<unk>  <unk>  is one of several names given to a poorly understood, variably debilitating disorder of uncertain causation.<unk>  is thought, based on a 1999 study, to affect approximately 4 per 1,000 adults in the United States.
Other names for this syndrome are:
Myalgic Encephalomyelitis
Systemic Exertion Intolerance Disease. Proposed by the Institute of Medicine in 2015.
For unknown reasons,<unk>  occurs more often in women than men, and in people in their 40s and 50s. The illness is estimated to be less prevalent among children and adolescents, but studies are contradictory as to the degree.<unk>  often manifests with widespread myalgia and arthralgia, cognitive difficulties,<unk>  mental and physical exhaustion, often severe, and other characteristic symptoms in a previously healthy and active person. Despite promising avenues of research, there remains no assay or pathological finding which is widely accepted to be diagnostic of<unk> . It remains a diagnosis of exclusion based largely on patient history and symptomatic criteria, although a number of tests can aid diagnosis. Whereas there is agreement on the genuine threat to health, happiness, and productivity posed by<unk> , various physicians' groups, researchers, and patient activists champion very different nomenclature, diagnostic criteria, etiologic hypotheses, and treatments, resulting in controversy about nearly all aspects of the disorder. Even the term<unk>  is controversial because a large part of the patient community believes the name trivializes the illness.<unk>  is not the same as<unk><unk> ".<unk>  is a common symptom in many illnesses, but<unk>  is a multi-systemic disease and is relatively rare by comparison. Definitions (other than the 1991 UK Oxford criteria) require a number of features, the most common being severe mental and physical exhaustion which is "unrelieved by rest" (1994 Fukuda definition), and may be worsened by even trivial exertion (a mandatory diagnostic criterion according to some systems). Most diagnostic criteria require that symptoms must be present for at least six months, and all state the symptoms must not be caused by other medical conditions.<unk>  patients may report many symptoms which are not included in all diagnostic criteria, including muscle weakness, cognitive dysfunction, hypersensitivity, orthostatic intolerance, digestive disturbances, depression, poor immune response, and cardiac and respiratory problems. It is unclear if these symptoms represent co-morbid conditions or are produced by an underlying etiology of<unk> . Some cases improve over time, and treatments (though none are universally accepted) bring a degree of improvement to many others, though full resolution may be only 5-10% according to the United States Centers for Disease Control and Prevention (CDC).
Chronic fatigue syndrome
Generalized anxiety disorder
Fibromyalgia
Somatic symptom disorder
Illness anxiety disorder
Post-viral fatigue syndrome
Nicotine addiction
Somatization disorder