Symptom-Level Comorbidity of Fibromyalgia and Depression: A Network Approach within a Large Clinical Sample

INTRODUCTION: Fibromyalgia syndrome (FMS) and major depressive disorder (MDD) frequently co-occur together, but the mechanisms linking these conditions remain poorly understood. This study aimed to delineate symptom clusters within the FMS-MDD network, identify bridging symptoms connecting these clusters, and evaluate the integrative role of Pain Intensity. METHODS: Cross-sectional data from 3,044 patients with FMS (94% female; mean age = 52.4, SD = 9.28) were analyzed using a mixed graphical model. From an initial pool of 238 items, 30 symptom nodes were selected through a systematic reduction process. RESULTS: The analysis revealed seven distinct symptom clusters: Pain Intensity and Functional Impact, Autonomic and Somatic Complaints, Trauma and Anxiety-driven Symptomatology, Sexual and Health Concerns, Anhedonia and Social Disconnection, Cognitive-Affective and Psychomotor Dysfunctions, and Sleep, Energy Levels, and Social Functioning. Six symptoms were identified as key bridges between clusters, with depressed mood (z = 2.43), fatigue (z = 2.06), and anxiety and nervousness (z = 2.09) showing the highest bridge centrality. Surprisingly, pain intensity exhibited minimal connectivity, ranking 18th in bridge strength (z = - 0.59), and primarily linked to sleeping problems and fatigue. CONCLUSION: Our findings suggest that emotional and fatigue-related symptoms play a more central role in linking FMS and depression than Pain Intensity alone. Bridge symptoms such as fatigue and depressed mood may represent clinically meaningful targets for symptom-focused interventions. As this study is cross-sectional, causal inferences cannot be drawn. Longitudinal studies are needed to examine temporal dynamics and test whether targeting bridge symptoms improves clinical outcomes.