RARE DISEASE
Idiopathic small fibers neuropathy
Idiopathic small fibers neuropathy
Idiopathic small fibers neuropathy
Synonyms: Idiopathic-SFN
Synonyms: Idiopathic-SFN
Synonyms: Idiopathic-SFN
Drug discovery
94
papers
On emerging therapies
Overview
Idiopathic Small Fiber Neuropathy (iSFN) is a peripheral neuropathy affecting small sensory and autonomic fibers, characterized by burning pain, dysesthesia, and autonomic symptoms (e.g., sweating abnormalities) without identifiable etiology. Diagnosis requires exclusion of secondary causes and confirmation via reduced intraepidermal nerve fiber density on skin biopsy. It predominantly presents in middle-aged adults, with a higher prevalence in women. Management focuses on symptomatic relief and addressing comorbidities.
Burden
Associated with high morbidity: chronic pain (87%), insomnia (86%), and cardiovascular comorbidities (46% myocardial infarction rate) [4][8].
Annual healthcare costs average €3,614 per patient, with reduced quality of life and productivity loss [12].
19% mortality rate post-diagnosis, linked to comorbidities and delayed large-fiber involvement [4][8].
Therapies
First-line: Anticonvulsants (gabapentin, pregabalin), antidepressants (amitriptyline, duloxetine), and topical agents (lidocaine) [3][7][15].
Lifestyle modifications (weight loss, glycemic control) for metabolic risk reduction [6][9].
Limited evidence for immunotherapies (e.g., IVIG) except in autoimmune-associated SFN [5][17].
Categories: rare neurological diseases
Research Papers
94 drug discovery papers about Idiopathic small fibers neuropathy, with 1 first-in-class emerging drug candidate forecasted to outperform the average preclinical success rate. Recent publications:
94 drug discovery papers about Idiopathic small fibers neuropathy, with 1 first-in-class emerging drug candidate forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
antibodies
2025-10-02 | Interferon-induced GTP-binding protein MX1 drives hyperexcitability in peripheral nerves: a novel mechanism in small fiber neuropathy.
Small fiber neuropathy (SFN) affects small-diameter sensory and autonomic nerve fibers, leading to chronic pain and autonomic dysfunction. While SFN can be associated with diabetes and autoimmune diseases, a significant proportion of cases are idiopathic. Although immune-mediated mechanisms are being recognized increasingly in SFN, their precise role remains unclear. This study investigates the presence of autoantibodies against interferon-induced GTP-binding protein MX (MX1) in SFN patients and explores their potential pathogenic role. A total of 59 patients with skin biopsy-confirmed SFN and 20 healthy controls were recruited. Serum samples were analyzed for the presence of anti-MX1 autoantibodies using enzyme-linked immunosorbent assay (ELISA). Immunohistochemistry was performed on rat sciatic nerves to assess the localization of patient IgG to unmyelinated nerve fibers, and immunocytochemistry and flow cytometry confirmed specific binding to MX1. Functional characterization of MX1 was conducted using whole-cell patch-clamp recordings in dorsal root ganglion (DRG) neurons overexpressing MX1. Additionally, protein interactions between MX1 and transient receptor potential cation channel subfamily C member 6 (TRPC6) were assessed using co-immunoprecipitation and surface biotinylation assays. Anti-MX1 autoantibody levels were significantly elevated in SFN patients compared to controls (p = 0.0278), particularly in the autoimmune SFN subgroup. Patient sera exhibited IgG binding to unmyelinated nerve fibers, with idiopathic and autoimmune SFN cases showing similar staining patterns, suggesting a similar immune-mediated mechanism. Immunocytochemistry showed binding to HEK293-MX1 cells and flow cytometry revealed higher MX1/WT fluorescence intensity ratios in patient sera, further confirming specific immune recognition of MX1. Patch-clamp recordings demonstrated that MX1 overexpression in DRG neurons led to significant membrane depolarization and increased action potential firing frequency (p < 0.0001), indicating heightened neuronal excitability. However, MX1 did not directly interact with TRPC6 or alter its function, suggesting an alternative pathway for its effects. The addition of anti-MX1 IgG did not further modify DRG electrophysiology, implying that the autoimmune component may contribute to SFN pathogenesis through indirect mechanisms. Our findings support the hypothesis that MX1 influences neuronal excitability and plays a role in SFN pathophysiology. Future studies should validate these findings in larger cohorts and explore potential therapeutic strategies targeting MX1-associated pathways in SFN.
2024-07-24 | Relapsing-Remitting Immunotherapy Responsive Small-Fiber Neuropathy: Longitudinal Tracking Through 10 Years Including Pregnancies.
To expand understanding of the pathogenesis, presentations, and treatment of initially idiopathic small fiber polyneuropathy (SFN). We longitudinally readministered validated metrics to track disease course and treatment responses in a previously healthy woman with acute, postinfectious, skin biopsy-confirmed, idiopathic SFN. During 5 years, viral respiratory infections triggered 3 separated episodes of acute, disabling burning hand, foot, and face pain (erythromelalgia). The initial 2 resolved with high-dose prednisone, and the third responded to repeated immunoglobulin treatments. Pregnancy with miscarriage triggered a fourth exacerbation refractory to corticosteroids and cyclosporin. Immunoglobulins restored total remission for 2 months; then, 2 rituximab doses slightly improved later flaring. Subsequently, daratumumab initiated 100-day remission later maintained by belimumab, initiated to permit another pregnancy. Remission continued after gestational week 13 all-treatment withdrawal. A week 30 fifth flare responded to plasmapheresis, with healthy birth at week 40. At 11-week postpartum, as symptoms returned, restarting belimumab restored remission maintained during ≥19 months of breastfeeding. This decade of tracking characterizes a relapsing-remitting course of SFN with initially separated monophasic episodes becoming more confluent, as with multiple sclerosis. This tempo and responsiveness to 5 immunotherapies suggest dysimmune causality. Validated metrics helped define the course and track treatment efficacy, particularly during pregnancy and breastfeeding. This is a single observational study without controls. This provides Class IV evidence.
