The specificity of the CDC-1994 criteria for chronic fatigue syndrome: comparison of health status in three groups of patients who fulfil the criteria
The definition of "chronic fatigue syndrome" set down by the Centers for Disease Control (CDC) in 1994 is used widely to specify patient groups used in research. To qualify, an individual must have experienced at least six months of chronic fatigue, as well as at least four symptoms from a list which includes muscle pain, cognitive problems and malaise following exercise. However, there is concern that this definition is too broad, and might include patients with different illnesses.
Comparisons were made of the symptoms of three groups of patients who all come under the CDC definition of "chronic fatigue syndrome", but who report different causes of their illness. Gulf War veterans had more severe fatigue, muscle pain and joint pain than agricultural workers exposed to insecticides and patients whose illness developed sporadically (which we would normally call ME/CFS). Patients with ME/CFS had better emotional and mental health then the other two groups.
These differences (as well as the results of the acetylcholine experiments) highlight the shortcomings of the current CDC definition of "chronic fatigue syndrome", which should be improved to take into account the distinct subgroups of patients it includes. It is also worth noting that fatigue itself is not actually the main problem for many of these people.