Utility of skin biopsy to evaluate peripheral neuropathy

Effectiveness of IVIG on Non-Length-Dependent Skin Biopsies in Small Fiber Neuropathy With Plexin D1, Trisulfated Heparin Disaccharide, and Fibroblast Growth Factor Receptor 3 Autoantibodies

OBJECTIVES

To demonstrate treatment efficacy on composite and non-length-dependent (NLD) punch biopsy specimens from intravenous immunoglobulin (IVIG) in pure small-fiber neuropathy (SFN) with trisulfated heparin disaccharide (TS-HDS), fibroblast growth factor-3 (FGFR-3), or Plexin D1 antibodies. SFN has an increasing prevalence, and over 30% of cases may be immune-mediated. TS-HDS, FGFR-3, and Plexin D1 autoantibodies have been shown to be present in 44%-55% of cryptogenic SFN cases, suggesting an immune mechanism. Reports have shown IVIG to be effective for this condition, but some controversy exists based on length-dependent (LD) post-IVIG treatment data in a recent trial.

METHODS

In a retrospective review, all pure SFN cases tested for the 3 antibodies from January 2021 to May 2022 were tabulated, and patients who underwent IVIG treatment were separated and analyzed for changes in epidermal nerve fiber density (ENFD) on skin biopsy, as well as SFN-specific questionnaire and pain scores.

RESULTS

Ninety-one patients with pure SFN had antibody testing. Sixty of these (66%) were seropositive, and 31 (34%) were seronegative. Seventeen seropositive patients (13 female patients, 4 male patients, 6 FGFR-3, 2 TS-HDS, 4 Plexin D1, 2 with all 3 antibodies, 1 with FGFR-3 and Plexin D1, 1 with FGFR-3 and TS-HDS, and 1 with TS-HDS and Plexin D1) underwent IVIG treatment. Of these, 2 patients stopped treatment due to side effects, and the remaining 15 completed at least 6 months of IVIG. Of these, 12 had a post-IVIG skin biopsy, and of these, 11 (92%) had a 55.1% improved mean composite ENFD (P = 0.01). NLD-ENFD specimens improved by 42.3% (P = 0.02), and LD-ENFD specimens improved by 99.7% (P = 0.01). Composite ENFD in Plexin D1-SFN patients improved by 139% (P = 0.04). In addition, 14 patients had questionnaires pre-IVIG/post-IVIG, and average pain decreased by 2.7 (P = 0.002).

CONCLUSIONS

IVIG shows disease-modifying effect in immune SFN with novel antibodies, especially Plexin D1-SFN, as well as significantly improved pain. NLD-ENFD should be examined as well as LD-ENFD to see this effect. Further randomized controlled trials looking at NLD-ENFD as well as LD-ENFD improvement, along with pain and SFN-specific questionnaires, are needed to confirm these findings.

Expanding the genetic causes of small-fiber neuropathy: SCN genes and beyond

Small-fiber neuropathy (SFN) is a disorder that exclusively affects the small nerve fibers, sparing the large nerve fibers. Thinly myelinated Aδ-fibers and unmyelinated C-fibers are damaged, leading to development of neuropathic pain, thermal dysfunction, sensory symptoms, and autonomic disturbances. Although many SFNs are secondary and due to immunological causes or metabolic disturbances, the etiology is unknown in up to half of the patients. Over the years, this proportion of "idiopathic SFN" has decreased, as familial and genetic causes have been discovered, thus shifting a proportion of once "idiopathic" cases to the genetic category. After the discovery of SCN9A-gene variants in 2012, SCN10A and SCN11A variants have been found to be pathogenic in SFN. With improved accessibility of SFN diagnostic tools and genetic tests, many non-SCN variants and genetically inherited systemic diseases involving the small nerve fibers have also been described, but only scattered throughout the literature. There are 80 SCN variants described as causing SFN, 8 genes causing hereditary sensory autonomic neuropathies (HSAN) described with pure SFN, and at least 7 genes involved in genetically inherited systemic diseases associated with SFN. This systematic review aims to consolidate and provide an updated overview on the genetic variants of SFN to date---SCN genes and beyond. Awareness of these genetic causes of SFN is imperative for providing treatment directions, prognostication, and management of expectations for patients and their health-care providers.

Immune-Mediated Small Fiber Neuropathy With Trisulfated Heparin Disaccharide, Fibroblast Growth Factor Receptor 3, or Plexin D1 Antibodies: Presentation and Treatment With Intravenous Immunoglobulin

OBJECTIVES

Up to 50% of small fiber neuropathy (SFN) cases are idiopathic, but novel antibodies to Trisulfated Heparin Disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR-3) have been implicated in half of these cases; the role of anti-Plexin D1 is less clear. We aimed to clarify presentation and management of these patients.

