Mild cognitive impairment: prevalence and incidence according to different diagnostic criteria. Results of the Leipzig Longitudinal Study of the Aged (LEILA75+).

BACKGROUND Although mild cognitive impairment is associated with an increased risk of developing dementia, there has been little work on its incidence and prevalence. AIMS To report age-specific prevalence, incidence and predictive validities for four diagnostic concepts of mild cognitive impairment. METHOD A community sample of 1045 dementia-free individuals aged 75 years and over was examined by neuropsychological testing in a three-wave longitudinal study. RESULTS Prevalence rates ranged from 3% to 20%, depending on the concept applied. The annual incidence rates applying different case definitions varied from 8 to 77 per 1000 person-years. Rates of conversion to dementia over 2.6 years ranged from 23% to 47%. CONCLUSIONS Mild cognitive impairment is frequent in older people. Prevalence, incidence and predictive validities are highly dependent on the diagnostic criteria applied.