Skin nerve pathology: Biomarkers of premanifest and manifest amyloid neuropathy

Cardiovascular autonomic failure in hereditary transthyretin amyloidosis and TTR carriers is an early and progressive disease marker

BACKGROUND

The cardiomyopathic and neuropathic phenotype of hereditary transthyretin amyloidosis are well recognized. Cardiovascular autonomic dysfunction is less systematically and objectively assessed.

METHODS

Autonomic and clinical features, quantitative cardiovascular autonomic function, and potential autonomic prognostic markers of disease progression were recorded in a cohort of individuals with hereditary transthyretin amyloidosis and in asymptomatic carriers of TTR variants at disease onset (T0) and at the time of the first quantitative autonomic assessment (T1). The severity of peripheral neuropathy and its progression was stratified with the polyneuropathy disability score.

RESULTS

A total of 124 individuals were included (111 with a confirmed diagnosis of hereditary transthyretin amyloidosis, and 13 asymptomatic carriers of TTR variants). Symptoms of autonomic dysfunction were reported by 27% individuals at T0. Disease duration was 4.5 ± 4.0 years [mean ± standard deviation (SD)] at autonomic testing (T1). Symptoms of autonomic dysfunction were reported by 78% individuals at T1. Cardiovascular autonomic failure was detected by functional testing in 75% individuals and in 64% of TTR carriers. Progression rate from polyneuropathy disability stages I/II to III/IV seemed to be shorter for individuals with autonomic symptoms at onset [2.33 ± 0.56 versus 4.00 ± 0.69 years (mean ± SD)].

CONCLUSIONS

Cardiovascular autonomic dysfunction occurs early and frequently in individuals with hereditary transthyretin amyloidosis within 4.5 years from disease onset. Cardiovascular autonomic failure can be subclinical in individuals and asymptomatic carriers, and only detected with autonomic function testing, which should be considered a potential biomarker for early diagnosis and disease progression.

Detailed clinical, physiological and pathological phenotyping can impact access to disease-modifying treatments in ATTR carriers

BACKGROUND

Hereditary transthyretin amyloidosis is a life-threatening autosomal dominant systemic disease due to pathogenic TTR variants (ATTRv), mostly affecting the peripheral nerves and heart. The disease is characterised by a combination of symptoms, organ involvement and histological amyloid deposition. The available disease-modifying ATTRv treatments (DMTs) are more effective if initiated early. Pathological nerve conduction studies (NCS) results are the cornerstone of large-fibre polyneuropathy diagnosis, but this anomaly occurs late in the disease. We investigated the utility of a multimodal neurological and cardiac evaluation for detecting early disease onset in ATTRv carriers.

METHODS

We retrospectively analysed a cohort of ATTRv carriers with normal NCS results regardless of symptoms. Multimodal denervation and infiltration evaluations included a clinical questionnaire (Lauria and New York Heart Association (NYHA)) and examination, intra-epidermal nerve fibre density assessment, autonomic assessment based on heart rate variability, Sudoscan, meta-iodo-benzyl-guanidine scintigraphy, cardiac biomarkers, echocardiography, MRI and searches for amyloidosis on skin biopsy and bone scintigraphy.

RESULTS

We included 130 ATTRv carriers (40.8% men, age: 43.6±13.5 years), with 18 amyloidogenic TTR gene mutations, the majority of which was the late-onset Val30Met variant (42.3%). Amyloidosis was detected in 16.9% of mutation carriers, including 9 (6.9%) with overt disease (Lauria>2 or NYHA>1) and 13 asymptomatic carriers (10%) with organ involvement (small-fibre neuropathy or cardiomyopathy). Most of these patients received DMT. Abnormal test results of unknown significance were obtained for 105 carriers (80.8%). Investigations were normal in only three carriers (2.3%).

CONCLUSIONS

Multimodal neurological and cardiac investigation of TTRv carriers is crucial for the early detection of ATTRv amyloidosis and initiation of DMT.

Cutaneous biomarkers of therapeutic efficacy in early treatment of hereditary ATTR amyloid polyneuropathy with tafamidis

BACKGROUND

ATTR (ATTRv) amyloidosis neuropathy is characterized by progressive sensorimotor and autonomic nerve degeneration secondary to amyloid deposition caused by a misfolded transthyretin protein (TTR). Small nerve fiber neuropathy is an early clinical manifestation of this disease resulting from the dysfunction of the Aδ and C small nerve fibers. Tafamidis, a selective TTR stabilizer, has proven its efficacy in the earlier stages of hATTR.

OBJECTIVES

To evaluate the clinical course and utility of cutaneous pathological biomarkers in patients with ATTR amyloidosis treated with tafamidis compared to control patients.

METHODS

Forty patients diagnosed with early stages of ATTRv amyloidosis (polyneuropathy disability [PND] scores 0-II) underwent small and large nerve fiber neurological evaluations, and annual skin biopsies for intraepidermal nerve fiber density (IENFD) and amyloid deposition index (ADI) estimation. Thirty patients were allocated to receive tafamidis, and 10 patients served as controls. Tafamidis pharmacokinetics analysis was performed in patients who received the treatment.

RESULTS

At baseline, 12% of patients in stage PND 0 and 28% in PND I displayed small nerve fiber denervation in the distal thigh, whereas 23% and 38%, respectively, in the distal leg. Similarly, 72% and 84% had amyloid deposition in the distal thigh and 56% and 69% in the distal leg. Following 1 year of treatment, the tafamidis group showed significant clinical improvement compared to the control group, revealed by the following mean differences (1) -9.3 versus -4 points (p = <.00) in the patient's neuropathy total symptom score 6 (NTSS-6) questionnaire, (2) -2.5 versus +2.8 points (p = <.00) in the Utah Early Neuropathy Score (UENS), and (3) +1.2°C versus -0.6 (p = .01) in cold detection thresholds. Among the patients who received tafamidis, 65% had stable or increased IENFD in their distal thigh and 27% in the distal leg. In contrast, all patients in the control group underwent denervation. The ADI either decreased or remained constant in 31% of the biopsies in the distal thigh and in 24% of the biopsies in the distal leg of the tafamidis-treated patients, whereas it rose across all the biopsies in the control group. At the 4-year follow-up, the tafamidis group continued to display less denervation in the distal thigh (mean difference [MD] of -3.0 vs. -9.3 fibers/mm) and the distal leg (mean difference [MD] -4.9 vs. -8.6 fibers/mm). ADI in tafamidis-treated patients was also lower in the distal thigh (10 vs. 30 amyloid/mm2) and the distal leg (23 vs. 40 amyloid/mm2) compared to control patients. Plasma tafamidis concentrations were higher in patients with IENFD improvement and in patients with reduced amyloid deposition. Patients without amyloid deposition in the distal leg at baseline displayed delayed disease progression at 4 years.

