Highlights Posterior cortices, hippocampus and amygdala track atrophy in EOAD over two years. The medial temporal cortex is unaltered in EOAD at early stages. EOAD exhibited a posterior-to-anterior gradient of cortical loss after two years. EOAD subcortical volume loss extends beyond hippocampus and amygdala after two years. Cerebrospinal fluid biomarkers might predict atrophy rates in EOAD.

Prior studies have described distinct patterns of brain gray matter and white matter alterations in Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD), as well as differences in their cerebrospinal fluid (CSF) biomarkers profiles. We aim to investigate the relationship between early-onset AD (EOAD) and FTLD structural alterations and CSF biomarker levels. We included 138 subjects (64 EOAD, 26 FTLD, and 48 controls), all of them with a 3T MRI brain scan and CSF biomarkers available (the 42 amino acid-long form of the amyloid-beta protein [Aβ42], total-tau protein [Ttau], neurofilament light chain [NfL], neurogranin [Ng], and 14-3-3 levels). We used FreeSurfer and FSL to obtain cortical thickness (CTh) and fraction anisotropy (FA) maps. We studied group differences in CTh and FA and described the "AD signature" and "FTLD signature." We tested multiple regression models to find which CSFbiomarkers better explained each disease neuroimaging signature. CTh and FA maps Neus Falgàs, Mariona Ruiz-Peris, Albert Lladó, and Raquel Sánchez-Valle authors contributed equally to this work.