Effects of previous major depressive illness on cognition in Alzheimer disease patients

Major Depressive Disorder (MDD) may be a risk factor for subsequent development of irreversible dementia; however, the influence of a premorbid history of MDD on the clinical course of patients diagnosed with probable Alzheimer disease (AD) has not been fully explored.

Forty-three AD patients with mild-to-moderate cognitive impairment were screened for a life-long history of MDD with the Clinical Assessment of Depression in Dementia Scale. Twenty-two subjects had a history of MDD before onset of cognitive impairment, but none was suffering from an MDD episode at time of cognitive assessment.

After controlling for age, education, duration of illness, gender, and medication status, subjects with a history of MDD had significantly lower scores, as a group, on cognitive performance tests, including the Mini-Mental State Exam, WAIS Full-Scale and Verbal Scale I.Q., and the Initiation/Perseveration subscale of the Mattis Dementia Rating Scale. These subjects also developed symptoms of dementia at a significantly earlier age than the subjects who had no premorbid history of MDD.

Although previous studies have shown that late-onset MDD may increase risk for subsequent dementia, the current results suggest that premorbid MDD is associated with more severe cognitive deficits during the actual course of dementia.