Sporadic early-onset Alzheimer’s disease (EOAD; symptomatic onset <65 years) is a rare and understudied but particularly devastating form of AD, affecting patients at a point in life when they may be balancing careers, family responsibilities, and community roles. Compared to the more common typical late-onset AD (LOAD), patients with EOAD often present with prominent impairments in executive function, language, visuospatial abilities, and/or somatosensory or motor functions rather than memory. These differences reflect more prominent neurodegeneration in the posterior lateral temporal, lateral and medial parietal, frontal, or occipital cortex relative to the medial and ventral temporal cortical localization of typical LOAD. Convergently, neuropathological investigations have identified a “hippocampal-sparing” form of AD that is often present in younger patients. For these reasons, imaging biomarkers of neurodegeneration in EOAD, such as magnetic resonance imaging (MRI) measures of atrophy, likely need to be different from those of neurodegeneration in typical LOAD.
