Depressive Symptoms Increase the Likelihood of Cognitive Impairment in Elderly People with Subclinical Alzheimer Pathology

Abstract

The objective of this study was to investigate whether the presence of depressive symptoms influences the clinical expression of Alzheimer's pathology. We have analysed the relationships between the severity of Alzheimer's pathology and cognitive decline in two patient groups defined by the presence or absence of depressive symptoms. The study included 89 subjects who participated in a longitudinal research programme prior to death, underwent post-mortem examination and were found to have only Alzheimer-type pathology in their brains, ranging in severity from the entorhinal to neocortical stages. Our results indicate that depressive symptoms did not influence cognition in the early (entorhinal) stages of Alzheimer's disease (AD; where cognition was good regardless of whether or not there was evidence for depressive symptoms) or in the late (neocortical) stages (where cognition was poor regardless of whether or not there was evidence for depression). However, in the intermediate (limbic) stages, patients with depressive symptoms had significantly worse cognitive performance (mean CAMCOG of 32) than those who did not (mean CAMCOG of 73). We conclude that depressive symptoms may contribute to the cognitive decline of AD patients in that pathology, that would be otherwise silent, becomes clinically apparent. Therefore, a multiple diagnosis of early AD and depression should be more widely considered in elderly persons presenting with mild cognitive decline and depression. Treating the depressive symptoms would benefit the patient, but the cognitive improvement may not indicate that AD is absent.