Amyloid neuropathy: immunocytochemical localization of intra- and extracellular immunoglobulin light chains

Amyloid Neuropathy: From Pathophysiology to Treatment in Light-Chain Amyloidosis and Hereditary Transthyretin Amyloidosis

Amyloid neuropathy is caused by deposition of insoluble β-pleated amyloid sheets in the peripheral nervous system. It is most common in: (1) light-chain amyloidosis, a clonal non-proliferative plasma cell disorder in which fragments of immunoglobulin, light or heavy chain, deposit in tissues, and (2) hereditary transthyretin (ATTRv) amyloidosis, a disorder caused by autosomal dominant mutations in the TTR gene resulting in mutated protein that has a higher tendency to misfold. Amyloid fibrils deposit in the endoneurium of peripheral nerves, often extensive in the dorsal root ganglia and sympathetic ganglia, leading to atrophy of Schwann cells in proximity to amyloid fibrils and blood-nerve barrier disruption. Clinically, amyloid neuropathy is manifested as a length-dependent sensory predominant neuropathy associated with generalized autonomic failure. Small unmyelinated nerves are involved early and prominently in early-onset Val30Met ATTRv, whereas other ATTRv and light-chain amyloidosis often present with large- and small-fiber involvement. Nerve conduction studies, quantitative sudomotor axon testing, and intraepidermal nerve fiber density are useful tools to evaluate denervation. Amyloid deposition can be demonstrated by tissue biopsy of the affected organ or surrogate site, as well as bone-avid radiotracer cardiac imaging. Treatment of light-chain amyloidosis has been revolutionized by monoclonal antibodies and stem cell transplantation with improved 5-year survival up to 77%. Novel gene therapy and transthyretin stabilizers have revolutionized treatment of ATTRv, improving the course of neuropathy (less change in the modified Neuropathy Impairment Score + 7 from baseline) and quality of life. With great progress in amyloidosis therapies, early diagnosis and presymptomatic testing for ATTRv family members has become paramount. ANN NEUROL 2024;96:423-440.

Magnetic resonance neurography and diffusion tensor imaging of the sciatic nerve in hereditary transthyretin amyloidosis polyneuropathy

The therapeutic advance in hereditary transthyretin amyloidosis (ATTRv amyloidosis) requires quantitative biomarkers of nerve involvement in order to foster early diagnosis and monitor therapy response. We aimed at quantitatively assessing Magnetic Resonance Neurography (MRN) and Diffusion Tensor Imaging (DTI) properties of the sciatic nerve in subjects with ATTRv-amyloidosis-polyneuropathy (ATTRv-PN) and pre-symptomatic carriers (ATTRv-C). Twenty subjects with pathogenic variants of the TTR gene (mean age 62.20 ± 12.04 years), 13 ATTRv-PN, and 7 ATTRv-C were evaluated and compared with 20 healthy subjects (mean age 60.1 ± 8.27 years). MRN and DTI sequences were performed at the right thigh from the gluteal region to the popliteal fossa. Cross-sectional-area (CSA), normalized signal intensity (NSI), and DTI metrics, including fractional anisotropy (FA), mean (MD), axial (AD), and radial diffusivity (RD) of the right sciatic nerve were measured. Increased CSA, NSI, RD, and reduced FA of sciatic nerve differentiated ATTRv-PN from ATTRv-C and healthy subjects at all levels (p < 0.01). NSI differentiated ATTRv-C from controls at all levels (p < 0.05), RD at proximal and mid-thigh (1.04 ± 0.1 vs 0.86 ± 0.11 p < 0.01), FA at mid-thigh (0.51 ± 0.02 vs 0.58 ± 0.04 p < 0.01). According to receiver operating characteristic (ROC) curve analysis, cutoff values differentiating ATTRv-C from controls (and therefore identifying subclinical sciatic involvement) were defined for FA, RD, and NSI. Significant correlations between MRI measures, clinical involvement and neurophysiology were found. In conclusion, the combination of quantitative MRN and DTI of the sciatic nerve can reliably differentiate ATTRv-PN, ATTRv-C, and healthy controls. More important, MRN and DTI were able to non-invasively identify early subclinical microstructural changes in pre-symptomatic carriers, thus representing a potential tool for early diagnosis and disease monitoring.

