A cardiometabolic perspective on post-exertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and Long COVID

Abstract:

Post-exertional malaise (PEM), the defining feature of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), is increasingly recognized in individuals with Long COVID. Although traditionally viewed as symptom exacerbation and/or emergence of new symptoms following exertion, PEM may reflect disrupted coordination across interconnected physiological systems operating over distinct post-exertional timescales. Such disruption may result in altered post-exertional physiological trajectories that contribute to multisystem manifestations and potential cardiometabolic consequences.

This perspective outlines a conceptual approach for investigating PEM through longitudinal assessment of post-exertional physiological trajectories while considering disease severity and underlying cardiometabolic health, including obesity and type 2 diabetes. Integrating these dimensions may help contextualize post-exertional responses, inform future longitudinal cardiometabolic profiling, facilitate patient stratification, and provide a framework for future mechanistic and interventional studies in ME/CFS and Long COVID.

Source: Westermeier F, Pretorius E, Untersmayr E, Bertinat R, Sepúlveda N, Fisman E. A cardiometabolic perspective on post-exertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and Long COVID. Cardiovasc Diabetol. 2026 Aug 20;25(1):250. doi: 10.1186/s12933-026-03316-8. PMID: 42625219. https://link.springer.com/article/10.1186/s12933-026-03316-8 (Full text)

Experimental hypoxia to probe neuro-metabolic and vascular dysregulation in ME/CFS: a multimodal proof-of-concept MRI study

Abstract:

Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a poorly understood, debilitating multisystem condition. Converging evidence implicates impaired cellular bioenergetics, neuroinflammation and defective neurovascular coupling that may manifest as “virtual hypoxia” only under physiological stress.

Methods: We performed a single-session multimodal 3T MRI study combining brain volumetry, arterial spin labelling (ASL) and multivoxel proton magnetic resonance spectroscopy under normoxia and two controlled hypoxic challenges (oxygen saturation 87 ± 3%) in 26 ME/CFS patients and 27 age- and sex-matched healthy controls.

Results: After intracranial-volume normalization, patients showed a reduced brainstem volume (1.46 ± 0.14 vs. 1.55 ± 0.18 % of eTIV; p = 0.013, FDR-p = 0.039), whereas deep grey matter and whole-brain parenchymal fraction did not differ between groups. Whole-brain cerebral blood flow (CBF) rose under hypoxia in both groups (controls +4.8 ± 13.0%, patients +3.7 ± 11.7%), with greater initial inter-individual variability in patients (patient-to-control variance ratio up to 6.94; FDR-p = 0.001). Thalamic lactate-to-creatine (Lac/tCr) ratios increased with hypoxia in controls (FDR-p = 0.028) but were already elevated at normoxia in patients (0.171 vs. 0.135; FDR-p = 0.021) and did not rise further (FDR-p = 0.38). In exploratory analyses, patients showed exaggerated inverse coupling between thalamic total N-acetylaspartate (tNAA/tCr) and white-matter CBF.

Conclusions: These findings provide in vivo evidence of impaired neuro-metabolic and vascular adaptive capacity in ME/CFS, supporting the virtual hypoxia hypothesis and highlighting candidate imaging markers for stratification that warrant validation.

Source:  Viola Bader, Katharina Estermann, Eva Niess, Tobias Zrzavy, Florian Fischmeister, Teresa Haider, Birgit Ludwig, Frederik Barkof, Henk JMM Mutsaerts, Gregor Kasprian, Fabian Niess, Wolfgang Bogner, Kathrin Kollndorfer, Lukas Haider. Experimental hypoxia to probe neuro-metabolic and vascular dysregulation in ME/CFS: a multimodal proof-of-concept MRI study. medRxiv 2026.08.10.26359935; doi: https://doi.org/10.64898/2026.08.10.26359935

Cerebrospinal fluid opening pressure in relation to symptomatology and craniocervical anatomy in patients with myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease that affects millions worldwide. Its cause remains unknown, although many physiological mechanisms are impaired. Structural abnormalities in the craniocervical region seem to be more prevalent in patients with ME/CFS, with a possible impact on intracranial pressure (ICP) and lumbar puncture (LP) measurements. This study aimed to quantify the occurrence of elevated cerebrospinal fluid (CSF) opening pressure and a possible association with clinical symptoms and radiological variables in craniocervical segments in a cohort of patients with ME/CFS.

