Causes of neuropathy in patients referred as “idiopathic neuropathy”

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.

A Patient With Charcot-Marie-Tooth Disease Type 4C (CMT4C) Presenting With Muscle Fasciculations and Motor Neuropathy

We report an unusual patient who, at age 47 years, had presented with complaints of muscle fasciculations. After neurological examination and electromyogram testing, he was diagnosed with motor neuropathy. Over the next 10 years, in addition to fasciculations, he developed numbness in his feet without any other symptoms. His current neurological examination at age 57 years was normal, except for mildly decreased light touch in the anterior portion of both feet. The nerve conduction studies performed repeatedly showed sensorimotor polyneuropathy with demyelination features. Blood tests, including anti-ganglioside antibodies, were normal. Genetic testing revealed two rare variants in trans in the SH3 domain and tetratricopeptide repeats 2gene, c.3413 G>A p.(S1138N) and c.3269 C>G p.(A1090G). Protein modeling suggests that these are disease-producing mutations and likely the cause of the neuropathy of our patient. Our study expands the clinical and genetic spectrum of patients with Charcot-Marie-Tooth disease type 4C.

Initial validation of the Mass. General Neuropathy Exam Tool (MAGNET) for evaluation of distal small-fiber neuropathy

INTRODUCTION/AIMS

Diagnosis of small-fiber neuropathy (SFN) is hampered by its subjective symptoms and signs. Confirmatory testing is insufficiently available and expensive, so predictive examinations have value. However, few support the 2020 SFN consensus-case-definition requirements or were validated for non-diabetes neuropathies. Thus we developed the Massachusetts General Hospital Neuropathy Exam Tool (MAGNET) and measured diagnostic performance in 160 symptomatic patients evaluated for length-dependent SFN from any cause and 37 healthy volunteers.

METHODS

We compared prevalences of abnormalities (vital signs, pupil responses, lower-limb appearance, pin, light touch, vibration and position sensitivity, great-toe strength, muscle stretch reflexes), and validated diagnostic performance against objective SFN tests: lower-leg skin-biopsy epidermal neurite densities and autonomic function testing (AFT). Sensitivity/specificity, feasibility, test-retest and inter-rater reliability, and convergence with the Utah Early Neuropathy Scale were calculated.

RESULTS

Patients' ages averaged 48.5 ± 14.7 years and 70.6% were female. Causes of neuropathy varied, remaining unknown in 59.5%. Among the 46 with abnormal skin biopsies, the most prevalent abnormality was reduced pin sharpness at the toes (71.7%). Inter-rater reliability, test-retest reliability, and convergent validity excelled (range = 91.3-95.6%). Receiver operating characteristics comparing all symptomatic patients versus healthy controls indicated that a MAGNET threshold score of 14 maximized predictive accuracy for skin biopsies (0.74) and a 30 cut-off maximized accuracy for predicting AFT (0.60). Analyzing patients with any abnormal neuropathy-test results identified areas-under-the-curves of 0.87-0.89 for predicting a diagnostic result, accuracy = 0.80-0.89, and Youden's index = 0.62. Overall, MAGNET was 80%-85% accurate for stratifying patients with abnormal versus normal neuropathy test results.

DISCUSSION

MAGNET quickly generates research-quality metrics during clinical examinations.

Approach to diagnosis, evaluation, and treatment of generalized and nonlocal dysesthesia: A review

Dysesthesia is an abnormal sensation in the skin that occurs in the absence of any extraordinary stimulus or other primary cutaneous disorders, excluding any delusions or tactile hallucinations. Clinicians have characterized dysesthesias to include sensations such as burning, tingling, pruritus, allodynia, hyperesthesia, or anesthesia. The etiology and pathogenesis of various generalized dysesthesias is largely unknown, though many dysesthesias have been associated with systemic pathologies including malignancy, infection, autoimmune disorders, and neuropathies. Dermatologists are often the first-line clinicians for patients presenting with such cutaneous findings, thus it is crucial for these physicians to be able to methodically work-up generalized dysesthesias to build a working differential diagnosis, follow up with key labs and/or imaging, and offer patients evidence-based treatment to relieve their symptoms. This broad literature review is an attempt to centralize key studies, cases, and series to help guide dermatologists in their assessment and evaluation of complaints of abnormal cutaneous sensations.

Neuropathy in prediabetes

Diabetic neuropathies are the most frequent complications of diabetes, contributing to high morbidity, excess mortality, reduced quality of life, and increased healthcare costs. Prediabetes is characterised by glucose levels within an intermediate range above normoglycaemia yet below the diagnostic threshold for diabetes. In 2021, 10.6% and 6.2% of adults worldwide were estimated to have impaired glucose tolerance and impaired fasting glucose, respectively, the majority of whom are unaware of having prediabetes. Evidence has accumulated suggesting that prediabetes is a predictor of cardiovascular disease (CVD) and increased mortality. The past 2 decades have witnessed an extensive debate, particularly among diabetologists and neurologists, as to whether prediabetes is associated with peripheral neuropathy. In this review, we elaborate on the current evidence, particularly from population-based studies supporting an increased risk of distal sensorimotor polyneuropathy (DSPN) and cardiovascular autonomic neuropathy (CAN) in people with prediabetes. Moreover, we discuss whether lifestyle interventions showing efficacy in preventing or delaying the transition from prediabetes to diabetes in persons with prediabetes may also exert favourable effects on the development and progression of DSPN and CAN. This review should help in raising the awareness of and translating the current knowledge on neuropathies in people with prediabetes into clinical practice and public health. The current recommendation that adults who are overweight or obese should be screened for prediabetes and referred to or offered preventive interventions should ultimately culminate in preventing not only CVD but also prediabetic neuropathy.

Localization and Diagnostic Evaluation of Peripheral Nerve Disorders

OBJECTIVE

This article provides a framework for the initial evaluation of patients with suspected peripheral nerve disease. The key clinical elements of peripheral nerve diseases can help the practicing neurologist differentiate among peripheral neuropathies with similar presentations.

LATEST DEVELOPMENTS

The wide range of peripheral nerve diseases with similar clinical presentations can pose a diagnostic challenge. The large array of available testing modalities (including imaging and electrodiagnostic, autonomic, laboratory, biopsy, and genetic testing) further complicates clinical decision making. Recent developments (eg, discovery of new autoantibodies, genetic variations, and histopathologic techniques) across the peripheral neuropathy spectrum have resulted in an increased need to evaluate patients logically and with a tailored diagnostic approach.

ESSENTIAL POINTS

A careful approach that focuses on key clinical elements combined with an understanding of purposeful diagnostic testing can lead to a successful diagnosis of peripheral nerve diseases.

