Associations between neuropsychiatric symptoms and functional decline in dementia: a systematic review.

BACKGROUND: Neuropsychiatric symptoms (NPS) occur in up to 80-90% of people with dementia and contribute substantially to clinical complexity, caregiver burden and health and social care use. However, it remains unclear which NPS domains are most consistently associated with functional decline. OBJECTIVES: To synthesise evidence on the association between NPS and functional decline in dementia, measured as activities of daily living (ADL) and instrumental activities of daily living (IADL). METHODS: This systematic review was registered in PROSPERO (CRD420261280442) and reported according to PRISMA 2020. MEDLINE, PubMed, Embase and PsycINFO were searched from inception to September 2025. Observational and mixed-design studies of adults aged ≥65 years with dementia reporting validated NPS and ADL/IADL measures were included. Given heterogeneity, findings were synthesised without meta-analysis. Certainty of longitudinal evidence was assessed using GRADE. RESULTS: Forty studies including 13 711 participants were included. Across study designs, NPS were frequently associated with poorer functional performance and greater dependence. In longitudinal studies, apathy was the most consistently associated domain overall (6/9 studies), while delusions showed fully consistent associations (5/5). Hallucinations were also consistently associated (3/3) and showed some of the strongest reported associations with subsequent decline. Other NPS domains and overall NPS burden were also associated with worsening ADL/IADL, although consistency varied across domains and dementia subtypes. Certainty of evidence was generally low to very low. CONCLUSIONS: NPS, particularly apathy and psychotic symptoms, are associated with functional decline in dementia and may help identify patients at risk of emerging dependency beyond cognitive impairment alone.