Myalgic Encephalomyelitis (ME) is a severe chronic illness in which symptoms are worsened by physical exertion. In some countries and some literature, ME is referred to as Chronic Fatigue Syndrome (CFS).

ME is an acquired illness that affects all body systems; predominantly the neurological, endocrine and immune systems. It is classified as a neurological illness in the World Health Organization (WHO) International Classification of Diseases and can be severely debilitating. Many people become ill after a bout of the flu or another illness.

Myalgic Encephalomyelitis — Explained

myelspinal cord


The four core symptoms of ME are:

New Onset of Fatigue

Unexplained recurrent physical and mental fatigue that significantly alters activity level


A significant degree of muscle pain. Pain can also be experienced in the joints and is often widespread and changes location. Often there is a new onset of headaches post illness. Headaches may be of a difference quality and in a different location than in the past.

Post-Exertional Fatigue

After physical activity, there is an increase in symptoms and/or an extended recovery period usually lasting a day or more.

Sleep Dysfunction

Unrefreshed sleep and/or difficult getting to or maintaining sleep

Symptoms include Neurological/Cognitive Manifestations, which consist of two or more of the following:

  • Confusion
  • Overload phenomena
  • Perceptual and sensory disturbances
  • Impairment of concentration and short term memory disorientation
  • Difficulty with information processing, categorizing, and word retrieval

The Expert Panel describes overload phenomena as cognitive and sensory, i.e. heightened sensitivity to lights and noise and/or emotional overload, which may lead to crash periods and/or emotional symptoms.

ME patients also experience at least one symptom from two of the following categories:

Autonomic Manifestations

  • Blood pressure abnormalities, particularly when rising from lying or seated position (“delayed postural hypotension”)
  • Light-headedness
  • Nausea and irritable bowel syndrome
  • Urinary frequency and bladder dysfunction
  • Heart palpitations
  • Shortness of breath with physical activity

Immune Manifestations

  • Tender lymph nodes
  • Recurrent sore throat
  • Recurrent flu like symptoms
  • General malaise new sensitivities to food, medications, and/or chemicals

Neuroendocrine Manifestations

  • Loss of thermostat regulation, presenting as:
    • Lowered body temperature with significant daily fluctuation
    • Sweating episodes
    • Recurrent feelings of feverishness and cold extremities
  • Intolerance of heat and cold extremes
  • Significant weight change, from a lack of or abnormal appetite
  • Worsening of symptoms with stress

ME is a chronic illness, diagnosed when symptoms last for at least

6 months in adults

3 months in children

It usually has a distinct onset, although it may be gradual.

Symptoms are in accordance to the Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols (Carruthers et al. Journal of Chronic Fatigue Syndrome 11, no 1 (2003) 7 115), also known as the Canadian Consensus Document.


Learn more about ME in the videos below.


A brief introduction about ME.

What Is ME?

An overview of the illness ME and the main symptom of debilitating physical and mental exhaustion.


As well as severe physical and mental exhaustion, people with ME suffer with a wide range of other debilitating symptoms.

Other Related Illnesses

Other names for ME / CFS, conditions which might be related, and similarities with other different illnesses.


Diagnosis of ME, and how important it is to get a correct diagnosis.

What is it like to have ME?

What is it really like to have this debilitating neurological illness, which is thought to affect millions throughout the world?

What To Do When Your Friend Has An Invisible Illness

The most important things you can do to help a friend who’s got ME.

Helping A Friend With ME

Seven ideas how you could help a friend who has ME

Support For Someone With ME

It’s worth making the most of any other support that you can find.


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