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Background: Pompe disease is a glycogen storage disease primarily affecting striated muscles. Despite its main manifestation in muscles, patients with Pompe disease may exhibit non-muscle symptoms, such as hearing loss, suggesting potential involvement of sensory organs or the nervous system due to glycogen accumulation. Aims: This study aimed to evaluate the presence of concomitant small and large fiber neuropathy in patients with Pompe disease. Methods: In this case series study, nine patients with Pompe disease without complaints of neuropathy were evaluated. Small fiber neuropathy was assessed using the Small Fiber Neuropathy Screening List (SFNSL) and SUDOSCANR, while the sympathetic system was evaluated through Sympathetic Skin Response (SSR), and large fiber neuropathy was assessed through electrodiagnostic findings. Results: Small fiber neuropathy was detected in seven patients (77.8%) according to the SFNSL. Three patients (3/9, approximately 30%) exhibited positive electrophysiological tests, including SSR, SUDOSCANR, and nerve conduction studies for neuropathy. They also had positive SFNSL results. Conclusions: This study indicates that neuropathy can be a comorbid condition in Pompe disease, emphasizing the importance of screening for this disabling condition. [ABSTRACT FROM AUTHOR]

Background: Diabetic neuropathy is diagnosed late due to lack of easy and readily available biomarkers; early identification can prompt proper interventions before the irreversible large fiber damage. The aim of this study is to assess small fiber dysfunction using cutaneous silent period (CSP) and sympathetic skin response (SSR) tests in patients with diabetic small fiber neuropathy (SFN) and compare results with clinical, neuropathy severity and quality of life measures. A total of 45 subjects were classified into: Group I: diabetic patients with pure SFN, group II: diabetic patients with mixed fiber neuropathy, and group III: healthy subjects. All underwent evaluation by anthropometric, clinical and quality of life measures, electrophysiological evaluation by CSP and SSR and distal leg skin biopsy. Results: Age and gender distribution did not significantly differ between the studied groups. Both patients' groups showed comparable poor quality of life in relation to healthy subjects. CSP onset latencies and SSR amplitudes significantly correlated with studied clinical and severity measures, but neither correlate with each other in diabetic pure SFN patients. Both CSP and SSR measures were specific in diagnosing diabetic pure SFN, but mostly with poor sensitivity. Combining sensitivities of different CSP and SSR measures improved the overall sensitivity to early screen for SFN in diabetic patients. Conclusions: Both CSP and SSR may have the potential to early detect diabetic pure SFN. Suspected diabetic patients with SFN should be separately screened for both somatosensory and sudomotor/autonomic affection. [ABSTRACT FROM AUTHOR]

ABSTRACT Introduction/Aims Methods Results Discussion Accurate assessment of diabetic peripheral neuropathy (DPN) is essential to prevent further complications, yet current methods have limitations. Perception threshold tracking (PTT) offers promise as a novel approach for rapid evaluation of both large and small fiber dysfunction. To enhance efficiency, this study explores the Psi method compared to the Method of Limits (MoL) in estimating perception thresholds. The aim is to assess agreement, uncertainty, and the number of stimuli required for adequate estimation by each method.Forty‐three participants with diabetes underwent an estimated sural nerve conduction study, quantitative sensory testing, vibration perception threshold testing, and PTT. PTT utilized both patch and pin electrode configurations to activate large and small fibers, respectively. The uncertainty of perception thresholds was estimated as the inverse slope of the psychometric functions.Perception thresholds were significantly higher for the patch electrode (2.5 [2.1–3.0] mA) compared to the pin electrode (0.71 [0.56–0.91] mA; rmANOVA, p < 0.001). Bland–Altman analysis revealed a non‐significant 3.3% bias between the methods, but wide limits of agreement (−42%–84%). Uncertainty was lower for the Psi method (0.80 [0.58;1.11] mA) compared to MoL (2.0 [1.2;2.9] mA; rmANOVA, p < 0.005). The Psi method achieved acceptable perception threshold estimation with only 30 stimuli.At the group level, the MoL and Psi methods produced similar perception thresholds. However, the Psi method required fewer stimuli and yielded less uncertainty in perception threshold estimation compared to MoL. Future studies should prioritize the Psi method for its efficiency and reliability. [ABSTRACT FROM AUTHOR]

