Skin denervation and cutaneous vasculitis in systemic lupus erythematosus

Clinical, histologic, and immunologic signatures of Small Fiber Neuropathy in Systemic Lupus Erythematosus

BACKGROUND AND OBJECTIVES

Systemic Lupus Erythematosus (SLE) often causes damage to small nerve fibers, leading to distressing painful and autonomic symptoms. Despite this, Small Fiber Neuropathy (SFN) remains an underrecognized complication for SLE patients. In this cross-sectional study, we aimed to assess SFN in patients with SLE and to explore its correlations with immunologic disease features and clinical manifestations.

METHODS

We recruited 50 SLE patients (1 male to 12.5 females, aged 20-80 years) reporting painful disturbances. We conducted a comprehensive clinical and neurophysiological evaluation, using Nerve Conduction Studies and Quantitative Sensory Testing. Additionally, we carried out an extensive laboratory assessment of disease-related serological parameters. We also performed a thorough skin biopsy analysis, investigating somatic and autonomic innervation while detecting complement and inflammatory cell infiltrates within the skin.

RESULTS

Out of 50 patients, 19 were diagnosed with SFN, primarily characterized by a non-length-dependent distribution; 7 had a mixed neuropathy, with both large and small fiber involvement. Patients with SFN were younger than patients with a mixed neuropathy (p = .0143); furthermore, they were more likely to have a history of hypocomplementemia (p = .0058) and to be treated with cyclosporine A (p = .0053) compared to patients without neuropathy. However, there were no significant differences in painful and autonomic symptoms between patients with and without SFN.

DISCUSSION

This study highlights the relevant frequency of SFN with a non-length-dependent distribution among SLE patients experiencing painful symptoms. Indeed, SFN emerges as an early manifestation of SLE-related neuropathy and is closely associated with hypocomplementemia, suggesting a potential pathogenic role of the complement system. Moreover, SFN may be influenced by disease-modifying therapies. However, the precise role of SFN in shaping painful and autonomic symptoms in patients with SLE remains to be fully elucidated.

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.

Investigation of nerve fibers in the skin by biopsy: technical aspects, indications, and contribution to diagnosis of small-fiber neuropathy

Skin biopsy with investigation of small-diameter nerve fibers in human epidermis and dermis has been proven to be a useful method for confirming small-fiber neuropathy. In medical practice, small-fiber neuropathy is increasingly recognized as a leading cause of neuropathic pain. It is a prevalent complaint in medical offices, brought by patients often as a “painful burning sensation”. The prevalence of neuropathic pain is high in small-fiber neuropathies of different etiologies, especially in the elderly; 7% of population in this age group present peripheral neuropathy. Pain and paresthesia are symptoms which might cause disability and impair quality of life of patients. The early detection of small-fiber neuropathy can contribute to reducing unhealthy lifestyles, associated to higher incidence of the disease.

Impaired brain network architecture as neuroimaging evidence of pain in diabetic neuropathy

AIMS

To investigate alterations in structural brain networks due to chronic diabetic neuropathic pain.

METHODS

The current study recruited 24 patients with painful diabetic neuropathy (PDN) to investigate the influences of chronic pain on the brain. Thirteen patients with painless diabetic neuropathy (PLDN) and 24 healthy adults were recruited as disease and healthy controls. White matter connectivity of the brain networks constructed by diffusion tractography was compared across groups using the Network-based statistic (NBS) method. Graph theoretical analysis was further applied to assess topological changes of the brain networks.

RESULTS

The PDN patients had a significant reduction in white matter connectivity compared with PLDN and controls in the limbic and temporal regions, particularly the insula, hippocampus and parahippocampus, the amygdala, and the middle temporal gyrus. The PDN patients also exhibited an altered topology of the brain networks with reduced global efficiency and betweenness centrality.

CONCLUSION

The current findings indicate that topological alterations of brain networks may serve as a biomarker for pain-induced maladaptive reorganization of the brain in PDN. Given the high prevalence of diabetes worldwide, novel insights from network sciences to investigate the central mechanisms of diabetic neuropathic pain are warranted.

Brain Mechanisms of Pain and Dysautonomia in Diabetic Neuropathy: Connectivity Changes in Thalamus and Hypothalamus

CONTEXT

About one-third of diabetic patients suffer from neuropathic pain, which is poorly responsive to analgesic therapy and associated with greater autonomic dysfunction. Previous research on diabetic neuropathy mainly links pain and autonomic dysfunction to peripheral nerve degeneration resulting from systemic metabolic disturbances, but maladaptive plasticity in the central pain and autonomic systems following peripheral nerve injury has been relatively ignored.

OBJECTIVE

This study aimed to investigate how the brain is affected in painful diabetic neuropathy (PDN), in terms of altered structural connectivity (SC) of the thalamus and hypothalamus that are key regions modulating nociceptive and autonomic responses.

METHODS

We recruited 25 PDN and 13 painless (PLDN) diabetic neuropathy patients, and 27 healthy adults as controls. The SC of the thalamus and hypothalamus with limbic regions mediating nociceptive and autonomic responses was assessed using diffusion tractography.

RESULTS

The PDN patients had significantly lower thalamic and hypothalamic SC of the right amygdala compared with the PLDN and control groups. In addition, lower thalamic SC of the insula was associated with more severe peripheral nerve degeneration, and lower hypothalamic SC of the anterior cingulate cortex was associated with greater autonomic dysfunction manifested by decreased heart rate variability.

CONCLUSION

Our findings indicate that alterations in brain structural connectivity could be a form of maladaptive plasticity after peripheral nerve injury, and also demonstrate a pathophysiological association between disconnection of the limbic circuitry and pain and autonomic dysfunction in diabetes.

