Aging and cerebrovascular lesions in pure and in mixed neurodegenerative and vascular dementia brains: a neuropathological study

Introduction
The prevalence of dementia is increasing in our aging population. Because of the complexity of disease pathology, dementia classifications remain controversial. The present post-mortem study investigates whether there are age differences between dementia brains with a single pure neurodegenerative or cerebrovascular disease and those with mixed pathological features. Also, the impact of these vascular lesions is compared.

Material and methods
A total of 132 dementia brains with a pure neurodegenerative or cerebrovascular disease and 84 with mixed features were examined. Main age and gender distribution were compared between the overall group of pure and of mixed dementia. Also, the most common subgroups were compared separately. In addition to the detection of macroscopic visible lesions, a whole coronal section of a cerebral hemisphere, at the level of the mamillary body, was taken for semi-quantitative microscopic evaluation of white matter changes (WMCs), cortical micro-bleeds (CoMBs), and cortical micro-infarcts (CoMIs).

Results
Overall, patients with mixed dementia were at death significantly older than those with pure dementia. According to the main diagnosis, the pure forms of Alzheimer’s disease (AD) and frontotemporal lobar degeneration (FTLD) were more common in the younger age groups while in the older ones the mixed form of Lewy body disease (LBD) predominated. Neuropathological examination revealed an increased severity of cerebral amyloid angiopathy (CAA), territorial infarcts, lobar haematomas, and CoMIs in the mixed AD group. In FTLD only CoMIs were increased in the mixed group, while in LBD no differences in severity of all cerebrovascular lesions were observed. Lacunar infarcts were more frequent in pure vascular dementia, while CAA predominated in the mixed one.

Conclusions
Mixed dementia during the aging process is mainly due to the severity of AD and LBD pathologies combined with CAA-related cerebrovascular lesions.