Category: Overlapping Illnesses

Inflammatory and neuroinjury blood biomarkers across COVID-19 severity groups in individuals with persistent neurological symptoms

Abstract:

Persistent neurological symptoms such as cognitive impairment, fatigue, and neuropsychiatric disturbances are increasingly reported in patients with long COVID, with chronic neuroinflammation and neuronal injury proposed as potential contributors. To characterize inflammatory and neuroinjury-related biomarker patterns, we conducted a case-control study including 325 participants recruited at King Chulalongkorn Memorial Hospital between January 2022 and December 2023, comprising 265 individuals with persistent neurological symptoms following COVID-19 infection and 60 asymptomatic COVID-19 participants who did not develop long COVID symptoms.

Blood samples were analysed for inflammatory cytokines (IL-1β, IL-6, IL-8, TNF-α, IFN-α, IL-4) using multiplex immunoassays, and for neuroinflammatory and neurodegenerative biomarkers, including neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), phosphorylated tau181, and beta-amyloid peptides (Aβ40, Aβ42) using SIMOA and ELISA platforms. Among 265 participants with complete data (critical = 7, severe = 22, moderate = 79, mild = 157), patients with severe and critical COVID-19 exhibited significantly higher concentrations of IL-6, IL-1β, TNF-α, and IL-8, together with elevated NfL, GFAP, and phosphorylated tau181 levels, and reduced Aβ42/40 ratios.

Strong positive correlations between neurodegenerative biomarkers and pro-inflammatory cytokines were observed in critically ill patients, whereas these associations were weak or absent in mild and moderate cases. Older age was also associated with greater disease severity and increased risk of persistent neurological complications.

These findings indicate that individuals with persistent neurological symptoms following COVID-19, particularly those with a history of severe or critical disease, exhibited higher inflammatory and neuroinjury-related biomarker levels, while blood-based biomarkers such as NfL, GFAP, and phosphorylated tau181 may serve as minimally invasive tools for characterizing neurological involvement and identifying patients at risk of long-term neurological sequelae.

Source: Ruchisrisarod C, Kaewpom T, Wanthong P, Luechaipanit W, Bunprakob S, Ampoot W, Yomrat S, Hemachudha P, Supharatpariyakorn T, Thanapornsangsuth P, Tammachote R, Saraya AW. Inflammatory and neuroinjury blood biomarkers across COVID-19 severity groups in individuals with persistent neurological symptoms. Int J Immunopathol Pharmacol. 2026 Jan-Dec;40:3946320261465568. doi: 10.1177/03946320261465568. Epub 2026 Jul 16. PMID: 42460883; PMCID: PMC13376473. https://pmc.ncbi.nlm.nih.gov/articles/PMC13376473/ (Full text)

Biomarkers of post-acute infection syndrome: a systematic literature review

Abstract:

Background: Post-acute infection syndrome (PAIS) remained underrecognized before the COVID-19 pandemic, which further increased exposure by introducing a novel global cause. The global burden of post-acute COVID syndrome (PACS) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) alone is estimated at several tens of millions affected worldwide. Biomarker discovery is central to improving PAIS diagnosis and may provide therapeutic targets. This review summarizes current knowledge on biomarkers for PAIS, including PACS and ME/CFS.

Methods: A systematic literature search was conducted in PubMed and Web of Science. Inclusion criteria were: (1) studies including PAIS patients; (2) reporting laboratory or omics biomarkers; and (3) investigating biomarkers or pathomechanisms of PAIS. Although Guillain-Barré syndrome (GBS) is not PAIS, we have included it as a separate mechanistic comparator due to its prevalence in search results and its clinical and immunological similarities to PAIS.

Results: A total of 142 studies analyzing PAIS biomarkers were included. GBS was analyzed separately and later compared with the other results. Overall, the reviewed studies employed heterogeneous approaches. While similar types of data were frequently investigated, analytical methods varied and often focused only on a subset of molecules. The results indicate that amino acid, energy, and lipid metabolism, microbiome, mitochondrial stress, and miRNA networks are affected. All pathways are connected via NF-κB.

Discussion: PAIS is a multisystem disorder rooted in persistent immune activation, metabolic reprogramming, and systemic inflammation, driven not by active viral infection, but by dysregulated host responses. The NF-κB pathway serves as a unifying hub, connecting molecular, cellular, and clinical phenotypes. Our framework enables a shift from symptom-based to mechanism-based classification, paving the way for biologically grounded interventions.