CONCLUSIONS

Cutaneous IENFD and amyloid deposition assessments in the skin of the distal thigh and distal leg are valuable biomarkers for early diagnosis of ATTR amyloidosis and for measuring the progression of small nerve fiber neuropathy. Early treatment with tafamidis slows the clinical progression of the disease, skin denervation, and amyloid deposition in the skin. Higher plasma concentrations of tafamidis are associated with better disease outcomes, suggesting that increasing the drug dose could achieve better plasma concentrations and response rates. This study describes the longest small nerve fiber neuropathy therapeutic trial with tafamidis and is the first to report small fiber symptoms, function, and structural assessments as outcomes.

Altered gut microbiota in Taiwanese A97S predominant transthyretin amyloidosis with polyneuropathy

Increasing evidence suggests that gut microbiota alterations are related to development and phenotypes of many neuropsychiatric diseases. Here, we evaluated the fecal microbiota and its clinical correlates in patients with hereditary transthyretin amyloidosis (ATTRv) and polyneuropathy. Fecal microbiota from 38 ATTRv patients and 39 age-matched controls was analyzed by sequencing 16S V3-V4 ribosomal RNA, and its relationships with clinical characteristics of polyneuropathy and cardiomyopathy were explored. The familial amyloidotic polyneuropathy stage was stage I, II, and III in 13, 18, and 7 patients. 99mTc-PYP SPECT showed a visual score of 2 in 15 and 3 in 21 patients. The gut microbiota of ATTRv patients showed higher alpha diversity (ASV richness and Shannon effective numbers) and dissimilar beta diversity compared to controls. Relative abundance of microbiota was dominated by Firmicutes and decreased in Bacteroidetes in ATTRv patients than in controls. Patients with more myocardial amyloid deposition were associated with increased alpha diversity, and the abundance of Clostridia was significantly correlated with pathophysiology of polyneuropathy in ATTRv patients. These findings demonstrated alterations in the gut microbiota, especially Firmicutes, in ATTRv. The association between altered microbiota and phenotypes of cardiomyopathy and polyneuropathy might suggest potential contributions of gut microbiota to ATTRv pathogenesis.

Nerve pathology of microangiopathy and thromboinflammation in hereditary transthyretin amyloidosis

OBJECTIVE

Despite amyloid deposition as a hallmark of hereditary transthyretin amyloidosis (ATTRv) with polyneuropathy, this pathology could not completely account for nerve degeneration. ATTRv patients frequently have vasomotor symptoms, but microangiopathy hypothesis in ATTRv was not systemically clarified.

METHODS

This study examined the vascular pathology of sural nerves in ATTRv patients with transthyretin (TTR) mutation of p.Ala117Ser (TTR-A97S), focusing on morphometry and patterns of molecular expression in relation to nerve degeneration. We further applied human microvascular endothelial cell (HMEC-1) culture to examine the direct effect of TTR-A97S protein on endothelial cells.

RESULTS

In ATTRv nerves, there was characteristic microangiopathy compared to controls: increased vessel wall thickness and decreased luminal area; both were correlated with the reduction of myelinated fiber density. Among the components of vascular wall, the area of collagen IV in ATTRv nerves was larger than that of controls. This finding was validated in a cell model of HMEC-1 culture in which the expression of collagen IV was upregulated after exposure to TTR-A97S. Apoptosis contributed to the endothelial cell degeneration of microvasculatures in ATTRv endoneurium. ATTRv showed prothrombotic status with intravascular fibrin deposition, which was correlated with (1) increased tissue factor and coagulation factor XIIIA and (2) reduced tissue plasminogen activator. This cascade led to intravascular thrombin deposition, which was colocalized with upregulated p-selectin and thrombomodulin, accompanied by complement deposition and macrophages infiltration, indicating thromboinflammation in ATTRv.

INTERPRETATION

Microangiopathy with thromboinflammation is characteristic of advanced-stage ATTRv nerves, which provides an add-on mechanism and therapeutic target for nerve degeneration.

Amyloid detection and typing yield of skin biopsy in systemic amyloidosis and polyneuropathy

OBJECTIVE

Disease-modifying therapies are available for amyloidosis but are ineffective if end-organ damage is severe. As small fiber neuropathy is an early and common feature of amyloidosis, we assessed detection and typing yield of skin biopsy for amyloid in patients with confirmed systemic amyloidosis and neuropathic symptoms.

METHODS

In this case-control study, patients with transthyretin and light chain amyloidosis (ATTRv, ATTRwt, and AL) were consecutively recruited. They were sex and age-matched to three control groups (1) non-neuropathic controls (NNC), (2) monoclonal gammopathy of undetermined significance (MGUS), and (3) other neuropathic disease controls (ONC). Patients underwent a double 3 mm skin biopsy in proximal and distal leg. Amyloid index and burden, protein typing by immuno-electron microscopy, intraepidermal nerve fiber density, electroneuromyography, and clinical characteristics were analyzed.

RESULTS

We studied 15 subjects with confirmed systemic amyloidosis, 20 NNC, 18 MGUS, and 20 ONC. Amyloid was detected in 100% of patients with amyloidosis (87% in ankle and 73% in thigh). It was not detected in any of the control groups. A small fiber neuropathy was encountered in 100% of amyloidosis patients, in 80% of MGUS, and in 78% of ONC. Amyloid burden was higher in ATTRv, followed by AL and ATTRwt. The ultrastructural examination allowed the identification of the precursor protein by immunotyping in most of the cases.

