Cognitive test completion time as an indicator of early brain atrophy: Findings from the Cognitive Assessment for Dementia, iPad version 2 (CADi2) in healthy adults

Background Although several cognitive screening tools are available, early-stage detection remains challenging because individuals in prodromal or mild cognitive impairment stages often score within normal ranges. Assessment of response time, rather than test score alone, may offer greater sensitivity to subtle decline. Objective To examine whether completion time on the Cognitive Assessment for Dementia, iPad version 2 (CADi2), is associated with early brain changes suggestive of preclinical dementia. Methods In this cross-sectional study of 511 cognitively unimpaired adults (290 men, 221 women; mean age, 61 years) at the Health Science Center, Japan, participants completed the 10-item CADi2 and underwent structural magnetic resonance imaging. Based on the ceiling effects in total scores, we analyzed associations between total test duration and regional brain atrophy. Results CADi2 time was significantly associated with hippocampal atrophy, while total scores were not. We applied a deep survival analysis model using Alzheimer's Disease Neuroimaging Initiative data to estimate 5-year dementia risk. Using a threshold of ≥0.25, receiver operating characteristic analysis showed that CADi2 time (area under the curve, 0.632) outperformed CADi2 (0.554) and Mini-Mental State Examination (0.582) scores. Only CADi2 time showed a significant odds ratio [OR] for high dementia risk (OR = 1.94; 95% confidence interval: 1.12–3.40; p = 0.018) after adjusting for covariates. Conclusions These findings indicate that completion time from a cognitive test without ceiling effects is more suitable than score-based measures for evaluating the predementia stage and that combining time and score metrics may further improve stratification in cognitively normal individuals.