The nomenclature of the condition(s) has been challenging, since consensus is lacking within the clinical, research, and patient communities regarding its defining features and causes. Authorities on the illness look upon the condition as a central nervous system, metabolic, (post-)infectious, cardiovascular, immune system or psychiatric disorder, and consider the possibility that it is not a single homogenous disorder (with a range of possible clinical presentations), but a group of several distinct disorders with many clinical characteristics in common.
Over time and in different countries many names have been associated with the condition(s). Aside from CFS, some other names used include Akureyri disease, benign myalgic encephalomyelitis, chronic fatigue immune dysfunction syndrome, chronic infectious mononucleosis, epidemic myalgic encephalomyelitis, epidemic neuromyasthenia, Iceland disease, myalgic encephalomyelitis (ME, particularly in the United Kingdom, Canada, New Zealand and Australia), myalgic encephalitis, myalgic encephalopathy, post-viral fatigue syndrome, raphe nucleus encephalopathy, Royal Free disease, Tapanui flu and yuppie flu (now considered pejorative).
