Brain Advance Access published online on January 17, 2008
Brain, doi:10.1093/brain/awm322
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EEG comparisons in early Alzheimer's disease, dementia with Lewy bodies and Parkinson's disease with dementia patients with a 2-year follow-up
1Department of Neurology, Aging Research Center, Ce.S.I., ‘Gabriele d'annunzio’ University Foundation, University G.D'annunzio of Chieti-Pescara, via Fonte Romana, 65124 Pescara, 2Department of Neurology, Niguarda Ca’ Granda Hospital, 20162 Milan and 3Fondazione Europea Ricerca Biomedica Centro Alzheimer Ospedale Briolini, Gazzaniga (Bergamo), Italy
Correspondence to:
Prof. Marco Onofrj, Neurophysiopathology, Department of Neurology, Aging Research Center, Ce.S.I., ‘Gabriele d'annunzio’, University Foundation, Chieti-Pescara, Via Fonte Romana, 65124 Pescara, Italy E-mail: onofrj{at}unich.it
EEG abnormalities have been reported for both dementia with Lewy bodies (DLB) and Alzheimer's disease (AD). Although it has been suggested that variations in mean EEG frequency are greater in the former, the existence of meaningful differences remains controversial. No evidence is as yet available for Parkinson's disease with dementia (PDD). The aim of this study was to evaluate whether EEG abnormalities can discriminate between DLB, AD and PDD in the earliest stages of dementia and to do this 50 DLB, 50 AD and 40 PDD patients with slight cognitive impairment at first visit (MMSE 
20) were studied. To improve clinical diagnostic accuracy, special emphasis was placed on identifying cognitive fluctuations and REM-sleep behaviour disorder. EEG variability was assessed by mean frequency analysis and compressed spectral arrays (CSA) in order to detect changes over time from different scalp derivations. Patients’ initial diagnoses were revised at a 2-year follow-up visit with neuroimaging evaluation. Initial diagnoses were confirmed in 36 DLB, 40 AD and 35 PDD patients. The most relevant group differences were observed between the AD and DLB patients in EEGs from posterior derivations (P<0.001). Dominant frequencies 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 5.6–7.9 Hz. Dominant frequency variability also differed between the AD (1.1 ± 0.4 Hz) and DLB groups (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 CSA from posterior derivations. A pattern with dominant alpha bands 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 bands appeared was related to the presence and severity of cognitive fluctuations. At follow-up, EEG abnormalities from posterior leads were seen in all 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 REM-sleep behaviour disorder 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. 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 act to support discrimination between AD and DLB at the earliest stages of dementia, since characteristic abnormalities may even precede the appearance of distinctive clinical features.
Key Words: Dementia with Lewy Bodies; Alzheimer's; disease; Parkinson's; disease with dementia; quantitative electroencephalography; compressed spectral array
Abbreviations: AD, Alzheimer's disease; CAF, clinician assessment of fluctuation; CSA, compressed spectral arrays; DF, dominant frequency; DLB, Dementia with Lewy bodies; FP, frequency prevalence; MFV, mean frequency variability; PDD, Parkinson's disease with dementia; RBD, REM Sleep Behaviour Disorder
Received August 2, 2007. Revised November 27, 2007. Accepted December 12, 2007.