Cross-sectional versus longitudinal cognitive assessments for the diagnosis of symptomatic Alzheimer's disease in adults with Down syndrome

Background: Down syndrome (DS) is a genetic form of Alzheimer's disease (AD). However, clinical diagnosis is difficult, and experts emphasize the need for detecting intra-individual cognitive decline. Objective: To compare the performance of baseline and longitudinal neuropsychological assessments for the diagnosis of symptomatic AD in DS. Methods: Longitudinal cohort study of adults with DS. Individuals were classified as asymptomatic, prodromal AD, or AD dementia. We performed receiver operating characteristic curve analyses to compare baseline and longitudinal changes of CAMCOG-DS and mCRT. Results: We included 562 adults with DS. Baseline assessments showed good to excellent diagnostic performance for AD dementia (AUCs between 0.82 and 0.99) and prodromal AD, higher than the 1-year intra-individual cognitive decline (area under the ROC curve between 0.59 and 0.79 for AD dementia, lower for prodromal AD). Longer follow-ups increased the diagnostic performance of the intra-individual cognitive decline. Discussion: Baseline cognitive assessment outperforms the 1-year intra-individual cognitive decline in adults with DS.