Category: Symptoms

Association between myalgic encephalomyelitis/chronic fatigue syndrome and irritable bowel syndrome: a systematic review and meta-analysis

Abstract:

Background: Irritable bowel syndrome (IBS) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic, debilitating disorders characterized by substantial symptom burden, impaired quality of life, and high healthcare utilization. IBS is a disorder of gut-brain interaction with a global prevalence ranging from 3.8% to 9.2%, while ME/CFS is defined by persistent, exertion-intolerant fatigue and multisystem dysfunction. Growing evidence suggests frequent co-occurrence of these conditions, implicating shared mechanisms such as immune dysregulation, autonomic imbalance, and altered gut-brain signaling. However, the magnitude of their association has not been comprehensively quantified.

Methods: We conducted a systematic review and meta-analysis by searching Embase, PubMed, Scopus, and Google Scholar databases from inception through February 2026. Eligible observational studies reporting associations or prevalence between IBS and ME/CFS were included. Random-effects meta-analyses were performed to pool odds ratios (ORs) and prevalence estimates. Heterogeneity was assessed using I2 statistics. We evaluated for publication bias and assessed for risk of bias.

Results: Twenty-two studies were included in the systematic review and 18 in the meta-analysis. Individuals with ME/CFS had significantly higher odds of IBS compared with controls (OR = 7.20; 95% CI: 2.77-18.76; I2 = 72.1%). The pooled prevalence of IBS among individuals with ME/CFS was 37% (95% CI: 23-54%), with substantial heterogeneity (I2 = 99.5%). Subgroup analysis revealed that diagnostic criteria significantly influenced prevalence (p < 0.0001), while meta-regression identified ME/CFS diagnostic criteria as a significant moderator.

Conclusion: IBS and ME/CFS are strongly associated, suggesting shared underlying mechanisms. These findings support integrated screening approaches and coordinated, multidisciplinary management to improve outcomes in affected patients.

Source: Rajabi N, Ramdass PVAK. Association between myalgic encephalomyelitis/chronic fatigue syndrome and irritable bowel syndrome: a systematic review and meta-analysis. Front Med (Lausanne). 2026 Jul 27;13:1881784. doi: 10.3389/fmed.2026.1881784. PMID: 42577233; PMCID: PMC13453825. https://pmc.ncbi.nlm.nih.gov/articles/PMC13453825/ (Full text)

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

Abstract:

Background: Myalgic 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.

Methods: Data 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.

Results: In 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.

Conclusions: Immune 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.

Source: Habermann-Horstmeier L, Horstmeier LM. Sex- and menopause-related differences in immune and gastrointestinal symptom architecture in ME/CFS: evidence from factor analysis and structural equation modeling. J Transl Med. 2026 Jul 27;24(1):970. doi: 10.1186/s12967-026-08699-6. PMID: 42522006. https://link.springer.com/article/10.1186/s12967-026-08699-6 (Full text)

Cardiopulmonary exercise test results do not change over two sequential days in patients with chronic fatigue syndrome

Abstract:

Background: Two consecutive cardiopulmonary exercise tests (CPETs) performed 24 hours apart are increasingly used to determine post-exertional malaise (PEM) and disability in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Declines in functional capacity on Day 2 reflect impaired recovery and PEM. However, reports have variably described a reduction in peak oxygen consumption (VO2) and/or VO2 at the anaerobic ventilatory threshold (VT). Given the inconsistent findings, we sought to replicate the studies by performing sequential 2-day CPETs in ME/CFS and age- and sex-matched sedentary controls.

Methods: Accordingly, maximal bicycle ergometer CPETs were performed on two consecutive days in 58 patients with ME/CFS (mean age 38.6 ± 9.6 years, Body Mass Index (BMI) 24.1 ± 3.3 kg/m2, 11 men and 47 women) and 25 age-matched sedentary control (CON) subjects (age 38.2 ± 9.9 years, BMI 24.2 ± 3.4 kg/m2, 5 men and 20 women). Peak VO2 was reported as the highest 30-sec average; VT was selected as the nadir of the VE/VO2 and PETCO2 curves, and VE/VCO2 as the slope throughout exercise.