METHODS

An 18-month retrospective analysis revealed 54 cases of cryptogenic SFN who had testing for the 3 autoantibodies. Demographics, clinical features, epidermal nerve fiber density, and Quantitative Sudomotor Axon Reflex Test results were analyzed. Intravenous immunoglobulin (IVIG) treatment response was assessed.

RESULTS

In total, 44.4% of patients had antibodies (62.5% TS-HDS, 29.2% FGFR-3, and 20.8% Plexin D1). Male patients were more likely to be FGFR-3 positive (P = 0.014). Facial involvement was more common in seropositive patients (P = 0.034), and patients with a higher Utah Early Neuropathy Scale score had a higher TS-HDS titer (P = 0.0469), but other clinical features were not significantly different. Seropositive patients trended toward a higher SFN screening list score (P = 0.16), abnormal Quantitative Sudomotor Axon Reflex Test (P = 0.052), and prior erroneous diagnosis (P = 0.19). In patients who completed IVIG, examinations and questionnaires improved and mean epidermal nerve fiber density increased by 297%.

CONCLUSIONS

TS-HDS, FGFR-3, and Plexin D1 antibodies are present in a high proportion of cryptogenic SFN cases with more facial involvement, and greater disease severity is associated with higher antibody titers. They are often misdiagnosed but may respond subjectively and objectively to IVIG.

Clinical Features and Treatment Response in Immune-Mediated Small Fiber Neuropathy with Trisulfated Heparin Disaccharide or Fibroblast Growth Factor Receptor 3 Antibodies

OBJECTIVE

Novel antibodies to trisulfated heparin disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR-3) have been recently described in otherwise cryptogenic small fiber neuropathy (SFN) cases. Our goal was to further describe clinical features in such cases and to analyze treatment responses.

METHODS

In a retrospective analysis, 40 cases of cryptogenic SFN in a university neuropathy clinic were identified. Of these, TS-HDS and FGFR-3 cases were identified, and clinical features and treatment responses were analyzed.

RESULTS

In this cohort, 95% were women, and 55% had either TS-HDS or FGFR-3 antibodies (77% of these had TS-HDS). Of the seropositive group, 41% had a nonlength dependent epidermal nerve fiber density on skin punch biopsy (OR = 1.80). In the seropositive group, 82% had neuropathic pain as their primary symptom (OR = 1.73). Also 32% of seropositive patients reported widespread pain (OR = 1.63). 63% of seropositive cases presented acutely (OR = 11.0). In the seropositive group, 23% had an initial erroneous diagnosis (OR = 1.47). Eight seropositive patients improved on intravenous immunoglobulin treatment, with a 42% reduction in pain scores (P = 0.02), a 44% reduction in the Utah Neuropathy Score, and improved epidermal nerve fiber density post-treatment.

CONCLUSIONS

TS-HDS and FGFR-3 antibodies may be present in a high proportion of cryptogenic SFN cases with acute onset, nonlength dependent pathology, and primary neuropathic and widespread pain. They are often misdiagnosed as other conditions including fibromyalgia. These cases may be responsive to immune treatment, especially with intravenous immunoglobulin.

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.

Sensory Polyneuropathies

PURPOSE OF REVIEW

This article describes the methods of diagnosis and management of the sensory-predominant polyneuropathies. To simplify the approach to this category of patients, sensory-predominant polyneuropathies are divided broadly into either small fiber (or pain-predominant) neuropathies and large fiber (or ataxia-predominant) neuropathies, of which the sensory neuronopathies (dorsal root ganglionopathies) are highlighted.

RECENT FINDINGS

Physicians can now easily perform skin biopsies in their offices, allowing access to the gold standard pathologic diagnostic tool for small fiber neuropathies. Additional diagnostic techniques, such as corneal confocal microscopy, are emerging. Recently, small fiber neuropathies have been associated with a broader spectrum of diseases, including fibromyalgia, sodium channel mutations, and voltage-gated potassium channel antibody autoimmune disease.

SUMMARY

Despite advances in diagnosing small fiber neuropathies and sensory neuronopathies, many of these neuropathies remain refractory to treatment. In select cases, early identification and treatment may result in better outcomes. "Idiopathic" should be a diagnosis of exclusion and a thorough investigation for treatable causes pursued.