Gadolinium contrast agents: dermal deposits and potential effects on epidermal small nerve fibers

Small fiber neuropathy (SFN) affects unmyelinated and thinly myelinated nerve fibers causing neuropathic pain with distal distribution and autonomic symptoms. In idiopathic SFN (iSFN), 30% of the cases, the underlying aetiology remains unknown. Gadolinium (Gd)-based contrast agents (GBCA) are widely used in magnetic resonance imaging (MRI). However, side-effects including musculoskeletal disorders and burning skin sensations were reported. We investigated if dermal Gd deposits are more prevalent in iSFN patients exposed to GBCAs, and if dermal nerve fiber density and clinical parameters are likewise affected. 28 patients (19 females) with confirmed or no GBCA exposure were recruited in three German neuromuscular centers. ISFN was confirmed by clinical, neurophysiological, laboratory and genetic investigations. Six volunteers (two females) served as controls. Distal leg skin biopsies were obtained according to European recommendations. In these samples Gd was quantified by elemental bioimaging and intraepidermal nerve fibers (IENF) density via immunofluorescence analysis. Pain phenotyping was performed in all patients, quantitative sensory testing (QST) only in a subset (15 patients; 54%). All patients reported neuropathic pain, described as burning (n = 17), jabbing (n = 16) and hot (n = 11) and five QST scores were significantly altered. Compared to an equal distribution significantly more patients reported GBCA exposures (82%), while 18% confirmed no exposures. Compared to unexposed patients/controls significantly increased Gd deposits and lower z-scores of the IENF density were confirmed in exposed patients. QST scores and pain characteristics were not affected. This study suggests that GBCA exposure might alter IENF density in iSFN patients. Our results pave the road for further studies investigating the possible role of GBCA in small fiber damage, but more investigations and larger samples are needed to draw firm conclusions.

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.

RFC1 repeat expansions and cerebellar ataxia, neuropathy and vestibular areflexia syndrome: Experience and perspectives from a neuromuscular disorders unit

INTRODUCTION

Pathogenic expansions in RFC1 have been described as a cause of a spectrum of disorders including late-onset ataxia, chronic cough, and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). Sensory neuronopathy/neuropathy appears to be a major symptom of RFC1-disorder, and RFC1 expansions are common in patients with sensory chronic idiopathic axonal neuropathy or sensory ganglionopathy. We aimed to investigate RFC1 expansions in patients with suspected RFC1-related disease followed-up in a Neuromuscular Diseases Unit, with a particular interest in the involvement of the peripheral nervous system.

METHODS

We recruited twenty consecutive patients based on the presence of at least two of the following features: progressive ataxia, sensory neuropathy/neuronopathy, vestibulopathy and chronic cough. Medical records were retrospectively reviewed for a detailed clinical description. More extensive phenotyping of the RFC1-positive patients and clinical comparison between RFC1 positive and negative patients were performed.

RESULTS

Biallelic AAGGG repeat expansions were identified in 13 patients (65%). The most frequent symptoms were chronic cough and sensory disturbances in the lower extremities (12/13). Only 4 patients (31%) had complete CANVAS. The phenotypes were sensory ataxia and sensory symptoms in extremities in 4/13; sensory ataxia, sensory symptoms, and vestibulopathy in 3/13; sensory symptoms plus chronic cough in 2/13. Chronic cough and isolated sensory neuronopathy were significantly more prevalent in RFC1-positive patients.

CONCLUSION

Pathogenic RFC1 expansions are a common cause of sensory neuropathy/neuronopathy and should be considered in the approach to these patients. Identification of key symptoms or detailed interpretation of nerve conduction studies may improve patient selection for genetic testing.

Observational case-control study of small-fiber neuropathies, with regards on smoking and vitamin D deficiency and other possible causes

Introduction

Small fiber neuropathies (SFNs) are disorders of skin nerve endings inducing pruritus, burning pain, numbness, and paresthesia. The aims of this study were to search for putative etiologies of SFN and their occurrence in a cohort of patients and to compare patients with SFN to a group of patients without SFN to highlight potential factors associated with SFN.

Methods

This study was observational, retrospective, and monocentric. All patients with symptoms of SFN who underwent skin biopsies with intraepidermal nerve density counts were included. Patients with a count lower than 5 percentiles were considered to be in the SFN group. Other patients were considered to be the control group.

Results

A total of 162 patients with SFN and 161 controls were included. No cause was identified for 108 patients (61.7%). The established causes were autoimmune diseases (9.1%), diabetes or glucose intolerance (8%), medication (4%), liver disease (3.4%), and monoclonal gammopathy of undetermined significance (2.9%). Current or former smokers were more numerous in the SFN group (26.5%) than in the control group (16.1%), while vitamin D amounts were significantly lower in the SFN group than in the control group.

Discussion

Hence, tobacco smoking and vitamin D deficiency might be new putative causes of SFN.

Ultrasound of peripheral nerves distinguishes inherited sensory neuronopathy of cerebellar ataxia with neuropathy and vestibular areflexia syndrome from inherited axonopathy

Introduction/Aims Recent studies have shown that ultrasound of peripheral nerves can distinguish inherited sensory neuronopathy from acquired axonopathy with a high degree of accuracy. In this study we aimed to determine whether ultrasound can also distinguish inherited sensory neuronopathy from inherited axonopathy. Methods We compared the ultrasound cross-sectional areas (CSAs) of the median, ulnar, sural, and tibial nerves of retrospectively recruited patients with cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS), in whom sensory neuronopathy is a cardinal feature, with Charcot-Marie-Tooth type 2 (CMT2) disease patients, who have an inherited axonopathy, using the Kruskal-Wallis test and receiver-operating characteristic curves. Results There were 17 patients with CANVAS and 18 with CMT2. The upper limb nerve CSAs were significantly smaller in CANVAS than in CMT2 (P < .001), with the CSAs of the median nerve at mid-forearm and ulnar nerve at mid-arm being a third or less the size of those of the CMT2 patients. Nerve ultrasound reliably distinguished CANVAS from CMT2 with ROC areas under the curve between 0.97 and 0.99. The lower limb CSAs of the two patient groups were not significantly different. Discussion Ultrasound of the upper limb nerves distinguishes CANVAS sensory neuronopathy from inherited axonopathy with high accuracy and can therefore be proposed as a reliable additional tool in the investigation of these diseases.

Profile of neurological disorders in a tertiary center of education in orthopedics

BACKGROUND

Neurological conditions can cause secondary orthopedic disorders and can result from orthopedic surgical procedures. In addition, misdiagnosis and overtreatment involve both specialties. Epidemiological studies of neurological patients in tertiary units are often performed in emergency departments of general hospitals or rehabilitation centers.

OBJECTIVE

Describe the clinical and epidemiologic profile of neurological disorders in a Brazilian federal tertiary center and education hospital in orthopedics in Rio de Janeiro.

