Course and predictors of somatic symptom disorder in irritable bowel syndrome and ulcerative colitis: A longitudinal analysis from the SOMA.GUT-RCT

BackgroundLongitudinal data on the course of somatic symptom disorder (SSD) in ulcerative colitis (UC) and irritable bowel syndrome (IBS) are lacking. Understanding SSD trajectories and predictors in IBS and UC may clarify clinical relevance and guide psychological treatment decisions. This study examined the 12-month course and biopsychosocial predictors of interview-based SSD in patients with UC or IBS. MethodsLongitudinal data from a randomised controlled trial were analysed. SSD was assessed using DSM-5-based structured interviews at baseline and 12 months. SSD Criteria A (Somatic symptom severity) and B (symptom-related distress) were measured with the Patient Health Questionnaire-15 (PHQ-15) and the Somatic Symptom Disorder - B Criteria Scale-12 (SSD-12), respectively. Further variables included gastrointestinal symptom severity, inflammatory markers, depression severity, illness perceptions, and neuroticism. Logistic and linear regression models identified baseline predictors of SSD diagnosis and Criteria A and B at 12 months. ResultsThe sample included 213 patients (73.7% female; Mage=40.5, SD=13.98) with UC (n=110) or IBS (n=103). SSD was present in 42.3% (95%CI: 35.2-49.3) at baseline and in 15.5% (95%CI: 11.3- 20.7) at follow-up. Baseline SSD and depression severity predicted follow-up SSD. Criterion A was predicted by somatic symptom severity, female gender, and neuroticism; the B criterion by symptom-related distress, somatic symptom severity, neuroticism, and negative illness perceptions. Inflammatory markers and gastrointestinal symptom severity showed no predictive value. ConclusionStructured interview-based SSD was frequent in patients with UC or IBS at baseline and declined over time. Psychosocial rather than disease-related variables predicted SSD, highlighting modifiable targets for early detection and tailored interventions. Results should be interpreted in light of the studys interventional context.