Findings: For ME/CFS and CON subjects, there were no significant changes in Peak VO2 between Day 1 and Day 2 studies (ME/CFS Day 1, 22.3 ± 5.4; Day 2, 22.5 ± 5.4 mL·kg-1·min-1; CON Day 1, 23.4 ± 3.5; Day 2, 22.8 ± 3.6 mL·kg-1·min-1; NS). Similarly, VO2VT and VE/VCO2 slopes were not significantly different between the ME/CFS patients and CON, and on Day 2, they did not show any differences within or between groups. Peak heart rate was significantly higher in CON versus ME/CFS. The level of perceived exertion was significantly greater at all levels of exercise on the Day 1 and Day 2 tests for ME/CFS patients versus CON.

Interpretation: Our data indicate that 2-day CPET provides exercise-related results that are the same in ME/CFS patients and CON subjects. ME/CFS patients have a greater perception of exertion throughout exercise and a lower maximum heart rate than CON. The data do not support using the 2-day CPET protocol to define PEM or disability.

Source: Mancini DM, Cook DB, Brunjes DL, Soto T, Blate M, Quan P, Yamazaki T, Norweg A, Natelson BH. Cardiopulmonary exercise test results do not change over two sequential days in patients with chronic fatigue syndrome. Front Physiol. 2026 May 13;17:1816082. doi: 10.3389/fphys.2026.1816082. PMID: 42212259; PMCID: PMC13213420. https://pmc.ncbi.nlm.nih.gov/articles/PMC13213420/ (Full text)

Sleep in myalgic encephalomyelitis/chronic fatigue syndrome shows marked night-to-night fluctuation under free-living conditions-results from a matched case-control study

Abstract:

Purpose: Unrefreshing and non-restorative sleep is a hallmark complaint in people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). However, little is known about their habitual sleep and night-to-night fluctuations under real-life conditions. This study aimed to characterize sleep, and the intraindividual variability (IIV) of sleep in people living with ME/CFS compared with matched controls.

Methods: In this case-control study, 38 ME/CFS and 38 controls wore a wrist accelerometer continuously for 7 days and completed concurrent sleep diaries, the Pittsburgh Sleep Quality Index (PSQI), and Epworth Sleepiness Scale (ESS). Within the ME/CFS group, participants were also stratified by symptom severity using the Bell Disability Scale. Sleep IIV was quantified using the coefficient of variation, the root mean square of successive differences, and the Bayesian variability model, respectively.

Results: Compared with controls, individuals with ME/CFS spent significantly more time in bed and exhibited poorer sleep efficiency (SE) (all p < 0.05). Despite a longer time in bed, total sleep time did not differ between groups. ME/CFS participants also displayed significantly greater IIV in SE. By contrast, sleep timing (bedtime) was more regular among ME/CFS. Exploratory analyses did not detect clear differences across ME/CFS severity subgroups for mean sleep variables or variability indices.

Conclusion: Under real-life conditions, people with ME/CFS exhibit poor sleep quality and unstable SE. These findings highlight sleep IIV as a clinically relevant dimension of sleep health in ME/CFS.

Current knowledge/study rationale: Unrefreshing sleep is a core symptom of ME/CFS, yet most evidence relies on single- or two-night laboratory assessments that may not reflect habitual sleep under real-life conditions. Moreover, night-to-night sleep variability, a potentially critical dimension of sleep health, has not been systematically examined in ME/CFS.

Study impact: Using week-long wrist accelerometry, this study shows that under free-living conditions sleep in ME/CFS is characterized not only by impaired sleep efficiency but also by pronounced night-to-night variability, despite relatively stable bedtime compared to controls. These findings highlight sleep efficiency variability as a clinically relevant feature of ME/CFS and underscore the need for multi-night assessment and targeted strategies addressing sleep variability.

