Comparison of polysomnographic variables and their relationship to cognitive impairment in patients with Alzheimer's disease and frontotemporal dementia

Polysomnographic studies in Alzheimer's disease (AD) show REM sleep abnormalities, which may be indicative for the deterioration of cholinergic pathways and probably closely linked to declarative memory impairment. To clarify the specificity of the association between sleep and cognitive impairment in dementia, we compared AD patients with patients suffering from frontotemporal dementia (FTD) with regard to polysomnographic and neuropsychological variables. 15 AD and 6 FTD patients underwent polysomnography and a neuropsychological battery (CERAD-NB). Group differences (age: AD > FTD; education level: AD < FTD) were considered as covariates. Polysomnography revealed a trend towards increased REM latency and reduced REM sleep in AD, as well as a decrease of stage 2 sleep, however, at least partly due to effects of age. Declarative memory was more impaired in AD than in FTD, but this difference disappeared when adjusted for covariates. While no relationship was found between REM sleep and CERAD-NB parameters, strong positive correlations between stage 2 sleep and declarative memory measures were observed, which were also detectable when analyzing both groups separately. Based on these results we conclude that REM sleep alterations may be specific for AD, distinguishable from other dementia diagnoses, whereas NonREM stage 2 sleep may be related to declarative memory formation in dementia independent of subtype.