Long coronavirus disease 2019 (COVID) (LC) symptoms including pain and autonomic dysfunction are in some patients associated with small‐fiber neuropathy (SFN). The pathomechanisms underlying SFN are mostly unclear. Natural killer (NK) cells play a crucial role in immune regulation, viral clearance and nerve metabolism. The aim of this study was to identify associations between development of small‐fiber dysfunction dependent and independent of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection, and human genetic markers associated with specific NK cell functions. The genetic markers assessed in all cohorts included: FCGR3A, IGHG1, HLA‐E, NKG2C, and rs9916629. Genotyping was performed using TaqMan assays, Sanger sequencing and touchdown polymerase chain reaction. We assessed human cytomegalovirus (HCMV) IgG serostatus in all participants, and screened for anti‐neuronal, anti‐glial and anti‐ganglioside autoantibodies in both patient cohorts. We included 50 LC patients with newly‐emerged symptoms of small‐fiber dysfunction after SARS‐CoV‐2 infection, 27 prepandemic SFN patients and 320 control persons. Markers associated with low NKG2C response, that is, deletion of the NKG2C gene and lack of prior HCMV infection (IgG seronegativity), occurred significantly more frequently in prepandemic SFN patients compared to LC patients and controls (p = 0.0109 and 0.0005, respectively). In conclusion, markers of impaired NKG2C pathways are associated with prepandemic SFN, but not with Long COVID‐associated small‐fiber dysfunction. [ABSTRACT FROM AUTHOR]

Background Method Results Conclusions Small fiber neuropathy (SFN) after both COVID‐19 infection or vaccination has been reported in sporadic cases, but a detailed description and comparison are missing. We aimed to screen a large cohort of patients complaining of pain and autonomic symptoms after COVID‐19 natural infection or vaccination to ascertain the presence of SFN and its correlation with autoimmune diseases.We prospectively recruited for this case–control study 66 patients: 33 developing sensory and autonomic symptoms after a natural COVID‐19 infection (P‐COVID) and 33 after a mRNA vaccination against COVID‐19 (P‐VAC). We also used 33 matched healthy controls (HC) collected before 2019 when the COVID‐19 virus appeared. Patients underwent neurological examination and clinical scales, an extensive serum screening, and skin biopsy to detect small nerve fiber involvement.Clinical scales showed higher scores for autonomic symptoms in P‐COVID patients than in P‐VAC patients, but the other scales did not differ. P‐COVID and P‐VAC patients showed a significant decrease in somatic small nerve fibers compared with HC, whereas autonomic innervation did not differ. SFN was more frequent in P‐COVID patients (94%) than in P‐VAC patients (79%). Epidermal innervation was correlated with clinical scales for pain and autonomic dysfunctions. Autoimmune abnormalities were frequent in both groups but importantly they were not correlated with SFN.Somatic SFN was frequently found in both P‐COVID and P‐VAC patients, with a higher incidence in the former group. Spared skin autonomic innervation was spared in both groups although a subtle autonomic involvement in P‐COVID patients was suggested by a high COMPASS‐31 scale score. SFN was not correlated with autoimmune dysfunctions, although autoimmune diseases were frequent in both groups. [ABSTRACT FROM AUTHOR]

Burning mouth syndrome (BMS) is a chronic idiopathic orofacial pain disorder, characterized by persistent burning sensations and pain without clear pathological causes. Recent research suggests that small fiber neuropathy (SFN) may play a significant role in the neuropathic pain and sensory disturbances associated with BMS. Following PRISMA guidelines, this systematic review aims to evaluate and synthesize current evidence supporting SFN's involvement in BMS. The protocol is registered in PROSPERO (CRD42024555839). The results show eight studies reported reductions in nerve fiber density in tongue biopsies (ranging from 30% to 60%), along with morphological changes indicative of small fiber damage. Additionally, an increase in TRPV1-positive, NGF-positive, and P2X3-positive fibers, overexpression of Nav1.7, and slight underexpression of Nav1.9 mRNA were observed in BMS patients. Quantitative Sensory Testing in seven studies revealed sensory abnormalities such as reduced cool detection and cold pain thresholds. Blink reflex and corneal confocal microscopy also indicated peripheral and central small fiber damage, along with increased artemin mRNA expression. The evidence strongly supports SFN as a key factor in the pathophysiology of BMS, particularly due to reductions in nerve fiber density and altered sensory thresholds. However, variability across studies highlights the need for larger, standardized research to establish causal relationships and guide therapeutic strategies. [ABSTRACT FROM AUTHOR]

