Fatigue-PEM Relationship: Definitional and Construct Validity Studies

1 IOM 2015 — Beyond ME/CFS: Redefining an Illness

• Full Citation:: Institute of Medicine. Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. Washington, DC: The National Academies Press; 2015. (Institute of Medicine 2015)
• DOI:: 10.17226/19012
• PMID:: 25695122
• Key Findings::
  • Introduced SEID (Systemic Exertion Intolerance Disease) diagnostic criteria with PEM as the hallmark symptom
  • Requires both PEM and fatigue for diagnosis; PEM characterized as multi-symptom worsening, not simply fatigue
  • Recommended that PEM be operationalized through frequency/severity of symptom exacerbation after exertion
  • Identified PEM, unrefreshing sleep, cognitive impairment, and orthostatic intolerance as core diagnostic features
• Conclusion:: The IOM 2015 report established PEM as the defining feature of ME/CFS, conceptually distinct from simple fatigue. Both constructs are required for diagnosis, but PEM is not reducible to fatigue.
• Limitations:: Institutional consensus report, not an empirical study; the SEID terminology was not widely adopted; diagnostic criteria have not been prospectively validated against biomarkers.

2 Conroy et al. 2023 — Empirical Case Definition via Factor Analysis

• Full Citation:: Conroy KE, Islam MF, Jason LA. Evaluating case diagnostic criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): toward an empirical case definition. Disability and Rehabilitation. 2023;45(5):840–847. (Conroy, Islam, and Jason 2023)
• DOI:: 10.1080/09638288.2022.2043462
• PMID:: 35236205
• Key Findings::
  • Factor analysis of n=2,308 international ME/CFS patients identified 7 symptom domains
  • PEM, cognitive dysfunction, and sleep dysfunction emerged as primary factors
  • Pain did NOT emerge as an independent factor — contrasts with CCC and ICC criteria
  • Factor solution best aligned with CCC (which requires PEM) rather than IOM or ME-ICC
• Conclusion:: PEM is an empirically distinct symptom domain, separable from other ME/CFS symptoms. The CCC framework most closely matches empirical symptom clustering.
• Limitations:: Self-report data; convenience sample recruited online; cross-cultural generalizability needs validation.

3 Davenport et al. 2023 — Two-Symptom PEM Clinical Prediction Rule

• Full Citation:: Davenport TE, Chu L, Stevens SR, Stevens J, Snell CR, Van Ness JM. Two symptoms can accurately identify post-exertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome. Work. 2023;74(4):1199–1213. (Davenport et al. 2023)
• DOI:: 10.3233/WOR-220554
• PMID:: 36938769
• Key Findings::
  • Only 1–2 symptoms needed to differentiate ME/CFS from sedentary controls after CPET
  • Fatigue, cognitive dysfunction, lack of positive feelings/mood, and decline in function were the most discriminating symptoms
  • Fatigue is one of four discriminating symptoms — PEM is multi-symptom, not solely fatigue
• Conclusion:: PEM can be identified efficiently with a small set of symptoms; fatigue is necessary but not sufficient for PEM identification.
• Limitations:: Small sample (n=49 ME/CFS, n=10 controls); Fukuda criteria used; CPET-based provocation may not capture all PEM triggers.

4 Brown & Jason 2020 — Meta-Analysis of PEM as Cardinal Symptom

• Full Citation:: Brown A, Jason LA. Meta-analysis investigating post-exertional malaise between patients and controls. Journal of Health Psychology. 2020;25(13–14):2053–2071. (Brown and Jason 2020)
• DOI:: 10.1177/1359105318784161
• PMID:: 29974812
• Key Findings::
  • PEM was 10.4× more likely in ME/CFS patients vs controls (meta-analytic odds ratio)
  • Patient recruitment strategy and control selection were significant moderators of effect size
  • Concluded PEM should be considered a cardinal symptom of ME/CFS
• Conclusion:: The strength of the PEM–ME/CFS association supports PEM as a defining feature that distinguishes ME/CFS from other fatiguing conditions.
• Limitations:: Studies used varied PEM operationalizations; heterogeneity in case definitions across included studies.

5 McManimen et al. 2019 — Deconstructing PEM: Two-Factor Structure

• Full Citation:: McManimen SL, Sunnquist ML, Jason LA. Deconstructing post-exertional malaise: an exploratory factor analysis. Journal of Health Psychology. 2019;24(2):188–198. (McManimen, Sunnquist, and Jason 2019)
• DOI:: 10.1177/1359105316664139
• PMID:: 27557649
• Key Findings::
  • Exploratory factor analysis found PEM is composed of two empirically distinct experiences
  • Factor 1: generalized fatigue (whole-body exhaustion)
  • Factor 2: muscle-specific fatigue (localized musculoskeletal exhaustion)
• Conclusion:: PEM is not a unitary fatigue construct. It has at least two sub-components, neither of which maps to simple “being tired.” This has implications for PEM operationalization in diagnostic criteria.
• Limitations:: Small sample; Fukuda criteria; self-report data; exploratory (not confirmatory) factor analysis.

