Smartphone Passive Digital Phenotyping in Frontotemporal Lobar Degeneration

Frontotemporal lobar degeneration (FTLD) is a serious disease causing early-onset dementia, but its rarity and heterogeneity limit large-scale research. The study included 567 adults (53% healthy, 21% prodromal FTLD, 26% symptomatic FTLD) who installed the ALLFTD Mobile App. The application passively collected data on smartphone usage and step count without active user participation. Passive monitoring proved reliable with correlation coefficients exceeding 0.9 over two weeks of monitoring. Data on smartphone usage and movement were sensitive to clinical markers of disease severity. A combined model of passive features with cognitive tests achieved 0.89 accuracy in detecting functional decline. Passive monitoring alone achieved 0.84 accuracy, comparable to cognitive screening (0.85). The research confirms that passive smartphone monitoring is a valid and burden-free tool for measuring FTLD severity and progression.