METHODS

We performed a retrospective study of the medical records of patients attended by neurology specialists of the internal medicine's department of the National Institute of Traumatology and Orthopedics from February 2014 to March 2020.

RESULTS

We reviewed neurological referrals in the medical records of 1,349 patients in the period. The mean age of patients was 49.67 years (standard deviation [SD] ± 18.99). There was a predominance of females, corresponding to 751 (55.7%) patients. Regarding ethnicity, 684 (50.7%) participants were white, 550 (40.8%) non-white, and 115 (8.5%) non-classified. Peripheral neuropathies (34.1%), osteoarticular diseases (10%), epilepsy (8.3%), developmental disorders (7.9%), and neuromuscular diseases (7.3%) were the 5 groups with the largest numbers of cases.

CONCLUSION

The sample consisted mostly of females and white individuals, and approximately one third of the cases were of peripheral neuropathies. Epidemiological studies in neurology from tertiary centers of another medical specialty can improve the professional development of both specialties. This interdisciplinary approach can also optimize resources, help avoid misdiagnosis, and reduce disability.

Monoclonal gammopathies of clinical significance (MGCS): In pursuit of optimal treatment

Monoclonal gammopathy of clinical significance (MGCS) represents a new clinical entity referring to a myriad of pathological conditions associated with the monoclonal gammopathy of undetermined significance (MGUS). The establishment of MGCS expands our current understanding of the pathophysiology of a range of diseases, in which the M protein is often found. Aside from the kidney, the three main organ systems most affected by monoclonal gammopathy include the peripheral nervous system, skin, and eye. The optimal management of these MGUS-related conditions is not known yet due to the paucity of clinical data, the rarity of some syndromes, and limited awareness among healthcare professionals. Currently, two main treatment approaches exist. The first one resembles the now-established therapeutic strategy for monoclonal gammopathy of renal significance (MGRS), in which chemotherapy with anti-myeloma agents is used to target clonal lesion that is thought to be the culprit of the complex clinical presentation. The second approach includes various systemic immunomodulatory or immunosuppressive options, including intravenous immunoglobulins, corticosteroids, or biological agents. Although some conditions of the MGCS spectrum can be effectively managed with therapies aiming at the etiology or pathogenesis of the disease, evidence regarding other pathologies is severely limited to individual patient data from case reports or series. Future research should pursue filling the gap in knowledge and finding the optimal treatment for this novel clinical category.

Medikamentös-induzierte Polyneuropathien jenseits von Chemotherapeutika und Antiinfektiva

Zahlreiche in der klinischen Routine eingesetzte Wirkstoffe jenseits von Chemotherapeutika und Antiinfektiva können eine Polyneuropathie verstärken oder hervorrufen. Kenntnis darüber, welche Medikamente mit Polyneuropathien assoziiert sind sowie über Risikofaktoren seitens der Patienten können die Häufigkeit reduzieren. Bei entsprechendem Risiko sollten alternative Präparate eingesetzt oder die Indikation zur Therapie generell überdacht werden.

Corneal Confocal Microscopy in the Diagnosis of Small Fiber Neuropathy: Faster, Easier, and More Efficient Than Skin Biopsy?

Chronic pain may affect 30–50% of the world’s population and an important cause is small fiber neuropathy (SFN). Recent research suggests that autoimmune diseases may be one of the most common causes of small nerve fiber damage. There is low awareness of SFN among patients and clinicians and it is difficult to diagnose as routine electrophysiological methods only detect large fiber abnormalities, and specialized small fiber tests, like skin biopsy and quantitative sensory testing, are not routinely available. Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible method for quantifying small nerve fiber degeneration and regeneration, and could be an important tool for diagnosing SFN. This review considers the advantages and disadvantages of CCM and highlights the evolution of this technique from a research tool to a diagnostic test for small fiber damage, which can be a valuable contribution to the study and management of autoimmune disease.

Approach to Neuropathic Pain

Neuropathic pain is a common chief complaint encountered by neurologists and primary care providers. It is caused by disorders involving the somatosensory nervous system. The clinical evaluation of neuropathic pain is challenging and requires a multifaceted systematic approach with an emphasis on a thorough history and physical examination to identify characteristic signs and symptoms. Ancillary laboratory investigations, targeted imaging, and electrodiagnostic studies further help identify underlying etiologies to guide specific treatments. Management of neuropathic pain encompasses treating the underlying pathology as well as symptomatic control with nonpharmacological, pharmacological, and interventional therapies. Here, we present an approach to help evaluate patients with neuropathic pain.

Evidence in peroneal nerve entrapment: A scoping review

BACKGROUND AND PURPOSE

Daily management of patients with foot drop due to peroneal nerve entrapment varies between a purely conservative treatment and early surgery, with no high-quality evidence to guide current practice. Electrodiagnostic (EDX) prognostic features and the value of imaging in establishing and supplementing the diagnosis have not been clearly established.

METHODS

We performed a literature search in the online databases MEDLINE, Embase, and the Cochrane Library. Of the 42 unique articles meeting the eligibility criteria, 10 discussed diagnostic performance of imaging, 11 reported EDX limits for abnormal values and/or the value of EDX in prognostication, and 26 focused on treatment outcome.

RESULTS

Studies report high sensitivity and specificity of both ultrasound (varying respectively from 47.1% to 91% and from 53% to 100%) and magnetic resonance imaging (MRI; varying respectively from 31% to 100% and from 73% to 100%). One comparative trial favoured ultrasound over MRI. Variable criteria for a conduction block (>20%-≥50) were reported. A motor conduction block and any baseline compound motor action potential response were identified as predictors of good outcome. Based predominantly on case series, the percentage of patients with good outcome ranged 0%-100% after conservative treatment and 40%-100% after neurolysis. No study compared both treatments.

CONCLUSIONS

Ultrasound and MRI have good accuracy, and introducing imaging in the standard diagnostic workup should be considered. Further research should focus on the role of EDX in prognostication. No recommendation on the optimal treatment strategy of peroneal nerve entrapment can be made, warranting future randomized controlled trials.

Safety and efficacy of alpha-lipoic acid oral supplementation in the reduction of pain with unknown etiology: A monocentric, randomized, double-blind, placebo-controlled clinical trial

INTRODUCTION

Extensive evidence suggests that alpha-lipoic acid (ALA) is effective in diabetic neuropathy pain management. However, little is known on its safety and efficacy in reducing idiopathic pain in normoglycemic subjects. The aim of this study was to evaluate ALA food supplement safety and efficacy in the reduction of different forms of idiopathic pain.

