The following is a summary of “Retrospective Evaluation of Neuropathologic Proxies of the Minimal Atrophy Subtype Compared to Corticolimbic Alzheimer Disease Subtypes,” published in the August 2023 issue of Neurology by Boon et al.
Alzheimer’s disease (AD) is categorized into corticolimbic subtypes based on neurofibrillary tangle distribution. A “minimal atrophy” subtype was also found through in vivo MRI. Researchers initiated a retrospective study to pinpoint a neuropathologic proxy for the neuroimaging-defined minimal atrophy subtype.
They utilized two FLorida Autopsied Multi-Ethnic (FLAME) approaches to assess a neuropathologic proxy for the minimal atrophy subtype in AD. AD cases were chosen with Braak IV tangle stage due to fewer neocortical tangles than Braak > IV. These Braak IV cases were contrasted with the AD subtypes. In an alternate method, they categorized typical AD cases by high brain weight (>75%) to define minimal atrophy.
The results showed Braak IV cases (n=37) differed from AD subtypes (limbic predominant [n=174], typical [n=986], hippocampal sparing [n=187] AD), least education (median [M] 12 years, P<0.001), higher brain weight (M 1140g, P=0.002). Braak IV cases resembled limbic predominant: APOE ε4 carriers (75%, P<0.001), amnestic syndrome (100%, P<0.001), older onset, and death age (M: 79, 85 years, P<0.001). Only 5% had amygdala Lewy bodies (lowest frequency, P=0.017), and 32% had coexisting Lewy body disease (> other subtypes, P=0.005). 47% of Braak IV samples had coexisting limbic-predominant TDP-43 encephalopathy. Higher brain weight cases (n=201) showed lower amygdala Lewy body presence (14%, P=0.006) and higher Lewy body disease likelihood (31%, P=0.042) than middle (n=455) and low brain weight cases (n=203).
They concluded Lewy body disease increased in neuropathologic proxies of minimal atrophy subtype, potentially causing cognitive decline.
Source: n.neurology.org/content/early/2023/08/14/WNL.0000000000207685
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