Combined Influence of Subjective Cognitive Complaints and Neuropsychiatric Symptoms on Cognitive Trajectories in Older Adults

Objective: Subjective cognitive complaints (SCC) and neuropsychiatric symptoms (NPS) are both recognized as early markers of dementia, but their combined predictive value is not well understood. This study investigated whether SCC and NPS, individually and jointly, predicted six-year cognitive decline and 12-year incident dementia in community-dwelling older adults. Methods: Participants were 468 dementia-free individuals aged 70–90 from the Sydney Memory and Ageing Study, followed for up to 12 years. Cognitive decline was assessed biennially via neuropsychological tests; dementia diagnoses were made by expert consensus. SCC were captured using two self-reported and one informant-reported item. NPS were assessed using the informant-rated Neuropsychiatric Inventory. SCC and NPS were each operationalised as ordinal scores ranging from 0 to 3, with higher scores reflecting more SCC items or more NPS clusters, respectively, and participants were categorized into SCC−/NPS−, SCC+/NPS−, SCC−/NPS+, SCC+/NPS+. Linear regression models assessed associations with six-year cognitive decline across domains and global cognition, and Cox proportional hazards models assessed incident dementia risk over 12 years. Results: SCC sum scores predicted dementia risk, whereas NPS sum scores were not significantly associated with dementia risk. In the combined SCC/NPS group analyses, SCC+/NPS+ participants had a 66% higher hazard of dementia (HR = 1.66, p = 0.041). For cognitive decline, the SCC−/NPS+ group showed significantly greater decline in executive function, visuospatial ability, and global cognition compared with SCC−/NPS−. Neither SCC+/NPS− nor SCC+/NPS+ predicted domain-specific decline. Discussion: SCC and NPS showed different patterns of association with later outcomes, with the combined SCC/NPS profile identifying a subgroup at elevated dementia risk. These findings support closer monitoring of older adults who present with co-occurring SCC and NPS, as this profile may help improve early identification of individuals at risk of adverse cognitive outcomes.