To investigate whether specific domains of cognitive functioning predict the natural course of depressive symptoms in older people.
Design and Participants:
Using the nationally representative, population-based cohort of the Longitudinal Aging Study Amsterdam, 281 participants with clinically relevant depressive symptoms (Center for Epidemiological Studies Depression Scale ≥16) aged 55 years and older were followed longitudinally during a period of 6 years.
Using a maximum of 14 successive Center for Epidemiological Studies Depression Scale observations, three clinical course types of depressive symptoms were defined. At baseline, general cognitive functioning was assessed using the Mini-Mental State Exam, memory performance (immediate recall and retention) by means of the auditory verbal learning test, and processing speed by means of a timed coding task.
Remission, fluctuating course, and chronic course were seen in 22%, 50%, and 28%, respectively. In univariate analyses, a slowed processing speed was associated with a chronic course of depressive symptoms, as compared with remission (mean: 21.5, SD: 6.6, versus mean: 24.6, SD: 6.8, t = 2.78, df = 139, p < 0.001). Using multivariate regression techniques, this association remained significant after correcting for potential confounders and a number of risk factors for vascular brain damage (odds ratio: 1.08, 95% confidence interval: 1.01–1.14). Neither global cognitive functioning nor memory performance was associated with any course type of depressive symptoms.
We found an independent association of a slowed processing speed with a poor natural course of depressive symptoms in older people. In clinical practice, when dealing with an older depressed person with comorbid cognitive decline, processing speed might be a more useful tool than the Mini-Mental State Exam in predicting the prognosis.