A new study suggests that depression often accompanies cognitive impairment but does not precede it.
"Traditionally, cognitive complaints and impairment in the presence of depression has been considered to be caused by the depression. Our study suggests that depression is not a cause of dementia but accompanies the onset of cognitive impairment," José Alejandro Luchsinger, MD, MPH, associate professor of medicine and epidemiology, Columbia University Medical Center, New York City, told Medscape Medical News.
The study was published online December 31, 2012 in Archives of Neurology.
Transition Time Crucial Period
Patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD) often have depressive symptoms, but the mechanisms underlying the association remain unclear.
"Depression could be a risk factor for dementia, an early dementia symptom, a reaction to cognitive and functional disability, or a symptom of a related risk factor, such as cerebrovascular disease," Dr. Luchsinger and colleagues point out. "Vascular factors have been linked to late-life depression, and cerebrovascular disease might be an important contributor to MCI…. However, there is a paucity of data examining the association between depression and MCI."
Dr. José Alejandro Luchsinger
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The researchers evaluated the association of late-life depression with MCI and dementia in a multiethnic group of 2160 community-dwelling Medicare recipients.
They report that depression at baseline was associated with prevalent MCI (odds ratio [OR], 1.4; 95% confidence interval [CI], 1.1 - 1.9) and prevalent dementia (OR, 2.2; 95% CI, 1.6 - 3.1).
Baseline depression was also associated with an increased risk for incident dementia (hazard ratio [HR], 1.7; 95% CI, 1.2 - 2.3) but not with incident MCI (HR, 0.9; 95% CI, 0.7 - 1.2).
In addition, individuals with MCI and coexisting depression at baseline had a higher risk for progression to dementia (HR, 2.0; 95% CI, 1.2 - 3.4), especially vascular dementia (HR, 4.3; 95% CI, 1.1 - 17.0), but not AD (HR, 1.9; 95% CI, 1.0 - 3.6).
"Our finding that depression was associated cross sectionally with both MCI and dementia and longitudinally only with dementia suggests that depression develops with the transition from normal cognition to dementia," the authors conclude.
Dr. Luchsinger said, "Clinicians should consider the possibility that depression and cognitive impairment could be the joint manifestation of a cognitive disorder, particularly in elderly persons. Our research did not directly address this, and more research is needed to understand if the depression is part of the cognitive process or a reaction to it."
Mechanisms?
"There has now been an accumulation of enough studies and enough data to say that people with a history of depression do have increased rates of cognitive decline and dementia in late life," Meryl Butters, PhD, neuropsychologist and associate professor of psychiatry, University of Pittsburgh School of Medicine, Pennsylvania, who was not involved in the study, noted in an interview with Medscape Medical News.
"The issue now really is, what are the mechanisms? What is it about a mood disorder earlier in life that might place you at risk for progressive dementia in late life? This study can't address that," she said.
Dr. Butters said "a handful" of researchers, including herself, are now looking at possible mechanisms behind depression and cognitive decline. "This is a very active area of investigation. It's likely that different mechanisms are at work in different people."
The authors have disclosed no relevant financial relationships.
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