Age-Dependent Functional Decline and Recovery Patterns After Dementia Diagnosis in the Oldest-Old

Background Dementia prevalence and incidence rise sharply among the oldest-old (≥85 years), yet whether age-at-diagnosis shapes functional trajectories remains unclear. Understanding age-specific patterns is critical for tailoring care strategies. Objectives To determine whether age at dementia diagnosis influences patterns of functional decline and recovery, and to identify the functional domains driving age-specific trajectories. Methods Using Manitoba Follow-up Study data, participants were grouped by age at dementia diagnosis (<85, 85–89, ≥90) or no dementia. We tracked Basic Activities of Daily Living (BADLs), Instrucmental Activities of Daily Living (IADLs), and SF-36 Physical/Mental scores. Generalized additive mixed models and mixed-effects random forest analyses assessed trajectories, dependence, and recovery. Results Age at diagnosis showed differences in trajectories. The ≥85 group showed steep post-diagnosis decline; the <85 group declined more steadily. Complex tasks (e.g., cutting toenail) were most impaired. Recovery occurred, particularly in IADLs and in the ≥90 group. Conclusions Age at dementia diagnosis showed meaningful differences in functional decline and recovery, supporting age-specific care strategies.