REM sleep parameters in the discrimination of probable Alzheimer's disease from old-age depression

Thirteen dementia of the Alzheimer type (DAT) patients and fifteen old-age major depressive disorder (OAD) patients were investigated by polysomnography. The sleep was recorded during two nights after a 1 week wash-out period of psychotropic drugs. No statistically significant differences between the two groups were found concerning sleep continuity or architecture. The amount of REM sleep was significantly lower in DAT in comparison with OAD patients (11.7% verses 18.5%). Also, total REM density as well as the density of the first REM period were significantly lower in the DAT compared with the OAD patient group (15.8% verses 32.5%, 14.9% verses 38.1%, respectively). REM latency did not differ between both groups. Because REM latency is known from other studies to be shortened in depressed patients due to a cholinergic hyperactivity, the opposite finding, i.e., prolongation of REM latency, was expected for DAT patients. This assumption, however, could not be confirmed in the present study. It is concluded that REM density may better differentiate between DAT and OAD.