Approximately 20% to 30% of patients diagnosed as having Alzheimer disease (AD) in an expert setting do not meet pathological criteria at autopsy.1,2 In 2 recent clinical trials, 20% of all patients (and more than 33% of those who were noncarriers of the apolipoprotein E ε4 allele) with mild or moderate Alzheimer dementia did not show an elevation in amyloid on positron emission tomography (PET) imaging.3,4 Individuals with a nonamyloid amnestic dementia in those 2 trials had a more benign clinical course.