Myalgic encephalomyelitis (ME) is characterised by a range of neurological symptoms and signs, muscle pain with intense physical or mental exhaustion, relapses, and specific cognitive disabilities. Early reports dating from 1934 described epidemics of the illness (see Research Publications on ME epidemics for more information) — such as the 1955 outbreak at the Royal Free Hospital in London — but nowadays it is more common for endemic (sporadic) cases to be identified. ME is classified by the World Health Organisation as a neurological illness (International Classification of Disease 10: G93.3).
http://www.meresearch.org.uk/information/whatisme.html