Cognitive trajectories preluding the imminent onset of Alzheimer's disease dementia in individuals with normal cognition: results from the HELIAD cohort

Background: The cognitive trajectories of cognitively normal (CN) individuals rapidly progressing to Alzheimer's disease dementia (AD) have not been investigated.

Aim: To explore the preclinical pattern of cognitive performance heralding the rapid progression from normal cognition to AD.

Methods: The HELIAD cohort underwent comprehensive neuropsychological assessments (memory, language, attention, executive and visuo-perceptual functions) at baseline and after approximately 3-year intervals. The cognitive trajectories of those with normal cognition at baseline were explored according to the follow-up diagnosis using adjusted generalised estimating equations analyses.

Results: A total of 932 predominantly female (61%), older (72.9 ± 4.9), CN participants were followed for 3.09 (± 0.83) years. Among them, 761 individuals remained CN, 29 progressed to AD and 142 developed MCI (33 single-domain amnestic, 41 multidomain amnestic, 37 single-domain non-amnestic and 31 multidomain non-amnestic). Those progressing to AD were already performing worse than the healthy reference in every single cognitive domain at baseline. Cognitive deficits ranged between ~ 0.5SD (attention, executive function and language) and ~ 1.0SD (memory and visuo-perceptual skills). Throughout the 3-year follow-up, memory constantly exhibited the most prominent impairment compared to the remaining cognitive domains while executive function diminished in the most abrupt fashion (~ 0.19SD yearly) separating from the remaining three cognitive functions before the development of full-blown AD. Heterogeneous patterns of cognitive decline clearly differentiated those progressing to MCI from those rapidly converting to AD, as well.

Discussion: Poor performance in every cognitive domain may characterise cognitively normal individuals at high risk of fast progression to AD.

Conclusion: Strict neuropsychological cut-offs fail to detect a considerable number of individuals at high risk of rapid progression to AD.