METHODS

Two-hundred and ten normoglycemic adults suffering from idiopathic pain (i.e. 57 subjects with primitive neuropathic pain, 141 subjects with arthralgia with unknown etiology, and 12 subjects with idiopathic myalgia) were randomized to receive placebo, 400 mg/day, or 800 mg/day of ALA. Participants underwent two visits (at baseline = t0, and after 2 months = t1) in which two validated questionaries for pain (numerical rating scale [NRS] and visual analogue scale [VAS]) were collected; fasting blood glucose assessment, adverse effects, and renal and hepatic toxicity were also monitored.

RESULTS

At t1, none of subjects treated with ALA reported a decreased glycemia or adverse effects. The treated subjects showed a significant reduction in NRS (p < 0.001) while the placebo group did not show any NRS reduction (p = 0.86). Similar results were also obtained for VAS. Statistical analysis aimed at detecting possible differences in NRS and VAS scores among treatment groups based on the source of pain did not reveal any significant effect.

CONCLUSIONS

Since the management of idiopathic pain is challenging for physicians, the use of ALA food supplements could be a feasible option, based on its safety and efficacy compared to commonly-used analgesic drugs.

Clinical Outcomes of Foot Infections in Patients Without Diabetes

The aim of this study was to report clinical outcomes of moderate and severe foot infections in patients without diabetes. Medical records of 88 nondiabetic patients with foot infections treated at a safety net hospital were retrospectively reviewed. Patients were grouped by the presence of soft-tissue infection (STI) or osteomyelitis (OM). The diagnosis of OM was determined by positive bone culture or histopathology. STIs were defined by negative bone biopsy or negative imaging with magnetic resonance imaging or computed tomography/dual-modality radiolabeled white blood cell single-photon emission computed tomography. Patient outcomes were recorded ≤1 year after admission. Eighty-eight nondiabetic patients admitted to our institution for moderate or severe foot infections were included, 45 OM and 43 STI. No differences were noted in patient characteristics except that OM patients had a higher prevalence of neuropathy (66.7% versus 39.5%, p = .02). OM patients required surgery more often (97.8% versus 67.4%, p < .01), a greater number of surgeries (2.0 ± 1.2 versus 1.4 ± 1.3, p = .02), and more amputations (75.6% versus 11.6%, p < .01) than STI patients. OM patients had a higher proportion of wounds that healed (82.2% versus 62.8%, p = .04). There were no significant differences in reinfection (35.6% versus 25.6%, p = .36), foot-related readmission to hospital (35.6% versus 23.3%, p = .25), or total duration of antibiotics (13.9 ± 10.2 versus 13.5 ± 12.9, p = .87) between OM and STI patients. In conclusion, OM patients required more surgeries and amputations than patients with STIs; however, they had similar rates of reinfection and readmission within a year after the index hospitalization.

RFC1 expansions are a common cause of idiopathic sensory neuropathy

After extensive evaluation, one-third of patients affected by polyneuropathy remain undiagnosed and are labelled as having chronic idiopathic axonal polyneuropathy, which refers to a sensory or sensory-motor, axonal, slowly progressive neuropathy of unknown origin. Since a sensory neuropathy/neuronopathy is identified in all patients with genetically confirmed RFC1 cerebellar ataxia, neuropathy, vestibular areflexia syndrome, we speculated that RFC1 expansions could underlie a fraction of idiopathic sensory neuropathies also diagnosed as chronic idiopathic axonal polyneuropathy. We retrospectively identified 225 patients diagnosed with chronic idiopathic axonal polyneuropathy (125 sensory neuropathy, 100 sensory-motor neuropathy) from our general neuropathy clinics in Italy and the UK. All patients underwent full neurological evaluation and a blood sample was collected for RFC1 testing. Biallelic RFC1 expansions were identified in 43 patients (34%) with sensory neuropathy and in none with sensory-motor neuropathy. Forty-two per cent of RFC1-positive patients had isolated sensory neuropathy or sensory neuropathy with chronic cough, while vestibular and/or cerebellar involvement, often subclinical, were identified at examination in 58%. Although the sensory ganglia are the primary pathological target of the disease, the sensory impairment was typically worse distally and symmetric, while gait and limb ataxia were absent in two-thirds of the cases. Sensory amplitudes were either globally absent (26%) or reduced in a length-dependent (30%) or non-length dependent pattern (44%). A quarter of RFC1-positive patients had previously received an alternative diagnosis, including Sjögren's syndrome, sensory chronic inflammatory demyelinating polyneuropathy and paraneoplastic neuropathy, while three cases had been treated with immune therapies.

Vitamin B-6-Induced Neuropathy: Exploring the Mechanisms of Pyridoxine Toxicity

Vitamin B-6 in the form of pyridoxine (PN) is commonly used by the general population. The use of PN-containing supplements has gained lots of attention over the past years as they have been related to the development of peripheral neuropathy. In light of this, the number of reported cases of adverse health effects due to the use of vitamin B-6 have increased. Despite a long history of study, the pathogenic mechanisms associated with PN toxicity remain elusive. Therefore, the present review is focused on investigating the mechanistic link between PN supplementation and sensory peripheral neuropathy. Excessive PN intake induces neuropathy through the preferential injury of sensory neurons. Recent reports on hereditary neuropathy due to pyridoxal kinase (PDXK) mutations may provide some insight into the mechanism, as genetic deficiencies in PDXK lead to the development of axonal sensory neuropathy. High circulating concentrations of PN may lead to a similar condition via the inhibition of PDXK. The mechanism behind PDXK-induced neuropathy is unknown; however, there is reason to believe that it may be related to γ-aminobutyric acid (GABA) neurotransmission. Compounds that inhibit PDXK lead to convulsions and reductions in GABA biosynthesis. The absence of central nervous system-related symptoms in PDXK deficiency could be due to differences in the regulation of PDXK, where PDXK activity is preserved in the brain but not in peripheral tissues. As PN is relatively impermeable to the blood-brain barrier, PDXK inhibition would similarly be confined to the peripheries and, as a result, GABA signaling may be perturbed within peripheral tissues, such as sensory neurons. Perturbed GABA signaling within sensory neurons may lead to excitotoxicity, neurodegeneration, and ultimately, the development of peripheral neuropathy. For several reasons, we conclude that PDXK inhibition and consequently disrupted GABA neurotransmission is the most plausible mechanism of toxicity.

Current View of Diagnosing Small Fiber Neuropathy

Small fiber neuropathy (SFN) is a disorder of the small myelinated Aδ-fibers and unmyelinated C-fibers [5, 6]. SFN might affect small sensory fibers, autonomic fibers or both, resulting in sensory changes, autonomic dysfunction or combined symptoms [7]. As a consequence, the symptoms are potentially numerous and have a large impact on quality of life [8]. Since diagnostic methods for SFN are numerous and its pathophysiology complex, this extensive review focusses on categorizing all aspects of SFN as disease and its diagnosis. In this review, sensitivity in combination with specificity of different diagnostic methods are described using the areas under the curve. In the end, a diagnostic work-flow is suggested based on different phenotypes of SFN.

