Mild amyloid pathology in the primary visual system of nonagenarians and centenarians.
In order to study the patterns of Alzheimer disease (AD)-related pathology in the primary visual system of the oldest old, we performed a quantitative analysis of senile plaques (SP), diffuse beta amyloid (A beta) deposit and neurofibrillary tangle (NFT) distribution in primary area 17, and a semi-quantitative analysis in the dorsal lateral geniculate nucleus (LGN), lateral inferior pulvinar (LIP) and superior colliculus (SC) of 21 individuals aged between 93 and 102 years. Among them, 10 cases were considered as non-demented (ND), while 9 presented very mild cognitive impairment (VMCI), and 2 cases had a clinical diagnosis of AD. Silver methenamine and Gallyas staining, A beta and tau immunostaining revealed the distribution of AD lesions. In primary area 17, most cases, either ND or with VMCI displayed a low to medium number of SP. There was no significant difference in SP and A beta deposit densities between ND and VMCI groups. On the whole, 0.4--2.4% of the cross-sectional cortical area was covered with A beta deposits. Only 6 cases, either ND or with VMCI, were totally devoid of SP and diffuse A beta deposits. Among the subcortical structures, the LIP and SC exhibited low densities of SP and A beta deposits in about half of the ND and VMCI cases, while the LGN was totally spared. NFT were almost absent in area 17 and subcortical nuclei of ND and VMCI cases. These data imply that the ageing of the primary visual system in ND and VMCI nonagenarians and centenarians is characterised by the frequent development of mild amyloid pathology in area 17 in the absence of NFT. In agreement with previous studies in very old cohorts, they also suggest that amyloid deposition is not related to the early stages of the dementia process in the oldest old.