Source: Saurel M, Fornasieri I, Del Sordo GC, Chatain C, Fantini ML, Gruet M, Saidi O. Sleep in myalgic encephalomyelitis/chronic fatigue syndrome shows marked night-to-night fluctuation under free-living conditions-results from a matched case-control study. J Clin Sleep Med. 2026 May 13;22(1):77. doi: 10.1007/s44470-026-00079-7. PMID: 42129014. https://link.springer.com/article/10.1007/s44470-026-00079-7 (Full text)

Digital Approaches for Managing Brain Fog in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Interventions, Monitoring, and Future Directions

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a high-burden, under-researched condition characterized by heterogeneous and fluctuating symptoms, including cognitive dysfunction commonly described by patients as “brain fog”. Despite growing interest in digital health technologies for symptom monitoring and personalized care, their application to the assessment and management of cognitive dysfunction in ME/CFS remains unclear. This descriptive review aimed to examine the current scientific evidence on digital approaches related to brain fog in ME/CFS.

A structured literature search following PRISMA guidance was conducted to identify relevant studies. The available literature remains limited in scope and methodological maturity. During synthesizing across studies, three main functional domains of digital application become apparent: (1) digital tools for cognitive assessment, which have the strongest evidence base; (2) digital platforms for longitudinal monitoring; and (3) digitally mediated interventions or rehabilitation approaches, both of which are less well studied.

Simultaneously, the findings suggest that patient-reported brain fog may represent a visible component of the broader ME/CFS disease spectrum and could serve as an early clinical indicator guiding diagnosis and management. Interpreting these symptoms within a biopsychosocial framework may facilitate understanding of the complex nature of the disease and optimize the use of digital technologies for monitoring cognitive dysfunction and supporting patient-centered care in ME/CFS.

Source: Araja D, Murovska M, Krumina A, Eory A, Berkis U. Digital Approaches for Managing Brain Fog in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Interventions, Monitoring, and Future Directions. Life (Basel). 2026 Apr 1;16(4):571. doi: 10.3390/life16040571. PMID: 42073381. https://www.mdpi.com/2075-1729/16/4/571 (Full text)

Symptom clusters in ME/CFS reflect distinct neuroimmune and autonomic pathophysiological mechanisms: a translational model

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem disease characterized by heterogeneous symptom patterns. Previous work suggested that specific symptoms tend to co‑occur, pointing toward underlying biological mechanisms. This study aimed to empirically validate literature‑based, hypothesis‑driven symptom clusters and assess whether they reflect distinct neuroimmune and autonomic pathophysiological pathways.

Methods: Symptom data from 748 adults with ME/CFS (≥20 years) participating in the APAV‑ME/CFS study were analyzed. Symptoms were assigned to predefined mechanistic groups informed by current pathophysiological hypotheses. Exploratory and Confirmatory Factor Analyses, followed by Structural Equation Modeling (SEM), evaluated the coherence, distinctiveness, and hierarchical structure of each cluster. Robustness was tested using a stratified, randomized training dataset.

Results: A coherent Brain factor (brain fog, sensory hypersensitivity, visual disturbances, sleep disturbances, headaches) showed excellent fit (RMSEA = 0.021; CFI = 0.996). Gastrointestinal symptoms demonstrated stronger internal consistency than Immune symptoms, and model comparisons supported a two‑factor Gut–Immune structure. Across all analyses, symptom groups emerged as internally consistent and statistically distinct. A higher‑order SEM including a common latent factor yielded excellent fit for the Autonomic symptom complex.

Conclusions: The findings support ME/CFS as a complex neuroimmune–autonomic multisystem disorder and suggest that symptom clusters align with functional biological systems. Mechanism-aligned symptom subgrouping may enable pathophysiology-guided diagnostics, patient stratification, and targeted therapeutic development. The proposed interpretations of underlying mechanisms derive from the integration of existing literature and were not directly measured in this study. The identified clusters therefore indicate mechanistic alignment rather than direct mechanistic validation.

