Dementia as a Predictor of Functional Disability: A Four-Year Follow-Up Study

BACKGROUND: Prospective studies have shown that cognitive impairment is a strong and consistent risk factor of physical disability. However, cognitive impairment has been based on the result of a single screening tool. OBJECTIVE: To investigate the role of cognition in the subsequent incidence and decline of functional disability in basic activities of daily living (ADL) and instrumental activities of daily living (IADL) after a full assessment of dementia. METHODS: A group of 1,358 Japanese atomic bomb survivors aged 61 years or older who lived in the community or in institutions in Hiroshima City were followed for 4 years. During the baseline survey (1993-1995), subjects were administered a screening test for cognitive impairment. Those suspected of dementia underwent a series of cognitive tests (Hasegawa's dementia scale, Clinical Dementia Rating) and a neurological examination. The diagnosis of dementia was made according to DSM-III-R criteria. Study subjects were questioned about their reported ADL and their IADL. During the follow-up period, deaths were recorded and a follow-up survey (1997-1999) used to assess ADL and IADL performance. RESULTS: Dementia, even after adjustment for age, sex and history of stroke, was a strong predictor of functional disability, as indicated by ADL (odds ratio, OR = 14.0; confidence interval, CI = 5.4-36.3), IADL (OR = 10.1, CI = 2.2-46.4), and also by assessment of decline in ADL (OR = 9.8, CI = 4.2-22.8) or IADL status (OR = 3.9, CI = 1.8-8.3). CONCLUSION: Dementia is an important determinant of functional status. Deterioration in ADL is more significant than deterioration in IADL, suggesting that factors other than cognition, such as motivation or perceptual, sensory and motor abilities, may be important in IADL performance. This study confirms previous findings on risk factors that affect functional ability and extends our knowledge by examining several criteria of function that are important in the daily lives of elderly people.