Methods: This study included 34 patients previously diagnosed with ME/CFS as part of a larger case-control study, for whom LP was performed only in the case group. Key measurements included age, sex, opening pressure from LP, symptomatic relief post-LP, and radiological variables with potential influence on CSF dynamics. Individuals were stratified into two groups according to opening pressure (OP) measurements using 20 cmH2O as the cutoff value, with subsequent statistical comparisons.

Results: Overall, the majority of participants reported moderate disease severity (65%) and concomitant self-reported low quality of life. The median CSF opening pressure was 18 (IQR 8) cmH2O, ranging from 11 to 29.5. Opening pressure stratification showed that 21 of the 34 cases (62%) had an OP measurement of <20 cmH2O (low-OP group) and 13 cases (38%) had an OP measurement of ≥20 cmH2O (high-OP group). The two OP groups did not differ significantly in baseline characteristics, including disease severity and quality of life. However, for certain radiological measurements, the high-OP group presented with measures reflecting a wider spinal canal, including a significantly larger foramen magnum diameter (33.9 mm), which was higher than the measures in the low-OP group (31.7 mm). Estimates of symptom relief 1-4 days post-LP were significantly higher among patients in the high-OP group (80%) than among those in the low-OP group (19%).

Conclusion: This study suggests that a proportion of patients with ME/CFS have elevated CSF opening pressures and may experience symptom relief following CSF subtraction. Our data indicate that some anatomical structures in the craniocervical area may be related to CSF pressure, although interpretation is challenging and merits further investigation.

Source: Jolley C, Bragée B, Soinne L, Huhmar H, Billing H, Bertilson B, Sjogren P. Cerebrospinal fluid opening pressure in relation to symptomatology and craniocervical anatomy in patients with myalgic encephalomyelitis/chronic fatigue syndrome. Front Med (Lausanne). 2026 Aug 4;13:1869714. doi: 10.3389/fmed.2026.1869714. PMID: 42614190; PMCID: PMC13481257. https://pmc.ncbi.nlm.nih.gov/articles/PMC13481257/ (Full text)

Orthostatic intolerance with small heart and/or disequilibrium in patients with myalgic encephalomyelitis/chronic fatigue syndrome: clinical update and paradigm shift

Abstract:

Orthostatic intolerance (OI) is characterized by the inability to maintain an upright posture without experiencing severe signs and symptoms, including hypotension, palpitations, light-headedness, pallor, fatigue, weakness, dizziness, impaired concentration, tremulousness, and nausea. The majority of patients with myalgic encephalomyelitis (ME) or chronic fatigue syndrome (CFS) exhibit OI, which is the primary factor restricting daily functional capacity.

During an upright posture, approximately 800 mL of blood is translocated from the intrathoracic venous compartment to the veins of the buttocks, pelvis, and legs. Under normal conditions, compensatory cardiovascular responses to this orthostatic stress include activation of the muscle pump through calf muscle contraction and a neurogenically mediated increase in heart rate and in systemic vascular resistance. The majority of the symptoms of OI are believed to be cardiovascular and related to reduced cerebral blood flow and excessive activation of the sympathetic nervous system.

However, compensatory sympathetic activation is essential for maintaining orthostasis. Many patients have a small left ventricle and associated low cardiac output. In addition, both the renin-aldosterone and antidiuretic hormone systems that regulate circulatory blood volume were downregulated.

Postural stability is necessary for maintaining the static balance critical for performing many daily activities. Recently studies have reported that postural instability or disequilibrium, potentially associated with central vestibular dysfunction, should be considered to be involved in the pathogenesis of OI among patients with ME/CFS. Disequilibrium should be recognized as an important cause of OI in those patients.