Purpose: Small fiber neuropathy (SFN) is characterized by neuropathic pain, associated with decreased quality of life (QOL). It remains unclear which psychosocial factors play a role in SFN. The experience sampling method (ESM) allows a profound understanding of the real-time fluctuations in reaction to events. The main goal of this study was to increase knowledge of the interrelationships between pain intensity, physical activity, and psychosocial factors in patients with SFN in daily practice over time. Patients and Methods: A prospective observational ESM study with the PsyMate© application (smart-eHealth GmbH, Luxembourg) was conducted at the Adelante location of Maastricht University Medical Center+ in the Netherlands. Participants with idiopathic SFN, older than 18 years, with an indication for rehabilitation, were included. Pain intensity, fatigue, positive and negative affect, physical activity, avoidance behavior, and pain catastrophic thoughts were incorporated into the ESM questions. Participants received 10 beep signals per day followed by the above-mentioned questions, for consecutive 7 days. The results were analyzed with linear mixed-effect models. Results: Twenty-one participants were included with a mean age of 48.24 (SD ± 13.89) years, of whom 76.2% were female. More pain (now) resulted in more physical activity (later) (a) and more physical activity (now) resulted in more pain (later) (b). The first association (a) is influenced by pain catastrophic thoughts and fatigue, and the second (b) by an increase in affective states and a lower level of avoidance behavior. Conclusion: In idiopathic SFN, pain intensity, and physical activity showed a 2-sided association, influenced by catastrophic thoughts, fatigue, affective states, and avoidance behavior. [ABSTRACT FROM AUTHOR]

Abstract Background Pompe disease is a glycogen storage disease primarily affecting striated muscles. Despite its main manifestation in muscles, patients with Pompe disease may exhibit non-muscle symptoms, such as hearing loss, suggesting potential involvement of sensory organs or the nervous system due to glycogen accumulation. Aims This study aimed to evaluate the presence of concomitant small and large fiber neuropathy in patients with Pompe disease. Methods In this case series study, nine patients with Pompe disease without complaints of neuropathy were evaluated. Small fiber neuropathy was assessed using the Small Fiber Neuropathy Screening List (SFNSL) and SUDOSCANR, while the sympathetic system was evaluated through Sympathetic Skin Response (SSR), and large fiber neuropathy was assessed through electrodiagnostic findings. Results Small fiber neuropathy was detected in seven patients (77.8%) according to the SFNSL. Three patients (3/9, approximately 30%) exhibited positive electrophysiological tests, including SSR, SUDOSCANR, and nerve conduction studies for neuropathy. They also had positive SFNSL results. Conclusions This study indicates that neuropathy can be a comorbid condition in Pompe disease, emphasizing the importance of screening for this disabling condition.

Abstract Background Diabetic neuropathy is diagnosed late due to lack of easy and readily available biomarkers; early identification can prompt proper interventions before the irreversible large fiber damage. The aim of this study is to assess small fiber dysfunction using cutaneous silent period (CSP) and sympathetic skin response (SSR) tests in patients with diabetic small fiber neuropathy (SFN) and compare results with clinical, neuropathy severity and quality of life measures. A total of 45 subjects were classified into: Group I: diabetic patients with pure SFN, group II: diabetic patients with mixed fiber neuropathy, and group III: healthy subjects. All underwent evaluation by anthropometric, clinical and quality of life measures, electrophysiological evaluation by CSP and SSR and distal leg skin biopsy. Results Age and gender distribution did not significantly differ between the studied groups. Both patients’ groups showed comparable poor quality of life in relation to healthy subjects. CSP onset latencies and SSR amplitudes significantly correlated with studied clinical and severity measures, but neither correlate with each other in diabetic pure SFN patients. Both CSP and SSR measures were specific in diagnosing diabetic pure SFN, but mostly with poor sensitivity. Combining sensitivities of different CSP and SSR measures improved the overall sensitivity to early screen for SFN in diabetic patients. Conclusions Both CSP and SSR may have the potential to early detect diabetic pure SFN. Suspected diabetic patients with SFN should be separately screened for both somatosensory and sudomotor/autonomic affection.

Background/Aims We investigated sudomotor dysfunction, small fiber neuropathy (SFN), and their clinical significance in female fibromyalgia patients. Methods Fibromyalgia patients and healthy controls (HCs) were recruited. Clinical and laboratory data were measured. Electrochemical skin conductance (ESC) values of hands and feet were assessed by SUDOSCAN. Additionally, several other methods were employed, including nerve conduction study (NCS), electromyography (EMG), and questionnaires. Spearman correlation coefficient was calculated to identify factors associated with ESC values of SUDOSCAN. Results Twenty-two female fibromyalgia patients and 22 female HCs were recruited. The fibromyalgia group had lower EQ5D and higher Toronto Clinical Neuropathy scores than the HC group. Most of the EMG/NCS findings of motor and proximal sensory nerves were comparable between the fibromyalgia and HC groups, whereas sensory nerve action potential amplitudes of distal sensory nerves were significantly lower in the fibromyalgia group. Mean ESC values of hands and feet were significantly lower in the fibromyalgia group than in the HC group (57.6 ± 16.2 vs. 68.8 ± 10.3 μS, p = 0.010 for hands, 64.9 ± 11.5 vs. 72.0 ± 8.2 μS, p = 0.025 for feet, respectively). Moderate to severe SFN was more common in the fibromyalgia group (68.2%) than in the HC group (68.2 vs. 50%, p = 0.019). Fibromyalgia disease duration was significantly correlated with the ESC values of hands/feet, and tricyclic antidepressant (TCA) responders had higher ESC values than non-responders. Conclusions SFN was commonly detected in fibromyalgia patients who had normal EMG/NCS findings and was more severe in fibromyalgia patients with longer disease duration. SUDOSCAN may predict response to TCA therapy.

