Cortical laminar distribution of β-amyloid deposits in five neurodegenerative disorders

Alzheimer's disease neuropathologic change (ADNC) in the form of β-amyloid (Aβ) deposits occurs not only in Alzheimer's disease (AD) and Down's syndrome (DS) but also as a 'co-pathology' in several disorders including dementia with Lewy bodies (DLB), corticobasal degeneration (CBD), and chronic traumatic encephalopathy (CTE). To determine whether cortical laminar degeneration, as measured by Aβ deposition, is similar in different disorders, changes in density of the diffuse, primitive, and classic morphological subtypes of Aβ deposit were studied across all cortical layers in the frontal and temporal cortex in AD, DS, DLB, CBD, and CTE using quantitative analysis and polynomial curve fitting. In AD, CTE, and DLB, the diffuse Aβ deposits were distributed most frequently in the upper cortical layers, distribution being more variable in DS and CBD. In all disorders, the primitive Aβ deposits were distributed primarily in the upper layers, but in DLB, a bimodal distribution with peaks of density in upper and lower layers was evident in some gyri. The distribution of the classic deposits varied both within and among disorders. The many similarities in laminar distribution among disorders suggest common patterns of cortical degeneration. Where differences occur, they may reflect variations in the 'prion-like' propagation of Aβ along anatomical pathways in the different disorders.