Azcue, Naiara, Teijeira-Portas, Sara, Tijero-Merino, Beatriz et al. · European journal of neurology · 2025 · DOI
This study found that both long-COVID patients and people with ME/CFS show signs of damage to small nerve fibers in the eyes and altered sensation to heat, compared to healthy people. Researchers used specialized imaging and tests to measure nerve fiber structure and how well patients could detect temperature changes. The findings suggest that small fiber nerve damage may contribute to symptoms like pain and abnormal sensations in these conditions.
This research provides objective, measurable evidence that ME/CFS patients have small fiber neuropathy—a finding often overlooked or dismissed—using validated diagnostic techniques. Demonstrating similar neuropathic patterns in both PCC and ME/CFS supports the biological basis of these conditions and could lead to better diagnostic tools and treatments targeting nerve fiber pathology.
This study does not establish whether small fiber damage causes ME/CFS symptoms or results from the disease process; it only shows an association. The cross-sectional design cannot determine if small fiber neuropathy develops before, during, or after symptom onset, nor can it prove that treating small fiber dysfunction will improve outcomes.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Azcue, Naiara, Teijeira-Portas, Sara, Tijero-Merino, Beatriz, Acera, Marian, Fernández-Valle, Tamara, Ayala, Unai, et al. (2025). Small fiber neuropathy in the post-COVID condition and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical significance and diagnostic challenges.. European journal of neurology. https://doi.org/10.1111/ene.70016
BibTeX
@article{mecfsatlas-azcue-2025-small-fiber,
author = {Azcue, Naiara and Teijeira-Portas, Sara and Tijero-Merino, Beatriz and Acera, Marian and Fernández-Valle, Tamara and Ayala, Unai and Barrenechea, Maitane and Murueta-Goyena, Ane and Lafuente, Jose Vicente and de Munain, Adolfo Lopez and Ruiz-Irastorza, Guillermo and Martín-Iglesias, Daniel and Gabilondo, Iñigo and Gómez-Esteban, Juan Carlos and Del Pino, Rocio},
title = {Small fiber neuropathy in the post-COVID condition and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical significance and diagnostic challenges.},
journal = {European journal of neurology},
year = {2025},
doi = {10.1111/ene.70016},
note = {PubMed: 39888240},
url = {https://www.mecfsatlas.com/evidence/azcue-2025-small-fiber},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/azcue-2025-small-fiber
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