Background: Recent evidence suggests that both serum neurofilament light chain (sNfL) levels and small fiber related diagnostic variables may be valuable disease biomarkers of hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN). Our study aimed to explore the relations between sNfL and small fiber related skin biopsy and quantitative sensory testing (QST) parameters in a cohort of ATTRv-PN patients and pre-symptomatic carriers. Methods: We retrospectively analyzed data from 13 ATTRv patients and 21 pre-symptomatic carriers who underwent sNfL dosage, skin biopsy, and QST, and analyzed correlations between sNFL, intraepidermal nerve fiber density (IENFD), and cold (CDT) and warm detection thresholds (WDT). Results: Both sNfL and small fiber related parameters significantly differed between carriers and patients (sNfL: p < 0.0001; IENFD: p = 0.0008; CDT, WDT: < 0.0001). sNFL levels were normal in all carriers, altered in 85% of patients, negatively correlated with distal IENFD (r = -0.47, p = 0.005), and significantly correlated with CDT (r = -0.68; p < 0.0001) and WDT (r = 0.57; p < 0.0001). Conclusions: Our study showed that sNfL reliably discriminates symptomatic ATTRv-PN patients from pre-symptomatic carriers, and found significant relations between sNfL, skin biopsy, and QST small fiber related parameters, suggesting that sNfL might be a valuable biomarker of peripheral nerve involvement in ATTRv-PN and a supportive criterion for symptomatic disease transition. [ABSTRACT FROM AUTHOR]

Purpose: Orofacial Pain (OFP) affects 15% of the general population. OFP conditions can be myofascial, also known as temporomandibular disorders (TMDs) or neuropathic. The underlying pathophysiology in several chronic OFP conditions, is unknown. Small fiber neuropathy (SFN) is a disorder of thinly myelinated A-delta and non-myelinated C-fibers and can manifest as sensory and autonomic neuropathies. SFN has been demonstrated in some OFP conditions. Our study aims to assess the presence of OFP in patients with sensory and autonomic neuropathies and assess the correlation between OFP, skin biopsy and autonomic dysfunction. Patients and Methods: This is a retrospective study (2018– 2020) of patients from the SFN registry, Massachusetts General Hospital, Boston, USA, for the presence of OFP. All patients were included. Primary outcome: Prevalence of OFP in patients with chronic neuropathies. Secondary outcomes: Correlation between OFP and skin biopsy, dysautonomia, headaches, chronic nociceptive pain, psychological conditions, and patient factors, such as mean age and BMI. Results: Charts of 450 patients with sensory and autonomic neuropathies were reviewed. 22.67% (n=102) had OFP. The mean (range) age at biopsy in patients with OFP was 48.36 (20– 81) years, female: male ratio 3.25:1. More OFP patients had negative skin biopsy results (p value< 0.05) than those with sensory neuropathies. Patients with OFP had significantly higher prevalence of psychological conditions (p value 0.000), and higher BMI > 30 (p value 0.025). Dysautonomia was significantly higher in patients with TMDs when compared to the ones without TMDs (p value 0.030). There was no significant difference in mean age, gender predilection, presence of headaches, peripheral neuropathies, and nociceptive pain between patients with and without OFP. Conclusion: OFP and sensory neuropathies can be overlapping conditions. Patients presenting with concomitant TMD and dysautonomia can be further tested for SFN. This can further help us understand a correlation if any, between idiopathic TMD/OFP conditions and SFN and further our understanding of the pathophysiology of these conditions. [ABSTRACT FROM AUTHOR]

