Cognitive deficits 3 to 6 years before dementia onset in a population sample: the Honolulu-Asia aging study

OBJECTIVE: To determine the type of cognitive deficits occurring 3 to 6 years before onset of dementia in a population sample. DESIGN: A prospective study in which cognitive deficits in participants who had incident dementia at the 6-year follow-up were examined at baseline and 3 years. SETTING: Honolulu, Hawaii. PARTICIPANTS: Three thousand seven hundred thirty-four Japanese-American men aged 71 to 93 at baseline. At the 6-year follow-up, there were 52 incident cases of dementia, and 1,559 controls. MEASUREMENTS: The Cognitive Abilities Screening Instrument (CASI) and a questionnaire on subjective memory problems were administered at baseline. Dementia was assessed at baseline and at 3-year and 6-year follow-ups. RESULTS: Subjects who had incident dementia at 6-year follow-up, had showed deficits 3 to 6 years earlier in the CASI domain of episodic memory and in the questionnaire covering subjective memory problems. Up to 3 years before onset, there was worsening of the episodic memory deficit from baseline and new deficits in language, verbal fluency, and orientation. CONCLUSION: Cognitive deficits and awareness of memory problems are frequently present several years before dementia onset. The predictive value of these deficits is not large enough to allow earlier diagnosis of dementia, but information about such deficits may be useful as criteria for mild cognitive impairment.