Corneal confocal microscopy identifies corneal nerve loss and increased Langerhans cells in presymptomatic carriers and patients with hereditary transthyretin amyloidosis

BACKGROUND

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is a rare, but life-threatening protein misfolding disorder due to TTR gene mutations. Cardiomyopathy (ATTRv-CM) and polyneuropathy (ATTRv-PN) with early small nerve fibre involvement are the most common manifestations. Timely diagnosis and treatment initiation are key to limiting progression of disease. Corneal confocal microscopy (CCM) is a non-invasive method to quantify corneal small nerve fibres and immune cell infiltrates in vivo.

METHODS

This cross-sectional study investigated the utility of CCM in 20 patients with ATTRv amyloidosis (ATTRv-CM, n = 6; ATTRv-PN, n = 14) and presymptomatic carriers (n = 5) compared to 20 age- and sex-matched healthy controls. Corneal nerve fibre density, corneal nerve fibre length, corneal nerve branch density, and cell infiltrates were assessed.

RESULTS

Corneal nerve fibre density and nerve fibre length were significantly lower in patients with ATTRv amyloidosis compared to healthy controls regardless of the clinical phenotype (ATTRv-CM, ATTRv-PN) and corneal nerve fibre density was significantly lower in presymptomatic carriers. Immune cell infiltrates were only evident in patients with ATTRv amyloidosis, which correlated with reduced corneal nerve fibre density.

CONCLUSIONS

CCM identifies small nerve fibre damage in presymptomatic carriers and symptomatic patients with ATTRv amyloidosis and may serve as a predictive surrogate marker to identify individuals at risk of developing symptomatic amyloidosis. Furthermore, increased corneal cell infiltration suggests an immune-mediated mechanism in the pathogenesis of amyloid neuropathy.

Corneal confocal microscopy to detect early immune-mediated small nerve fibre loss in AL amyloidosis

Objective

Light chain (AL) amyloidosis is a life‐threatening disorder characterised by extracellular deposition of amyloid leading to dysfunction of multiple organs. Peripheral nerve involvement, particularly small fibre neuropathy, may be associated with poorer survival. Corneal confocal microscopy (CCM) is a rapid and non‐invasive imaging technique to quantify corneal small nerve fibres and immune cells in vivo. We aimed to evaluate CCM as a tool for early diagnosis of peripheral nerve involvement in AL amyloidosis.

Methods

CCM and nerve conduction studies (NCS) were undertaken in 21 newly diagnosed, treatment‐naïve AL amyloidosis patients and 21 age‐ and sex‐matched healthy controls. Corneal nerve fibre density (CNFD), corneal nerve branch density and fibre length, and cell infiltrates were quantified in the sub‐basal layer of the cornea.

Results

There was a significant reduction in CNFD and nerve fibre length, even without large fibre affection and an increase in cell density, particularly around corneal nerve fibres in patients with AL amyloidosis compared to controls. Additionally, cell infiltration correlated with reduced nerve fibre density in patients with AL amyloidosis, but reduced CNFD did not correlate with laboratory parameters of organ dysfunction.

Interpretation

Our study is the first to show that CCM allows rapid non‐invasive identification of early small nerve fibre damage associated with immune cell infiltration in patients with AL amyloidosis. CCM detects peripheral nerve involvement more sensitively than NCS.

