What is ME/CFS?

Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS) is:

… A complex, multi-system, neuroimmune condition with a multitude of symptoms related to the dysfunction of:

  • The brain
  • Gastro-intestinal system
  • Immune system
  • Endocrine and cardiac systems

Illnesses resembling ME/CFS have been described for at least two hundred years (Lorusso et al. 2009, Shorter 1993). For a timeline of these reports and history see Wikipedia.

Since 1969, ME has been classified as a neurological disorder by the World Health Organisation (International Classification of Diseases) (ICD- code: 10 G93.3).

ME/CFS can range from mild to severe and can cause profound disability in those affected. In the young, for example social and school, higher education life can be severely impacted. In those of working age, many are unable to stay in employment due to their illness. Social and family life can become drastically restricted and sometimes very strained. Many lose contact with pre-illness friends and non-supportive family members. For those at the severe end in terms of symptoms, they can remain housebound or bedbound for months or years.

What does Myalgic Encephalomyelitis mean???

MYA                     muscles

ALGIC                  painful

ENCEPHALO       brain

MYEL                   nerve

ITIS                      inflammation

By Any Other Name

ME was one of the first labels for the illness (Shorter, 1993, Lindan, 1956), but it goes by several names. Apart from Chronic Fatigue Syndrome (CFS), the illness is also known as Post-Viral Fatigue Syndrome (PVFS – an older term, now largely fallen into disuse), Chronic Fatigue Immune Dysfunction Syndrome (CFIDS – a rarer term) and more recently as a result of a US Institute of Medicine review (Report Brief, Report Clinicians Guide, Report Full), a new name was suggested – Systemic Exertion Intolerance Disease (SEID – as an aside it is “dies” backwards – it has received some criticism from patients, Jason et al, 2015).


Quick Links:

What Causes ME/CFS?



Who Gets ME/CFS?

Further Reading

Think you might have ME/CFS?

Just diagnosed?

Managing symptoms in daily life.

Related conditions

Studies and Research


The US Centers for Disease Control and Prevention (CDC) page for ME/CFS (The CDC uses the 1994 Case Definition or Fukuda criteria for diagnosis (Fukuda et al., 1994). This has largely been superseded by the Canadian Consensus Criteria in 2003 (Carruthers et al., 2003) and then the International Consensus Criteria in 2011 (Carruthers et al., 2011))

The PubMed Health (US National Library of Medicine) page on ME/CFS

Victorian Government Better Heath page on ME/CFS

The UK ME Association


Jason, L. A., et al. “Reflections on the Institute of Medicine’s systemic exertion intolerance disease.” Pol Arch Med Wewn, 2015, 125(7-8): 576-581.

Carruthers, B. M., et al. “Myalgic encephalomyelitis: International Consensus Criteria.” J Intern Med, 2011, 270(4): 327-338.

Carruthers, B. M. et al. “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols.”  Journal of Chronic Fatigue Syndrome, 2003, 11(1): 7-36.

Fukuda, K., et al. “The chronic fatigue syndrome: a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group.” Ann Intern Med, 1994, 121(12): 953-959.

Shorter, E. “Chronic fatigue in historical perspective.” Ciba Found Symp, 1993, 173: 6-16; discussion 16-22.

Lindan, R. “Benign Myalgic Encephalomyelitis.” Can Med Assoc J, 1956, 75(7): 596-597.