The prevalence of psychological distress in Parkinson's disease patients: The brief symptom inventory (BSI-18) versus the Hopkins symptom checklist (SCL-90-R).

The prevalence of psychological distress in Parkinson's disease (PD) patients has been evaluated by many different assessment instruments and with diverse control groups. The most frequently used distress symptom scale has been the Hopkins Symptom Checklist (SCL-90-R), although it contains many symptoms with problematic validity clinically. The 18-item subscale of the SCL-90-R, the Brief Symptom Inventory (BSI-18) has recently been shown to have a sufficient validity to screen for the prevalence of psychological distress (somatization) in PD patients. We have performed a clinimetric analysis by comparing the BSI-18 with SCL-90-R relevant subscales in PD patients. Our micro-analysis has focused on the Mokken model to test the scalability of the subscales. The macro-analysis has focused both on effect size statistics and the normative level of psychological distress with reference to the Italian general population data using T-score metric. The Mokken analysis indicated acceptable scalability for all the subscales of BSI-18. The effect size statistics identified somatization in both BSI-18 and SCL-90-R as the most prevalent and intense symptom of psychological distress. The T-score metric identified the phobic anxiety subscale of SCL-90-R to be clinically much more important than the BSI-18 anxiety subscale in the PD patients. We have found the SCL-90-R subscale of phobic anxiety and the BSI-18 somatization subscale most clinically valid when measuring psychological distress in PD patients.