Paraproteinemia and neuropathy

Paraproteinemia is associated with different peripheral neuropathies. The major causes of neuropathy correlated with paraproteinemia are the deposition of immunoglobulin in the myelin, represented by anti-myelin-associated glycoprotein (MAG) neuropathy; deposition of immunoglobulin or its fragment in the interstitium, represented by immunoglobulin light chain amyloidosis (AL amyloidosis); and paraneoplastic mechanisms that cannot be solely attributed to the deposition of immunoglobulin or its fragment, represented by polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin change (POEMS) syndrome. Patients with anti-MAG neuropathy and POEMS syndrome present with slowing of nerve conduction parameters. This characteristic fulfills the electrodiagnostic criteria for chronic inflammatory demyelinating polyneuropathy (CIDP) defined by the European Academy of Neurology and Peripheral Nerve Society (EAN/PNS). Although direct damage caused by the deposition of amyloid can induce axonal damage in AL amyloidosis, some patients with this condition have features fulfilling the EAN/PNS electrodiagnostic criteria for CIDP. Conventional immunotherapies for CIDP, such as steroids, intravenous immunoglobulin, and plasma exchange, offer no or only minimal-to-modest benefit. Although rituximab can reduce the level of circulating autoantibodies, it may only be effective in some patients with anti-MAG neuropathy. Drugs including melphalan, thalidomide, lenalidomide, and bortezomib for POEMS syndrome and those including melphalan, thalidomide, lenalidomide, pomalidomide, bortezomib, ixazomib, and daratumumab for AL amyloidosis are considered. Since there will be more therapeutic options in the future, thereby enabling appropriate treatments for individual neuropathies, there is an increasing need for early diagnosis.

Significance of Oligomeric and Fibrillar Species in Amyloidosis: Insights into Pathophysiology and Treatment

Amyloidosis is a term referring to a group of various protein-misfolding diseases wherein normally soluble proteins form aggregates as insoluble amyloid fibrils. How, or whether, amyloid fibrils contribute to tissue damage in amyloidosis has been the topic of debate. In vitro studies have demonstrated the appearance of small globular oligomeric species during the incubation of amyloid beta peptide (Aβ). Nerve biopsy specimens from patients with systemic amyloidosis have suggested that globular structures similar to Aβ oligomers were generated from amorphous electron-dense materials and later developed into mature amyloid fibrils. Schwann cells adjacent to amyloid fibrils become atrophic and degenerative, suggesting that the direct tissue damage induced by amyloid fibrils plays an important role in systemic amyloidosis. In contrast, there is increasing evidence that oligomers, rather than amyloid fibrils, are responsible for cell death in neurodegenerative diseases, particularly Alzheimer’s disease. Disease-modifying therapies based on the pathophysiology of amyloidosis have now become available. Aducanumab, a human monoclonal antibody against the aggregated form of Aβ, was recently approved for Alzheimer’s disease, and other monoclonal antibodies, including gantenerumab, solanezumab, and lecanemab, could also be up for approval. As many other agents for amyloidosis will be developed in the future, studies to develop sensitive clinical scales for identifying improvement and markers that can act as surrogates for clinical scales should be conducted.

The Ultrastructure of Tissue Damage by Amyloid Fibrils

Amyloidosis is a group of diseases that includes Alzheimer’s disease, prion diseases, transthyretin (ATTR) amyloidosis, and immunoglobulin light chain (AL) amyloidosis. The mechanism of organ dysfunction resulting from amyloidosis has been a topic of debate. This review focuses on the ultrastructure of tissue damage resulting from amyloid deposition and therapeutic insights based on the pathophysiology of amyloidosis. Studies of nerve biopsy or cardiac autopsy specimens from patients with ATTR and AL amyloidoses show atrophy of cells near amyloid fibril aggregates. In addition to the stress or toxicity attributable to amyloid fibrils themselves, the toxicity of non-fibrillar states of amyloidogenic proteins, particularly oligomers, may also participate in the mechanisms of tissue damage. The obscuration of the basement and cytoplasmic membranes of cells near amyloid fibrils attributable to an affinity of components constituting these membranes to those of amyloid fibrils may also play an important role in tissue damage. Possible major therapeutic strategies based on pathophysiology of amyloidosis consist of the following: (1) reducing or preventing the production of causative proteins; (2) preventing the causative proteins from participating in the process of amyloid fibril formation; and/or (3) eliminating already-deposited amyloid fibrils. As the development of novel disease-modifying therapies such as short interfering RNA, antisense oligonucleotide, and monoclonal antibodies is remarkable, early diagnosis and appropriate selection of treatment is becoming more and more important for patients with amyloidosis.