Source: Habermann-Horstmeier L, Horstmeier LM. Symptom clusters in ME/CFS reflect distinct neuroimmune and autonomic pathophysiological mechanisms: a translational model. J Transl Med. 2026 Apr 28;24(1):606. doi: 10.1186/s12967-026-08159-1. PMID: 42050709; PMCID: PMC13126800. https://pmc.ncbi.nlm.nih.gov/articles/PMC13126800/ (Full text)

Identifying post-exertional malaise subtypes: Differentiating physical and mental PEM manifestations

Abstract:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic illness with post-exertional malaise (PEM) as a key symptom. This study categorized participants with ME/CFS who met PEM criteria into four groups based on severity of physical and mental PEM: severe physical PEM (Physical group), severe mental PEM (Mental group), both severe (Both group), or neither severe (Neither group). A control group was also included.

The Both group exhibited the highest symptom severity, while the Neither group displayed lower scores. The Neither group experienced less disability than other ME/CFS subtypes but was significantly more disabled than Controls. Health assessments revealed that Controls had the highest functioning, followed by the Neither group, with the Both group showing greatest impairment. These results indicate distinct PEM subtypes, emphasizing the need to recognize different manifestations of this complex symptom. Future research should include diverse control groups, longitudinal data, and biological measures to further understand PEM subtypes.

Source: Tuzzolino K, Jason LA, Furst J. Identifying post-exertional malaise subtypes: Differentiating physical and mental PEM manifestations. J Health Psychol. 2026 Feb 28:13591053261420598. doi: 10.1177/13591053261420598. Epub ahead of print. PMID: 41761780. https://pubmed.ncbi.nlm.nih.gov/41761780/

Temporal dynamics of the plasma proteomic landscape reveals maladaptation in ME/CFS following exertion

Abstract:

The overarching symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is post-exertional malaise (PEM), an exacerbation of symptoms following physical or mental exertion. To investigate the molecular underpinnings of PEM, we performed longitudinal plasma proteomics using the Somascan® 7K aptamer-based assay to monitor 6,361 unique plasma proteins in 132 individuals (96 females and 36 males) subjected to two maximal cardiopulmonary exercise tests separated by a 24-hour recovery period.

The cohort included 79 ME/CFS cases compared to 53 age- and BMI-matched sedentary controls, allowing us to distinguish disease-specific molecular alterations from those due to physical deconditioning. Longitudinal profiling revealed widespread proteomic changes following exertion, with the most pronounced alterations observed in ME/CFS participants during the recovery phase, coinciding with the onset of PEM.

Compared to controls, ME/CFS subjects showed persistent dysregulation of immune, metabolic, and neuromuscular pathways. Key findings included suppression of T and B cell signaling, downregulation of IL-17 and cell-cell communication pathways, and upregulation of glycolysis/gluconeogenesis, suggestive of mitochondrial stress and impaired immune recovery from exercise. Proteomic associations with physiological performance (VO2max, anaerobic threshold) revealed disruptions between protein abundance and exercise capacity in ME/CFS versus controls.

Correlations with symptom severity linked changes in immune-related proteins and ME/CFS symptoms including muscle pain, recurrent sore throat, and lymph node tenderness. Sex-stratified analyses revealed distinct molecular responses between females and males, emphasizing the importance of considering sex as a biological variable in ME/CFS research.

Finally, our analysis of sedentary controls contributes new data of molecular responses to acute exertion in a predominantly female sedentary cohort, a population historically underrepresented in exercise physiology studies. Together, these findings underscore the value of dynamic, proteomic profiling over time for characterizing maladaptive responses to exertion in ME/CFS and provide a foundation for deeper mechanistic investigation into PEM.