INTERPRETATION

Skin biopsy is a minimally invasive test with optimal sensitivity for amyloid. It allows amyloid typing by electron microscope to identify the precursor protein. The diagnostic work up of systemic amyloidosis should include a skin biopsy.

Hereditary transthyretin amyloid neuropathies: advances in pathophysiology, biomarkers, and treatment

Hereditary transthyretin (TTR) amyloid polyneuropathy is an autosomal dominant life-threatening disorder. TTR is produced mainly by the liver but also by the choroid plexus and retinal pigment epithelium. Detailed clinical characterisation, identification of clinical red flags for misdiagnosis, and use of biomarkers enable early diagnosis and treatment. In addition to liver transplantation and TTR stabilisers, three other disease-modifying therapies have regulatory approval: one antisense oligonucleotide (inotersen) and two small interfering RNAs (siRNAs; patisiran and vutrisiran). The siRNAs have been shown to stop progression of neuropathy and improve patients' quality of life. As none of the disease-modifying therapies can cross the blood-brain barrier, TTR deposition in the CNS, which can cause stroke and cognitive impairment, remains an important unaddressed issue. CRISPR-Cas9-based one-time TTR editing therapy is being investigated in a phase 1 clinical study. Identification of the earliest stages of pathogenesis in TTR variant carriers is a major challenge that needs addressing for optimal management.

Quantitative sensory testing and skin biopsy findings in late-onset ATTRv presymptomatic carriers: Relationships with predicted time of disease onset (PADO)

INTRODUCTION

Hereditary transthyretin amyloidosis polyneuropathy (ATTRv-PN) presymptomatic carriers often show preclinical abnormalities at small fiber-related diagnostic tests. However, no validated biomarker is currently available to use for presymptomatic carriers' follow-up, thus helping therapeutic decision making. Our study aimed at assessing nerve conduction study (NCS), quantitative sensory testing (QST), and skin biopsy parameters in a large cohort of late-onset ATTRv presymptomatic carriers and to evaluate whether they correlated with predicted age of disease onset (PADO).

METHODS

Late-onset ATTRv presymptomatic carriers were consecutively enrolled and underwent NCS, QST, and skin biopsy with intraepidermal nerve fiber density (IENFD) evaluation from a distal and a proximal site. Douleur Neuropathique-4 (DN4) and Small Fiber Neuropathy-Symptoms Inventory (SFN-SIQ) were used to assess painful and small fiber neuropathy-related symptoms. PADO and time-to-PADO (delta-PADO) were estimated for each carrier, and correlations with diagnostic test measures were analyzed.

RESULTS

Forty presymptomatic ATTRv subjects were enrolled. Twenty carriers (50%) had distal IENFD reduction, with a non-length-dependent distribution in 73% of cases. Eleven subjects (27.5%) had cold and/or warm detection threshold (CDT and/or WDT) abnormalities at QST. Delta-PADO positively correlated with sural sensory nerve action potential (SNAP) amplitude (r = .416, p = .004), and z-values of QST parameters like CDT (r = .314, p = .028), WDT (r = -.294, p = .034), and mechanical detection threshold (MDT; r = -.382, p = .012). Simple linear regression models showed a linear relation between delta-PADO and sural SAP, CDT, and MDT.

CONCLUSIONS

Our findings confirm that IENFD reduction and QST abnormalities may occur early in ATTRv presymptomatic carriers, often with a non-length-dependent pattern. However, only sural SAP amplitude and QST parameters correlated with delta-PADO, suggesting that serial combined QST and NCS evaluation could be useful in ATTRv presymptomatic carriers' follow-up.

A molecular basis for tetramer destabilization and aggregation of transthyretin Ala97Ser

Transthyretin (TTR)-related amyloidosis (ATTR) is a syndrome of diseases characterized by the extracellular deposition of fibrillar materials containing TTR variants. Ala97Ser (A97S) is the major mutation reported in Taiwanese ATTR patients. Here, we combine atomic resolution structural information together with the biochemical data to demonstrate that substitution of polar Ser for a small hydrophobic side chain of Ala at residue 97 of TTR largely influences the local packing density of the FG-loop, thus leading to the conformational instability of native tetramer, the increased monomeric species, and thus the enhanced amyloidogenicity of apo-A97S. Based on calorimetric studies, the tetramer destabilization of A97S can be substantially altered by interacting with native stabilizers via similarly energetic patterns compared to that of wild-type (WT) TTR; however, stabilizer binding partially rearranges the networks of hydrogen bonding in TTR variants while FG-loops of tetrameric A97S still remain relatively flexible. Moreover, TTR in complexed with holo-retinol binding protein 4 is slightly influenced by the structural and dynamic changes of FG-loop caused by A97S substitution with an approximately five-fold difference in binding affinity. Collectively, our findings suggest that the amyloidogenic A97S mutation destabilizes TTR by increasing the flexibility of the FG-loop in the monomer, thus modulating the rate of amyloid fibrillization.

Ser77Tyr transthyretin amyloidosis in Israel: Initial manifestations and diagnostic features

OBJECTIVE

Amyloidosis due to the transthyretin Ser77Tyr mutation (ATTRS77Y) is a rare autosomal-dominant disorder, characterized by carpal-tunnel syndrome, poly- and autonomic-neuropathy, and cardiomyopathy. However, related symptoms and signs are often nonspecific and confirmatory tests are required. We describe the age and frequency of early symptoms and diagnostic features among individuals of Jewish Yemenite descent in Israel.

METHODS

Records of mutation carriers were retrospectively reviewed. ATTRS77Y diagnosis was defined by the presence of amyloid in tissue and/or amyloid-related cardiomyopathy.

