Quantification of beta A4 protein deposition in the medial temporal lobe: a comparison of Alzheimer's disease and senile dementia of the Lewy body type

A quantitative study of tau pathology in 11 cases of chronic traumatic encephalopathy

AIMS

To quantify tau pathology of chronic traumatic encephalopathy (CTE) and investigate influence of dot-like lesions (DL), brain region, comorbidity and sporting career length.

METHODS

Densities of neurofibrillary tangles (NFT), astrocytic tangles (AT), DL, oligodendroglial inclusions (GI), neuropil threads (NT), vacuoles, neurons and enlarged neurons (EN) were measured in tau-immunoreactive sections of upper cortical laminae of frontal and temporal lobes, hippocampus (HC), amygdala and substantia nigra (SN) in 11 cases of CTE.

RESULTS

DL were a consistent finding in CTE. Densities of NFT, NT and DL were greatest in sectors CA1 and CA2 of the HC. Densities of AT were lower than NFT, small numbers of GI were recorded in temporal lobe and low densities of vacuoles and EN were consistently present. β-Amyloid-containing neuritic plaques (NP) also occurred at low density. Densities of NFT, NT, DL and AT were greater in sulci than gyri, while vacuole density was greater in gyri. Principal components analysis (PCA) suggested that sporting career length and densities of NFT in entorhinal cortex, NT in CA2 and SN and vacuolation in the DG were significant sources of variation among cases.

CONCLUSION

DL are frequent in CTE suggesting affinity with argyrophilic grain disease (AGD) and Parkinson's disease dementia (PD-Dem). Densities of AT in all regions and NT/DL in sectors CA2/4 were consistent features of CTE. The 11 cases are neuropathologically heterogeneous which may result from genetic diversity, and variation in anatomical pathways subjected to trauma.

Clinical amyloid imaging in Alzheimer's disease

BACKGROUND

The hypothesis that amyloid deposition is the leading cause of Alzheimer's disease (AD) is supported by findings in transgenic animal models and forms the basis of clinical trials of anti-amyloid agents. According to this theory, amyloid deposition causes severe damage to neurons many years before onset of dementia via a cascade of several downstream effects. This hypothesis has, however, not yet been directly tested in human beings because of the very limited possibility of diagnosing amyloid deposition in vivo, which until recently required either brain biopsy or PET imaging with an on-site cyclotron and radiochemistry laboratory. Moreover, a clinical diagnosis of AD requires that patients have dementia, at which stage any effective treatment aimed at reducing amyloid deposition will probably be too late.

RECENT DEVELOPMENTS

The amyloid imaging tracers flutemetamol, florbetapir, and florbetaben labelled with (18)F have been developed for PET; they can be produced commercially at central cyclotron sites and subsequently delivered to clinical PET scanning facilities. These tracers are currently undergoing formal clinical trials to establish whether they can be used to accurately image fibrillary amyloid and to distinguish patients with AD from normal controls and those with other diseases that cause dementia. They might also be used as biomarkers to predict development of AD before onset of dementia and to assess the effect of anti-amyloid therapy. Negative amyloid scans indicate absence of AD with a high level of accuracy, but healthy elderly volunteers might have positive amyloid scans, so their predictive value in isolation is less clear. Close association of in-vivo amyloid imaging results with post-mortem histopathological findings was shown with florbetapir in a phase 3 study. WHERE NEXT?: Therapeutic studies of anti-amyloid agents that include amyloid tracers as biomarkers are expected to be useful for drug development and to clarify the relation between amyloid removal and clinical effects. Once the (18)F tracers become available for diagnostic use, large-scale longitudinal studies will be needed to clarify their prognostic and diagnostic power in relation to age, risk factors, and AD subtypes. Ultimately, these tracers will hopefully clarify the pathophysiological role of amyloid in AD and contribute to development of new treatments.

Neuroimaging in dementia with Lewy bodies: metabolism, neurochemistry, and morphology

Dementia with Lewy bodies (DLB) is recognized as one of the most common forms of neurodegenerative dementia. Neuroimaging contributes to a better understanding of the pathophysiology of DLB by examining alterations in brain metabolism, neurochemisty, and morphology in living patients. Neuroimaging can provide objective and quantifiable antemortem markers for the presence of and the progression of DLB and permits differentiation from other dementias. This article reviews current neuroimaging findings in DLB with particular attention to occipital hypometabolism, dopaminergic and cholinergic deficits, and medial temporal lobe atrophy as measured by positron emission tomography, single-photon emission computed tomography, and magnetic resonance imaging.

