London CriteriaThe criteria for defining myalgic encephalomyelitis/post-viral fatigue syndrome (ME/PVFS).
Diagnostic criteria for ME/PVFS research subjects
(a) Exercise-induced fatigue precipitated by minimal exertion relative to patient's previous exercise tolerance.
(b) Impairment of short-term memory—loss of concentration, usually coupled with other neurologic and psychological disturbances such as emotional lability, nominal dysphasia, disturbed sleep patterns, disequilibrium or tinnitus.
(c) Fluctuation of symptoms, usually precipitated by either physical or mental exercise, (b) above.
These symptoms should have been present for at least 6 months and should be ongoing.