Subclinical Corneal Nerve Fiber Damage and Immune Cell Activation in Systemic Lupus Erythematosus: A Corneal Confocal Microscopy Study

Purpose

The purpose of this study was to evaluate the utility of corneal confocal microscopy (CCM) in identifying small nerve fiber damage and immune cell activation in patients with systemic lupus erythematosus (SLE).

Methods

This cross-sectional comparative study included 39 consecutive patients with SLE and 30 healthy control participants. Central corneal sensitivity was assessed using a Cochet-Bonnet contact corneal esthesiometer and a laser scanning CCM (Heidelberg, Germany) was used to quantify corneal nerve fiber density (CNFD), nerve branch density (CNBD), nerve fiber length (CNFL), and Langerhans cell (LC) density.

Results

Age was comparable among patients with SLE (33.7 ± 12.7) and controls (35.0 ± 13.7 years, P = 0.670) and the median duration of disease was 3.0 years (2.0–10.0 years). CNBD (P = 0.003) and CNFL (P = 0.019) were lower and mature LC density (P = 0.002) was higher, but corneal sensitivity (P = 0.178) and CNFD (P = 0.198) were comparable in patients with SLE compared with controls. The SELENA-SLEDAI score correlated with CNFD (ρ = −0.319, P = 0.048) and CNFL (ρ = −0.373, P = 0.019), and the total and immature LC densities correlated with CNBD (ρ = −0.319. P = 0.048, and ρ = −0.328, P = 0.041, respectively). Immature LC density was higher (P = 0.025), but corneal sensitivity and nerve fiber parameters were comparable between patients with (33%) and without neuropsychiatric symptoms and SLE.

Conclusions

Corneal confocal microscopy identifies distal corneal nerve fiber loss and increased immune cell density in patients with SLE and corneal nerve loss was associated with disease activity.

Translational Relevance

Corneal confocal microscopy may enable the detection of subclinical corneal nerve loss and immune cell activation in SLE.

Short- and Long-Term Outcome of Systemic Lupus Erythematosus Peripheral Neuropathy: Bimodal Pattern of Onset and Treatment Response

BACKGROUND/OBJECTIVE

Our aim was to describe the short- and long-term outcome of peripheral neuropathy (PN) attributed exclusively to systemic lupus erythematosus (SLE).

METHODS

Systemic lupus erythematosus patients with defined PN (clinical and electroneuromyography) were retrospectively evaluated at onset, 1-year, and 5-year follow-up using a standardized electronic chart database that started in 2000. Exclusion criteria were comorbidities, drugs, and infections. Age-, sex-, and disease duration-matched SLE patients without PN were selected as controls.

RESULTS

Lupus PN was identified in 38 (1.8%) of 2074 patients, and almost two thirds had PN onset in the first 5 years of SLE (63.2%). Peripheral neuropathy SLE had higher frequencies of cutaneous vasculitis (50% vs 21.1%, p = 0.002), lymphopenia (60.5% vs 36.8%, p = 0.027), anti-Sm (52.6% vs 27.6%, p = 0.013), and higher SLEDAI-2K scores (11.5 ± 10.5 vs 4.9 ± 6.7, p < 0.001) compared with controls. The most common type was polyneuropathy (71.1%) with sensory-motor pattern (68.4%). At PN diagnosis, all patients received glucocorticoid and 97.4% started immunosuppressive therapy (50% intravenous cyclophosphamide, 42.1% azathioprine). After 1-year follow-up, 92.1% had a favorable outcome with complete (36.8%) or partial remission (55.2%), in parallel with a decrease in prednisone dose (48.3 ± 17.9 vs 15.3 ± 13.4 mg/d, p < 0.001), symptomatic therapy (57.9% vs 29.7%, p = 0.02), and SLEDAI-2K score (11.5 ± 10.5 vs 1.7 ± 3.7, p < 0.001). SLEDAI-2K scores were higher in patients who had PN onset with less than 1 year of SLE duration, compared with those with more than 5 years of disease (21.3 ± 9.1 vs 3.9 ± 5.3, p < 0.001). Early-PN-onset group had a better response to treatment (complete remission at 1-year follow-up 61.5% vs 25%, p = 0.039). At 5-year follow-up, 89.3% remained with complete/partial remission.

CONCLUSIONS

Peripheral neuropathy attributed to SLE itself is a rare manifestation with a bimodal pattern, characterized by a predominant early-onset group associated with high disease activity and a higher rate of complete remission, and a late-onset group with low disease activity and a partial therapy response.

Skin reaction to capsaicin in patients with systemic lupus erythematosus compared to healthy controls

Background:

The interaction between nervous and immune systems has been under investigation. Transient receptor potential vanilloid type 1(TRPV1) is a ligand gated calcium channel expressed by sensory neurons which mediates neurogenic inflammatory response. Substance p which can be released following exposure to capsaicin is a TRPV1 inducer, shown to have altered concentration and function in mice with systemic lupus erythematosus (SLE). We evaluated skin reaction to capsaicin in newly diagnosed and established SLE patients compared to healthy controls.

Methods:

Twenty-nine SLE patients (12 newly diagnosed cases under treatment, and 17 established ones, not receiving medications) who referred to rheumatologic disease research center, and 33 healthy subjects of the control group were recruited in this study. A topical solution of capsaicin (0.075%) was applied on the volar forearm during skin test, and time to the tingling sensation, area of induration and area of redness (centimeters²) were recorded after 5, 10, and 20 minutes.

Results:

The area of redness and area of induration within 15 minutes, time to the tingling sensation (P=0.02), and the overall frequency of tingling sensation (P=0.01) after capsaicin skin test was considerably higher in SLE patients than the healthy controls. Redness, induration and tingling sensation were more frequent but not statistically significant among the established SLE group compared to the newly diagnosed patients.