Initiation and propagation stages of beta-amyloid are associated with distinctive apolipoprotein E, age, and gender profiles

Several recent studies have defined a relationship between apo-lipoprotein E (apoE) genotype and the risk of various neurodegenerative disorders. However, few studies have examined the influence of apoE on quantitative measures of beta-amyloid (Abeta) accumulation in a large population of autopsy cases. Using a multi-level analysis model, the interrelationships among apoE genotype, gender, age, and Abeta accumulation were investigated. In the population of these cases, there was a strong relationship between the presence of an epsilon4 allele and extent of Abeta in the frontal and entorhinal cortex. That is, when evaluating the presence or absence of significant Abeta (>1% Abeta load), subjects with one and two epsilon4 alleles were 1.9 and 3.5 times more likely to have significant Abeta accumulation than those with no epsilon4 alleles. These risks increased by a multiplicative factor of 1.014 for each year of age (at the time of death). In the subset of cases with significant Abeta (>1% Abeta load), the degree of Abeta load was best predicted by the presence of an epsilon2 allele and gender; females with no epsilon2 alleles had the highest Abeta loads (mean=12.3%), while males with one epsilon2 allele had the lowest amount of Abeta accumulation (mean=8.6%). Our results suggest that the presence of an epsilon4 allele predicts an earlier onset of Abeta deposition that is independent of gender. In contrast, once Abeta deposition has been initiated, the presence of an epsilon2 allele is associated with slower rates of accumulation, with males benefiting from the protective effect more than females.

Amyloid beta protein (A beta) deposition in dementia with Lewy bodies: predominance of A beta 42(43) and paucity of A beta 40 compared with sporadic Alzheimer's disease

Amyloid beta protein (A-beta) deposition was investigated by quantitative immunohistochemistry in 13 cases of dementia with Lewy bodies (DLB) and compared with that in a series of age, gender and ApoE genotype matched cases of Alzheimer's disease (AD). In DLB the predominant A-beta peptide species deposited was A-beta-42(43) and this was similar in amount to that in AD. By contrast, A-beta(40) deposition was sparse in DLB and was lower than that in AD as was the total A-beta (A-beta-40 + A-beta-42(43) deposition. These data reinforce the viewpoint that in all disorders in which A-beta deposition is characteristics, the initial and predominant peptide species deposited is the longer form, A-beta-42(43). The density of Lewy bodies (LB) in DLB was unrelated to the extent of A-beta deposition, although those cases possessing one or more copies of the apolipoprotein E E4 allele had a higher LB density than those without an E4 allele. This suggests that the apolipoprotein E E4 isoform might facilitate, though not necessarily trigger, the formation of LB in susceptible individuals.

Simplified neuropathological diagnosis of dementia with Lewy bodies

Pathological criteria have recently been developed to differentiate those cases where Lewy bodies contribute to the dementing process. We applied consensus criteria to 20 cases with a pathological diagnosis of Alzheimer's disease (all demented) and/or Parkinson's disease (three without dementia) and eight controls. In addition, we applied the criteria to the different cortical layers to determine whether the site of the semiquantification affected the diagnosis. In the parietal lobe, few Lewy bodies were observed, and this region could be excluded. Rare Lewy bodies present in the frontal association cortex in a number of Parkinson's disease cases resulted in their classification as limbic or transitional cases with Lewy bodies. Exclusion of this non-limbic association cortex resulted in many of these cases with rare cortical Lewy bodies being re-classified as having brain stem predominant Lewy bodies, thus improving the diagnostic accuracy of the criteria. Most of these cases were non-demented. No other case was re-classified by excluding these cortical regions from the analysis. Few Lewy bodies were present in cortical layers I and II, and these layers could be excluded from the semiquantitative procedure without change to the overall classification of cases. The occasional presence of possible Lewy bodies in cases with Alzheimer's disease and controls incorrectly classified these cases as having brain stem predominant Lewy body disease, although these cases had no brain stem Lewy bodies. These modifications to the consensus criteria for assessing Lewy body disease (i.e. exclude parietal and frontal lobe, cortical layers I and II, and cases without brain stem Lewy bodies), provide significant time and cost savings for neuropathologists and researchers using this criteria to diagnose and study dementia with Lewy bodies.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.

Pathological diagnostic criteria for dementia associated with cortical Lewy bodies: review and proposal for a descriptive approach

In recent years dementia histologically characterised by the presence of cortical Lewy bodies has been increasingly recognised. There is now need for a scheme for an internationally acceptable scheme for pathological diagnosis and classification so that clinical, pathological and molecular features of disease can be correlated. Recent observations made by different groups in large patient series have used slightly different pathological criteria resulting in at least seven different diagnostic terms. In some patients the only cortical pathology is the presence of Lewy bodies, while in the majority of patients there are coexisting pathological changes which either overlap with those seen in Alzheimer's disease (AD). Cortical Lewy bodies can also be present in patients who do not have any obvious cognitive abnormality. A problem with equating studies from different groups is that different criteria have been used to define AD, so that establishing the relevance of cortical Lewy bodies themselves to cognitive decline and separating this from the contribution which may be related to the AD pathology is problematic. The lesions which appear to be of most relevance to potential cognitive decline in DLB are cortical Lewy bodies, Lewy-related neurites, senile plaques, neurofibrillary tangles, neuronal and synaptic loss, spongiform change, and cortical cholinergic deficits. It is possible to operationally classify patients with cognitive decline and cortical Lewy bodies into three main groups, Cortical Lewy body disease, Cortical Lewy body disease with plaques, and Cortical Lewy body disease with plaques and tangles. There are frequent cases which overlap these groups making operational classification difficult in practice. A descriptive classification, in which the severity of different pathological changes is rated, is easy to use in practice. As new molecular risk factors for AD or DLB are revealed they will need to be related to morphological and clinical features. A descriptive diagnostic assessment for DLB will facilitate such studies and makes no judgements as to what these relationships will be.

