Diagnostic accuracy of the Dutch version of the Somatic Symptom Disorder – B Criteria Scale (SSD-12) compared to the Whiteley Index (WI) and PHQ-15 in a clinical population

Abstract

ObjectiveSomatic Symptom and Related Disorders(SSRD) are characterised by an intense focus on somatic symptoms that causes significant distress. A self-report scale developed to assess distress as symptom-related thoughts, feelings, and behaviors (SSD-12) has proved to be a reliable, valid and time-efficient measure for Somatic Symptom Disorder(SSD). This cross-sectional study aimed to compare the SSD-12 with psychiatric assessment as gold standard in a Dutch clinical population for SSRD compared to other widely used measures. MethodsData were collected from adult patients visiting a specialised mental health outpatient clinic for SSRD in the Netherlands, between 2015 and 2017. Analyses included item evaluation, scale reliability, construct validity, diagnostic utility and cut points. Performance of SSD-12, Whiteley Index(WI) and PHQ-15 were compared in Receiver operating characteristics (ROC) curves. Results223 patients with SSD, Functional Neurological Disorder, Illness Anxiety(IA) and no SSRD participated. SSD-12 items were normally distributed; total scores correlated with measures of health anxiety, anxiety and depression. The optimal cut point for the SSD-12 was 22 (sensitivity 75.9%, specificity 63.6%). The ROC area under the curve for SSD-12 was 0.75 compared to 0.68 for the WI and 0.65 for the PHQ-15. Combinations of those questionnaires did not yield better results than for the SSD-12 alone. ConclusionThe SSD-12 alone outperformed the WI and PHQ-15 and combined scales in effectively distinguishing SSRDs from other mental disorders. This may suggest that distress is a more accurate indicator of SSRD than earlier diagnostic criteria as operationalised in the WI and PHQ-15.