RESULTS

We identified the Ser77Tyr mutation at the heterozygous state in 19 amyloidosis patients (mean age at diagnosis: 62 ± 5.7 years, range 49-70) and 30 amyloid-negative carriers. The probability for disease diagnosis increased from 4.4% at age 49 to 100% at 70 and occurred earlier in males. Initial symptoms preceded diagnosis by 5 ± 3.8 years (range 0-12) and were commonly sensory changes in the extremities. Erectile dysfunction predated these in 8/13 (62%) males. In two patients cardiac preceded neurological symptoms. Two patients declined symptoms. Electrophysiological studies near the time of diagnosis indicated a median neuropathy at the wrist in 18/19 (95%) and polyneuropathy in 13/19 (68%). Skin biopsy revealed epidermal denervation in 15/16 (94%) patients. Cardiomyopathy was identified in 16/19 (84%). Sensory complaints or epidermal denervations were present in 17/30 (57%) of amyloid-negative carriers and co-occurred in 10/30 (33%).

INTERPRETATION

ATTRS77Y symptoms commonly occur after age 50, but may begin earlier. Median neuropathy, skin denervation and cardiomyopathy are frequently identified. Symptoms may be absent in patients and common in amyloid-negative carriers.

Cutaneous amyloid is a biomarker in early ATTRv neuropathy and progresses across disease stages

Objective

To determine the sensitivity and specificity of cutaneous amyloid deposition in relation to patient‐reported measures in the earliest disease stage of hereditary ATTR amyloidosis (ATTRv).

Methods

In a cross‐sectional study, we analyzed 88 individuals with TTR mutations, 47 of whom were in the earliest disease stage and without clinically evident neuropathy, 12 healthy controls, and 13 disease controls with diabetes. All participants' neuropathy symptoms and signs were assessed using validated patient and clinician‐reported measures and 3‐mm skin punch biopsies were immunostained using protein gene product 9.5 and Congo Red.

Results

Amyloid can be detected in the earliest disease stages in up to 86% of patients with ATTRv amyloidosis. Amyloid was not detected in healthy individuals or individuals with diabetic peripheral neuropathy supporting a sensitivity of 86% and a specificity of 100%. The cutaneous deposition of amyloid correlates with neuropathy sensory symptoms, measured with the Neuropathy Total Symptom Score‐6 (R = 0.46, p < 0.01); pain measured with the Brief Pain Symptom Inventory (R = 0.44, p < 0.05); autonomic symptoms, measured with the Boston Autonomic Symptom Questionnaire (R = 0.38, p < 0.05); and quality of life measured with the Norfolk Diabetic Neuropathy Quality of Life Questionnaire (R = 0.44, p < 0.05). Individuals with amyloid deposition were more likely to have sensory symptoms, pain, autonomic impairment, and reduced quality of life than ATTRv patients without amyloid deposition.

Interpretation

These findings have implications for understanding the earliest manifestations of the clinical phenotype of ATTRv‐associated neuropathy, for the pathophysiological construct of disease staging, and for timing the introduction of disease‐modifying therapy.

Cardiomyopathy correlates to nerve damage in p.A117S late-onset transthyretin amyloid polyneuropathy

Objective

Late‐onset hereditary transthyretin amyloidosis with polyneuropathy (ATTRv‐PN) is often associated with heart involvement. Recent advances in cardiac imaging allow the detection of cardiac amyloidosis. This study aimed to explore cardiomyopathy by cardiac imaging and its clinical correlates with polyneuropathy in late‐onset ATTRv‐PN.

Methods

Polyneuropathy was assessed by intraepidermal nerve fiber (IENF) density, nerve conduction study (NCS), autonomic function tests, quantitative sensory testing, and clinical questionnaires. Cardiomyopathy was evaluated by echocardiography, ^99mTc‐pyrophosphate (PYP) single‐photon emission computed tomography (SPECT) imaging, cardiac magnetic resonance imaging (CMR), and serum Pro‐B‐type natriuretic peptide. Healthy controls and patients with Brugada syndrome were enrolled for comparison of CMR.

Results

Fifty late‐onset ATTRv‐PN patients (38 men, 46 with p. A117S mutation), aged 63.7 ± 5.5 years, of polyneuropathy disability stage 1–4 were enrolled. All patients presented polyneuropathy in NCS, and 74.5% of patients had reduced IENF density in distal legs. All patients showed significant radiotracer uptake in the heart on ^99mTc‐PYP SPECT imaging, and 87.8% of patients had abnormally increased left ventricular (LV) septum thickness on echocardiography. CMR showed longer myocardial native T1, larger extracellular volume, greater LV mass index, and higher LV mass to end‐diastolic volume ratio in ATTRv‐PN patients than healthy controls and patients with Brugada syndrome. These CMR parameters were associated with skin denervation, absent sympathetic skin responses, elevated thermal thresholds, worsened NCS profiles, and functional deficits of polyneuropathy.

Interpretation

Late‐onset ATTRv‐PN coexisted with cardiomyopathy regardless of the clinical severity of polyneuropathy. The cardiac amyloid burden revealed by CMR was correlated with pathophysiology and clinical disability of nerve degeneration.

Diabetic visceral neuropathy of gastroparesis: gastric mucosal innervation and clinical significance

BACKGROUND

The pathogenesis of diabetic gastroparesis due to visceral neuropathy involves multi-dimensional mechanisms with limited exploration of gastric mucosal innervation. This study aimed to quantitatively examine this topic and its relationship with gastroparesis symptoms and gastric emptying in diabetes.

METHODS

We prospectively enrolled 22 patients with type 2 diabetes and gastroparesis symptoms and 25 age- and gender-matched healthy controls for comparison. The assessments include (1) neuropathology with quantification of gastric mucosal innervation density (MID) on endoscopic biopsy, (2) clinical manifestations with questionnaire of gastroparesis cardinal symptom index (GCSI), and (3) functional tests of gastric emptying scintigraphy (GES).

RESULTS

In diabetic patients, stomach fullness, bloating, and feeling excessively full after meals constituted the most common GCSI symptoms. Seven (32%) diabetic patients had prolonged gastric emptying patterns. In diabetes, gastric MID was significantly lower in all examined parts compared with the controls: antrum (294.8±237.0 vs. 644.0±222.0mm/mm³ , p<0.001), body (292.2±239.0 vs. 652.6±260.9mm/mm³ , p<0.001), and fundus (238.0±109.1 vs. 657.2±332.8mm/mm³ , p<0.001). Gastric MID was negatively correlated with gastroparesis symptoms and total scores of GCSI (p<0.001). Furthermore, gastric MID in the fundus was negatively correlated with fasting glucose and HbA1c levels. Gastric emptying parameters, including T_1/2 and gastric retention, were prolonged in diabetes and gastric retention at 3h was correlated with fasting glucose level.

