[Neuropathic pain as a symptom in autonomic neuropathies and other rare diseases : Small fiber neuropathy: its recognition, diagnosis, and treatment]. / Neuropathische Schmerzen als Symptom bei autonomen Neuropathien und anderen seltenen Erkrankungen : Kleinfaserneuropathie erkennen, diagnostizieren und behandeln.

BACKGROUND: Neuropathic pain is difficult to diagnose and treat. Small fiber neuropathy (SFN) flies under the radar of nerve conduction studies. OBJECTIVES: The importance of a structured patient history and physical examination in the context of neuropathic pain is emphasized. Describing SFN as an important cause, the authors consider rare but partially treatable differential diagnoses. They conclude that autonomic symptoms are frequently associated, often presenting with diverse symptoms. METHODS: A selective literature research to present SFN symptoms as well as differential diagnostic and therapeutic steps in the context of SFN and rare diseases focusing on the autonomic nervous system. RESULTS: Neuropathic pain significantly reduces quality of life. To shorten the time until diagnosis and to initiate therapy, the authors recommend a structured patient history including sensory plus and minus symptoms and non-specific autonomic signs. If the initial search for the cause is not successful, rare causes such as treatable transthyretin (ATTR) amyloidosis and Fabry's disease or autoimmune causes should be considered, particularly in the case of progressive and/or autonomic symptoms. CONCLUSION: The diagnosis and therapy of rare SFN requires interdisciplinary collaboration and, in many cases, a referral to specialized centers to achieve the best patient care.

[Small Fiber Neuropathy with Inadequate Response to Medical Therapy: Diagnosis of The Etiology of Small Fiber Neuropathy and Treatment Option].

Small-fiber neuropathy (SFN) has few significant laboratory findings and is difficult to diagnose. In 70% of the cases, the cause of SFN is unknown. Among the cases with known etiology, 50% are associated with diabetes, and the causes are autoimmune, amyloidosis, or multifactorial. In recent years, a specific autoantibody-positive group has been identified and has attracted attention because immunotherapy was successful in the autoantibody-positive SFN groups. In the cases reporting to our department, abnormalities could not be detected by various tests, including nerve conduction studies, and the response to symptomatic treatment was poor. An abnormality was identified in the current perception threshold test result, and a positive blood anti-plexin D1 antibody was detected via enzyme-linked immunosorbent assay. Therefore, autoimmune SFN was diagnosed, and plasma exchange therapy was remarkably effective. Subsequently, we aim to introduce general treatments for SFN and COVID-19-related SFN.

Peripheral neuropathy in sarcoidosis.

Peripheral nerve disorders in sarcoidosis consist of granulomatous neuropathy and non-granulomatous small fiber neuropathy (SFN), which differ in their underlying pathology, diagnostic methods and treatment. While granulomatous nerve involvement is rare in sarcoidosis, SFN is reported in over 40% of systemic cases. Distal symmetric polyneuropathy and asymmetric polyradiculoneuropathy are the most common presentations of granulomatous neuropathy, which typically responds to corticosteroids. In contrast, SFN is often manifested as non-length dependent pain and paresthesias that may improve with intravenous immune globulin or infliximab. Early recognition and treatment of sarcoidosis neuropathy can lead to improved outcomes and patient quality of life.

Small Fiber Neuropathy.

PURPOSE OF REVIEW: This narrative review aims to summarize advances in the field of small fiber neuropathy made over the last decade, with emphasis on novel research highlighting the distinctive features of SFN. RECENT FINDINGS: While the management of SFNs is ideally aimed at treating the underlying cause, most patients will require pain control via multiple, concurrent therapies. Herein, we highlight the most up-to-date information for diagnosis, medication management, interventional management, and novel therapies on the horizon. Despite the prevalence of small fiber neuropathies, there is no clear consensus on guidelines specific for the treatment of SFN. Despite the lack of specific guidelines for SFN treatment, the most recent general neuropathic pain guidelines are based on Cochrane studies and randomized controlled trials (RCTs) which have individually examined therapies used for the more commonly studied SFNs, such as painful diabetic neuropathy and HIV neuropathy. The recommendations from current guidelines are based on variables such as number needed to treat (NNT), safety, ease of use, and effect on quality of life.

