Distinction between preclinical Alzheimer's disease and depression

OBJECTIVE: To assess the prevalence of depression in subjects with preclini cal Alzheimer's disease (AD) and to investigate the possibility of differen tiating subjects with preclinical AD and depression from subjects with depr ession-related cognitive impairment. DESIGN: A prospective, observational cohort study. SETTING: An outpatient memory clinic of a university-affiliated hospital. PARTICIPANTS: Nondemented subjects with cognitive impairment older than 55 years (n = 111) without neurological or somatic causes for the cognitive im pairment. MEASUREMENTS: At baseline, data were collected on patient characteristics, the severity of depression, and cognitive functioning. The course of the co gnitive impairment and the presence of dementia were assessed after 2 and 5 years. RESULTS: Twenty-five subjects had preclinical dementia with Alzheimer's typ e dementia at follow-up. Sixty percent of these subjects (n = 15) were depr essed at baseline. Subjects with depression and preclinical AD had at basel ine a poorer performance on the cognitive tasks and were older than the sub jects with depression-related cognitive impairment. Logistic regression wit h backward step selection selected age and memory performance as the best p redictors for Alzheimer's type dementia in the depressed subjects. The spec ificity of these predictors for the diagnosis of future Alzheimer's type de mentia in depressed subjects was 94%, sensitivity was 90%, positive predict ive value was 90%, and negative predictive value was 94%. CONCLUSIONS: Depression is common in preclinical AD. Depressed subjects wit h preclinical AD can be accurately differentiated from subjects with depres sion-related cognitive impairment by age and the severity of the memory imp airment. Research that aims to investigate preclinical AD should not exclud e a priori subjects with depression inasmuch as preclinical AD is often acc ompanied by depression.