Contribution of Skin Biopsy in Peripheral Neuropathies

In the last three decades the study of cutaneous innervation through 3 mm-punch-biopsy has provided an important contribution to the knowledge of small fiber somatic and autonomic neuropathies but also of large fiber neuropathies. Skin biopsy is a minimally invasive technique with the advantage, compared to sural nerve biopsy, of being suitable to be applied to any site in our body, of being repeatable over time, of allowing the identification of each population of nerve fiber through its target. In patients with symptoms and signs of small fiber neuropathy the assessment of IntraEpidermal Nerve Fiber density is the gold standard to confirm the diagnosis while the quantification of sudomotor, pilomotor, and vasomotor nerve fibers allows to evaluate and characterize the autonomic involvement. All these parameters can be re-evaluated over time to monitor the disease process and to evaluate the effectiveness of the treatments. Myelinated fibers and their receptors can also be evaluated to detect a “dying back” neuropathy early when nerve conduction study is still normal. Furthermore, the morphometry of dermal myelinated fibers has provided new insight into pathophysiological mechanisms of different types of inherited and acquired large fibers neuropathies. In genetic neuropathies skin biopsy has become a surrogate for sural nerve biopsy, no longer necessary in the diagnostic process, to study genotype–phenotype correlations.

Idiopathic distal sensory polyneuropathy: ACTTION diagnostic criteria

OBJECTIVE

To present standardized diagnostic criteria for idiopathic distal sensory polyneuropathy (iDSP) and its subtypes: idiopathic mixed fiber sensory neuropathy (iMFN), idiopathic small fiber sensory neuropathy (iSFN), and idiopathic large fiber sensory neuropathy (iLFN) for use in research.

METHODS

The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities and Networks (ACTTION) public-private partnership with the Food and Drug Administration convened a meeting to develop consensus diagnostic criteria for iMFN, iSFN, and iLFN. After background presentations, a collaborative, iterative approach was used to develop expert consensus for new criteria.

RESULTS

An iDSP diagnosis requires at least 1 small fiber (SF) or large fiber (LF) symptom, at least 1 SF or LF sign, abnormalities in sensory nerve conduction studies (NCS) or distal intraepidermal nerve fiber density (IENFD), and exclusion of known etiologies. An iMFN diagnosis requires that at least 1 of the above clinical features is SF and 1 clinical feature is LF with abnormalities in sensory NCS or IENFD. Diagnostic criteria for iSFN require at least 1 SF symptom and at least 1 SF sign with abnormal IENFD, normal sensory NCS, and the absence of LF symptoms and signs. Diagnostic criteria for iLFN require at least 1 LF symptom and at least 1 LF sign with normal IENFD, abnormal sensory NCS, and absence of SF symptoms and signs.

CONCLUSION

Adoption of these standardized diagnostic criteria will advance research and clinical trials and spur development of novel therapies for iDSPs.

Neuropathy of the elderly

There is an aging of the peripheral nervous system characterized by a decrease in sensory and motor nerve conduction, amplitudes of motor and above all sensory potentials, an abolition of the ankle jerk reflexes and an alteration of proprioceptive sensitivity in almost two-thirds of individuals over 65 years old. These anomalies tend to increase beyond 80 years. However, these signs of aging do not affect the quality of life of the subjects. The causes of peripheral neuropathies in the elderly differ little from those observed before age 65. Of course, hereditary causes are much less frequent, except cases with a late onset, now easily detectable, such as familial amyloidosis. In our climates and in the most developed countries, diabetes remains the most common cause, the prevalence of neuropathy increasing with age. The so-called idiopathic causes are also frequent and despite extensive investigations, nearly 20% of cases remain without etiological diagnosis, but this type of neuropathy is generally mild and not very progressive. The presence of peripheral neuropathy in the elderly can cause real problems in daily life, including the frequency of falls that can be responsible for deleterious bone damage.

Peripheral neuropathy symptoms in wild type transthyretin amyloidosis

To propose a correlation between polyneuropathy and ATTRwt based on retrospective analysis of patients with ATTRwt. We reviewed 151 ATTRwt patients followed by the amyloid cardiac clinic (group A) for symptoms of neuropathy and 12 patients with ATTRwt evaluated in the Neurology Department (group B) with objective measures of neuropathy. Medical history, electrodiagnosis, laboratory and skin biopsies were assessed; 30.5% of group A had neuropathy symptoms. Alternative explanations for neuropathy symptoms were explored, including, age, gender, BMI, diabetes mellitus, B12 deficiency. No difference was observed for BMI, age, gender and spine disease for those with and without neuropathic symptoms (P > .05). All of group B (n = 12) were diagnosed with neuropathy, confirmed by electrodiagnostic testing or skin biopsy, while two patients had not yet developed cardiac symptoms. We observe a higher prevalence of neuropathic symptoms in ATTRwt patients than previously believed. Neuropathic symptoms may precede cardiac symptoms. Our findings suggest a possible causative relationship that requires further investigation.

Peripheral neuropathy and depressive symptoms: examining the association in a primary health care setting among persons with and without diabetes mellitus

PURPOSE

The purpose of this study was to measure the association between peripheral neuropathy symptoms and depressive symptoms among a sample of patients with and without diabetes mellitus (DM).

METHODS

Patients were administered the 15-item Michigan Neuropathy Screening Instrument (MNSI) and the patient health questionnaire depression scale (PHQ-8). Patients with an MNSI score ≥ 4 were categorized as having PN and patients with a PHQ-8 score ≥ 10 were considered to have current depression. Log-binomial regression was used to analyze the relationship between PN and depressive symptoms.

RESULTS

406 patients were included in the final analysis. There were no statistically significant differences by diabetes status in PN symptoms (Diabetes = 61.8%; No diabetes = 55.4%; p = .20) or in depression status (Diabetes = 37.6%; No diabetes = 36.6%; p =  .83). After adjustment for covariates, PN was associated with depression (aRR = 4.46; 95% CI 2.91,6.85) independent of diabetes status.

CONCLUSIONS

PN symptoms may be common among aging persons even in the absence of DM. Past literature and our study demonstrate that PN and depression are closely associated. More work is needed to understand the etiology and potential utility of intervention for depression symptoms among patients with neuropathy.

Guidelines for diagnosis and treatment in neurology - Lyme neuroborreliosis

Lyme borreliosis is the most common tick-borne infectious disease in Europe. A neurological manifestation occurs in 3–15% of infections and can manifest as polyradiculitis, meningitis and (rarely) encephalomyelitis.

