myalgic encephalomyelitis (ME), post-viral fatigue syndrome (PVFS) is a syndrome (or group of syndromes) of unknown and possibly multiple etiologies, affecting the central nervous system (CNS), immune, and many other systems and organs. There is no simple diagnostic test; CFS is a diagnosis of exclusion, although recent research indicates biological hallmarks of the syndrome, and a diagnostic test is predicted soon. Most definitions (other than the 1991 UK Oxford criteria[1]) require a number of features, the most common being severe mental and physical exhaustion or depletion which is "unrelieved by rest" (according to the 1994 Fukuda definition),[2] and is often worsened by even trivial exertion (controversially, the Oxford and Fukuda criteria require this to be optional only). CFS occurs more often, but not exclusively, in women, possibly due to immunological factors (women are overall more susceptible to similar disorders). CFS is most easily diagnosed when formerly active adults become ill, but it has been reported in persons of all ages, including young children and particularly teenagers.
