Medically unexplained symptoms (MUS) – those lacking identifiable underlying physical disease – are common in all levels of the health care system, and can be associated with severe disability and distress to patients and high cost to health services. Common MUS include pain (including back, chest, abdominal pain, and headache), fatigue, dizziness and ENT (Ear, Nose and Throat) symptoms. Similarly, functional somatic syndromes refer to groups of symptoms lacking disease-specific, demonstrable abnormalities of structure, and are usually defined by specialty or organ system.1 They include irritable bowel syndrome, fibromyalgia, chronic fatigue syndrome, multiple chemical sensitivity, chronic pelvic pain, temporomandibular joint dysfunction and more recently Gulf War syndrome. These conditions overlap in their symptoms, aetiology and treatment; prompting some to point out that the similarities outweigh differences between them and that there is utility in considering them collectively rather than separately.2
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Source: Cho HJ, Wessely S. Chronic fatigue syndrome: an overview. Rev Bras Psiquiatr. 2005 Sep;27(3):174-5. Epub 2005 Oct 4. http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-44462005000300003&lng=en&nrm=iso&tlng=en (Full article)