Validity of a Brazilian version of the Zung self-rating depression scale for screening of depression in patients with Parkinson's disease.

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder with prominent motor manifestations and many other non-motor symptoms that significantly decrease quality-of-life and are frequently under-recognized, for example depression.

Objective: To study the validity of a Brazilian version of the Zung Self-rating Depression Scale (SDS) for the diagnosis of depression in patients with PD.

Methods: We evaluated 78 consecutive non demented patients over the age of 40 with diagnosis of PD at a Movement Disorders Outpatient Clinic, who could read and understand questionnaires. They completed the SDS and the Geriatric Depression Scale with 15 items (GDS-15). The diagnosis of depression was made after a structured clinical interview based on DSM-IV criteria for the diagnosis of major depression (SCID-CV).

Results: The prevalence of major depression was 23.1%. Cronbach's alpha was 0.73 and the area under the ROC curve was 0.93 for the SDS. The score index of 55 had a sensitivity of 88.9% and a specificity of 83.3% for the diagnosis of depression. The total scores of the SDS and GDS-15 were highly correlated (0.652, p < 0.0001) and correlated weakly with the scores of a motor scale.

Discussion: The SDS is a valid tool for screening depression in patients with PD since the specific SDS index of 55 is adopted. Two shortened versions could be used with good results.