Small fiber neuropathy.

Small fiber neuropathy (SFN) is a peripheral nervous system disease due to affection of A-delta or C-fibers in a proximal, distal, or diffuse distribution. Selective SFN (without large fiber affection) manifests with pain, sensory disturbances, or autonomic dysfunction. Though uniform diagnostic criteria are unavailable, most of them request typical clinical features and reduced intra-epidermal nerve fiber density on proximal or distal skin biopsy. Little consensus has been reached about the treatment of SFN, why this narrative review aims at summarizing and discussing treatment options for SFN. Treatment of SFN can be classified as symptomatic, pathophysiologic, or causal. Prerequisites for treating SFN are an established diagnosis, knowledge about the symptoms and signs, and the etiology. Pain usually responds to oral/intravenous pain killers, antidepressants, anti-seizure drugs, or topical, transdermal specifications. Some of the autonomic disturbances respond favorably to symptomatic treatment. SFN related to Fabry disease or hATTR are accessible to pathogenesis-related therapy. Immune-mediated SFN responds to immunosuppression or immune-modulation. Several of the secondary SFNs respond to causal treatment of the underlying disorder. In conclusion, treatment of SFN relies on a multimodal concept and includes causative, pathophysiologic, and symptomatic measures. It strongly depends on the clinical presentation, diagnosis, and etiology, why it is crucial before initiation of treatment to fix the diagnosis and etiology. Due to the heterogeneous clinical presentation and multi-causality, treatment of SFN should be individualized with the goal of controlling the underlying cause, alleviating pain, and optimizing functionality.

Therapeutic plasma exchange for peripheral neuropathy associated with trisulfated heparan disaccharide IgM antibodies: A case series of 17 patients.

BACKGROUND: Small fiber neuropathy (SFN) can be associated with autoantibodies, including those of IgM class with specificity for the trisulfated heparan disaccharide (TS-HDS) antigen. We hypothesized that, as an IgM autoantibody-mediated disorder, TS-HDS-associated SFN symptoms may be reduced with therapeutic plasma exchange (TPE). STUDY METHODS: This was an observational analysis of all patients referred for TPE from 2018 to 2020 following laboratory confirmation of SFN with TS-HDS autoantibodies; a loading course of 3 to 5 procedures over 2 weeks was completed, with some patients returning for monthly procedures. The following data were collected: demographics, symptoms and duration, TS-HDS levels, skin biopsy results, reported responses to TPE, and TPE-associated adverse events. RESULTS: Of the 17 subjects, 12 (71%) were female and the mean age was 57.5 years (range 27-94). The most common reported symptom was lower extremity paresthesia (88% of subjects). The mean number of TPE procedures completed per subject was 9 (range 3-18), with 71% (12/17) reporting symptomatic improvement or slowed disease progression. About 15% of procedures were associated with an adverse event, with vasovagal reactions being the most common; 53% of patients had at least one adverse event. CONCLUSIONS: Given a reported symptomatic response rate of more than 70%, TPE may be a treatment option for individuals with autoimmune-mediated SFN associated with increased titers of TS-HDS IgM autoantibodies. Since TPE-associated adverse events appear common in this population, close monitoring during procedures is warranted.

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

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

Metabolic syndrome and peripheral neuropathy.

Diabetic peripheral neuropathy and metabolic syndrome (MetS) are both global health challenges with well-established diagnostic criteria and significant impacts on quality of life. Clinical observations, epidemiologic evidence, and animal models of disease have strongly suggested MetS is associated with an elevated risk for cryptogenic sensory peripheral neuropathy (CSPN). MetS neuropathy preferentially affects small unmyelinated axons early in its course, and it may also affect autonomic and large fibers. CSPN risk is linked to MetS and several of its components including obesity, dyslipidemia, and prediabetes. MetS also increases neuropathy risk in patients with established type 1 and type 2 diabetes. In this review we present animal data regarding the role of inflammation and dyslipidemia in MetS neuropathy pathogenesis. Several studies suggest exercise-based lifestyle modification is a promising treatment approach for MetS neuropathy.

Advances in the Management of Small Fiber Neuropathy.