Background and Objectives: Systemic Lupus Erythematosus (SLE) often causes damage to small nerve fibers, leading to distressing painful and autonomic symptoms. Despite this, Small Fiber Neuropathy (SFN) remains an underrecognized complication for SLE patients. In this cross‐sectional study, we aimed to assess SFN in patients with SLE and to explore its correlations with immunologic disease features and clinical manifestations. Methods: We recruited 50 SLE patients (1 male to 12.5 females, aged 20–80 years) reporting painful disturbances. We conducted a comprehensive clinical and neurophysiological evaluation, using Nerve Conduction Studies and Quantitative Sensory Testing. Additionally, we carried out an extensive laboratory assessment of disease‐related serological parameters. We also performed a thorough skin biopsy analysis, investigating somatic and autonomic innervation while detecting complement and inflammatory cell infiltrates within the skin. Results: Out of 50 patients, 19 were diagnosed with SFN, primarily characterized by a non‐length‐dependent distribution; 7 had a mixed neuropathy, with both large and small fiber involvement. Patients with SFN were younger than patients with a mixed neuropathy (p =.0143); furthermore, they were more likely to have a history of hypocomplementemia (p =.0058) and to be treated with cyclosporine A (p =.0053) compared to patients without neuropathy. However, there were no significant differences in painful and autonomic symptoms between patients with and without SFN. Discussion: This study highlights the relevant frequency of SFN with a non‐length‐dependent distribution among SLE patients experiencing painful symptoms. Indeed, SFN emerges as an early manifestation of SLE‐related neuropathy and is closely associated with hypocomplementemia, suggesting a potential pathogenic role of the complement system. Moreover, SFN may be influenced by disease‐modifying therapies. However, the precise role of SFN in shaping painful and autonomic symptoms in patients with SLE remains to be fully elucidated. [ABSTRACT FROM AUTHOR]

Introduction: Chronic muscle pain is common in myotonic dystrophies (DM). Little is known about its pathophysiology. We aimed to investigate the characteristics of the neuropathic pain component contributing contributes to the pathogenesis of chronic pain in DM. Methods: Twenty-one DM1 and 32 DM2 patients completed pain questionnaires (Brief pain inventory--BPI, PAIN-DETECT, pain disability index--PDI) and underwent neurological examination, nerve conduction studies (NCS), quantitative sensory testing (QST, dorsum of the right hand and right thigh) and skin biopsy to determine the intraepidermal nerve fiber density (IENFD, distal and proximal site of lower extremity). NCS and QST results at the thigh were compared to 27 healthy controls and IENFD and QST at the dorsum of the hand to published reference values. Results: The sensory profile of DM2 patients was characterized by a loss in thermal and mechanical detection, while DM1 patients showed reduced mechanical and heat pain thresholds and higher mechanical pain sensitivity. Both DM groups showed pressure hyperalgesia. IENFD was reduced in 63% of DM1 patients and 50% of DM2. The slightly higher pain interference and disability found in DM2 was rather due to age difference than disease. Conclusion: Similar pain mechanisms likely occur in both DM1 and DM2, even though a tendency toward more pain sensitivity was observed in DM1 and more sensory loss in DM2. Both QST and reduced IENFD highlight the presence of peripheral nerve damage in DM. This must be considered for the best pain management strategies. [ABSTRACT FROM AUTHOR]

Post-COVID-19 (PC) and post-COVID-19 vaccination (PCV) syndromes are considered emergent multidisciplinary disorders. PC/PCV small fiber neuropathy (SFN) was rarely described and its association with undifferentiated arthritis (UA) was never defined. We aimed to evaluate PC/PCV-UA associated with the recent onset of severe lower limb paresthesia, compare SFN positive (+) to negative (−) patients, and evaluate changes in biomarkers in SFN+ during treatments. Nineteen PC/PCV-UA-patients with possible SFN underwent skin biopsy at the Usl Tuscany Center (Florence) early arthritis outpatient clinic from September 2021 to March 2024. Eight selected SFN+ were compared to ten SFN− patients. In SFN+ patients, baseline joint ultrasound (US), electromyography (EMG), optical coherence tomography (OCT), and skin biopsy were repeated at six months. Moreover, SFN+ patients were clinically assessed by a 0–10 numeric rating scale for neurological symptoms and DAS28/ESR up to 12 months follow-up. SFN+ patients showed a lower intraepidermal nerve fiber density at histopathological examination of skin biopsies and a higher frequency of OCT and EMG abnormalities in comparison to SFN− patients. In SFN+ patients, US and DAS28/ESR significantly improved, while intraepidermal nerve fiber density did not significantly change at the six-month follow-up. Fatigue, motor impairment, burning pain, brain fog, and sensitivity disorders decreased at long-term follow-up (12 months). [ABSTRACT FROM AUTHOR]

