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In page Medically unexplained physical symptoms:

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For certain MUPSs that occur within recognized syndromes (e.g. chronic fatigue syndrome and fibromyalgia), there is wide disagreement across disciplines as to the causes of the symptoms. Research in the domains of psychology and psychiatry frequently emphasizes psychological causal factors,[3][4][5] whereas research in the biomedical sciences – relating to immunology and rheumatology, for example – commonly emphasizes biological factors.[6][7][8][9]