Differences in depression symptoms in patients with Alzheimer's and Parkinson's diseases: evidence from the 15‐item Geriatric Depression Scale (GDS‐15)

Abstract

Objective Depression occurs frequently in patients with both Alzheimer's disease (AD) and Parkinson's disease (PD), but there has been little comparison of depression symptoms in the two populations. Method The 15‐item Geriatric Depression Scale (GDS‐15) was administered as a depression screening instrument to 232 AD patients and 266 PD specialty care patients with at most mild dementia. Logistic regression models were used to determine disease‐specific associations with individual GDS‐15 items, and factor analysis was used to assess GDS‐15 factor structure in the two populations. Results Controlling for total GDS‐15 score and other covariates, AD patients reported more dissatisfaction with life (p = 0.03) and memory problems (p < 0.001), while PD patients reported more fearfulness (p = 0.01), helplessness (p < 0.01), a preference to stay at home (p = 0.02), and diminished energy (p < 0.01). Three factors were generated in PD (explaining 55% of the total variance) and five in AD (explaining 59% of the total variance), and the two main factors generated in both populations related primarily to unhappiness and negative thoughts. Conclusions The factor structure of the GDS‐15 is similar in AD and PD patients with at most mild stage dementia, but between‐group differences on 6 of the GDS‐15 items suggests the non‐specificity of certain items in the two populations. Copyright © 2007 John Wiley & Sons, Ltd.