2024-06-13 | The role of antibodies in small fiber neuropathy: a review of currently available evidence.
Small fiber neuropathy (SFN) is a peripheral nerve condition affecting thin myelinated Aδ and unmyelinated C-fibers, characterized by severe neuropathic pain and other sensory and autonomic symptoms. A variety of medical disorders can cause SFN; however, more than 50% of cases are idiopathic (iSFN). Some investigations suggest an autoimmune etiology, backed by evidence of the efficacy of IVIG and plasma exchange. Several studies suggest that autoantibodies directed against nervous system antigens may play a role in the development of neuropathic pain. For instance, patients with CASPR2 and LGI1 antibodies often complain of pain, and in vitro and in vivo studies support their pathogenicity. Other antibodies have been associated with SFN, including those against TS-HDS, FGFR3, and Plexin-D1, and new potential targets have been proposed. Finally, a few studies reported the onset of SFN after COVID-19 infection and vaccination, investigating the presence of potential antibody targets. Despite these overall findings, the pathogenic role has been demonstrated only for some autoantibodies, and the association with specific clinical phenotypes or response to immunotherapy remains to be clarified. The purpose of this review is to summarise known autoantibody targets involved in neuropathic pain, putative attractive autoantibody targets in iSFN patients, their potential as biomarkers of response to immunotherapy and their role in the development of iSFN.
2002-07-08 | Sensory‐predominant, painful, idiopathic neuropathy: Inflammatory changes in sural nerves
Sensory-predominant, painful, idiopathic neuropathies are a common clinical problem. In this retrospective study of 11 patients with such a neuropathy, we found axonal loss in 9, with multifocal axonal loss in 4 patients; there were large perivascular mononuclear inflammatory infiltrates (>50 cells) in 4 and smaller infiltrates (10-20 cells) in 4. These findings suggest that some cases of this neuropathy may be due to autoimmune vasculopathy and therefore may respond to immunotherapy.
1997-04-01 | Indications for an immune-mediated etiology of idiopathic sensory neuronopathy
To investigate immune mechanisms in the etiology of idiopathic sensory neuronopathy (ISN), we studied neurite outgrowth inhibition and antibody binding to neuronal tissue of serum from 4 patients with ISN. Rat dorsal root ganglion (DRG) cells were cultured in the presence of serum from ISN patients and controls. After 48 h of incubation, neurite outgrowth was quantified with a neurofilament ELISA. Serum from ISN patients significantly inhibited DRG neurite outgrowth compared to controls. ISN serum also strongly immunostained fixed cultured and cryostat rat DRG neurons (at dilutions up to 1:10,240), whereas serum from controls did not. Western blots showed unique binding patterns to DRG proteins in 3 ISN patients compared with controls, but a single band corresponding in all ISN patients was not found. The inhibitory effect of ISN serum on neurite outgrowth and the presence of circulating anti-DRG antibodies in the acute phase of the disease supports an immune-mediated pathogenesis of ISN.
small molecules
2024-05-26 | Age-dependent small fiber neuropathy: Mechanistic insights from animal models.
Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions.
2023-10-10 | Resiniferatoxin: Nature’s Precision Medicine to Silence TRPV1-Positive Afferents
Resiniferatoxin (RTX) is an ultrapotent capsaicin analog with a unique spectrum of pharmacological actions. The therapeutic window of RTX is broad, allowing for the full desensitization of pain perception and neurogenic inflammation without causing unacceptable side effects. Intravesical RTX was shown to restore continence in a subset of patients with idiopathic and neurogenic detrusor overactivity. RTX can also ablate sensory neurons as a “molecular scalpel” to achieve permanent analgesia. This targeted (intrathecal or epidural) RTX therapy holds great promise in cancer pain management. Intra-articular RTX is undergoing clinical trials to treat moderate-to-severe knee pain in patients with osteoarthritis. Similar targeted approaches may be useful in the management of post-operative pain or pain associated with severe burn injuries. The current state of this field is reviewed, from preclinical studies through veterinary medicine to clinical trials.
2023-09-27 | Myelin barrier breakdown, mechanical hypersensitivity, and painfulness in polyneuropathy with claudin-12 deficiency.
The blood-nerve and myelin barrier shield peripheral neurons and their axons. These barriers are sealed by tight junction proteins, which control the passage of potentially noxious molecules including proinflammatory cytokines via paracellular pathways. Peripheral nerve barrier breakdown occurs in various neuropathies, such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and traumatic neuropathy. Here, we studied the functional role of the tight junction protein claudin-12 in regulating peripheral nerve barrier integrity and CIDP pathogenesis. Sections from sural nerve biopsies from 23 patients with CIDP and non-inflammatory idiopathic polyneuropathy (PNP) were analyzed for claudin-12 and -19 immunoreactivity. Cldn12-KO mice were generated and subjected to the chronic constriction injury (CCI) model of neuropathy. These mice were then characterized using a battery of barrier and behavioral tests, histology, immunohistochemistry, and mRNA/protein expression. In phenotype rescue experiments, the proinflammatory cytokine TNFα was neutralized with the anti-TNFα antibody etanercept; the peripheral nerve barrier was stabilized with the sonic hedgehog agonist smoothened (SAG). Compared to those without pain, patients with painful neuropathy exhibited reduced claudin-12 expression independently of fiber loss. Accordingly, global Cldn12-KO in male mice, but not fertile female mice, selectively caused mechanical allodynia associated with a leaky myelin barrier, increased TNFα, decreased sonic hedgehog (SHH), and loss of small axons accompanied by reduced peripheral myelin protein 22 (Pmp22). Other barriers and neurological functions remained intact. The Cldn12-KO phenotype could be rescued either by neutralizing TNFα with etanercept or stabilizing the barrier with SAG, which both also upregulated the Schwann cell barrier proteins Cldn19 and Pmp22. These results point to a critical role for claudin-12 in maintaining the myelin barrier presumably via Pmp22 and highlight restoration of the hedgehog pathway as a potential treatment strategy for painful inflammatory neuropathy.
