Category: Pathophysiology

3D Virtual Reality Performance Metrics as a Future Fatigue Biomarker in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disorder, characterized by symptoms such as post-exertional malaise (PEM) and cognitive impairments. This study assessed reaction time (RT) metrics in three-dimensional (3D) visual tasks with the aim of objectively quantifying the cognitive impairments in ME/CFS patients compared to controls.

Methods: A total of 120 participants (60 ME/CFS patients and 60 controls) were recruited at the Department of Ophthalmology, Universität of Erlangen-Nürnberg. RT was assessed using a virtual reality-oculomotor test system, presenting 3D stimuli at three disparity levels (275″, 550″, and 1100″) within three gaming repetitions (R1, R2, and R3). Mixed-effects models were used to evaluate group differences, with age and gender as covariates. Pairwise contrasts were calculated to assess changes across repetitions. Fatigue self-assessments were recorded by validated questionnaires, (FACIT Fatigue Scale, Chalder Fatigue Scale, Bell Score and Health Assessment Questionnaire), and their correlation with RT metrics was portrayed using a Spearman correlation matrix.

Results: Estimated means (EM-means) for RT were significantly prolonged in ME/CFS patients compared to controls at disparity 275″ (1969 ms vs. 1384 ms; p = 0.0001), 550″ (1409 vs. 1071 ms; p = 0.0012) and 1100″ (1126 ms vs. 891 ms; p = 0.00223). Age was a significant covariate (p < 0.001), while gender showed no effect. Both groups demonstrated improvements in RT over repetitions; however, ME/CFS patients showed a significantly lower improvement compared to controls, reaching significance in R3 (p = 0.0042). RT metrics did not correlate with patients’ self-assessment scores.

Conclusions: ME/CFS patients showed consistently slower RTs compared to controls, particularly in later, easier gaming repetitions, potentially reflecting the impact of fatigue.

Source: Ladek AM, Priebe L, Harrer T, Harrer E, Michelson G, Knauer TS, Dias-Nunes DX, Mardin CY, Bergua A, Hohberger B. 3D Virtual Reality Performance Metrics as a Future Fatigue Biomarker in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Biomedicines. 2026 Apr 9;14(4):855. doi: 10.3390/biomedicines14040855. PMID: 42072397. https://www.mdpi.com/2227-9059/14/4/855 (Full text)

 

Cardiopulmonary Exercise Testing Reveals Functional Limitations and Work Disability in Severe Post-COVID-19 and ME/CFS Patients

Abstract:

Background: Patients severely affected by post-COVID-19 condition (PCC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often experience long-term work incapacity, contributing to a growing economic burden. Organ-centered clinical diagnostics frequently fail to explain their work disability.

Objectives: We aimed to objectively assess physical work ability using cardiopulmonary exercise testing (CPET) in a cohort of long-standing and severely affected PCC patients. We hypothesized: (1) patients with ME/CFS exhibit lower peak oxygen uptake (VO₂peak [mL/min/kg]) and peak power output (PPO [W/kg]) than those without; (2) most patients demonstrate objective work disability, closely aligned with subjective perception of disability; (3) oxygen pulse (O2 pulse [mL/bpm]) is reduced in ME/CFS, independent of comorbidity.

Methods: The study was conducted in the Department of Sports Medicine, Prevention and Rehabilitation at Johannes Gutenberg-University Mainz (Mainz, Germany). Between July 31, 2023, and March 31, 2025, a total of 92 PCC patients with suspected occupational disease underwent symptom-limited CPET and completed the Canadian Consensus Criteria, Bell Disability Scale (Bell-Score), and DePaul Symptom Questionnaire (Post-Exertional Malaise) Short Form (DSQ-PEM).

Results: Nearly half of the patients (49%) met ME/CFS criteria and 79% screened positive on the DSQ-PEM. ME/CFS patients showed significantly lower VO₂peak (13.0 ± 3.1 vs. 15.4 ± 4.9, p = 0.012), PPO (0.9 ± 0.3 vs. 1.1 ± 0.5, p = 0.014), and O₂ pulse (7.7 ± 2.0 vs. 8.5 ± 1.9, p = 0.047) compared to those without ME/CFS. Overall, 66% of patients met objective thresholds for work disability (VO₂peak < 15 mL/min/kg or PPO < 1 W/kg). Forty-five patients (51%) had a Bell-Score ≤ 30 and 82% from those had VO₂peak < 15 and/or PPO < 1. VO₂peak and PPO significantly correlated with Bell-Score (r = 0.3, p = 0.005 and r = 0.3, p = 0.003) and were the lowest among patients on medical sick leave (13.3 ± 3.3 and 0.9 ± 0.3), compared to those in occupational reintegration (16.0 ± 3.9, p = 0.04 and 1.2 ± 0.5, p = 0.024) or currently working (18.0 ± 7.1, p = 0.036 and 1.2 ± 0.5, p = 0.015).

