Ruiz, E, Alegre, J, García Quintana, A M et al. · Revista clinica espanola · 2011 · DOI
This study looked at 824 people with ME/CFS (91% women, average age 48) seen at two specialized clinics between 2008 and 2010. The researchers found that most people had severe fatigue that worsened with activity, sleep problems, and memory/concentration difficulties. Many also had anxiety, dry eyes (sicca syndrome), and fibromyalgia. On average, it took over 9 years for people to get a diagnosis after their symptoms started.
This large, specialized clinical cohort provides detailed characterization of ME/CFS presentation and validates that Canadian consensus criteria identify a homogeneous patient population. The documentation of the 9-year diagnostic delay and high rates of comorbidity highlights the clinical and social burden of ME/CFS, informing clinical recognition and treatment strategies.
This descriptive cross-sectional study cannot establish causation or why these comorbidities occur with ME/CFS. The lack of age-matched or disease controls means we cannot determine which features are specific to ME/CFS versus general chronic illness. The study does not explain whether the long diagnostic delay is due to physician recognition gaps or disease progression patterns.
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
Ruiz, E, Alegre, J, García Quintana, A M, Aliste, L, Blázquez, A, & Fernández de Sevilla, T (2011). [Chronic fatigue syndrome: study of a consecutive series of 824 cases assessed in two specialized units].. Revista clinica espanola. https://doi.org/10.1016/j.rce.2011.02.013
BibTeX
@article{mecfsatlas-ruiz-2011-chronic-fatigue,
author = {Ruiz, E and Alegre, J and García Quintana, A M and Aliste, L and Blázquez, A and Fernández de Sevilla, T},
title = {[Chronic fatigue syndrome: study of a consecutive series of 824 cases assessed in two specialized units].},
journal = {Revista clinica espanola},
year = {2011},
doi = {10.1016/j.rce.2011.02.013},
note = {PubMed: 21794854},
url = {https://www.mecfsatlas.com/evidence/ruiz-2011-chronic-fatigue},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/ruiz-2011-chronic-fatigue
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