2023-05-05 | Genetic Profiling of Sodium Channels in Diabetic Painful and Painless and Idiopathic Painful and Painless Neuropathies
Neuropathic pain is a frequent feature of diabetic peripheral neuropathy (DPN) and small fiber neuropathy (SFN). Resolving the genetic architecture of these painful neuropathies will lead to better disease management strategies, counselling and intervention. Our aims were to profile ten sodium channel genes (SCG) expressed in a nociceptive pathway in painful and painless DPN and painful and painless SFN patients, and to provide a perspective for clinicians who assess patients with painful peripheral neuropathy. Between June 2014 and September 2016, 1125 patients with painful-DPN (n = 237), painless-DPN (n = 309), painful-SFN (n = 547) and painless-SFN (n = 32), recruited in four different centers, were analyzed for SCN3A, SCN7A-SCN11A and SCN1B-SCN4B variants by single molecule Molecular inversion probes-Next Generation Sequence. Patients were grouped based on phenotype and the presence of SCG variants. Screening of SCN3A, SCN7A-SCN11A, and SCN1B-SCN4B revealed 125 different (potential) pathogenic variants in 194 patients (17.2%, n = 194/1125). A potential pathogenic variant was present in 18.1% (n = 142/784) of painful neuropathy patients vs. 15.2% (n = 52/341) of painless neuropathy patients (17.3% (n = 41/237) for painful-DPN patients, 14.9% (n = 46/309) for painless-DPN patients, 18.5% (n = 101/547) for painful-SFN patients, and 18.8% (n = 6/32) for painless-SFN patients). Of the variants detected, 70% were in SCN7A, SCN9A, SCN10A and SCN11A. The frequency of SCN9A and SCN11A variants was the highest in painful-SFN patients, SCN7A variants in painful-DPN patients, and SCN10A variants in painless-DPN patients. Our findings suggest that rare SCG genetic variants may contribute to the development of painful neuropathy. Genetic profiling and SCG variant identification should aid in a better understanding of the genetic variability in patients with painful and painless neuropathy, and may lead to better risk stratification and the development of more targeted and personalized pain treatments.
2023-04-27 | Efficacy and safety of vixotrigine in idiopathic or diabetes-associated painful small fibre neuropathy (CONVEY): a phase 2 placebo-controlled enriched-enrolment randomised withdrawal study
No pharmacological treatments are specifically indicated for painful small fibre neuropathy (SFN). CONVEY, a phase 2 enriched-enrolment study, evaluated the efficacy and safety of vixotrigine, a voltage- and use-dependent sodium channel blocker, in participants with idiopathic or diabetes-associated painful SFN.CONVEY was a phase 2, multicentre, placebo-controlled, double-blind (DB), enriched-enrolment, randomised withdrawal study. The study was conducted at 68 sites in 13 countries (Europe and Canada) between May 17, 2018, and April 12, 2021. Following a 4-week open-label period in which 265 adults with painful SFN (a mixture of large and small fibre neuropathy was not exclusionary) received oral vixotrigine 350 mg twice daily (BID), 123 participants (with a ≥30% reduction from baseline in average daily pain [ADP] score during the open-label period) were randomised 1:1:1 to receive 200 mg BID, 350 mg BID or placebo for a 12-week double-blind (DB) period. Primary endpoint was change from baseline in ADP at DB Week 12. Secondary endpoints included the proportion of participants with a ≥30% reduction from baseline in ADP and the proportion of Patient Global Impression of Pain (PGIC) responders at DB Week 12. Treatment-emergent adverse events (AEs) were monitored. Statistical significance was set at 0.10 (2-sided). The trial was registered on ClinicalTrials.gov (NCT03339336) and on ClinicalTrialsregister.eu (2017-000991-27).A statistically significant difference from placebo in least squares mean reduction in ADP score from baseline to DB Week 12 was observed with vixotrigine 200 mg BID (-0.85; SE, 0.43; 95% CI, -1.71 to 0.00; p = 0.050) but not 350 mg BID (-0.17; SE, 0.43; 95% CI, -1.01 to 0.68; p = 0.70). Numerically, but not statistically significantly, more participants who received vixotrigine vs placebo experienced a ≥30% ADP reduction from baseline (68.3-72.5% vs 52.5%), and only the 350 mg BID group had significantly more PGIC responders vs placebo (48.8% vs 30.0%; odds ratio = 2.60; 95% CI, 0.97-6.99; p = 0.058) at DB Week 12. AEs were mostly mild to moderate in the vixotrigine groups. The most common AEs (≥5% of vixotrigine-treated participants) in the DB 200 mg BID and 350 mg BID vixotrigine groups were falls, nasopharyngitis, muscle spasm, and urinary tract infection.In our study, vixotrigine 200 mg BID, but not 350 mg BID, met the primary endpoint; more vixotrigine-treated participants experienced a ≥30% reduction from baseline in ADP at DB Week 12. Vixotrigine (at both dosages) was well tolerated in participants with SFN.Biogen, Inc.
proteins
2026-07-09 | Use of Intravenous Immunoglobulin Therapy for Small Fiber Neuropathy: A Systematic Review of Current Clinical Evidence.
Small fiber neuropathy (SFN) is a clinically heterogeneous and difficult-to-manage condition for which intravenous immunoglobulin (IVIG) is increasingly used despite inconsistent evidence and substantial cost. We therefore systematically evaluated the clinical effectiveness of IVIG in SFN, with attention to the variation across etiological subtypes. In accordance with PRISMA 2020 guidelines, the review protocol was registered in PROSPERO (CRD420251247780). PubMed, Embase, and the Cochrane Library databases were searched from inception to 31 August 2025. Eligible studies included adults with clinically or histologically confirmed SFN receiving IVIG, reporting at least one predefined outcome. Two reviewers independently screened and extracted data. Risk of bias was assessed, and certainty of evidence was evaluated using GRADE. Due to heterogeneity, a narrative synthesis was performed. A total of seven studies (2 randomized controlled trials [RCTs], 5 observational studies) involving 165 IVIG-treated patients were included. RCTs in idiopathic or broadly defined SFN showed no significant benefit of IVIG over placebo in pain reduction, autonomic symptoms, quality of life, or intraepidermal nerve fiber density. In contrast, observational studies reported improvements in pain, autonomic function, and, in some cases, nerve fiber density, particularly in autoimmune-associated SFN subtypes. However, these studies were limited by small sample sizes, lack of controls, and high risk of bias. GRADE assessment indicated low to very low certainty of evidence across outcomes. Current evidence does not support routine IVIG use in SFN. Apparent benefits in selected immune-mediated subtypes remain inconclusive and warrant further research with biologically stratified, adequately powered trials.
