Associations Between Cognitive Performance and Motor Signs in Older Adults with Alzheimer's Dementia

Background and Objectives: The interplay between motor tasks and cognition in Alzheimer's dementia (AD) remains insufficiently characterised. We hypothesised that prefrontal-mediated cognitive functions could contribute to motor impairments in older adults with AD. Materials and Methods: Cross-sectional data from the National Alzheimer's Coordinating Centre (NACC) were analysed. Our sample included older adults (≥60 years) with a baseline diagnosis of AD. The Unified Parkinson's Disease Rating Scale Part-III was used to assess the presence or absence of motor signs. Episodic memory, language, confrontation naming, attention, processing speed, and executive function were assessed using a neuropsychological battery. Binary logistic models examined the relationship between cognitive performance and motor manifestations. Results: Of 44,713 NACC participants, 5124 individuals with complete covariate data were included in the analysis, 1339 with and 3785 without motor signs. Participants were predominantly female (~55%), with an average age of 76.5 ± 7.9 years and mean education of 14.2 ± 3.7 years. The presence of motor manifestations was related to slower processing speed (Trail Making Test-Part A) and impaired executive function (Trail Making Test-Part B). No covariate modified these associations. Among specific motor domains, impaired chair rise was related to executive dysfunction, whereas postural instability, impaired posture-gait, and bradykinesia were related to slower mental processing. Hypophonia, masked facies, resting tremor, action-postural tremor and rigidity were not associated with any cognitive measure. Conclusions: Processing speed and, to a lesser extent, executive function emerged as the main cognitive functions associated with motor manifestations in older adults with AD. Further research is needed to clarify the nature of this association, including potential causal pathways.