King's College London

Introduction: Neuropsychiatric symptoms (NPS) in dementia are associated with poor cognitive outcomes in longitudinal studies. Whether this is due to differences in symptom burden between persons (BP) or changes within persons (WP) is unknown. Methods: Patients with mild Alzheimer’s disease (AD, n = 111) and Lewy-body dementia (LBD, n = 85) were assessed annually for 8 years. We modelled the association between NPS assessed by the Neuropsychiatric Inventory (NPI) and Mini-Mental State Examinations (MMSE) using Tobit mixed-effects model with NPS as individual means over time (BP) and its deviance (WP). Results: The association between higher NPS and poorer cognitive outcomes was mostly due to BP differences for the NPI-total score, and in particular for delusions, hallucinations, agitation, aberrant motor behavior, and apathy scores. Discussion: The NPS trait (BP) effect on cognitive decline is considerably stronger than the state effect (WP). Clinically, long-term rather than episodic NPS better identifies patients with poor cognitive outcomes.