Sex- and menopause-related differences in immune and gastrointestinal symptom architecture in ME/CFS: evidence from factor analysis and structural equation modeling.

backgroundMyalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a multisystem disorder characterized by neuroimmune, autonomic, and gastrointestinal dysfunction. Previous studies identified coherent symptom domains involving Brain, Autonomic, Gut, and Immune manifestations and demonstrated pronounced sex-specific differences in neurocognitive-sensory and autonomic symptom organization. However, whether immune-related and gastrointestinal symptoms form distinct or integrated latent structures in women and men with ME/CFS remains unclear. In addition, the potential influence of menopausal status on these symptom domains has not been systematically investigated.

methodsData from 748 adults with a medical diagnosis of ME/CFS were included in this cross-sectional analysis (608 women, 137 men, and 3 non-binary participants). Sex-stratified analyses were restricted to women and men. Symptoms were coded dichotomously. Sex-stratified analyses included cross-tabulations, Cramér's V, tetrachoric correlations, logistic and linear regression models, exploratory factor analysis, and structural equation modeling (SEM). Additional subgroup analyses compared pre- and postmenopausal women. Model robustness was evaluated using a stratified training dataset.

resultsIn women, Immune (flu-like symptoms, susceptibility to infections) and Gut (gastrointestinal complaints, food intolerances) symptoms formed two distinct but related clusters, characterized by moderate within-cluster correlations (tetrachoric ρ = 0.47-0.60) and weaker cross-cluster associations (ρ = 0.30-0.35). Exploratory factor analysis (EFA) supported a two-factor solution. Consistent with this result, the alternative one-factor SEM showed comparatively poor fit (CFI = 0.913; RMSEA = 0.119), whereas the specified two-factor model was just-identified and therefore not suitable for global fit evaluation. In men, all four symptoms loaded onto a single integrated Gut/Immune factor, with within- and cross-domain tetrachoric correlations ranging from 0.43 to 0.68. SEM confirmed excellent fit for a one-factor model (CFI = 0.981; RMSEA = 0.074). Susceptibility to infections emerged as the dominant predictor in regression analyses. Among women, menopausal status selectively affected immune-related symptoms. Women classified as premenopausal reported flu-like symptoms more frequently than women classified as postmenopausal, whereas gastrointestinal symptoms and food intolerances remained stable across groups. These findings suggest differential hormonal sensitivity of immune versus gastrointestinal symptom trajectories.

conclusionsImmune and gastrointestinal symptoms in ME/CFS exhibit sex-specific latent structures. Women demonstrate two partially separable but related symptom domains, whereas men show a more integrated immune-gastrointestinal architecture. Furthermore, menopausal status appears to selectively modulate immune-related symptom expression while leaving gastrointestinal symptom patterns comparatively stable. Taken together, these results provide an exploratory framework that supports the concept of sex-dependent neuroimmune-autonomic mechanisms in ME/CFS and aligns with a dynamic, hormonally modulated immune component as well as a more persistent, gut-related process. The results highlight the importance of sex- and hormone-sensitive approaches to phenotyping, mechanistic research, and therapeutic stratification in ME/CFS.