2025-08-11 | Immunoglobulin Therapy in Patients with Painful Small Fiber Neuropathy: A Systematic Review.
Small fiber neuropathy (SFN) affects pain and autonomic function, and there is increasing evidence that immune pathways are linked to its pathology. Intravenous immunoglobulin (IVIG) has been proposed as a treatment option for patients with painful SFN but has yielded mixed results. This review evaluates the effectiveness of IVIGs in the treatment of painful SFN. According to PRISMA guidelines, a thorough literature search was conducted using five major electronic databases (PubMed, Google Scholar, Scopus, EMBASE, and Web of Science) up to August 17, 2023. Data extraction was performed independently by two reviewers, and quality assessments were performed using Joanna Briggs Institute tools. The PRISMA guidelines ensured the transparency of the review. This systematic review included seven studies to evaluate the effectiveness of IVIG for the treatment of SFN. The review included 458 patients from various studies conducted between 2005 and 2023, covering various neuropathy subtypes such as idiopathic SFN, sarcoidosis-associated SFN, etc. Both double-blind RCTs reported no significant differences between IVIG and placebo in neuropathy severity or pain reduction. Retrospective cohort studies varied in quality and produced mixed results. Of note, some studies showed significant pain reduction with IVIG, while others did not. The effectiveness of IVIG on neuropathy severity and intraepidermal nerve fiber density was similarly variable, with some studies reporting efficacy and others indicate no significant changes. Overall, IVIG showed potential benefits, but the results were inconsistent across studies. IVIG shows potential efficacy in select SFN subtypes, particularly autoimmuneassociated forms (e.g., TS-HDS/FGFR-3 positive), with some retrospective studies reporting pain and functional improvements. However, two high-quality RCTs found no significant benefit over placebo. Marked heterogeneity in study design, IVIG protocols, diagnostic criteria, and outcome measures limits comparability and generalizability. Adverse events, including infusion reactions were common. These findings highlight IVIG's possible role in immunologically mediated SFN but underscore the need for standardized protocols, biomarker-based patient selection, and large, wellcontrolled trials to establish definitive efficacy. Some evidence suggests the potential benefit of IVIG therapy for certain subgroups of patients with SFN. However, the overall effectiveness is still unclear, and further studies are needed.
2023-12-30 | Small fiber neuropathy with normal intra-epidermal nerve fiber density but reduced sweat gland density after third BNT162b2 shot
Small fiber neuropathy (SFN) has not been reported after the third dose of BNT162b2 in a previously healthy vaccinee. A 44-year-old previously healthy female developed pain and sensory disturbances in varying locations after the third BNT162b2 dose. Additionally, she developed recurrent tinnitus, headaches, arthralgia, neck stiffness, and motor dysfunction. A skin biopsy five months after symptom onset revealed normal intra-epidermal nerve fiber density (IENFD) but reduced sweat gland nerve fiber density. She is intended for a first series of intravenous immunoglobulins. SARS-CoV-2 vaccinations may be complicated by SFN; the diagnosis SARS-CoV-2 vaccination SFN may be delayed; IENFD may be normal, but sweat gland nerve fiber density may document SFN; and full recovery after SFN cannot always be achieved quickly.
2023-09-20 | A role for pathogenic autoantibodies in small fiber neuropathy?
The immune system has a role in neuropathic pain which includes autoimmune mechanisms (e.g., autoantibodies). Clinical studies have identified a number of conditions where neuropathic pain is common and that are associated with autoantibodies targeting antigens within the nervous system. Interestingly sensory symptoms can be relieved with immunotherapies or plasma exchange, suggesting that pain in these patients is antibody-mediated. Recent preclinical studies have directly addressed this. For example, passive transfer of CASPR2 autoantibodies from patients cause increased pain sensitivity and enhanced sensory neuron excitability in mice confirming pathogenicity and demonstrating that patient autoantibodies are a mechanism to cause neuropathic pain. Small fiber neuropathy (SFN) exclusively affects small sensory fibers (typically nociceptors) and is characterized by severe neuropathic pain. Known causes include diabetes, B12 deficiency and rare variants in sodium channel genes, although around 50% of cases are idiopathic. SFN is associated with autoimmune conditions such as Sjorgen’s syndrome, Sarcoidosis and Celiac disease and immunotherapy in the form of Intravenous immunoglobulin (IVIG) has proved an effective treatment. Autoantibodies have been identified and, in some cases, passive transfer of SFN patient IgG in mice can recapitulate neuropathic pain-like behavior. Here we will discuss clinical and preclinical data relating to the idea that pathogenic autoantibodies contribute to SNF. We discuss putative pathogenic antibodies, cellular targets and the molecular mechanisms by which they cause sensory neuron damage and the development of neuropathic pain. Finally, we will comment on future directions which may provide further insights into the mechanisms underlying SFN in patients.
2023-02-16 | Small fiber polyneuropathy: A new therapeutic target in patients with interstitial cystitis/bladder pain syndrome?
