Clinical-pathologic study of depressive symptoms and cognitive decline in old age

Objective: To clarify the relationship between depressive symptoms and the clinical and neuropathologic manifestations of dementia. Methods: In a clinical-pathologic cohort study, 1,764 older persons without cognitive impairment at enrollment completed annual clinical evaluations for a mean of 7.8 years. The evaluations included assessment of depressive symptoms (10-item Center for Epidemiological Studies Depression Scale) and cognitive function (battery of 17 performance tests). A total of 582 individuals died during follow-up and underwent a uniform neuropathologic examination to quantify beta-amyloid plaques and tau tangle density in multiple brain regions and identify neocortical Lewy bodies, hippocampal sclerosis, and gross and microscopic cerebral infarcts. Results: Level of depressive symptoms slightly increased during follow-up. Incident mild cognitive impairment (52.2%) was associated with higher level of depressive symptoms before the diagnosis but not with change in symptoms after the diagnosis; incident dementia (17.9%) was associated with higher symptom level before dementia onset and with more rapid decline in symptoms after dementia onset. None of the neuropathologic markers was related to level of depressive symptoms or change in symptoms over time. In a mixed-effects model adjusted for the neuropathologic markers, higher level of depressive symptoms averaged over evaluations was associated with more rapid global cognitive decline, accounting for 4.4% of the variability in decline not attributable to the neuropathologic markers. Depressive symptoms did not modify the association of the neuropathologic markers with cognitive decline. Conclusion: In old age, depressive symptoms have an association with cognitive decline that is independent of the neuropathologic hallmarks of dementia.