Conclusion: This review synthesizes a broad spectrum of biomarkers in PAIS, integrating findings across pathogens and molecular levels rather than restricting to individual conditions or symptom clusters. This study highlights the differences and commonalities among pathogens and diseases that lead to post-acute sequelae, fills a critical knowledge gap, and provides a foundation for future research and clinical practice. Future studies incorporating multi-omics approaches, longitudinal designs, and larger patient cohorts are needed to validate specific biomarkers and advance the understanding of PAIS.

Source: Wendt K, Schieck M, Gille C, Marschollek M, Illig T, Wolff D, Nee S. Biomarkers of post-acute infection syndrome: a systematic literature review. Front Immunol. 2026 Jun 30;17:1741761. doi: 10.3389/fimmu.2026.1741761. PMID: 42454043; PMCID: PMC13365053. https://pmc.ncbi.nlm.nih.gov/articles/PMC13365053/ (Full text)

Therapeutic plasma exchange and immunomodulatory strategies in post-infectious syndromes: A review of immune dysregulation in PTLDS, long COVID, ME/CFS, and PANS/PANDAS

Abstract:

Post-infectious syndromes including post-treatment Lyme disease syndrome (PTLDS), long COVID, myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and pediatric acute-onset neuropsychiatric syndrome (PANS)/pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) share overlapping clinical phenotypes characterized by fatigue, cognitive dysfunction, sleep disturbance, and neuropsychiatric symptoms. Increasing evidence suggests that immune dysregulation-including persistent inflammation, autoantibody production, and cellular immune dysfunction-may underlie these conditions.

This narrative review synthesizes peer-reviewed literature describing immune abnormalities across these syndromes and evaluates the rationale for immunomodulatory therapies, including intravenous immunoglobulin (IVIG), rituximab, and therapeutic plasma exchange (TPE). Evidence supporting immune-targeted treatment strategies is strongest in subsets of patients with identifiable immunologic abnormalities. Notably, the phase III RituxME trial in ME/CFS and a phase II trial of TPE in post-COVID condition both failed to demonstrate efficacy in unselected populations, reinforcing the importance of biomarker-guided patient stratification. TPE functions by removing circulating immune complexes, autoantibodies, and inflammatory mediators, and observational data suggest benefit in patients with demonstrable autoantibody burden. Further controlled studies incorporating immunologic phenotyping and early intervention are needed to define the therapeutic role of immune-directed interventions across these conditions.

Source: Kaplan G. Therapeutic plasma exchange and immunomodulatory strategies in post-infectious syndromes: A review of immune dysregulation in PTLDS, long COVID, ME/CFS, and PANS/PANDAS. Transfus Apher Sci. 2026 Jun 26;65(4):104482. doi: 10.1016/j.transci.2026.104482. Epub ahead of print. PMID: 42391726.  https://pubmed.ncbi.nlm.nih.gov/42391726/

Systems neuroendocrinology in ME/CFS and long COVID: a chronobiological framework for hormone-based research

Abstract:

Hormonal dysregulation is increasingly reported in ME/CFS and Long COVID, yet the broader role of neuroendocrine disruption in these conditions remains underexplored. While changes in steroid, peptide, and neuropeptide hormones have been identified, these findings are often considered in isolation and without attention to their timing or integration within broader physiological systems. The hypothalamic-pituitary axes regulate endocrine, immune, autonomic, nervous, and metabolic functions, systems commonly affected in both conditions, yet their circadian and menstrual dynamics are rarely investigated.

In this review, we examine the evidence for neuroendocrine dysfunction in ME/CFS and Long COVID, focusing on hormone output, functional assays, receptor expression, and the coordination of endocrine biorhythms. Sex hormone signalling emerges as a key area of vulnerability, particularly given the female predominance in both conditions and the complexity of reproductive hormone regulation.

We argue that accurate hormone measurement and time-structured sampling, including circadian and menstrual rhythms, are essential for detecting meaningful biological differences. By embedding chronobiology-aware, dense-sampling strategies and integrating multi-omic analyses into multi-system study designs, we outline a framework for investigating dynamic endocrine mechanisms underlying symptom variability and multisystem dysfunction, which may ultimately support the development of more targeted, personalised interventions.