Conclusion:

Since skin reaction to capsaicin is more prominent in SLE patients than the healthy individuals, neurogenic inflammation and the role of P substance should be investigated more in ongoing lupus. Capsaicin test can not predict lupus activity.

Brain imaging signature of neuropathic pain phenotypes in small-fiber neuropathy: altered thalamic connectome and its associations with skin nerve degeneration

ABSTRACT

Small-fiber neuropathy (SFN) has been traditionally considered as a pure disorder of the peripheral nervous system, characterized by neuropathic pain and degeneration of small-diameter nerve fibers in the skin. Previous functional magnetic resonance imaging studies revealed abnormal activations of pain networks, but the structural basis underlying such maladaptive functional alterations remains elusive. We applied diffusion tensor imaging to explore the influences of SFN on brain microstructures. Forty-one patients with pathology-proven SFN with reduced skin innervation were recruited. White matter connectivity with the thalamus as the seed was assessed using probabilistic tractography of diffusion tensor imaging. Patients with SFN had reduced thalamic connectivity with the insular cortex and the sensorimotor areas, including the postcentral and precentral gyri. Furthermore, the degree of skin nerve degeneration, measured by intraepidermal nerve fiber density, was associated with the reduction of connectivity between the thalamus and pain-related areas according to different neuropathic pain phenotypes, specifically, the frontal, cingulate, motor, and limbic areas for burning, electrical shocks, tingling, mechanical allodynia, and numbness. Despite altered white matter connectivity, there was no change in white matter integrity assessed with fractional anisotropy. Our findings indicate that alterations in structural connectivity may serve as a biomarker of maladaptive brain plasticity that contributes to neuropathic pain after peripheral nerve degeneration.

Integrins protect sensory neurons in models of paclitaxel-induced peripheral sensory neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect from cancer treatment with no known method for prevention or cure in clinics. CIPN often affects unmyelinated nociceptive sensory terminals. Despite the high prevalence, molecular and cellular mechanisms that lead to CIPN are still poorly understood. Here, we used a genetically tractable Drosophila model and primary sensory neurons isolated from adult mouse to examine the mechanisms underlying CIPN and identify protective pathways. We found that chronic treatment of Drosophila larvae with paclitaxel caused degeneration and altered the branching pattern of nociceptive neurons, and reduced thermal nociceptive responses. We further found that nociceptive neuron-specific overexpression of integrins, which are known to support neuronal maintenance in several systems, conferred protection from paclitaxel-induced cellular and behavioral phenotypes. Live imaging and superresolution approaches provide evidence that paclitaxel treatment causes cellular changes that are consistent with alterations in endosome-mediated trafficking of integrins. Paclitaxel-induced changes in recycling endosomes precede morphological degeneration of nociceptive neuron arbors, which could be prevented by integrin overexpression. We used primary dorsal root ganglia (DRG) neuron cultures to test conservation of integrin-mediated protection. We show that transduction of a human integrin β-subunit 1 also prevented degeneration following paclitaxel treatment. Furthermore, endogenous levels of surface integrins were decreased in paclitaxel-treated mouse DRG neurons, suggesting that paclitaxel disrupts recycling in vertebrate sensory neurons. Altogether, our study supports conserved mechanisms of paclitaxel-induced perturbation of integrin trafficking and a therapeutic potential of restoring neuronal interactions with the extracellular environment to antagonize paclitaxel-induced toxicity in sensory neurons.

Relevant domains and outcome measurement instruments in Neuropsychiatric Systemic Lupus Erythematosus: a systematic literature review

OBJECTIVES

Although neuropsychiatric involvement in Systemic Lupus Erythematosus (NPSLE) is one of the most complex and troubling manifestations of the disease, validated outcome instruments to be used as sensitive endpoints in controlled clinical trials are lacking. We set out a systematic literature review (SLR) to identify outcome measurement instruments and domains used to assess NPSLE.

METHODS

The Preferred Reporting Items for systematic reviews and Meta-analysis (PRISMA) guidelines were used. Articles available in English (1967-2020), listed in PubMed, EMBASE, PsycINFO, Cochrane Library and EULAR outcome measures library were screened. All domains and outcome measurement instruments were characterized according to the OMERACT Filter 2.1, considering core areas (manifestations/abnormalities, life impact, death/lifespan, societal/resource use) and contextual factors.

RESULTS

Of 3,392 abstracts evaluated, 83 studies were included in the SLR (15,974 patients, females 89.9%). Eligible studies included domains and instruments pertinent to all core areas defined by OMERACT, except for "societal/resource use". The most common core areas were "manifestations/abnormalities", covering 10 domains pertinent to laboratory and instrumental markers, indexes and neuropsychiatric dimension (cognitive, neurologic and psychiatric field), and "life impact", covering 7 domains related to physical function (from both the perspective of the patient and the physician), pain and quality of life.

CONCLUSION

Our study revealed great heterogeneity in the instruments derived from populations with NPSLE and none of these had high-quality evidence. This supports the need to develop and further validate a core domain set and outcome measurement instruments to promote clinical research in this field, enhancing comparability across studies.

Small fiber neuropathy and related factors in patients with systemic lupus erythematosus; the results of cutaneous silent period and skin biopsy

INTRODUCTION

Evaluating small nerve fibers in patients with systemic lupus erythematosus (SLE) using cutaneous silent period (CSP) and skin biopsy and assesssing the relationship between clinical signs, autoantibodies and neuropathic pain score.

OBJECTIVE - METHODS

Fifty one SLE patients and 46 healthy volunteers were included in this study. Nerve conduction studies and CSP were performed both on upper and lower limbs in subjects. Skin biopsy was performed and the number of epidermal nerve density and IL-6 staining were evaluated.