Two distinct mechanisms of neuropathy in immunoglobulin light chain (AL) amyloidosis

INTRODUCTION

Although polyneuropathy in patients with immunoglobulin light chain (AL) amyloidosis has been considered to be attributable to axonal degeneration resulting from amyloid deposition, patients with nerve conduction parameters indicating demyelination that mimics chronic inflammatory demyelinating polyneuropathy (CIDP) have also been reported anecdotally.

METHODS

We evaluated the electrophysiological and pathological features of 8 consecutive patients with AL amyloidosis who were referred for sural nerve biopsy.

RESULTS

Although findings of axonal neuropathy predominantly in the lower limbs were the cardinal feature, all patients showed one or more abnormalities of nerve conduction velocities or distal motor latencies. In particular, 2 of these patients fulfilled the definite electrophysiological for CIDP defined by the European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS). On electron microscopic examination of sural nerve biopsy specimens, Schwann cells apposed to amyloid fibrils became atrophic in all patients, suggesting that amyloid deposits directly affect neighboring tissues. Additionally, detachment of the neurilemma from the outermost compacted myelin lamella was seen where amyloid fibrils were absent in 4 patients. Electrophysiological findings suggestive of demyelination were more conspicuous in these patients compared with the other patients. The detachment of the neurilemma from the outermost compacted myelin lamella was particularly conspicuous in patients who fulfilled the definite EFNS/PNS electrophysiological criteria for CIDP.

CONCLUSION

Abnormalities of myelinated fibers unrelated to amyloid deposition may frequently occur in AL amyloidosis. Disjunction between myelin and the neurilemma may induce nerve conduction abnormalities suggestive of demyelination.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Diseases of the peripheral nerves

This chapter reviews the diseases of the peripheral nerves from a neuropathologic point of view, with a special focus on specific morphologic changes, and includes a summary of the histopathologic methods available for their diagnosis. As the rate of obesity and the prevalence of type 2 diabetes increase, diabetic neuropathy is the most common cause of peripheral neuropathy. Many systemic disorders with metabolic origin, like amyloidosis, hepatic failure, vitamin deficiencies, uremia, lipid metabolism disorders, and others, can also cause axonal or myelin alterations in the peripheral nervous system. The most notable causes of toxic neuropathies are chemotherapeutic agents, alcohol consumption, and exposure to heavy metals and other environmental or biologic toxins. Inflammatory neuropathies cover infectious neuropathies (Lyme disease, human immunodeficiency virus, leprosy, hepatitis) and neuropathies of autoimmune origin (sarcoidosis, Guillain-Barré syndrome/acute inflammatory demyelinating polyneuropathy, chronic inflammatory demyelinating polyneuropathy, and diverse forms of vasculitis. The increasing number of known diseases causing gene mutations in hereditary peripheral neuropathies requires precise characterization, which includes histopathology.

Diagnostic hallmarks and pitfalls in late-onset progressive transthyretin-related amyloid-neuropathy

