Quantitative electroencephalogram utility in predicting conversion of mild cognitive impairment to dementia with Lewy bodies

Abstract

Mild cognitive impairment (MCI) as a precursor of dementia with Lewy bodies (DLB) is the focus of recent research, trying to explore the early mechanisms and possible biomarkers of DLB. Quantitative electroencephalogram (QEEG) methods are able to differentiate early DLB from Alzheimer's disease (AD). The aim of the present study was to assess whether QEEG abnormalities, characterized by dominant frequency <8 Hz and dominant frequency variability >1.5 Hz, typical of early DLB, are already present at the stage of MCI and to evaluate whether EEG abnormalities can predict the development of DLB. Forty-seven MCI subjects were followed for 3 years. EEG recordings were obtained at admission and at the end of the study. At the end of follow-up, 20 subjects had developed probable DLB (MCI-DLB), 14 had probable AD (MCI-AD), 8 did not convert to dementia, 5 developed a non-AD/DLB dementia. One hundred percent of MCI-DLB showed EEG abnormalities at admission. Ninety three percent of MCI-AD maintained a normal EEG throughout the study. QEEG may represent a powerful tool to predict the progression from MCI to DLB with a sensitivity and specificity close to 100%.

Keywords: Dementia with Lewy bodies; Mild cognitive impairment; Quantitative EEG.

Fig. 1

Study design flow chart. Abbreviations: AD, Alzheimer's disease; CTL, control subjects; DLB, dementia with Lewy bodies; DRS-2, Dementia Rating Scale-2; EEG, electroencephalogram; FTD, frontotemporal dementia; GerDepScale, Geriatric Depression Scale; MCI, mild cognitive impairment; MMSE, Mini Mental State Examination; MRI, magnetic resonance imaging; MSA, multiple system atrophy; PSP, progressive supranuclear palsy; SPECT-DAT scan, single photon emission computerized tomography-dopamine transporter scan.

Fig. 2

CSA of EEG recording from occipital derivations in 2 MCI patients (first 2 traces) and 4 DLB patients, showing the 6 EEG patterns described in the present study and in the previous EEG study (Bonanni et al., 2008). Pattern 1: dominant frequency (DF) in the alpha range with stable alpha frequency recorded at admission to the study in an MCI subject (later converted to AD). Pattern 1 plus: DF in the alpha frequency band with intrinsic variability = 1.5 Hz (DF variable between 8 and 9.5 Hz). This pattern was never observed in the previous EEG study (Bonanni et al., 2008) in patients with definite dementia. Pattern 2: notice variability of the dominant frequencies shifting from alpha (8.5 Hz) to dominant pre-alpha (6 Hz). Pattern 3: notice stable DF at 6.5 Hz. Pattern 4: DF variability, with the fastest frequency at 6 Hz and inscription of lower frequencies at 2 Hz. Pattern 5: degraded EEG pattern with the fastest frequencies slower than 5 Hz and delta activity at 1–4 Hz. Under each trace numbers in frames indicate the frequencies (in Hz) corresponding to power peaks. Abbreviations: AD, Alzheimer's disease; CSA, compressed spectral arrays; DLB, dementia with Lewy bodies; EEG, electroencephalogram; MCI, mild cognitive impairment.

Fig. 3

ANOVA results on EEG parameters at onset. (A) Statistical comparison on DFV among MCI groups: MCI-DLB, MCI-AD, and MCI-NC. (B) Statistical comparison on DFV among MCI-DLB, DLB, AD, and controls. (C) Statistical comparison on DF between MCI-DLB, DLB, AD, and controls; *p < 0.05, **p < 0.01, and ***p < 0.001. Abbreviations: AD, Alzheimer's disease; ANOVA, analysis of variance; DF, dominant frequency; DFV, dominant frequency variability; EEG, electroencephalogram; MCI, mild cognitive impairment; MCI-AD, MCI patients converted to AD at follow-up; MCI-DLB, MCI patients converted to DLB at follow-up; MCI-NC, MCI patients stable at follow-up.

Fig. 4

Correspondence analysis evidencing the relationship between the compressed spectral array (CSA) patterns at admission to the study and patients' condition at follow-up. Abbreviations: AD, Alzheimer's disease; DLB, dementia with Lewy bodies; EEG, electroencephalogram; MCI, mild cognitive impairment; MCI-AD, MCI subjects converted to AD at follow-up; MCI-DLB, MCI subjects converted to DLB at follow-up; MCI-NC, MCI subjects stable at follow-up; MCI-others, MCI subjects converted to other types of dementia; P1, EEG CSA pattern 1; P2, EEG CSA pattern 1 plus+ CSA pattern 2; P3, EEG CSA pattern 3; P4, EEG CSA pattern 4; P5, EEG CSA pattern 5.