Natural history of decline in instrumental activities of daily living performance over the 10 years preceding the clinical diagnosis of dementia: a prospective population-based study.

OBJECTIVES: To study the subtle changes in instrumental activities of daily living (IADLs) over the 10 years preceding the clinical diagnosis of dementia.
DESIGN: Prospective cohort designed in 1988 to study cerebral and functional aging.
SETTING: Community-based study in southwestern France. PARTICIPANTS: The sample included 104 incident cases of dementia at the 10-year follow-up (T10) and 882 subjects free of dementia at the same visit, all forming part of the PAQUID Study. MEASUREMENTS: Restriction in four IADLs was studied (telephone, transportation, medication, and finances) 2, 5, 7, and 10 years before the T10 visit.
RESULTS: The future dementia cases had greater IADL restrictions 10 years before the clinical diagnosis of dementia and more-rapid functional deterioration over time. Controlled for age, sex, and education, subjects restricted in at least two IADLs at baseline had a higher risk of dementia 10 years later (odds ratio (OR)=2.59, 95% confidence interval (CI)=1.24-5.38). In finances, difficulty at baseline was a predictor of dementia 10 years later (OR=2.15, 95% CI=1.13-4.08).
CONCLUSION: This study is the first to show that, 10 years before the clinical diagnosis of dementia, subjects who later developed dementia performed worse in complex activities of daily living, which may constitute an early marker of the disease. In practice, restriction in IADLs may be a simple and useful tool for screening subjects at risk of developing dementia in the long term.