Conclusions: Severely affected PCC patients exhibit objective work disability, particularly those with ME/CFS. VO₂peak and PPO are associated with subjective disability and occupational status. Therefore, early integration of CPET into clinical and occupational evaluations can inform individualized therapy planning and return-to-work decisions.

Trial registration DRKS, DRKS00032394. Registered 28 July 2023, https://drks.de/search/de/trial/DRKS00032394.

Source: Tomaskovic A, Weber V, Ochmann DT, Hillen B, Neuberger EWI, Brahmer A, Lachtermann E, Lieb K, Simon P. Cardiopulmonary Exercise Testing Reveals Functional Limitations and Work Disability in Severe Post-COVID-19 and ME/CFS Patients. Sports Med Open. 2026 Apr 27;12(1):50. doi: 10.1186/s40798-026-00995-1. PMID: 42043742. https://link.springer.com/article/10.1186/s40798-026-00995-1 (Full text)

Neuroendocrine signature of ME/CFS: Meta-analytic evidence for bioactive cortisol deficit and exaggerated feedback sensitivity

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a major clinical challenge as a complex multisystemic disorder with no well-established pathophysiological mechanism, characterized by persistent fatigue and post-exertional malaise, along with unrefreshing sleep, cognitive impairment, and impaired stress recovery. Despite decades of investigation into the hypothalamic-pituitary-adrenal (HPA) axis, a definitive neuroendocrine hallmark has remained elusive due to inconsistent findings across various cortisol matrices. Therefore, this systematic review and meta-analysis aimed to provide an integrated understanding of HPA-axis regulation in ME/CFS.

We identified 46 case-control studies (comprising 46 independent datasets, including 12 pharmacological challenge studies), involving 1388 ME/CFS patients (71.9% female; mean age 37.3 ± 6.2 years) and 1349 matched healthy controls. Meta-analyses showed lower salivary cortisol at awakening and in the morning. Reductions were also observed in 24-h urinary cortisol and hair cortisol. In pharmacological challenge tests, patients exhibited impaired cortisol release in response to adrenocorticotropic hormone (ACTH) stimulation and exaggerated suppression following glucocorticoid administration.

Collectively, these alterations indicate reduced free cortisol availability and enhanced HPA-axis negative feedback sensitivity, consistent with a hyporeactive endocrine state in ME/CFS. This neuroendocrine hypo-reactivity may underlie hallmark clinical features such as unrefreshing sleep, post-exertional malaise, and severe fatigue, as well as cognitive slowing, emotional blunting, and diminished stress resilience frequently observed in ME/CFS and related functional disorders. Integrating neuroendocrine and psychological perspectives may help clarify mechanisms of chronic stress maladaptation and inform psychobiological interventions for fatigue syndromes.

Source: Woo TW, Choi YJ, Kim JY, Lee JS, Son CG. Neuroendocrine signature of ME/CFS: Meta-analytic evidence for bioactive cortisol deficit and exaggerated feedback sensitivity. Mol Psychiatry. 2026 Apr 23. doi: 10.1038/s41380-026-03608-1. Epub ahead of print. PMID: 42026257. https://pubmed.ncbi.nlm.nih.gov/42026257/

Pathophysiological, Translational, and Diagnostic Aspects of ME/CFS: A Focus on Skeletal Muscle Involvement

Abstract:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic, multisystemic disorder characterized by severe, persistent fatigue not alleviated by rest and worsened by minimal exertion, often accompanied by post-exertional malaise (PEM), unrefreshing sleep, cognitive dysfunction, and autonomic disturbances. Despite decades of research, its pathophysiology remains incompletely understood, and skeletal muscle involvement has only recently gained attention.