Small fiber neuropathy (SFN) is a prevalent neurologic syndrome. Testing methods have emerged in recent years to better diagnose it, including autonomic tests and skin punch biopsy. SFN can present in a non-length-dependent fashion and can be mistaken for syndromes such as fibromyalgia and complex regional pain syndrome. SFN is caused by a variety of metabolic, infectious, genetic, and inflammatory diseases. Recently treatments have emerged for TTR amyloid neuropathy and Fabry disease, and novel biomarkers have been found both in genetic and inflammatory SFN syndromes. Ongoing trials attempt to establish the efficacy of intravenous immunoglobulin in inflammatory SFN syndromes.

Clinical diagnosis and management of small fiber neuropathy: an update on best practice.

INTRODUCTION: Small fiber neuropathy (SFN) is a heterogeneous group of disorders affecting thin myelinated Aδ and unmyelinated C fibers. Common symptoms include neuropathic pain and autonomic disturbances, and the typical clinical presentation is that of a length-dependent polyneuropathy, although other distributions could be present. AREA COVERED: This review focuses on several aspects of SFN including etiology, clinical presentation, diagnostic criteria and tests, management, and future perspectives. Diagnostic challenges are discussed, encompassing the role of accurate and standardized assessment of symptoms and signs and providing clues for the clinical practice. The authors discuss the evidence in support of skin biopsy and quantitative sensory testing as diagnostic tests and present an overview of other diagnostic techniques to assess sensory and autonomic fibers dysfunction. The authors also suggest a systematic approach to the etiology including a set of laboratory tests and genetic examinations of sodium channelopathies and other rare conditions that might drive the therapeutic approach based on underlying cause or symptoms treatment. EXPERT OPINION: SFN provides a useful model for neuropathic pain whose known mechanisms and cause could pave the way toward personalized treatments.

Neuropatía de fibras pequeñas: una revisión / Small fibre neuropathy: a review

La neuropatía de fibras pequeñas es una afectación del sistema nervioso periférico cuya principal manifestación es un cuadro de dolor neuropático crónico, acompañado generalmente de alteraciones del sistema nervioso autónomo. Esta enfermedad afecta a fibras nerviosas mielinizadas (Adelta) y no mielinizadas (C), de pequeño calibre. Sus causas pueden ser primarias o secundarias a trastornos del metabolismo, infecciones, enfermedades autoinmunes, neurológicas o tóxicos. Los estudios neurofisiológicos habituales suelen ser negativos. El diagnóstico puede realizarse con exploraciones complementarias de difícil acceso desde la atención primaria, como la microneurografía, test con estímulos sensitivos y otras, aunque la prueba más utilizada es la biopsia cutánea. El tratamiento debe dirigirse a las causas y/o a los síntomas neurológicos. Dada la variabilidad de síntomas con los que puede iniciarse, creemos que es importante conocer esta entidad para aumentar la sospecha clínica, orientar el diagnóstico y poder ofrecer la posibilidad de tratamiento

Small fibre neuropathy is a disorder of the peripheral nervous system for which main clinical manifestation is chronic neuropathic pain, often accompanied by alterations of the autonomic nervous system. This disease affects the small diameter myelinated (ADelta) and non-myelinated nerve fibres (C). Its causes are primary or secondary, such as metabolism defects, infection, and autoimmune, neurological or toxic diseases, among others. Routine neurophysiological tests are usually negative. Diagnosis can be made with complementary tests which are difficult to access from Primary Health Care. These include microneurography, and the sensory stimulation test; but the most used technique is the skin biopsy. Treatment is directed at the causes and the neurological symptoms. Due to the variability of symptoms that can be presented, the importance of being aware of this condition is emphasised in order to reach a diagnosis and offer the appropriate treatment

Efficacy of Electrical Stimulation on Nerve Fiber Growth in Small Fiber Neuropathy.

