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What is myalgic encephalomyelitis?

Myalgic encephalomyelitis (ME), formerly known as chronic fatigue syndrome (CFS) and often still referred to as ME/CFS, is a devastating, chronic, complex, multi-system disease that afflicts approximately 600,000 Canadians, 2.5 million people in the United States and millions more globally. ME is found in children, adolescents and adults of all ages. The name ME stands for muscle pain (myalgic) and inflammation of the brain and spinal cord (encephalomyelitis).

There is a growing recognition that ME is a serious disease rooted in fundamental multi-system dysfunctions that impair energy production, the immune system and the nervous system. There is much to learn about these dysfunctions and there is a pressing need for biomarkers and laboratory tests for diagnosis.

The symptoms of ME cannot easily be captured in a few words, as so many systems are involved. The onset of ME is often sudden, typically following a viral or other type of infection but it can develop gradually. Patients often describe feeling chronic, severe ‘flu-like’ symptoms such as tender or swollen lymph nodes, fever, muscular pain, headache, and sore throat. They also describe unrelenting ‘pathological’ exhaustion and, although they don’t often have the word for it, they will describe a (often delayed) relapse or exacerbation of symptoms or ‘crash’ following any, even minimal, activity/exertion (physical or mental). This ‘crash’ is called post-exertional malaise (PEM) and is a characteristic symptom.

In addition, patients may also experience a whole range of symptoms including cognitive impairment, unrefreshing sleep/sleep disturbances, autonomic manifestations including orthostatic intolerance/postural orthostatic tachycardia syndrome (POTS), gastrointestinal/irritable bowel syndrome and muscle/joint pain and sound, light, and chemical sensitivity.

Given the heterogeneous nature of the symptomatology of ME, it is now widely accepted that its pathophysiology may result from a combination of predisposing genetic factors, infections, and/or other environmental exposures.

People with ME find it difficult (or impossible) to function as they did before they became ill including with tasks of daily living (e.g., showering, making meals). ME can present with a wide range of severity and up to one quarter are bedbound or housebound at some point in their illness, many indefinitely.

Diagnosis is made using one of several accepted criteria. In line with the US National Institutes of Health recommendations and international practice, the ICanCME Research Network is intending to use the Canadian Consensus Criteria (CCC) and the IOM (now Academy of Medicine) definitions.