Mapping the network of persistent somatic symptoms across diseases: Cross-sectional and longitudinal analyses from the SOMACROSS research unit.

BACKGROUND

Persistent somatic symptoms (PSS) are common, functionally disruptive, and stable over time. Understanding symptom interactions may clarify transdiagnostic patterns and inform treatment. This study investigated symptom interrelations in a transdiagnostic sample to identify central symptoms and assess temporal stability.

METHODS

Patients (n = 1134; 63.5% female; mean age 50.6 ± 16.3 years) from the transdiagnostic SOMACROSS research unit were analysed regarding the Patient Health Questionnaire-15 (PHQ-15), the modified Pain Disability Index (PDI), and two items on symptom severity and impairment (EURONET-SOMA) at baseline and 6-month follow-up. Regularised partial correlation networks were compared between patients with functional somatic/mental disorders (n=316) and patients with somatic diseases (n=818), as well as across different measurements. Stability and invariance was tested with the Network Comparison Test (NCT).

RESULTS

Four symptom clusters emerged: gastrointestinal, musculoskeletal, cardiopulmonary, and general symptoms. Fatigue/low energy emerged as a central node linking domains. Global symptom severity and impairment (EURONET-SOMA) showed the highest connectivity. Disability in home responsibilities and recreation (PDI) bridged somatic symptoms and daily functioning. The NCT confirmed temporal stability (global strength: p = .815; structure invariance: p = .180), indicating that symptom clusters and central nodes remained consistent over time. The somatic diseases network showed significantly higher connectivity than the functional somatic/mental disorders network (global strength: p = .001), while structural invariance was not significant (p = .197).