Interstitial cystitis/bladder pain syndrome (IC/BPS) is a debilitating chronic disease that, based on the variable efficacy observed with most therapeutic options, is difficult to treat effectively. A more targeted patient selection process for current and emerging therapeutic options would likely help to improve outcomes. This narrative review explores small fiber polyneuropathy (SFPN) in IC/BPS as part of a larger widespread pain phenotype and as a potential therapeutic target. Because SFPN is becoming increasingly implicated in polysyndromic pain disorders (e.g., IC/BPS, chronic pelvic pain, and fibromyalgia) in which immune dysregulation is a suspected pathophysiologic etiology, continued consideration should be given to immunomodulatory therapies such as intravenous immunoglobulin (IVIg). Moreover, since the small fibers affected in SFPN continue to grow even as people age, targeted treatment may prevent further destruction and provide long-term benefits as the fibers are given time to repair. In addition to therapeutic potential, having a definitive SFPN diagnosis may provide psychological benefit in a patient population for which symptoms have historically been attributed to negative psychological factors. Finally, based on emerging data in this area, we propose consideration be given to include SFPN testing in the work-up of patients with IC/BPS that are refractory to treatments or have multiple comorbid pain syndromes since it may be an indicator of the need for alternative therapies. We believe that SFPN will play an increasingly larger role in the clinical evaluation and management of polysyndromic pain disorders, including IC/BPS.
antibodies
2025-10-02 | Interferon-induced GTP-binding protein MX1 drives hyperexcitability in peripheral nerves: a novel mechanism in small fiber neuropathy.
Small fiber neuropathy (SFN) affects small-diameter sensory and autonomic nerve fibers, leading to chronic pain and autonomic dysfunction. While SFN can be associated with diabetes and autoimmune diseases, a significant proportion of cases are idiopathic. Although immune-mediated mechanisms are being recognized increasingly in SFN, their precise role remains unclear. This study investigates the presence of autoantibodies against interferon-induced GTP-binding protein MX (MX1) in SFN patients and explores their potential pathogenic role. A total of 59 patients with skin biopsy-confirmed SFN and 20 healthy controls were recruited. Serum samples were analyzed for the presence of anti-MX1 autoantibodies using enzyme-linked immunosorbent assay (ELISA). Immunohistochemistry was performed on rat sciatic nerves to assess the localization of patient IgG to unmyelinated nerve fibers, and immunocytochemistry and flow cytometry confirmed specific binding to MX1. Functional characterization of MX1 was conducted using whole-cell patch-clamp recordings in dorsal root ganglion (DRG) neurons overexpressing MX1. Additionally, protein interactions between MX1 and transient receptor potential cation channel subfamily C member 6 (TRPC6) were assessed using co-immunoprecipitation and surface biotinylation assays. Anti-MX1 autoantibody levels were significantly elevated in SFN patients compared to controls (p = 0.0278), particularly in the autoimmune SFN subgroup. Patient sera exhibited IgG binding to unmyelinated nerve fibers, with idiopathic and autoimmune SFN cases showing similar staining patterns, suggesting a similar immune-mediated mechanism. Immunocytochemistry showed binding to HEK293-MX1 cells and flow cytometry revealed higher MX1/WT fluorescence intensity ratios in patient sera, further confirming specific immune recognition of MX1. Patch-clamp recordings demonstrated that MX1 overexpression in DRG neurons led to significant membrane depolarization and increased action potential firing frequency (p < 0.0001), indicating heightened neuronal excitability. However, MX1 did not directly interact with TRPC6 or alter its function, suggesting an alternative pathway for its effects. The addition of anti-MX1 IgG did not further modify DRG electrophysiology, implying that the autoimmune component may contribute to SFN pathogenesis through indirect mechanisms. Our findings support the hypothesis that MX1 influences neuronal excitability and plays a role in SFN pathophysiology. Future studies should validate these findings in larger cohorts and explore potential therapeutic strategies targeting MX1-associated pathways in SFN.
2024-07-24 | Relapsing-Remitting Immunotherapy Responsive Small-Fiber Neuropathy: Longitudinal Tracking Through 10 Years Including Pregnancies.
To expand understanding of the pathogenesis, presentations, and treatment of initially idiopathic small fiber polyneuropathy (SFN). We longitudinally readministered validated metrics to track disease course and treatment responses in a previously healthy woman with acute, postinfectious, skin biopsy-confirmed, idiopathic SFN. During 5 years, viral respiratory infections triggered 3 separated episodes of acute, disabling burning hand, foot, and face pain (erythromelalgia). The initial 2 resolved with high-dose prednisone, and the third responded to repeated immunoglobulin treatments. Pregnancy with miscarriage triggered a fourth exacerbation refractory to corticosteroids and cyclosporin. Immunoglobulins restored total remission for 2 months; then, 2 rituximab doses slightly improved later flaring. Subsequently, daratumumab initiated 100-day remission later maintained by belimumab, initiated to permit another pregnancy. Remission continued after gestational week 13 all-treatment withdrawal. A week 30 fifth flare responded to plasmapheresis, with healthy birth at week 40. At 11-week postpartum, as symptoms returned, restarting belimumab restored remission maintained during ≥19 months of breastfeeding. This decade of tracking characterizes a relapsing-remitting course of SFN with initially separated monophasic episodes becoming more confluent, as with multiple sclerosis. This tempo and responsiveness to 5 immunotherapies suggest dysimmune causality. Validated metrics helped define the course and track treatment efficacy, particularly during pregnancy and breastfeeding. This is a single observational study without controls. This provides Class IV evidence.
2024-06-13 | The role of antibodies in small fiber neuropathy: a review of currently available evidence.
Small fiber neuropathy (SFN) is a peripheral nerve condition affecting thin myelinated Aδ and unmyelinated C-fibers, characterized by severe neuropathic pain and other sensory and autonomic symptoms. A variety of medical disorders can cause SFN; however, more than 50% of cases are idiopathic (iSFN). Some investigations suggest an autoimmune etiology, backed by evidence of the efficacy of IVIG and plasma exchange. Several studies suggest that autoantibodies directed against nervous system antigens may play a role in the development of neuropathic pain. For instance, patients with CASPR2 and LGI1 antibodies often complain of pain, and in vitro and in vivo studies support their pathogenicity. Other antibodies have been associated with SFN, including those against TS-HDS, FGFR3, and Plexin-D1, and new potential targets have been proposed. Finally, a few studies reported the onset of SFN after COVID-19 infection and vaccination, investigating the presence of potential antibody targets. Despite these overall findings, the pathogenic role has been demonstrated only for some autoantibodies, and the association with specific clinical phenotypes or response to immunotherapy remains to be clarified. The purpose of this review is to summarise known autoantibody targets involved in neuropathic pain, putative attractive autoantibody targets in iSFN patients, their potential as biomarkers of response to immunotherapy and their role in the development of iSFN.
