Structural MRI Biomarkers of Mild Cognitive Impairment from Young Elders to Centenarians

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.