Research progress in neuroimaging of sporadic early-onset Alzheimer's disease.

Early-onset Alzheimer's disease (EOAD) is defined as Alzheimer's disease (AD) with an age at onset younger than 65 years, accounting for approximately 5% of all AD cases. More than 90% of EOAD cases do not carry autosomal dominant pathogenic mutations. Although its prevalence is lower than that of late-onset Alzheimer's disease (LOAD), EOAD follows a more aggressive clinical course. A subset of EOAD patients present with non-amnestic variant phenotypes, including logopenic variant of primary progressive aphasia (lvPPA), frontal variant Alzheimer's disease (fvAD), posterior cortical atrophy (PCA), and corticobasal syndrome (CBS). However, the neuroimaging characteristics of EOAD and their differences from those of LOAD remain poorly elucidated to date. Therefore, this review systematically summarizes the recent research progress in neuroimaging of EOAD, including structural, functional, and metabolic imaging modalities. We also discuss the potential pathogenesis of EOAD, with the aim to provide evidence-based reference for the development of EOAD-specific imaging assessment systems and the optimization of disease efficacy monitoring protocols in future research.