Cognitive differences between early- and late-onset Alzheimer's disease.

Although neuropathologic studies showed that early-onset Alzheimer's disease (EAD) and "senile dementia" were indistinguishable, clinical studies suggested that EAD and late-onset Alzheimer's disease (LAD) were cognitively distinct. We sought to investigate whether EAD and LAD are cognitively different by comparing patients at the extremes of the ages of onset in order to maximize features that might separate them. We compared 44 men with EAD (age of onset less than 65 years) with 44 men with LAD (age of onset 84 years or older) on an intake cognitive screening examination on initial presentation. The EAD and LAD groups did not differ on dementia or most cognitive variables. Compared with EAD, the LAD group had worse verbal fluency and motor-executive functions. These differences disappeared when age differences were taken into account. We conclude that Alzheimer's disease is a clinically heterogeneous disorder whose manifestations can vary with age of onset. These differences indicate age-related vulnerabilities in this disease.