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

•The factor structure of the BSI-18 was tested in Parkinson disease patients.•Psychological distress due to somatization was the most prevalent.•The originally proposed second-order three-factor structure was validated.

ObjectivePsychological 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.MethodsAnalysis 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.ResultsIn 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.ConclusionThe 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.