6 Lim & Son 2020 — Systematic Review of 25 ME/CFS Case Definitions

• Full Citation:: Lim EJ, Son CG. Review of case definitions for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Journal of Translational Medicine. 2020;18(1):289. (Lim and Son 2020)
• DOI:: 10.1186/s12967-020-02455-0
• PMID:: 32727489
• Key Findings::
  • Reviewed 25 case definitions from 1986 to 2020; categorized into ME, ME/CFS, CFS, and SEID
  • PEM is compulsory in ME and ME/CFS definitions (CCC, ICC, IOM) but optional or absent in CFS/Fukuda
  • Fatigue, cognitive impairment, PEM, sleep disorder, and orthostatic intolerance were the overlapping symptoms across all four categories
  • SEID (IOM 2015) requires both fatigue AND PEM
• Conclusion:: The historical evolution of case definitions shows progressive recognition of PEM as a compulsory feature. Older definitions (Fukuda) that do not require PEM capture a more heterogeneous, potentially less specific patient population.
• Limitations:: Review, not meta-analysis; did not empirically test which definition produces the most valid cohort.

7 Stussman et al. 2025 — Self-Reported vs Objectively-Assessed PEM in Long COVID

• Full Citation:: Stussman B, Camarillo N, McCrossin G, et al. Post-exertional malaise in Long COVID: subjective reporting versus objective assessment. Frontiers in Neurology. 2025;16:1534352. (Stussman et al. 2025)
• DOI:: 10.3389/fneur.2025.1534352
• PMID:: 40337174
• Key Findings::
  • Self-reported PEM was 67% in Long COVID questionnaire cohort (n=244)
  • Only 5.9% (2/34) had observable PEM after standardized CPET in the exercise cohort
  • Long COVID PEM responses to CPET were less severe and prolonged than in ME/CFS
  • 64.7% of Long COVID patients expressed positive themes after CPET
• Conclusion:: Self-reported PEM substantially overestimates objectively-provocable PEM in Long COVID. Exercise testing to determine PEM presence may have clinical utility. The self-report/objective gap suggests many patients conflate fatigue with PEM.
• Limitations:: Small exercise cohort (n=34 Long COVID, n=9 ME/CFS); CPET as sole provocation method may miss PEM triggered by cognitive/emotional exertion.

8 May et al. 2020 — PEM Severity Stratifies Symptom Burden in Fukuda-Diagnosed CFS

• Full Citation:: May M, Milrad SF, Perdomo DM, et al. Post-exertional malaise is associated with greater symptom burden and psychological distress in patients diagnosed with Chronic Fatigue Syndrome. Journal of Psychosomatic Research. 2020;129:109893. (May et al. 2020)
• DOI:: 10.1016/j.jpsychores.2019.109893
• PMID:: 31884303
• Key Findings::
  • n=261 CFS patients (Fukuda criteria); hiPEM vs loPEM groups compared
  • hiPEM patients had significantly greater symptom intensity, frequency, interference, depressive symptoms, and mood disturbance
  • PEM status stratified patients on outcomes even though Fukuda criteria do not require PEM
• Conclusion:: PEM severity captures clinically meaningful heterogeneity within Fukuda-diagnosed CFS that baseline fatigue alone does not. This supports PEM as a construct distinct from and additive to fatigue.
• Limitations:: Cross-sectional; self-reported PEM severity; Fukuda criteria may include patients without true ME/CFS.

9 Cotler et al. 2018 — Brief PEM Questionnaire Operationalization

• Full Citation:: Cotler J, Holtzman C, Dudun C, Jason LA. A brief questionnaire to assess post-exertional malaise. Diagnostics. 2018;8(3):66. (Cotler et al. 2018)
• DOI:: 10.3390/diagnostics8030066
• PMID:: 30208578
• Key Findings::
  • Five supplementary DSQ PEM duration items correctly classified ME/CFS patients 81.7% of the time
  • Incorrectly classified MS and post-polio syndrome as ME/CFS only 16.6% of the time
  • Second-step PEM operationalization per NIH/CDC Common Data Elements recommendations
• Conclusion:: PEM can be operationalized with brief instruments that discriminate ME/CFS from other fatiguing neurological conditions. This supports PEM’s construct validity as specific to ME/CFS.
• Limitations:: Small validation cohort; did not test against other fatiguing conditions (cancer fatigue, depression).