RESULTS

In SLE patients, CSP latencies were significantly prolonged both in lower and upper limbs and lower and upper extremity CSP durations were significantly shorter when compared to controls (p < 0.001). The number of epidermal nerve was significantly lower in SLE patients when compared to healthy controls (p < 0.001).

CONCLUSION

We detected marked small nerve fiber damage in both lower and upper limbs in SLE patients using CSP. Decreased epidermal nerve density also supports this finding.

Objectively Assessed Foot and Ankle Characteristics in Patients With Systemic Lupus Erythematosus: A Comparison With Age- and Sex-Matched Controls

OBJECTIVE

To objectively identify foot and ankle characteristics in patients with systemic lupus erythematosus (SLE) compared to age- and sex-matched controls.

METHODS

A total of 54 patients with SLE and 56 control participants attended a study visit designed to comprehensively assess the foot and ankle. Objectively assessed foot characteristics included muscle strength, joint motion, foot posture, foot problems, protective sensation, vibration perception threshold (VPT), ankle brachial index (ABI), plantar pressure, and spatiotemporal gait characteristics. Self-reported measure of foot pain and impairment were also assessed using a 100-mm foot pain visual analog scale. Data were analyzed using regression models. Plantar pressure and gait models were adjusted for walking velocity, body mass index, and foot pain.

RESULTS

Compared to controls, participants with SLE had lower muscle force for plantarflexion, dorsiflexion, inversion, and eversion (all P < 0.001), higher foot posture indices (P = 0.007), higher foot problem scores (P = 0.001), higher VPT (P = 0.001), and more frequent abnormal ABI (odds ratio [OR] 3.13, P = 0.044). Participants with SLE also had lower peak pressure and higher pressure time integrals for all foot regions (all P < 0.001), lower step and stride length, velocity, and cadence, and higher step, swing, stance, and single and double support times compared to controls (all P < 0.001). Compared to controls, participants with SLE also reported greater foot pain (P < 0.001).

CONCLUSION

Patients with SLE experience a wide range of foot symptoms. This study has provided objective evidence of foot and ankle disease in patients with SLE, including reduced muscle strength and altered gait patterns when compared to controls. This highlights the importance of foot health assessments as part of SLE management.

Foot and ankle characteristics in systemic lupus erythematosus: A systematic review and meta-analysis

OBJECTIVE

To determine characteristics of the foot and ankle in people with systemic lupus erythematosus (SLE).

METHODS

Medline, CINAHL, Sports-Discus, Scopus and Cochrane Library databases were searched up to January 2018. Studies reporting foot- and ankle-related outcomes in the following domains were included: vascular, neurological, musculoskeletal, cutaneous (skin and nail) or pain/function. The Quality Index tool was used to assess methodological quality. Where appropriate, odds ratio (OR) and mean difference meta-analyses were conducted for case-control studies; and pooled mean prevalence meta-analyses for studies assessing characteristics in SLE.

RESULTS

Forty-nine studies were included with mean (range) quality scores of 75% (38-100%). Twenty-three studies assessed vascular characteristics, followed by musculoskeletal (n = 16), neurological (n = 11), cutaneous (n = 5) and pain/function (n = 4). Foot and ankle characteristics in people with SLE included impaired vascular supply, abnormal nerve function, musculoskeletal pathology, skin and nail pathology, and pain and functional disability. Twenty-four studies were included in meta-analyses. Pooled OR for abnormal ankle brachial index was 3.08 for SLE compared with controls. Pooled mean difference in brachial-ankle pulse-wave velocity between SLE and controls was significant (161.39 cm/s, P = 0.004). Pooled prevalence was 0.54 for intermittent claudication, 0.50 for Raynaud's phenomenon, 0.28 for chilblains, 0.00 for gangrene, 0.30 for hallux valgus, 0.15 for onychomycosis, 0.76 for history of foot pain, and 0.36 for current foot pain.

CONCLUSION

People with SLE experience a wide range of foot and ankle manifestations. Published research highlights the impact of peripheral arterial disease, peripheral neuropathy, musculoskeletal deformity, skin and nail pathology and patient-reported foot pain and disability.

Valproic acid prevents glucocorticoid‑induced osteonecrosis of the femoral head of rats

Glucocorticoids (GCs) are the most common cause of atraumatic osteonecrosis of the femoral head (ONFH) because their effect compromises the osteogenic capability of bone marrow-derived mesenchymal stem cells (BMSCs). Valproic acid (VPA) is a widely used anti-epileptic and anticonvulsant drug. Previous studies have reported that VPA promotes osteogenic differentiation of MSCs in vitro and osteogenesis in vivo as a histone deacetylase (HDAC) inhibitor. The purpose of the present study was to investigate the efficacy of VPA as a precautionary treatment of ONFH after GC treatment in rats. In vitro, the effect of VPA, dexamethasone or a combination treatment of the two on the proliferation and osteogenic differentiation of human BMSCs was assessed using a Cell Counting Kit-8 and apoptosis assays, and by measuring the expression of proteins associated with osteogenesis. In vivo, a GC-induced ONFH model was established in rats and VPA was added during GC treatment to investigate the preventive effect of VPA against ONFH. Rat BMSCs were also extracted to investigate the osteogenic capacity. The results of micro-computed tomography scanning, angiography of the femoral head and histological and immunohistochemical analyses indicated that 11 of 15 rats induced with methylprednisolone (MP) presented with ONFH, while only 2 of 15 rats treated with a combination of MP and VPA developed ONFH. VPA produced beneficial effects on subchondral bone trabeculae in the femoral head with significant preservation of bone volume and blood supply, as well as improved osteogenic capability of BMSCs compared with those in rats treated with GC alone. In conclusion, VPA attenuated the inhibitory effect of GC on BMSC proliferation and osteogenesis by inhibiting apoptosis and elevating the expression of proteins associated with osteogenesis, which may contribute to the prevention of GC-induced ONFH in rats.

