Nocturnal sleep dynamics alterations in the early stages of behavioral variant frontotemporal dementia

Study Objectives: Sleep disorders have been recognized as an integral component of the clinical syndrome in several neurodegen- erative diseases, including Alzheimer’s disease (AD). However, limited data exist for rarer types of neurodegenerative diseases, such as behavioral variant frontotemporal dementia (bvFTD). This study aims to analyze EEG power spectra and sleep stage transitions in bvFTD patients, hypothesizing that bvFTD may show distinctive sleep stage transitions compared to patients with AD. Methods: Eighteen probable bvFTD patients and 18 age- and sex-matched probable patients with AD underwent overnight polysom- nography (PSG) and completed sleep disorders questionnaires. Sleep questionnaires, full-night EEG spectra, and sleep stage transition indexes were compared between groups. Results: bvFTD patients had higher Insomnia Severity Index (ISI) scores (95% confidence intervals [CI]: 0, 5) and reported poorer sleep quality than AD patients (p < .01). Compared to AD, bvFTD patients showed higher N1 percentage (95% CI: 0.1, 6), lower N3 percentage (95% CI: −13.6, −0.6), higher sleep–wake transitions (95% CI: 1.49, 8.86) and N1 sleep–wake transitions (95% CI: 0.32, 6.1). EEG spectral analysis revealed higher spectral power in bvFTD compared to patients with AD in faster rhythms, especially sigma rhythm, across all sleep stages. In bvFTD patients, sleep–wake transitions were positively associated with ISI. Conclusions: Patients with bvFTD present higher rates of transitions between wake and sleep than patients with AD. The increased frequency of sleep transitions indicates a higher degree of sleep instability in bvFTD, which may reflect an imbalance in sleep– wake-promoting systems. Sleep stage transitions analysis may provide novel insights into the sleep alterations of patients with bvFTD.