Chronic fatigue syndrome (CFS), also referred to as myalgic encephalomyelitis (ME), is a complex, fatiguing, long-term medical condition that causes worsening symptoms after physical or mental activity, a greatly diminished capacity to accomplish tasks that had been routine prior to the illness, and unrefreshing sleep. Difficulty sitting and standing upright or cognitive dysfunction are also present. Other common symptoms may involve numerous body systems in those affected.
While the cause is not understood, proposed mechanisms include biological, genetic, infectious, and physical or psychological stress affecting body chemistry. Diagnosis is based on a person's symptoms because there is no confirmed diagnostic test. The fatigue in CFS is not due to strenuous ongoing exertion, is not much relieved by rest and is not due to a previous medical condition. Fatigue is a common symptom in many illnesses, but the unexplained fatigue and severity of functional impairment found in CFS is comparatively rare in these other illnesses.
Persons with CFS may recover or improve over time, but there are no approved therapies or medications for the illness; treatment is directed toward symptomatology. The CDC recommends the use of pacing (personal activity management) to reduce the worsening of symptoms resulting from mental or physical activity. Limited evidence suggests rintatolimod, counseling therapies, and graded exercise therapy might benefit some patients.
The incidence of CFS is approximately 1 in every 100 persons seen in primary care settings, but estimates vary widely due to different criteria used in epidemiological studies. Studies estimate that 836,000 to 2.5 million Americans and 250,000 people in the UK have CFS. CFS occurs 1.5 to 2 times more often in women than in men. It most commonly affects adults between ages 40 and 60 years, but can occur at other ages including in children. Other studies suggest that around 1 in 200 children have CFS, and is more common in adolescents than younger children. Chronic fatigue syndrome is a major cause of school absence. There is agreement that CFS has a negative effect on health, happiness and productivity, but there is also controversy over many aspects of the disorder. Physicians, researchers and patient advocates promote different names and diagnostic criteria, while evidence for proposed causes and treatments is often contradictory or of low quality.