Mitochondrial damage and "plugging" of transport selectively in myelinated, small-diameter axons are major early events in peripheral neuroinflammation

Background

Small-diameter, myelinated axons are selectively susceptible to dysfunction in several inflammatory PNS and CNS diseases, resulting in pain and degeneration, but the mechanism is not known.

Methods

We used in vivo confocal microscopy to compare the effects of inflammation in experimental autoimmune neuritis (EAN), a model of Guillain-Barré syndrome (GBS), on mitochondrial function and transport in large- and small-diameter axons. We have compared mitochondrial function and transport in vivo in (i) healthy axons, (ii) axons affected by experimental autoimmune neuritis, and (iii) axons in which mitochondria were focally damaged by laser induced photo-toxicity.

Results

Mitochondria affected by inflammation or laser damage became depolarized, fragmented, and immobile. Importantly, the loss of functional mitochondria was accompanied by an increase in the number of mitochondria transported towards, and into, the damaged area, perhaps compensating for loss of ATP and allowing buffering of the likely excessive Ca²⁺ concentration. In large-diameter axons, healthy mitochondria were found to move into the damaged area bypassing the dysfunctional mitochondria, re-populating the damaged segment of the axon. However, in small-diameter axons, the depolarized mitochondria appeared to “plug” the axon, obstructing, sometimes completely, the incoming (mainly anterograde) transport of mitochondria. Over time (~ 2 h), the transported, functional mitochondria accumulated at the obstruction, and the distal part of the small-diameter axons became depleted of functional mitochondria.

Conclusions

The data show that neuroinflammation, in common with photo-toxic damage, induces depolarization and fragmentation of axonal mitochondria, which remain immobile at the site of damage. The damaged, immobile mitochondria can “plug” myelinated, small-diameter axons so that successful mitochondrial transport is prevented, depleting the distal axon of functioning mitochondria. Our observations may explain the selective vulnerability of small-diameter axons to dysfunction and degeneration in a number of neurodegenerative and neuroinflammatory disorders.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1094-8) contains supplementary material, which is available to authorized users.

Intraepidermal nerve fibre density in POEMS (Crow-Fukase) syndrome and the correlation with sural nerve pathology

OBJECTIVE

To examine intraepidermal nerve fibre densities (IENFDs) in patients with polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin change (POEMS) syndrome.

METHODS

The IENFDs of 11 patients with POEMS syndrome were estimated. We determined whether IENFD was associated with patient clinical features or the estimated number of nerve fibres on complete cross-sections of biopsied sural nerves.

RESULTS

IENFD was significantly reduced (9.7±4.4fibres/mm) compared with normal controls (p<0.05), although the individual values varied from 1.4 to 14.4fibres/mm. The presence of glucose intolerance was significantly associated with a reduction of IENFD (p<0.05). The number of unmyelinated fibres was preserved at the sural nerve level and was not correlated with IENFD. In contrast, the number of myelinated fibres was correlated with IENFD (p<0.05).

CONCLUSIONS

Some of the patients presented with a severe IENFD reduction. Because the number of unmyelinated fibres was well preserved at the level of the sural nerve biopsy, this severe reduction may indicate involvement at the most distal nerve terminals of unmyelinated fibres. Although the reduction of IENFD becomes evident as polyneuropathy becomes severe, the effects of glucose intolerance should also be considered in patients with moderate to severe reductions.

Advances in diagnostics and outcome measures in peripheral neuropathies

Peripheral neuropathies are a group of acquired and hereditary disorders presenting with different distribution and nerve fiber class involvement. The overall prevalence is 2.4%, increasing to 8% in the elderly population. However, the frequency may vary depending on the underlying pathogenesis and association with systemic diseases. Distal symmetric polyneuropathy is the most common form, though multiple mononeuropathies, non-length dependent neuropathy and small fiber neuropathy can occur and may require specific diagnostic tools. The use of uniform outcome measures in peripheral neuropathies is important to improve the quality of randomized controlled trials, enabling comparison between studies. Recent developments in defining the optimal set of outcome measures in inflammatory neuropathies may serve as an example for other conditions. Diagnostic and outcome measure advances in peripheral neuropathies will be discussed.

Progress in the treatment of small fiber peripheral neuropathy

Small fiber neuropathy is a syndrome of diverse disease etiology because of multiple pathophysiologic mechanisms with major presentations of neuropathic pain and autonomic symptoms. Over the past decade, there has been substantial progress in the treatments for neuropathic pain, dysautonomia and disease-modifying strategy. In particular, anticonvulsants and antidepressants alleviate neuropathic pain based on randomized clinical trials.

