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

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.