10 Kielland et al. 2023 — Diagnostic Criteria Impact on Patient Experience

• Full Citation:: Kielland A, Liu J, Jason LA. Do diagnostic criteria for ME matter to patient experience with services and interventions? Key results from an online RDS survey targeting fatigue patients in Norway. Journal of Health Psychology. 2023;28(13):1189–1203. (Kielland, Liu, and Jason 2023)
• DOI:: 10.1177/13591053231169191
• PMID:: 37114822
• Key Findings::
  • n=660 fatigue patients in Norway; compared CCC proxy vs Fukuda proxy
  • PEM score was strongly associated with experience of most interventions
  • Patients meeting CCC (PEM-required) differed significantly from Fukuda (PEM-optional) on key intervention responses
  • Most interventions perceived as having low-to-negative health effects
• Conclusion:: PEM score is a strong determinant of intervention tolerance. Diagnostic criteria that require PEM identify patients at higher risk of harm from exertion-based interventions.
• Limitations:: Respondent-driven sampling; self-reported diagnoses; Norway-specific healthcare context.

11 Kuczyk et al. 2025 — German DSQ-PEM Psychometric Validation

• Full Citation:: Kuczyk C, Nöhre M, Herrmann-Lingen C, et al. Reliability and validity of the German version of the DePaul Symptom Questionnaire Post-Exertional Malaise (DSQ-PEM). Frontiers in Psychiatry. 2025;16:1647040. (Kuczyk et al. 2025)
• DOI:: 10.3389/fpsyt.2025.1647040
• PMID:: 40980044
• Key Findings::
  • Validated German DSQ-PEM in general population (n=2,263) and PCC clinical sample (n=1,448)
  • Excellent internal consistency in both samples
  • DSQ-PEM correlated with Chalder Fatigue Scale (convergent validity) but remained a distinct instrument
  • Known-group validity: DSQ-PEM effectively differentiates PCC from general population
• Conclusion:: DSQ-PEM is a psychometrically sound, distinct instrument for measuring PEM. Correlation with fatigue scales confirms PEM captures a related but separate construct.
• Limitations:: German-language only; PCC sample may not fully represent ME/CFS; cross-sectional validation.

12 Peter et al. 2025 — EPILOC: PEM in Persistent PCS at 2 Years

• Full Citation:: Peter RS, Nieters A, Göpel S, et al. Persistent symptoms and clinical findings in adults with post-acute sequelae of COVID-19/post-COVID-19 syndrome in the second year after acute infection: a population-based, nested case-control study. PLOS Medicine. 2025;22(1):e1004511. (Peter et al. 2025)
• DOI:: 10.1371/journal.pmed.1004511
• PMID:: 39847575
• Key Findings::
  • Population-based German study: n=982 PCS patients, n=576 controls
  • PEM for >14h reported by 35.6% of persistent PCS patients; 11.6% met IOM ME/CFS criteria
  • Patients with persistent PCS and PEM reported more pain and had worse results in nearly all objective tests
  • PEM associated with lower VO2peak, lower handgrip strength, and worse ventilatory efficiency
• Conclusion:: PEM stratifies PCS patients on both subjective and objective measures at 2 years post-infection. PEM presence identifies a more severely affected subgroup within PCC.
• Limitations:: No pre-infection baseline; excluded patients too ill to attend clinic; self-reported PEM with objective correlates.

13 Jason et al. 2015 — Problems in Defining PEM

• Full Citation:: Jason LA, Evans M, So S, Scott J, Brown A. Problems in defining post-exertional malaise. Journal of Prevention and Intervention in the Community. 2015;43(1):20–31. (Jason et al. 2015)
• DOI:: 10.1080/10852352.2014.973239
• PMID:: 25584525
• Key Findings::
  • n=32 CFS patients (Fukuda criteria)
  • Slight differences in wording of self-report PEM items significantly affected PEM classification
  • Operationalizing PEM matters — shallow self-report conflates PEM with other constructs
• Conclusion:: The way PEM is assessed affects whether a patient is classified as having it. This has implications for diagnostic reliability and for studies that compare PEM vs non-PEM subgroups.
• Limitations:: Small sample; single diagnostic criterion (Fukuda); self-report only.

14 Roma et al. 2019 — Pediatric PEM and Health-Related Quality of Life

• Full Citation:: Roma M, Marden CL, Flaherty MAK, Jasion SE, Cranston EM, Rowe PC. Impaired health-related quality of life in adolescent myalgic encephalomyelitis/chronic fatigue syndrome: the impact of core symptoms. Frontiers in Pediatrics. 2019;7:26. (Roma et al. 2019)
• DOI:: 10.3389/fped.2019.00026
• PMID:: 30828572
• Key Findings::
  • n=55 adolescent ME/CFS patients (Fukuda criteria); 85% also met IOM criteria
  • PEM frequency significantly associated with severity of impaired HRQOL (p < 0.001)
  • Patients meeting IOM criteria (PEM-required) had worse HRQOL than those meeting only Fukuda (PEM-optional)
  • Orthostatic intolerance present in 96% of the cohort
• Conclusion:: PEM is a core driver of impaired quality of life in pediatric ME/CFS. Diagnostic criteria requiring PEM identify a more severely affected subgroup.
• Limitations:: Small sample; single tertiary center; cross-sectional; parent-proxy reporting for younger children.

