Usefulness of EEG Techniques in Distinguishing Frontotemporal Dementia from Alzheimer's Disease and Other Dementias

Abstract

The clinical distinction of frontotemporal dementia (FTD) and Alzheimer's disease (AD) may be difficult. In this narrative review we summarize and discuss the most relevant electroencephalography (EEG) studies which have been applied to demented patients with the aim of distinguishing the various types of cognitive impairment. EEG studies revealed that patients at an early stage of FTD or AD displayed different patterns in the cortical localization of oscillatory activity across different frequency bands and in functional connectivity. Both classical EEG spectral analysis and EEG topography analysis are able to differentiate the different dementias at group level. The combination of standardized low-resolution brain electromagnetic tomography (sLORETA) and power parameters seems to improve the sensitivity, but spectral and connectivity biomarkers able to differentiate single patients have not yet been identified. The promising EEG findings should be replicated in larger studies, but could represent an additional useful, noninvasive, and reproducible diagnostic tool for clinical practice.

Figure 1

Significant group × electrode interaction effects in the 8–10 Hz frequency band (a) and the 10–13 Hz frequency band (b). Error bars indicate standard deviations. Legend: FTLD = frontotemporal lobar degeneration; AD = Alzheimer's disease; SMC = subjective memory complaints. Reproduced with permission from Pijnenburg et al. [23], in 2008.

Figure 2

Comparison of current density images in Talairach space obtained by sLORETA for the FTD and control groups. Red areas correspond to significantly higher activity in the FTD group, and yellow areas correspond to significantly higher activity in the control group (p < 0.047, log-F-ratio threshold = 0.344). Legend: A = anterior; P = posterior; FTD = frontotemporal dementia; AD = Alzheimer's disease; NC = normal control. Reproduced with permission from Nishida et al. [26] in 2011.

Figure 3

Boxplots of selected features: AD versus DLBPD: 23 of 25 features resulted in significant differences. The features with the lowest p values (p = 6.80e − 08) were the GC at P7/P8 and P8/P7 (a). Center frequency and relative band power α and β1 were higher in AD patients than in DLBPD patients at all sites with significantly different results. The opposite was true for automutual information, band ratios, relative band power θ, and cross-mutual information. AD versus bvFTD: 17 features resulted in significant differences with GC and phase coherence β1 reaching the lowest p value of 7.21e − 8 at T7/T8. GC was significantly higher in bvFTD patients than in AD patients while phase coherence was significantly higher in AD patients (b). Phase coherences α and β1 were significantly higher in AD patients than in bvFTD patients at all sites with significantly different results. The opposite was observed for coherence β1 and GC. bvFTD versus DLBPD: 12 features resulted in significant differences with relative band power β1 at P8 and ratio 4 at P8 having the lowest p value of 2.53e − 5 and 2.83e − 5, respectively. Automutual information and mutual information were higher in DLBPD patients than in bvFTD patients at all sites with significantly different results. The opposite was then evident for center frequency. Legend: DLBPD = PDD or probable DLB; bvFTD = behavioral variant of FTD; AD = Alzheimer's disease; GC = Granger causality. Reproduced with permission from Garn et al. [28] in 2017.