CONCLUSION

In diabetes, gastric MID was reduced and GES parameters were prolonged. Both were correlated with gastroparesis symptoms and glycemic control. These findings provide pathology and functional biomarkers for diabetic visceral neuropathy of gastroparesis and underlying pathophysiology.

Skin amyloid deposits and nerve fiber loss as markers of neuropathy onset and progression in hereditary transthyretin amyloidosis

OBJECTIVE

To assess skin biopsy as marker of disease onset and severity in hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN), a treatable disease.

METHODS

In this single center retrospective study, skin Congo red staining and intraepidermal nerve fiber density (IENFD) were evaluated in symptomatic ATTRv-PN patients and asymptomatic TTR gene mutation carriers between 2012 and 2019. Non-ATTRv subjects with small fiber neuropathy suspicion who underwent skin biopsy in the same timespan were used as controls.

RESULTS

One-hundred-eighty-three symptomatic ATTRv-PN, 36 asymptomatic carriers, and 537 non-ATTRv patients were included. Skin biopsy demonstrated amyloid depositions in 80% of the 183 symptomatic cases. Skin amyloid deposits were found in 75% of early-stage ATTRv-PN patients, and in 14% of asymptomatic carriers. All 183 symptomatic and 34/36 asymptomatic patients displayed decreased ankle IENFD with a proximal-distal gradient distribution, and reduced IEFND correlated with disease severity and duration.

CONCLUSIONS

Our study demonstrates skin amyloid deposits are a marker of ATTRv-PN disease onset, and decreased IENFD a marker of disease progression. These results are of major importance for the early identification of ATTRv-PN patients in need of disease-modifying treatments.

Maladaptive motor cortical excitability and connectivity in polyneuropathy with neuropathic pain

BACKGROUND

Sensory symptoms, especially neuropathic pain, are common in polyneuropathy. Conventional diagnostic tools can evaluate structural or functional impairment of nerves but cannot reveal mechanisms of neuropathic pain. Changes in the brain after polyneuropathy may play roles in the genesis of neuropathic pain.

METHODS

This cross-sectional study investigated changes of cortical excitability within left primary motor cortex (M1) by measuring resting motor thresholds, short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and afferent inhibition between polyneuropathy patients and controls, and investigated the correlates of these parameters with neuropathic pain and the M1 structural and functional connectivity assessed by diffusion tractography imaging and functional MRI.

RESULTS

Thirty-three painful and 15 non-painful neuropathic patients and 21 controls were enrolled. There were no differences in intraepidermal nerve fiber density, nerve conduction study, thermal thresholds, or autonomic functional tests between patients with and without neuropathic pain. Compared to controls, neuropathic patients exhibited similar resting motor thresholds or afferent inhibition, but attenuated SICI and augmented ICF, especially in painful patients. Changes of intracortical excitability in neuropathic patients were correlated with intensities of neuropathic pain, and different presentations of SICI and ICF were noted between patients with and without thermal paresthesia. Additionally, short latency afferent inhibition at interstimulus intervals of 20 ms was associated with structural connectivity of left M1 with brain areas associated with pain perception.

CONCLUSIONS

Maladaptive cortical excitability with altered structural connectivity in left M1 developed after peripheral nerve degeneration and was associated with neuropathic pain and sensory symptoms in polyneuropathy.

Vagus nerve ultrasound in transthyretin familial amyloid polyneuropathy: A pilot study

BACKGROUND AND PURPOSE

Autonomic dysfunction is common in transthyretin familial amyloid polyneuropathy (TTR-FAP). Because ultrasonography is a powerful tool to study peripheral neuropathy, vagus nerve (VN) ultrasonography was used in our study to investigate the possible changes of the dimension of VN in TTR-FAP.

METHODS

Eighteen patients with TTR-FAP and 17 age- and gender-matched individuals without any neuropathies were enrolled in a pilot study. The cross-sectional areas (CSAs) were measured bilaterally on transverse scans of vagus, median, and ulnar nerves. Clinical data were collected to explore the correlations with CSAs of VN.

RESULTS

The median CSAs of VN in TTR-FAP were 3.5 (2.0-6.0) mm² on the right side and 2.5 (1.0-6.0) mm² on the left side, compared with 2.0 (1.0-3.0) mm² and 1.0 (1.0-2.0) mm² for healthy controls (HCs). There was a significant difference between the two groups on both sides (p < .001). The mean VN CSAs were correlated positively with the course of disease (r = .7203, p = .0016)（not including the patient with the longest disease course), the Composite Autonomic Symptom Score 31 (r = .5252, p = .0252), the left ventricular posterior wall thickness (r = .5426, p = .0200), and the interventricular septum thickness (r = .5103, p = .0305). The cutoff values of right and left VN CSAs to identify TTR-FAP from HCs were 2.5 and 1.5 mm² and the areas under the curve were .9395 and .8856, with a high sensitivity (.889 and .889) and specificity (.941 and .765), respectively.

CONCLUSION

VN enlargement is prevalent among TTR-FAP patients. VN ultrasonography may be an important clinical tool for assessing the severity of autonomic dysfunction in TTR-FAP.

Skin biopsy and quantitative sensory assessment in an Italian cohort of ATTRv patients with polyneuropathy and asymptomatic carriers: possible evidence of early non-length dependent denervation

AIM

Study of intraepidermal nerve fiber density (IENFD) by skin biopsy represents a promising tool in the evaluation of patients with ATTRv polyneuropathy (ATTRv-PN). Herein, we retrospectively analyze intraepidermal innervation and quantitative sensory test (QST) data from an Italian cohort of Italian ATTRv-PN patients and asymptomatic carriers aimed to provide insights into early nerve pathological and functional changes in this disease.

METHODS

IENFD and QST data of 14 ATTRv-PN patients and 14 asymptomatic carriers were retrospectively analyzed together with clinical and paraclinical data such as disease stage and severity, neuropathic pain scales, and sural SNAP amplitude.