2002-07-08 | Sensory‐predominant, painful, idiopathic neuropathy: Inflammatory changes in sural nerves
Sensory-predominant, painful, idiopathic neuropathies are a common clinical problem. In this retrospective study of 11 patients with such a neuropathy, we found axonal loss in 9, with multifocal axonal loss in 4 patients; there were large perivascular mononuclear inflammatory infiltrates (>50 cells) in 4 and smaller infiltrates (10-20 cells) in 4. These findings suggest that some cases of this neuropathy may be due to autoimmune vasculopathy and therefore may respond to immunotherapy.
1997-04-01 | Indications for an immune-mediated etiology of idiopathic sensory neuronopathy
To investigate immune mechanisms in the etiology of idiopathic sensory neuronopathy (ISN), we studied neurite outgrowth inhibition and antibody binding to neuronal tissue of serum from 4 patients with ISN. Rat dorsal root ganglion (DRG) cells were cultured in the presence of serum from ISN patients and controls. After 48 h of incubation, neurite outgrowth was quantified with a neurofilament ELISA. Serum from ISN patients significantly inhibited DRG neurite outgrowth compared to controls. ISN serum also strongly immunostained fixed cultured and cryostat rat DRG neurons (at dilutions up to 1:10,240), whereas serum from controls did not. Western blots showed unique binding patterns to DRG proteins in 3 ISN patients compared with controls, but a single band corresponding in all ISN patients was not found. The inhibitory effect of ISN serum on neurite outgrowth and the presence of circulating anti-DRG antibodies in the acute phase of the disease supports an immune-mediated pathogenesis of ISN.
small molecules
2024-05-26 | Age-dependent small fiber neuropathy: Mechanistic insights from animal models.
Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions.
2023-10-10 | Resiniferatoxin: Nature’s Precision Medicine to Silence TRPV1-Positive Afferents
Resiniferatoxin (RTX) is an ultrapotent capsaicin analog with a unique spectrum of pharmacological actions. The therapeutic window of RTX is broad, allowing for the full desensitization of pain perception and neurogenic inflammation without causing unacceptable side effects. Intravesical RTX was shown to restore continence in a subset of patients with idiopathic and neurogenic detrusor overactivity. RTX can also ablate sensory neurons as a “molecular scalpel” to achieve permanent analgesia. This targeted (intrathecal or epidural) RTX therapy holds great promise in cancer pain management. Intra-articular RTX is undergoing clinical trials to treat moderate-to-severe knee pain in patients with osteoarthritis. Similar targeted approaches may be useful in the management of post-operative pain or pain associated with severe burn injuries. The current state of this field is reviewed, from preclinical studies through veterinary medicine to clinical trials.
2023-09-27 | Myelin barrier breakdown, mechanical hypersensitivity, and painfulness in polyneuropathy with claudin-12 deficiency.
The blood-nerve and myelin barrier shield peripheral neurons and their axons. These barriers are sealed by tight junction proteins, which control the passage of potentially noxious molecules including proinflammatory cytokines via paracellular pathways. Peripheral nerve barrier breakdown occurs in various neuropathies, such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and traumatic neuropathy. Here, we studied the functional role of the tight junction protein claudin-12 in regulating peripheral nerve barrier integrity and CIDP pathogenesis. Sections from sural nerve biopsies from 23 patients with CIDP and non-inflammatory idiopathic polyneuropathy (PNP) were analyzed for claudin-12 and -19 immunoreactivity. Cldn12-KO mice were generated and subjected to the chronic constriction injury (CCI) model of neuropathy. These mice were then characterized using a battery of barrier and behavioral tests, histology, immunohistochemistry, and mRNA/protein expression. In phenotype rescue experiments, the proinflammatory cytokine TNFα was neutralized with the anti-TNFα antibody etanercept; the peripheral nerve barrier was stabilized with the sonic hedgehog agonist smoothened (SAG). Compared to those without pain, patients with painful neuropathy exhibited reduced claudin-12 expression independently of fiber loss. Accordingly, global Cldn12-KO in male mice, but not fertile female mice, selectively caused mechanical allodynia associated with a leaky myelin barrier, increased TNFα, decreased sonic hedgehog (SHH), and loss of small axons accompanied by reduced peripheral myelin protein 22 (Pmp22). Other barriers and neurological functions remained intact. The Cldn12-KO phenotype could be rescued either by neutralizing TNFα with etanercept or stabilizing the barrier with SAG, which both also upregulated the Schwann cell barrier proteins Cldn19 and Pmp22. These results point to a critical role for claudin-12 in maintaining the myelin barrier presumably via Pmp22 and highlight restoration of the hedgehog pathway as a potential treatment strategy for painful inflammatory neuropathy.
