A PROSPECTIVE-STUDY OF COGNITIVE FUNCTION AND ONSET OF DEMENTIA IN COGNITIVELY HEALTHY ELDERS

Objective: To examine the earliest cognitive changes associated with t he onset of dementia as well as changes associated with normal aging. Design: Longitudinal evaluation of participants with annual clinical a nd psychometric examinations for up to 15 1/2 years. Setting and Parti cipants: Elderly volunteers (n=82) enrolled with a Clinical Dementia R ating of 0 (cognitively intact) in longitudinal studies. Interventions : None. Main Outcome Measures: Clinical Dementia Rating and results of a 1 1/2-hour psychometric battery. Results: As estimated with surviva l analysis, 40% of participants had a Clinical Dementia Rating greater than 0 (cognitive decline) within 12 years of enrollment; 59% of thes e were judged to have dementia of the Alzheimer type or incipient deme ntia. Participants with poorer performance on psychometric testing at enrollment were at higher risk for cognitive decline subsequently. The rate of change in psychometric performance before clinically detectab le cognitive change occurred was not significantly different between t hose who eventually developed dementia and those who remained stable, except for performance on the logical Memory subtest of the Wechsler M emory Scale. When subtle cognitive decline was clinically detected, ho wever, an abrupt deterioration in performance on independently adminis tered psychometric tests was observed. Conclusions: Cognitively health y elderly people maintain stable cognitive performance when measured l ongitudinally by both careful clinical evaluation and repeated psychom etric testing. This stability is maintained unless and until they deve lop a dementing illness, at which time a sharp decline in performance is observed.