Underpinnings of mild cognitive impairment (MCI) change with increasing age. We hypothesize
that MRI signatures of mild cognitive impairment (MCI) would be different at a higher age
compared to younger elders. Methods – 244 participants (71-103 years) from the Sydney Memory and Ageing Study and
the Sydney Centenarian Study were categorized as amnestic MCI (aMCI), non-amnestic MCI (naMCI) or cognitively
normal (CN). Brain “atrophy” and white matter hyper-intensities (WMHs) associated with MCI subtypes and age effects
were examined by general linear models, controlling for confounding factors. Reduced logistic regressions were performed
to determine structures that best discriminated aMCI from CN in individuals <85 and those ≥85 years. Results –
aMCI was associated with smaller volumes of overall cortex, medial temporal structures, anterior corpus callosum, and
select frontal and parietal regions compared to CN; such associations did not significantly change with age. Structures that
best discriminated aMCI from CN differed however in the <85 and ≥85 age groups: cortex, putamen, parahippocampal,
precuneus and superior frontal cortices in <85 years, and the hippocampus, pars triangularis and temporal pole in ≥85
years. Differences between naMCI and CN were small and non-significant in the sample. WMHs were not significantly
associated with MCI subtypes. Conclusions – Structural MRI distinguishes aMCI, but not naMCI, from CN in elderly individuals.
The structures that best distinguish aMCI from CN differ in those <85 from those ≥85, suggesting different neuropathological
underpinnings of cognitive impairment in the very old.