This S3 guideline is directed at physicians in private practices and clinics who treat Lyme neuroborreliosis in children and adults.

Twenty AWMF member societies, the Robert Koch Institute, the German Borreliosis Society and three patient organisations participated in its development. A systematic review and assessment of the literature was conducted by the German Cochrane Centre, Freiburg (Cochrane Germany).

The main objectives of this guideline are to define the disease and to give recommendations for the confirmation of a clinically suspected diagnosis by laboratory testing, antibiotic therapy, differential diagnostic testing and prevention.

Association of small-fiber polyneuropathy with three previously unassociated rare missense SCN9A variants

BACKGROUND

Small fiber polyneuropathy (SFN) involves ectopic firing and degeneration of small-diameter, somatic/autonomic peripheral axons. Causes include diabetes, inflammation and rare pathogenic mutations, including in SCN9-11 genes that encode small fiber sodium channels.

AIMS

The aim of this study is to associate a new phenotype-immunotherapy-responsive SFN-with rare amino acid-substituting SCN9A variants and present potential explanations.

METHODS

A retrospective chart review of two Caucasians with skin biopsy confirmed SFN and rare SCN9A single nucleotide polymorphisms not previously reported in neuropathy.

RESULTS

A 47-year-old with 4 years of disabling widespread neuropathic pain and exertional intolerance had nerve- and skin biopsy-confirmed SFN, with blood tests revealing only high-titer antinuclear antibodies and low complement C4 consistent with B cell dysimmunity. Six years of intravenous immunoglobulin (IVIg) therapy markedly improved sensory and autonomic symptoms and normalized his neurite density. After whole exome sequencing revealed a potentially pathogenic SCN9A-A3734G variant, sodium channel blockers were tried. Herpes zoster left a 32-year-old with disabling exertional intolerance ("chronic fatigue syndrome"), postural syncope and tachycardia, arm and leg paresthesias, reduced sweating, and distal hairloss. Screening revealed antinuclear and potassium channel autoantibodies, so prednisone and then IVIg were prescribed with great benefit. During 4 years of immunotherapy, his symptoms and function improved, and all abnormal biomarkers (autonomic testing and skin biopsies) normalized. Whole exome sequencing then revealed two nearby compound heterozygous SCN9A variants that were computer-predicted to be deleterious.

CONCLUSIONS

These cases newly associate three novel amino acid-substituting SCN9A variants with immunotherapy-responsive neuropathy. Only larger studies can determine whether these are contributory or coincidental, but they associate new variants with moderate or high likelihood of pathogenicity with a new highly related phenotype.

Scientific Advances in and Clinical Approaches to Small-Fiber Polyneuropathy: A Review

IMPORTANCE

Small-fiber polyneuropathy involves preferential damage to the thinly myelinated A-delta fibers, unmyelinated C sensory fibers, or autonomic or trophic fibers. Although this condition is common, most patients still remain undiagnosed and untreated because of lagging medical and public awareness of research advances. Chronic bilateral neuropathic pain, fatigue, and nausea are cardinal symptoms that can cause disability and dependence, including pain medication dependence.

OBSERVATIONS

Biomarker confirmation is recommended, given the nonspecificity of symptoms. The standard test involves measuring epidermal neurite density within a 3-mm protein gene product 9.5 (PGP9.5)-immunolabeled lower-leg skin biopsy. Biopsies and autonomic function testing confirm that small-fiber neuropathy not uncommonly affects otherwise healthy children and young adults, in whom it is often associated with inflammation or dysimmunity. A recent meta-analysis concluded that small-fiber neuropathy underlies 49% of illnesses labeled as fibromyalgia. Initially, patients with idiopathic small-fiber disorders should be screened by medical history and blood tests for potentially treatable causes, which are identifiable in one-third to one-half of patients. Then, secondary genetic testing is particularly important for familial and childhood cases. Treatable genetic causes include Fabry disease, transthyretin and primary systemic amyloidosis, hereditary sensory autonomic neuropathy-1, and ion-channel mutations. Immunohistopathologic evidence suggests that small-fiber dysfunction and denervation, especially of blood vessels, contributes to diverse symptoms, including postexertional malaise, postural orthostatic tachycardia, and functional gastrointestinal distress. Preliminary evidence implicates acute or chronic autoreactivity in some cases, particularly in female patients and otherwise healthy children and young adults. Different temporal patterns akin to Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy have been described; here, corticosteroids and immunoglobulins, which are often efficacious for inflammatory neuropathic conditions, are increasingly considered.

CONCLUSIONS AND RELEVANCE

Because small fibers normally grow throughout life, improving contributory conditions may permit regrowth, slow progression, and prevent permanent damage. The prognosis is often hopeful for improving quality of life and sometimes for abatement or resolution, particularly in the young and otherwise healthy individuals. Examples include diabetic, infectious, toxic, genetic, and inflammatory causes. The current standard of care requires prompt diagnosis and treatment, particularly in children and young adults, to restore life trajectory. Consensus diagnostic and tracking metrics should be established to facilitate treatment trials.

Intraepidermal Nerve Fiber Analysis in Human Patients and Animal Models of Peripheral Neuropathy: A Comparative Review

Analysis of intraepidermal nerve fibers (IENFs) in skin biopsy samples has become a standard clinical tool for diagnosing peripheral neuropathies in human patients. Compared to sural nerve biopsy, skin biopsy is safer, less invasive, and can be performed repeatedly to facilitate longitudinal assessment. Intraepidermal nerve fiber analysis is also more sensitive than conventional nerve histology or electrophysiological tests for detecting damage to small-diameter sensory nerve fibers. The techniques used for IENF analysis in humans have been adapted for large and small animal models and successfully used in studies of diabetic neuropathy, chemotherapy-induced peripheral neuropathy, HIV-associated sensory neuropathy, among others. Although IENF analysis has yet to become a routine end point in nonclinical safety testing, it has the potential to serve as a highly relevant indicator of sensory nerve fiber status in neurotoxicity studies, as well as development of neuroprotective and neuroregenerative therapies. Recently, there is also interest in the evaluation of IENF via skin biopsy as a biomarker of small fiber neuropathy in the regulatory setting. This article provides an overview of the anatomic and pathophysiologic principles behind IENF analysis, its use as a diagnostic tool in humans, and applications in animal models with focus on comparative methodology and considerations for study design.

