Perceived Causal Networks in Patients with Fibromyalgia and Depression: Construction of a Structured Interview and Testing Reliability

Background The PErceived CAusal Network (PECAN) approach offers a novel, idiographic method for mapping perceived causal relations between symptoms. While promising for clinical case formulation, prior studies have shown limited test-retest reliability and have been based on self-reported or non-clinical samples. This observational two-wave study examined the feasibility, test-retest reliability, and subjective clinical utility of a structured, interview-based PECAN assessment in patients with Major Depressive Disorder (MDD) and Fibromyalgia Syndrome (FMS). Methods A structured symptom list was developed through literature review and expert and patient input. A total of 100 clinically diagnosed adult patients (n = 50 MDD; n = 50 FMS) completed two semi-structured PECAN interviews, spaced one week apart. Participants selected ten personally relevant symptoms from the pre-defined list of symptoms, and rated the perceived causal influence between these. Feasibility and clinical utility were assessed via standardized feedback; test-retest reliability was examined using Spearman correlations for edge weights and centrality indices. Qualitative data were analyzed to identify reasons for inconsistencies between interviews. Results The PECAN interviews were rated as comprehensible and manageable. Mean test-retest reliability was r = .62 for edge weights and r = .76 for out-degree centrality. Qualitative inconsistencies were mainly attributed to symptom variation (49.5%) or methodological factors (25.5%). Most participants reported increased awareness of symptom interactions. Conclusions The PECAN interview proved feasible and moderately reliable in clinically diagnosed populations. It shows promise as a tool for individualized case conceptualization in psychosomatic and psychotherapeutic settings.