Mild cognitive impairment: Risk of Alzheimer disease and rate of cognitive decline

We read with interest the study by Boyle et al. reporting findings from the Rush Memory and Aging Project, in which over an average of 2.5 years of follow-up, 57 persons with mild cognitive impairment (MCI) (25.8% of 221) and 23 persons without cognitive impairment developed Alzheimer disease (AD) (4.1% of 565); 32 persons with MCI (14.4% of 221) showed no subsequent evidence of cognitive impairment on follow-up.1 Furthermore, Boyle et al. found that persons with MCI were almost seven times more likely to develop AD than comparable persons without cognitive impairment. In addition, persons with MCI declined considerably more rapidly each year on a measure of global cognitive function than those without cognitive impairment.1 The authors reported in the Introduction and Discussion some clinical features of the progression to dementia of MCI and other predementia syndromes, citing the findings of the Italian Longitudinal Study on Aging (ILSA)2 and other population-based or clinical-based studies.3,4 In the ILSA, a population-based study with a 3.5-year follow-up, involving a total of 2,963 individuals from age 65 to 84, we found a progression rate to dementia of 3.8/100 person-years (2.3/100 person-years to AD), and among those who progressed to dementia, 60% …