Mapping the Network of Persistent Somatic Symptoms Across Diseases: A Longitudinal Analysis from the SOMACROSS Research Unit

Background Persistent Somatic Symptoms (PSS) are common, functionally disruptive, multifactorial, and often remain stable over time. Understanding how symptoms interact may clarify transdiagnostic patterns and inform treatment. This study investigated symptom networks in a transdiagnostic sample to identify central symptoms and assess temporal stability.

Patients (n=1134; 63.7% female; mean age 50.6±16.3 years) from the transdiagnostic SOMACROSS research unit were analysed with the Patient Health Questionnaire-15 (PHQ-15), modified Pain Disability Index (PDI), and two global items on overall symptom severity and impairment due to symptoms (EURONET-SOMA) at baseline and 6-month follow-up. Networks were estimated with regularised partial correlations (EBICglasso). Network stability and change were tested with bootstrap procedures and the Network Comparison Test (NCT).

At baseline, four symptom clusters were identified: gastrointestinal, musculoskeletal pain, cardio-autonomic, and fatigue-sleep. Fatigue/low energy was a central symptom linking different network domains. Global symptom severity and impairment (EURONET-SOMA items) showed the strongest connectivity, reflecting their broad influence. Functional disability in home responsibilities and recreation (PDI items) acted as bridging nodes, connecting somatic symptoms with daily functioning. The follow-up network closely resembled the baseline structure. NCT confirmed temporal stability (global strength p=.815, structure invariance p=.180). Thus, both symptom clusters and central nodes remained consistent over six months.

Fatigue, overall symptom severity, impairment, and functional disability emerged as central drivers within network. Their stable centrality highlights them as possible intervention targets, suggesting that reducing fatigue and disability may interrupt self-reinforcing symptom cycles. These findings support a transdiagnostic view on PSS as a stable, interconnected system. Highlights Symptom clusters: gastrointestinal, musculoskeletal pain, cardio-autonomic and fatigue-sleep Fatigue and functional impairment were central symptom nodes across time points Global impairment and global symptom severity ratings were connected to somatic symptoms PSS network remained stable over 6 months, with no changes in strength or configuration Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG). The DFG project number for the coordination project is 445297796 (speaker: Professor Bernd Löwe, MD); see https://gepris.dfg.de/gepris/projekt/445297796 Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study presents cross-project results from the DFG Research Unit RU 5211 - SOMACROSS. Ethics committees of the Medical Chambers Hamburg and Münster gave ethical approval for all individual SOMACROSS studies. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All data produced in the present study are available upon reasonable request to the authors