FAQ
ME/CFS research — common questions
Answers to common questions about myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) research, post-exertional malaise, diagnostic criteria, biomarkers, Long COVID overlap, and how the atlas works.
For informational purposes only. Not medical advice. About the atlas →
What is ME/CFS?
Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, chronic, multi-system illness characterised by profound fatigue, post-exertional malaise, sleep dysfunction, cognitive impairment, and autonomic abnormalities. It affects millions of people worldwide and is associated with documented immune, metabolic, neurological, and autonomic abnormalities across the research literature. ME/CFS is not explained by deconditioning, psychiatric illness, or lifestyle factors.
What is post-exertional malaise (PEM)?
Post-exertional malaise is the worsening of symptoms following physical, cognitive, or emotional exertion. The worsening is typically delayed by hours to days and can take days, weeks, or longer to resolve. PEM is the defining feature of ME/CFS and a required criterion for diagnosis under the Canadian Consensus Criteria, International Consensus Criteria, and IOM 2015 guidelines. It distinguishes ME/CFS from deconditioning and most other fatiguing conditions. Two-day cardiopulmonary exercise testing studies document reproducible impairment on the second test day, a pattern not seen in healthy controls or other fatiguing conditions. Browse PEM research →
Is ME/CFS linked to neuroinflammation?
Yes. PET imaging studies have shown elevated microglial activation in ME/CFS patients compared with healthy controls, consistent with neuroinflammation. MRI studies document structural and functional brain abnormalities in a significant proportion of patients. Central nervous system involvement is a plausible mechanism underlying cognitive impairment, sensory sensitivity, and the neurological features of ME/CFS. Browse neuroinflammation research →
What biomarkers are being studied in ME/CFS?
Research is investigating cytokine profiles, autoantibodies against G-protein coupled receptors, metabolomics signatures, gene expression patterns, ion channel function in immune cells, plasma proteomics, and functional biomarkers such as two-day cardiopulmonary exercise test results. No single diagnostic biomarker has yet reached clinical use, but multi-omics approaches have shown promise in identifying patient subgroups and distinguishing ME/CFS from other conditions. Browse biomarker research →
How does Long COVID overlap with ME/CFS?
A significant proportion of people with Long COVID meet clinical criteria for ME/CFS. Both conditions share post-exertional malaise, fatigue, cognitive impairment, and autonomic dysfunction. Proposed shared mechanisms include immune dysregulation, viral persistence, microbiome disruption, and autonomic nervous system impairment. Understanding this overlap has brought new research resources and attention to mechanisms that have been studied in ME/CFS for decades. Browse Long COVID overlap research →
What diagnostic criteria are used in ME/CFS research?
The most commonly used case definitions are: Fukuda 1994 (CDC criteria), Oxford criteria, Canadian Consensus Criteria (CCC, 2003), International Consensus Criteria (ICC, 2011), and IOM/SEID criteria (2015). The CCC, ICC, and IOM criteria require post-exertional malaise as a mandatory diagnostic criterion. The Fukuda and Oxford criteria do not, meaning studies using them may include a broader and more heterogeneous population. The atlas classifies each study by the case definition used. Browse diagnostics research →
Is ME/CFS caused by psychological factors?
No. The dominant research consensus has shifted decisively toward biomedical explanations. Documented abnormalities include immune activation, mitochondrial dysfunction, HPA axis dysregulation, autonomic dysfunction, and neurological changes. While some older studies used psychosocial frameworks, the current evidence base strongly supports ME/CFS as a biological illness with measurable physiological abnormalities. Psychosocial research now represents a small minority of the overall literature.
What is autonomic dysfunction in ME/CFS?
Autonomic dysfunction refers to impaired regulation of the autonomic nervous system, which controls heart rate, blood pressure, digestion, and other automatic body functions. In ME/CFS, this manifests as orthostatic intolerance, postural orthostatic tachycardia syndrome (POTS), reduced heart rate variability, and abnormal blood pressure responses to positional change. These findings have been documented in multiple independent studies using tilt-table testing, heart rate monitoring, and physiological assessments. Browse autonomic dysfunction research →
What is mitochondrial dysfunction in ME/CFS?
