Modifiable factors for somatic symptom persistence in patients with somatic symptom disorder: study protocol for a longitudinal cohort with an embedded ecologically momentary assessment (SOMA.SSD).

Introduction: Somatic symptom disorder (SSD) is a distressing mental disorder characterised by the presence of at least one persistent somatic symptom and a significant psychological burden due to the symptom(s), as well as excessive thoughts, feelings or behaviours related to them or associated health concerns. The primary aim of our study is to deepen the understanding of risk factors and mechanisms for somatic symptom persistence. Specifically, we will investigate the role of patients' expectations and somatic comorbidity regarding symptom persistence.

Methods and analysis: In a prospective 12-month cohort study, n=240 patients with SSD will be recruited from the outpatient clinics of the Department of Psychosomatic Medicine and Psychotherapy at the University Medical Center Hamburg-Eppendorf. The roles of two hypothesised predictors (ie, expectations and comorbidity) will be analysed together with known predisposing and maintaining factors of persistent somatic symptoms. The study entails macrolevel and microlevel assessments to investigate symptom severity over different timespans. Assessments at the macrolevel take place at baseline, 6 and 12 months. At the microlevel, a 10-day ecological momentary assessment study will be implemented to elucidate patients' dynamic experience with somatic symptoms in their natural environments. In order to elicit possible framing effects on the 10-day course of symptom severity, participants are randomised to either a positive or a negative expectation framing group. Cross-lagged panel models will be used to analyse data at the macrolevel. At the microlevel, multivariate latent growth curve models will be conducted to relate temporal changes in predictor and outcome variables to one another.

Ethics and dissemination: The study was approved by the Ethics Committee of the Medical Associations Hamburg, Germany (2020-10197-BO-ff). The results will enable us to draw conclusions regarding the role of expectations for future targeted treatment options and regarding the utility of somatic comorbidity as a potential diagnostic specifier of SSD. Dissemination of our results will be achieved through scientific publications, and lay summaries for study participants, patient advocacy groups and the general public.

Trial registration number: ISRCTN36251388.