Familial amyloid polyneuropathy (FAP) is a progressive systemic autosomal dominant disease caused by pathogenic mutations in the transthyretin (TTR) gene. We studied clinical, electrophysiological, histopathological, and genetic characteristics in 15 (13 late-onset and two early-onset) patients belonging to 14 families with polyneuropathy and mutations in TTR. In comparison, we analysed the features of nine unrelated patients with an idiopathic polyneuropathy, in whom TTR mutations have been excluded. Disease occurrence was familial in 36 % of the patients with TTR-associated polyneuropathy and the late-onset type was observed in 86 % (mean age at onset 65.5 years). Clinically, all late-onset TTR-mutant patients presented with distal weakness, pansensory loss, absence of deep tendon reflexes, and sensorimotor hand involvement. Afferent-ataxic gait was present in 92 % leading to wheelchair dependence in 60 % after a mean duration of 4.6 years. Autonomic involvement was observed in 60 %, and ankle edema in 92 %. The sensorimotor polyneuropathy was from an axonal type in 82 %, demyelinating or mixed type in 9 % each. Compared to the TTR-unmutated idiopathic polyneuropathy patients, we identified rapid progression, early ambulatory loss, and autonomic disturbances, associated with a severe polyneuropathy as red flags for TTR-FAP. In 18 % of the late-onset TTR-FAP patients, no amyloid was found in nerve biopsies. Further diagnostic pitfalls were unspecific electrophysiology, and coincident diabetes mellitus (23 %) or monoclonal gammopathy (7 %). We conclude that a rapid disease course, severely ataxic gait, hand involvement, and autonomic dysfunction are diagnostic hallmarks of late-onset TTR-FAP. Genetic analysis should be performed even when amyloid deposits are lacking or when polyneuropathy-causing comorbidities are concomitant.

Mass spectrometry analysis reveals non-mutated apolipoprotein A1 lumbosacral radiculoplexus amyloidoma

INTRODUCTION

In rare instances, amyloidosis presents as a focal, macroscopic lesion involving peripheral neural tissues (amyloidoma). In all known reported cases, peripheral nerve amyloidomas have had immunoglobulin light-chain fibril composition and occurred in the context of paraproteinemia.

METHODS

A 46-year-old man presented with progressive insidious-onset right lumbosacral radiculoplexus neuropathy without paraproteinemia. MRI-targeted fascicular nerve biopsy was performed on an enlarged sciatic nerve after earlier distal fibular nerve biopsy was nondiagnostic. Laser dissected mass spectroscopy of the discovered amyloid protein was performed after immunohistochemistry failed to identify the specific amyloid protein. Complete gene sequencing of apolipoprotein A1 (ApoA1) was performed.

RESULTS

Only wild-type ApoA1 amyloid was found in the congophilic component in the nerve.

CONCLUSIONS

This case highlights the utility of MRI-guided fascicular nerve biopsy combined with laser-dissected mass spectrometric analysis. Importantly, the case expands the known causes of amyloidomas to include wild-type ApoA1.

Mechanism of amyloid plaque formation suggests an intracellular basis of Abeta pathogenicity

The formation of extracellular amyloid plaques is a common patho-biochemical event underlying several debilitating human conditions, including Alzheimer's disease (AD). Considerable evidence implies that AD damage arises primarily from small oligomeric amyloid forms of Abeta peptide, but the precise mechanism of pathogenicity remains to be established. Using a cell culture system that reproducibly leads to the formation of Alzheimer's Abeta amyloid plaques, we show here that the formation of a single amyloid plaque represents a template-dependent process that critically involves the presence of endocytosis- or phagocytosis-competent cells. Internalized Abeta peptide becomes sorted to multivesicular bodies where fibrils grow out, thus penetrating the vesicular membrane. Upon plaque formation, cells undergo cell death and intracellular amyloid structures become released into the extracellular space. These data imply a mechanism where the pathogenic activity of Abeta is attributed, at least in part, to intracellular aggregates.

