Factor Structure of the Geriatric Depression Scale and its Relationship to Cognition in Alzheimer's Disease
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Evidence suggests that patients with Alzheimer’s disease (AD) experience more frequent and severe apathy and depression than their healthy age counterparts. Moreover, some studies have shown that apathy and depression are associated with greater cognitive and functional decline in these patients. Previous research has shown the Geriatric Depression Scale to be capable of identifying symptoms of both apathy and dysphoria in older adults. However, no study to date has systematically explored whether the Geriatric Depression Scale measures symptoms of apathy and dysphoria in patients with AD and related these constructs to performance on neuropsychological measures. This study employed exploratory factor analysis to identify factors of the Geriatric Depression Scale in a sample of 569 patients with pure probable AD. A four-factor solution was obtained, yielding factors associated with apathy, dysphoria, social withdrawal, and cognitive impairment. It was hypothesized that symptoms of apathy would be associated with cognitive and functional impairment, even after controlling for dysphoria. Two-way ANOVAs showed that endorsement of Apathy factor items was associated with greater impairment in verbal memory and motor speed, as well as functional impairment. Dysphoria was not associated with any cognitive or functional variables. Findings suggest that the GDS may be used as a screening measure for symptoms of apathy in AD, hopefully aiding early identification and intervention to reduce patient and caregiver burden.