2023-05-05 | Genetic Profiling of Sodium Channels in Diabetic Painful and Painless and Idiopathic Painful and Painless Neuropathies
Neuropathic pain is a frequent feature of diabetic peripheral neuropathy (DPN) and small fiber neuropathy (SFN). Resolving the genetic architecture of these painful neuropathies will lead to better disease management strategies, counselling and intervention. Our aims were to profile ten sodium channel genes (SCG) expressed in a nociceptive pathway in painful and painless DPN and painful and painless SFN patients, and to provide a perspective for clinicians who assess patients with painful peripheral neuropathy. Between June 2014 and September 2016, 1125 patients with painful-DPN (n = 237), painless-DPN (n = 309), painful-SFN (n = 547) and painless-SFN (n = 32), recruited in four different centers, were analyzed for SCN3A, SCN7A-SCN11A and SCN1B-SCN4B variants by single molecule Molecular inversion probes-Next Generation Sequence. Patients were grouped based on phenotype and the presence of SCG variants. Screening of SCN3A, SCN7A-SCN11A, and SCN1B-SCN4B revealed 125 different (potential) pathogenic variants in 194 patients (17.2%, n = 194/1125). A potential pathogenic variant was present in 18.1% (n = 142/784) of painful neuropathy patients vs. 15.2% (n = 52/341) of painless neuropathy patients (17.3% (n = 41/237) for painful-DPN patients, 14.9% (n = 46/309) for painless-DPN patients, 18.5% (n = 101/547) for painful-SFN patients, and 18.8% (n = 6/32) for painless-SFN patients). Of the variants detected, 70% were in SCN7A, SCN9A, SCN10A and SCN11A. The frequency of SCN9A and SCN11A variants was the highest in painful-SFN patients, SCN7A variants in painful-DPN patients, and SCN10A variants in painless-DPN patients. Our findings suggest that rare SCG genetic variants may contribute to the development of painful neuropathy. Genetic profiling and SCG variant identification should aid in a better understanding of the genetic variability in patients with painful and painless neuropathy, and may lead to better risk stratification and the development of more targeted and personalized pain treatments.
2023-04-27 | Efficacy and safety of vixotrigine in idiopathic or diabetes-associated painful small fibre neuropathy (CONVEY): a phase 2 placebo-controlled enriched-enrolment randomised withdrawal study
No pharmacological treatments are specifically indicated for painful small fibre neuropathy (SFN). CONVEY, a phase 2 enriched-enrolment study, evaluated the efficacy and safety of vixotrigine, a voltage- and use-dependent sodium channel blocker, in participants with idiopathic or diabetes-associated painful SFN.CONVEY was a phase 2, multicentre, placebo-controlled, double-blind (DB), enriched-enrolment, randomised withdrawal study. The study was conducted at 68 sites in 13 countries (Europe and Canada) between May 17, 2018, and April 12, 2021. Following a 4-week open-label period in which 265 adults with painful SFN (a mixture of large and small fibre neuropathy was not exclusionary) received oral vixotrigine 350 mg twice daily (BID), 123 participants (with a ≥30% reduction from baseline in average daily pain [ADP] score during the open-label period) were randomised 1:1:1 to receive 200 mg BID, 350 mg BID or placebo for a 12-week double-blind (DB) period. Primary endpoint was change from baseline in ADP at DB Week 12. Secondary endpoints included the proportion of participants with a ≥30% reduction from baseline in ADP and the proportion of Patient Global Impression of Pain (PGIC) responders at DB Week 12. Treatment-emergent adverse events (AEs) were monitored. Statistical significance was set at 0.10 (2-sided). The trial was registered on ClinicalTrials.gov (NCT03339336) and on ClinicalTrialsregister.eu (2017-000991-27).A statistically significant difference from placebo in least squares mean reduction in ADP score from baseline to DB Week 12 was observed with vixotrigine 200 mg BID (-0.85; SE, 0.43; 95% CI, -1.71 to 0.00; p = 0.050) but not 350 mg BID (-0.17; SE, 0.43; 95% CI, -1.01 to 0.68; p = 0.70). Numerically, but not statistically significantly, more participants who received vixotrigine vs placebo experienced a ≥30% ADP reduction from baseline (68.3-72.5% vs 52.5%), and only the 350 mg BID group had significantly more PGIC responders vs placebo (48.8% vs 30.0%; odds ratio = 2.60; 95% CI, 0.97-6.99; p = 0.058) at DB Week 12. AEs were mostly mild to moderate in the vixotrigine groups. The most common AEs (≥5% of vixotrigine-treated participants) in the DB 200 mg BID and 350 mg BID vixotrigine groups were falls, nasopharyngitis, muscle spasm, and urinary tract infection.In our study, vixotrigine 200 mg BID, but not 350 mg BID, met the primary endpoint; more vixotrigine-treated participants experienced a ≥30% reduction from baseline in ADP at DB Week 12. Vixotrigine (at both dosages) was well tolerated in participants with SFN.Biogen, Inc.
proteins
2026-07-09 | Use of Intravenous Immunoglobulin Therapy for Small Fiber Neuropathy: A Systematic Review of Current Clinical Evidence.
Small fiber neuropathy (SFN) is a clinically heterogeneous and difficult-to-manage condition for which intravenous immunoglobulin (IVIG) is increasingly used despite inconsistent evidence and substantial cost. We therefore systematically evaluated the clinical effectiveness of IVIG in SFN, with attention to the variation across etiological subtypes. In accordance with PRISMA 2020 guidelines, the review protocol was registered in PROSPERO (CRD420251247780). PubMed, Embase, and the Cochrane Library databases were searched from inception to 31 August 2025. Eligible studies included adults with clinically or histologically confirmed SFN receiving IVIG, reporting at least one predefined outcome. Two reviewers independently screened and extracted data. Risk of bias was assessed, and certainty of evidence was evaluated using GRADE. Due to heterogeneity, a narrative synthesis was performed. A total of seven studies (2 randomized controlled trials [RCTs], 5 observational studies) involving 165 IVIG-treated patients were included. RCTs in idiopathic or broadly defined SFN showed no significant benefit of IVIG over placebo in pain reduction, autonomic symptoms, quality of life, or intraepidermal nerve fiber density. In contrast, observational studies reported improvements in pain, autonomic function, and, in some cases, nerve fiber density, particularly in autoimmune-associated SFN subtypes. However, these studies were limited by small sample sizes, lack of controls, and high risk of bias. GRADE assessment indicated low to very low certainty of evidence across outcomes. Current evidence does not support routine IVIG use in SFN. Apparent benefits in selected immune-mediated subtypes remain inconclusive and warrant further research with biologically stratified, adequately powered trials.
2025-08-11 | Immunoglobulin Therapy in Patients with Painful Small Fiber Neuropathy: A Systematic Review.