Source: Miwa K. Orthostatic intolerance with small heart and/or disequilibrium in patients with myalgic encephalomyelitis/chronic fatigue syndrome: clinical update and paradigm shift. Front Med (Lausanne). 2026 Jul 29;13:1744154. doi: 10.3389/fmed.2026.1744154. PMID: 42591853; PMCID: PMC13463185.  https://pmc.ncbi.nlm.nih.gov/articles/PMC13463185/ (Full text)

Central noradrenergic deficiency in post-infectious chronic fatigue: Neurobehavioral correlates

Abstract:

Fatigue, brain fog and post-exertional malaise are major features of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome and post-acute sequelae of severe acute respiratory syndrome coronavirus 2. To date, no specific neurotransmitter abnormalities have been found in either condition. We examined the possibility of central catecholaminergic involvement and clinical correlates in post-infectious myalgic encephalomyelitis/chronic fatigue syndrome and post-acute sequelae of severe acute respiratory syndrome coronavirus 2 groups compared to healthy volunteers and, as positive controls, Parkinson’s disease patients.

In an observational, cross-sectional cohort study conducted at the National Institutes of Health Clinical Center we measured CSF levels of catecholamines and metabolites in the four groups and assessed correlations with neurobehavioral measures. CSF indices of the central Norepinephrine Pathway (norepinephrine + 3,4-dihydroxyphenylglycol + 3-methoxy-4-hydroxyphenylglycol) and Dopamine Pathway (dopamine + 3,4-dihydroxyphenylacetic acid + homovanillic acid) were measured and related to patient-recorded outcomes and physiological assessments.

Mean values for Norepinephrine Pathway activity (in pmol/mL) were lower in the post-infectious myalgic encephalomyelitis/chronic fatigue syndrome, post-acute sequelae of severe acute respiratory syndrome coronavirus 2, and Parkinson’s disease groups compared to the healthy volunteer cohort (post-infectious myalgic encephalomyelitis/chronic fatigue syndrome (-15.9, 95% confidence interval [-26.1, -5.7], P = 0.0006); post-acute sequelae of severe acute respiratory syndrome coronavirus 2 (-9.62, [-17.9, -1.4], P = 0.015); Parkinson’s disease (-19.4, [-27.5, -11.3], P < 0.0001)).

Post-acute sequelae of severe acute respiratory syndrome coronavirus 2 participants with post-exertional malaise had evidence of central noradrenergic deficiency compared to healthy volunteers (-18.3 [-31.3, -5.3], P = 0.0018). The post-infectious myalgic encephalomyelitis/chronic fatigue syndrome and post-acute sequelae of severe acute respiratory syndrome coronavirus 2 groups did not differ from the healthy group in values for the Dopamine Pathway index. Across all participants, Norepinephrine Pathway activity correlated positively with handgrip duration and general health and negatively with fatigue.

We conclude that post-infectious myalgic encephalomyelitis/chronic fatigue syndrome and post-acute sequelae of severe acute respiratory syndrome coronavirus 2 feature a specific central neurotransmitter pattern involving noradrenergic but not dopaminergic deficiency. The noradrenergic abnormality is associated with major symptoms such as post-exertional malaise.

Source: Aregawi L, Walitt B, Sullivan P, Norato G, Benjamin RN, Goldstein DS. Central noradrenergic deficiency in post-infectious chronic fatigue: neurobehavioral correlates. Brain Commun. 2026 May 13;8(3):fcag173. doi: 10.1093/braincomms/fcag173. PMID: 42205163; PMCID: PMC13202209. https://pmc.ncbi.nlm.nih.gov/articles/PMC13202209/ (Full text)

Perioperative outcomes in patients with myalgic encephalomyelitis/chronic fatigue syndrome undergoing general anesthesia: a retrospective matched-pair study

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic multisystem disease characterized by profound fatigue, post-exertional malaise, cognitive impairment, and autonomic dysfunction. Despite features with potential relevance for anesthesia and perioperative care, empirical data on perioperative outcomes in patients with ME/CFS remains limited. We therefore performed a retrospective matched-pair analysis to generate clinical data on perioperative responses and identify areas for future research.

