The analytical strategy was deliberately layered. First, the researchers used multivariable logistic regression to ask which of 14 symptom domains independently predicted the presence of muscle problems. In the full model, three symptoms emerged as significant independent predictors: breathing problems carried an odds ratio of 2.49 (95 percent confidence interval 1.42 to 4.38, p = 0.001), flu-like symptoms an odds ratio of 1.97 (1.14 to 3.42, p = 0.015), and temperature-regulation disorders an odds ratio of 1.97 (1.10 to 3.51, p = 0.021). When the model was restricted to a reduced set of physiological symptoms, cardiovascular symptoms additionally reached significance with an odds ratio of 1.87 (1.09 to 3.24, p = 0.024). These odds ratios indicate that patients reporting each of these symptoms had roughly double the odds of also reporting muscle problems compared with patients who did not, after accounting for the other symptoms in the model.

Correlation analysis reinforced the impression that muscle symptoms travel with a distinct physiological cluster. Tetrachoric correlations, which estimate the latent association between binary symptom variables, showed substantial relationships between muscle problems and breathing difficulties (rho = 0.52), cardiovascular symptoms (rho = 0.49), and temperature-regulation disorders (rho = 0.49), with somewhat weaker but still notable links to visual disturbances (rho = 0.39) and flu-like symptoms (rho = 0.39). Values in this range suggest that the co-occurrence of these symptoms is far from random and points toward a common underlying driver rather than a coincidental clustering of unrelated complaints.

The centerpiece of the study, however, was its latent-variable modeling. Using exploratory factor analysis followed by structural equation modeling (SEM), the authors tested whether the physiological symptoms could be explained by a single latent factor, an unobserved variable hypothesized to generate the observed symptom pattern. The model fit was strong by conventional standards: the root mean square error of approximation (RMSEA) was 0.046, well below the 0.06 threshold typically considered acceptable; the comparative fit index (CFI) was 0.971 and the Tucker-Lewis index (TLI) was 0.952, both close to the 0.95 benchmark; and the standardized root mean square residual (SRMR) was 0.026, far under the 0.08 cutoff. Together these indices indicate that a single latent physiological dysregulation factor provides a parsimonious and statistically credible account of how these symptoms co-occur in the sample.

Not every symptom behaved identically within this structure. Gastrointestinal complaints loaded substantially on the latent factor even though they showed no independent association with muscle problems in the multivariable regression, suggesting they belong to the broader physiological pattern but are not tightly coupled to the muscle-specific manifestation. Urogenital symptoms also displayed a smaller but significant loading on the factor alongside substantial item-specific variance, indicating that they are partly woven into the shared dysregulation and partly driven by their own distinct processes. This kind of decomposition, separating shared from symptom-specific variance, is precisely what latent-variable approaches are designed to deliver, and it hints that ME/CFS pathology may involve both a common multisystem thread and parallel, partially independent symptom channels.

The sex-stratified analyses produced a striking descriptive asymmetry. In women, all five physiological symptoms, breathing, cardiovascular, thermoregulatory, visual, and flu-like, independently predicted muscle problems. In men, only breathing problems and temperature-regulation disorders remained significant. Yet when the authors formally tested the overall symptom-by-sex interaction, the result did not reach statistical significance, meaning the data do not establish that the symptom associations genuinely differ between the sexes. One exception appeared at the individual symptom level: the association between breathing-related symptoms and muscle problems showed a statistically significant interaction with sex, hinting that this particular link may be stronger in one sex than the other. The authors urge caution here, noting that the overall interaction test was non-significant and the confidence interval for the interaction estimate was wide, leaving the finding exploratory at best.

Menopausal status, approximated by age-defined proxy groups, added another descriptive layer. Women classified as premenopausal by this proxy showed significant associations between muscle problems and cardiovascular symptoms, visual disturbances, and temperature-regulation disorders, whereas women classified as postmenopausal showed significant associations with breathing difficulties and flu-like symptoms. Flu-like symptoms were independently associated with muscle problems in the postmenopausal subgroup but not in the premenopausal one. Once again, however, the formal test told a more conservative story: the overall menopausal-by-symptom interaction was not statistically significant (Wald chi-square of 5.96 on 5 degrees of freedom, p = 0.310). The authors therefore frame these subgroup contrasts as exploratory differences in association rather than evidence of a menopause-specific effect, a distinction that matters enormously for how the findings should be cited and built upon.

Stability across disease duration offered further reassurance about the latent factor’s measurement properties. The specified physiological factor showed statistical comparability across cross-sectional disease-duration groups, meaning there was no overall evidence that the factor means something different in patients early versus late in their illness. This kind of measurement invariance is a prerequisite for meaningful comparison across patient subgroups and lends weight to the idea that the dysregulation factor is a stable feature of the disease rather than an artifact of illness stage, survivorship bias, or shifting symptom reporting over time.

What could the latent factor represent biologically? The authors are careful not to overclaim, but they note that the findings are compatible with the hypothesis that the symptom-dysregulation factor reflects a chronic post-exertional malaise-associated multisystem response. The symptom cluster it captures, spanning respiratory, cardiovascular, thermoregulatory, visual, and flu-like domains, overlaps substantially with the territory of autonomic dysfunction, vascular dysregulation, immune activation, and metabolic disturbance, all of which have been implicated in ME/CFS by prior physiological studies. Whether the latent factor corresponds to genuinely interacting mechanisms across these systems is a question the present cross-sectional design cannot answer, and the authors explicitly call for longitudinal and biomarker-based studies to test it.

The practical implications could be considerable. If muscle symptoms indeed serve as a candidate integrative symptom within a measurable latent dysregulation factor, then symptom-based phenotyping may help stratify patients for clinical trials, a persistent challenge in a disease as heterogeneous as ME/CFS. Better stratification could, in turn, accelerate the development of mechanism-based therapeutic approaches by ensuring that patients sharing a common physiological signature are studied together. The study was conducted in 2022 under Declaration of Helsinki protocols approved by the Ethics Committee of Furtwangen University, Germany, and was partially funded by the Ministry of Social Affairs, Health and Integration using state funds approved by the Baden-Württemberg State Parliament, with the subsequent analyses unfunded. As an exploratory, cross-sectional analysis of registry data, it cannot establish causality or direction, and its subgroup findings demand replication. But by quantifying how tightly muscle symptoms are woven into a broader physiological web, and by providing a statistically well-fitting latent structure that future biomarker studies can interrogate, the work offers ME/CFS researchers a concrete, testable framework for one of medicine’s most perplexing chronic illnesses.

Subject of Research: Latent physiological symptom-dysregulation and muscle symptoms in ME/CFS analyzed by sex and menopausal-status proxy group

Article Title: Muscle symptoms and a latent physiological symptom-dysregulation factor in ME/CFS: exploratory analyses by sex and age-defined menopausal-status proxy group

Article References: Habermann-Horstmeier, L., & Horstmeier, L. M. (2026). Muscle symptoms and a latent physiological symptom-dysregulation factor in ME/CFS: exploratory analyses by sex and age-defined menopausal-status proxy group. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09018-9

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09018-9

Keywords: ME/CFS, chronic fatigue syndrome, muscle symptoms, physiological dysregulation, post-exertional malaise, structural equation modeling, factor analysis, sex differences, menopausal status, autonomic dysfunction, symptom phenotyping, Journal of Translational Medicine