The factor structure of the Brief Symptom Inventory-18 (BSI-18) in Parkinson disease patients

Psychological distress is common among Parkinson disease (PD) patients. Screening tools, such as the Brief Symptom Inventory-18 (BSI-18), help clinicians to identify and manage PD patients with psychiatric symptoms. The objective of this study is to test the factor structure of the BSI-18 in PD patients.

Analysis was conducted on PD patients who had initial visits at a movement disorders center from 2004 to 2015. Univariate analysis was used to describe the distribution of socio-demographic and clinical characteristics. The BSI-18 was used to determine the prevalence of clinically significant psychological distress. Confirmatory factor analyses (CFA) treating BSI-18 items as ordered categorical data were conducted. Five competing models were tested. Multiple fit indices, parsimony, and past theory were used to select the final model.

In the study sample (n=1067), 18.7%, 22.5%, 15.4%, and 15.0% of patients had BSI-18 T-scores indicative of clinically significant global psychological distress, somatization, depression, and anxiety, respectively. Of the competing models, the final model chosen was the second-order three-factor structure with somatization, depression, and anxiety loaded on psychological distress.

The original proposed factor structure of the BSI-18 was validated in this patient population. Consequently, this study confirms the construct validity of the BSI-18 for screening of psychological distress in PD patients. Findings highlight somatization as a particularly important component of psychological distress in PD patients.