OBJECTIVES: To define whether electrical nerve stimulation (ENS) therapy would promote intraepidermal nerve growth and nerve regeneration in patients with small fiber neuropathy (SFN). METHODS: This was a prospective study conducted on 8 subjects with previously diagnosed SFN. Nerve conduction testing, punch biopsies, and clinical examinations with a calculation of revised total neuropathy score were conducted on subjects before beginning ENS therapy and at 30 and 60 days after the start of ENS therapy. RESULTS: Clinical examination findings and intraepidermal nerve fiber density measurements on day 30 and day 60 did not show statistically significant changes in the treated group compared with the untreated group. CONCLUSIONS: Despite the success of previous animal studies, no meaningful nerve growth and regeneration in SFN was demonstrated with ENS therapy in this study. Studies of larger subject larger populations with longer duration of ENS treatment are warranted to confirm our findings.

Complex syndromes of chronic pain, fatigue and cognitive impairment linked to autoimmune dysautonomia and small fiber neuropathy.

Chronic fatigue syndrome, postural orthostatic tachycardia syndrome, complex regional pain syndrome and silicone implant incompatibility syndrome are a subject of debate among clinicians and researchers. Both the pathogenesis and treatment of these disorders require further study. In this paper we summarize the evidence regarding the role of autoimmunity in these four syndromes with respect to immunogenetics, autoimmune co-morbidities, alteration in immune cell subsets, production of autoantibodies and presentation in animal models. These syndromes could be incorporated in a new concept of autoimmune neurosensory dysautonomia with the common denominators of autoantibodies against G-protein coupled receptors and small fiber neuropathy. Sjogren's syndrome, which is a classical autoimmune disease, could serve as a disease model, illustrating the concept. Development of this concept aims to identify an apparently autoimmune subgroup of the disputable disorders, addressed in the review, which may most benefit from the immunotherapy.

Thromboembolic risk with IVIg: Incidence and risk factors in patients with inflammatory neuropathy.

Our objective was to evaluate whether IV immunoglobulin (IVIg) increases the risk of thromboembolic events in neurology outpatients with inflammatory neuropathies, as there is conflicting evidence supporting this hypothesis, mainly from non-neurologic cohorts. We investigated this question over 30 months in our cohort of patients with inflammatory neuropathies receiving regular IVIg and found a greater incidence of arterial and venous thromboembolic events than population-based rates determined by hospital admissions data. Vascular risk factors were more common in the event group but there were no IVIg administration factors that contributed to the risk. This study suggests that IVIg may have a small but contributory role in determining thromboembolic risk in the inflammatory neuropathy cohort and more evidence is required before it is clear whether the current primary prevention guidelines are appropriate in this group of patients.

Current Diagnosis and Treatment of Painful Small Fiber Neuropathy.

PURPOSE OF REVIEW: Small fiber neuropathy (SFN) could cause significant morbidity due to neuropathic pain and autonomic dysfunction. SFN is underdiagnosed and the knowledge on the condition is limited among general public and health care professionals. This review is intended to enhance the understanding of SFN symptoms, causes, diagnostic tools, and therapeutic options. RECENT FINDINGS: There is evidence of SFN in up to 40% patients with fibromyalgia. The causes of SFN are glucose metabolism defect, dysimmune, gluten sensitivity and celiac disease, monoclonal gammopathy, vitamin deficiencies, toxic agents, cancer, and unknown etiology. Auto-antibodies targeting neuronal antigens trisulfated heparin disaccharide (TS-HDS) and fibroblast growth factor 3 (FGFR3) are found in up to 20% of patients with SFN. Treatment of SFN includes treating the etiology and managing symptoms. SFN should be considered in patients with wide-spread body pain. The search for known causes of SFN is a crucial step in disease management.

Investigating stimulation parameters for preferential small-fiber activation using exponentially rising electrical currents.