Source: Thomas N, Huang K, Schneider-Futschik EK, Pollack B, Tal MC, Fineberg D, Wang X, Gurvich C, Pretorius R, Bergquist J, Armstrong CW. Systems neuroendocrinology in ME/CFS and long COVID: a chronobiological framework for hormone-based research. Front Neuroendocrinol. 2026 Jun 19:101268. doi: 10.1016/j.yfrne.2026.101268. Epub ahead of print. PMID: 42320559. https://www.sciencedirect.com/science/article/abs/pii/S0091302226000385 (Full text)

Two-timepoint multidomain follow-up of post-COVID condition and ME/CFS: overlapping autonomic, small-fiber, and cognitive changes

Abstract:

Background: Post-COVID condition (PCC) and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) show marked clinical overlap, suggesting a shared post-infectious pathophysiology. This study aims to characterize the longitudinal change of autonomic function, small-fiber integrity, cognitive performance, and clinical symptoms in PCC and ME/CFS, and to determine whether trajectories differ between diagnostic groups.

Methods: Thirty-eight participants (21 PCC, 17 ME/CFS) underwent two standardized evaluations separated by a median of 31 months. Assessments included comprehensive autonomic testing, small-fiber evaluation, and an extensive neuropsychological battery.

Results: ME/CFS showed longer disease duration than PCC at baseline (median 42 vs. 12 months), while the interval between evaluations was comparable (31 vs. 30 months). Baseline profiles were largely overlapping, although ME/CFS showed nominally higher QST warm detection thresholds (p = 0.034), greater autonomic symptom burden (p = 0.038), and lower hemodynamic scores (p = 0.019), none surviving FDR correction. Cross-domain analyses linked small-fiber symptoms with autonomic symptom burden (Rho = 0.65, pFDR = 0.002) and fatigue (Rho = 0.55, pFDR = 0.018), while fatigue was negatively associated with processing speed (Rho = – 0.57, pFDR = 0.004), attention (Rho = – 0.49, pFDR = 0.018), and executive function (Rho = – 0.44, pFDR = 0.047). Rank-transformed mixed-effects models identified FDR-corrected Time effects, with increases in CHEPs (pFDR < 0.001) and verbal memory (pFDR = 0.010), and decreases in processing speed (pFDR = 0.006) and QST cold thresholds (pFDR = 0.038).

Conclusions: PCC and ME/CFS showed broadly overlapping multidomain profiles, with particularly similar profiles at follow-up. This suggests that, among individuals with persistent symptoms, PCC may increasingly resemble longer-standing ME/CFS across autonomic, small-fiber/sensory, and cognitive domains. These findings are consistent with overlapping post-infectious mechanisms, but do not establish identical disease trajectories or definitive disease convergence.

Source: Azcue N, Barranco C, Tijero-Merino B, Acera M, Fernández-Valle T, Lafuente JV, Gabilondo I, Ruiz-Lopez M, Del Pino R, Gómez-Esteban JC. Two-timepoint multidomain follow-up of post-COVID condition and ME/CFS: overlapping autonomic, small-fiber, and cognitive changes. J Transl Med. 2026 Jun 12. doi: 10.1186/s12967-026-08321-9. Epub ahead of print. PMID: 42286686. https://link.springer.com/article/10.1186/s12967-026-08321-9 (Full study available as PDF file)

Dynamic microclot profiling: thromboelastography advances precision management in long COVID and myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) share overlapping symptoms, and emerging evidence implicates persistent fibrinoid microclots in their pathophysiology, contributing to impaired microcirculation. This review explores the role of microclots and evaluates thromboelastography (TEG) as a potential diagnostic tool.

A comprehensive literature review was conducted using major biomedical databases. Studies indicate microclots are prevalent in both conditions. Long COVID patients demonstrate a TEG profile of increased clot strength (maximum amplitude) and reduced fibrinolysis (LY30), suggesting a persistent hypercoagulable state. Despite its advantages in real-time assessment, TEG interpretation faces challenges from preanalytical variability and a lack of standardized protocols. Promising therapeutic trials, including anticoagulants (e.g., apixaban) and fibrinolytics (e.g., lumbrokinase), require further validation. Technological advancements like AI-driven TEG analysis and portable devices could improve diagnostic precision.

In conclusion, persistent microclots are a key pathophysiological feature. TEG provides a promising, novel approach for detecting coagulation abnormalities and could guide treatment, but requires standardization in future clinical trials. Future research should integrate multiomics biomarkers for precision therapeutics to improve patient outcomes.