Source: Germain A, Glass KA, Eckert MA, Giloteaux L, Hanson MR. Temporal dynamics of the plasma proteomic landscape reveals maladaptation in ME/CFS following exertion. Mol Cell Proteomics. 2025 Nov 12:101467. doi: 10.1016/j.mcpro.2025.101467. Epub ahead of print. PMID: 41237904. https://www.mcponline.org/article/S1535-9476(25)00566-3/fulltext (Full text)

Understanding concussion in myalgic encephalomyelitis/chronic fatigue syndrome: Findings from the 2023 National Health Interview study

Abstract:

Background: Although myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) symptoms (dysautonomia, dizziness, balance impairments) may theoretically contribute to an association with concussion, the nature of this association has not been determined. This study explored the association between ME/CFS and concussion, as well as risk factors for concussion, history of recent falls, and feelings of being dizzy or off balance.

Method: 2023 National Health Interview Survey data were utilized. United States adults (unweighted N = 29,373) responded to items regarding sociodemographic factors, ME/CFS status, and history of concussion, falls, and feeling off balance or dizzy. Logistic regression analyses assessed the association between ME/CFS and concussion, falls, and feeling dizziness or balance problems within the past year, adjusting for sociodemographic factors.

Results: Individuals with ME/CFS had 4.89 times greater odds of reporting concussion in the past year compared to individuals without ME/CFS. Individuals with ME/CFS also had 2.86 times greater odds of having fallen within the past year and 5.88 times greater odds of reporting feeling dizzy or off balance in the past year.

Conclusions: ME/CFS status may be associated with concussion status. Healthcare practitioners should improve concussion screening and referrals for reducing concussion risk among individuals with ME/CFS.

Source: Sirotiak Z, Adamowicz JL, Thomas EBK. Understanding concussion in myalgic encephalomyelitis/chronic fatigue syndrome: Findings from the 2023 National Health Interview study. Brain Inj. 2025 Oct 16:1-8. doi: 10.1080/02699052.2025.2575479. Epub ahead of print. PMID: 41103060. https://pubmed.ncbi.nlm.nih.gov/41103060/

The association of fatigue and pain with cognitive test performance in patients with myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Objectives: Patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) typically perform worse on cognitive tasks compared to controls. The present study explored the independent associations of fatigue and pain symptoms with cognitive performance in a large sample of patients who met CDC criteria of CFS (n = 1375), of whom most also met NICE/ IOM criteria (n = 1072). Moreover, we tested the hypothesis that these associations become stronger with older age and longer symptom duration.

Methods: Questionnaires and diaries were employed assessing fatigue and pain severity, together with the impact of health problems on daily life (using the SF-36 ‘Physical Functioning’ and ‘Bodily Pain’ subscales). Cognitive outcomes consisted of speeded performance measures, namely the Symbol Digit Test, motor speed, simple and choice reaction time (RT), and response inhibition. Categorical regression with lasso penalization was employed to identify relevant correlates of cognitive performance.

Results: Fatigue severity remained as only correlate of response inhibition. For the other cognitive outcomes, fatigue severity consistently emerged together with contributions of pain severity, bodily pain and/or physical functioning. Restricting these analyses to those patients meeting NICE/IOM criteria revealed overall similar results. Age, not symptom duration, moderated several relationships, showing more pronounced associations between cognitive performance and pain severity, physical functioning, and bodily pain with older age.

Conclusions: This study highlights that a multidimensional nature of symptoms, including fatigue and pain severity, and the impact on daily-life functioning, relate to lower cognitive performance in patients with ME/CFS. Studies are needed to identify the direction and potential causality of these associations.

Source: Oosterman JM, van der Schaaf M, de Kleijn WPE, Kuut TA, Brazil IA, Knoop H. The association of fatigue and pain with cognitive test performance in patients with myalgic encephalomyelitis/chronic fatigue syndrome. J Psychosom Res. 2025 Oct 3;199:112401. doi: 10.1016/j.jpsychores.2025.112401. Epub ahead of print. PMID: 41101039. https://www.sciencedirect.com/science/article/pii/S0022399925003654 (Full text)