Visual association pathology in preclinical Alzheimer disease

The transition from normal aging to mild cognitive impairment to Alzheimer disease (AD) is often indistinct. Imaging studies suggest early changes in posterior brain regions, including posterior temporoparietal and occipital cortex, but pathologic studies show initial changes in the medial temporal lobe with progressive neocortical involvement as cognition deteriorates. We evaluated the regional distribution of AD pathology in 41 elderly brain donors from the Framingham Heart Study who were cognitively intact, mildly impaired, or demented on the basis of probable AD. We found that 52% of the cognitively intact subjects, and all subjects with mild cognitive impairment or dementia, had dense neurofibrillary tangles (NFTs), neuropil threads, and tau-immunoreactive neurites surrounding neuritic plaques (NPs) in visual association cortex Brodmann area 19. All cognitively intact subjects with area 19 NFTs also had dense core NP and β amyloid (Aβ) angiopathy in area 19. Area 19 pathology was occasionally present in the absence of substantial pathology in the hippocampus or entorhinal cortex and was not correlated with medial temporal lobe pathology. Dense AD pathology in area 19 is present in some cognitively intact subjects with preclinical AD. The unique metabolic, connectional, and vascular features of this region may confer enhanced vulnerability to neurodegeneration.