The cutaneous nerve biopsy: technical aspects, indications, and contribution

Skin biopsy with a 3mm disposable circular punch is easy to perform and allows, after proper processing, the visualization of epidermal, dermal, and sweat gland nerve fibers. A technique of sampling the epidermis alone by applying a suction capsule, the "blister" technique, has also been developed. It is most common to stain immunohistochemically for the pan-axonal marker protein gene product 9.5 (PGP 9.5), an ubiquitin C-terminal hydroxylase. The sections are then observed and analyzed with bright-field microscopy or with indirect immunofluorescence with or without confocal microscopy. Most studies report quantification of intraepidermal nerve fiber density displayed in bright-field microscopy. Normative values have been established, particularly from the distal part of the leg, 10cm above the external malleolus. In diabetes mellitus early degeneration of intraepidermal nerve fibers is induced and there is slower regeneration even when there is no evidence of neuropathy. Skin biopsy is of particular value in the diagnosis of small fiber neuropathy when nerve conduction studies are normal. It may also be repeated in order to study the progressive nature of the disease and also has the potential of studying regeneration of nerve fibers and thus the effects of treatment. Inflammatory demyelinating neuropathies may also involve loss of small-diameter nerve fibers and IgM deposits in dermal myelinated nerve fibers in anti-MAG neuropathy. In some cases the presence of vasculitis in skin may indicate a nonsystemic vasculitic neuropathy and in HIV neuropathy intraepidermal nerve fiber density is reduced in a length-dependent manner. In several hereditary neuropathies intraepidermal nerve fiber density may be reduced but other abnormalities can also be demonstrated in dermal myelinated fibers. Some small swellings and varicosities may be present in the distal leg skin biopsy of healthy individuals but large axonal swellings are considered as evidence of a pathological process affecting the normal structure of nerves. The indirect immunofluorescence technique with confocal microscopy provides the opportunity to study the complex structure of sensory receptors and cutaneous myelinated fibers and the innervation of sweat glands, arrector pilorum muscles, and vessels.

Genetic polymorphism of the growth arrest-specific 6 gene is associated with cutaneous vasculitis in Taiwanese patients with systemic lupus erythematosus

The growth arrest-specific 6 (GAS6) gene product participates in platelet activation and granulocyte interaction with the endothelium. Our case-control study aimed to determine whether polymorphism of GAS6 was associated with predisposing risk or specific clinical manifestations of systemic lupus erythematosus (SLE). Two of the single-nucleotide polymorphisms (SNPs) of the GAS6 gene, GAS6 834 + 7G/A (rs8191974) and GAS6 +1332C/T (rs1803628), were investigated in 83 SLE patients and 89 non-lupus control subjects. We demonstrated that among lupus patients, the GAS6 +1332 T allele was more prevalent in patients with cutaneous vasculitis (allele T 41.7 % in patients with cutaneous vasculitis compared with 18.3 % in patients without vasculitis, odds ratio (OR) 3.2, 95 % confidence interval 1.3-8.0, p = 0.016). In conclusion, GAS6 polymorphism is positively associated with cutaneous vasculitis in SLE patients, which suggests that GAS6 polymorphism could be a genetic marker for SLE with cutaneous vasculitis.

fMRI evidence of degeneration-induced neuropathic pain in diabetes: enhanced limbic and striatal activations

Persistent neuropathic pain due to peripheral nerve degeneration in diabetes is a stressful symptom; however, the underlying neural substrates remain elusive. This study attempted to explore neuroanatomical substrates of thermal hyperalgesia and burning pain in a diabetic cohort due to pathologically proven cutaneous nerve degeneration (the painful group). By applying noxious 44°C heat stimuli to the right foot to provoke neuropathic pain symptoms, brain activation patterns were compared with those of healthy control subjects and patients with a similar degree of cutaneous nerve degeneration but without pain (the painless group). Psychophysical results showed enhanced affective pain ratings in the painful group. After eliminating the influence of different pain intensity ratings on cerebral responses, the painful group displayed augmented responses in the limbic and striatal structures, including the perigenual anterior cingulate cortex (ACC), superior frontal gyrus, medial thalamus, anterior insular cortex, lentiform nucleus (LN), and premotor area. Among these regions, blood oxygen level-dependent (BOLD) signals in the ACC and LN were correlated with pain ratings to thermal stimulations in the painful group. Furthermore, activation maps of a simple regression analysis as well as a region of interest analysis revealed that responses in these limbic and striatal circuits paralleled the duration of neuropathic pain. However, in the painless group, BOLD signals in the primary somatosensory cortex and ACC were reduced. These results suggest that enhanced limbic and striatal activations underlie maladaptive responses after cutaneous nerve degeneration, which contributed to the development and maintenance of burning pain and thermal hyperalgesia in diabetes.

[Usefulness of skin biopsy in the diagnosis of small fiber neuropathy]

Diagnosis of small fiber neuropathy may be challenging due to subtle clinical signs and to the normality of nerve conduction studies. Skin biopsy is a non invasive method which allows to quantify intraepidermal nerve fiber density after a simple immunostaining. The values measured must ideally be compared to normative data obtained on control subjects in order to determine their significance. When the diagnosis of small fiber neuropathy has been made by means of skin biopsy, possibly combined with laser evoked potentials, a diagnostic work up has to be done in order to find one of the classical causes of this disorder. To date, skin biopsy is useful to confirm the diagnosis of small fiber neuropathy but lacks utility to find its etiology.

Quantitation of sudomotor innervation in skin biopsies of patients with diabetic neuropathy

Previous assessments of the sudomotor system have depended on functional tests, and only a few studies document the pathologic findings of postganglionic nerve degeneration quantitatively and at the ultrastructural level. We developed a quantitative system of sudomotor innervation in skin biopsies of the distal leg by immunostaining of nerve fibers with anti-protein gene product 9.5 (PGP9.5) and by counterstaining with Congo red. A computerized area-based morphometric analysis was used to quantify the sweat gland innervation index (SGII), defined as the area of nerve fibers normalized to the area of sweat glands. This approach reduced the variations in measurements of sweat gland areas compared to the commonly used method by ∼5.6-fold (2.47% ± 2.54% vs 13.97% ± 14.24%, p < 0.001); hence, variations in SGII were also reduced. We examined 35 Type 2 diabetic patients (24 men and 11 women; mean age, 56.5 ± 12.8 years), with symmetrical length-dependent neuropathy and reduced intraepidermal nerve fiber density (0.76 ± 0.95 fibers/mm). By light and electron microscopy, PGP9.5-positive nerve terminals surrounded Congo red-positive sweat gland secretory coils in controls; these periglandular nerve terminals were either absent or markedly reduced in diabetic patients. Diabetic patients had lower SGII values than age- and sex-matched controls (2.60% ± 1.96% vs 4.84% ± 1.51%, p < 0.0001). The SGII values were lower in patients with anhidrosis of the feet versus those with normal sweating of the feet (0.89% ± 0.71% vs 3.10% ± 1.94%, p < 0.01). Thus, skin biopsy offers combined assessment of sudomotor innervation.

