Depression, cognition, and functional ability in patients with Alzheimer's disease.

OBJECTIVE: To investigate the relationship of depression to functional and cognitive impairment in patients with Alzheimer's disease (AD).
DESIGN: Clinic-based study comparing AD patients with and without depression.
SETTING: Geriatric outpatient clinic at the University of Washington Medical Center, Seattle, WA. PARTICIPANTS: Ninety-one AD patients, 46 with major depression and 45 without. MEASUREMENTS: The relationship of the Mattis Dementia Rating Scale (mDRS), DSM-III-R diagnosis of depression, and Hamilton Depression Rating Scale (HDRS) to daily functioning as measured by the Activities of Daily Living (ADL), Independent Activities of Daily Living (IADL), and Communication subscales of the Record of Independent Living (RIL) was examined. MAIN
RESULTS: Both depression and mDRS related significantly to functional impairment, but the amount of variance contributed differed by level of cognitive impairment and functional area investigated. In mildly cognitively impaired subjects, diagnosis and severity of depression (combined) was significantly related to IADL and Communication subscales, after controlling for age and mDRS. No predictor was significantly related to ADL functioning. In contrast, for moderately cognitively impaired subjects, depression diagnosis was significantly related to ADL and Communication performance, but not to IADL functioning. mDRS also significantly predicted ADL, IADL, and Communication subscales. Severity of depression was not significant.
CONCLUSIONS: These findings, that the presence (diagnosis) and severity (HDRS score) of depression significantly predicted functional status, but that the degree of association varied by level of cognitive severity, has important diagnostic and treatment implications. In particular, the importance of examining whether functional impairment in depressed AD patients can be modified by depression treatment is discussed.