RESULTS

Given an estimated time to the predicted age of onset of symptomatic disease of 20.27 + / - 7.9 years, small nerve fiber loss seems to be unexpectedly early in carriers. Moreover, carriers showed skin denervation at the proximal (thigh) site, suggesting a non-length-dependent neuropathic process. IENFD at ankle correlated with disease severity and other paraclinical variables such as sural nerve potential amplitude and QST parameters. Patients at earlier stages of the disease did not show significant differences in ankle IENFD compared with asymptomatic carriers, but significant differences in terms of QST parameters, small fiber neuropathy symptoms, and neuropathic pain.

CONCLUSIONS

Skin biopsy can disclose an early non-length-dependent small fiber loss in ATTRv-PN and, together with QST, could provide a useful insight disease onset and progression.

Multidisciplinary Approaches for Transthyretin Amyloidosis

Amyloidosis caused by systemic deposition of transthyretin (TTR) is called ATTR amyloidosis and mainly includes hereditary ATTR (ATTRv) amyloidosis and wild-type ATTR (ATTRwt) amyloidosis. Until recently, ATTRv amyloidosis had been considered a disease in the field of neurology because neuropathic symptoms predominated in patients described in early reports, whereas advances in diagnostic techniques and increased recognition of this disease revealed the presence of patients with cardiomyopathy as a predominant feature. In contrast, ATTRwt amyloidosis has been considered a disease in the field of cardiology. However, recent studies have suggested that some of the patients with ATTRwt amyloidosis present tenosynovial tissue complications, particularly carpal tunnel syndrome, as an initial manifestation of amyloidosis, necessitating an awareness of this disease among neurologists and orthopedists. Although histopathological confirmation of amyloid deposits has traditionally been considered mandatory for the diagnosis of ATTR amyloidosis, the development of noninvasive imaging techniques in the field of cardiology, such as echocardiography, magnetic resonance imaging, and nuclear imaging, enabled nonbiopsy diagnosis of this disease. The mechanisms underlying characteristic cardiac imaging findings have been deciphered by histopathological studies. Novel disease-modifying therapies for ATTR amyloidosis, such as TTR stabilizers, short interfering RNA, and antisense oligonucleotides, were initially approved for ATTRv amyloidosis patients with polyneuropathy. However, the indications for the use of these disease-modifying therapies gradually widened to include ATTRv and ATTRwt amyloidosis patients with cardiomyopathy. Since the coronavirus disease 2019 (COVID-19) pandemic, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, occurred, the minimization of hospital visits and telemedicine have become increasingly important. As older age and cardiovascular disease are major factors associated with increased disease severity and mortality of COVID-19, many ATTR amyloidosis patients are at increased risk of disease aggravation when they are infected with SARS-CoV-2. From this viewpoint, close interspecialty communication to determine the optimal interval of evaluation is needed for the management of patients with ATTR amyloidosis.

Acquired and inherited amyloidosis: Knowledge driving patients' care

Until recently, systemic amyloidoses were regarded as ineluctably disabling and life-threatening diseases. However, this field has witnessed major advances in the last decade, with significant improvements in therapeutic options and in the availability of accurate and non-invasive diagnostic tools. Outstanding progress includes unprecedented hematological response rates provided by risk-adapted regimens in light chain (AL) amyloidosis and the approval of innovative pharmacological agents for both hereditary and wild-type transthyretin amyloidosis (ATTR). Moreover, the incidence of secondary (AA) amyloidosis has continuously reduced, reflecting advances in therapeutics and overall management of several chronic inflammatory diseases. The identification and validation of novel therapeutic targets has grounded on a better knowledge of key molecular events underlying protein misfolding and aggregation and on the increasing availability of diagnostic, prognostic and predictive markers of organ damage and response to treatment. In this review, we focus on these recent advancements and discuss how they are translating into improved outcomes. Neurological involvement dominates the clinical picture in transthyretin and gelsolin inherited amyloidosis and has a significant impact on disease course and management in all patients. Neurologists, therefore, play a major role in improving patients' journey to diagnosis and in providing early access to treatment in order to prevent significant disability and extend survival.

Transient receptor potential vanilloid subtype 1 depletion mediates mechanical allodynia through cellular signal alterations in small-fiber neuropathy

Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodal nociceptor that monitors noxious thermal sensations. Few studies have addressed the role of TRPV1 in mechanical allodynia in small-fiber neuropathy (SFN) caused by sensory nerve damage. Accordingly, this article reviews the putative mechanisms of TRPV1 depletion that mediates mechanical allodynia in SFN. The intraepidermal nerve fibers (IENFs) degeneration and sensory neuronal injury are the primary characteristics of SFN. Intraepidermal nerve fibers are mainly C-polymodal nociceptors and Aδ-fibers, which mediated allodynic pain after neuronal sensitization. TRPV1 depletion by highly potent neurotoxins induces the upregulation of activating transcription factor 3 and IENFs degeneration which mimics SFN. TRPV1 is predominately expressed by the peptidergic than nonpeptidergic nociceptors, and these neurochemical discrepancies provided the basis of the distinct pathways of thermal analgesia and mechanical allodynia. The depletion of peptidergic nociceptors and their IENFs cause thermal analgesia and sensitized nonpeptidergic nociceptors respond to mechanical allodynia. These distinct pathways of noxious stimuli suggested determined by the neurochemical-dependent neurotrophin cognate receptors such as TrkA and Ret receptors. The neurogenic inflammation after TRPV1 depletion also sensitized Ret receptors which results in mechanical allodynia. The activation of spinal TRPV1(+) neurons may contribute to mechanical allodynia. Also, an imbalance in adenosinergic analgesic signaling in sensory neurons such as the downregulation of prostatic acid phosphatase and adenosine A1 receptors, which colocalized with TRPV1 as a membrane microdomain also correlated with the development of mechanical allodynia. Collectively, TRPV1 depletion-induced mechanical allodynia involves a complicated cascade of cellular signaling alterations.

