Dementia is increasingly recognized as a common feature in patients with Parkinson disease (PD)and dementia with Lewy bodies (DLB), both sharing many clinical and morphological features and believed to form a continuum within the spectrum of Lewy body diseases. Based on a large autopsy series of parkinsonism (31-37% with dementia) and review of the recent literature, the pathological changes underlying cognitive impairment in PD with dementia (PDD) and DLB are discussed. PD cases with Lewy body stages 3-5, i.e. only mild to moderate cortical alpha-synuclein (alphaSyn) depositions,and no additional pathologies, are rarely associated with cognitive impairment, which is frequently seen in PD and DLB cases with considerable cortical and limbic alphaSyn load (increasing Lewy body densities) and/or associated widespread Alzheimer-type pathology. Clinicopathological studies show a negative relation between cognitive impairment and both cortical Lewy body pathology and Alzheimer type changes, suggesting that these either alone or in combination are major causes of cognitive dysfunction, while others related them to presynaptic alphaSyn aggregates. The neuropathology of PDD and DLB is similar, without significant differences between cortical and subcortical Lewy bodies and the pattern of synuclein pathology in the brainstem, but there are topographic differences in nigral lesions, more frequent affection of the hippocampal CA 2/3 subareas and more severe diffuse amyloid plaque load in the striatum of DLB. In conclusion, the pathology underlying cognitive impairment in PDD and DLB is heterogeneous, but there are some differences in the topography and severity of lesions between both phenotypes that need further evaluation.
"The neuropathology of DLB is similar to that of PD but a more severe diffuse load of Lewy bodies (eosinophilic, neuronal inclusions, which can be stained by actin, neurofilament, ubiquitin and -synuclein), is present in brain stem, diencephalon, anterior cingulate, amygdala and cerebral cortex. Many cases have substantial AD pathology (amyloid plaque and neocortical tangle) and this could explain the reason why many cases with Lewy body pathology present with an insidious amnestic syndrome are more similar to AD. Cognitive impairment seems to correlate with the presence of an AD-like pathology along with cortical and limbic -synuclein load which is the main constituent of Lewy body both in PD and DLB . The contribution of the AD pathology to the dementia has been debated but mixed cases are more demented than pure cases. "
[Show abstract][Hide abstract] ABSTRACT: Genetic, neuropathological and biochemical evidence implicates α-synuclein, a 140 amino acid presynaptic neuronal protein, in the pathogenesis of Parkinson’s disease and other neurodegenerative disorders. The aggregated protein inclusions mainly containing aberrant α-synuclein are widely accepted as morphological hallmarks of α-synucleinopathies, but their composition and location vary between disorders along with neuronal networks affected. α-Synuclein exists physiologically in both soluble and membran-bound states, in unstructured and α-helical conformations, respectively, while posttranslational modifications due to proteostatic deficits are involved in β-pleated aggregation resulting in formation of typical inclusions. The physiological function of α-synuclein and its role linked to neurodegeneration, however, are incompletely understood. Soluble oligomeric, not fully fibrillar α-synuclein is thought to be neurotoxic, main targets might be the synapse, axons and glia. The effects of aberrant α-synuclein include alterations of calcium homeostasis, mitochondrial dysfunction, oxidative and nitric injuries, cytoskeletal effects, and neuroinflammation. Proteasomal dysfunction might be a common mechanism in the pathogenesis of neuronal degeneration in α-synucleinopathies. However, how α-synuclein induces neurodegeneration remains elusive as its physiological function. Genome wide association studies demonstrated the important role for genetic variants of the SNCA gene encoding α-synuclein in the etiology of Parkinson’s disease, possibly through effects on oxidation, mitochondria, autophagy, and lysosomal function. The neuropathology of synucleinopathies and the role of α-synuclein as a potential biomarker are briefly summarized. Although animal models provided new insights into the pathogenesis of Parkinson disease and multiple system atrophy, most of them do not adequately reproduce the cardinal features of these disorders. Emerging evidence, in addition to synergistic interactions of α-synuclein with various pathogenic proteins, suggests that prionlike induction and seeding of α-synuclein could lead to the spread of the pathology and disease progression. Intervention in the early aggregation pathway, aberrant cellular effects, or secretion of α-synuclein might be targets for neuroprotection and disease-modifying therapy.
[Show abstract][Hide abstract] ABSTRACT: There are several consensus criteria for both the clinical and neuropathological diagnosis of different types of dementias. The clinical diagnostic accuracy using revised research criteria and newly developed biomarkers (MRI, PET, CSF analysis, genetic markers) ranges from 65 to 96% (for Alzheimer disease) with a specificity of diagnostic criteria versus other dementias of 23-88%. Neuropathological assessment of dementing disorders using immunohistochemistry, molecular biologic and genetic methods can achieve a diagnosis/classification, based on the homogeneous definitions, harmonized inter-laboratory methods and standards for the assessment of nervous system lesions, in about 99%, without, however, being able to clarify the causes/etiology of most of these disorders. Further prospective and concerted clinicopathological studies using revised methodological and validated protocols and uniform techniques are required to establish the nature, distribution pattern and grades of lesions and; thus, to overcome the limitations of the current diagnostic framework. By data fusion this my allow their more uniform application and correlation with the clinical data in order to approach a diagnostic "gold standard", and to create generally accepted criteria for differentiating cognitive disorders from healthy brain aging. The detection of disease-specific pathologies will be indispensable to determinate the efficacy of new therapy options.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.