PORTO, PORTUGAL – Quantitative EEG shows promise as a clinical diagnostic tool that is sensitive enough to distinguish mild from moderate subcortical dementia, according to one study presented at the Fourth International Congress on Vascular Dementia.
“Quantitative EEG results correlated strongly with mental impairment in subcortical vascular dementia,” said Dr. Malgorzata Gawel, of the Medical University of Warsaw.
The white matter lesions and lacunar ischemic stroke that are associated with subclinical vascular dementia lead to the destruction of neurons and neuronal synapses and also cause cholinergic deficits. In turn, cholinergic deficits lead to changes in synaptic bioelectric potential, which may be picked up in EEG signals. In particular, these changes result in a slowing of background brain activity and the presence of slow brain waves (delta and theta), Dr. Gawel said.
The researchers used visual and quantitative EEG to evaluate 31 patients with subcortical vascular dementia (mean age 72 years, 19 women) and 14 healthy controls (mean age 70 years, 8 women). Subcortical vascular dementia was diagnosed using the National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) criteria and criteria developed by Timo Erkinjuntti of the University of Helsinki.
The group with dementia was further divided into two subgroups based on severity of cognitive impairment. The first group (16 patients) had mild cognitive impairment, defined as a score of 19–23 on the Mini-Mental State Examination (MMSE). The second group (15 patients) had moderate cognitive impairment, defined as a score of 11–18 on the MMSE.
EEG was performed for 20 minutes with eyes closed. Visual inspection of EEGs involved an 8-point scale, with 1 being normal and 8 representing severe abnormalities. There was no significant difference between visual EEG results for the two vascular dementia subgroups. There was a significant difference on the visual EEG results between the control group and both subcortical vascular dementia subgroups. There was no correlation between visual EEG results and cognitive impairment measured by the MMSE.
Quantitative EEG was performed for 5 minutes, following the visual EEG. The researchers calculated the power ratio of alpha waves to theta waves (A/T); the ratio of alpha waves to delta waves (A/D); and the ratio of alpha waves to the sum of theta and delta waves (A/T+D). They also calculated the mean waves frequency for all derivations (amplifier/electrode configurations), with particular interest in the occiptal and temporal derivations.
There was significant difference between the quantitative EEG results for the patients with mild and moderate dementia for all parameters. There was a significant correlation between all parameters and cognitive impairment.