Nonamnestic mild cognitive impairment progresses to dementia with Lewy bodies

Objective: To determine the rate of progression of mild cognitive impairment (MCI) to dementia with Lewy bodies (DLB). Methods: We followed 337 patients with MCI in the Mayo Alzheimer's Disease Research Center (range 2-12 years). Competing risks survival models were used to examine the rates of progression to clinically probable DLB and Alzheimer disease (AD). A subset of patients underwent neuropathologic examination. Results: In this clinical cohort, 116 remained as MCI, while 49 progressed to probable DLB, 162 progressed to clinically probable AD, and 10 progressed to other dementias. Among nonamnestic MCI, progression rate to probable DLB was 20 events per 100 person-years and to probable AD was 1.6 per 100 person-years. Among amnestic MCI, progression rate to probable AD was 17 events per 100 person-years, and to DLB was 1.5 events per 100 person-years. In 88% of those who developed probable DLB, the baseline MCI diagnosis included attention and/or visuospatial deficits. Those who developed probable DLB were more likely to have baseline daytime sleepiness and subtle parkinsonism. In 99% of the clinically probable AD group, the baseline MCI diagnosis included memory impairment. Neuropathologic confirmation was obtained in 24 of 30 of those with clinically probable AD, and in 14 of 18 of those with clinically probable DLB. Conclusion: In a clinical sample, patients with nonamnestic MCI were more likely to develop DLB, and those with amnestic MCI were more likely to develop probable AD.