This review aims to provide a historical and pathophysiological synthesis of ME/CFS, emphasizing the pivotal role of skeletal muscle in the onset and persistence of symptoms, and to integrate molecular, cellular, and pathophysiological evidence into a coherent explanatory framework.

This is a narrative review of published literature (1990-2025) with critical integration of clinical, biochemical, and experimental data on oxidative stress, mitochondrial dysfunction, Excitation-Contraction (E-C coupling) dysregulation, and muscle secretome alterations in ME/CFS also in relation to post-viral syndromes (e.g., Long COVID).

Evidence consistently points to mitochondrial oxidative stress, redox imbalance, impaired Ca2+ handling, and altered signaling pathways in skeletal muscle of patients with ME/CFS. Historical milestones show an evolution from psychogenic interpretations toward recognition of ME/CFS as a biological disorder with neuromuscular and metabolic underpinnings.

ME/CFS can be interpreted as a skeletal muscle-metabolic disorder characterized by oxidative distress, mitochondrial dysfunction, and impaired energy regulation, leading to the clinical picture of exercise intolerance and post-exertional malaise. Integrating basic and clinical research through a translational approach provides the foundation for new diagnostic tools, targeted therapies, and biomarkers.

Source: Fanò-Illic G, Coscia F, Gigliotti PV, Checcaglini F, Carraro U, Fulle S, Mancinelli R. Pathophysiological, Translational, and Diagnostic Aspects of ME/CFS: A Focus on Skeletal Muscle Involvement. Diagnostics (Basel). 2026 Mar 28;16(7):1019. doi: 10.3390/diagnostics16071019. PMID: 41975732. https://www.mdpi.com/2075-4418/16/7/1019 (Full text)

Proteomic signatures in cerebrospinal fluid and their clinical associations in patients with ME/CFS

Abstract:

This study evaluated the cerebrospinal fluid (CSF) proteomes from 31 patients diagnosed with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). We quantified 902 proteins, each expressed in at least eleven samples, and systematically categorized clinical factors relevant to ME/CFS symptoms-including autonomic dysfunction, neuroinflammation and metabolic disturbances.

Differentially expressed protein and pathway analyses evaluated protein features associated with both postural orthostatic tachycardia syndrome (POTS) status and disease severity among the patients, while ratio-based analysis further explored associations with severity ratings.

Data are available via ProteomeXchange with identifier PXD076216. Neutrophil degranulation and platelet activation were enriched in patients with POTS, and several pathways, such as the complement cascade, coagulation-related pathways and IGFBP‑mediated insulin-like growth factor transport, were enriched in severe cases. Ratio-based analysis identified four biologically interpretable severity-associated protein ratios related to cellular stress, extracellular remodelling and immune-neuronal interaction.

Together, these findings provide insight into the biological processes associated with clinical heterogeneity in ME/CFS and generate hypotheses for future validation in larger independent cohorts.

Source: Bragée B, Li P, Meadows D, Widgren A, Sjögren P, Ghatan PH, Bertilson BC, Xiao W, Bergquist J. Proteomic signatures in cerebrospinal fluid and their clinical associations in patients with ME/CFS. Sci Rep. 2026 Apr 3. doi: 10.1038/s41598-026-46965-1. Epub ahead of print. PMID: 41932997.  https://www.nature.com/articles/s41598-026-46965-1 (Full text available as PDF file)

Charting the circulating proteome in ME/CFS using cross-system profiling to uncover mechanistic insights

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition often triggered by infections, with unclear mechanisms and no established biomarkers or treatments. We apply aptamer-based serum proteomics to 50 ME/CFS patients and 29 healthy controls, analyzing 7,326 protein targets.

We identify 1,823 aptamers with significant differences between the groups (845 after false discovery rate [FDR] correction). Distinct patterns of tissue- and process-specific changes are seen. There is a broad increase in secreted proteins, while intracellular proteins, e.g., from skeletal muscle, particularly show reduction. Immune cell-associated signatures indicate immune reprogramming, including a distinct reduction in proteins secreted by activated neutrophils. Focused secretome analysis supports intensified regulatory interactions related to immune activity, inflammation, vasculature, and metabolism.

Validation of measurements using antibody-based methods confirms findings for a selection of proteins. The uncovered serum proteome patterns in ME/CFS patients may contribute to understanding the pathophysiology and inform future biomarker research and therapeutic development.