Electrical stimulation is widely used in pain research and profiling, but current technologies lack selectivity toward small sensory fibers. Pin electrodes deliver high current density in upper skin layers, and it has been proposed that slowly rising exponential pulses can elevate large-fiber activation threshold and thereby increase preferential small-fiber activation. Optimal stimulation parameters for the combined pin electrode and exponential pulse stimulation have so far not been established, which is the aim of this study. Perception thresholds were compared between pin and patch electrodes using single 1- to 100-ms exponential and rectangular pulses. Stimulus-response functions were evaluated for both pulse shapes delivered as single pulses and pulse trains of 10 Hz using intensities from 0.1 to 20 times perception threshold. Perception thresholds (mA) decreased when duration was increased for both electrodes with rectangular pulses and the pin electrode with exponential pulses. For the patch electrode, perception thresholds for exponential pulses decreased for durations ≤10 ms but increased for durations ≥15 ms, indicating accommodation of large fibers. Stimulus-response curves for single pulses were similar for the two pulse shapes. For pulse trains, the slope of the curve was higher for rectangular pulses. Maximal large-fiber accommodation to exponential pulses was observed for 100-ms pulses, indicating that 100-ms exponential pulses should be applied for preferential small-fiber activation. Intensity of 10 times perception threshold was sufficient to cause maximal pain ratings. The developed methodology may open new opportunities for using electrical stimulation paradigms for small-fiber stimulation and diagnostics.NEW & NOTEWORTHY Selective activation of small cutaneous nerve fibers is pivotal for investigations of the pain system. The present study demonstrated that patch electrode perception thresholds increase with increased duration of exponential currents from 20 to 100 ms. This is likely caused by large-fiber accommodation, which can be utilized to activate small fibers preferentially through small-diameter pin electrodes. This finding may be utilized in studies of fundamental pain mechanisms and, for example, in small-fiber neuropathy.

Biopsy-Proven Small-Fiber Neuropathy in Primary Sjögren's Syndrome: Neuropathic Pain Characteristics, Autoantibody Findings, and Histopathologic Features.

OBJECTIVE: Painful small-fiber neuropathies (SFNs) in primary Sjögren's syndrome (SS) may present as pure or mixed with concurrent large-fiber involvement. SFN can be diagnosed by punch skin biopsy results that identify decreased intra-epidermal nerve-fiber density (IENFD) of unmyelinated nerves. METHODS: We compared 23 consecutively evaluated patients with SS with pure and mixed SFN versus 98 patients without SFN. We distinguished between markers of dorsal root ganglia (DRG) degeneration (decreased IENFD in the proximal thigh versus the distal leg) versus axonal degeneration (decreased IENFD in the distal leg versus the proximal thigh). RESULTS: There were no differences in pain intensity, pain quality, and treatment characteristics in the comparison of 13 patients with pure SFN versus 10 patients with mixed SFN. Ten patients with SFN (approximately 45%) had neuropathic pain preceding sicca symptoms. Opioid analgesics were prescribed to approximately 45% of patients with SFN. When compared to 98 patients without SFN, the 23 patients with SFN had an increased frequency of male sex (30% versus 9%; P < 0.01), a decreased frequency of anti-Ro 52 (P = 0.01) and anti-Ro 60 antibodies (P = 0.01), rheumatoid factor positivity (P < 0.01), and polyclonal gammopathy (P < 0.01). Eleven patients had stocking-and-glove pain, and 12 patients had nonstocking-and-glove pain. Skin biopsy results disclosed patterns of axonal (16 patients) and DRG injury (7 patients). CONCLUSION: SS SFN had an increased frequency among male patients, a decreased frequency of multiple antibodies, frequent treatment with opioid analgesics, and the presence of nonstocking-and-glove pain. Distinguishing between DRG versus axonal injury is significant, especially given that mechanisms targeting the DRG may result in irreversible neuronal cell death. Altogether, these findings highlight clinical, autoantibody, and pathologic features that can help to define mechanisms and treatment strategies.

Autonomic Disorders.

Autonomic complaints are frequently encountered in clinical practice. They can be due to primary autonomic disorders or secondary to other medical conditions. Primary autonomic disorders can be categorized as orthostatic intolerance syndromes and small fiber neuropathies; the latter are associated with autonomic failure, pain, or their combinations. The review outlines orthostatic intolerance syndromes (neurally mediated syncope, orthostatic hypotension, postural tachycardia syndrome, inappropriate sinus tachycardia, orthostatic cerebral hypoperfusion syndrome, and hypocapnic cerebral hypoperfusion) and small fiber neuropathies (sensory/autonomic/mixed, acute/subacute/chronic, idiopathic/secondary, inflammatory and noninflammatory). Several specific autonomic syndromes (diabetic neuropathy, primary hyperhidrosis, paroxysmal sympathetic hyperactivity, autonomic dysreflexia), neurogenic bladder, and gastrointestinal motility disorders are discussed as well.