Depression and dementia in elderly individuals have a complicated relationship. Cognitive changes are common in the context of depression, and mood symptoms frequently accompany cognitive disorders. This comorbidity represents a challenge for clinicians assessing older, functionally impaired patients with signs and symptoms of mood and cognitive disorders.
Clinically and scientifically, the picture becomes more complex when we consider a longitudinal perspective. That there is a high incidence of depression among patients with dementia is well established and hardly surprising. What is less intuitive is an established literature linking depression with subsequent cognitive decline and development of dementia. It is this latter observation that is the focus for Singh-Manoux et al1 in this issue of JAMA Psychiatry. Here, in a 28-year follow-up cohort study, the authors found that depressive symptoms later in life were significantly associated with development of dementia, while depressive symptoms earlier in the study were not. Similarly, they reported that those with chronic or recurrent depressive symptoms early in the study did not have an increased dementia risk, but among those with such symptoms later in the study, there was an association. The investigators concluded that depressive symptoms may represent a prodrome of dementia or that the 2 conditions share common causes. They found no support for the construct that depressive symptoms are a risk factor for dementia.
Steffens DC. Late-Life Depression and the Prodromes of Dementia. JAMA Psychiatry. 2017;74(7):673–674. doi:10.1001/jamapsychiatry.2017.0658
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