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

Objective: 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. Methods: 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 Results: 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 bad no premorbid history of MDD. Conclusions: 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.