Myalgic Encephalomyelitis (ME) or What? An Operational Definition.

Abstract

Myalgic encephalomyelitis (ME), identified as a new clinical entity with distinctive features in 1956, was originally considered as a neuromuscular  disease. In 1988 the Centers for Disease Control and Prevention introduced the  ill-defined concept of chronic fatigue syndrome (CFS). As predicted, CFS,  unjustly considered to be a synonym for ME, pushed ME to the background. To  develop effective therapies for of ME and CFS, it is essential to investigate  patients with ME specifically. For that reason, an operational definition of ME  is indispensable. This article proposes an operational definition based on the  most recent formal definitions and symptoms observed in ME. ME is a  multi-systemic illness, which (1) often has a sudden onset, in most cases a  respiratory and/or gastro-intestinal infection, but a gradual or more dramatic  onset is also possible; (2) has an epidemic and an endemic form; (3) has an  unique clinical pattern deviating from other post-viral states; (4) is  distinguished by muscle fatigability/prolonged muscle weakness after trivial  exertion; (5) is accompanied by symptoms relating to neurological disturbance,  especially of cognitive, autonomic, and sensory functions; (6) can be accompanied  by symptoms associated with cardiac and other systems; (7) is characterized by  fluctuation of symptoms (within and between "episodes"); (8) has a prolonged  relapsing course; and (9) has a tendency to become chronic. In conclusion, a  discriminative definition for ME contains four mandatory elements: (1) muscle  fatigability/post-exertional muscle weakness lasting for days; (2) operational  criteria for "neurological disturbance, especially of cognitive, autonomic and  sensory functions"; (3) fluctuation of symptoms; and (4) a prolonged relapsing  course. This tentative definition of ME justifies the qualification  "neuromuscular disease".