Neuropathology of Charcot-Marie-Tooth and related disorders

The peripheral nervous system (PNS), with all its branches and connections, is so complex that it is impossible to study all components at the light or electron microscopic level in any individual case; nevertheless, in certain diseases a simple nerve biopsy may suffice to arrive at a precise diagnosis. Structural changes of the PNS in neuropathies of the Charcot-Marie-Tooth (CMT) type and related disorders comprise various components of the PNS. These include peripheral motor, sensory, and autonomous neurons with their axons, Schwann cells, and myelin sheaths in the radicular and peripheral nerves as well as satellite cells in spinal and autonomous ganglia. Astrocytes, oligodendroglial cells, and microglial cells around motor neurons in the anterior horn and around sensory neurons in other areas of the spinal cord are also involved. In addition, connective tissue elements such as endoneurial, perineurial, and epineurial components including blood and lymph vessels play an important role. This review focuses on the cellular components and organelles involved, that is, myelin sheaths, axons with their micro-tubules and neurofilaments; nuclei, mitochondria, endoplasmic reticulum, and connective tissue including the perineurium and blood vessels. A major role is attributed to recent progress in the pathomorphology of various types of CMT1, 2,4, CMTX, and HMNSL, based on light and electron microscopic findings, morphometry, teased fiber studies, and new immunohisto-chemical results such as staining of certain periaxin domains in CMT4F.

Amyloid neuropathy: a retrospective study of 35 peripheral nerve biopsies

We performed a retrospective study of 35 peripheral nerve biopsies (PNBs) with amyloid deposits in the endoneurium. In every case, nerve lesions were studied on paraffin-embedded fragments (PEFs) and by ultrastructural examination (USE). In addition, muscle fragments were taken and embedded in paraffin. Immunohistochemistry was performed with anti-transthyretin (TTR) serum on 19 nerve and 15 muscle PEFs. Direct immunofluorescence with anti-light-chain sera was performed on frozen nerve fragments in 19 cases. Endoneurial amyloid deposits were easily identified on routine PEF in 26 cases, after Congo red or thioflavine staining in three, and by USE in six. A dramatic myelinated fiber loss was evidenced in 34 cases (77-2970 per mm2), and features of axonal degeneration were present in every case. Segmental demyelination was observed in 10 cases. A mutation in the TTR gene was present in 14 cases, with Met30 mutation in 10 and Ala49 in four members of the same family. Amyloid deposits were strongly marked by the anti-TTR serum in 11 other cases, twice in the endoneurium, five around muscle fibers, and four in both locations. In eight patients, light-chain positivity was evidenced in endoneurial deposits, lambda in six and kappa in two. Two other patients with monoclonal gammopathy did not present any light-chain fixation. In 17 cases, amyloidosis was disclosed by PNB and 13 had a TTR pathology; eight of them, over 65 years old, correspond to a late-onset form of familial amyloid polyneuropathy which is an underdiagnosed condition.

Complement activation in acquired and hereditary amyloid neuropathy

The pathogenesis of the axonal degeneration in acquired or hereditary amyloidosis is unknown. In this immunohistochemistry study, we examined 20 sural nerve biopsies from individuals with amyloid neuropathy (14 acquired and 6 hereditary) for evidence of complement activation. Complement activation products were detected on and around amyloid deposits within peripheral nerves. We found no difference in the extent, location or pattern of complement activation products between the 2 forms of amyloidosis. The presence of early classical pathway activation markers in the absence of antibody in hereditary cases suggests an antibody-independent activation of the classical pathway through binding of C1q. The lack of Factor Bb-suggested alternative pathway activation was not significant in these cases. The detection of C5b-9 neoantigen on amyloid deposits demonstrated that the full complement cascade was activated. Complement activation on amyloid deposits and the generation of C5b-9 in vivo may contribute to bystander injury of axons in the vicinity of amyloid deposits.