Canadian Guidelines for Hereditary Transthyretin Amyloidosis Polyneuropathy Management

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive disease caused by mutations in the TTR gene leading to multisystem organ dysfunction. Pathogenic TTR aggregation, misfolding, and fibrillization lead to deposition of amyloid in multiple body organs and frequently involve the peripheral nerve system and the heart. Common neurologic manifestations include: sensorimotor polyneuropathy (PN), autonomic neuropathy, small-fiber PN, and carpal tunnel syndrome. Many patients have significant progression due to diagnostic delays as hATTR PN is not considered within the differential diagnosis. Recently, two effective novel disease-modifying therapies, inotersen and patisiran, were approved by Health Canada for the treatment of hATTR PN. Early diagnosis is crucial for the timely introduction of these disease-modifying treatments that reduce impairments, improve quality of life, and extend survival. In this guideline, we aim to improve awareness and outcomes of hATTR PN by making recommendations directed to the diagnosis, monitoring, and treatment in Canada.

Early changes of nerve integrity in preclinical carriers of hereditary transthyretin Ala117Ser amyloidosis with polyneuropathy

BACKGROUND AND PURPOSE

Disease-modifying therapies provide new horizons for hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) to slow neuropathic progression. Initiating treatment at the earliest time requires biomarkers reflecting both small- and large-fiber degeneration in carriers.

METHODS

This study included examinations of pathology (intraepidermal nerve fiber [IENF] density), physiology (nerve conduction studies, autonomic function test, and nerve excitability), and psychophysics (thermal thresholds) in carriers to compare to healthy controls and asymptomatic diabetic patients.

RESULTS

There were 43 carriers (44.2 ± 11.4 years, p.Ala117Ser in 42 carriers), 43 controls (43.4 ± 12.7 years) including 26 noncarrier families, and 50 asymptomatic diabetic patients (58.1 ± 9.5 years). Carriers had lower IENF densities than controls and similar densities as diabetic patients. Median nerve conduction parameters, especially distal motor latency, were the most frequent neurophysiological abnormality in carriers, could differentiate carriers from controls and diabetic patients, were correlated with IENF densities in carriers but not in controls and diabetic patients, and were correlated with nerve excitability parameters in carriers but not in controls. Fifteen carriers (34.9%) with electrophysiological evidence of median nerve entrapment at the wrist had lower IENF densities and more abnormal conduction parameters than carriers without. We defined nerve dysfunction index-the ratio of median distal motor latency to IENF density-which differentiated carriers from controls.

CONCLUSIONS

In late-onset ATTRv-PN carriers with predominant p.Ala117Ser, median conduction parameters were the most common neurophysiological abnormalities and served as surrogate signatures of small- and large-fiber impairment. Combination of median distal motor latency and IENF density can reflect early neuropathy in carriers.

Skin Biopsy in Evaluation of Autonomic Disorders

PURPOSE OF REVIEW

This article provides an up-to-date assessment of the role of skin biopsy in the evaluation of autonomic disorders. The standard methodology for completing a skin biopsy, the anatomic structures of interest detected within a skin biopsy, and the disease states in which skin biopsies may provide valuable information are reviewed.

RECENT FINDINGS

Several recent advances in the studies of hereditary amyloidosis and the various degenerative synucleinopathies have demonstrated that simple skin biopsies can provide valuable pathologic evidence of neurologic disease. In addition to diagnosis of the underlying disorder, skin biopsies provide a quantitative structural measurement of the associated autonomic damage.

SUMMARY

Skin biopsies are making great inroads into the study of autonomic and peripheral nerve disorders. Complex immunohistochemical staining protocols are challenging to complete, but the rich data derived from these studies in the diagnosis and monitoring of different disease states suggest that the role of skin biopsies in the study of the autonomic nervous system will continue to expand in the years to come.

hATTR Pathology: Nerve Biopsy Results from Italian Referral Centers

Pathological evidence of amyloid on nerve biopsy has been the gold standard for diagnosis in hereditary transthyretin amyloidosis polyneuropathy (hATTR-PN) for a long time. In this article, we reviewed the pathological findings of a large series of sural nerve biopsies from a cohort of hATTR-PN patients, collected by different Italian referral centers. Patients and Methods: We reviewed clinical and pathological data from hATTR-PN patients, diagnosed and followed in five Italian referral centers for peripheral neuropathies. Diagnosis was formulated after a positive genetic test for transthyretin (TTR) mutations. Sural nerve biopsy was performed according to standard protocols. Results: Sixty-nine sural nerve biopsies from hATTR-PN patients were examined. Congo red positive deposits were found in 73% of cases. Only the Phe64Leu mutation failed to show amyloid deposits in a high percentage of biopsies (54%), as already described. Unusual pathological findings, such as myelin abnormalities or inflammatory infiltrates, were detected in occasional cases. Conclusions: Even if no longer indicated to confirm hATTR-PN clinical suspicion, nerve biopsy remains, in expert hands, a rapid and inexpensive tool to detect amyloid deposition. In Italy, clinicians should be aware that a negative biopsy does not exclude hATTR-PN, particularly for Phe64Leu, one of the most frequent mutations in this country.

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.

Involvement of small nerve fibres and autonomic nervous system in AL amyloidosis: comprehensive characteristics and clinical implications

Peripheral nerve involvement in immunoglobulin light chain (AL) amyloidosis is common, characterised by severe progressive mixed neuropathy with autonomic dysfunction but there is limited data on the implications and the characteristics of small nerve fibres dysfunction (SNFD). The aim of our prospective study was to evaluate SNFD and its clinical implications in newly diagnosed AL patients. Twenty-three consecutive patients (10 male, mean age 61.78 years) and 21 age- and gender-matched healthy controls (8 male, mean age 61.28 years) underwent clinical evaluation and standard nerve conduction studies (NCS), baroreflex sensitivity (BRS) test, quantitative sensory testing (QST) and skin biopsy at the lower leg for measuring the density of the nerve fibres innervating the epidermis (IENFD). Axonal degeneration of the large nerve fibres was revealed in 15 out of 23 patients while SNFD was indicated by QST and skin biopsy in 56% and 61% of the patients respectively. BRS index significantly correlated with the IENFD and the QST results while low IENFD was associated with significantly poorer survival. Our study provides new insights and also an initial evaluation of new tools for assessment of the involvement of autonomic and small nerve fibres in AL amyloidosis. These findings also appear to have prognostic implications.