Diagnosis and management of sensory polyneuropathy

Sensory polyneuropathies, which are caused by dysfunction of peripheral sensory nerve fibers, are a heterogeneous group of disorders that range from the common diabetic neuropathy to the rare sensory neuronopathies. The presenting symptoms, acuity, time course, severity, and subsequent morbidity vary and depend on the type of fiber that is affected and the underlying cause. Damage to small thinly myelinated and unmyelinated nerve fibers results in neuropathic pain, whereas damage to large myelinated sensory afferents results in proprioceptive deficits and ataxia. The causes of these disorders are diverse and include metabolic, toxic, infectious, inflammatory, autoimmune, and genetic conditions. Idiopathic sensory polyneuropathies are common although they should be considered a diagnosis of exclusion. The diagnostic evaluation involves electrophysiologic testing including nerve conduction studies, histopathologic analysis of nerve tissue, serum studies, and sometimes autonomic testing and cerebrospinal fluid analysis. The treatment of these diseases depends on the underlying cause and may include immunotherapy, mitigation of risk factors, symptomatic treatment, and gene therapy, such as the recently developed RNA interference and antisense oligonucleotide therapies for transthyretin familial amyloid polyneuropathy. Many of these disorders have no directed treatment, in which case management remains symptomatic and supportive. More research is needed into the underlying pathophysiology of nerve damage in these polyneuropathies to guide advances in treatment.

Causes of chronic neuropathies: a single-center experience

OBJECTIVES

Chronic neuropathies are a common cause of neurological disability worldwide. However, few reports have evaluated, in real life, the prevalence of the several conditions which can cause it.

PATIENTS AND METHODS

The authors reviewed informatic database for outpatient office to confirm identification of chronic neuropathy in a 3-year interval period.

RESULTS

Among the 100 selected patients with chronic neuropathies, almost one fifth (19%) remained idiopathic. The most common etiologies were diabetes (17%), dysimmune neuropathies (38%), and vitamin B12 deficiency (9%). In the "dysimmune neuropathies" group, we distinguished various etiologies, including dysimmune neuropathies associated or not with systemic autoimmune diseases (7 and 3%, respectively), chronic inflammatory polyneuropathy (CIDP) (8%), multifocal motor neuropathy (MMN) (3%), paraproteinemic (8%), celiac disease-related (6%), and paraneoplastic (3%) neuropathies.

CONCLUSIONS

In this report from a single neurological center, treatable causes of chronic neuropathies, such as dysimmune neuropathies, including CIDP, and celiac disease-associated neuropathy, were common. These findings suggest the utility of routine screening with blood testing for dysimmune neuropathy and celiac disease for all patients presenting with idiopathic chronic polyneuropathy in whom primary diagnostic testings had failed to identify an etiology for the disease.

SIGNIFICANCE

Our results indicate that patients with peripheral neuropathy could receive a benefit from being evaluated routinely in a specialized neurological center, as many of the conditions that were discovered represented potentially treatable causes of neuropathy.

Electrodiagnosis in the Patient with Metabolic Syndrome: Adding Value to Patient Care

Patients with metabolic syndrome are at increased risk of peripheral neuropathy; entrapment neuropathies, such as carpal tunnel syndrome; and spine disease that can lead to radiculopathy or spinal stenosis. Electrodiagnostic studies are a valuable part of patient care in this population. They can confirm suspected diagnoses, uncover additional conditions, and lead to the diagnosis of other causes of neuropathy that require treatment. By assessing the severity of neuropathy, patients at high risk for falls, functional decline, and foot ulcers are identified to guide prevention, treatment, and patient education.

Approach to Peripheral Neuropathy for the Primary Care Clinician

Peripheral neuropathy is commonly encountered in the primary care setting and is associated with significant morbidity, including neuropathic pain, falls, and disability. The clinical presentation of neuropathy is diverse, with possible symptoms including weakness, sensory abnormalities, and autonomic dysfunction. Accordingly, the primary care clinician must be comfortable using the neurologic examination-including the assessment of motor function, multiple sensory modalities, and deep tendon reflexes-to recognize and characterize neuropathy. Although the causes of peripheral neuropathy are numerous and diverse, careful review of the medical and family history coupled with limited, select laboratory testing can often efficiently lead to an etiologic diagnosis. This review offers an approach for evaluating suspected neuropathy in the primary care setting. It will describe the most common causes, suggest an evidence-based workup to aid in diagnosis, and highlight recent evidence that allows for selection of symptomatic treatment of patients with neuropathy.

General Approach to Peripheral Nerve Disorders

PURPOSE OF REVIEW

This article provides a conceptual framework for the evaluation of patients with suspected polyneuropathy to enhance the clinician's ability to localize and confirm peripheral nervous system pathology and, when possible, identify an etiologic diagnosis through use of rational clinical and judicious testing strategies.

RECENT FINDINGS

Although these strategies are largely time-honored, recent insights pertaining to the pathophysiology of certain immune-mediated neuropathies and to evolving genetic testing strategies may modify the way that select causes of neuropathy are conceptualized, evaluated, and managed.

SUMMARY

The strategies suggested in this article are intended to facilitate accurate bedside diagnosis in patients with suspected polyneuropathy and allow efficient and judicious use of supplementary testing and application of rational treatment when indicated.

Gluten neuropathy: prevalence of neuropathic pain and the role of gluten-free diet

BACKGROUND AND AIM

Peripheral neuropathy is a common extraintestinal manifestation of gluten sensitivity (gluten neuropathy). We aimed to establish the prevalence of neuropathic pain in patients with otherwise idiopathic PN and gluten sensitivity (positive antigliadin, endomysial, and/or transglutaminase antibodies, with or without enteropathy) and to describe any contributory factors.

METHODS

All consecutive patients with gluten neuropathy (GN) attending a specialist gluten/neurology clinic were invited to participate. Pain was assessed via the DN4 questionnaire and the visual analog scale. Overall Neuropathy Limitations Scale was used to assess the severity of neuropathy. The Mental Health Index (MHI-5) was used to measure participants' general mental health status.

RESULTS

In total, 60 patients (76.7% males, mean age 69.9 ± 10.1 years) with GN were recruited. Neuropathic pain was present in 33 patients (55.0%). Comparison between groups of painful and not painful GN did not show significant differences regarding age, gender, neuropathy severity and neuropathy type. Patients with painless GN were more likely to be on a strict gluten-free diet (55.6 versus 21.2%, p = 0.006). Patients with painful GN presented with significantly worse MHI-5 score (75.9 ± 13.8 versus 87.4 ± 8.1, p < 0.001). Multivariate analysis showed that, after adjusting for age, gender and MHI-5, strict gluten-free diet was associated with lowering the odds of peripheral neuropathic pain by 88.7% (95% CI 47.2-97.6%, p = 0.006).

CONCLUSION

Neuropathic pain is very prevalent in GN and is associated with poorer mental health status. Strict gluten-free diet might be protective as it is associated with a significant reduction of the odds of peripheral neuropathic pain associated to GN.