Several studies have documented impaired mitochondrial function and reduced ATP production in ME/CFS patients. Metabolomics analyses show altered energy metabolism profiles consistent with cellular energy stress. These findings may help explain why patients experience symptom worsening after exertion — the inability to meet energy demand at the cellular level may contribute directly to post-exertional malaise. Browse metabolic dysfunction research →
What is the Canadian Consensus Criteria (CCC)?
The Canadian Consensus Criteria (2003) is a diagnostic framework for ME/CFS that requires post-exertional malaise as a mandatory criterion, along with fatigue, sleep dysfunction, pain, neurological/cognitive manifestations, and autonomic, neuroendocrine, or immune dysfunction. It is widely considered the most clinically specific of the major case definitions and identifies a more homogeneous patient population than the Fukuda or Oxford criteria.
What is the difference between ME/CFS and chronic fatigue?
Chronic fatigue is a symptom present in many conditions including anaemia, depression, thyroid disorders, and cancer. ME/CFS is a specific diagnosed illness requiring multiple core criteria including post-exertional malaise, unrefreshing sleep, cognitive dysfunction, and orthostatic intolerance. Studies that rely on fatigue alone — without requiring PEM or other cardinal features — typically capture a broader and more heterogeneous population than studies using strict ME/CFS criteria.
How can I use the atlas to find research on a specific topic?
The atlas can be explored in two main ways. Topic pages at /research provide structured synthesis of what is known, uncertain, and emerging for each research domain. The evidence browser at /evidence allows filtering and searching across all studies by evidence level, diagnostic criteria, PEM status, and disease context. Ask the Atlas offers evidence-grounded answers to specific questions with study citations.
What is post-infectious illness?
Post-infectious illness refers to conditions that develop following infection, in which recovery is incomplete and persistent symptoms continue long after the acute phase. ME/CFS has long been recognised as frequently triggered by viral or other infections. Long COVID is the most recent prominent example. Research into post-infectious illness has expanded substantially since 2020 and now informs ME/CFS mechanism research and vice versa.
Are there effective treatments for ME/CFS?
No disease-modifying treatments are currently approved for ME/CFS. Evidence for most interventions is limited, inconsistent, or contested. The NICE 2021 guidelines advise against graded exercise therapy and support symptom management, energy conservation, and pacing. Research is ongoing in areas including immunomodulation, metabolic support, autonomic therapies, and pharmacological approaches. Browse intervention research →
What does “editor-reviewed” mean in the atlas?
Editor-reviewed means that a human editor has manually checked the study’s classification for diagnostic criteria quality and PEM requirement status. Machine-drafted entries have been classified by AI and may await further human verification. Review status is visible on every study card and detail page. The atlas is transparent about which entries have been through human review and which have not. Learn more about the review process →
What are evidence levels E0–E3?
The atlas classifies studies by evidence level based on study design and replication status:
- E0 Consensus — systematic reviews, meta-analyses, guidelines, and major evidence syntheses.
- E1 Replicated — replicated human evidence from multiple independent studies, including RCTs and controlled trials.
- E2 Moderate — single-study observational evidence, case-control studies, and cross-sectional designs.
- E3 Preliminary — early-stage findings, preprints, mechanistic studies, and editorials.
Higher levels indicate stronger and more generalisable findings. Read more about evidence levels →
What is case definition quality in the atlas?
Case definition quality reflects whether the study used a diagnostic framework that required post-exertional malaise and other core ME/CFS features. The atlas assigns one of four labels:
- Strict — requires PEM, uses CCC, ICC, or IOM criteria.
- Adequate — uses Fukuda or similar criteria without mandatory PEM.
- Weak — uses Oxford or other broad fatigue-based criteria.
- Unclear — case definition not clearly stated in the study.
Studies with strict case definitions capture a more homogeneous patient population and are more likely to reflect the core ME/CFS phenotype.
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