Pathology of familial Alzheimer's disease with Lewy bodies

The neuropathological findings of three cases from two pedigrees with early onset familial Alzheimer's disease (FAD) are reported. Affected members of the first family, including cases 1 and 2 reported here, are known to have 717 valine to isoleucine mutation of the amyloid precursor protein (APP) gene, while the genetic background of the disease has not been clarified yet in the second family. In all three cases, in addition to the classical histological findings associated with Alzheimer's disease (AD), both nigral and cortical Lewy bodies (LBs) occurred. The association of LBs with AD type pathology, which may be observed in both sporadic and familial AD, raises important nosological issues. These include a possible overlap between AD and other neurodegenerative conditions presenting primarily with LBs. In this respect the clinically and neuropathologically distinct disease entity described under the terms of "senile dementia of the Lewy body type" and "Lewy body variant of AD" may be especially important. The occurrence of LBs in association with severe AD-type histological changes in sporadic and especially in some familial AD cases indicate that these inclusions may be another expression of the altered cytoskeleton in AD.

Neuropsychiatric manifestations of diffuse Lewy body disease

This article reviews the nature and prevalence of Lewy bodies (LBs) found during postmortem examination of demented individuals. Neuropathologic findings associated with diffuse Lewy body disease (DLBD) are contrasted with those of other causes of dementia (e.g., Pick's disease and Alzheimer's disease). A sufficiently specific clinical syndrome is suggested to enhance the antemortem diagnosis of DLBD. Current and speculative clinical management strategies of DLBD are discussed.

Concentrations of amyloid beta protein in cerebrospinal fluid of patients with Alzheimer's disease

Deposition of fibrillar amyloid beta protein (A beta) is increased in brains of patients with Alzheimer's disease. Concentrations of A beta were measured in cerebrospinal fluid with an enzyme-linked immunosorbent assay in 10 neurological patients free from neurodegenerative disease, 28 patients with Parkinson's disease, and 18 patients with probable Alzheimer's disease. Levels of A beta in cerebrospinal fluid were not significantly different among these groups. This observation suggests that concentrations of soluble A beta in cerebrospinal fluid as measured in this study do not reflect the amount of fibrillar, aggregated A beta in the brain of patients with Alzheimer's disease.

The topographic distribution of brain atrophy in cortical Lewy body disease: comparison with Alzheimer's disease

The topographic distribution of brain atrophy was quantified by image analysis of fixed coronal brain slices from four patients dying with cortical Lewy body disease (CLBD) all with Alzheimer-type pathology and compared to that in four other patients of similar age and gender dying with Alzheimer's disease (AD) alone. The pattern of atrophy in CLBD (+AD) was broadly similar to that in AD alone, suggesting that tissue loss was due mostly to parallel Alzheimer-type pathological changes and that the presence of Lewy bodies in cortical and subcortical neurons contributed little, if anything, to the overall degree of atrophy.

Immunoreactivity profile of hippocampal CA2/3 neurites in diffuse Lewy body disease

Ubiquitin-immunoreactive dystrophic neurites in the CA2/3 region of the hippocampus are characteristic of diffuse Lewy body disease (DLBD). The origin of dystrophic CA2/3 neurites is unknown, but their extent correlates with the number of cortical Lewy bodies (LBs). To examine the molecular composition of these lesions, hippocampal sections were obtained at postmortem from cases of DLBD, Parkinson's disease and Alzheimer's disease. The tissue samples were fixed in a variety of fixatives and immunostained with antibodies to ubiquitin, ubiquitin C-terminal hydrolase (PGP9.5), neurofilament protein subunits, tau protein, paired helical filaments and tyrosine hydroxylase (TH). In addition to being ubiquitin positive, both cortical LBs and CA2/3 dystrophic neurites were positive with a neurofilament monoclonal antibody (RM032) and PGP9.5; however, fewer lesions were detected with these antibodies compared to ubiquitin immunocytochemistry. The dystrophic CA2/3 neurites were not stained with antibodies to tau proteins, paired helical filaments or TH. Absence of TH immunoreactivity suggests that CA2/3 neuritic processes are not derived from brain stem dopaminergic afferents to the hippocampus. Since CA2/3 neurites are immunologically similar to cortical LB, the pathogenesis of these lesions may be similar. Characterization of dystrophic CA2/3 neurites and cortical LBs may clarify how these lesions contribute to the emergence of dementia in DLBD.