Revisiting P300 cognitive studies for dementia diagnosis: Early dementia with Lewy bodies (DLB) and Alzheimer disease (AD).

Aims of the study: Earlier P300 studies were conducted when the prevalence of dementia with Lewy Bodies (DLB) was unknown. Our study aims to examine whether P300 abnormalities are present in DLB and to evidence possible differences between DLB and Alzheimer's disease (AD). A second aim of this study is to look for correlations between P300 recordings and EEG, as abnormal EEG variability has been described in DLB. Patients and methods: Auditory P300 responses were recorded by a classic oddball paradigm in 50 controls, in 36 DLB patients, and in 40 AD patients with MMSE > 20. Results: Reliable auditory P300 responses were obtained in 26 DLB (72%), 33 AD (82.5%), and 46 controls (92%). P300 was more delayed and had lower amplitude in DLB compared to AD groups. P300 topography was also different as the anterior-to-posterior scalp amplitude gradient was reversed in DLB. P300 latency correlated with neuropsychological test scores and with EEG variables. Gradient inversion and delayed P300 responses in frontal derivations evidenced differences between DLB and AD patients with a sensitivity of 70% and a specificity of 97%. Conclusions: P300 recordings are abnormal in DLB and can be useful to distinguish DLB from AD.