Progression of mild cognitive impairment to dementia: a challenge to current thinking.

BACKGROUND Studies of conversion from mild cognitive impairment to dementia suggest a linear progression over time. Conversion rates during lifetime may extend to 80-90%. AIMS This study examines the time-dependent evolution from mild cognitive impairment to dementia. Current assumptions regarding yearly and lifetime conversion rates are challenged. METHOD A community sample of 1045 dementia-free individuals aged 75 years and over was examined by neuropsychological testing based on 6 years of observation. RESULTS Approximately 60-65% of people with mild cognitive impairment develop clinical dementia during their life. Progression from mild cognitive impairment to dementia appears to be time dependent, occurring primarily within the initial 18 months. CONCLUSIONS Further long-term studies are needed to examine the time-dependent evolution from mild cognitive impairment to dementia and to establish age-specific conversion rates during lifetime.