Methods: We conducted a retrospective matched-pair analysis at a single tertiary center. All patients with ME/CFS undergoing general anesthesia from 2015 to 2026 were identified using ICD-10-GM codes with additional manual verification and matched 1:1 to controls for comparison. Patients with confounding diagnoses or American Society of Anesthesiologists physical status above III were excluded. The analysis focused on intraoperative hemodynamic parameters, including baseline, post-induction, median, and lowest recorded systolic blood pressure and heart rate, as well as early postoperative outcomes in the post-anesthesia care unit (PACU), including maximum pain scores and requirement for rescue analgesia.

Results: Out of 189 individuals identified through ICD-10 codes, 15 matched pairs were included after application of exclusion criteria. Patients with ME/CFS exhibited lower minimum intraoperative systolic blood pressure (90.0 [82.5-95.0] vs. 100.0 [90.0-110.0] mmHg, p = 0.044) and lower minimum heart rate (50.0 [40.0-57.5] vs. 60.0 [50.0-65.0] bpm, p = 0.012). Vasopressor use and fluid administration did not differ, and no episodes of severe hypotension or perioperative adverse events were observed. Postoperative pain was higher in ME/CFS, with higher maximum pain scores (NRS 5.0 [4.0-6.0] vs. 1.0 [0.0-4.0], p = 0.008) and more frequent opioid rescue analgesia (80% vs. 33%, p = 0.039). Postoperative nausea or vomiting, oxygen supplementation, and PACU length of stay were similar between groups.

Conclusions: In this small exploratory cohort, general anesthesia was not associated with clinically relevant hemodynamic instability in patients with ME/CFS. Postoperative pain scores and opioid rescue requirements were higher in the ME/CFS group. Post-exertional malaise, a key disease feature with potentially delayed onset and significant impact, was not captured and remains an important target for future research. These findings should be considered hypothesis-generating and support prospective studies evaluating perioperative management and patient-relevant outcomes in ME/CFS.

Source: Steinkirchner FM, Kaufmann CK, Kraus RF, Käss M, Schieffer E, Graf BM, Lassen C, Kimmerling V, Dejaco A. Perioperative outcomes in patients with myalgic encephalomyelitis/chronic fatigue syndrome undergoing general anesthesia: a retrospective matched-pair study. BMC Anesthesiol. 2026 Jul 16;26(1):426. doi: 10.1186/s12871-026-04102-5. PMID: 42464211. https://link.springer.com/article/10.1186/s12871-026-04102-5 (Full text available as PDF file)

Metabolomic Classification of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome via Explainable Ensemble Learning and Pareto-Guided Feature Selection

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem illness characterised by post-exertional malaise, non-restorative sleep, and cognitive impairment, yet no objective diagnostic biomarkers have been established. Untargeted plasma metabolomics provides a broad view of the biochemical disturbances underlying ME/CFS; however, the high dimensionality of omics datasets and the limited interpretability of conventional classifiers nevertheless hinder translation into clinical practice. This study evaluates three ensemble classifiers-Explainable Boosting Machine (EBM), XGBoost, and LightGBM-for binary ME/CFS classification using plasma metabolomic and lipidomic profiles from 197 participants (106 ME/CFS; 91 healthy controls; 888 features).

Feature dimensionality was reduced using a Pareto-Guided Recursive Neural Network (PRNN) pipeline. Model performance was assessed via 50-repeat stratified hold-out validation. EBM achieved the highest accuracy (0.909; 95% CI: 0.868-0.949) and area under the receiver operating characteristic curve (AUC: 0.940; 95% CI: 0.909-0.983), with XGBoost and LightGBM performing comparably. Interpretability analyses revealed that pairwise metabolite interaction terms-particularly proline & indole-3-lactate, tyrosine & N-acetylornithine, and maleic acid & arachidic acid-contributed the greatest discriminative signal.