Neuromuscular abnormality and autonomic dysfunction in patients with cerebrotendinous xanthomatosis

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a rare lipid-storage disease. Neuromuscular abnormality and autonomic system (ANS) dysfuction in CTX are rarely examined in large-scale studies in the literature. We studied the peripheral nervous system, myopathology, and autonomic system of four CTX patients and performed a literature review of the reported CTX patients with peripheral neuropathy.

METHODS

Four biochemically and genetically confirmed CTX patients, belonging to two families, were included for study and all received nerve conduction study (NCS), muscle biopsy for histopathologic and ultrastructural study, skin biopsy for intraepidermal nerve fiber (INEF) density measurement, autonomic testings including sympathetic skin response, R-R interval variation and head-up tilt test using an automated tilt table to record the changes of blood pressure and heart rate in different postures. The Q-Sweat test was also applied for the detection of sweat amount and onset time of response. The clinical characteristics, study methods and results of 13 studies of peripheral neuropathy in CTX patients in the literature were also recorded for analysis.

RESULTS

The results of NCS study showed axonal sensory-motor polyneuropathy in three CTX cases and mixed axonal and demyelinating sensor-motor polyneuropathy in one. The myopathological and histopathologic studies revealed mild denervation characteristics, but the ultrastructural study revealed changes of mitochondria and the membranous system, and increased amounts of glycogen, lipofuscin and lipid deposition. The ANS study revealed different degrees of abnormalities in the applied tests and the INEF density measurement showed small fiber neuropathy in three of the four CTX patients. The literature review of peripheral neuropathy in CTX revealed different types of peripheral neuropathy, of which axonal peripheral neuropathy was the most common.

CONCLUSIONS

Peripheral neuropathy, especially the subtype of axonal sensori-motor neuropathy, is common in patients with CTX. Evidence of lipid metabolic derangement in CTX can be reflected in ultrastructural studies of muscles. With an adequate multi-parametric evaluation, a high incidence of ANS abnormalities can be seen in this rare lipid-storage disease, and a high incidence of small fiber involvement is also reflected in the IENF density measurement of skin biopsies.

European Federation of Neurological Societies/Peripheral Nerve Society Guideline on the use of skin biopsy in the diagnosis of small fiber neuropathy. Report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society

BACKGROUND

Revision of the guidelines on the use of skin biopsy in the diagnosis of peripheral neuropathy, published in 2005, has become appropriate owing to publication of more relevant articles. Most of the new studies focused on small fiber neuropathy (SFN), a subtype of neuropathy for which the diagnosis was first developed through skin biopsy examination. This revision focuses on the use of this technique to diagnose SFN.

METHODS

Task force members searched the Medline database from 2005, the year of the publication of the first EFNS guideline, to June 30th, 2009. All pertinent articles were rated according to the EFNS and PNS guidance. After a consensus meeting, the task force members created a manuscript that was subsequently revised by two experts (JML and JVS) in the field of peripheral neuropathy and clinical neurophysiology, who were not previously involved in the use of skin biopsy.

RESULTS AND CONCLUSIONS

Distal leg skin biopsy with quantification of the linear density of intraepidermal nerve fibers (IENF), using generally agreed upon counting rules, is a reliable and efficient technique to assess the diagnosis of SFN (Recommendation Level A). Normative reference values are available for bright-field immunohistochemistry (Recommendation Level A) but not yet for confocal immunofluorescence or the blister technique. The morphometric analysis of IENF density, either performed with bright-field or immunofluorescence microscopy, should always refer to normative values matched for age (Recommendation Level A). Newly established laboratories should undergo adequate training in a well-established skin biopsy laboratory and provide their own stratified for age and gender normative values, intra- and interobserver reliability, and interlaboratory agreement. Quality control of the procedure at all levels is mandatory (Good Practice Point). Procedures to quantify subepidermal nerve fibers and autonomic innervated structures, including erector pili muscles, and skin vessels, are under development but need to be confirmed by further studies. Sweat gland innervation can be examined using an unbiased stereologic technique recently proposed (Recommendation Level B). A reduced IENF density is associated with the risk of developing neuropathic pain (Recommendation Level B), but it does not correlate with its intensity. Serial skin biopsies might be useful for detecting early changes of IENF density, which predict the progression of neuropathy, and to assess degeneration and regeneration of IENF (Recommendation Level C). However, further studies are warranted to confirm its potential usefulness as an outcome measure in clinical practice and research. Skin biopsy has not so far been useful for identifying the etiology of SFN. Finally, we emphasize that 3-mm skin biopsy at the ankle is a safe procedure based on the experience of 10 laboratories reporting absence of serious side effects in approximately 35,000 biopsies and a mere 0.19% incidence of non-serious side effects in about 15 years of practice (Good Practice Point).

