EEG comparisons in early Alzheimer's disease, dementia with Lewy bodies and Parkinson's disease with dementia patients with a 2-year follow-up

Background: EEG abnormalities have been reported for both Dementia with Lewy bodies (DLB) and Alzheimer Disease (AD). Although it has been suggested that variations in mean EEG frequency are greater in DLB than AD, the existence of meaningful differences between these diseases remains controversial. No evidence is so far available for Parkinson disease with dementia (PDD). Objective: To evaluate whether EEG abnormalities can discriminate among DLB, PDD, and AD patients in the earliest stages of dementia. Methods and Subjects: 50 AD, 50 DLB, and 40 PDD patients with slight cognitive impairment at first visit (MMSE ≥ 20) were included. To improve clinical diagnostic accuracy, a special emphasis was put on identifying cognitive fluctuations and REM-sleep behaviour disorder (RBD). EEG variability was assessed by mean frequency analysis and Compressed Spectral Arrays (CSA), in order to detect changes across time from different scalp derivations. Patients’ initial diagnoses were revised at a 2-year follow-up visit, comprehensive of neuroimaging evaluation. Results: Initial diagnoses were confirmed in 40 AD, 36 DLB, and 35 PDD patients. The most relevant group differences at presentation were observed between AD and DLB patients in EEGs from posterior derivations (p <0.001). Dominant Frequencies (DFs) were 8.3 0.6 Hz for the AD group and 7.4 1.6 Hz for the DLB group, in which most of the patients (88%) exhibited a frequency band of 5.6 to 7.9 Hz. DF variability (DFV) also differed between the AD (1.1 0.4 Hz) and the DLB group (1.8 1.2 Hz, p <0.001). Of note, less than a half (46%) of the patients with PDD exhibited the EEG abnormalities seen in those with DLB. Graded according to the presence of alpha activity, five different patterns were identified on EEG CSAs from posterior derivations. A pattern with dominant alpha was observed in patients with AD alone while, in those with DLB and PDD, the degree to which residual alpha and 5.6-7.9 band appeared at presentation was related to the presence and severity of cognitive fluctuations. At follow-up examination, EEG abnormalities from posterior leads were seen in all of the subjects with DLB and in three quarters of those with PDD. Of interest, in four patients initially labelled as having AD, in whom the occurrence of fluctuations and/or RBD during the 2-year follow-up had made the diagnosis of AD questionable, the initial EEG was characterized by the features observed in the DLB group. Conclusions: If revised consensus Criteria for DLB diagnosis are properly applied (i.e, emphasizing the diagnostic weight of fluctuations and REM sleep behaviour disorder), EEG recording may well perform as a supportive method to discriminate DLB from AD in the earliest stages of dementia. Since characteristic abnormalities may even precede the appearance of distinctive clinical features, EEG can be particularly helpful in cases with still uncertain diagnosis, especially those who meet both the “possible” DLB and the “possible” AD category.