Understanding Myalgic Encephalomyelitis

Myalgic Encephalomyelitis (ME, also referred to as ME/CFS) is a debilitating multisystem disease. Depending on its severity, ME/CFS can cause considerable physical and cognitive impairment, loss of the ability to work and, in the most severe cases, the need for full nursing care, including artificial nutrition.

Terminology: Myalgic Encephalomyelitis (ME) is the preferred term. The name Chronic Fatigue Syndrome (CFS), introduced in the 1980s, has long been criticised for failing to reflect the nature and severity of the disease. The combined term ME/CFS was adopted in the 2003 Canadian Consensus Criteria (CCC) and has subsequently become widely used in research and clinical literature. ME/CFS is also the terminology used in the DISCOVER-ME Horizon Europe application and project documentation, and is therefore used throughout this website for consistency.

Symptoms and diagnosis

The hallmark symptom of ME/CFS is post-exertional malaise (PEM): a worsening of symptoms following physical, cognitive or emotional exertion that is disproportionate to the effort involved, often delayed in onset and lasting for days or weeks. This distinguishes ME/CFS from ordinary tiredness, since rest does not resolve the underlying exhaustion.

Alongside PEM, people with ME/CFS commonly experience unrefreshing sleep, cognitive impairment often described as “brain fog,” muscle and joint pain, and orthostatic intolerance (symptoms that worsen on standing). The disease also involves immune, autonomic and neuroendocrine dysfunction. ME and CFS are classified within the neurological chapter of the World Health Organization’s International Classification of Diseases (ICD-10 G93.3 and ICD-11 8E49).

In the absence of a diagnostic test, ME/CFS is diagnosed clinically using symptom-based criteria. A number of case definitions and diagnostic criteria have been developed over time, including the Fukuda criteria (1994), Canadian Consensus Criteria (CCC, 2003), International Consensus Criteria (ICC, 2011), Institute of Medicine criteria (IOM, 2015) and NICE guidance (2021) [1-5].

Diagnosis also varies considerably across Europe. The 2024 European ME Alliance (EMEA) Pan-European ME Patient Survey, based on 11,297 responses, found that case definitions, diagnostic guidelines and diagnostic practices vary greatly between European countries, with substantial differences in access to and rates of diagnosis. Across Europe, the average reported delay from disease onset to diagnosis was 6.8 years, with considerable variation between countries [6].

Why DISCOVER-ME is needed

There is currently no single diagnostic test or validated biomarker for ME/CFS, and no approved curative treatment. Diagnosis therefore continues to rely on clinical assessment and symptom-based criteria.

DISCOVER-ME was established to address this gap by identifying and validating biological markers of the disease, with the aim of supporting earlier and more accurate diagnosis, biologically defined patient subgroups and, ultimately, more targeted approaches to treatment.

References

1. Fukuda K, Straus SE, Hickie I, et al. (1994). The chronic fatigue syndrome: a comprehensive approach to its definition and study. Annals of Internal Medicine, 121(12), 953-959. DOI: 10.7326/0003-4819-121-12-199412150-00009.
2. Carruthers BM, Jain AK, De Meirleir KL, et al. (2003). Myalgic encephalomyelitis/chronic fatigue syndrome: clinical working case definition, diagnostic and treatment protocols. Journal of Chronic Fatigue Syndrome, 11(1), 7-115. DOI: 10.1300/J092v11n01_02.
3. Carruthers BM, van de Sande MI, De Meirleir KL, et al. (2011). Myalgic encephalomyelitis: International Consensus Criteria. Journal of Internal Medicine, 270(4), 327-338. DOI: 10.1111/j.1365-2796.2011.02428.x.
4. Institute of Medicine (2015). Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. Washington, DC: The National Academies Press. DOI: 10.17226/19012.
5. National Institute for Health and Care Excellence (2021). Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management. NICE guideline NG206. Published 29 October 2021.
6. Angelsen A, Schei T. (2024). EMEA Survey of ME/CFS Patients in Europe: Same disease, different approaches and experiences. European ME Alliance. Pan-European survey of 11,297 respondents.