Vascular basement membrane pathology and Alzheimer's disease

We have previously demonstrated that the capillary vascular basement membrane (VBM) is pathologically altered in Alzheimer's disease (AD). This microangiopathy is highlighted by the immunocytochemical localization of the three principal intrinsic VBM components: heparan sulfate proteoglycan, collagen type IV, and laminin. These three VBM components also immunolable amyloid deposits and senile plaque-associated glial processes. The present study examines the ultrastructure of the VBM in one brain region severely affected (temporal gyrus) and one relatively spared (cerebellum) from the lesions of AD in both AD and neurological control cases. The cross-sectional area as well as the width of the VBM were found to be greater in AD cortical capillaries. In addition, we found ultrastructural evidence for the activation of microglial-related perivascular cells, and their apparent extravasation through the VBM, findings consistent with the hypothesis that these cells are being recruited as part of a disease-related immune response. The recruitment of these "resting" microglial-like cells from their intra-VBM location to plaques and tangles in AD may explain (1) the thickening and vacuolization of the VBM; (2) the specificity of this VBM alteration to brain regions where there are plaques and tangles; and (3) the source of some of the large number of activated microglia in these affected areas. Thus, while VBM alterations may not be specific to AD, these changes appear to be specifically related to the disease process.

Ultrastructural immunolabelling of amyloid fibrils in acquired and hereditary amyloid neuropathies

Both acquired and familial amyloid neuropathies carry a poor prognosis. In addition, amyloid is sometimes difficult to visualise in nerve biopsy specimens, and the pathogenesis of nerve lesions is still a matter of controversy. In order to learn more on the subject, we studied nerve specimens from seven patients with proven amyloid neuropathy by ultrastructural immunocytochemistry in order to better understand their pathogeny and to evaluate the reliability of the method for detection of amyloid antigens in the endoneurium. An indirect immunolabelling technique using protein A-gold complex (pA-g) was applied. Polyclonal antisera against human IgG, IgM, lambda and kappa light chains and prealbumin were assayed. Amyloid fibrils were labelled in six of seven cases: in four cases with anti-transthyretin (TTR) antibodies and in two with anti-lambda light chain antibodies. The type of immunolabelling correlated with the biochemical type of the amyloidosis as defined by TTR gene analysis and serum immunoelectrophoresis. The amyloid fibrils and gold labelling were always located in the endoneurial space. No intracellular deposit or labelling was found. The immunolabelling was highly specific, gold particles being detected only near to amyloid fibrils with no background gold labelling. Ultrastructural immunolabelling with pA-g could be used for detection of amyloid in progressive axonal neuropathy of unknown origin, with important therapeutic implications.

Familial amyloid polyneuropathy associated with transthyretin Gly42 mutation: a quantitative light and electron microscopic study of the peripheral nervous system

We performed extensive quantitative analyses of the peripheral nervous system (PNS) of two siblings with familial amyloid polyneuropathy (FAP) caused by a transthyretin (TTR) Gly42 mutation. Pronounced amyloid deposition was found in the sympathetic ganglia (SyG), dorsal root ganglia (DRG) and throughout the length of the peripheral nerve fibers with some accumulation in the more proximal portion. There was severe neuronal loss in the SyG and DRG together with nerve fiber depletion in the nerve trunk, while only a small amount of amyloid deposition with mild fiber loss was seen in the spinal roots. Sprouts of regenerating axons were very scanty even in the spinal nerves or roots. A teased fiber study mainly showed demyelinating fibers, but axonal degeneration was also present throughout peripheral nerves. An electron microscopic study showed fine amyloid fibrils in direct contact with the axoplasmic membrane of demyelinated axons and destruction of axons in some areas. Amyloid deposition within the PINS in this type of FAP resembled that in type I FAP (TTR Met30). However, direct axonal damage by amyloid fibrils appeared to be more prominent in our cases than in type I FAP. Lectin histochemistry using Ulex europaeus agglutinin I demonstrated preferential depletion of small neurons in the DRG and their primary afferent fibers in the spinal dorsal horn. Primary axonal degeneration and ganglionopathy due to amyloid deposition appear to be the pathogenetic mechanisms for peripheral neuropathy in this type of FAP.