An ablation analysis comparing the full interaction-augmented EBM (AUC = 0.940) with a main-effects-only EBM (AUC = 0.882) confirmed that pairwise metabolite co-variation contributes additional discriminative value beyond individual metabolite levels, implicating amino acid catabolism, tryptophan-kynurenine pathway dysregulation, mitochondrial energy impairment, and lipid remodelling as central pathophysiological features. Global and instance-level explanations jointly demonstrated population-level metabolic signatures alongside individual heterogeneity, highlighting the added clinical value of explainable artificial intelligence (XAI) in metabolomics.

These findings support EBM-based metabolomic profiling as an internally validated approach for ME/CFS classification, subject to external validation, calibration assessment, and prospective testing.

Source: Yagin FH, Korkmaz Y, Colak C, Alzakari SA, Alkhalifa AK, Al-Hashem F, Aghaei M. Metabolomic Classification of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome via Explainable Ensemble Learning and Pareto-Guided Feature Selection. Int J Mol Sci. 2026 Jun 30;27(13):5920. doi: 10.3390/ijms27135920. PMID: 42450188. https://www.mdpi.com/1422-0067/27/13/5920 (Full text)

Disrupted glymphatic function and its relationship with sleep and cognitive impairment in ME/CFS assessed via DTI-ALPS

Abstract:

The glymphatic system is a recently discovered brain waste clearance system that is mostly active during sleep and disengaged during wakefulness. Impaired glymphatic function leads to the deposition of metabolic waste products in the brain potentially causing inflammation leading to various symptoms in ME/CFS. While the glymphatic function has been assessed in other neurodegenerative diseases using ‘diffusion tensor imaging along the perivascular space’ (DTI-ALPS), it has not been studied in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS).

This preliminary study investigates glymphatic function in 58 participants (ME/CFS = 31 and healthy controls = 27) using the DTI-ALPS index derived from DTI data acquired with 3 T MRI. The bilateral hemispheric DTI-ALPS index was estimated to assess glymphatic function, and an asymmetry index was calculated to determine interhemispheric asymmetry in glymphatic function.

We found that the global DTI-ALPS index was significantly lower in ME/CFS patients compared to healthy controls (ME/CFS: 1.44 ± 0.086; healthy controls: 1.51 ± 0.11, p = 0.014), indicating reduced glymphatic function in ME/CFS. Examining the hemispheres separately, showed the right hemisphere DTI-ALPS index was lower in ME/CFS than healthy controls (ME/CFS = 1.41 ± 0.097; healthy controls = 1.49 ± 0.12; p = 0.009) but not different on the left. Additionally, we did not find any significant difference in asymmetry index between ME/CFS and healthy controls. We observed an association between the global DTI-ALPS index and severity of ‘sleep disturbance’ (p = 0.013, r = -0.47) and “impaired concentration” (p = 0.026, r = -0.43).

This study demonstrated impaired glymphatic function in ME/CFS which may lead to symptoms such as cognitive dysfunction and sleep disturbance experienced by ME/CFS.

Source: Thapaliya K, Marshall-Gradisnik S, Inderyas M, Barnden L. Disrupted glymphatic function and its relationship with sleep and cognitive impairment in ME/CFS assessed via DTI-ALPS. Front Neurosci. 2026 Jun 19;20:1875420. doi: 10.3389/fnins.2026.1875420. PMID: 42403482; PMCID: PMC13329448. https://pmc.ncbi.nlm.nih.gov/articles/PMC13329448/ (Full text)

Association between light exposure patterns and multidimensional health outcomes in individuals with myalgic encephalomyelitis/chronic fatigue syndrome: findings from an observational cross-sectional cohort study

Abstract:

Background: Light is a major environmental factor regulating circadian rhythms, sleep- wake cycles, and mood-related behaviors. Patients with Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often experience circadian disruption and poor sleep quality, which severely compromise their quality of life; however, the relationship between light exposure and illness severity remains largely unknown.

Methods: An observational cross-sectional cohort secondary study used collected data from 100 ME/CFS patients and 56 healthy controls to explore the impact of spontaneous light exposure on multidimensional health status and circulating biochemical parameters. Demographic and clinical features were assessed using validated patient-reported outcome measures. Light intensity, wrist temperature, and physical activity were continuously monitored at home over one week using wrist-worn actigraphy. Light intensity during predefined intervals and rhythmic variables of light cycle were calculated. Principal component analysis (PCA) was applied to reduce dimensionality of light variables. Multivariable analysis was performed adjusting for age, sex, body mass index, and physical activity.

