Actigraphic and subjective sleep parameters in their relationship to cognitive impairment in patients referred to a memory clinic

Sleep disturbances are prevalent in various dementia subtypes, but rarely investigated in early stages. The study aimed to examine subjective and objective sleep variables in their relation to cognitive impairment in patients referred to memory clinic. On two consecutive days, patients underwent routine diagnostic procedures including a neuropsychological examination, the Pittsburgh Sleep Quality Index (PSQI) evaluating sleep quality as well as an overnight actigraphy. 31 patients were analyzed: n = 1 with subjective cognitive impairment (SCI), n = 13 with mild cognitive impairment (MCI) with or without depression, n = 17 with dementia due to Alzheimer's and/or vascular disease. Dementia patients showed – compared to those with SCI and MCI – an increased nocturnal acceleration magnitude, whereas other differences in both subjective and objective sleep measures remained non-significant. Comparing patients with PSQI> 5 (“poor sleep”, n = 9) vs. PSQI≤5 (“good sleep”, n = 22) yielded no differences in any neuropsychological and clinical variables. Patients with low actigraphic sleep efficiency (n = 11< 85%) compared with the high sleep efficiency group (n = 20≥85%) exhibited a more impaired cognitive performance. Correlation analyses demonstrated that actigraphic assessed disturbed sleep continuity was associated to cognitive deficits. Our findings highlight the functional role of sleep disturbances in early dementia, which appear to be more detectable by actigraphy than by self-reports.