Fatigue across physical and mental health conditions: results from a multicenter study at the German Center for Mental Health

Background Fatigue is a frequent and disabling symptom across many physical and mental health conditions. Despite similar phenomenology, research has largely focused on single conditions using heterogeneous assessments, limiting cross-condition comparability. This study examines fatigue-related symptom burden across diverse clinical conditions within a shared framework. Methods In this multicenter cross-sectional study, adult outpatients (18–65 years) were recruited at five German university hospitals into seven cohorts: chronic primary pain, multiple sclerosis, cancer, chronic renal failure, inflammatory bowel disease, post-COVID condition, and chronic fatigue syndrome. Fatigue was assessed using established self-report measures, including the Fatigue Severity Scale and the Chalder Fatigue Scale, alongside mental health measures. Group differences were analyzed using ANOVA and chi-square tests with adjusted post hoc comparisons. Results A total of 538 patients were included. Fatigue burden varied substantially across cohorts, with a largely consistent pattern across assessment instruments. Despite significant overall between-cohort differences, the post-COVID ( n = 91), chronic primary pain ( n = 110), and cancer ( n = 124) cohorts showed comparable fatigue levels across several assessment instruments. Multiple sclerosis ( n = 63) showed intermediate levels, whereas inflammatory bowel disease ( n = 95) consistently showed the lowest fatigue burden. Due to the small sample size, chronic renal failure ( n = 30) and chronic fatigue syndrome ( n = 25) were analyzed descriptively. Across cohorts, fatigue and most psychological and somatic symptom measures were elevated relative to population reference values. Conclusions Using a harmonized assessment framework across seven diagnostic cohorts, this study demonstrates meaningful differences in fatigue burden, with convergent patterns across instruments. The findings provide a reference for contextualizing fatigue severity across conditions and support future hypothesis-driven and mechanistic analyses.