A comparison of three depression scales as screening tools for depression in Parkinson’s disease

Background: This study aimed to evaluate the validity of the Edinburgh Depression Scale (EDS) as a screening measure for depression in patients with Parkinson’s disease (PD) and to compare the performance with the two questions recommended for depression screening by the National Institute for Health and Clinical Excellence (NICE) and the 15-item Geriatric Depression Scale (GDS-15). Methods: A sample of 120 patients attending PD out-patient clinics were interviewed in a standardised manner using the relevant sections of the Present State Examination-Schedules for Clinical Assessment in Neuropsychiatry to identify depression according to DSM-IV criteria. Participants then completed the three depression screening measures. Results: The sensitivity, specificity, positive and negative predictive values (PPV and NPV) of each screening measure for the identification of major and minor depression were calculated for different cut-off scores, and receiver operating characteristics (ROC) analyses were conducted. The EDS gave sensitivity of 74%, specificity of 92% (PPV 64%, NPV 95%) at the cut-off score of 10/11. The questions recommended by NICE gave sensitivity of 100% and specificity of 84% (PPV 54%, NPV 100%) at a threshold of 0/1, and the GDS-15 showed sensitivity of 84% and specificity of 89% (PPV 59%,NPV 97%) at a cut-off of 5/6. The areas under the ROC curve were 0.90, 0.95 and 0.92 respectively. The relative benefits of a two-stage screening process were explored. Conclusion: This study shows that the EDS, NICE questions and GDS-15 are valid screening measures for depression in PD provided the appropriate threshold scores are applied. The NICE questions showed the highest sensitivity but low PPV; a positive response to either of these two questions should highlight to the clinician that further diagnostic assessment of the patient may be warranted. A second screening measure, such as the EDS, could then be used to reduce the number of false-positives.