15 Park et al. 2024 — Systematic Review of Fatigue Severity in ME/CFS RCTs

• Full Citation:: Park JW, Park BJ, Lee JS, Lee EJ, Ahn YC, Son CG. Systematic review of fatigue severity in ME/CFS patients: insights from randomized controlled trials. Journal of Translational Medicine. 2024;22(1):529. (Park et al. 2024)
• DOI:: 10.1186/s12967-024-05349-7
• PMID:: 38831460
• Key Findings::
  • Meta-analysis of 60 RCTs, n=7,088 ME/CFS patients; pooled fatigue severity 77.9/100 (95% CI 74.7–81.0)
  • Physical fatigue (74.3) and cognitive fatigue (74.2) higher than mental fatigue (70.1)
  • Severity varied by diagnostic criteria (ICC 54.2 to Canadian 83.6) and assessment tool (MFS 54.2 to CIS 88.6)
  • Non-pharmacological trial participants showed higher baseline fatigue (79.1) than pharmacological trials (75.5)
• Conclusion:: ME/CFS patients in RCTs show severe, persistent fatigue across all domains. Measurement heterogeneity highlights the need for standardized fatigue assessment.
• Limitations:: Heterogeneous trial populations; mostly Fukuda/CES criteria; no PEM-required subgroup analysis.

16 Liu et al. 2025 — Genetic Variants in CFS Predict Population Fatigue and Actigraphy

• Full Citation:: Liu PZ, Raizen DM, Skarke C, Brooks TG, Anafi RC. Genetic variants associated with chronic fatigue syndrome predict population-level fatigue severity and actigraphic measurements. Sleep. 2025;48(2):zsae243. (Liu et al. 2025)
• DOI:: 10.1093/sleep/zsae243
• PMID:: 39442002
• Key Findings::
  • UK Biobank: n=295 CFS vs n=63,133 controls; CFS patients had decreased overall movement (d=0.220), lower activity amplitudes (d=-0.377), lower wrist temperature amplitudes (d=-0.173)
  • 30 CFS-associated SNVs tested; one associated with subjective fatigue in controls, one with actigraphy
  • Genetic overlap of CFS risk with fatigue phenotypes suggests shared biology between clinical and population-level fatigue
• Conclusion:: CFS fatigue shares genetic architecture with population-level fatigue, supporting a continuum model and validating actigraphy as an objective correlate.
• Limitations:: CFS diagnosed by self-report in UK Biobank; small CFS group (n=295); cross-sectional actigraphy.

17 Lee et al. 2025 — Fatigue-Dominant Long COVID: Clinical and Laboratory Characteristics

• Full Citation:: Lee JS, Choi Y, Joung JY, Son CG. Clinical and laboratory characteristics of fatigue-dominant long-COVID subjects: a cross-sectional study. American Journal of Medicine. 2025;138(2):346–353.e1. (Lee et al. 2025)
• DOI:: 10.1016/j.amjmed.2024.01.025
• PMID:: 38331137
• Key Findings::
  • n=100 fatigue-dominant Long COVID (mKCFQ11 >60, VAS fatigue >5); severe fatigue across all measures
  • No differences by sex, post-COVID period, or age
  • Plasma cortisol negatively correlated with fatigue scores (more specific to mental than physical fatigue)
  • Fatigue scales (mKCFQ11, MFI, VAS) strongly inter-correlated
• Conclusion:: Post-viral fatigue is a coherent construct measurable by validated instruments. Cortisol association supports endocrine contribution to fatigue without explaining physical/motivational dimensions.
• Limitations:: Single time point; Korean population; no healthy controls; self-referred sample.

18 Bileviciute-Ljungar et al. 2020 — ICF Core Set for ME/CFS

• Full Citation:: Bileviciute-Ljungar I, Schult ML, Borg K, Ekholm J. Preliminary ICF core set for patients with myalgic encephalomyelitis/chronic fatigue syndrome in rehabilitation medicine. Journal of Rehabilitation Medicine. 2020;52(6):jrm00074. (Bileviciute-Ljungar et al. 2020)
• DOI:: 10.2340/16501977-2697
• PMID:: 32488281
• Key Findings::
  • n=100 ME/CFS patients assessed by rehabilitation team; ICF Body Functions impairments in energy/fatigue (100%), physical endurance (99%), fatigability (96%), sleep (91%), pain (82%)
  • Activity/Participation most frequently limited: housework (93%), assisting others (92%), employment (87%), handling stress (83%)
  • Fatigue and fatigability emerged as distinct ICF categories (b1300 energy level vs b4552 fatigability)
  • Majority of impairments rated light-to-moderate, except employment restrictions (severe)
• Conclusion:: Fatigue and fatigability are distinct ICF constructs. ME/CFS disability spans all ICF domains, with fatigue/fatigability as the most prevalent body-function impairments.
• Limitations:: Single-center; team consensus rather than formal Delphi; preliminary core set.

