Higher risk of progression to dementia in mild cognitive impairment cases who revert to normal.

Abstract

To estimate rates of progression from mild cognitive impairment (MCI) to dementia and of reversion from MCI to being cognitively normal (CN) in a population-based cohort. Participants (n = 534, aged 70 years and older) enrolled in the prospective Mayo Clinic Study of Aging were evaluated at baseline and every 15 months to identify incident MCI or dementia. Over a median follow-up of 5.1 years, 153 of 534 participants (28.7%) with prevalent or incident MCI progressed to dementia (71.3 per 1,000 person-years). The cumulative incidence of dementia was 5.4% at 1 year, 16.1% at 2, 23.4% at 3, 31.1% at 4, and 42.5% at 5 years. The risk of dementia was elevated in MCI cases (hazard ratio [HR] 23.2, p < 0.001) compared with CN subjects. Thirty-eight percent (n = 201) of MCI participants reverted to CN (175.0/1,000 person-years), but 65% subsequently developed MCI or dementia; the HR was 6.6 (p < 0.001) compared with CN subjects. The risk of reversion was reduced in subjects with an APOE ε4 allele (HR 0.53, p < 0.001), higher Clinical Dementia Rating Scale-Sum of Boxes (HR 0.56, p < 0.001), and poorer cognitive function (HR 0.56, p < 0.001). The risk was also reduced in subjects with amnestic MCI (HR 0.70, p = 0.02) and multidomain MCI (HR 0.61, p = 0.003). MCI cases, including those who revert to CN, have a high risk of progressing to dementia. This suggests that diagnosis of MCI at any time has prognostic value.