Skin biopsy as an additional diagnostic tool in non-systemic vasculitic neuropathy

Sural nerve biopsy is considered mandatory for diagnosing non-systemic vasculitic neuropathy (NSVN). This invasive technique may be associated with unpleasant sequelae and cannot easily be repeated. Skin punch biopsy from an affected area may be a less invasive and repeatable diagnostic method. Here we assessed the potential diagnostic value of skin punch biopsies in NSVN by analyzing skin biopsies in 20 patients with sural nerve biopsy-proven NSVN and in 11 patients with non-inflammatory axonal neuropathy. As further controls, skin biopsies were studied in nine healthy volunteers. Five millimeter skin punch biopsies were taken under local anesthesia from the distal lateral calf and T cells and macrophages were quantified after immunostaining. The diagnostic sensitivity and specificity compared to sural nerve biopsy was determined using receiver operating characteristic (ROC) analysis. ROC analysis revealed that the highest sensitivity (94%) and specificity (79%) for NSVN was obtained when perivascular macrophages were quantified. Quantification of scattered T cells yielded a sensitivity and specificity of 65%. Inflammatory cells were very rare in controls. Quantification of inflammatory cells in skin biopsies may thus be a sensitive and specific additional tool for diagnosing NSVN.

Pathogenesis, diagnosis and management of neuropsychiatric SLE manifestations

Neuropsychiatric events are common in patients with systemic lupus erythematosus (SLE), but less than one-third of these events can be directly attributed to SLE. Increased generalized SLE disease activity or damage, previous or concurrent major neuropsychiatric SLE (NPSLE) events, and persistently positive moderate-to-high antiphospholipid antibody titers are established risk factors, and their presence could facilitate proper attribution to the disease itself. Diagnostic evaluation is guided by the presenting manifestation; MRI is used to visualize brain or spinal pathologies. For neuropsychiatric events believed to reflect an immune or inflammatory process, or when these events occur in the context of active generalized disease, evidence (primarily from uncontrolled studies) supports the use of glucocorticoids alone or in combination with immunosuppressive therapy. Antiplatelet and/or anticoagulation therapy is recommended for NPSLE manifestations related to antiphospholipid antibodies, especially for thrombotic cerebrovascular disease. For the future, we anticipate that novel biomarkers and advanced neuroimaging tests will better define the underlying pathologic mechanisms of SLE-related neuropsychiatric disease, and help guide therapeutic decisions.

Evaluation of distal symmetric polyneuropathy: the role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review)

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of autonomic testing, nerve biopsy, and skin biopsy for the assessment of polyneuropathy. A literature review using MEDLINE, EMBASE, Science Citation Index, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based on the level of evidence. (1) Autonomic testing may be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). (2) Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). (3) Skin biopsy is a validated technique for determining intraepidermal nerve fiber (IENF) density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy.

Skin biopsy for the diagnosis of peripheral neuropathy

Skin biopsy has become an accepted tool for investigating small nerve fibres, which are invisible to conventional neurophysiological tests even though they are affected early on in peripheral neuropathies of varying aetiology. Morphometric analysis of epidermal and dermal nerves has proved to be reliable, reproducible and unaffected by the severity of neuropathy, making skin biopsy useful for diagnosing small fibre neuropathy (SFN) in clinical practice. The possibility of obtaining skin biopsy specimens from different sites of the body, to repeat them within the area of the same sensory nerve, to distinguish between somatic and autonomic nerves and to investigate the expression of nerve-related proteins has widened the potential applications of this technique to clinical research. Skin biopsy performed using a minimally invasive disposable punch is a safe and painless procedure. Using specific antibodies with bright-field immunohistochemistry or immunofluorescence technique, it is possible to investigate unmyelinated fibres innervating the epidermis of hairy and glabrous skin, large myelinated fibres supplying specialized corpuscles in glabrous skin, and autonomic fibres innervating sweat glands, blood vessels and arrector pilorum muscles. This review discusses the features of skin innervation in hairy and glabrous skin, the functional properties of skin nerve fibres and their changes in peripheral neuropathies.

Neuropathic changes in equine laminitis pain

Laminitis is a common debilitating disease in horses that involves painful disruption of the lamellar dermo-epidermal junction within the hoof. This condition is often refractory to conventional anti-inflammatory analgesia and results in unremitting pain, which in severe cases requires euthanasia. The mechanisms underlying pain in laminitis were investigated using quantification of behavioural pain indicators in conjunction with histological studies of peripheral nerves innervating the hoof. Laminitic horses displayed consistently altered or abnormal behaviours such as increased forelimb lifting and an increased proportion of time spent at the back of the box compared to normal horses. Electron micrographic analysis of the digital nerve of laminitic horses showed peripheral nerve morphology to be abnormal, as well as having reduced numbers of unmyelinated (43.2%) and myelinated fibers (34.6%) compared to normal horses. Sensory nerve cell bodies innervating the hoof, in cervical, C8 dorsal root ganglia (DRG), showed an upregulated expression of the neuronal injury marker, activating transcription factor-3 (ATF3) in both large NF-200-immunopositive neurons and small neurons that were either peripherin- or IB4-positive. A significantly increased expression of neuropeptide Y (NPY) was also observed in myelinated afferent neurons. These changes are similar to those reported in other neuropathic pain states and were not observed in the C4 DRG of laminitic horses, which is not associated with innervation of the forelimb. This study provides novel evidence for a neuropathic component to the chronic pain state associated with equine laminitis, indicating that anti-neuropathic analgesic treatment may well have a role in the management of this condition.

Skin biopsy in the management of peripheral neuropathy

Skin biopsy has been widely used in recent years for the investigation of small-calibre sensory nerves, including somatic unmyelinated intraepidermal nerve fibres, dermal myelinated nerve fibres, and autonomic nerve fibres in peripheral neuropathies, with different techniques for tissue processing and nerve fibre assessment. Here, we review the techniques for skin biopsy, the processing and assessment of the biopsy sample, their possible uses in different types of peripheral neuropathy, and their use in the follow-up of patients and in clinical trials. We also review the association between morphological measures of skin innervation and function and the limits of this method in the aetiological classification of peripheral neuropathies.