Pejovic, Slobodanka, Natelson, Benjamin H, Basta, Maria et al. · BMC neurology · 2015 · DOI
This study looked at whether ME/CFS and fibromyalgia are actually the same condition or different disorders. Researchers compared patients with sleep-breathing problems, sleep insomnia, and healthy controls, measuring how often each group had ME/CFS, fibromyalgia, or both. They found that while both conditions occurred in sleep disorder patients, fibromyalgia was much more common in insomnia patients, whereas ME/CFS appeared in both groups equally—suggesting these may be separate conditions with different causes.
This study challenges the hypothesis that ME/CFS and fibromyalgia are manifestations of the same underlying process, which has important implications for diagnosis and treatment. Understanding whether these conditions have different causes could lead to more targeted, effective interventions for each disorder. The finding that sleep disorders associate differently with ME/CFS versus fibromyalgia also suggests screening for sleep problems should be part of ME/CFS evaluation.
This study does not prove that ME/CFS and fibromyalgia are definitely separate diseases—only that they may be, based on their different associations with sleep disorders. It cannot establish causation; sleep disorders might not cause ME/CFS or fibromyalgia, but rather share common underlying mechanisms. The cross-sectional design means we cannot determine temporal relationships or long-term 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
Pejovic, Slobodanka, Natelson, Benjamin H, Basta, Maria, Fernandez-Mendoza, Julio, Mahr, Fauzia, & Vgontzas, Alexandros N (2015). Chronic fatigue syndrome and fibromyalgia in diagnosed sleep disorders: a further test of the 'unitary' hypothesis.. BMC neurology. https://doi.org/10.1186/s12883-015-0308-2
BibTeX
@article{mecfsatlas-pejovic-2015-chronic-fatigue,
author = {Pejovic, Slobodanka and Natelson, Benjamin H and Basta, Maria and Fernandez-Mendoza, Julio and Mahr, Fauzia and Vgontzas, Alexandros N},
title = {Chronic fatigue syndrome and fibromyalgia in diagnosed sleep disorders: a further test of the 'unitary' hypothesis.},
journal = {BMC neurology},
year = {2015},
doi = {10.1186/s12883-015-0308-2},
note = {PubMed: 25884538},
url = {https://www.mecfsatlas.com/evidence/pejovic-2015-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/pejovic-2015-chronic-fatigue
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