THE VALUE OF REM-SLEEP PARAMETERS IN DIFFERENTIATING ALZHEIMERS-DISEASE FROM OLD-AGE DEPRESSION AND NORMAL AGING

Pseudodementia as a common trait in elderly depressives presents a maj or problem in gerontopsychiatry, especially for the differential diagn osis between Old-Age Depression (OAD) and Dementia of the Alzheimer Ty pe (DAT). The present poly somnographic study examined parameters of s leep continuity, sleep architecture, and REM sleep to differentiate DA T from OAD. The investigation was based on the theoretical framework o f the cholinergic-aminergic imbalance model of depression, the choline rgic deficit hypothesis of Alzheimer's disease and the reciprocal inte raction model of Non-REM/REM sleep regulation, according to which REM sleep parameters should have high discriminative value to differentiat e OAD and DAT. We investigated 35 DAT patients, 39 OAD patients and 42 healthy controls for two consecutive nights in the sleep laboratory. The DAT patients were in relatively early/mild stages of the disease, the severity of depression in the OAD group was moderate to severe. De pressed patients showed characteristic 'depression-like' EEG sleep alt erations, i.e. a lower sleep efficiency, a higher amount of nocturnal awakenings and decreased sleep stage 2. Sleep continuity and architect ure in DAT was less disturbed. Nearly all REM sleep measures different iated significantly between the diagnostic groups. OAD patients showed a shortened REM latency, increased REM density and a high rate of Sle ep Onset REM periods (SOREM), whereas in DAT REM density was decreased in comparison to control subjects. REM latency in DAT was not prolong ed as expected. To assess the discriminative power of REM sleep variab les a series of discriminant analyses were conducted. Overall, 86% of patients were correctly classified, using REM density and REM latency measures. Our findings suggest that REM density as an indicator of pha sic activity appears to be more sensitive as a biological marker for t he differential diagnosis of OAD and DAT than REM latency. The results support the role of central cholinergic neurotransmission in REM slee p regulation and the pathogenesis of DAT and OAD. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.