a dysfunction of sensory neurons in the dorsal ganglion that is reflected as a reduction of dermal nerve endings in skin biopsies without a distal gradient.