Currently, there are more than 10 million patients with diabetes mellitus in Japan. Therefore, the need to explore the pathogenesis of diabetes and the complications leading to its cure is becoming increasingly urgent. Pathological examination of pancreatic tissues from patients with type 2 diabetes reveals a decrease in the volume of beta cells because of a combination of various stresses. In human type 2 diabetes, islet amyloid deposition is a unique pathological change characterized by proinflammatory macrophage (M1) infiltration into the islets. The pathological changes in the pancreas with islet amyloid were different according to clinical factors, which suggests that type 2 diabetes can be further subclassified based on islet pathology. On the other hand, diabetic peripheral neuropathy is the most frequent diabetic complication. In early diabetic peripheral neuropathy, M1 infiltration in the sciatic nerve evokes oxidative stress or attenuates retrograde axonal transport, as clearly demonstrated by in vitro live imaging. Furthermore, islet parasympathetic nerve density and beta cell volume were inversely correlated in type 2 diabetic Goto‐Kakizaki rats, suggesting that diabetic peripheral neuropathy itself may contribute to the decrease in beta cell volume. These findings suggest that the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy may be interrelated. [ABSTRACT FROM AUTHOR]

BackgroundDiabetic peripheral neuropathy (DPN) is a common complication of diabetes. Proactive treatment options remain limited, which is exacerbated by a lack of sensitive and convenient diagnostics, especially early in disease progression or specifically to assess small fiber neuropathy (SFN), the loss of distal small diameter axons that innervate tissues and organs.MethodsWe designed, fabricated, tested, and validated a first-of-its-kind medical diagnostic device for the functional assessment of transdermal small fiber nerve activity. This device, the Detecting Early Neuropathy (DEN), is an electrically conductive needle array designed to record nerve electrical activity in the skin and subdermal tissues, as a feature of a broader theragnostic platform.ResultsDEN recordings were validated across a time course of diet-induced PN in mice, using statistical and computational analyses and compared to other SFN measures. Based on these preclinical mouse data, the device design was adapted to obtain recordings in human with a flexible printed circuit board to mold to the leg or other skin regions. The DEN successfully recorded various types of neural activity in mouse and human, with or without stimulation, including validated action potentials and electromyography signals.ConclusionNew functional diagnostic tools like DEN offer a promising outlook for patients needing an earlier or more sensitive diagnosis of DPN/SFN, to allow for earlier and more effective treatment options, especially as more become available in the clinic in future years.

Purpose: To report the prevalence of scleritis and episcleritis in patients with idiopathic small fiber neuropathy (SFN). Methods: The Mass General Brigham (MGB) hospital database was queried for patients with SFN, scleritis and episcleritis using diagnostic codes and natural language processing. Electronic medical chart review of patients diagnosed with SFN and episcleritis/scleritis who had at least one ophthalmology visit was conducted. The prevalence of scleritis and episcleritis in patients diagnosed with SFN was compared to those without SFN using logistic regression to adjust for covariates. All statistical analyses were performed in RStudio 4.2.1. Results: From the 2100 SFN patients with an eye exam in the MGB database, 23 patients had episcleritis or scleritis (1.1 %) confirmed by chart review. Ten patients had episcleritis (0.48 %) and thirteen patients had scleritis (0.62 %). Of the episcleritis and scleritis patients, 16 (69.6 %) were women and 7 (30.4 %) were men. Ten (43.5 %) had bilateral ocular disease. The mean age of ocular diagnosis was 51.0 years (range, 22–77 years). Out of the 507,128 controls without SFN in the MGB database, 1481 (0.29 %) had scleritis and 1430 (0.28 %) had episcleritis. Episcleritis and scleritis were more prevalent in patients with SFN than in those without SFN: 0.48 % vs. 0.28 % for episcleritis and 0.62 % vs 0.29 % for scleritis (P values = 0.32 and 0.02, respectively). Conclusions and Importance: There were higher rates of scleritis in SFN patients compared to non-SFN patients. This potential systemic disease association had not been previously reported.

