Validation of the Somatic Symptom Disorder-B Criteria Scale (SSD-12) in a Clinical Centre of Excellence in the Netherlands

Aim: In Somatic Symptom Disorder (SSD), a new classification in the DSM-5, the focus moved towards dysfunctional psychological coping with somatic symptoms rather than on the underlying cause of the symptoms. These psychological components are assessed as part of the B criterion. Toussaint et al. (2015) developed the self-report Somatic Symptom Disorder–B Criteria Scale (SSD-12) a and this study aims to validate the SSD-12, to establish its predictive validity, and to establish cutoff points for clinical practice. Method: The SSD-12 and questionnaires for assessing anxiety (GAD-7), depression (PHQ-9), and somatic symptom severity (PSC) were administered as part of the clinical intake at the Clinical Centre of Excellence Body, Mind and Health, Tilburg, the Netherlands. The three-factor model was evaluated using principal component analysis (PCA) with varimax rotation. Psychometric properties of the SSD-12 were explored calculating reliability and validity estimates. A receiver operating characteristic (ROC) and an area under the curve (AUC) were calculated using semi structured psychiatric examination as validation criterion. Results: A total of 48 patients (mean age 39.4 (SD=16.2) years, 56.3% women) completed the SSD-12, 26 (54.2%) met clinical diagnostic criteria for a SSD. The mean SSD-12 score was 28.3 (SD=11.2). The reliability of the SSD-12 excellent (Cronbach’s α = 0.93; lambda2 = 0.93). Factor analysis showed a one-factor structure with intermediate to high inter-item correlations (.20<r>.78). The SSD-12 total sum score was significantly associated with anxiety (r = .60), depression (r = .68), and somatic symptom burden (r = .41 and r = .31). ROC analysis showed a low accuracy of the SSD-12 (AUC = .52 (SE=.09, 95%CI: .34-.70). Conclusions: The SSD-12 is a reliable instrument to assess criterion B. A one-factor structure fitted the SSD-12 and the SSD-12 did not perform well when clinical diagnosis of SSD was used as gold standard. Furthermore, SSD-12 scores were related with somatic symptom burden, with anxiety and depression scores