Diagnostic criteria for small fibre neuropathy in clinical practice and research

The diagnostic criteria for small fibre neuropathy are not established, influencing the approach to patients in clinical practice, their access to disease-modifying and symptomatic treatments, the use of healthcare resources, and the design of clinical trials. To address these issues, we performed a reappraisal study of 150 patients with sensory neuropathy and a prospective and follow-up validation study of 352 new subjects with suspected sensory neuropathy. Small fibre neuropathy diagnostic criteria were based on deep clinical phenotyping, quantitative sensory testing (QST) and intraepidermal nerve fibre density (IENFD). Small fibre neuropathy was ruled out in 5 of 150 patients (3.3%) of the reappraisal study. Small fibre neuropathy was diagnosed at baseline of the validation study in 149 of 352 patients (42.4%) based on the combination between two clinical signs and abnormal QST and IENFD (69.1%), abnormal QST alone (5.4%), or abnormal IENFD alone (20.1%). Eight patients (5.4%) had abnormal QST and IENFD but no clinical signs. Further, 38 patients complained of sensory symptoms but showed no clinical signs. Of those, 34 (89.4%) had normal QST and IENFD, 4 (10.5%) had abnormal QST and normal IENFD, and none had abnormal IENFD alone. At 18-month follow-up, 19 of them (56%) reported the complete recovery of symptoms and showed normal clinical, QST and IENFD findings. None of those with one single abnormal test (QST or IENFD) developed clinical signs or showed abnormal findings on the other test. Conversely, all eight patients with abnormal QST and IENFD at baseline developed clinical signs at follow-up. The combination of clinical signs and abnormal QST and/or IENFD findings can more reliably lead to the diagnosis of small fibre neuropathy than the combination of abnormal QST and IENFD findings in the absence of clinical signs. Sensory symptoms alone should not be considered a reliable screening feature. Our findings demonstrate that the combined clinical, functional and structural approach to the diagnosis of small fibre neuropathy is reliable and relevant both for clinical practice and clinical trial design.

Electrophysiological parameters that contribute to the pathogenesis of familial amyloid polyneuropathy caused by transthyretin mutations

Familial amyloid polyneuropathy (FAP) is a rare, hereditary peripheral neuropathy commonly caused by mutations in human transthyretin (TTR) gene. Clinically, FAP caused by TTR mutations (TTR-FAP) involves both large and small nerve fibers. Details of early electrophysiological features in TTR-FAP remain unclear. To address this issue, we evaluated nerve excitability (NET) results in motor axons of control mice and two transgenic mouse models carrying V30M (TTR^V30M) or A97S (TTR^A97S) mutations that simulate clinical features of TTR-FAP. Transgenic TTR^V30M and TTR^A97S mice demonstrated significant increases in latency in hindlimb withdraw tests, as well as, poor rotarod test performance, compared to TTR^ORF mice. NET evaluation showed reduced S2 accommodation, and increased TEd_undershoot during threshold electrotonus (TE) in motor axons of both TTR^V30M and TTR^A97S mice, indicating that axonal membranes were in a depolarized state. Decreased rheobase combined with increased refractoriness in the transgenic mice suggested that there were reduced sodium currents. Further immunohistochemical study of the sciatic nerves revealed the significantly decrease of voltage-gated sodium channel expression in the transgenic mice. Moreover, superexcitability during the recovery cycle is significantly increased in transgenic mice compared with control mice, which is attributed to increased internodal capacitance. Finally, the electron microscopy demonstrated the reduced g-ratio in TTR^A97S mice may correlate with an atrophic change of axons and/or increase of myelin thickness. In summary, we evaluated NET results in transgenic mice which modeled the clinical features presented in TTR-FAP patients. Reduced sodium channel expression and increased internodal capacitance are factors contributing to the electrophysiological changes in TTR-FAP.

Expert consensus recommendations to improve diagnosis of ATTR amyloidosis with polyneuropathy

Amyloid transthyretin (ATTR) amyloidosis with polyneuropathy (PN) is a progressive, debilitating, systemic disease wherein transthyretin protein misfolds to form amyloid, which is deposited in the endoneurium. ATTR amyloidosis with PN is the most serious hereditary polyneuropathy of adult onset. It arises from a hereditary mutation in the TTR gene and may involve the heart as well as other organs. It is critical to identify and diagnose the disease earlier because treatments are available to help slow the progression of neuropathy. Early diagnosis is complicated, however, because presentation may vary and family history is not always known. Symptoms may be mistakenly attributed to other diseases such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), idiopathic axonal polyneuropathy, lumbar spinal stenosis, and, more rarely, diabetic neuropathy and AL amyloidosis. In endemic countries (e.g., Portugal, Japan, Sweden, Brazil), ATTR amyloidosis with PN should be suspected in any patient who has length-dependent small-fiber PN with autonomic dysfunction and a family history of ATTR amyloidosis, unexplained weight loss, heart rhythm disorders, vitreous opacities, or renal abnormalities. In nonendemic countries, the disease may present as idiopathic rapidly progressive sensory motor axonal neuropathy or atypical CIDP with any of the above symptoms or with bilateral carpal tunnel syndrome, gait disorders, or cardiac hypertrophy. Diagnosis should include DNA testing, biopsy, and amyloid typing. Patients should be followed up every 6–12 months, depending on the severity of the disease and response to therapy. This review outlines detailed recommendations to improve the diagnosis of ATTR amyloidosis with PN.

C-Fiber Assays in the Cornea vs. Skin

C-fibers are unmyelinated nerve fibers that transmit high threshold mechanical, thermal, and chemical signals that are associated with pain sensations. This review examines current literature on measuring altered peripheral nerve morphology and discusses the most relevant aspects of corneal microscopy, especially whether corneal imaging presents significant method advantages over skin biopsy. Given its relative merits, corneal confocal microscopy would seem to be a more practical and patient-centric approach than utilizing skin biopsies.