19 Eaton-Fitch & Marshall-Gradisnik 2026 — Australian ME/CFS Registry: Symptom Clusters and HRQoL

• Full Citation:: Eaton-Fitch N, Marshall-Gradisnik S. Australian registry reports poor health and wellbeing in people living with ME/CFS. Journal of Translational Medicine. 2026. (Eaton-Fitch and Marshall-Gradisnik 2026)
• DOI:: 10.1186/s12967-026-08618-9
• PMID:: 42443918
• Key Findings::
  • n=2,873 ME/CFS vs n=797 non-fatigued controls; largest Australian ME/CFS registry analysis
  • HRQoL significantly impaired vs controls (SF-36); worse outcomes for ICC vs Fukuda-defined patients
  • K-means clustering identified 4 symptom-severity clusters differing by case definition stringency
  • Symptom severity/frequency predicted by case definition strictness; not a predictor of HRQoL outcomes
• Conclusion:: ME/CFS symptom burden is severe and consistent across diagnostic criteria, but ICC criteria identify patients with poorest HRQoL. Empirical clustering supports phenotypic subgroups.
• Limitations:: Self-reported data; voluntary registry recruitment (selection bias); cross-sectional.

20 Tankisi et al. 2024 — Clinical Neurophysiology of Fatigue and Fatigability

• Full Citation:: Tankisi H, Versace V, Kuppuswamy A, Cole J. The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability. Clinical Neurophysiology Practice. 2024;9:39–50. (Tankisi et al. 2024)
• DOI:: 10.1016/j.cnp.2023.12.004
• PMID:: 38274859
• Key Findings::
  • Conceptual distinction: fatigue = subjective perception; fatigability = objective performance decline
  • Central fatigability assessed by twitch interpolation, TMS, EEG/MEG, readiness potentials
  • Peripheral fatigability assessed by surface/needle EMG, single-fiber EMG, nerve conduction
  • Framework applicable across neurological disorders and post-COVID fatigue
• Conclusion:: Differentiating fatigue (perceived) from fatigability (measurable) is essential for understanding ME/CFS. Neurophysiological tools can objectively quantify central vs peripheral contributions.
• Limitations:: Narrative review, not systematic; no ME/CFS-specific neurophysiological data.

21 Eguchi et al. 2026 — EV-miRNA Biomarkers Differentiating ME/CFS from Other Fatigue Conditions

• Full Citation:: Eguchi A, Kuratsune H, Nakatomi Y, Yasui T, Nakagawa R, Watanabe Y, Fukuda S. Circulating extracellular vesicles-microRNAs as potential biomarkers for the identification of ME/CFS: differentiating fatigue-related conditions. Journal of Translational Medicine. 2026;24(1):979. (Eguchi et al. 2026)
• DOI:: 10.1186/s12967-026-08695-w
• PMID:: 42533331
• Key Findings::
  • n=6 ME/CFS, n=6 idiopathic chronic fatigue, n=8 depression; 62 EV-miRNA signature with 87% sensitivity and 94% specificity
  • ME/CFS EVs had unique subpopulation (high calcein intensity, larger diameter) vs ICF and depression
  • Top candidate miRNAs (miR-21-5p, let-7f-5p, miR-26b-5p, miR-20a-5p) elevated only in ME/CFS, not HC
  • Pathway enrichment in focal adhesion, PI3K-Akt, insulin signaling, endocrine functions
• Conclusion:: ME/CFS fatigue is biologically distinguishable from idiopathic chronic fatigue and depression at the EV-miRNA level, supporting the existence of a distinct ME/CFS fatigue phenotype.
• Limitations:: Very small discovery cohort (n=6 ME/CFS); limited HC validation (n=4); requires independent replication.

22 Habermann-Horstmeier & Horstmeier 2025 — Symptom Clusters as Translational Model

• Full Citation:: Habermann-Horstmeier L, Horstmeier LM. Symptom clusters in ME/CFS reflect distinct neuroimmune and autonomic pathophysiological mechanisms: a translational model. Journal of Translational Medicine. 2025;24(1):606. (Habermann-Horstmeier and Horstmeier 2025)
• DOI:: 10.1186/s12967-026-08159-1
• PMID:: 42050709
• Key Findings::
  • n=748 adults with ME/CFS; hypothesis-driven symptom clusters tested via EFA, CFA, SEM
  • Brain factor (brain fog, sensory hypersensitivity, visual disturbances, sleep, headaches) showed excellent fit (RMSEA=0.021, CFI=0.996)
  • Gut-Immune two-factor structure superior to one-factor; Autonomic symptom complex as higher-order latent factor
  • Clusters aligned with functional biological systems (not random co-occurrence)
• Conclusion:: ME/CFS symptom clusters map onto distinct neuroimmune-autonomic biological axes. This supports mechanism-aligned subgrouping for diagnostics and treatment stratification.
• Limitations:: Self-reported symptoms; mechanistic alignment inferred from literature, not directly measured; cross-sectional.

