Classifying anatomical subtypes of subjective memory impairment

We aimed to categorize subjective memory impairment (SMI) individuals based on their patterns of cortical thickness and to propose simple models that can classify each subtype. We recruited 613 SMI individuals and 613 age- and gender-matched normal controls. Using hierarchical agglomerative cluster analysis, SMI individuals were divided into 3 subtypes: temporal atrophy (12.9%), minimal atrophy (52.4%), and diffuse atrophy (34.6%). Individuals in the temporal atrophy (Alzheimer's disease-like atrophy) subtype were older, had more vascular risk factors, and scored the lowest on neuropsychological tests. Combination of these factors classified the temporal atrophy subtype with 73.2% accuracy. On the other hand, individuals with the minimal atrophy (non-neurodegenerative) subtype were younger, were more likely to be female, and had depression. Combination of these factors discriminated the minimal atrophy subtype with 76.0% accuracy. We suggest that SMI can be largely categorized into 3 anatomical subtypes that have distinct clinical features. Our models may help physicians decide next steps when encountering SMI patients and may also be used in clinical trials.