Source: Hoel A, Hoel F, Dyrstad SE, Chapola H, Rekeland IG, Risa K, Alme K, Sørland K, Brokstad KA, Marti HP, Mella O, Fluge Ø, Tronstad KJ. Charting the circulating proteome in ME/CFS using cross-system profiling to uncover mechanistic insights. Cell Rep Med. 2026 Mar 4:102647. doi: 10.1016/j.xcrm.2026.102647. Epub ahead of print. PMID: 41785863. https://www.cell.com/cell-reports-medicine/fulltext/S2666-3791(26)00064-9?rss=yes (Full text)

Genetic depletion of the early autophagy protein ATG13 impairs mitochondrial energy metabolism, augments oxidative stress, induces the polarization of macrophages to the M1 inflammatory mode, and compromises myelin integrity in skeletal muscle

Abstract:

Objective: M1 macrophage activation is crucial in chronic inflammatory diseases, yet its molecular mechanism is unclear.

Results: Our study showed that hemizygous deletion of the early autophagy gene atg13 (Tg+/-ATG13) disrupts cellular autophagy, hinders mitochondrial oxidative metabolism, and increases reactive oxygen species (ROS) levels in splenic macrophages, leading to M1 polarization. After reducing the expression of the autophagy markers WDFY3 and LC3, flow cytometric analysis of M1/M2 markers (CD40, CD86, CD115, CD163, and CD206), decreasing oxygen metabolism, as evaluated by the ROS-sensor dye DCFDA, and Seahorse oxygen consumption studies revealed that ablation of the atg13 gene impairs mitochondrial function, triggering M1 polarization.

Additionally, redox imbalance may impair Sirtuin-1 activity via nitrosylation, increasing the level of acetylated p65 in macrophages and contributing to the inflammatory response in M1Mφs. Additionally, ablation of the atg13 gene resulted in increased infiltration of M1Mφs into the muscle vasculature, deterioration of myelin integrity in nerve bundles, and a reduction in muscle strength following treadmill exercise.

Conclusions: Our study shows that impaired ATG13-driven autophagy increases inflammation through sirtuin-1 inactivation and NF-κB activation, suggesting a role for ATG13 in post-exertional malaise (PEM).

Source: Toriola MA, Timlin E, Bulbule S, Reyes A, Adedeji OM, Gottschalk CG, Barua A, Arnold LA, Roy A. Genetic depletion of the early autophagy protein ATG13 impairs mitochondrial energy metabolism, augments oxidative stress, induces the polarization of macrophages to the M1 inflammatory mode, and compromises myelin integrity in skeletal muscle. Inflamm Res. 2026 Jan 27;75(1):26. doi: 10.1007/s00011-025-02158-6. PMID: 41591477; PMCID: PMC12847126. https://pmc.ncbi.nlm.nih.gov/articles/PMC12847126/ (Full text)

Systematic Examination of Gene Expression and Proteomic Evidence Across Tissues Supports the Role of Mitochondrial Dysregulation in ME/CFS

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic, multisystem disease characterized by post-exertional malaise and persistent fatigue. The cause of ME/CFS is not well understood, and there are no established biomarkers or FDA-approved pharmacotherapies. The clinical heterogeneity of ME/CFS presents challenges to diagnosis and treatment and necessitates collaborative efforts to generate robust findings. This study leveraged gene and protein expression data from the mapMECFS data repository and the DecodeME Genome-Wide Association Study (GWAS) to assess consistent gene signatures across studies.

The mitochondrial genes MT-RNR1 and MT-RNR2 exhibited lower expression in ME/CFS cases in two studies. Combining this with increased expression of mitochondrial genes in platelets from another study, this supports mitochondrial dysregulation as having a role in ME/CFS.

Furthermore, ME/CFS-associated genes were mapped to compounds in drug databases as possible treatments for further investigation. In muscle gene expression data, 107 approved compounds target 26 genes with functions relevant to mitochondrial support and immunomodulators. From the DecodeME GWAS, 83 approved compounds target 24 genes with functions related to energy metabolism and mitochondrial function.

Though little consistency in specific genes was observed across studies, which highlights the need for larger studies, mitochondrial dysfunction in ME/CFS cases was evident across studies.

