Background: Late-onset Alzheimer disease (LOAD) is a clinically heterogeneous complex disease defined by progressively disabling cognitive impairment. Psychotic symptoms which affect approximately one-half of LOAD subjects have been associated with more rapid cognitive decline. However, the variety of cognitive trajectories in LOAD, and their correlates, have not been well defined. We therefore used latent class modeling to characterize trajectories of cognitive and behavioral decline in a cohort of AD subjects.

Methods: 201 Caucasian subjects with possible or probable Alzheimer's disease (AD) were evaluated for cognitive and psychotic symptoms at regular intervals for up to 13.5 years. Cognitive symptoms were evaluated serially with the Mini-mental State Examination (MMSE), and psychotic symptoms were rated using the CERAD behavioral rating scale (CBRS). Analyses undertaken were latent class mixture models of quadratic trajectories including a random intercept with initial MMSE score, age, gender, education, and APOE ϵ4 count modeled as concomitant variables. In a secondary analysis, psychosis status was also included.

Results: AD subjects showed six trajectories with significantly different courses and rates of cognitive decline. The concomitant variables included in the best latent class trajectory model were initial MMSE and age. Greater burden of psychotic symptoms increased the probability of following a trajectory of more rapid cognitive decline in all age and initial MMSE groups. APOE ϵ4 was not associated with any trajectory.

Conclusion: Trajectory modeling of longitudinal cognitive and behavioral data may provide enhanced resolution of phenotypic variation in AD.

Background: Psychotic symptoms in Alzheimer disease (AD + P) identify a heritable phenotype associated with greater cognitive impairment. Knowing when the cognitive course of AD + P subjects diverges from that of subjects without psychosis would enhance understanding of how genetic variation results in AD + P and its associated cognitive burden. This study seeks to determine whether the degree of cognitive impairment and cognitive decline in early AD predicts subsequent AD + P onset.

Methods: 361 subjects with possible or probable AD or mild cognitive impairment (MCI) without psychosis were evaluated every 6 months until psychosis onset.

Results: Severity of cognitive dysfunction was a strong predictor of AD + P up to two years prior to psychosis onset. Cognition did not decline more rapidly prior to onset of AD + P.

Conclusions: Individuals who will develop AD + P already demonstrate excess cognitive impairment during the mild stages of disease. Genetic variation and brain pathophysiology may lead to a cognitive risk phenotype which is present prior to dementia onset.