HLA-DR expression in peripheral neuropathies: the role of Schwann cells, resident and hematogenous macrophages, and endoneurial fibroblasts

The expression of HLA-DR and the macrophage marker CD 68 was studied in 44 sural nerve biopsies from patients with inflammatory and non-inflammatory neuropathies and controls using immunohistochemistry on non-osmicated semithin sections, a technique that has not been used before in such a biopsy study. Most HLA-DR-immunoreactive (ir) cells were fibroblasts, macrophages or perineural cells, some were perivascular and endothelial cells, and only few were Schwann cells. Counts of immunoreactive cells revealed (a) increased HLA-DR expression in severe as compared to less severe neuropathies and to controls, (b) no correlation between the numbers of HLA-DR-ir cells and CD 68-ir macrophages, and (c) no close correlation between diagnostic groups and the number of HLA-DR-ir cells, but higher numbers in inflammatory neuropathies. We conclude that endoneurial fibroblasts and macrophages as antigen-presenting cells may be mediators in various peripheral nerve diseases, not only in inflammatory disorders.

Microvascular pathology and vascular basement membrane components in Alzheimer's disease

Several factors have highlighted the vasculature in Alzheimer's disease (AD): Cerebral amyloid angiopathy (CAA) is common, amyloid fibrils emanate from the vascular basement membrane (VBM), and similar forms of beta-amyloid are found in vascular and parenchymal amyloid accumulations. The present article discusses the presence of microvascular pathology in AD. Microangiopathy, in addition to neurofibrillary tangles, senile plaques, and CAA, is a common pathologic hallmark of AD. VBM components are associated with amyloid plaques, and nonamyloidotic alterations of the VBM occur in brain regions susceptible to AD lesions. Also, intra-VBM perivascular cells (traditionally called pericytes), a subset of which share the immunophenotype of microglia and other mononuclear phagocytic system (MPS) cells, have been implicated in vascular alterations and cerebrovascular amyloid deposition. Perivascular and parenchymal MPS cells have access to several sources of the beta-amyloid protein precursor, including platelets, circulating white cells, and neurons. MPS cells would thus be ideally situated to uptake and process the precursor, and deposit beta-amyloid in a fashion analogous to that seen in other forms of systemic and cerebral amyloidoses.

Vascular basement membrane components and the lesions of Alzheimer's disease: light and electron microscopic analyses

Alzheimer's disease (AD) is one of several systemic and cerebral diseases that involve the abnormal deposition of fibrillar proteins called amyloids. All amyloids share conformational and staining characteristics, as well as an association with resident tissue macrophages and two extracellular matrix components [heparan sulfate proteoglycan (HSPG) and amyloid P component]. Vascular, glomerular, and Schwann cell basement membrane pathologies have been documented in many forms of amyloidosis, and often amyloid fibrils fuse to and project from the basement membrane in these diseases. The present report demonstrates the vascular basement membrane (VBM) alterations in AD autopsy samples, and details the methodologies used. Electron microscopy reveals the fusion of amyloid fibrils with the VBM and the alteration of the VBM in the absence of amyloid accumulation. Double-labelling and pre-embed immuno-electron microscopy techniques demonstrate the colocalization of amyloid P component and VBM components with amyloid, and also reveal that amyloid P component is not localized to the cerebral VBM. Finally, a novel correlative light/electron microscopy technique demonstrates the association between amyloid P component and cerebral resident tissue macrophages, the microglia. Taken together, these data suggest that the physicochemical processes of amyloid formation, rather than amyloid deposition, may be responsible for VBM pathology.

Complement neoantigen and vitronectin are components of plaques in amyloid AL neuropathy

We studied three patients with late onset, chronic sensorimotor and autonomic neuropathy in course of plasma cell dyscrasia with Bence Jones proteinuria. Histopathological findings of nerve biopsies consisted in diffuse loss of myelinated and unmyelinated fibers associated with perivascular deposits of amorphous material with physico-chemical and ultrastructural features of amyloid. By immunohistochemistry, light chains of the same type as Bence Jones protein, components of the classic and lytic pathways of the complement and vitronectin were detected at the level of amyloid nodules. The colocalization of complement neoantigen and vitronectin suggests that this complex derives from the circulation. The elucidation of the chemical composition of amyloid might shed some light in the pathogenesis of these disorders.