Diabetes represents a spectrum of disease in which metabolic dysfunction damages multiple organ systems including liver, kidneys and peripheral nerves1,2. Although the onset and progression of these co-morbidities are linked with insulin resistance, hyperglycaemia and dyslipidaemia3-7, aberrant non-essential amino acid (NEAA) metabolism also contributes to the pathogenesis of diabetes8-10. Serine and glycine are closely related NEAAs whose levels are consistently reduced in patients with metabolic syndrome10-14, but the mechanistic drivers and downstream consequences of this metabotype remain unclear. Low systemic serine and glycine are also emerging as a hallmark of macular and peripheral nerve disorders, correlating with impaired visual acuity and peripheral neuropathy15,16. Here we demonstrate that aberrant serine homeostasis drives serine and glycine deficiencies in diabetic mice, which can be diagnosed with a serine tolerance test that quantifies serine uptake and disposal. Mimicking these metabolic alterations in young mice by dietary serine or glycine restriction together with high fat intake markedly accelerates the onset of small fibre neuropathy while reducing adiposity. Normalization of serine by dietary supplementation and mitigation of dyslipidaemia with myriocin both alleviate neuropathy in diabetic mice, linking serine-associated peripheral neuropathy to sphingolipid metabolism. These findings identify systemic serine deficiency and dyslipidaemia as novel risk factors for peripheral neuropathy that may be exploited therapeutically.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating disease with a broad overlap of symptomatology with Post-COVID Syndrome (PCS). Despite the severity of symptoms and various neurological, cardiovascular, microvascular, and skeletal muscular findings, no biomarkers have been identified. The Transient receptor potential melastatin 3 (TRPM3) channel, involved in pain transduction, thermosensation, transmitter and neuropeptide release, mechanoregulation, vasorelaxation, and immune defense, shows altered function in ME/CFS. Dysfunction of TRPM3 in natural killer (NK) cells, characterized by reduced calcium flux, has been observed in ME/CFS and PCS patients, suggesting a role in ineffective pathogen clearance and potential virus persistence and autoimmunity development. TRPM3 dysfunction in NK cells can be improved by naltrexone in vitro and ex vivo, which may explain the moderate clinical efficacy of low-dose naltrexone (LDN) treatment. We propose that TRPM3 dysfunction may have a broader involvement in ME/CFS pathophysiology, affecting other organs. This paper discusses TRPM3's expression in various organs and its potential impact on ME/CFS symptoms, with a focus on small nerve fibers and the brain, where TRPM3 is involved in presynaptic GABA release. [ABSTRACT FROM AUTHOR]

Background: The investigation of C-fiber-evoked ultralow-level responses (ULEPs) at somatic sites is difficult in clinical practice but may be useful in patients with small fiber neuropathy. Aim: The aim of the study was to investigate changes in LEPs and ULEPs in patients with fibromyalgia affected or not by abnormal intraepidermal innervation. Methods: We recorded LEPs and ULEPs of the hand, thigh and foot in 13 FM patients with a normal skin biopsy (NFM), 13 patients with a reduced intraepidermal nerve fiber density (IENFD) (AFM) and 13 age-matched controls. We used a YAP laser, changing the energy and spot size at the pain threshold for LEPs and at the heat threshold for ULEPs. Results: ULEPs occurred at a small number of sites in both the NFM and AFM groups compared to control subjects. The absence of ULEPs during foot stimulation was characteristic of AFM patients. The amplitude of LEPs and ULEPs was reduced in patients with AFM at the three stimulation sites, and a slight reduction was also observed in the NFM group. Conclusions: The present preliminary results confirmed the reliability of LEPs in detecting small fiber impairments. The complete absence of ULEPs in the upper and lower limbs, including the distal areas, could confirm the results of LEPs in patients with small fiber impairments. Further prospective studies in larger case series could confirm the present findings on the sensitivity of LEP amplitude and ULEP imaging in detecting small fiber impairments and the development of IENFD in FM patients. [ABSTRACT FROM AUTHOR]

We report the case of a 27-year-old man with transthyretin amyloidosis secondary to the p.Val142Ile mutation with an atypical clinical presentation of predominantly lower limb polyneuropathy without cardiac involvement. p.Val142Ile is mainly associated with cardiopathy, whereas the neuropathic phenotype is mainly associated with p.Val50Met. Our patient belongs to a non-endemic region and due to his lack of support network a possible familial component is unknown. His case represents a diagnostic challenge given the wide heterogeneity of clinical manifestations associated with the disease, with other possible diagnoses of polyneuropathy being reasonably excluded according to prevalence and frequency. The particularly unusual genotype-phenotype association distinguishes this case from the classic description of transthyretin amyloidosis secondary to p.Val142Ile. [ABSTRACT FROM AUTHOR]

IntroductionChronic muscle pain is common in myotonic dystrophies (DM). Little is known about its pathophysiology. We aimed to investigate the characteristics of the neuropathic pain component contributing contributes to the pathogenesis of chronic pain in DM.MethodsTwenty-one DM1 and 32 DM2 patients completed pain questionnaires (Brief pain inventory–BPI, PAIN-DETECT, pain disability index–PDI) and underwent neurological examination, nerve conduction studies (NCS), quantitative sensory testing (QST, dorsum of the right hand and right thigh) and skin biopsy to determine the intraepidermal nerve fiber density (IENFD, distal and proximal site of lower extremity). NCS and QST results at the thigh were compared to 27 healthy controls and IENFD and QST at the dorsum of the hand to published reference values.ResultsThe sensory profile of DM2 patients was characterized by a loss in thermal and mechanical detection, while DM1 patients showed reduced mechanical and heat pain thresholds and higher mechanical pain sensitivity. Both DM groups showed pressure hyperalgesia. IENFD was reduced in 63% of DM1 patients and 50% of DM2. The slightly higher pain interference and disability found in DM2 was rather due to age difference than disease.ConclusionSimilar pain mechanisms likely occur in both DM1 and DM2, even though a tendency toward more pain sensitivity was observed in DM1 and more sensory loss in DM2. Both QST and reduced IENFD highlight the presence of peripheral nerve damage in DM. This must be considered for the best pain management strategies.