23 Bedard et al. 2026 — Central Origin of Fatigability in ME/CFS (Multimodal Neuroimaging)

• Full Citation:: Bedard P, Knutson KM, McGurrin PM, Vial F, Popa T, Horovitz SG, Hallett M, Nath A, Walitt B. Central origin of fatigability in Myalgic encephalomyelitis/chronic fatigue syndrome revealed by multimodal neuroimaging. NeuroImage: Clinical. 2026;51:104041. (Bedard et al. 2026)
• DOI:: 10.1016/j.nicl.2026.104041
• PMID:: 42551185
• Key Findings::
  • n=15 ME/CFS vs n=19 healthy controls; grip force fatigability task with simultaneous fMRI, EEG, EMG
  • ME/CFS patients developed fatigue significantly earlier despite same maximum voluntary force
  • Healthy controls increased muscle and brain activity until fatigue onset; ME/CFS showed minimal fluctuations
  • Central (brain) failure to upregulate motor output, not peripheral muscle failure
• Conclusion:: Fatigability in ME/CFS has a central neural origin — the brain fails to increase motor drive. This distinguishes ME/CFS fatigue from peripheral fatigue states.
• Limitations:: Small sample (n=15 ME/CFS); NIH intramural cohort (selection bias); female underrepresented (7 per group).

24 Campos et al. 2022 — Post-Viral Fatigue Assessment Methods Review

• Full Citation:: Campos MC, Nery T, Starke AC, de Bem Alves AC, Speck AE, Aguiar AS. Post-viral fatigue in COVID-19: a review of symptom assessment methods, mental, cognitive, and physical impairment. Neuroscience and Biobehavioral Reviews. 2022;142:104902. (Campos et al. 2022)
• DOI:: 10.1016/j.neubiorev.2022.104902
• PMID:: 36202253
• Key Findings::
  • Subjective fatigue assessed via structured questionnaires (Chalder, MFI, FSS, VAS)
  • Objective fatigability assessed via physical performance tests (handgrip, CPET) and cognitive tests
  • Both subjective and objective domains are impaired in post-COVID fatigue
  • Multi-domain assessment framework recommended for clinical and research settings
• Conclusion:: Post-viral fatigue assessment requires both subjective (perceived fatigue) and objective (fatigability) tools across physical, cognitive, and mental domains. Framework directly applicable to ME/CFS.
• Limitations:: Narrative review, not systematic; COVID-19-specific; limited pre-COVID post-viral fatigue data.

25 Aditi et al. 2026 — Long-Term Risk of Dementia Following Encephalitis (TriNetX EHR Cohort)

• Full Citation:: Aditi, Blackwell T, Fang X, Sharma S, Mendoza M, Landay A, Golovko G, Samir P. Long-term risk of dementia following encephalitis: a large-scale retrospective cohort study of electronic health records. Journal of Neurology. 2026;273(9):511. (Aditi et al. 2026)
• DOI:: 10.1007/s00415-026-14017-3
• PMID:: 42557422
• Study Design:: Retrospective cohort, TriNetX US electronic health records (~129M patients, 72 healthcare organizations); encephalitis (onset ≥2005) vs propensity-score-matched controls, 10-year follow-up; comparator cohorts sepsis/meningitis/stroke.
• Key Findings::
  • Cumulative incidence 74.3/100,000; prevalence 90.2/100,000 (2014–2024).
  • Composite dementia risk ratio (RR) by age: >60y = 2.11 (95% CI 1.98–2.25); 40–60y = 5.16 (4.46–5.98); younger groups elevated in composite but driven by post-encephalitic G31 sequelae, not AD/F03.
  • 10-year hazard ratios: >60y = 3.26 (3.05–3.49); 40–60y = 6.74.
  • Etiology composite dementia RR: non-infectious/post-infectious inflammatory (autoimmune: anti-NMDA, Hashimoto’s, ADEM) = 3.93 (3.35–4.61) HIGHEST; viral = 1.99 (1.77–2.24); fungal/parasitic = 1.42 (1.30–1.55); unspecified = 1.35; bacterial = 1.35 (0.97–1.87) NOT significant.
  • vs sepsis/meningitis/stroke: encephalitis higher risk for composite and individual dementia codes; vascular dementia exception (higher in stroke). Epilepsy risk increased (positive control). Mortality higher in encephalitis.
• Conclusion:: Acute brain-parenchymal inflammation (encephalitis) confers a markedly elevated long-term dementia risk that is strongest for non-infectious/post-infectious inflammatory (autoimmune) etiologies and most pronounced in midlife (40–60y). Establishes “acute CNS inflammation → long-term neurodegeneration” as a generalizable, population-scale relationship.
• Limitations:: EHR/administrative-code ascertainment (no neuropathological/biomarker confirmation); residual confounding despite propensity matching; no CSF/imaging inflammatory markers; general-population (non-ME/CFS) cohort.
• ME/CFS Relevance:: Indirect/cross-disease evidence — supports the neuroinflammation→neurodegeneration causal template the ME/CFS reasoning borrows. Does NOT demonstrate any dementia link in ME/CFS itself; the autoimmune-encephalitis excess parallels ME/CFS autoantibody hypotheses only by analogy.

