We report EEG findings in 33 elderly patients with mixed symptoms of depression and
dementia, followed longitudinally to confirm diagnosis. Two groups of patients,
dementia with depressive features (mixed-DEM, group I, n = 23) and patients with depressive
pseudodementia (mixed-
DEP, group II, n = 10), were defined. In addition, we also included, for comparison purposes, 35 patients with probable AD without depressive features (group III), 23 patients with major depression without
cognitive impairment (group IV), and 61 healthy elderly controls (group V). We found significant group differences on waking EEGs between those mixed patients who did well
after treatment for depression (depressive
pseudodementia) compared to patients having
dementia with secondary depression. The differences paralleled those between the 'pure' groups of demented and depressed patients. In patients with either depression or depressive
pseudodementia, the EEG was usually normal or showed only mild abnormalities. In contrast, the majority of patients with either
dementia or
dementia with secondary depression had abnormal EEGs, with approximately one-third having moderate (or severe) abnormalities. Although the EEG was usually normal or only mildly abnormal in patients with
pseudodementia or depression, these groups (II and IV) did show a significant slowing of the dominant posterior rhythm compared to controls. They also had a higher percentage of generalized abnormal EEGs than controls and this difference was significant between group IV (depression) and controls.