Results: Following PCA of the light patterns, two components emerged across groups with high consistency: PC1 (explaining 61.7% of the total variance) reflected higher daytime light and rhythm stability, and PC2 (explaining 16.1%) represented nocturnal/early-morning light and rhythm instability. In ME/CFS patients, light variables were more extensively associated with clinical outcomes measures (FIS-40, PSQI and SF-36) than in healthy controls (all p < 0.05). Furthermore, PC2 was associated with higher levels of VCAM-1 and triglycerides, and lower serotonin concentrations (all p < 0.05). Four distinct light patterns were identified based on PCA scores: nocturnal light, healthy, adverse, and low diurnal light. ME/CFS patients exhibiting the healthy light pattern showed significantly lower fatigue, fewer sleep complaints, reduced autonomic dysfunction, and higher quality of life compared to those with the adverse light pattern (all p < 0.05). No significant differences were observed among healthy controls.

Conclusions: Light exposure patterns show distinct associations with symptom variability in ME/CFS compared to healthy controls. More stable daytime light appears to relate to better symptom profiles, whereas irregular exposure and nocturnal light are linked to poorer health outcomes. Although causality cannot be inferred, these findings highlight light exposure as a potentially modifiable, non-invasive target for behavioral interventions aimed at improving the quality of life in ME/CFS, representing a promising emerging for future translational research.

Source: Cambras T, Domingo JC, Sanmartín-Sentañes R, Alegre-Martín J, Castro-Marrero J. Association between light exposure patterns and multidimensional health outcomes in individuals with myalgic encephalomyelitis/chronic fatigue syndrome: findings from an observational cross-sectional cohort study. J Transl Med. 2026 Jul 3. doi: 10.1186/s12967-026-08556-6. Epub ahead of print. PMID: 42399727. https://link.springer.com/article/10.1186/s12967-026-08556-6 (Full text available as PDF file)

Tryptophan Metabolism and Aryl-Hydrocarbon Receptor Agonists in the Gut Microbiome of People With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic disease with unknown biological basis and no cure. Microbiome dysbiosis has been reported in people with ME/CFS but its relevance to pathophysiology is unknown. Gut microbes are an important source of tryptophan metabolites that activate the aryl hydrocarbon receptor (AHR), a regulator of homeostatic and inflammatory genes. Dysregulated activation of AHR contributes to pathophysiology of several neuroimmune and chronic diseases but its role in ME/CFS has not been investigated. The purpose of this study was to investigate the production of tryptophan metabolites and AHR agonists by gut microbes of people with ME/CFS.

We found lower diversity and altered microbiome community structure in people with ME/CFS and changes in the subcommunity of microbes that correlated with tryptophan metabolites. Using targeted metabolomics we identified nine metabolites elevated in the stool of people with ME/CFS, including three AHR agonists. Stool ex vivo cultures were tested for their capacity to activate AHR in a reporter cell line and by qPCR. AHR activation did not differ between people with ME/CFS and controls, however, we detected elevated agonist activity in people with neurocognitive symptoms, regardless of underlying disease.

These findings are consistent with previous work revealing changes in the gut microbiome of people with ME/CFS and adds further support to alterations in tryptophan metabolism associated with the disease. Altered AHR activity by gut microbial metabolites may be a common mechanism contributing to neurocognitive symptoms in diseases including ME/CFS.

Source: Esteban DJ, Conrad B, Cullinan A, Luong S, Albaum J, Wilk V. Tryptophan Metabolism and Aryl-Hydrocarbon Receptor Agonists in the Gut Microbiome of People With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Microbiologyopen. 2026 Jun;15(3):e70333. doi: 10.1002/mbo3.70333. PMID: 42325052. https://onlinelibrary.wiley.com/doi/10.1002/mbo3.70333 (Full text)