Source: Saleem S, Hussain A, Haroon M, Raza A, Afzal U, Anwar MF, Imran S, Iqbal MU, Hajj F. Dynamic microclot profiling: thromboelastography advances precision management in long COVID and myalgic encephalomyelitis/chronic fatigue syndrome. Blood Coagul Fibrinolysis. 2026 Jun 11. doi: 10.1097/MBC.0000000000001439. Epub ahead of print. PMID: 42274123. https://pubmed.ncbi.nlm.nih.gov/42274123/

Multi-omics analysis of long COVID (post-COVID-19 condition) reveals persistent mitochondrial dysfunction, suppressed oxidative phosphorylation, and immune dysregulation

Abstract:

Introduction: Post-COVID Syndrome (PCS), or long-COVID, is a major public health burden, but its underlying mechanisms remain poorly understood. Because acute SARS-CoV-2 infection induces marked suppression of mitochondrial oxidative phosphorylation (OXPHOS), we investigated whether persistent immunometabolic remodeling is a recurring transcriptional, metabolic, and proteomic feature of PCS.

Methods: We performed an integrated multi-omics analysis of transcriptomic, proteomic, and metabolomic datasets across multiple tissues from Syrian hamster models and human cohorts spanning acute infection through post-acute and PCS stages extending up to 12 months post-infection.

Results: Across species and tissues, we observed overlapping signatures of mitochondrial dysfunction, including sustained suppression of OXPHOS, activation of mitochondrial stress responses, and enrichment of inflammatory pathways. Skeletal muscle exhibited the most pronounced and persistent mitochondrial repression in both hamsters and PCS patient biopsies, consistent with fatigue-associated phenotypes. Hamster heart and kidney tissues also showed persistent OXPHOS suppression, while lung tissue demonstrated prolonged inflammatory signaling despite partial metabolic recovery. In the nervous system, transcriptional profiles revealed region-specific patterns, including persistent cortical mitochondrial repression and partial recovery in sensory-associated regions. Peripheral blood mononuclear cells (PBMCs) transcriptomics and serum metabolic datasets suggested prolonged downregulation of OXPHOS-associated programs up to 12 months post-infection, potentially contributing to persistent immune dysregulation in susceptible individuals with underlying conditions. Longitudinal serum proteomics in PCS patients revealed sustained mitochondrial stress responses, increased oxidative stress signatures, and persistent immune activation at 1 and 6 months post-infection compared to recovered controls.

Discussion: Together, these multi-omics results identify persistent mitochondrial repression and immune dysregulation as recurring features across PCS-associated datasets, providing a framework linking bioenergetic dysfunction with chronic immune activation and supporting future mechanistic and therapeutic investigation.

Source: Tasoula A, Arif S, Waisberg E, Bauer L, Aslinger E, Guarnieri JW. Multi-omics analysis of long COVID (post-COVID-19 condition) reveals persistent mitochondrial dysfunction, suppressed oxidative phosphorylation, and immune dysregulation. Front Immunol. 2026 May 21;17:1776555. doi: 10.3389/fimmu.2026.1776555. PMID: 42253978; PMCID: PMC13234542. https://pmc.ncbi.nlm.nih.gov/articles/PMC13234542/ (Full text)

Health-related quality of life changes in patients with Q-fever fatigue syndrome: a four-year follow-up study, 10 years post-infection

Abstract:

Purpose: Q-fever can cause long-term health complications such as Q-fever Fatigue Syndrome (QFS), which may severely impact patients’ Health-Related Quality of Life (HRQoL). This study investigated change of HRQoL in QFS patients over time, and explored predictors associated with change using longitudinal data.

Methods: In this prospective observational study questionnaires were administered among Dutch individuals with self-reported QFS who were registered at Q-support, a foundation that supports, advises and informs Q-fever patients. Participants completed four annual questionnaires between 2021 and 2024, including EQ-5D-5L and EQ VAS to measure HRQoL. Changes in HRQoL were categorized as “improvement”, “deterioration”, or “stable”, using an anchor-based minimal important difference approach. Multinomial logistic regression analyses identified predictors of change.

Results: A total of 199 patients were included in the final analysis. At baseline, median EQ-5D-5L utility index and EQ VAS scores were 0.647 (IQR: 0.352-0.774), and 50.0 (IQR: 34.0-60.0), respectively. After four years, 37% of patients showed improvement in EQ-5D-5L utility, 30% deterioration, and 33% remained stable. Female sex and higher baseline EQ-5D-5L utility were associated with lower odds of improvement or being stable.

Conclusion: More than 10 years post-infection, HRQoL remains consistently low at group level among patients with QFS, with substantial long-term variability in individual outcomes. These findings underscore the chronic nature of QFS, its long-lasting consequences, and the importance of continued monitoring of individual health trajectories. Further studies are warranted to better understand the mechanisms underlying individual differences in recovery and to inform targeted interventions for this patient population.

