In Alzheimer's dementia (AD) axonal disruption and cholinergic deficit lead to impaired cortical connectivity and to a decrease in EEG alpha coherence. The aim of the present study was to assess the usefulness of coherence parameters of the EEG for the diagnostics of AD. Quantitative EEG analyses were performed in 31 AD patients and 17 cognitively unimpaired depressive controls, both groups without psychopharmacological treatment. Differences between groups were examined and the diagnostic significance of EEG parameters was assessed by means of stepwise logistic regression analyses. In the AD patients global theta power was increased, left temporal alpha coherence and interhemispheric theta coherence were decreased. Left temporal alpha coherence and global theta power allowed an identification of AD patients with a sensitivity of 87% and a specificity of 77%. Quantitative analyses, especially the determination of left temporal alpha coherence, may enhance the usefulness of the EEG in the diagnostics of AD.

Mild cognitive impairment (MCI) is frequent in patients with late-life depression. Previous studies indicate that cognitive performance in these patients is not or only marginally improved when they recover from depression. However, recovery from cognitive impairments due to depression may have a longer time course than recovery from affective symptoms. In a group of 34 elderly depressed patients (mean age: 73.4 years) admitted to a gerontopsychiatric day-clinic, severity of depression and cognitive performance were assessed before the initiation of treatment and were reassessed 6 months later. At admission, 18 of 34 patients (53%) fulfilled the criteria for MCI, with a preponderance of impairments in short-term memory and visuospatial capabilities. At the 6-month follow-up, cognitive performance had not significantly improved for the entire group; 12 of 27 patients (44%) still were fulfilling the criteria for MCI. No relationships could be ascertained between cognitive impairment or functional level and severity or course of depression. Patients with diurnal variations of the depressive symptomatology were less likely to fully recover from depression.

Reversible dementia in geriatric depression is known to be a risk factor for irreversible dementia. Whether just mild cognitive deficits in elderly depressed patients hold a similar risk is not known yet. It may be suggested that elderly depressed patients with mild cognitive deficits, who are prone to develop dementia, show EEG alterations similar to those observed in demented patients. We studied the relationships between cognitive performance, severity of depressive symptoms and quantitative EEG parameters in 31 unmedicated, nondemented, depressed patients aged 60 years or more. Twenty-one of the patients showed a cognitive performance characteristic of mild cognitive impairment. In these patients, the mean delta and theta power was significantly higher than in the patients without cognitive impairment. Total delta power was negatively correlated with cognitive performance. There was no relationship between cognitive performance or EEG parameters and the severity of depression.

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Zusammenfassung: Bei älteren depressiven Patienten bestehen gelegentlich kognitive Beeinträchtigungen vom Ausmaß einer Demenz. Dieses dementielle Syndrom bildet sich bei einem Teil der Patienten mit dem Abklingen der Depression zurück, stellt aber einen Risikofaktor für die Entwicklung einer irreversiblen Demenz dar. Unklar ist bislang die prognostische Bedeutung leichter kognitiver Einschränkungen, die nicht das Ausmaß einer Demenz erreichen. Wir untersuchten bei 24 älteren depressiven Patienten (mittleres Alter: 72,2 Jahre) die Schwere der depressiven Symptomatik und das Ausmaß kognitiver Beeinträchtigungen vor und nach einer sechswöchigen antidepressiven Behandlung. Ausschlußkriterium war ein Mini-Mental-State Wert unter 24. 16 von 24 Patienten litten vor Behandlung an einer leichten kognitiven Beeinträchtigung. Bei der Nachuntersuchung von 14 dieser Patienten zeigte sich bei 10 ein Fortbestehen leichter kognitiver Beeinträchtigungen. Prädiktiv für das Weiterbestehen der Beeinträchtigungen war das Ausmaß der Einschränkungen im Kurzzeitgedächtnis vor Behandlung. Kein Zusammenhang bestand zwischen dem Ausmaß kognitiver Einschränkungen und der Schwere der Depression. Diese Befunde weisen auf eine eigenständige Bedeutung leichter kognitiver Beeinträchtigungen bei älteren depressiven Patienten hin. Eine engmaschige Betreuung dieser Patienten erscheint vor diesem Hintergrund angebracht, um bei einer weiteren Verschlechterung des kognitiven Leistungsvermögens frühzeitig intervenieren zu können.