Small fiber neuropathy (SFN) affects pain and autonomic function, and there is increasing evidence that immune pathways are linked to its pathology. Intravenous immunoglobulin (IVIG) has been proposed as a treatment option for patients with painful SFN but has yielded mixed results. This review evaluates the effectiveness of IVIGs in the treatment of painful SFN. According to PRISMA guidelines, a thorough literature search was conducted using five major electronic databases (PubMed, Google Scholar, Scopus, EMBASE, and Web of Science) up to August 17, 2023. Data extraction was performed independently by two reviewers, and quality assessments were performed using Joanna Briggs Institute tools. The PRISMA guidelines ensured the transparency of the review. This systematic review included seven studies to evaluate the effectiveness of IVIG for the treatment of SFN. The review included 458 patients from various studies conducted between 2005 and 2023, covering various neuropathy subtypes such as idiopathic SFN, sarcoidosis-associated SFN, etc. Both double-blind RCTs reported no significant differences between IVIG and placebo in neuropathy severity or pain reduction. Retrospective cohort studies varied in quality and produced mixed results. Of note, some studies showed significant pain reduction with IVIG, while others did not. The effectiveness of IVIG on neuropathy severity and intraepidermal nerve fiber density was similarly variable, with some studies reporting efficacy and others indicate no significant changes. Overall, IVIG showed potential benefits, but the results were inconsistent across studies. IVIG shows potential efficacy in select SFN subtypes, particularly autoimmuneassociated forms (e.g., TS-HDS/FGFR-3 positive), with some retrospective studies reporting pain and functional improvements. However, two high-quality RCTs found no significant benefit over placebo. Marked heterogeneity in study design, IVIG protocols, diagnostic criteria, and outcome measures limits comparability and generalizability. Adverse events, including infusion reactions were common. These findings highlight IVIG's possible role in immunologically mediated SFN but underscore the need for standardized protocols, biomarker-based patient selection, and large, wellcontrolled trials to establish definitive efficacy. Some evidence suggests the potential benefit of IVIG therapy for certain subgroups of patients with SFN. However, the overall effectiveness is still unclear, and further studies are needed.
2023-12-30 | Small fiber neuropathy with normal intra-epidermal nerve fiber density but reduced sweat gland density after third BNT162b2 shot
Small fiber neuropathy (SFN) has not been reported after the third dose of BNT162b2 in a previously healthy vaccinee. A 44-year-old previously healthy female developed pain and sensory disturbances in varying locations after the third BNT162b2 dose. Additionally, she developed recurrent tinnitus, headaches, arthralgia, neck stiffness, and motor dysfunction. A skin biopsy five months after symptom onset revealed normal intra-epidermal nerve fiber density (IENFD) but reduced sweat gland nerve fiber density. She is intended for a first series of intravenous immunoglobulins. SARS-CoV-2 vaccinations may be complicated by SFN; the diagnosis SARS-CoV-2 vaccination SFN may be delayed; IENFD may be normal, but sweat gland nerve fiber density may document SFN; and full recovery after SFN cannot always be achieved quickly.
2023-09-20 | A role for pathogenic autoantibodies in small fiber neuropathy?
The immune system has a role in neuropathic pain which includes autoimmune mechanisms (e.g., autoantibodies). Clinical studies have identified a number of conditions where neuropathic pain is common and that are associated with autoantibodies targeting antigens within the nervous system. Interestingly sensory symptoms can be relieved with immunotherapies or plasma exchange, suggesting that pain in these patients is antibody-mediated. Recent preclinical studies have directly addressed this. For example, passive transfer of CASPR2 autoantibodies from patients cause increased pain sensitivity and enhanced sensory neuron excitability in mice confirming pathogenicity and demonstrating that patient autoantibodies are a mechanism to cause neuropathic pain. Small fiber neuropathy (SFN) exclusively affects small sensory fibers (typically nociceptors) and is characterized by severe neuropathic pain. Known causes include diabetes, B12 deficiency and rare variants in sodium channel genes, although around 50% of cases are idiopathic. SFN is associated with autoimmune conditions such as Sjorgen’s syndrome, Sarcoidosis and Celiac disease and immunotherapy in the form of Intravenous immunoglobulin (IVIG) has proved an effective treatment. Autoantibodies have been identified and, in some cases, passive transfer of SFN patient IgG in mice can recapitulate neuropathic pain-like behavior. Here we will discuss clinical and preclinical data relating to the idea that pathogenic autoantibodies contribute to SNF. We discuss putative pathogenic antibodies, cellular targets and the molecular mechanisms by which they cause sensory neuron damage and the development of neuropathic pain. Finally, we will comment on future directions which may provide further insights into the mechanisms underlying SFN in patients.
2023-02-16 | Small fiber polyneuropathy: A new therapeutic target in patients with interstitial cystitis/bladder pain syndrome?
Interstitial cystitis/bladder pain syndrome (IC/BPS) is a debilitating chronic disease that, based on the variable efficacy observed with most therapeutic options, is difficult to treat effectively. A more targeted patient selection process for current and emerging therapeutic options would likely help to improve outcomes. This narrative review explores small fiber polyneuropathy (SFPN) in IC/BPS as part of a larger widespread pain phenotype and as a potential therapeutic target. Because SFPN is becoming increasingly implicated in polysyndromic pain disorders (e.g., IC/BPS, chronic pelvic pain, and fibromyalgia) in which immune dysregulation is a suspected pathophysiologic etiology, continued consideration should be given to immunomodulatory therapies such as intravenous immunoglobulin (IVIg). Moreover, since the small fibers affected in SFPN continue to grow even as people age, targeted treatment may prevent further destruction and provide long-term benefits as the fibers are given time to repair. In addition to therapeutic potential, having a definitive SFPN diagnosis may provide psychological benefit in a patient population for which symptoms have historically been attributed to negative psychological factors. Finally, based on emerging data in this area, we propose consideration be given to include SFPN testing in the work-up of patients with IC/BPS that are refractory to treatments or have multiple comorbid pain syndromes since it may be an indicator of the need for alternative therapies. We believe that SFPN will play an increasingly larger role in the clinical evaluation and management of polysyndromic pain disorders, including IC/BPS.
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