Source: Stemerdink NC, Heemskerk SCM, Hartman E, Wesseling M, Tieleman P, Burdorf A, Haagsma JA. Health-related quality of life changes in patients with Q-fever fatigue syndrome: a four-year follow-up study, 10 years post-infection. Qual Life Res. 2026 Jun 8;35(7):191. doi: 10.1007/s11136-026-04295-9. PMID: 42260029; PMCID: PMC13246837. https://pmc.ncbi.nlm.nih.gov/articles/PMC13246837/ (Full text)

Comparative Gut Microbiome Alterations in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome & Long COVID-19 Syndrome

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID-19 syndrome (LC) show substantial clinical overlap, but direct comparative microbiome studies remain limited.
Methods: In this cross-sectional study, we compared the fecal gut microbiome of patients with ME/CFS, LC, and healthy controls (HC) within a unified analytical framework using 16S rRNA profiling, differential abundance testing, and multivariate modeling. We also examined associations between microbiome variation and questionnaire-derived symptom-domain scores.
Results: Alpha-diversity did not differ significantly among groups, whereas beta-diversity analyses showed small but significant disease-associated community differences with broad overlap between cohorts. Differential abundance analysis identified stronger signals in disease-versus-control contrasts than in the direct ME/CFS vs. LC contrast. Both ME/CFS and LC shared enrichment of Sutterella and depletion of Terrisporobacter and Lachnospiraceae relative to HC. Predicted functional profiling showed shared disease-versus-control changes in pathways related to anaerobic acetate/H2 carbon flow, inositol/polyol degradation, phosphonate/C1-related metabolism, and lysine-derived fermentation. Regression analyses showed the strongest microbiome associations with fatigue-related and physiosomatic domains, while affective, cognitive, and gastrointestinal outcomes showed weaker signals.
Conclusions: Overall, these findings support the presence of overlapping but non-identical gut microbiome alterations in ME/CFS and LC. The results provide a basis for future longitudinal and multi-omics studies aimed at clarifying the stability, functional relevance, and clinical utility of these microbial patterns.
Source: Donchev D, Nikolova R, Vaseva K, Taskov H, Murdjeva M, Maes M, Ivanov IN. Comparative Gut Microbiome Alterations in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Long COVID-19 Syndrome. Biomedicines. 2026; 14(6):1183. https://doi.org/10.3390/biomedicines14061183 https://www.mdpi.com/2227-9059/14/6/1183 (Full text available as PDF file)

Immune remodeling and metabolic reprogramming in chronic fatigue: insights into GPCR signaling and epigenetic regulation

Abstract:

Inflammation-driven fatigue is a clinically significant feature of several chronic inflammatory conditions, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), post-COVID condition, autoimmune disease, and cancer-related fatigue. Across these conditions, partially overlapping disturbances in immune regulation, cellular metabolism, and neuroimmune signaling may contribute to persistent fatigue, despite important differences in initiating context and biological substrate. Current evidence implicates mitochondrial dysfunction, altered glycolysis and fatty acid utilization, lactate- and succinate-associated signaling, metabolite-sensing G protein-coupled receptor (GPCR) pathways, epigenetic acylation, and immune remodeling in the maintenance of fatigue.

This narrative review synthesizes both shared and disease-context-specific mechanisms underlying inflammation-associated fatigue, with particular emphasis on immunometabolism, peripheral-central neuroimmune crosstalk, metabolite-GPCR signaling, and epigenetic regulation.

We highlight GPCR signaling as a potentially important regulatory interface in inflammatory and metabolic pathways relevant to fatigue, while recognizing that direct causal evidence in human fatigue syndromes remains limited.

The review also examines how metabolite-mediated epigenetic acylation may influence immune cell function and fatigue-related biology, although this association remains incompletely validated in fatigue-specific settings. By integrating metabolic dysregulation, neuroimmune signaling, and immune dysfunction, this review consolidates current knowledge on candidate biomarkers, mechanistic pathways, and emerging therapeutic targets in chronic inflammation-driven fatigue.

Overall, this review provides a multidimensional framework for understanding fatigue across inflammatory disorders and for guiding future mechanistic and translational research.

Source: Hu Z, Wang J, Ma S, Zhuang J, Shi J, Zhu Y. Immune remodeling and metabolic reprogramming in chronic fatigue: insights into GPCR signaling and epigenetic regulation. Front Immunol. 2026 May 15;17:1806420. doi: 10.3389/fimmu.2026.1806420. PMID: 42220511; PMCID: PMC13218923. https://pmc.ncbi.nlm.nih.gov/articles/PMC13218923/ (Full text)