Utility of quantitative EEG in early Lewy body disease

The reduction of background activity and the increase of low-frequency powers on electroencephalogram (EEG) correlate with cognitive impairment and have been suggested to be underpinned by cholinergic deficit. We aimed to investigate the ratio between α and θ band power (α/θ ratio), as a synoptic index of quantitative EEG (qEEG) slowing-down, in a peculiar group of patients with mild cognitive impairment (MCI) due to an early-stage Lewy body disease (MCI-LBD), as compared to de novo PD patients without cognitive impairment (PD-MOT), to patients with MCI due to Alzheimer's disease (MCI-AD), and to healthy controls (HC).

Twelve patients with MCI-LBD (8 males; mean age 74.8 ± 3.6), 11 PD-MOT, 11 MCI-AD and 24 HC subjects undergoing qEEG were matched for gender, age, and education. Following logarithmic transformation, the α/θ ratio was compared among groups and brain regions by repeated measures ANOVA, also exploring group*regions interactions.

A significant effect of group (p = 0.0003), regions (p = 0.0001), and group*regions interaction (p = 0.0001) on the α/θ ratio was observed. At post-hoc analysis, α/θ ratio was significantly lower in MCI-LBD (p = 0.001) and in PD-MOT (p = 0.02) compared to HC, and in MCI-LBD than MCI-AD (p = 0.05). No significant differences were found between MCI-AD and HC, as well as between MCI-LBD and PD-MOT.

The α/θ power ratio as a synoptic index of EEG background slowing-down could be a simple and easy-to-use qEEG index which might indirectly mirror a cholinergic failure, useful to pick-up those MCI patients at higher risk of developing a Lewy-body disease.