Source: Keele GR, Enger M, Barnette Q, Ruiz-Esparza R, Alvarado M, Mathur R, Stratford JK, Giamberardino SN, Brown LM, Webb BT, Carnes MU. Systematic Examination of Gene Expression and Proteomic Evidence Across Tissues Supports the Role of Mitochondrial Dysregulation in ME/CFS. Int J Mol Sci. 2026 Feb 19;27(4):1997. doi: 10.3390/ijms27041997. PMID: 41752134. https://www.mdpi.com/1422-0067/27/4/1997 (Full text)

The potential causes of myasthenia and fasciculations in severely ill ME/CFS patients: the role of disturbed electrophysiology

Abstract:

Patients with severe myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are bedridden and suffer from hypersensitivities to light and noise, severe orthostatic intolerance reducing cerebral blood flow, and skeletal muscle symptoms, including loss of force, fatigue, pain, fasciculations, and cramps. Because neurological investigations exclude neuronal causes of myasthenia, we hypothesize a muscular pathomechanism.

In previous articles, we considered insufficient activity of the Na+/K+-ATPase to be the main cause of mitochondrial damage via high intracellular sodium that reverses the transport mode of the sodium-calcium-exchanger to import calcium, causing calcium overload. Low Na+/K+-ATPase activity also causes sarcolemmal depolarization, leading to less effective action potential propagation and loss of force. Depolarization brings the membrane potential closer to the threshold potential, causing hyperexcitability that explains fasciculations and cramps. These increase sodium influx during excitation to further increase the workload of Na+/K+-ATPase. Thereby, depolarization causes further depolarization.

Higher intracellular sodium favors calcium overload and mitochondrial damage, which lowers the energy supply of Na+/K+-ATPase and increases the reactive oxygen species, further inhibiting Na+/K+-ATPase. The muscle is in a state of depolarization even at rest. Depolarization and mitochondrial damage reinforce each other. Thus, dysfunction of Na+/K+-ATPase as a single mechanism can explain the different skeletal muscle symptoms of severely ill ME/CFS patients, comprising loss of force, fatigue, and fasciculations.

Source: Wirth KJ, Steinacker JM. The potential causes of myasthenia and fasciculations in severely ill ME/CFS patients: the role of disturbed electrophysiology. Front Physiol. 2026 Feb 2;16:1693589. doi: 10.3389/fphys.2025.1693589. PMID: 41705124; PMCID: PMC12907180. https://pmc.ncbi.nlm.nih.gov/articles/PMC12907180/ (Full text)

ME/CFS and Long COVID Demonstrate Similar Bioenergetic Impairment and Recovery Failure on Two-Day Cardiopulmonary Exercise Testing

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and Long Covid are characterized by post-exertional malaise (PEM). Similarities in disease presentation suggest important commonalities in bioenergetic impairment, but this hypothesis has not been demonstrated. The metabolic underpinnings of each disease can be elucidated by two cardiopulmonary exercise tests (CPET) administered 24 hours apart. This retrospective study examined physiological responses on two-day CPET in people with ME/CFS (63 females and 21 males), Long Covid (52 females and 27 males), and matched non-disabled control participants (51 females and 20 males).

Data were analyzed within sexes using repeated measures analysis of variance. All participants met maximal effort criteria. There were significant reductions in oxygen consumption (O₂) and workload at the ventilatory anaerobic threshold (VAT) in both patient groups compared to non-disabled controls, with larger effect sizes at VAT than at peak exertion. Performance decrements were observed in both sexes.

Females exhibited more pronounced abnormalities and significant group by test effects. No significant differences were observed between patient groups. Severe disability based on impaired O₂ was prevalent in both patient groups. Hemodynamic and ventilatory measures were within normal ranges. ME/CFS and Long Covid both involve a functionally significant bioenergetic failure complicated by inadequate post-exertional recovery, which is similar between the conditions and unexplained by hemodynamic and ventilatory changes.

Findings support the utility of two-day CPET as an objective measure of PEM and functional impairment. Future studies may integrate mechanistic biomarkers with two-day CPET as trial endpoints and to establish likely responses to treatments for PEM.

Source: Todd Davenport, Staci Stevens, Jared Stevens et al. ME/CFS and Long COVID Demonstrate Similar Bioenergetic Impairment and Recovery Failure on Two-Day Cardiopulmonary Exercise Testing, 22 January 2026, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-8606329/v1] https://www.researchsquare.com/article/rs-8606329/v1 (Full text available as PDF file)