Chronic fatigue syndrome (CFS) is the most common name used to designate a significantly debilitating medical disorder or group of disorders. Generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months in adults (and 3 months in children/adolescents), not due to ongoing exertion, not substantially relieved by rest, and not caused by other medical conditions. The disorder may also be referred to as myalgic encephalomyelitis (ME), post-viral fatigue syndrome (PVFS), chronic fatigue immune dysfunction syndrome (CFIDS), or several other terms.
Biological, genetic, infectious and psychological mechanisms have been proposed for the development and persistence of symptoms but the etiology of CFS is not understood and may have multiple causes. There is no diagnostic laboratory test or biomarker for CFS. Symptoms of CFS include post-exertional malaise; unrefreshing sleep; widespread muscle and joint pain; sore throat; headaches of a type not previously experienced; cognitive difficulties; chronic, often severe, mental and physical exhaustion; and other characteristic symptoms in a previously healthy and active person . Persons with CFS may report additional symptoms such as muscle weakness, increased sensitivity to light, sounds and smells, orthostatic intolerance, digestive disturbances, depression, and cardiac and respiratory problems. It is unclear if these symptoms represent co-morbid conditions or are produced by an underlying etiology of CFS. CFS symptoms vary from person to person in number, type, and severity.
Chronic fatigue syndrome
Sufferers of chronic fatigue syndrome experience tiredness and unrefreshing sleep.
The majority of CFS cases start suddenly, usually accompanied by a "flu-like illness"while a significant proportion of cases begin within several months of severe adverse stress. An Australian prospective study found that after infection by viral and non-viral pathogens, a sub-set of individuals met the criteria for CFS, with the researchers concluding that "post-infective fatigue syndrome is a valid illness model for investigating one pathophysiological pathway to CFS". However, accurate prevalence and exact roles of infection and stress in the development of CFS are currently unknown.