Rates of progression in mild cognitive impairment and early Alzheimer's disease

Objective: To compare rates of progression in the very mildest stages of AD, including the stage currently identified as mild cognitive impairment (MCI), and to identify predictors of those rates. Methods: Demented (n = 289) and nondemented (n = 230) individuals enrolled in longitudinal studies at an Alzheimer Disease Research Center received annual clinical and psychometric examinations for up to 20 years. In order of increasing dementia severity, demented individuals were diagnosed with incipient, very mild, or mild dementia; the incipient stage is equivalent to MCI. Outcome measures included death, nursing home placement, and psychometric scores. Results: Rate of progression increased with dementia severity as staged by the Clinical Dementia Rating at entry into the study. With respect to the dichotomous outcomes, the increase with dementia severity was more dramatic for the endpoint of nursing home entry than it was for the endpoint of death. Increased rates of cognitive decline with increased dementia severity were also obtained for psychometric scores. There was limited evidence of other predictors of progression. Conclusions: The lack of effective predictors of the rate of dementia progression extends to the very earliest stages of the disease, including what is often called MCI. A new approach to the identification of correlates of rates of progression is needed.