26 Granerod et al. 2017 — Increased Sequelae Post-Encephalitis (UK CPRD Cohort)

• Full Citation:: Granerod J, Davies NWS, Ramanuj PP, Easton A, Brown DW, Thomas SL. Increased rates of sequelae post-encephalitis in individuals attending primary care practices in the United Kingdom: a population-based retrospective cohort study. Journal of Neurology. 2017;264(2):407–415. (Granerod et al. 2017)
• DOI:: 10.1007/s00415-016-8316-8
• PMID:: 27766471
• Study Design:: UK Clinical Practice Research Datalink (CPRD) population-based retrospective cohort; 2,460 incident encephalitis cases vs 47,914 unexposed controls; multivariable Poisson regression.
• Key Findings::
  • Encephalitis survivors had increased risk of ALL investigated outcomes, including cognitive problems and dementia.
  • Highest adjusted RR for epilepsy (31.9; 95% CI 25.4–40.1); psychiatric outcomes also elevated (bipolar 6.34; psychotic 3.48).
  • RRs highest in first year of follow-up for all outcomes except headache.
• Conclusion:: Sequelae including cognitive decline and dementia are common in encephalitis survivors — an earlier, independent population-level confirmation of the acute-CNS-inflammation → cognitive/neurodegenerative-outcome relationship.
• Limitations:: Primary-care record ascertainment; 2017 (older than the 2026 primary); no etiology-specific dementia RRs.

27 Heneka et al. 2025 — Neuroinflammation in Alzheimer Disease

• Full Citation:: Heneka MT, van der Flier WM, Jessen F, Hoozemans J, Thal DR, Boche D, et al. Neuroinflammation in Alzheimer disease. Nature Reviews Immunology. 2025;25(5):321–352. (Heneka et al. 2025)
• DOI:: 10.1038/s41577-024-01104-7
• PMID:: 39653749
• Key Findings::
  • Authoritative multi-author consensus on microglial and astroglial activation, NLRP3/inflammasome, and complement in AD.
  • Chronic neuroinflammation is mechanistically implicated in driving proteinopathy and neurodegeneration, not merely accompanying it.
• Conclusion:: Provides the mechanism pathway by which CNS inflammation drives neurodegeneration — the biological template the post-encephalitis dementia finding instantiates at the population level.
• Limitations:: AD-focused review (dementia population); mechanisms not ME/CFS-specific; general-population discount applies.

28 Ising et al. 2019 — NLRP3 Inflammasome Activation Drives Tau Pathology

• Full Citation:: Ising C, Venegas C, Zhang S, Scheiblich H, Schmidt SV, Vieira-Saecker A, et al. NLRP3 inflammasome activation drives tau pathology. Nature. 2019;575(7784):669–673. (Ising et al. 2019)
• DOI:: 10.1038/s41586-019-1769-z
• PMID:: 31748742
• Key Findings::
  • NLRP3 inflammasome activation in microglia causally drives tau pathology in tauopathy mice.
• Conclusion:: Direct mechanistic demonstration that neuroinflammation can causally drive a core neurodegenerative proteinopathy — supporting a causal (not epiphenomenal) role for neuroinflammation in neurodegeneration.
• Limitations:: Animal/model evidence; tauopathy (not ME/CFS); population discount applied.

29 Heneka et al. 2013 — NLRP3 Activation in Alzheimer’s Disease

• Full Citation:: Heneka MT, Kummer MP, Stutz A, Delekate A, Schwartz S, Vieira-Saecker A, et al. NLRP3 is activated in Alzheimer’s disease and contributes to pathology in APP/PS1 mice. Nature. 2013;493(7434):674–678. (Heneka et al. 2013)
• DOI:: 10.1038/nature11729
• PMID:: 23254930
• Key Findings::
  • NLRP3 inflammasome activated in human MCI/AD brain; Nlrp3−/−/Casp1−/− familial-AD mice protected from memory loss with reduced IL-1β and enhanced Aβ clearance.
• Conclusion:: Foundational causal evidence linking microglial inflammasome activation to AD pathology.
• Limitations:: Animal/model + human post-mortem; AD-specific; population discount applied.