Pyridoxine Toxicity Small Fiber Neuropathy With Dysautonomia: A Case Report

Pyridoxine (vitamin B6) toxicity is a well-known cause of primary sensory, length-dependent, axonal polyneuropathy. Although sensory symptoms predominate, autonomic symptoms have also been reported in some cases. To date, there is no objective evidence of autonomic dysfunction reported in the literature. We present the case of a 41-year-old woman with 2 years of progressive burning pain, numbness, tingling, and weakness in a stocking-glove distribution who was found to have severe pyridoxine toxicity. Concurrent presence of large and small fiber nerve dysfunction was noted in the form of abnormal electromyography/nerve conduction study demonstrating a chronic sensory polyneuropathy and autonomic testing demonstrating abnormal responses to quantitative sweat testing and cardiovagal function testing. This case highlights the need for consideration of small fiber nerve damage by obtaining autonomic testing in cases of pyridoxine toxicity.

Nerve function varies with hemoglobin A1c in controls and type 2 diabetes

AIMS

To determine the cross-sectional threshold at which hemoglobin A1c (HbA1c) is associated with polyneuropathy in healthy controls, and the values associated with the most pronounced decline in nerve function in patients with diabetes.

METHODS

We used data from a cross-sectional cohort study of healthy controls and type 2 diabetes patients assessed between November 2010 and May 2013. Healthy controls and patients with diabetes were compared at different HbA1c ranges: <5.5%, 5.5-5.9%, and 6-6.4% for controls, and 6.5-7.4% and >7.5% for patients with diabetes.

RESULTS

The total cohort included 53 controls and 164 patients with diabetes. Subclinical small nerve fiber impairments were observed in controls at HbA1c levels of 5.5-6%, compared with HbA1c <5.5%, for example: lower Laser Doppler flare imaging area of 2.8 ± 1.4 versus 3.9 ± 2 mm². The most prominent decline in both small and large nerve fiber function was seen with less impaired glycemic control and shorter duration of diabetes, i.e. at HbA1c levels of 6.5-7.4%, compared with >7.5%.

CONCLUSIONS

These findings underscore the importance of early treatment at the prediabetes and early diabetes stages to prevent nerve fiber decline that is likely irreversible.

IVIg for apparently autoimmune small-fiber polyneuropathy: first analysis of efficacy and safety

OBJECTIVES

Small-fiber polyneuropathy (SFPN) has various underlying causes, including associations with systemic autoimmune conditions. We have proposed a new cause; small-fiber-targeting autoimmune diseases akin to Guillain-Barré and chronic inflammatory demyelinating polyneuropathy (CIDP). There are no treatment studies yet for this 'apparently autoimmune SFPN' (aaSFPN), but intravenous immunoglobulin (IVIg), first-line for Guillain-Barré and CIDP, is prescribed off-label for aaSFPN despite very high cost. This project aimed to conduct the first systematic evaluation of IVIg's effectiveness for aaSFPN.

METHODS

With IRB approval, we extracted all available paper and electronic medical records of qualifying patients. Inclusion required having objectively confirmed SFPN, autoimmune attribution and other potential causes excluded. IVIg needed to have been dosed at ⩾1 g/kg/4 weeks for ⩾3 months. We chose two primary outcomes - changes in composite autonomic function testing (AFT) reports of SFPN and in ratings of pain severity - to capture objective as well as patient-prioritized outcomes.

RESULTS

Among all 55 eligible patients, SFPN had been confirmed by 3/3 nerve biopsies, 62% of skin biopsies, and 89% of composite AFT. Evidence of autoimmunity included 27% of patients having systemic autoimmune disorders, 20% having prior organ-specific autoimmune illnesses and 80% having ⩾1/5 abnormal blood-test markers associated with autoimmunity. A total of 73% had apparent small-fiber-restricted autoimmunity. IVIg treatment duration averaged 28 ± 25 months. The proportion of AFTs interpreted as indicating SFPN dropped from 89% at baseline to 55% (p ⩽ 0.001). Sweat production normalized (p = 0.039) and the other four domains all trended toward improvement. Among patients with pre-treatment pain ⩾3/10, severity averaging 6.3 ± 1.7 dropped to 5.2 ± 2.1 (p = 0.007). Overall, 74% of patients rated themselves 'improved' and their neurologists labeled 77% as 'IVIg responders'; 16% entered remissions that were sustained after IVIg withdrawal. All adverse events were expected; most were typical infusion reactions. The two moderate complications (3.6%) were vein thromboses not requiring discontinuation. The one severe event (1.8%), hemolytic anemia, remitted after IVIg discontinuation.

CONCLUSION

These results provide Class IV, real-world, proof-of-concept evidence suggesting that IVIg is safe and effective for rigorously selected SFPN patients with apparent autoimmune causality. They provide rationale for prospective trials, inform trial design and indirectly support the discovery of small-fiber-targeting autoimmune/inflammatory illnesses.

The Influence of Clinically Diagnosed Neuropathy on Respiratory Muscle Strength in Type 2 Diabetes Mellitus

OBJECTIVES

This cross-sectional study investigated the influence of clinically diagnosed neuropathy (cdNP) on respiratory muscle strength in patients with type 2 diabetes mellitus (T2DM).

METHODS

110 T2DM patients and 35 nondiabetic healthy controls (≥60 years) were allocated to one of three groups depending on the presence of cdNP: T2DM without cdNP (D-; n = 28), T2DM with cdNP (D+; n = 82), and controls without cdNP (C; n = 35). Clinical neurological diagnostic examination consisted of Vibration Perception Threshold and Diabetic Neuropathy Symptom score. Respiratory muscle strength was registered by maximal Inspiratory and Expiratory Pressures (PI_max and PE_max), and respiratory function by Peak Expiratory Flow (PEF). Isometric Handgrip Strength and Short Physical Performance Battery were used to evaluate peripheral skeletal muscle strength and physical performance. Univariate analysis of covariance was used with age, level of physical activity, and body mass index as covariates.

RESULTS

PI_max, PE_max, and PEF were higher in C compared to D- and D+. Exploring more in detail, PI_max, PE_max, and PEF were significantly lower in D+ compared to C. PE_max and PEF were also significantly lower in D- versus C. Measures of peripheral muscle strength and physical performance showed less associations with cdNP and T2DM.

CONCLUSIONS

The presence of cdNP affects respiratory muscle strength in T2DM patients compared to healthy controls. Both cdNP and diabetes in themselves showed a distinctive impact on respiratory muscle strength and function; however, an accumulating effect could not be ascertained in this study. As commonly used measures of peripheral muscle strength and physical performance seemed to be less affected at the given time, the integration of PI_max, PE_max, and PEF measurements in the assessment of respiratory muscle weakness could be of added value in the (early) screening for neuropathy in patients with T2DM.