Comparison of quantitative EEG between patients with Alzheimer’s disease and those with Parkinson’s disease dementia
Introduction
The two commonest neurodegenerative diseases afflicting the aged are Alzheimer’s disease (AD) and Parkinson’s disease (PD), both with increasing prevalence due to the increasing mean age of the populations, and with intense psychosocial consequences.
The fundamental expression of AD is that of dementia, but PD, of which the manifestations are essentially motor is frequently accompanied by cognitive impairments, and dementia is characterized in about 30% of these patients – Parkinson’s disease dementia (PDD) (Aarsland et al., 2005).
The electroencephalogram (EEG) registers brain electrical activity, has a wide spectrum of clinical applications, is of low cost and represents no risk to the patient. The development of the digital EEG allows one to expand the quantitative analyses (qEEG), amongst which the analysis of the absolute power of the various frequency bands of the brain rhythms, and analyses of the temporal relationships between the different locations of the register, such as coherence, which evaluates the phase consistency between two temporal series. This measurement provides information about the functional connectivity between the regions (Thatcher et al., 2005).
For its part, by analyzing the frequencies, the qEEG makes it possible to detect and measure the excess of slow activity. When compared to normal controls, individuals with AD show an increase in theta activity and decreases in the alpha and beta bands (Miyauchi et al., 1994), and the qEEG measurements correlate with the neuropsychological tests (Fonseca et al., 2011a).
The study of the coherence of brain electrical activity in demented patients can be used in association with the analysis of frequencies in the search for greater sensitivity and specificity of the qEEG in the diagnosis of Alzheimer’s disease (Calderón González et al., 2004).
The qEEG of patients at rest with their eyes closed has been indicated as a promising marker of the neurodegenerative processes present in AD (Babiloni et al., 2009, Jelic and Kowalski, 2009), and represents a widely available, non-invasive method for the diagnostic evaluation of demented patients (Jelic and Kowalski, 2009).
For PD, an increase in slow activities was reported for the quantitative electroencephalogram (Sinanovic et al., 2005), and alterations in the EEG and qEEG only occurred when cognitive impairment was also present, whether mild cognitive impairment or dementia (Caviness et al., 2007, Fonseca et al., 2009).
Greater preservation of alpha activity was found in AD than in PDD, and slow abnormalities were more frequent in posterior areas in PD with dementia (Bonanni et al., 2008). Recently, differences in the cortical sources of resting state electroencephalographic rhythms were found (Babiloni et al., 2011).
Studies comparing the quantitative electroencephalograms (qEEGs) of patients with Alzheimer’s disease (AD) with those of patients with (PDD) are rare, and no references of comparative studies concerning coherence on the EEG were found.
Although there is not usually any difficulty in making a differential diagnosis between AD and PDD, it is important to understand the diversity of physiopathological mechanisms involved in these two clinical conditions, as a foundation for better knowledge about the prognosis and use of drugs.
The objective of the present study was to comparatively evaluate the absolute potential and coherence on the EEG of patients with AD and with PDD.
Section snippets
Subjects
Four groups of subjects were included in this study:
1. Group with Alzheimer’s disease (AD) – 38 patients who conformed to the dementia criteria according to the DSM IV (American Psychiatric Association, 1994), and with AD according to the criteria of the NINCDS/ADRDA (McKhann et al., 1984) were included.
2. Group with Parkinson’s disease with dementia (PDD) – 12 patients with a clinical diagnosis of PD according to the criteria of Calne et al. (1992) and also diagnosed with dementia according to
Results
Table 1 shows the socio-demographic data and MMSE, CDR, Pfeffer questionnaire, Hoehn and Yahr scale results for the groups AD, PDD and CG. There was a difference between the groups with respect to age and the MMSE results (ANOVA, p < 0.05), but the Duncan post hoc tests showed no significant difference between the groups AD and PDD. There was also no significant difference between the scholastic levels of groups AD and PDD. The mean age of the AD group was higher than that of the CG. The MMSE
Discussion
The present study indicated, in an original way, that differences in beta coherence exist between AD and PDD, with an increase in PDD and decrease in AD, apart from a greater increase in the slow absolute powers (delta and theta) in PDD. These neurophysiological differences must be related to the distinct mechanisms involved in the genesis of dementia in Alzheimer and Parkinson’s diseases.
The similar results observed in Pfeffer functional activities questionnaire and clinical dementia rating
Disclosure/Conflict of interest
Lineu C. Fonseca, Gloria M. A. S. Tedrus, Priscila N. Carvas, and Elaine C.F.A. Machado have no conflicts of interest in relation to this article.
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