The Role and Importance of Small Fiber Neuropathy in Fibromyalgia Pain

Serious investigators of fibromyalgia (FM) realize the profound implications of finding features of small fiber neuropathy (SFN) in this disorder. For the first time, an easily reproducible and generally agreed upon, peripheral tissue lesion has been reported from multiple investigative centers. Understanding how this discovery relates to other features of FM, and how one might utilize it to better comprehend, and care for, afflicted patients' painful complaints remains a challenge, however. In this article we review how the SFN seen in FM may be placed in context, and suggest how such a tissue abnormality might be used to better understand the pathophysiology of FM, and plan for its effective treatment. We also suggest how finding SFN in FM implies the need for continued focused research within the area of neuropathic disease in FM.

Clinical approach to peripheral neuropathy: anatomic localization and diagnostic testing

PURPOSE OF REVIEW

This article provides a clinical approach to peripheral neuropathy based on anatomic localization and diagnostic testing.

RECENT FINDINGS

Advances have been made in the evaluation of small fiber neuropathy and in the known genetic causes of neuropathy.

SUMMARY

History and physical examination remain the most useful tools for evaluating peripheral neuropathy. Characterization of a neuropathy aids in limiting the differential diagnosis and includes consideration of temporal profile (tempo of onset and duration), heredity, and anatomic classification. Anatomic classification involves (1) fiber type (motor versus sensory, large versus small, somatic versus autonomic), (2) portion of fiber affected (axon versus myelin), and (3) gross distribution of nerves affected (eg, length-dependent, length-independent, multifocal). Diagnostic testing may include serologic and CSF evaluation, electrodiagnosis, skin biopsy, quantitative sensory testing, autonomic testing, nerve biopsy, confocal corneal microscopy, and laser Doppler imager flare.

Prediabetic neuropathy: does it exist?

It is now increasingly being appreciated that a substantial proportion of subjects with prediabetes may exhibit peripheral neuropathy and/or neuropathic pain. The reverse is also true, inasmuch as examining patients with idiopathic peripheral neuropathy will frequently reveal prediabetes. In the general population, the prevalence of neuropathy in prediabetes is intermediate between overt diabetes and subjects with normoglycemia. This prediabetic neuropathy is, generally, milder in comparison to diabetic neuropathy and mainly affects small fibers mediating sensory function. Hyperglycemia, microangiopathy, dyslipidemia and the metabolic syndrome have been implicated as pathogenic mechanisms. In practice, therapy of prediabetic neuropathy should be addressed towards normoglycemia and correction of cardiovascular risk factors. However, additional work is needed to establish the long-term results of this approach.

Sarcoidosis and small-fiber neuropathy

Chronic pain is one of the most commonly reported symptoms among sarcoidosis patients. Not only does it significantly affect quality of life, but it also is a source of frustration for both the patient and physician because the etiology for pain often is unknown. Although patients typically complain of neuropathic-type pain, nerve conduction studies and other conventional diagnostic procedures frequently fail to reveal objective evidence of neurologic disease. However, in recent years, the growing use of specialized tests such as skin biopsy and sudomotor testing has helped to establish the diagnosis of small-fiber neuropathy as the cause of pain in these patients via objective and quantifiable means. Management of sarcoidosis small-fiber neuropathy should consist of target-directed treatment of the underlying disease and appropriate symptomatic therapy.

Neuropathy in prediabetes: does the clock start ticking early?

Between 25% and 62% of patients with idiopathic peripheral neuropathy are reported to have prediabetes, and among individuals with prediabetes 11-25% are thought to have peripheral neuropathy, and 13-21% have neuropathic pain. Population-based studies suggest a gradient for the prevalence of neuropathy, being highest in patients with manifest diabetes mellitus, followed by individuals with impaired glucose tolerance then impaired fasting glucose and least in those with normoglycemia. The most sensitive test to assess glucose metabolism status is the oral glucose tolerance test. Pathogenesis involves hyperglycemia, microvascular abnormalities, dyslipidemia and the metabolic syndrome. Individuals with prediabetes have less severe neuropathy than those with manifest diabetes mellitus. Sensory modalities are more frequently affected than motor modalities, but impairment of small nerve fibers could be the earliest detectable sign. Diagnosis should rely on careful clinical examination, with emphasis on the evaluation of small fibers. An oral glucose tolerance test should be performed in patients with idiopathic neuropathy. The only treatment with any efficacy is lifestyle modification to improve control of hyperglycemia and cardiovascular risk factors, but long-term efficacy of this approach has not been established. This Review summarizes the current evidence on the association between prediabetes and neuropathy.