30 Javonillo et al. 2026 — Neurotropic Murine Coronavirus Effects on AD Pathology (5xFAD)

• Full Citation:: Javonillo DI, Furman S, Le L, Fernandez K, Mulford J, Singla V, et al. Characterization of effects of a neurotropic murine coronavirus infection on Alzheimer’s disease neuropathology of 5xFAD mice. bioRxiv. 2026. (Javonillo et al. 2026)
• DOI:: 10.64898/2026.02.23.707587
• PMID:: 42124663
• Key Findings::
  • Viral encephalitis (JHMV) in aged 5xFAD mice induced minimal overall Aβ change at 12 dpi but caused T-cell infiltration, Lgals3/MAC2+ macrophages around plaques, and down-regulated disease-associated-microglia (DAM) Aβ-clearance pathways.
• Conclusion:: Acute viral neuroinflammation does NOT simply accelerate amyloid pathology in this model — the viral-encephalitis ↔︎ AD interplay is bidirectional and model-dependent (contextualizing/partial-null result).
• Limitations:: Preprint (not yet peer reviewed); animal model; 12-day timepoint only; no tau assessment.

31 Cohen et al. 2024 — Recent Trends in Neuroinflammatory and Neurodegenerative Disorders

• Full Citation:: Cohen J, Mathew A, Dourvetakis KD, Sanchez-Guerrero E, Pangeni RP, Gurusamy N, et al. Recent Research Trends in Neuroinflammatory and Neurodegenerative Disorders. Cells. 2024;13(6):511. (Cohen et al. 2024)
• DOI:: 10.3390/cells13060511
• PMID:: 38534355
• Key Findings::
  • Neuroinflammatory/neurodegenerative disorders (AD, PD, TBI, ALS) share glial activation and neuroimmune dysfunction driving neurodegeneration.
  • Explicitly groups ME/CFS with Gulf War Illness as chronic neuroimmune-dysfunction disorders lacking disease-modifying therapy.
• Conclusion:: Bridges the neuroinflammation→neurodegeneration template directly to ME/CFS, grounding the cross-disease analogy.
• Limitations:: Narrative review (not systematic); mechanism extrapolated from other diseases; no ME/CFS dementia data.

32 Maguire et al. 2026 — Virus Reactivation in Acute and Long COVID-19 (IMPACC)

• Full Citation:: Maguire C, Chen J, Rouphael N, Morse BA, Hoch A, Pickering H, et al. Virus reactivation in acute and long COVID-19. Nature. 2026. (Maguire et al. 2026)
• DOI:: 10.1038/s41586-026-10740-z
• Study Design:: Longitudinal prospective multi-omic cohort (IMPACC; n=1154 hospitalized COVID-19 patients).
• Key Findings::
  • Widespread reactivation of chronic Herpesviridae (EBV, CMV, HSV1) and Anelloviridae in immunocompetent COVID-19 patients, not explained by immunosuppression.
  • Anelloviridae transcripts significantly more prevalent in the long COVID physical-disability (PROMIS) patient-reported-outcome group, even after controlling for age, sex, immunosuppression, and acute COVID-19 severity.
  • Anelloviridae associated with enrichment of neutrophil-degranulation genes; negatively associated with oxidative-stress-protective metabolites (methylcysteine sulfoxide, 6-bromotryptophan).
  • Anelloviridae previously linked to chronic fatigue syndrome and multiple sclerosis.
• Conclusion:: Chronic viral reactivation — including Anelloviridae — associates with persistent physical disability in long COVID and may represent an immune-dysregulation (dysvirosis) signature relevant to post-infectious fatigue conditions.
• Limitations:: COVID-19 cohort (unvaccinated, ancestral strain), not a ME/CFS cohort; transcripts not qPCR; three compartments only; convalescent dropout limited long-COVID power; association not causation.

33 Briese et al. 2023 — Multicenter Virome Analysis in ME/CFS

• Full Citation:: Briese T, Tokarz R, Bateman L, Che X, Guo C, Jain K, et al. A multicenter virome analysis of blood, feces, and saliva in myalgic encephalomyelitis/chronic fatigue syndrome. Journal of Medical Virology. 2023;95(8):e28993. (Briese et al. 2023)
• DOI:: 10.1002/jmv.28993
• Study Design:: Multicenter case–control viral-nucleic-acid surveillance using PCR and high-throughput sequencing of blood, feces, and saliva.
• Key Findings::
  • No consistent group-specific differences in viral nucleic acid between ME/CFS cases and healthy controls.
  • Only exception: lower prevalence of anelloviruses in ME/CFS cases compared to controls.
  • Conclusion: future investigations into viral infection in ME/CFS should focus on adaptive immune responses rather than surveillance for viral gene products.
• Conclusion:: Viral-gene-product surveillance does not identify an ongoing productive viral infection in ME/CFS; supports an immune-dysregulation (adaptive immune response) focus over a persistent-viral-replication model.
• Limitations:: Abstract-level detail available to this integration; full sample-size and cohort-stratification details not retrieved; cross-sectional sampling.

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