We aimed to investigate to what extent small fiber tests were abnormal in an unselected retrospective patient material with symptoms suggesting that small fiber neuropathy (SFN) could be present, and to evaluate possible gender differences.

Background and purpose: Diagnosing small fiber neuropathies can be challenging. To address this issue, whether serum neurofilament light chain (sNfL) could serve as a potential biomarker of damage to epidermal Aδ‐ and C‐fibers was tested. Methods: Serum NfL levels were assessed in 30 patients diagnosed with small fiber neuropathy and were compared to a control group of 19 healthy individuals. Electrophysiological studies, quantitative sensory testing and quantification of intraepidermal nerve fiber density after skin biopsy were performed in both the proximal and distal leg. Results: Serum NfL levels were not increased in patients with small fiber neuropathy compared to healthy controls (9.1 ± 3.9 and 9.4 ± 3.8, p = 0.83) and did not correlate with intraepidermal nerve fiber density at the lateral calf or lateral thigh or with other parameters of small fiber impairment. Conclusion: Serum NfL levels cannot serve as a biomarker for small fiber damage. [ABSTRACT FROM AUTHOR]

Peripheral and autonomic neuropathy are common disease manifestations in systemic amyloidosis. The neurofilament light chain (NfL), a neuron-specific biomarker, is released into the blood and cerebrospinal fluid after neuronal damage. There is a need for an early and sensitive blood biomarker for polyneuropathy, and this systematic review provides an overview on the value of NfL in the early detection of neuropathy, central nervous system involvement, the monitoring of neuropathy progression, and treatment effects in systemic amyloidosis. A literature search in PubMed, Embase, and Web of Science was performed on 14 February 2024 for studies investigating NfL levels in patients with systemic amyloidosis and transthyretin gene-variant (TTRv) carriers. Only studies containing original data were included. Included were thirteen full-text articles and five abstracts describing 1604 participants: 298 controls and 1306 TTRv carriers or patients with or without polyneuropathy. Patients with polyneuropathy demonstrated higher NfL levels compared to healthy controls and asymptomatic carriers. Disease onset was marked by rising NfL levels. Following the initiation of transthyretin gene-silencer treatment, NfL levels decreased and remained stable over an extended period. NfL is not an outcome biomarker, but an early and sensitive disease-process biomarker for neuropathy in systemic amyloidosis. Therefore, NfL has the potential to be used for the early detection of neuropathy, monitoring treatment effects, and monitoring disease progression in patients with systemic amyloidosis. [ABSTRACT FROM AUTHOR]

Introduction/aims: Diabetic small fiber neuropathy (SFN) is caused by damage to thinly myelinated A‑fibers (δ) and unmyelinated C‑fibers. This study aimed to assess associations between quantitative sensory testing (QST) and parameters of peripheral nerve perfusion obtained from dynamic contrast enhanced (DCE) magnetic resonance neurography (MRN) in type 2 diabetes patients with and without SFN. Methods: A total of 18 patients with type 2 diabetes (T2D, 8 with SFN, 10 without SFN) and 10 healthy controls (HC) took part in this cross-sectional single-center study and underwent QST of the right leg and DCE-MRN of the right thigh with subsequent calculation of the sciatic nerve constant of capillary permeability (Ktrans), extravascular extracellular volume fraction (Ve), and plasma volume fraction (Vp). Results: The Ktrans (HC 0.031 min−1 ± 0.009, T2D 0.043 min−1 ± 0.015; p = 0.033) and Ve (HC 1.2% ± 1.5, T2D: 4.1% ± 5.1; p = 0.027) were lower in T2D patients compared to controls. In T2D patients, compound z‑scores of thermal and mechanical detection correlated with Ktrans (r = 0.73; p = 0.001, and r = 0.57; p = 0.018, respectively) and Ve (r = 0.67; p = 0.002, and r = 0.69; p = 0.003, respectively). Compound z‑scores of thermal pain and Vp (r = −0.57; p = 0.015) correlated negatively. Discussion: The findings suggest that parameters of peripheral nerve microcirculation are related to different symptoms in SFN: A reduced capillary permeability may result in a loss of function related to insufficient nutritional supply, whereas increased capillary permeability may be accompanied by painful symptoms related to a gain of function. [ABSTRACT FROM AUTHOR]