Validity of the 30-item geriatric depression scale in patients with Parkinson's disease

Abstract

Depression in Parkinson's disease (dPD) is difficult to diagnose because depressive symptoms can overlap with symptoms of Parkinson's disease (PD). Subject-rated scales such as the 30-item Geriatric Depression Scale (GDS) may be useful in screening for dPD. There were 57 patients (33 men, 24 women; mean age, 58.6 years [SD +/- 8.4]) enrolled in a study of pallidotomy for intractable PD who were evaluated for depression before and after surgery. Subjects were evaluated using the 17-item Hamilton Depression Rating Scale (HDRS), Structured Clinical Interview for Diagnostic and Statistical Manual-III (SCID), and the GDS. SCID was used to diagnose major depression with confirmation by an expert geropsychiatrist. Receiver-operating curves (ROC) were used to identify cutoff points with maximal discriminant validity for diagnosing dPD. A total of 213 evaluation time points were included for the 52 patients with time points that included a valid SCID diagnosis, GDS, and HDRS. A ROC established points of maximum specificity/sensitivity for the GDS at a cutoff of 9/10 (sensitivity = 0.809, specificity = 0.837, positive predictive value [PPV] = 0.584, negative predictive value [NPV] = 0.939) and for the HDRS at a cutoff of 12/13 (sensitivity = 0.810, specificity = 0.821, PPV = 0.580, NPV = 0.934). The GDS was moderately correlated with the HDRS (Pearson's r = 0.54; P < 0.001). The GDS is useful in screening for dPD. A cutoff score of 9/10 has acceptable discriminant validity for dPD, and the GDS has a moderate correlation with the HDRS in PD patients.