Quantifying fluctuation in dementia with Lewy bodies, Alzheimer's disease, and vascular dementia

Background: Case reports and clinical observations suggest that fluctuating cognition (FC) is common in the major dementias, particularly dementia with Lewy bodies (DLB), where it is one of three core clinical diagnostic features. Objectives: To examine the frequency, characteristics, and diagnostic utility of FC in dementia using clinical, attentional, and EEG markers. Method: A total of 155 subjects (61 with AD, 37 with DLB, 22 with vascular dementia [VaD], 35 elderly controls) received clinical evaluation for FC using a semiquantified measure applied by experienced clinicians and 90-second cognitive choice reaction time (CRT) and vigilance reaction time (VIGRT) trials. Forty subjects also received an evaluation of mean EEG frequency across 90 seconds. Results: Patients with DLB had a greater prevalence and severity of FC than did patients with AD or VaD rated using clinical, attentional, and EEG measures. The 90-second cognitive and EEG trials demonstrated that FC occurs on a second-to-second basis in patients with DLB. Patients with VaD had a higher prevalence of FC than did those with AD, although the profile of FC was different from that expressed by DLB cases. Optimal cutoff values on the clinical scale achieved good discrimination between the dementia groups (sensitivity 81%, specificity 92%, DLB versus AD; sensitivity 81%, specificity 82%, DLB versus VaD; sensitivity 64%, specificity 77%, VaD versus AD). Conclusion: Standardized assessment methods demonstrate that FC is significantly more common and severe in DLB than in other major dementias. The periodicity of FC is different in DLB and VaD cases, with important implications for the underlying causal mechanisms and for differential diagnosis.